Hostname: page-component-7b7567c8c-mnklg Total loading time: 0 Render date: 2026-11-12T05:57:57.482Z Has data issue: false hasContentIssue false
  • English
  • Français

Clay dispersion in adobe soil resources by ultrasonic treatment: method development and performance assessment on adobe products

Published online by Cambridge University Press:  10 November 2026

Meltem ErdilOpen the ORCID record for Meltem Erdil[Opens in a new window],
Ayse DumanOpen the ORCID record for Ayse Duman[Opens in a new window] and
Emine N. Caner-SaltıkOpen the ORCID record for Emine N. Caner-Saltık[Opens in a new window]
Meltem Erdil
Affiliation:
Middle East Technical University: Orta Dogu Teknik Universitesi , Türkiye
Ayse Duman*
Affiliation:
Middle East Technical University: Orta Dogu Teknik Universitesi , Türkiye
Emine N. Caner-Saltık
Affiliation:
Middle East Technical University: Orta Dogu Teknik Universitesi , Türkiye
*
Corresponding author: Ayşe Duman; Email: tayse@metu.edu.tr
Rights & Permissions [Opens in a new window]

Abstract

Depletion of adobe soil resources and the need for affordable and sustainable dwelling construction demand effective use of the remaining resources. The present study focused on developing a treatment method to disperse the naturally occurring clay content in adobe soil resources. The impact of the ultrasonic treatment method proposed was assessed by performance analysis conducted on treated adobe soil and the adobe materials produced. The ultrasonic treatment was conducted on three soil resources: montmorillonite-rich, kaolinite-rich, and montmorillonite- and kaolinite-rich, in their respective clay fractions. The clay dispersion in the mixture was monitored using the methylene blue test and confirmed by particle-size distribution and consistency limits analyses. The order of the treatment process and optimum durations of between 4 and 5 h for mixing the soil samples were key factors in the efficient dispersion of clay in the soils. This research showed that the clay dispersion treatment: (1) increased the dispersed clay fraction, enabling soil resources with initially insufficient clay content (<10%) to reach the recommended range of 10–40% for adobe production and bringing the consistency limits of the three soil resources within the acceptable range; and (2) was particularly effective for montmorillonite-rich soil resources, indicating that its effectiveness depends on clay type. The performance analyses conducted on adobe products showed that: (1) compared with untreated adobe samples using natural adobe soil, the treated samples produced by the dispersed clay in adobe soil exhibited greater compressive and flexural strengths reaching 8.18 MPa and 0.53 MPa, respectively; (2) the dispersed clay content, the presence of clay-sized calcite, and significant pozzolanic activity were the determinative compositional features of adobe mixtures for improved mechanical performance.

Keywords

adobeclayconsistency limitsmechanical propertiesultrasonic treatment

Information

Type
Original Paper
Information
Clays and Clay Minerals , Volume 74 , 2026, e39
Check for updates
Creative Commons
Creative Common License - CCCreative Common License - BYCreative Common License - NCCreative Common License - ND
This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives licence (http://creativecommons.org/licenses/by-nc-nd/4.0), which permits non-commercial re-use, distribution, and reproduction in any medium, provided that no alterations are made and the original article is properly cited. The written permission of Cambridge University Press or the rights holder(s) must be obtained prior to any commercial use and/or adaptation of the article.
Copyright
© The Author(s), 2026. Published by Cambridge University Press on behalf of The Clay Minerals Society

Introduction

Adobe is a local, sustainable, and environmentally friendly construction material. Since the Neolithic period, adobe soil resources have been used to produce adobe building materials and houses, as in the Çatalhöyük (Konya, 7400–6150 BC) and Çayönü (Diyarbakır, 7250–6750 BC) archeological settlements in Anatolia, Turkey (Schirmer, Reference Schirmer1990; Minke, Reference Minke2009; Tringham and Stevanović, Reference Tringham and Stevanović2012; Schroeder, Reference Schroeder2015; Bektaş, Reference Bektaş2018). Anatolia is rich in adobe soil resources and hosts various traditional adobe architecture (State Institute of Statistics Prime Ministry, Republic of Turkey, 2001). Careful selection of soil resources to be used as raw materials is essential for the preparation of good-quality adobe material which will last for a long time (Houben and Guillaud, Reference Houben and Guillaud1994; Delgado and Guerrero, Reference Delgado and Guerrero2007). Clay type(s), pozzolans, clay-sized calcite contents in the soil resource, particle-size distribution, as well as consistency limits, and shrinkage behavior are the key features that contribute to greater durability of adobe (Blondet et al., Reference Blondet, Vargas-Neumann and Tarque2008; Işık, Reference Işık2011; Widder, Reference Widder2017; Giuffrida et al., Reference Giuffrida, Caponetto, Nocera and Cuomo2021):

  • – Among the clay minerals, kaolinite and illite are those known for their non-expansive or limited-expansion behaviors, respectively (Carroll, Reference Carroll1970; Torraca, Reference Torraca1988; Guggenheim et al., Reference Guggenheim, Adams, Bain, Bergaya, Brigatti, Drits, Formoso, Galán, Kogure and Stanjek2007). On the other hand, montmorillonite is an expansive clay mineral that swells dramatically in the presence of water (Barton and Karathanasis, Reference Barton, Karathanasis and Lal2002; Alther, Reference Alther2004; Velde and Meunier, Reference Velde and Meunier2008). In short, soil resources containing kaolinite or illite are preferable for preparing good-quality adobe material with volumetric stability. However, local soil resources in Anatolia contain multiple clay types together. For instance, illite, montmorillonite, and/or other clay types may co-exist with or without kaolinite.

  • – The presence of clay-sized calcite and pozzolans in the adobe soil resource, and the presence of fiber and straw additives in the adobe matrix, enhance the volumetric stability, mechanical strengths, and water impermeability of adobe material (Norton, Reference Norton1997; Sharma et al., Reference Sharma, Marwaha and Vinayak2016; Choobbasti et al., Reference Choobbasti, Samakoosh and Kutanaei2019; Ouedraogo et al., Reference Ouedraogo, Dao, Millogo, Aubert, Messan, Seynou and Zerbo2019; Lagouin et al., Reference Lagouin, Laborel-Préneron, Magniont, Geoffroy and Aubert2021).

  • – Appropriate particle-size distribution in soil is a compositional property that controls volumetric stability and physical and mechanical performance. The recommended ratios of clay, silt, and sand-gravel contents for a good-quality adobe mixture can vary in the ranges of 10–40%, 10–30%, and 30–75%, respectively (Schwalen, Reference Schwalen1935; Norton, Reference Norton1997; Walker, Reference Walker2001). The clay and silt contents act as binders in the adobe mixture by keeping the particles together and enhance compressive strength by enhancing cohesion between aggregates.

  • – The >2 mm aggregates contribute to the volume stability of the adobe (Stefanidou and Papayianni, Reference Stefanidou and Papayianni2005).

  • – The recommended consistency limits for a good-quality adobe material can be defined in terms of two main performance properties, namely plasticity index value in the range of 16–33% and liquid limit value in the range of 31–50% (Houben and Guillaud, Reference Houben and Guillaud1994; Delgado and Guerrero, Reference Delgado and Guerrero2007). The linear shrinkage ratio of 8% is defined as the critical level for the adobe mixture, and if it is exceeded, cracking problems may occur (Dawson et al., Reference Dawson, Altmeyer, Barber and Dubose1956).

  • – The required levels for compressive and flexural strengths, capillary-water absorption, and water-vapor permeability of adobe according to some codes/standards and literature data have been compiled in Table 1. These parameters define some key performance indicators for good-quality adobe.

    Table 1.

    The required levels for compressive and flexural strengths, capillary-water absorption, and water-vapor permeability of adobe according to various codes/standards and literature data

    A multi-section table detailing adobe performance standards for compressive and flexural strength, capillary-water absorption, and water-vapor permeability across various international codes and literature. See long description.
    Table 1. Long description

    The table is divided into three main horizontal sections.

    Section 1: Mechanical Strengths.

    Columns list Normative document, Compressive strength class, Compressive strength in M P a (Minimum and Average), and Flexural strength in M P a (Minimum).

    - I B C 2018: Minimum 1.72, Average 2.07, Flexural 0.24.

    - N M A C 2015: Minimum 1.73, Average 2.07, Flexural 0.34.

    - Nigeria 2006: Minimum 1.60, Average 1.70 to 2.75.

    - N Z S 2020: Minimum 1.3, Flexural 0.25.

    - N T E 2000: Minimum 1.18.

    - Pakistan I B C 2021: Minimum 1.72, Average 2.07.

    - Australia Walker 2001: Minimum 1.15.

    - D I N norms 2018: Five classes (2 through 6) with minimum compressive strengths matching the class number (2 to 6) and average strengths ranging from 2.5 to 7.5.

    Section 2: Capillary-water absorption (D I N norms).

    Columns list Class, Application, and Time in hours.

    - Class I a: External wall exposed to weathering, greater than or equal to 24 hours.

    - Class I b: Coated external wall, greater than or equal to 3 hours.

    - Class I I: Internal wall, greater than or equal to 0.5 hours.

    - Class I I I: Dry applications, no requirement.

    Section 3: Water-vapor permeability (dry-cup method).

    Columns list Reference, Sample, and mu-value (unitless).

    - Ergin-Oruç 2004: Traditional adobe brick (Diyarbakır), 16 to 18.

    - Narloch et al. 2021: Rammed adobe lab sample, 17.

    - Belarbi et al. 2022: Cob adobe lab sample, 12.

    - Maillard and Aubert Reference Maillard and Aubert2014: Extruded adobe lab sample (parallel), 11 to 23; (perpendicular), 19 to 44.

Numerous studies aimed at performance improvement have concentrated on incorporating additives such as lime, gypsum, cement, various plant fibers, waste-tea residues, boron waste, and polymer fibers into the adobe mixture (Binici et al., Reference Binici, Aksogan and Shah2005; Binici et al., Reference Binici, Aksogan, Bodur, Akca and Kapur2007; Binici et al., Reference Binici, Aksogan, Bakbak, Kaplan and Isik2009; Vilane, Reference Vilane2010; Işık, Reference Işık2011; Bahobail, Reference Bahobail2012; Pekmezci et al., Reference Pekmezci, Kafescioglu and Agahzadeh2012; Danso et al., Reference Danso, Martinson, Ali and Mant2015; Al-Ajmi et al., Reference Al-Ajmi, Abdalla, Abdelghaffar and Almatawah2016; Calatan et al., Reference Calatan, Hegyi, Dico and Mircea2016; Sharma et al., Reference Sharma, Marwaha and Vinayak2016; Abanto et al., Reference Abanto, Karkri, Lefebvre, Horn, Solis and Gómez2017; Pekrioglu Balkis, Reference Pekrioglu Balkis2017). Stabilizing additives, such as nano-CaO and nano-Ca(OH)2, in adobe mixtures are also used in the control of adobe performance properties. Recent studies have shown that the durability of adobe ruins in archaeological settlements was improved by application of Ca(OH)2 dispersions on their surfaces, which provided better abrasion resistance (Camerini et al., Reference Camerini, Chelazzi, Giorgi and Baglioni2018; Elert et al., Reference Elert, Jroundi, Benavides-Reyes, Correa Gómez, Gulotta and Rodriguez-Navarro2022). Instead of the application of Ca(OH)2 solution on adobe surfaces, adding CaCO3 nanoparticles in the soil mixture is an alternative approach. A study by Mohammadi et al. (Reference Mohammadi, Khodaparast and Rajabi2021) indicated that the addition of 0.7 CaCO3 nanoparticles to soils containing 10% and 20% clay, and 1.1% CaCO3 nanoparticles to soils containing 30%, can enhance the compressive strength of clay mixtures up to three times, as well as improve their pozzolanic activity and decrease swelling behavior. Some studies have mentioned that the addition of 1% CaCO3 nanoparticles to the soil as a stabilizer is the optimum amount for improving the compressive strength and plastic limit values (Yazarloo et al., Reference Yazarloo, Katooli, Golestani, Asadi and Ebrahimi2017; Choobbasti et al., Reference Choobbasti, Samakoosh and Kutanaei2019; Mohammadi et al., Reference Mohammadi, Khodaparast and Rajabi2021). As a stabilizer in a clay mixture, CaO is expected to be more reactive and soluble than CaCO3 (Getahun et al., Reference Getahun, Etana, Munkholm and Kirchmann2021; Greipsland et al., Reference Greipsland, Tesfai and Bechmann2014). While lime stabilization has been investigated widely in geotechnical soil improvement, there is limited literature which has examined the impact of CaO nanoparticles on the performance properties of adobe building material. Considering the information in the literature, the involvement of CaO has the potential to interact through ion exchange, pozzolanic reaction, and carbonation processes in the adobe material (Goldberg and Klein, Reference Goldberg, Klein and Mielenz1953; Norton, Reference Norton1997). Due to their enhanced reactivities with large specific surface areas, CaO nanoparticles can promote these reactions, leading to localized cementation, which improves particle bonding within the clay matrix.

Clay as an additive in the adobe mixture

Clay is one of the remarkable inorganic raw materials that can be used as an additive, binder, or filler within a polymer matrix or component to produce nanocomposite construction materials (Uddin, Reference Uddin2008; Sanchez and Sobolev, Reference Sanchez and Sobolev2010; Pacheco-Torgal and Jalali, Reference Pacheco-Torgal and Jalali2011; Nazir et al., Reference Nazir, Mohamad Kassim, Mohapatra, Gilani, Raza, Majeed, Jawaid, el K. Qaiss and Bouhfid2016). Studies in the fields of soil engineering state that the use of non-expansive kaolinite as an additive in soil mixtures improves the dimensional stability and mechanical properties of clay-rich soil (Khalid et al., Reference Khalid, Arshad, Mukri, Mohamad and Kamarudin2014; Zainuddin et al., Reference Zainuddin, Norullain, Mukri, Azizah and Che Lat2015). One study focused particularly on the impact of clay on the mechanical strength of adobe material and mentioned that adding 5% kaolinite can provide five times more compressive strength than achieved from the reference adobe mixture (Niroumand et al., Reference Niroumand, Zain and Alhosseini2013). On the contrary, the addition of expansive montmorillonite clay to clay-rich soil increases the plasticity and swelling behavior, and leads to the formation of drying cracks; these are not desirable properties for adobe building materials (Azzam et al., Reference Azzam, Sayyah and Abdelrahman2013; Tabassum and Bheemasetti, Reference Tabassum and Bheemasetti2020; Taha, Reference Taha2018). There have been few studies of the use of clay in the stabilization of adobe building materials, and its use in the fields of adobe material technology deserves some attention.

Definition of clay-size ranges vary across disciplines in terms of classification. In sedimentology and according to the Udden and Wentworth scale, clay is classified as particle sizes of <4 μm (Guggenheim et al., Reference Guggenheim, Martin, Alietti, Drits, Formoso, Galán, Köster, Morgan, Paquet, Watanabe, Bain, Ferrell, Bish, Fanning, Kodama and Wicks1995; Tucker, Reference Tucker2001). In geology, soil sciences, and Turkish standards, particle sizes of <2 μm are accepted as clay (Guggenheim et al., Reference Guggenheim, Martin, Alietti, Drits, Formoso, Galán, Köster, Morgan, Paquet, Watanabe, Bain, Ferrell, Bish, Fanning, Kodama and Wicks1995; TS EN ISO, 2018). In colloid science, clay corresponds to particle sizes of <1 μm (Guggenheim et al., Reference Guggenheim, Martin, Alietti, Drits, Formoso, Galán, Köster, Morgan, Paquet, Watanabe, Bain, Ferrell, Bish, Fanning, Kodama and Wicks1995).

Clay exists in the form of nanoparticles to a certain extent. The individual clay mineral layers have a basal surface diameter ranging between 100 and 7000 nm, while the thickness of a single, fully delaminated layer and its interlayer spaces varies between 0.7 and 2 nm (Grim, Reference Grim1968; Reeves et al., Reference Reeves, Sims and Cripps2006; Ercan et al., Reference Ercan, Ece, Çiftçi and Aydın2022; Khong et al., Reference Khong, Jimoh, Zabidi and Ariffin2025). Although clay minerals generally occur as stacked tactoids or larger aggregates rather than as fully delaminated layers, the dimensions of their individual layers fall within the nanoscale range. The nanoscale is accepted as being in the range of 1 to 100 nm (ISO/TR, 2017). Thus, clay minerals are nanomaterials and the terms ‘clay’ and ‘nano-sized clay’ are interchangeable (Kertmen et al., Reference Kertmen, Dalbaşi, Körlü, Özgüney and Yapar2020).

Enhancing the fraction of discrete nano-sized clay particles is made possible by the dispersion of ‘flocculated’ clay mineral layers (Luckham and Rossi, Reference Luckham and Rossi1999; Du et al., Reference Du, Pushkarova and Smart2009). Following the dispersion treatment, aggregated clay mineral layers form denser structures and have greater bonding strength to each other (Luckham and Rossi, Reference Luckham and Rossi1999; Ravisangar et al., Reference Ravisangar, Sturm and Amirtharajah2005), which improves the mechanical properties of the clay mixture. The use of clay additives in adobe products can be provided either by synthetic production or by extracting them from natural clay sources. Both approaches are labor-intensive. Practical solutions are needed to enhance the clay which exists within adobe soil rather than adding clay from an external source.

Clay dispersion can be conducted by mechanical treatments such as ultrasonic, grinding, and high-shear mixing, or by chemical dispersion treatments. Here, two prominent guiding criteria should be considered in determining the most appropriate treatment method: (1) producing as much clay as possible with the least energy, and (2) keeping the inherent chemical compositions of the clay particles during the clay dispersion process.

Studies have been conducted to disperse the clay particles in construction materials by chemical treatments (e.g. Corradi et al., Reference Corradi, Manfredini, Pellacani and Pozzi2005; Moevus et al., Reference Moevus, Jorand, Olagnon, Maximilien, Anger, Fontaine and Arnaud2016). Those treatments using chemical dispersants such as inorganic salts (e.g. sodium polymethacrylate, sodium hexametaphosphate) are questionable as they change the inherent chemical properties of the clay particles (Min et al., Reference Min, Hwang and Lee2007; Tan et al., Reference Tan, Liu, Hu, Reed, Furukawa and Zhang2017). The ‘ultrasonic treatment’ allows the dispersion of flocculated clay particles of coarser sizes in a clay-rich soil mixture by transmitting high-frequency vibrations to the water in ultrasonic baths or ultrasonic horn/sonicator instruments while maintaining their original chemical properties and physical properties of their plate-like morphological shape (Niu et al., Reference Niu, Li, Hu, Tan and Liu2021; Pérez-Maqueda et al., Reference Pérez-Maqueda, de Haro, Poyato and Pérez-Rodríguez2004; Poli et al., Reference Poli, Batista, Schmitt, Gessner and Neumann2008). In addition, ultrasonic treatment produces greater amounts of clay in smaller particle sizes with much less energy compared with methods using grinding instruments or the high-shear mixer (Garrison, Reference Garrison2003; Pérez-Maqueda et al., Reference Pérez-Maqueda, de Haro, Poyato and Pérez-Rodríguez2004; Lam et al., Reference Lam, Lau, Cheung and Ling2005; Pérez-Rodríguez et al., Reference Pérez-Rodríguez, Pascual, Franco, Jiménez de Haro, Duran, Ramírez del Valle and Pérez-Maqueda2006; Hoke et al., Reference Hoke, Schmitz and Bowring2014; Janica et al., Reference Janica, Del Buffa, Mikołajczak, Ededia, Pakulski, Ciesielski and Samorì2018). The ultrasonic treatment is therefore an efficient method in terms of preserving the original properties of the clay, as well as providing larger amounts of clay with less energy consumption.

The present study focused on proposing and developing a method which would enable the dispersion of the clay particles naturally existing in an adobe soil, rather than using a clay additive, as well as conventional stabilization techniques using cement and/or lime additives. Dispersing the clay particles is promising in terms of reducing the need for additives and preserving the original chemical and physical properties of the adobe soil, while having the potential to be a more practical and sustainable solution for improving local soil resources used in adobe production.

The key research aims were: to develop a sustainable and practical method by using ultrasonic treatment to disperse the amount of clay in natural adobe soil resources; and to assess the performance properties of adobe soil and products with dispersed clay content.

Materials and methods

The adobe soil samples for this study were selected from three different soil types, where the clay fractions differed in terms of their clay composition. They are rich in montmorillonite (Konya Küçükköy), rich in kaolinite (Çorum Karapınar), and rich in a mixture of montmorillonite and kaolinite (Çorum Kınık), respectively. Method development consisted of several stages: material characterization of the soil resources; development of a practical method of clay dispersion in those soils using the ultrasonic bath technique; effectiveness verification of the proposed clay-dispersion method; preparation of adobe products with dispersed clay (with/without added CaO nanoparticles) by the proposed clay dispersion method; and assessment of the performance of the adobe products with dispersed clay.

Soil samples were collected from three villages in Central Anatolia (Fig. 1), namely Küçükköy village in Konya/Çumra, which is close to the Çatalhöyük archaeological site (ca BC 7000), and Karapınar and Kınık villages in Çorum. The Konya Küçükköy soil sample was taken from a historical adobe soil resource that villagers used in traditional adobe constructions for many years. The Çorum Karapınar samples, belonging to an old adobe soil resource, and the Çorum Kınık samples, belonging to a recently discovered adobe soil resource in the region, were supplied by a local fired-brick manufacturing company (Vesfa factory). Samples of these soils were used for the development of the clay-dispersion method proposed in the present study.

Figure 1.

Location map of the soil resources, indicating the city and village names, geographic coordinates, and sample codes (top), and the three sets of adobe samples and their corresponding sample codes (bottom).

A two-part graphic featuring a map of Turkey with soil sample locations and three rows of adobe brick and disc samples categorized by village and treatment type. See long description.
Figure 1. Long description

The top panel is a map of Turkey showing two primary sampling regions. In the North, a red pin marks Corum_Karapinar- Corum_Kinik at coordinates 40.55341578586159, 34.92518898280127, with circular soil photos for Karapinar village and Kinik village. In the South, a red pin marks Konya_Kucukkoy at 37.68994810349527, 32.833824906965205 with a corresponding soil photo.

The bottom panel contains three horizontal sections of adobe samples, each showing six rectangular bricks and three circular discs per treatment.

Top row: Kucukkoy samples.

- K u U: Kucukkoy- Untreated, showing dark reddish-brown earth tones.

- K u T: Kucukkoy- Treated, showing a lighter, more uniform brown.

- K u T C: Kucukkoy- Treated plus C a O, showing a pale, yellowish-tan hue.

Middle row: Karapinar samples.

- K a U: Karapinar- Untreated, showing a medium reddish-orange.

- K a T: Karapinar- Treated, showing a textured, lighter orange-brown.

- K a T C: Karapinar- Treated plus C a O, showing a muted, grayish-tan.

Bottom row: Kinik samples.

- K i U: Kinik- Untreated, showing a light sandy brown.

- K i T: Kinik- Treated, showing a consistent light tan.

- K i T C: Kinik- Treated plus C a O, showing the lightest yellowish-beige in the set.

Each sample set includes a black and white scale bar measuring 1 to 10 centimeters.

Three sets of adobe material samples were prepared from soil resources and represented the mixtures of adobe block samples (Fig. 1). The wheat straw, between 0.5 and 3 cm long, was used in the mixture of untreated and treated adobe samples as a fiber additive. The optimum straw content ratio for the production of adobe samples using these local soil resources is accepted to be 1 wt.% (Tringham and Stevanović, Reference Tringham and Stevanović2012). The adobe samples were prepared in 4 cm × 4 cm × 16 cm prismatic shapes for compressive and tensile strength and capillary-water absorption tests, and the cylindrical adobe samples with 10 cm diameters and heights of 2.5 cm were used for the bulk-density, porosity, and water-vapor permeability analyses. Nine samples were prepared for each mixture, with three samples for each test; a total of 81 samples was obtained (Fig. 1). The adobe sample codes Ku, Ka, and Kı were used to refer to the soil resources collected from Konya_Küçükköy, Çorum Karapınar, and Çorum Kınık, respectively (Fig. 1). The three sets of adobe samples were:

  • – KuU, KaU, KıU: the untreated (reference) adobe samples representing the natural use of soil resources with 1 wt.% straw;

  • – KuT, KaT, KıT: the treated (dispersed clay) adobe samples with 1 wt.% straw;

  • – KuTC, KaTC, KıTC: the treated (dispersed clay) adobe samples with 1 wt.% straw and calcium oxide (CaO) 1 wt.% nanoparticles (Aldrich particle size ˂160 nm, BET 98%).

The relationships between research objectives, laboratory tests, and sample sets are listed in Table 2.

Table 2.

Laboratory tests and sample sets summarizing the analyses related to method development

A table summarizing laboratory tests and sample sets for soil characterization, clay dispersion assessment, and adobe material performance. See long description.
Table 2. Long description

The table consists of four columns: Tasks, Sample sets, Laboratory analyses, and References.

Row 1: Material characterization of soil resources.

- Sample sets: Soils from Konya Küçükköy, Çorum Karapınar, and Çorum Kınık.

- Laboratory analyses: Consistency Atterberg limits including Plastic limit P L percent, Liquid limit L L percent, Plasticity index P I percent, and Linear shrinkage L S percent.

- References: T S, 2017.

- Additional analyses for this task: Particle-size distribution by laser diffraction; X R D plus M A U D analyses for clay-type identification; Loss on ignition L o I for clay-sized calcite content; and Pozzolanic activity E D T A titration method.

Row 2: Performance assessment of clay dispersion by ultrasonic treatment.

- Sample sets: Same soils as Row 1.

- Laboratory analyses: Methylene blue M B test; Particle-size distribution; and Atterberg limits.

Row 3: Performance assessment of adobe material samples.

- Sample sets: Untreated reference samples K u U, K a U, K ı U; Treated dispersed clay adobe products K u T, K a T, K ı T; and Treated plus C a O nanoparticle K u T C, K a T C, K ı T C.

- Laboratory analyses: Basic physical properties including bulk density g cm sub minus 3, particle density g cm sub minus 3, and porosity percent by volume; Scanning electron microscope S E M analyses; Compressive and flexural strength M P a; Water-vapor permeability including water-vapor diffusion resistance factor mu and air layer thickness S D; and Capillary-water absorption coefficient A-value kg/m super 2 s super 0.5.

Analyses of the material characterization of the soils

The behaviors of the soils and their mineralogical compositions were analyzed with respect to soil consistency limits, the linear shrinkage ratio, and the particle-size distribution, including examinations of clay content, types of clay minerals, clay-sized CaO content, and pozzolanic activity (Table 2).

The quality of soil resources was examined by the consistency (Atterberg) limits analyses in terms of the recommended ranges of plastic limit (PL), liquid limit (LL), plasticity index (PI), and linear shrinkage (LS) ratio for the production of adobe material (TS, 2017).

The particle-size distribution (PSD) analyses, with particular emphasis on the nanosized fraction of the soil samples, were conducted on representative treated and untreated soil suspensions using the laser diffraction method (wet analysis with a Malvern Mastersizer 2000, METU Central Laboratory), based on dynamic light scattering. Prior to PSD analysis, representative treated soil suspensions were prepared by magnetic stirring for 1 day, followed by ultrasonic bath treatment for optimized durations of 4 and 5 h, as described in detail in the section ‘Method Development – Clay Dispersion in Soil Resources’. There are various ranges of particle size in soil classifications, as well as in clay-size classification. Clay particles started to appear in soil containing particles of <4 μm in size during microscope analyses, while particles between 2 μm and 4 μm in size contain small amounts of clay with silt particles predominating (Erdil Bölükbaşı, Reference Erdil Bölükbaşı2024). On the other hand, particle sizes of <1 μm were all clay particles, and the particles between 1 μm and 2 μm involved small amounts of fine silt with dominant clay particles (Erdil Bölükbaşı, Reference Erdil Bölükbaşı2024). The present study focused on the clay-size portion of the soil resources, considering the two scales: one was the range <1 μm and the other was the range <2 μm, consistent with the scales defined by Turkish standards, colloid, geology, and soil sciences (Guggenheim et al., Reference Guggenheim, Martin, Alietti, Drits, Formoso, Galán, Köster, Morgan, Paquet, Watanabe, Bain, Ferrell, Bish, Fanning, Kodama and Wicks1995; TS EN ISO, 2018). The data were interpreted in such a way that soil particles of <1 μm and <2 μm defined the minimum and maximum amounts of clay in the soils.

To discover whether clay dispersion in soil resources enhanced the quality of the soil for adobe material production, the treated soil samples were tested through PSD, soil consistency limits, and LS ratio tests for comparison.

The mineralogical compositions of soil resources on <4 μm particles, with a focus on the clay-sized content, were determined through X-ray diffraction analyses (XRD) using a Bruker D8 Advance instrument at a 2θ scale in the range of 5–70°2 θ with 0.002°2θ increments and CuKα radiation. To discriminate smectite-type clay minerals, particularly montmorillonite, from non-swelling clay minerals such as kaolinite, illite-mica, and chlorite, the soil samples were treated with glycol vapor, expanding the swelling clays more (Carroll, Reference Carroll1970; Mosser-Ruck et al., Reference Mosser-Ruck, Devineau, Charpentier and Cathelineau2005; Poppe et al., Reference Poppe, Paskevich, Hathaway and Blackwood2001). This made the montmorillonite more visible in XRD traces. The glycol-treated samples were gradually heated at 600, 700, and 800°C for about 2 h for each heating level to decompose the kaolinite, illite-mica/calcite, and chlorite, respectively (Carroll, Reference Carroll1970; Ilic et al., Reference Ilic, Mitrović and Ljiljana2010; Lakshmi et al., Reference Lakshmi, Velmurugan and Swamiappan2013; Loy et al., Reference Loy, Amin Matori, Lim, Schmid, Zainuddin, Abdul Wahab, Nadakkavil Alassan and Mohd Zaid2016).

MAUD (Materials Analysis Using Diffraction) software (version 2.99) was used to calculate the relative amounts (%) of montmorillonite, kaolinite, illite-mica, and chlorite in the untreated soil samples (particle size <4 μm) by evaluating the XRD traces. The MAUD software uses an iterative technique to fit the calculated diffraction pattern to the experimental XRD data by the Rietveld refinement process (Volz et al., Reference Volz, Vogel, Necker, Roberts, Lawson, Williams, Daemen, Lutterotti and Pehl2006).

The clay-sized calcite (CaCO3) content of the soils was estimated by two-step loss on ignition (LoI) tests by heating samples in the oven first at 550°C and then at 950°C (Heiri et al., Reference Heiri, Lotter and Lemcke2001). The first stage accounted mainly for the removal of organic matter (Carroll, Reference Carroll1970; Grim, Reference Grim1968; Heiri et al., Reference Heiri, Lotter and Lemcke2001) and structural water from clay minerals, whereas the second stage reflected the decomposition of carbonate minerals. The carbonate content was therefore estimated from the mass loss between 550 and 950°C. The pozzolanic properties of the soil samples were determined by testing the particle sizes of <125 μm with the chemical titration method using ethylenediaminetetraacetic acid (EDTA titration method) according to the TS EN 196-1:2016 standard (TS EN, 2016).

Method development: clay dispersion in soils

Following the characterization of the adobe soils, the clay-dispersion process involved the stages of mixing the soil samples with water to disperse coarser aggregates, followed by ultrasonic bath treatment, and checking the optimum durations for mixing and ultrasonic bath treatment by using methylene blue (MB) tests.

The soil samples diluted with distilled water were mixed with a magnetic stirrer (IKA lab disc) or the laboratory mixer (Utest laboratory equipment) to disperse coarser aggregates. These diluted and mixed samples were treated in an ultrasonic bath (MEL at 22 kHz, 80 W) to disperse the flocculated clay particles (Fig. 2) (Ganguly et al., Reference Ganguly, Das, Das, Ghosh, Das, Bose, Mondal, Das and Das2020).

Figure 2.

Dispersion methods of clay-mineral layers: mixing using a magnetic stirrer or laboratory mixer (top), ultrasonic treatment (sonication) for dispersion of clay mineral layer (middle), and a schematic illustration of the sonication-induced dispersion of flocculated clay mineral layer (bottom).

A multi-panel display showing laboratory methods for clay mineral dispersion and a schematic of sonication-induced particle separation. See long description.
Figure 2. Long description

The image consists of five panels arranged in three rows.

Top row: Two photos show mechanical mixing. The left photo features a conical flask containing a brown clay suspension on an I K A magnetic stirrer. The right photo shows a larger U T E S T laboratory mixer with a metal bowl and blue frame.

Middle row: Two photos show ultrasonic treatment. The left photo shows a rectangular sonication bath filled with a brown liquid. The right photo is a close-up of the liquid surface inside the bath, with a yellow circle highlighting white foam or bubbles. A yellow arrow points from this circle down to the schematic below.

Bottom row: A schematic diagram illustrates the dispersion process from left to right.

1. On the left, a cluster of gray rectangular bars is labeled Flocculated clay with Edge-to-edge contact and Edge-to-face contact. The bars are arranged in a chaotic, house-of-cards structure.

2. A horizontal arrow labeled Dispersion of clay particles by ultrasound points to the center. Here, three bars are shown separating, surrounded by green wavy lines representing ultrasonic waves.

3. A second horizontal arrow labeled Sedimentation points to the right.

4. On the far right, the bars are stacked neatly in parallel layers, labeled Aggregated clay with Face-to-face contact.

The MB test was a practical test method to decide the optimum durations for mixing and ultrasonic treatment. The cation exchange capacity (CEC), which was the ability of clay to adsorb the MB cations of dye, was the property tested here (NF, 1998). Through the clay-dispersion process, the CEC properties of the samples increased; consequently, the specific surface area of clay content increased (Reeves et al., Reference Reeves, Sims and Cripps2006). The consumption of MB dye measured that change. The test was used to determine the optimum duration of ultrasonic treatment for each sample by monitoring clay dispersion in the mixture. That dispersion was measured and confirmed by particle-size distribution and consistency limit analyses. The timing of the ultrasonic treatments that produced the largest amount of clay particles for each sample was as follows:

  • – 1 day of mixing with a magnetic stirrer, followed by a 4 h ultrasonic bath process for the Konya Küçükköy and Çorum Kınık soil samples;

  • – 1 day of mixing with a magnetic stirrer, followed by a 5 h ultrasonic bath treatment for the Çorum Karapınar soil sample (Fig. 3).

Figure 3.

CEC values showing the optimum mixing durations for the magnetic stirrer and ultrasonic bath that yielded the highest clay particle content in the three soil resources (top), the optimum mixing durations for the laboratory mixer and ultrasonic bath for the Konya Küçükköy soil resource (bottom left), and the optimum soil:water ratio for preparing treated adobe samples from the three soil resources (bottom right).

Three bar charts showing C E C values across different soil types, mixing durations, and soil to water ratios. See long description.
Figure 3. Long description

A multi-panel figure containing three bar charts. All charts measure C E C in m e q per 100 g on the y-axis.

Top Panel: A large bar chart comparing three soil resources: Konya Küçükköy (blue), Çorum Karapınar (orange), and Çorum Kınık (green).

- For Konya Küçükköy, values increase from 5.2 (Untreated) to a peak of 38.8 (circled) at 1 day-Magnetic plus 4h-Ultrasonic, then plateau.

- For Çorum Karapınar, values increase from 6.0 (Untreated) to a peak of 35.3 (circled) at 1 day-Magnetic plus 5h-Ultrasonic.

- For Çorum Kınık, values increase from 9.5 (Untreated) to a peak of 31.6 (circled) at 1 day-Magnetic plus 4h-Ultrasonic.

Bottom Left Panel: A bar chart for Konya Küçükköy comparing mixing methods.

- Untreated: 5.2.

- 1 day-Magnetic plus 4h-Ultrasonic: 38.8.

- 1h-Lab mixer plus 4h-Ultrasonic: 30.9.

- 3h-Lab mixer plus 4h-Ultrasonic: 37.7 (circled).

Bottom Right Panel: A grouped bar chart showing the effect of soil to water ratios (Untreated, 1 to 6, 1 to 2, and 1 to 4) across the three soil types.

- For Konya Küçükköy, the 1 to 6 ratio is highest at 38.8.

- For Çorum Karapınar, the 1 to 2 ratio is highest at 35.8 (circled).

- For Çorum Kınık, the 1 to 2 ratio is highest at 34.0 (circled).

By the end of the MB testing, the largest amount of dispersed clay particles produced by the ultrasonic treatment process was accepted as the control data and success indicator.

Additional experiments by MB tests were conducted to discover the optimum durations for the mixing stage of samples in large amounts by laboratory mixer, and the optimum soil:water ratio. That information is necessary not only for the analyses examining the clay-production potential of soils in laboratory conditions but also for the further industrial use of the clay dispersion method. Here, the laboratory mixer had to be used instead of the magnetic stirrer for mixing larger amounts of soil samples (Fig. 2). The Utest laboratory mixer rotated both on its axis (62 rpm speed) and in an orbit within the chamber (140 rpm speed). The optimum mixing period by the laboratory mixer, followed by the ultrasonic bath process for soil samples in large amounts, was as follows (Fig. 3):

  • – 3 h of mixing with the laboratory mixer, followed by a 4 h ultrasonic bath process for the Konya Küçükköy and Çorum Kınık soil samples;

  • – 3 h of mixing with the laboratory mixer, followed by a 5 h ultrasonic bath process for the Çorum Karapınar soil sample.

The soil samples for ultrasonic treatment and then standard MB testing were prepared at a soil:water ratio of ~1:6 by weight (NF, 1998). These diluted soil samples required a weeks-long drying period, so it was both time-consuming and also had biological implications, as the presence of water in the soil increased the microbial load. To eliminate this challenging drying period, the water content was reduced from its ratio of 1:6 soil:water to an optimum value of 1:2, which exhibits similar CEC values to those achieved with the standard 1:6 ratio (Fig. 3).

Sample preparation: adobe samples with dispersed clay

The preparation steps for the adobe sample with dispersed clay are given in detail below (Fig. 4):

  • – Clay dispersion: the diluted soils (1:2 soil:water ratio by weight) were mixed using the laboratory mixer for 3 h. The Konya Küçükköy and Çorum Kınık soil mixtures were treated in the ultrasonic bath for 4 h, and the Çorum Karapınar soil mixture was treated for 5 h.

  • – Additives: the straw and CaO nanoparticle were added and mixed to control the volumetric stability of the treated soil mixtures. As the calcite causes the flocculation of clay particles, it was added after the clay dispersion process.

  • – Drying for molding: the soil mixtures prepared contained more water than required for molding; therefore, they were kept in an oven at 60°C for drying until the soil reached the proper consistency for molding. Whether the soil mixtures reached appropriate consistency was checked by the Casagrande apparatus (TS, 2017). The soil placed in the Casagrande cup was divided into two parts by a standard groove, and the liquid limit was determined when the two sides of the groove closed after 25 blows of the Casagrande cup; the soil was considered to have achieved appropriate liquid limit values for molding (for samples prepared in 4 cm × 4 cm × 16 cm in prismatic shapes: ⌀10 cm and 2.5 cm thick in cylindrical shapes). The soil mixtures were placed into the molds and compacted manually according to the traditional production techniques of Anatolia.

  • – Curing and drying of adobe samples: the demolded adobe samples were cured and dried in the laboratory for 28 days. The adobe samples were cured in chambers providing 88±6% RH at 20±0.5°C to encourage the pozzolanic reaction during curing as well as to control possible crack formations during initial shrinkage. The extent of the curing process for each sample was determined by checking its pH values over time until reaching <7. By the end of the curing process, the samples were left to dry in laboratory conditions, i.e. ~40% RH and 26°C ambient temperature.

  • – Smoothening the sample surfaces: roughness on the surface of dried adobe samples was smoothed with sandpaper to enhance the accuracy of test measurements.

Figure 4.

Preparation of the treated (top) and untreated (bottom) adobe samples.

A multi-panel flowchart with photos detailing the seven-stage preparation of treated adobe and the four-stage preparation of untreated adobe samples. See long description.
Figure 4. Long description

The flowchart is divided into two horizontal sections.

Top section: Preparation of Treated Adobe Samples. This section is organized into three columns.

1. Clay Dispersion (Stages 1 to 3): First Stage involves diluting soil with water at a 1:2 ratio. Second Stage shows a photo of a blue laboratory mixer used for 3 hours. Third Stage shows a photo of an ultrasonic bath used for 4 or 5 hours.

2. Additive Mixing (Stage 4): This stage is split into two variants. The first variant, Treated adobe, involves adding 1 percent wheat straw to the soil. The second variant, Treated plus C a O adobe, involves adding 1 percent wheat straw and C a O nanoparticles. Photos show the dark brown soil, yellow straw, and white C a O powder.

3. Curing and drying (Stages 5 to 7): Fifth Stage shows a photo of an oven set to 60 degrees Celsius and a liquid limit testing device. Sixth Stage involves putting samples into molds. Seventh Stage shows a photo of samples in a curing chamber for 28 days.

Bottom section: Preparation of Untreated Adobe Samples. This section follows a four-stage process.

1. First Stage: Mixing soil with water at the liquid limit and adding 1 percent wheat straw. A photo shows the thick brown mixture next to a pile of straw.

2. Second Stage: Keeping the mixture at laboratory conditions for 1 day.

3. Third Stage: Placing samples into molds.

4. Fourth Stage: Drying the samples over a period of 28 days.

The preparation of untreated adobe samples involved: (1) mixing the soil taken directly from the resource with water and straw; (2) waiting for 1 day under laboratory conditions to allow the clay layers to reorient into face-to-face associations; (3) molding the soil mixtures; and (4) drying the demolded samples at laboratory conditions of ~40% RH and 26°C ambient temperature for 28 days. The sample-preparation set-up was inspired by the traditional adobe production technique of Anatolia (Aşanlı, Reference Aşanlı2021) and adapted for laboratory conditions.

Physical and mechanical properties of treated adobe samples

The laboratory tests involved basic physical properties (bulk density, particle density, and porosity), water-vapor permeability properties (water-vapor diffusion resistance factor, μ, unitless; water-vapor diffusion-equivalent air-layer thickness, S D, m), capillary-water absorption analyses (capillary-water absorption coefficient, A-value, kg/m2.s0.5), and mechanical properties (flexural strength and compressive strength, MPa) of the treated and untreated adobe samples (RILEM, 1980; ASTM, 2015; TS EN ISO, 2016; ASTM, 2017; TS EN, 2020; ASTM, 2021). In addition, scanning electron microscope (SEM, FEI-Quanta 400F Field Emission in the METU Central Lab, Turkey) analyses were conducted on the Konya Küçükköy and Çorum Karapınar adobe samples to examine the morphological characteristics of clay particles. The samples prepared as powders were attached firmly to carbon tape on an aluminum SEM sample holder by blowing nitrogen gas on the samples with a gun to remove any loose particles.

The bulk density of the adobe samples was calculated from their volumes measured by the method of Archimedes using paraffin-coating on specimens to prevent water absorption and clay swelling during the measurement. The particle density was measured on powdered samples using the pycnometer method, and the total porosity values were derived using the experimentally determined bulk density and the particle density.

The unconfined compression and flexural tests were conducted with the manual testing machine (Losenhausen, Maschinenbau AG Dusseldorf, Germany, LOS), equipped with 2 kg loading per second (Fig. 5). The adobe samples were placed between two square metal pads with dimensions of 3 cm × 3 cm, as the samples have cross-section dimensions of <4 cm due to the shrinkage (Fig. 5).

Figure 5.

Flexural strength testing of prismatic adobe samples and compressive strength testing of the broken sample halves using a manual testing machine (left); water vapor permeability testing of adobe samples by the dry-cup method in a test chamber (right).

A multi-panel photo and diagram set showing mechanical flexural and compressive strength testing of adobe samples alongside water vapor permeability testing in a controlled chamber. See long description.
Figure 5. Long description

The figure consists of two main sections.

Left section: Mechanical testing.

Top: Two photos show a green manual testing machine. The first photo shows the full machine with a circular dial gauge. The second is a close-up of the mechanical grip holding a sample.

Bottom: A technical diagram illustrates the flexural test setup. A rectangular sample measuring 4 c m high and 16 c m long is placed on two steel roller supports spaced 9 c m apart. A central steel support applies force F from above. A second diagram shows a cross-section of a broken sample half being tested for compression using 3 c m by 3 c m square metal pads.

Right section: Permeability testing.

Top: A photo shows three cylindrical adobe samples sealed in orange containers.

Middle: A photo shows several samples inside a digital test chamber.

Bottom: A diagrammatic photo explains the dry-cup method. The test chamber environment is 50 plus or minus 5 percent R H and 23 plus or minus 1 degree Celsius. Blue arrows labeled Water vapor point downward through a sample sealed with wax into an air gap. At the bottom is silica gel maintained at 0 percent R H and 23 plus or minus 1 degree Celsius.

The capillary-water absorption tests were conducted to determine the capillary-water absorption coefficient values of the adobe samples by the partial immersion method in laboratory conditions at ~18°C and 40% RH. The adobe samples were also evaluated visually according to DIN norms (DIN, 2018; Muguda et al., Reference Muguda, Lucas, Hughes, Augarde, Perlot, Bruno and Gallipoli2020). The standard test method conducted on the plastic supports in plastic containers filled with water at a certain level was adapted by placing 3 mm-thick water-saturated absorbent tissue as a bedding layer under the adobe samples to prevent direct contact with the water, which would lead to excessive material loss (Costi de Castrillo et al., Reference Costi de Castrillo, Ioannou and Philokyprou2021; Ribeiro et al., Reference Ribeiro, Oliveira and Bracci2022) (Fig. 6). The capillary water absorption of the samples was measured by weighing the samples at regular time intervals at 15 min, 60 min and 240 min, respectively. The test was conducted for up to 240 min, as some adobe samples lost their integrity after that time. In that time interval, negligible material loss was observed in all samples. The capillary water absorption coefficient (A-value) in kg/m2.s0.5 was determined by the slope of the mass of capillary absorbed water per unit area plotted versus the square root of each time (√t) in the time interval of the test (RILEM, 1980).

Figure 6.

Test configuration for the capillary water absorption experiment.

A two-panel figure showing a technical diagram and a photo of a capillary water absorption test setup with samples in a plastic container. See long description.
Figure 6. Long description

The figure consists of two panels.

Left panel: A technical cross-section diagram of a plastic container. At the base is a plastic perforated surface with a water level at 3 mm height. Two 4 cm by 4 cm by 16 cm samples stand vertically on plastic supports. Between the sample base and the support is a 3 mm thick water-saturated absorbent tissue. Spatial dimensions show approximately 4 cm between the container walls and the samples, and approximately 5 cm between the two samples. A cover is shown at the top.

Right panel: A photo of the physical experiment. Six rectangular stone-like samples are arranged vertically inside a clear plastic bin. Red-capped plastic supports are placed around the samples, with a label pointing to them stating ‘Plastic supports to prevent overturning of the samples’. The samples sit on white absorbent material at the bottom of the container.

Results and Discussion

Clay-composition characteristics of soil resources

The mineralogical compositions of three soil resources were analyzed in terms of their clay content, clay-sized CaCO3 content, and pozzolanic activity to identify their clay composition characteristics. The data obtained from XRD, MAUD analyses, LoI, and pozzolanic activity tests are summarized below (Table 3).

Table 3.

The mineralogical compositions of three soils in terms of <4 μm particle content, clay content, clay-sized CaCO3, and pozzolanic activity

A data table detailing the mineralogical compositions and pozzolanic activity of three soil resources: Konya Küçükköy, Çorum Karapınar, and Çorum Kınık. See long description.
Table 3. Long description

The table consists of five columns: Soil resources, Amount of less than 4 mu m particles in the soil resource (Vol. percent), Mineralogical composition of the less than 4 mu m particles (Minerals and Percentage), and Pozzolanic activity (mg C a O H sub 2 / 1 g pozzolan).

1. Konya Küçükköy: Total volume of particles is 26.4. Minerals include Montmorillonite at 26.1 plus or minus 1.9 percent, Illite-mica at 19 plus or minus 0.7 percent, Kaolinite at 11.4 plus or minus 1.1 percent, and Calcite at 6.2 percent. Trace minerals include Feldspar, goethite, and quartz. Pozzolanic activity is 44.5.

2. Çorum Karapınar: Total volume of particles is 32.8. Minerals include Montmorillonite at 0.7 plus or minus 0.6 percent, Illite-mica at 8.3 plus or minus 1.8 percent, Kaolinite at 24.3 plus or minus 4.9 percent, Chlorite at 20.8 plus or minus 1.3 percent, and Calcite at 5.9 percent. Trace minerals include Feldspar, diopside, quartz, goethite, opal A, and gypsum. Pozzolanic activity is 227.9.

3. Çorum Kınık: Total volume of particles is 14.1. Minerals include Montmorillonite at 8.4 plus or minus 0.3 percent, Illite-mica at 2.9 plus or minus 1.5 percent, Kaolinite at 7.9 plus or minus 0.0 percent, Chlorite at 3.1 plus or minus 0.7 percent, and Calcite at 6.9 percent. Trace minerals include Feldspar, diopside, quartz, and goethite. Pozzolanic activity is 61.1.

The clay compositional characteristics of the <4 μm soils were as follows:

  • – Among the three soil samples, Çorum Kınık soil contained the fewest clay-sized (<2 μm) particles (and these included both swelling and non-swelling clay types), and required the most clay dispersion of all the soils.

  • – Mineralogical analysis revealed substantial differences in clay composition among the soil samples. Konya Küçükköy is dominated by montmorillonite, a swelling clay that can enhance water retention and plasticity but may also increase the risk of shrinkage and volumetric instability; the Çorum Karapınar soil was inherently more volumetrically stable than the others because its clays were mostly non-swelling, containing kaolinite and chlorite in particular. Its consistency limits supported this assessment (Fig. 9), and this made it preferable in terms of adobe production.

  • – <4 μm CaCO3 was detected in all three soils. The dominance of calcite peaks in XRD traces of the Çorum Kınık soil between 0.05 μm and 0.25 μm (Fig. 7) signaled that the clay-sized CaCO3 content in that soil was greater than those in the Konya Küçükköy and Çorum Karapınar soils.

  • – All of the soils showed significant pozzolanic activity; the Çorum Karapınar soil was most prominent in this regard (Table 3). The presence of opal A, a natural pozzolan, identified by XRD analysis of the Çorum Karapınar soil, supported the EDTA test results (Fig. 7).

    Figure 7.

    XRD traces of the Konya Küçükköy, Çorum Karapınar and Çorum Kınık soil resources (C = calcite; CH = chlorite; I-MI = illite-mica; K= kaolinite; M = montmorillonite).

    Three stacked X R D line graphs showing mineral intensity peaks for soil resources from Çorum Kınık, Çorum Karapınar, and Konya Küçükköy. See long description.
    Figure 7. Long description

    The figure consists of three panels, each plotting Intensity on the Y-axis against degrees 2 theta on the X-axis from 5 to 70.

    Top Panel: Çorum Kınık soil. The graph shows a dominant, sharp peak for C at approximately 30 degrees with an intensity near 400. Smaller peaks are labeled from left to right: M and C H at 6 degrees, I-M I at 9 degrees, C H at 12 degrees, I-M I at 20 degrees, C H and I-M I near 25 to 27 degrees, and several C peaks between 35 and 50 degrees.

    Middle Panel: Çorum Karapınar soil. This graph features a broad hump labeled Opal A between 15 and 30 degrees. Distinct peaks include M and C H at 6 degrees, I-M I at 9 degrees, K at 12 degrees, and a cluster of peaks for M, C H, and K between 18 and 22 degrees. A sharp C peak appears at 30 degrees with an intensity of 160. Further peaks for C, M, I-M I, and C H are scattered between 30 and 50 degrees.

    Bottom Panel: Konya Küçükköy soil. The graph shows a broad peak for M at 6 degrees with an intensity of 130. Subsequent peaks include I-M I at 9 degrees, K at 12 degrees, M at 18 degrees, and a series of peaks for I-M I and K between 25 and 28 degrees. A prominent C peak is located at 30 degrees with an intensity of 80, followed by smaller C peaks at 36, 39, 43, and 48 degrees.

Among the three soils, that from Çorum Karapınar was deemed most suitable for our purposes as it has non-swelling clay types in its composition, a significant clay content, it contains clay-sized CaCO3, it shows pozzolanic activity, and has appropriate consistency limits. On the other hand, the Çorum Kınık soil was not suitable for adobe because of the presence of swelling clay types in its composition, it had a smaller clay content, it exhibits less pozzolanic activity and has poorer consistency limits properties. The Konya Küçükköy soil is appropriate for adobe purposes because of its significant clay content and the presence of clay-sized CaCO3 in its composition; it too has appropriate consistency limits. However, there is a dominance of swelling clay content (over non-swelling) and little pozzolanic activity in this soil, and these are properties that cannot be ignored.

In brief, three soil resources had various combinations of clay types in variable amounts, different clay-sized CaCO3 content, pozzolanic characteristics, and consistency limits properties. Adobe materials produced from these soil resources are expected to exhibit different performances regarding volumetric stability, water- and moisture-related, and mechanical properties.

Verification of clay dispersion in soil resources

Soils that were both untreated and treated for clay dispersion were tested by laser diffractometry PSD (particle-size determination) analyses to verify the dispersion of the clay particles in the soils (Fig. 8). The analyses focused on data for particle sizes of <1 μm and <2 μm. Tests for soil consistency limits and LS ratios were also performed to assess the quality of the treated soils for adobe production (Fig. 9).

Figure 8.

Laser diffractometry particle size distributions (PSDs) of the soil resources before and after ultrasonic treatment.

Three line graphs showing particle size distributions for soil resources before and after ultrasonic treatment. See long description.
Figure 8. Long description

The figure consists of three line graphs. Each graph shares the same axes: the x-axis represents Particle sizes in mu m on a logarithmic scale from 0.3 to 1000, and the y-axis represents Percentage by vol., % from 0 to 7. Vertical dashed lines mark the 1 mu m and 2 mu m thresholds.

Top Panel: Konya_Küçükköy. The untreated blue line shows a bimodal distribution with peaks near 0.6 mu m and 4 mu m. The treated red line shows a significant increase in volume for particles smaller than 10 mu m, with a primary peak at 0.6 mu m reaching nearly 6%. Text labels indicate the less than 1 mu m clay fraction increased from 9.5% to 24.2%, and the less than 2 mu m fraction increased from 15.6% to 37.6%.

Bottom-Left Panel: Çorum_Karapınar. The untreated blue line has peaks at 0.6 mu m and 10 mu m. After treatment, the red line shows a higher concentration in the 0.4 to 0.8 mu m range. The less than 1 mu m clay fraction increased from 12.6% to 18.3%, and the less than 2 mu m fraction increased from 19% to 28.1%.

Bottom-Right Panel: Çorum_Kınık. The untreated blue line is concentrated in the 2 to 100 mu m range with a peak near 20 mu m. The treated red line shows a dramatic shift toward smaller particles, creating new peaks between 0.5 and 10 mu m. The less than 1 mu m clay fraction increased from 0% to 7.9%, and the less than 2 mu m fraction increased from 5% to 21.2%.

Figure 9.

Casagrande plasticity chart showing the liquid limit (LL) and plasticity index (PI) of the untreated and treated soil samples relative to the recommended consistency limits for adobe soils (yellow shaded area: PI = 16–33% and LL = 31–50%) (top), and the linear shrinkage (LS) ratio values of the untreated and treated soil samples (at bottom).

A two-panel figure featuring a Casagrande plasticity chart for soil samples and a data table with linear shrinkage ratios and sample photos. See long description.
Figure 9. Long description

The top panel is a line graph titled Casagrande plasticity chart. The y-axis is P I percent (Plasticity Index) from 0 to 50. The x-axis is L L percent (Liquid Limit) from 0 to 80. A diagonal line labeled A-line P I equals 0.73 times (L L minus 20) divides the chart. A yellow shaded rectangle represents the recommended adobe soil range with P I between 16 and 33 percent and L L between 31 and 50 percent. Six data points are plotted: Untreated Konya Küçükköy (purple), Treated Konya Küçükköy (pink), Untreated Çorum Karapınar (green), Treated Çorum Karapınar (orange), Untreated Çorum Kınık (blue), and Treated Çorum Kınık (red). Most treated samples shift toward the yellow adobe range compared to untreated counterparts.

The bottom panel is a table showing Linear Shrinkage (L S) ratio percentages for three samples.

1. Konya Küçükköy: Untreated 17.1, Treated 21.

2. Çorum Karapınar: Untreated 10.7, Treated 14.3.

3. Çorum Kınık: Untreated 8.6, Treated 11.4.

To the right of the data are three horizontal photographs of soil bars in molds, showing varying degrees of cracking and shrinkage, accompanied by a 10 centimeter scale bar.

Increases in the amounts of clay and silt were observed in the treated Konya Küçükköy and Çorum Kınık soil samples (particle sizes of <15 μm), and the treated Çorum Karapınar soil (particle sizes of <5 μm). A sharp decrease was observed in the amount of larger particles. Supporting that, the >2 mm particles were no longer detected after the ultrasonic treatment (Fig. 8), indicating that the coarse aggregates had been dispersed into finer particles, which may increase the possibility of shrinkage problems (Stefanidou and Papayianni, Reference Stefanidou and Papayianni2005). Changes in PSD confirmed that the dispersion of the flocculated clay particles and the dispersion of clay particles stuck to the coarser aggregates was achieved by the ultrasonic treatment.

Considering the clay content in the <1 μm particle-size fraction as a lower limit and in the <2 μm particle size fraction as an upper limit, the amounts of clay in the untreated soil samples from Konya Küçükköy, Çorum Karapınar, and Çorum Kınık soils were 9.5–15.6%, 12.6–19%, and 0–5% by volume, respectively (Fig. 8). After ultrasonic treatment, the clay contents increased to 24.2–37.6%, 18.3–28.1%, and 7.9–21.2% by volume, respectively (Fig. 8). Among the three soil samples, that from Çorum Kınık was least suitable for adobe production as its clay content was <10%. Ultrasonic treatment made the soil suitable for use in adobe production by dispersing the clay content to within acceptable limits. While no clay was detected in the <1 μm fraction of the untreated Çorum Kınık soil, ultrasonic treatment dispersed the flocculated clay into this size fraction, resulting in a clay content of 7.9% (Fig. 8). In short, treated soil samples achieved sufficient clay content for adobe bricks (between 10 and 40%; Schwalen, Reference Schwalen1935; Brown et al., Reference Brown, Robbins and Clifton1979; Houben and Guillaud, Reference Houben and Guillaud1994; Norton, Reference Norton1997; Walker, Reference Walker2001). The greater increases in clay content were observed for Konya Küçükköy and Çorum Kınık soils in which the montmorillonite content was dominant (Fig. 8; Table 3). Although the Çorum Karapınar soil had the largest clay content among the three soils, it had the lowest rate of increase in clay content after treatment due to its mainly kaolinite content. The combined interpretation of laser diffractometry PSD analyses and MAUD analyses (Fig. 8; Table 3) showed that the soils rich in montmorillonite had significant potential to benefit from the clay-particles dispersion process (Rolfe et al., Reference Rolfe, Miller and McQueen1960).

The consistency limits of the soil samples are the properties related directly to the amounts of clay present. Increases in the consistency limits (i.e. liquid [LL] and plastic [PL] limits) and LS ratio parameters were indicators of the successful dispersion of clay in soil by increasing the specific surface area of the clay content. The data obtained for the untreated and treated soil samples are summarized in Fig. 9:

  • – The Konya Küçükköy and Çorum Karapınar soils had greater LL values (39.8% and 37.8%, respectively) than the Çorum Kınık soil (LL of 26.6%). The PI values of all soil samples were in the range 13–17.4%. According to these consistency limits, the Konya Küçükköy and Çorum Karapınar soils had medium plasticity and medium shrinkage potential, while the Çorum Kınık soil resource had low plasticity and medium shrinkage potential. Based on the recommended PI range of 16–33% and LL range of 31–50% for adobe production (Delgado and Guerrero, Reference Delgado and Guerrero2007; Houben and Guillaud, Reference Houben and Guillaud1994), the Konya Küçükköy and Çorum Karapınar soil resources are deemed appropriate for adobe production, while that from Çorum Kınık was not.

  • – After the ultrasonic treatment, the consistency limits of the Çorum Kınık soil changed remarkably. Dispersion of the clay content shifted the consistency limits from values unsuitable for adobe production to the recommended range for adobe production.

  • – The LL values of the treated soil samples are between 31.5 and 42.6%, and their PI values are between 15.6 and 19.1%, corresponding to medium plasticity and medium shrinkage potential. The data fell into the PI and LL ranges recommended for adobe soils and indicated that all soil resources after ultrasonic treatment were appropriate for adobe production.

  • – The LS ratios of the soils, which vary between 8.6 and 17.1%, are above the critical level of 8%, indicating a significant possibility of shrinkage and cracking problems in the resultant adobe material (Dawson et al., Reference Dawson, Altmeyer, Barber and Dubose1956). The treatment increased the initial LS ratios by ~3–4%; therefore, the treated soils became more susceptible to volumetric instability problems. The loss of >2 mm aggregates after treatment increased the linear shrinkage problem of treated soil samples. To control the shrinkage and crack problems, straw fibers (1 wt.%) were integrated into the adobe matrix as a stabilizing agent. Optimization of particle-size distribution (PSD) through fiber content and the re-addition of coarse aggregates should be investigated in future studies.

  • – In brief, the results of PSD and consistency limits tests verified that ultrasonic treatment increased the dispersed clay content in the soils. The success of ultrasonic treatment was related to the amount of montmorillonite in the soil mixture, as montmorillonite showed the greatest dispersion characteristics relative to the other clay types, such as illite and kaolinite (Rolfe et al., Reference Rolfe, Miller and McQueen1960).

Performance assessment of treated adobe samples

The bulk density (dry density) of KuT, KaT, and KıT (treated samples) increased from 1.96±0.0, 2.20±0.2, and 1.82±0.1 g cm–3 to 2.03±0.0, 2.25±0.2, and 1.92±0.2 g cm–3, respectively. The densities of KuTC, KaTC, and KıTC were 2.06±0.0, 2.13±0.0, and 1.75±0.0 g cm–3, respectively (Fig. 10). The porosities of adobe samples produced from the Konya Küçükköy, Çorum Karapınar, and Çorum Kınık soils ranged between 22.2–26.0%, 12.4–18.6%, and 25.6–34.8%, with particle densities in the ranges of 2.63–2.65, 2.57–2.61, and 2.59–2.69 g cm–3, respectively (Fig. 10).

Figure 10.

Bulk density (dry density), particle density, and porosity of the adobe samples.

A grouped bar and scatter chart comparing density and porosity across nine adobe samples categorized by mineral content. See long description.
Figure 10. Long description

A clustered bar chart with an overlaid scatter plot. The primary y-axis on the left measures Bulk Density and Particle Density in g/cm cubed, ranging from 0.0 to 3.0. The secondary y-axis on the right measures Porosity percentage, ranging from 0 to 40. The x-axis lists nine samples divided into three mineralogical groups.

Group 1: Rich in Montmorillonite (Samples K u U, K u T, K u T C)

* Particle Density (dotted white bar): Constant between 2.63 and 2.65.

* Bulk Density (solid orange bar): Increases slightly from 1.96 to 2.06.

* Porosity (blue square): Decreases from 26.0 to 22.2.

Group 2: Rich in Kaolinite (Samples K a U, K a T, K a T C)

* Particle Density: Constant between 2.57 and 2.61.

* Bulk Density: Fluctuates between 2.13 and 2.25.

* Porosity: Lowest values in the set, ranging from 12.4 to 18.6.

Group 3: Rich in Kaolinite plus Montmorillonite (Samples K l U, K l T, K l T C)

* Particle Density: Ranges from 2.59 to 2.69.

* Bulk Density: Decreases from 1.82 to 1.75.

* Porosity: Highest values in the set, peaking at 34.8 for sample K l T C.

The adobe samples produced from the Çorum Karapınar soil were found to have the greatest bulk density, followed by those produced from the Konya Küçükköy soil resource, while the lowest bulk density range belonged to the adobe samples produced from the Çorum Kınık soil resource. The reason for the greatest bulk density and the smallest porosity for the Çorum Karapınar adobe samples might be due to the greatest pozzolanic activity and its high clay content (Meddah and Tagnit-Hamou, Reference Meddah and Tagnit-Hamou2009). A very slight increase in the bulk densities of the treated adobe samples compared with the untreated ones was determined, as expected. However, porosity was a more determinative parameter than bulk density, following the changes in clay content in the soil compositions, and its impact on physical and mechanical properties.

The SEM images show that flocculated clay associations, with edge-to-edge or edge-to-face connections, were found together with aggregated clay particles with face-to-face connections in the untreated adobe samples. The aggregated clay particles composed of face-to-face stacked clay layers were observed in the treated adobe samples (Fig. 11). In addition, some flocculated clay particles in the KaTC sample may be due to the additive effect of the CaO nanoparticles.

Figure 11.

SEM images of adobe samples produced from Konya Küçüköy and Çorum Karapınar soil resources.

Six S E M micrographs showing the microscopic structure of untreated and treated adobe soil samples from two different regions. See long description.
Figure 11. Long description

A multi-panel set of six S E M micrographs arranged in two columns.

Top-left panel K u U: Küçükköy-Untreated. Shows a dense network of clay particles. Blue arrows point to Flocculated Clay Mineral layers at the top and Aggregated Clay Mineral Layers at the bottom. Scale bar is 2 micrometers at 50,000 times magnification.

Top-right panel K a U: Karapınar-Untreated. Displays a more porous and fragmented texture. Scale bar is 20 micrometers at 5,000 times magnification.

Middle-left panel K u T: Küçükköy-Treated. Shows flatter, more cohesive plate-like structures. Blue arrows point to Aggregated Clay Mineral Layers. Scale bar is 2 micrometers at 50,000 times magnification.

Middle-right panel K a T: Karapınar-Treated. Features large, distinct stacked plates. Blue arrows point to Aggregated Clay Mineral Layers. Scale bar is 5 micrometers at 20,000 times magnification.

Bottom-left panel K u T C: Küçükköy-Treated plus C a O. Shows a highly dense, cemented texture. Blue arrows point to Aggregated Clay Mineral Layers. Scale bar is 2 micrometers at 50,000 times magnification.

Bottom-right panel K a T C: Karapınar-Treated plus C a O. Displays a mix of textures. Blue arrows point to Flocculated Clay Mineral Layers at the top and Aggregated Clay Mineral Layers at the bottom. Scale bar is 2 micrometers at 50,000 times magnification.

All panels include a black data strip at the bottom with technical parameters including date, detector E T D, H V 20.00 k V, and M E T U CENTRAL LAB.

The comparison of untreated and treated samples showed that treated adobe samples have greater compressive and flexural strengths than the untreated ones (Fig. 12). In addition, treated samples were denser and less porous than untreated ones (Fig. 10). These results signaled the positive impact of using dispersed-clay soil in adobe production; providing aggregated clay layers formed a denser particle framework and stronger interparticle bonds, which improved the mechanical behavior of the adobe samples. The average compressive strengths of the treated KuT, KaT, and KıT adobe samples increased from 6.8±0.7 MPa to 8.3±1.2 MPa, from 6.9±1.7 MPa to 7.7±0.7 MPa, and from 2.8±0.5 MPa to 5.4±0.1 MPa, respectively, corresponding to the 21.4, 10.4, and 91.5% increases in their respective compressive strengths. The greatest increase in compressive strength was observed in the KıT adobe sample, followed by the KuT sample, while the smallest increase was determined in the KaT adobe sample. The order of enhancement in compressive strength was consistent with the increase in clay content, with ratios of 1.41, 0.78, and 3.76, for the <2 μm particle sizes of the Konya Küçükköy, Çorum Karapınar, and Çorum Kınık soils, respectively. That relationship is visible in Fig. 12 which shows the correlation between clay content and compressive strength. The difference between the trend lines of untreated and treated adobe samples might be due to their clay-type contents.

Figure 12.

Compressive and flexural strengths of the adobe samples relative to the minimum requirements specified in national and international standards (Table 1) (top), and the correlation between compressive strength and clay content (bottom).

A two-panel figure with a bar chart of mechanical strengths and a scatter plot showing the correlation between compressive strength and clay content. See long description.
Figure 12. Long description

The top panel is a bar chart with a y-axis labeled Mechanical Strength, M P a, ranging from 0 to 9. The x-axis lists adobe samples grouped by mineral composition. Blue bars represent Rich in Montmorillonite (K u U, K u T, K u T C), orange bars represent Rich in Kaolinite (K a U, K a T, K a T C), and green bars represent Rich in Kaolinite plus Montmorillonite (K i U, K i T, K i T C).

Under Compressive Strength, values range from 2.81 to 8.72 M P a, all exceeding the red dashed minimum requirement lines at 1.15 and 1.73 M P a. Under Flexural Strength, values are much lower, ranging from 0.14 to 0.53 M P a, with some samples falling below the minimum requirement lines at 0.24 and 0.34 M P a.

The bottom panel is a scatter plot with x-axis Clay Content, percentage (0 to 50) and y-axis Compressive Strength, M P a (0 to 10). Three linear trends are shown.

1. Untreated adobe samples (blue dots): y = 0.3135x + 1.3962, R-squared = 0.9554. This shows a gradual linear increase.

2. Treated adobe samples (red dots): y = 4.9533x minus 6.2285, R-squared = 0.8416. This shows a steep linear increase starting at 20 percent clay.

3. Treated plus C a O adobe samples (yellow dots): y = 0.3404x minus 3.8325, R-squared = 0.9676. This shows a linear increase parallel to the untreated samples but at a higher clay content threshold.

The average flexural strengths of the KuT, KaT, and KıT samples increased from 0.26±0 MPa to 0.30±0 MPa, from 0.31±0 MPa to 0.53±0.1 MPa, and from 0.14±0 MPa to 0.36±0 MPa, respectively, corresponding to 17.6, 72.8, and 147.9% increases, respectively.

The greatest flexural strength performance belongs to KaT, which signaled the impact of the very pozzolanic nature of the Çorum Karapınar soil. Pozzolanic activity is known to decrease porosity and enhance the cohesion between straw and adobe matrix (Sharma et al., Reference Sharma, Marwaha and Vinayak2016; Ouedraogo et al., Reference Ouedraogo, Dao, Millogo, Aubert, Messan, Seynou and Zerbo2019). The largest increase in flexural strength was observed in the KıT sample, which had a significant pozzolanic structure and the greatest rate of clay increase (Fig. 8; Table 3).

In short, the increase in the dispersed clay mineral layer and the pozzolanic activity strengthened the adhesion between the straw fibers and the adobe matrix and contributed to the increase in the flexural strength in the treated adobe samples.

Except for the KuTC adobe sample, the addition of CaO nanoparticles to the treated KaTC and KıTC adobe sample mixtures reduced the compressive strength performance. In other words, the positive effects of the clay dispersion process, which increased the compressive strength and bulk density, decreased when the CaO additive was added (Figs 10 and 12). Similarly, the flexural strength of all treated adobe samples decreased when the CaO additive was mixed with their adobe composition (Fig. 12). The improvement observed in the compressive strength of the KuTC adobe sample (reaching 8.72 MPa) could be attributed to the characteristics of the untreated Konya Küçükköy soil, which has a dominant montmorillonite content (26.1%) which may have facilitated the interaction between the clay and the CaO additive. In brief, the data showed that the CaO additive reduced the compressive and flexural strengths of the treated adobe samples. Contrary to the commonly reported improvement in strength and bearing capacity of lime-stabilized soils, its negative effect here might be due to the clay-sized CaCO3 content and/or the presence of non-swelling clay types inherently existing in their soil compositions. Addition of CaO may have promoted particle flocculation, resulting in reduced dense particle packing and reduced mechanical performance. Furthermore, the relatively small amount of CaO (1 wt.%) may have been insufficient to generate substantial pozzolanic strengthening. However, the exact mechanisms responsible for this behavior remain unclear. The role of clay-sized CaCO3 and CaO nanoparticles in clay flocculation, particle arrangement, and bonding needs to be investigated in detail by further microstructural investigations.

All treated adobe samples and the KuU, KaU, and KaTC samples presented compressive and flexural strength performances above the minimum required levels (Table 1; Fig. 12). Although two untreated samples were sufficient for the required mechanical strength for adobe, they were treated to observe the effect of clay dispersion on the samples including different clay minerals compositions and to further improve the quality of adobe soils, which can be used efficiently in areas with a shortage of adobe soil resources.

In addition, according to the classification of DIN norms (Table 1), the compressive strengths of treated KuT and KaT adobe samples exceeded the sixth highest class, while their untreated samples belonged to the fourth and fifth classes, respectively. The treated KıT adobe increased to the fourth and fifth classes, but its untreated version was in the second class (DIN, 2018) (Fig. 13).

Figure 13.

Minimum and average compressive strengths of the untreated and treated adobe samples in relation to the strength classes defined by the DIN standards (DIN, 2018).

A grouped bar chart comparing minimum and average compressive strengths of adobe samples across three mineral compositions and D I N strength classes. See long description.
Figure 13. Long description

The Y-axis represents Compressive Strength in M p a, ranging from 0 to 9. Horizontal shaded bands indicate D I N strength classes: 2nd Class (2.2 to 2.8), 3rd Class (3.2 to 4.1), 4th Class (4.4 to 5.5), 5th Class (5.8 to 6.6), and 6th Class (6.8 to 8.0). The X-axis categorizes samples into three mineral groups, each with an untreated (U) and treated (T) pair. Blue bars represent minimum values and orange bars represent average values.

* Rich in Montmorillonite: K u U shows a minimum of 5.8 and average of 6.8. K u T shows a minimum of 6.8 and average of 8.3.

* Rich in Kaolinite: K a U shows a minimum of 4.3 and average of 6.9. K a T shows a minimum of 6.8 and average of 7.7.

* Rich in Kaolinite plus Montmorillonite: K l U shows a minimum of 2.2 and average of 2.8. K l T shows a minimum of 4.1 and average of 5.4.

Across all groups, treated samples (T) exhibit higher compressive strengths than untreated samples (U), often moving the material into a higher D I N strength class.

The μ values (unitless) measured by the dry-cup method for KuT, KaT, and KıT increased from 17.4±0.5, 32.2±1.9, and 7.2±0.1 to 18.4±0.5, 33.8±2.3, and 17.5±1.6, respectively. The μ values of KuTC, KaTC, and KıTC were 21.8±2.1, 31.1±0.7, and 10.2±1.6, respectively. The measured μ values fell within the range of μ values (11–44) reported in the literature, measured by the dry-cup method, corresponding to the adobe samples produced in the laboratory (Table 1). The SD2.5 cm values for KuT, KaT, and KıT also increased from 0.4±0, 0.7±0, and 0.2±0 m to 0.4±0, 0.8±0.1, and 0.3±0 m, respectively. The SD2.5 cm values of KuTC, KaTC, and KıTC were found to be 0.4±0, 0.6±0, and 0.2±0 m (Fig. 14). Among all adobe samples, those produced from the Çorum Karapınar soil were the least vapor-permeable adobe products, while those produced from the Çorum Kınık soil were the most vapor-permeable adobe products. As observed in the Çorum Karapınar adobe samples, adobe mixtures with more pozzolanic activity properties had the potential to produce denser, less porous adobe materials that exhibited less vapor permeability.

Figure 14.

Water vapor diffusion resistance factor (μ) and SD2.5 cm values of the adobe samples determined by the dry cup method.

A bar and scatter chart comparing water vapor resistance and diffusion thickness across nine adobe samples grouped by mineral composition. See long description.
Figure 14. Long description

A bar chart with two Y-axes. The left Y-axis represents the Water vapor resistance factor, mu, unitless, ranging from 0 to 40. The right Y-axis represents the Water vapor diffusion-equivalent air layer thickness, S D, in meters, ranging from 0.0 to 0.9. The X-axis lists nine adobe samples divided into three sections by vertical dashed lines.

* Section 1: Rich in Montmorillonite. Samples K u U, K u T, and K u T C show mu values of 17.32, 18.43, and 21.85 respectively. Corresponding S D sub 2.5 values, marked by yellow diamonds, are 0.38, 0.40, and 0.41.

* Section 2: Rich in Kaolinite. Samples K a U, K a T, and K a T C show the highest resistance with mu values of 32.17, 33.80, and 31.15. Corresponding S D sub 2.5 values are 0.70, 0.78, and 0.61.

* Section 3: Rich in Kaolinite plus Montmorillonite. Samples K i U, K i T, and K i T C show mu values of 7.16, 17.48, and 10.20. Corresponding S D sub 2.5 values are 0.16, 0.35, and 0.23.

A legend at the bottom identifies blue bars as the Water vapor resistance factor, mu, and yellow diamonds as the Water vapor diffusion-equivalent air layer thickness, S D.

Compared with the untreated samples, the treated adobe samples produced from dispersed-clay soils had slightly more resistance to water-vapor diffusion (Fig. 14). These data confirm statements in the literature that an increase in the clay content in the adobe mixture decreased the water-vapor permeability (Dondi et al., Reference Dondi, Principi, Raimondo and Zanarini2003; Maillard and Aubert, Reference Maillard and Aubert2014). Among the treated adobe samples, the greatest increase in μ and SD2.5 cm values was observed for the KıT sample as the greatest ratio of clay content produced vs the existing clay content, especially for the particle sizes of <2 μm (Fig. 8), and the largest reduction in porosity with 5.2% was observed in that sample (Fig. 10).

During the capillary-water absorption tests, all untreated and treated adobe samples, produced from the Konya Küçükköy, Çorum Karapınar, and Çorum Kınık soils, exhibited cracks and deformations due to swelling after 1 h. According to the DIN norms (DIN, 2018), this performance signaled that all adobe samples are in Class II, under the internal wall category (Table 1). The capillary-water absorption coefficient values (A-values) of KuT, KaT, and KıT increased slightly from 0.3±0.1, 0.3±0, and 0.3±0 kg/m2.s0.5 to 0.4±0, 0.4±0, and 0.3±0.1 kg/m2.s0.5, respectively (Fig. 15). These values indicated high capillary-water suction characteristics within the range of 0.01–0.3 kg/m2.s0.5 given in the literature (Lanzón and García-Ruiz, Reference Lanzón and García-Ruiz2009; Türkmen et al., Reference Türkmen, Ekinci, Kantarcı and Sarıcı2017; Roopa Baliga et al., Reference Roopa Baliga, Prathibha, Nayak and Sumanth2018; Costi de Castrillo et al., Reference Costi de Castrillo, Ioannou and Philokyprou2021). In other words, if used as construction materials, these adobe samples will be susceptible to water absorption and need to be protected from direct exposure to wetting conditions.

Figure 15.

Capillary water absorption coefficient (A-value) of the adobe samples.

A bar chart comparing capillary water absorption coefficients across nine adobe samples grouped by mineral composition. See long description.
Figure 15. Long description

The y-axis represents the Capillary water absorption coefficient, A-value, measured in k g forward slash m squared dot s super 0.5, with a scale from 0.0 to 0.8. The x-axis lists nine adobe samples. A legend in the top right identifies three color-coded groups.

Group 1: Rich in Montmorillonite (blue bars)

- K u U: 0.33

- K u T: 0.42

- K u T C: 0.50

Group 2: Rich in Kaolinite (orange bars)

- K a U: 0.35

- K a T: 0.38

- K a T C: 0.36

Group 3: Rich in Kaolinite plus Montmorillonite (green bars)

- K l U: 0.32

- K l T: 0.33

- K l T C: 0.39

The data shows that the Montmorillonite-rich group reaches the highest absorption levels, specifically in the K u T C sample.

Compared with the untreated sample, clay-dispersion treatment and the addition of CaO to the treated sample increased the A-value of the KuTC to 0.5±0.1 kg/m2.s0.5 while the A-values of the KaTC and KıTC adobe samples, 0.4±0.1 kg/m2.s0.5 and 0.4±0.1 kg/m2.s0.5, were similar to the values of untreated samples (Fig. 15). Control of the capillary-suction characteristics of the treated samples (KaT, KaTC, KıT, and KıTC) might be attributed to: (1) the presence of non-swelling clay types; and (2) significant pozzolanic activity, and a large amount of clay-sized calcite in the clay content. On the other hand, a slight increase in capillary suction observed in treated Konya Küçükköy samples (KuT and KuTC) might be due to the largest amount of <2 μm clay particles, with as much as 38% montmorillonite.

The greater mechanical strengths of treated adobe samples were achieved by creating a denser, less porous matrix, leading to an increase in the water-vapor diffusion resistance (μ), making the treated adobe samples less ‘breathable’ than the untreated ones. Furthermore, capillary suction was probably increased by dispersed clay content, as evidenced by the slightly higher A-values in the treated samples. On the other hand, their μ values (17.48–33.80) of the treated adobe samples remained within the breathable range for earthen materials given in the literature, and continued to be suitable for interior applications in terms of water sensitivity.

Conclusions

The present study has shown that adobe material with greater mechanical strengths can be achieved by the dispersion of clay content which exists naturally in adobe soil resources. The clay content was dispersed in the soils by ultrasonic treatment, and an improved performance of treated soil resources compared with untreated soils was achieved.

Treated adobe samples had greater compressive and flexural strengths with denser and less porous characteristics compared with untreated samples, while treated adobe samples did not contribute to volumetric stability, breathability, or capillary-suction properties. The enhanced compressive and flexural strengths of the treated adobe samples, in the ranges of 5.17–8.18 MPa and 0.30–0.53 MPa, respectively, were obtained; these exceed the minimum levels required in various regulations/codes (Table 1).

The results presented an applicable clay-dispersion treatment that improved the quality of adobe soil. The treatment was efficient for adobe soils rich in montmorillonite but was less efficient for soils rich in kaolinite. If montmorillonite was present in adobe soils with otherwise insufficient clay contents, the soil could become appropriate for use as adobe after the clay-dispersion treatment. While more complex than traditional methods, the proposed method enables the production of high-strength adobe products that meet modern building standards and offer a sustainable solution for regions facing soil-resource depletion.

The addition of CaO nanoparticles to treated adobe samples (which were dominated by montmorillonite in their clay composition) provided a slight increase in the compressive strength. On the other hand, the CaO additive had an adverse impact on the mechanical strength of the treated adobe samples, particularly those which already contain clay-sized CaCO3 and non-swelling clay types in their clay composition.

The present study has established the fundamental mechanical and physical performances of treated adobe; further investigations regarding long-term durability performance, including freeze-thaw resistance and salt erosion, would validate its practical suitability in diverse climate conditions, however. In addition, evaluation of energy-cost efficiency is required to fully assess its large-scale applicability in the construction industry.

Acknowledgments

None.

Author contributions

Investigation: M.E.; Methodology: M.E.; Supervision: A.D., E.C.-S.; Validation: A.D.; Writing – original draft: M.E.; Writing – review and editing: M.E., A.D.

Data availability statement

Data will be made available on reasonable request of the authors.

Financial support

The study was partially funded by the Scientific and Technological Research Council of Turkey (TUBITAK No. 123M641).

Competing interests

The authors declare none.

References

Abanto, G. A., Karkri, M., Lefebvre, G., Horn, M., Solis, J. L., & Gómez, M. M. (2017). Thermal properties of adobe employed in Peruvian rural areas: experimental results and numerical simulation of a traditional bio-composite material. Case Studies in Construction Materials, 6, 177–191. https://doi.org/10.1016/j.cscm.2017.02.001CrossRefGoogle Scholar
Al-Ajmi, F., Abdalla, H., Abdelghaffar, M., & Almatawah, J. (2016). Strength behavior of mud brick in building construction. Open Journal of Civil Engineering, 6, 482–494. https://doi.org/10.4236/ojce.2016.63041CrossRefGoogle Scholar
Alther, G. (2004). Some practical observations on the use of bentonite. Environmental & Engineering Geoscience, 10, 347–359. https://doi.org/10.2113/10.4.347CrossRefGoogle Scholar
Aşanlı, M. (2021). Geleneksel Yapı Teknikleri: Doğal ve Ekolojik Yapı Rehberi. Yeni İnsan Yayınevi. https://books.google.com.tr/books?id=ptwmEAAAQBAJGoogle Scholar
ASTM (2015). Standard Test Method for Rate of Water Absorption of Masonry Mortars (ASTM C1403-15:2015). https://doi.org/10.1520/C1403-15CrossRefGoogle Scholar
ASTM (2017). Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer (ASTM D 854–02:2017). https://doi.org/10.1520/D0854-02CrossRefGoogle Scholar
ASTM (2021). Standard Test Methods for Laboratory Determination of Density and Unit Weight of Soil Specimens (ASTM D7263−21:2021). https://doi.org/10.1520/D7263-21CrossRefGoogle Scholar
Azzam, E. M. S., Sayyah, S. M., & Abdelrahman, A. (2013). Fabrication and characterization of nanoclay composites using synthesized polymeric thiol surfactants assembled on gold nanoparticles. Egyptian Journal of Petroleum, 22, 493–499. https://doi.org/10.1016/j.ejpe.2013.11.011CrossRefGoogle Scholar
Bahobail, M. A. (2012). The mud additives and their effect on thermal conductivity of adobe bricks. Journal of Engineering Sciences, Assiut University, 40, 21–34. https://doi.org/10.21608/jesaun.2012.112711Google Scholar
Barton, C., & Karathanasis, A. D. (2002). Clay minerals. In Encyclopedia of Soil Science, ed. Lal, R., pp. 187–192. Marcel Dekker, New York.Google Scholar
Bektaş, C. (2018). Türk evi. Yapımevi Yayıncılık. https://books.google.com.tr/books?id=6O21vQEACAAJGoogle Scholar
Belarbi, Y., Sawadogo, M., Poullain, P., Issaadi, N., Hamami, A. E. A., Bonnet, S., & Belarbi, R. (2022). Experimental characterization of raw earth properties for modeling their hygrothermal behavior. Buildings, 12, 648. https://doi.org/10.3390/buildings12050648CrossRefGoogle Scholar
Binici, H., Aksogan, O., & Shah, T. (2005). Investigation of fibre reinforced mud brick as a building material. Construction and Building Materials, 19, 313–318. https://doi.org/10.1016/j.conbuildmat.2004.07.013CrossRefGoogle Scholar
Binici, H., Aksogan, O., Bodur, M. N., Akca, E., & Kapur, S. (2007). Thermal isolation and mechanical properties of fibre reinforced mud bricks as wall materials. Composites in Civil Engineering, 21, 901–906. https://doi.org/10.1016/j.conbuildmat.2005.11.004Google Scholar
Binici, H., Aksogan, O., Bakbak, D., Kaplan, H., & Isik, B. (2009). Sound insulation of fibre reinforced mud brick walls. Construction and Building Materials, 23, 1035–1041. https://doi.org/10.1016/j.conbuildmat.2008.05.008CrossRefGoogle Scholar
Blondet, M., Vargas-Neumann, J., & Tarque, N. (2008). Available low-cost technologies to improve the seismic performance of earthen houses in developing countries. The 14th World Conference on Earthquake Engineering.Google Scholar
Brown, P. W., Robbins, C. R., & Clifton, J. R. (1979). Adobe. II: Factors affecting the durability of adobe structures. Studies in Conservation, 24, 23–39. JSTOR. https://doi.org/10.2307/1505920Google Scholar
Calatan, G., Hegyi, A., Dico, C., & Mircea, C. (2016). Determining the optimum addition of vegetable materials in adobe bricks. 9th International Conference Interdisciplinarity in Engineering, INTER-ENG 2015, 8-9 October 2015, Tirgu Mures, Romania, 22, 259–265. https://doi.org/10.1016/j.protcy.2016.01.077Google Scholar
Camerini, R., Chelazzi, D., Giorgi, R., & Baglioni, P. (2018). Hybrid nano-composites for the consolidation of earthen masonry. Journal of Colloid and Interface Science, 539. https://doi.org/10.1016/j.jcis.2018.12.082Google ScholarPubMed
Carroll, D. (1970). Clay Minerals: A Guide to Their X-ray Identification. Geological Society of America. https://doi.org/10.1130/SPE126Google Scholar
Choobbasti, A. J., Samakoosh, M. A., & Kutanaei, S. S. (2019). Mechanical properties soil stabilized with nano calcium carbonate and reinforced with carpet waste fibers. Construction and Building Materials, 211, 1094–1104. https://doi.org/10.1016/j.conbuildmat.2019.03.306CrossRefGoogle Scholar
Corradi, A., Manfredini, T., Pellacani, G., & Pozzi, P. (2005). Deflocculation of concentrated aqueous clay suspensions with sodium polymethacrylates. Journal of the American Ceramic Society, 77, 509–513. https://doi.org/10.1111/j.1151-2916.1994.tb07022.xCrossRefGoogle Scholar
Costi de Castrillo, M., Ioannou, I., & Philokyprou, M. (2021). Reproduction of traditional adobes using varying percentage contents of straw and sawdust. Construction and Building Materials, 294, 123516. https://doi.org/10.1016/j.conbuildmat.2021.123516CrossRefGoogle Scholar
Danso, H., Martinson, B., Ali, M., & Mant, C. (2015). Performance characteristics of enhanced soil blocks: a quantitative review. Building Research & Information, 43, 253–262. https://doi.org/10.1080/09613218.2014.933293CrossRefGoogle Scholar
Dawson, R. F., Altmeyer, W. T., Barber, E. S., & Dubose, L. A. (1956). Discussion of engineering properties of expansive clays. Transactions of the American Society of Civil Engineers, 121, 664–675. https://api.semanticscholar.org/CorpusID:113351229 10.1061/TACEAT.0007284CrossRefGoogle Scholar
Delgado, M. C. J., & Guerrero, I. C. (2007). The selection of soils for unstabilised earth building: a normative review. Construction and Building Materials, 21, 237–251. https://doi.org/10.1016/j.conbuildmat.2005.08.006CrossRefGoogle Scholar
DIN (2018). Earth Blocks – Requirements, Test and Labelling (DIN 18945:2018-12). German Institute for Standardization.Google Scholar
Dondi, M., Principi, P., Raimondo, M., & Zanarini, G. (2003). Water vapour permeability of clay bricks. Construction and Building Materials, 17, 253–258. https://doi.org/10.1016/S0950-0618(02)00117-4CrossRefGoogle Scholar
Du, J., Pushkarova, R. A., & Smart, R. St C. (2009). A cryo-SEM study of aggregate and floc structure changes during clay settling and raking processes. International Journal of Mineral Processing, 93, 66–72. https://doi.org/10.1016/j.minpro.2009.06.004CrossRefGoogle Scholar
Elert, K., Jroundi, F., Benavides-Reyes, C., Correa Gómez, E., Gulotta, D., & Rodriguez-Navarro, C. (2022). Consolidation of clay-rich earthen building materials: a comparative study at the Alhambra Fortress (Spain). Journal of Building Engineering, 50, 104081. https://doi.org/10.1016/j.jobe.2022.104081CrossRefGoogle Scholar
Ercan, H. Ü., Ece, Ö. I., Çiftçi, E., & Aydın, A. (2022). Comparison of epithermal kaolin deposits from the Etili Area (Çanakkale, Turkey): mineralogical, geochemical, and isotopic characteristics. Clays and Clay Minerals, 70, 753–779. https://doi.org/10.1007/s42860-022-00214-4CrossRefGoogle Scholar
Erdil Bölükbaşı, M. (2024). Development of Nano Characteristics of Clay Resources for Adobe Production. PhD thesis, Middle East Technical University.Google Scholar
Ergin-Oruç, Ş. (2004). Kerpiç duvarlara uygulanan kil bağlayıcılı dış sıva hasarlarının irdelenmesi. Master’s thesis, Dicle University. https://www.ulusaltezmerkezi.net/kerpic-duvarlara-uygulanan-kil-baglayicili-dis-siva-hasarlarinin-irdelenmesi/Google Scholar
Federal Republic of Nigeria (2006). National Building Code (NBCN:2006; 1st edn). Butterworths, Capetown: LexisNexis.Google Scholar
Ganguly, S., Das, P., Das, T. K., Ghosh, S., Das, S., Bose, M., Mondal, M., Das, A. K., & Das, N. Ch. (2020). Acoustic cavitation assisted destratified clay tactoid reinforced in situ elastomer-mimetic semi-IPN hydrogel for catalytic and bactericidal application. Ultrasonics Sonochemistry, 60, 104797. https://doi.org/10.1016/j.ultsonch.2019.104797CrossRefGoogle ScholarPubMed
Garrison, E. (2003). Techniques in Archaeological Geology. Springer-Verlag Berlin and Heidelberg GmbH & Co. https://doi.org/10.1007/978-3-662-05163-4CrossRefGoogle Scholar
Getahun, G. T., Etana, A., Munkholm, L. J., & Kirchmann, H. (2021). Liming with CaCO3 or CaO affects aggregate stability and dissolved reactive phosphorus in a heavy clay subsoil. Soil and Tillage Research, 214, 105162. https://doi.org/10.1016/j.still.2021.105162CrossRefGoogle Scholar
Giuffrida, G., Caponetto, R., Nocera, F., & Cuomo, M. (2021). Prototyping of a novel rammed earth technology. Sustainability, 11948. https://doi.org/10.3390/su132111948Google Scholar
Goldberg, I., & Klein, A. (1953). Some effects of treating expansive clays with calcium hydroxide. In Mielenz, R. C. (ed), Symposium on Exchange Phenomena in Soils (vols STP142-EB). ASTM International. https://doi.org/10.1520/STP46254SGoogle Scholar
Greipsland, I., Tesfai, M., & Bechmann, M. (2014). Bioforsk Report: Knowledge status for structure liming in Norway (vol 9, no. 81). Bioforsk.Google Scholar
Grim, R. E. (1968). Clay Mineralogy (2nd edn). McGraw-Hill.Google Scholar
Guggenheim, S., Martin, R. T., Alietti, A., Drits, V. A., Formoso, M., Galán, E., Köster, H. M., Morgan, D. J., Paquet, H., Watanabe, T., Bain, D. C., Ferrell, R. E., Bish, D., Fanning, D. S., Kodama, H., & Wicks, F. J. (1995). Definition of clay and clay mineral: Joint report of the AIPEA nomenclature and CMS nomenclature committees. Clays and Clay Minerals, 43, 255–256. https://doi.org/10.1346/CCMN.1995.0430213CrossRefGoogle Scholar
Guggenheim, S., Adams, J. M., Bain, D. C., Bergaya, F., Brigatti, M. F., Drits, V. A., Formoso, M. L. L., Galán, E., Kogure, T., & Stanjek, H. (2007). Erratum to: Summary of recommendations of nomenclature committees relevant to Clay mineralogy: Report of the Association Internationale pour l’etude des argiles (AIPEA) Nomenclature Committee for 2006. Clays and Clay Minerals, 55, 646–647. https://doi.org/10.1346/CCMN.2007.0550611CrossRefGoogle Scholar
Heiri, O., Lotter, A., & Lemcke, G. (2001). Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results. Journal of Paleolimnology, 25. https://doi.org/10.1023/A:1008119611481CrossRefGoogle Scholar
Hoke, G. D., Schmitz, M. D., & Bowring, S. A. (2014). An ultrasonic method for isolating nonclay components from clay-rich material. Geochemistry, Geophysics, Geosystems, 15, 492–498. https://doi.org/10.1002/2013GC005125CrossRefGoogle Scholar
Houben, H., & Guillaud, H. (1994). Earth Construction: A Comprehensive Guide. Intermediate Technology Publications.10.3362/9781780444826CrossRefGoogle Scholar
IBC (2018). Empirical Design of Adobe Masonry (IBC 2018 Section 2109:2018). International Building Code, International Code Council, Washington DC.Google Scholar
IBC (2021). Building Code of Pakistan (IBC 2021:2021). International Building Code, International Code Council, Washington DC. https://codes.iccsafe.org/content/PKBC2021P1/copyrightGoogle Scholar
Ilic, B., Mitrović, A., & Ljiljana, M. (2010). Thermal treatment of kaolin clay to obtain metakaolin. Hemijska Industrija, 64, 351–356. https://doi.org/10.2298/HEMIND100322014ICrossRefGoogle Scholar
Işık, B. (2011) Conformity of gypsum stabilized earth-Alker construction with ‘Disaster Code 97’ in Turkey. International Journal of Civil & Environmental Engineering, 11.Google Scholar
ISO/TR (2017). Nanotechnologies – Plain language explanation of selected terms from the ISO/IEC 80004 series (ISO/TR 18401:2017).Google Scholar
Janica, I., Del Buffa, S., Mikołajczak, A., Ededia, M., Pakulski, D., Ciesielski, A., & Samorì, P. (2018). Thermal insulation with 2D materials: liquid phase exfoliated vermiculite functional nanosheets. Nanoscale, 10. https://doi.org/10.1039/C8NR08364ACrossRefGoogle Scholar
Kertmen, N., Dalbaşi, E. S., Körlü, A., Özgüney, A., & Yapar, S. (2020). A study on coating with nanoclay on the production of flame retardant cotton fabrics. Textile and Apparel, 30, article 4. https://doi.org/10.32710/tekstilvekonfeksiyon.675352Google Scholar
Khalid, N., Arshad, M., Mukri, M., Mohamad, K., & Kamarudin, F. (2014). The properties of Nano-kaolin mixed with kaolin. 19, 4247–4255.Google Scholar
Khong, L. H., Jimoh, O. A., Zabidi, H., & Ariffin, K. S. (2025). Occurrence and physico-chemical properties of aplite-derived kaolin from eastern Kinta valley, Malaysia. Kuwait Journal of Science, 52, 100379. https://doi.org/10.1016/j.kjs.2025.100379CrossRefGoogle Scholar
Lagouin, M., Laborel-Préneron, A., Magniont, C., Geoffroy, S., & Aubert, J.-E. (2021). Effects of organic admixtures on the fresh and mechanical properties of earth-based plasters. Journal of Building Engineering, 41, 102379. https://doi.org/10.1016/j.jobe.2021.102379CrossRefGoogle Scholar
Lakshmi, R., Velmurugan, V., & Swamiappan, S. (2013). Preparation and phase evolution of wollastonite by sol-gel combustion method using sucrose as the fuel. Combustion Science and Technology, 185. https://doi.org/10.1080/00102202.2013.835308CrossRefGoogle Scholar
Lam, C., Lau, K., Cheung, H., & Ling, H. (2005). Effect of ultrasound sonication in nanoclay clusters of nanoclay/epoxy composites. Materials Letters, 59, 1369–1372. https://doi.org/10.1016/j.matlet.2004.12.048CrossRefGoogle Scholar
Lanzón, M., & García-Ruiz, P. A. (2009). Evaluation of capillary water absorption in rendering mortars made with powdered waterproofing additives. Construction and Building Materials, 23, 3287–3291. https://doi.org/10.1016/j.conbuildmat.2009.05.002CrossRefGoogle Scholar
Loy, C. W., Amin Matori, K., Lim, W. F., Schmid, S., Zainuddin, N., Abdul Wahab, Z., Nadakkavil Alassan, Z., & Mohd Zaid, M. H. (2016). Effects of calcination on the crystallography and nonbiogenic aragonite formation of ark clam shell under ambient condition. Advances in Materials Science and Engineering, 2016, 2914368. https://doi.org/10.1155/2016/2914368CrossRefGoogle Scholar
Luckham, P. F., & Rossi, S. (1999). The colloidal and rheological properties of bentonite suspensions. Advances in Colloid and Interface Science, 82, 43–92. https://doi.org/10.1016/S0001-8686(99)00005-6CrossRefGoogle Scholar
Maillard, P., & Aubert, J. E. (2014). Effects of the anisotropy of extruded earth bricks on their hygrothermal properties. Construction and Building Materials, 63, 56–61. https://doi.org/10.1016/j.conbuildmat.2014.04.001CrossRefGoogle Scholar
Meddah, S., & Tagnit-Hamou, A. (2009). Pore structure of concrete with mineral admixtures and its effect on self-desiccation shrinkage. ACI Materials Journal, V, 106, 241–250.Google Scholar
Min, T.-K., Hwang, K.-M., & Lee, S.-H. (2007). The effects on the Atterberg limits of clays with heat treatment. Journal of the Korean Geotechnical Society, 23.Google Scholar
Minke, G. (2009). Building with Earth: Design and Technology of a Sustainable Architecture (2nd edn). Birkhäuser Architecture. https://books.google.com.tr/books?id=IKs9PgAACAAJ 10.1515/9783034612623CrossRefGoogle Scholar
Moevus, M., Jorand, Y., Olagnon, C., Maximilien, S., Anger, R., Fontaine, L., & Arnaud, L. (2016). Earthen construction: an increase of the mechanical strength by optimizing the dispersion of the binder phase. Materials and Structures, 49, 1555–1568. https://doi.org/10.1617/s11527-015-0595-5CrossRefGoogle Scholar
Mohammadi, M., Khodaparast, M., & Rajabi, A. M. (2021). Effect of nano calcium carbonate (nano CaCO3) on the strength and consolidation properties of clayey sand soil. Road Materials and Pavement Design, 1–22. https://doi.org/10.1080/14680629.2021.1976255CrossRefGoogle Scholar
Mosser-Ruck, R., Devineau, K., Charpentier, D., & Cathelineau, M. (2005). Effects of ethylene glycol saturation protocols on XRD patterns: a critical review and discussion. Clays and Clay Minerals, 53, 631–638. https://doi.org/10.1346/CCMN.2005.0530609CrossRefGoogle Scholar
Muguda, S., Lucas, G., Hughes, P. N., Augarde, C. E., Perlot, C., Bruno, A. W., & Gallipoli, D. (2020). Durability and hygroscopic behaviour of biopolymer stabilised earthen construction materials. Construction and Building Materials, 259, 119725. https://doi.org/10.1016/j.conbuildmat.2020.119725CrossRefGoogle Scholar
Narloch, P., Piątkiewicz, W., & Pietruszka, B. (2021). The effect of cement addition on water vapour resistance factor of rammed earth. Materials, 14. https://doi.org/10.3390/ma14092249CrossRefGoogle ScholarPubMed
Nazir, M. S., Mohamad Kassim, M. H., Mohapatra, L., Gilani, M. A., Raza, M. R., & Majeed, K. (2016). Characteristic properties of nanoclays and characterization of nanoparticulates and nanocomposites. In Jawaid, M., el K. Qaiss, A., & Bouhfid, R. (eds), Nanoclay Reinforced Polymer Composites: Nanocomposites and Bionanocomposites (pp. 35–55). Springer Singapore. https://doi.org/10.1007/978-981-10-1953-1_2CrossRefGoogle Scholar
NF (1998). Soils: Recognition and tests – Measure of the blue methylene adsorption capacity of a soil or rocky material – Determining the blue methylene value of a soil or rocky material with the stain test. (NF P94-068:1998). French Association of Normalization (ANFOR). La Défense, Paris, France.Google Scholar
Niroumand, H., Zain, M. F. M., & Alhosseini, S. N. (2013). The influence of nano-clays on compressive strength of earth bricks as sustainable materials. Procedia – Social and Behavioral Sciences, 89. https://doi.org/10.1016/j.sbspro.2013.08.945CrossRefGoogle Scholar
Niu, X.-J., Li, Q.-B., Hu, Y., Tan, Y.-S., & Liu, C.-F. (2021). Properties of cement-based materials incorporating nano-clay and calcined nano-clay: a review. Construction and Building Materials, 284, 122820. https://doi.org/10.1016/j.conbuildmat.2021.122820CrossRefGoogle Scholar
NMAC (2015). New Mexico earthen building materials code (NMAC 14.7.4:2015). New Mexico State: Construction Industries Division of the Regulation and Licensing Department.Google Scholar
Norton, J. (1997). Building with Earth: A Handbook. Intermediate Technology Publications. https://books.google.com.tr/books?id=jHROAAAAYAAJ 10.3362/9781780443959CrossRefGoogle Scholar
NTE (2000). Adobe: Reglamento nacional de construcciones: Norma técnica de edificación (NTE E.080:2000). Ministerio de Transportes y Comunicaciones, Peru.Google Scholar
NZS (2020). Materials and Construction for Earth Buildings (NZS 4298:2020). Standards New Zeland, Wellington.Google Scholar
Ouedraogo, M., Dao, K., Millogo, Y., Aubert, J.-E., Messan, A., Seynou, M., & Zerbo, L. (2019). Physical, thermal and mechanical properties of adobes stabilized with fonio (Digitaria exilis) straw. Journal of Building Engineering, 23. https://doi.org/10.1016/j.jobe.2019.02.005CrossRefGoogle Scholar
Pacheco-Torgal, F., & Jalali, S. (2011). Nanotechnology: Advantages and drawbacks in the field of construction and building materials. Composite Materials and Adhesive Bonding Technology, 25, 582–590. https://doi.org/10.1016/j.conbuildmat.2010.07.009Google Scholar
Pekmezci, B., Kafescioglu, R., & Agahzadeh, E. (2012). Improved performance of earth structures by lime and gypsum addition. METU Journal of the Faculty of Architecture, 29. https://doi.org/10.4305/METU.JFA.2012.2.9Google Scholar
Pekrioglu Balkis, A. (2017). The effects of waste marble dust and polypropylene fiber contents on mechanical properties of gypsum stabilized earthen. Construction and Building Materials, 134, 556–562. https://doi.org/10.1016/j.conbuildmat.2016.12.172CrossRefGoogle Scholar
Pérez-Maqueda, L. A., de Haro, M. C. J., Poyato, J., & Pérez-Rodríguez, J. L. (2004). Comparative study of ground and sonicated vermiculite. Journal of Materials Science, 39, 5347–5351. https://doi.org/10.1023/B:JMSC.0000039242.67213.4dCrossRefGoogle Scholar
Pérez-Rodríguez, J. L., Pascual, J., Franco, F., Jiménez de Haro, M. C., Duran, A., Ramírez del Valle, V., & Pérez-Maqueda, L. A. (2006). The influence of ultrasound on the thermal behaviour of clay minerals. Journal of the European Ceramic Society, 26, 747–753. https://doi.org/10.1016/j.jeurceramsoc.2005.07.015CrossRefGoogle Scholar
Poli, A. L., Batista, T., Schmitt, C. C., Gessner, F., & Neumann, M. G. (2008). Effect of sonication on the particle size of montmorillonite clays. Journal of Colloid and Interface Science, 325, 386–390. https://doi.org/10.1016/j.jcis.2008.06.016CrossRefGoogle ScholarPubMed
Poppe, L. J., Paskevich, V. F., Hathaway, J. C., & Blackwood, D. S. (2001). A Laboratory Manual for X-ray Powder Diffraction (Report Nos. 2001–41; Open-File Report). USGS Publications Warehouse. https://doi.org/10.3133/ofr0141CrossRefGoogle Scholar
Ravisangar, V., Sturm, T. W., & Amirtharajah, A. (2005). Influence of sediment structure on erosional strength and density of kaolinite sediment beds. Journal of Hydraulic Engineering, 131, 356–365. https://doi.org/10.1061/(ASCE)0733-9429(2005)131:5(356)CrossRefGoogle Scholar
Reeves, G. M., Sims, I., Cripps, J. C., & London, G. S. of. (2006). Clay Materials Used in Construction. Geological Society, London.Google Scholar
Ribeiro, T., Oliveira, D. V., & Bracci, S. (2022). The use of contact sponge method to measure water absorption in earthen heritage treated with water repellents. International Journal of Architectural Heritage, 16, 85–96. https://doi.org/10.1080/15583058.2020.1751344CrossRefGoogle Scholar
RILEM (1980). Tentative Recommendations, Comission-25-PEM, Recommended test to measure the deterioration of stone and to access the effectiveness of treatment methods. Material and Structures, 13, 173–253.Google Scholar
Rolfe, B. N., Miller, R. F., & McQueen, I. S. (1960). Dispersion characteristics of montmorillonite, kaolinite, and illite clays in waters of varying quality, and their control with phosphate dispersants (Report No. 334G; Professional Paper). USGS Publications Warehouse. https://doi.org/10.3133/pp334GCrossRefGoogle Scholar
Roopa Baliga, B., Prathibha, C., Nayak, Bhavana C. & Sumanth, V. (2018). Examination of compressive strength and water absorption of adobe blocks prepared using black cotton soil and granite sludge. International Journal of Applied Engineering Research, 13, 110–113.Google Scholar
Sanchez, F., & Sobolev, K. (2010). Nanotechnology in concrete – a review. Construction and Building Materials, 24, 2060–2071. https://doi.org/10.1016/j.conbuildmat.2010.03.014CrossRefGoogle Scholar
Schirmer, W. (1990). Some aspects of building at the ‘aceramic-neolithic’ settlement of Çayönü Tepesi. World Archaeology, 21, 363–387. https://doi.org/10.1080/00438243.1990.9980114CrossRefGoogle Scholar
Schroeder, H. (2015). Sustainable Building with Earth. Springer. https://doi.org/10.1007/978-3-319-19491-2Google Scholar
Schroeder, H. (2018). The New DIN Standards in Earth Building – the current situation in Germany. Journal of Civil Engineering and Architecture, 12. https://doi.org/10.17265/1934-7359/2018.02.005Google Scholar
Schwalen, H. C. (1935). Effect of Soil Texture Upon the Physical Characteristics of Adobe Bricks. University of Arizona.Google Scholar
Sharma, V., Marwaha, B. M., & Vinayak, H. K. (2016). Enhancing durability of adobe by natural reinforcement for propagating sustainable mud housing. International Journal of Sustainable Built Environment, 5, 141–155. https://doi.org/10.1016/j.ijsbe.2016.03.004CrossRefGoogle Scholar
State Institute of Statistics Prime Ministry Republic of Turkey (2001). Building Census 2000.Google Scholar
Stefanidou, M. A., & Papayianni, I. (2005). The role of aggregates on the structure and properties of lime mortars. Cement and Concrete Composites, 27, 914–919. https://doi.org/10.1016/j.cemconcomp.2005.05.001CrossRefGoogle Scholar
Tabassum, T., & Bheemasetti, T. (2020). Self-healing and desiccation crack behavior of kaolinite-rich clay soil. Geo-Congress 2020: Foundations, Soil Improvement, and Erosion, 582–591. https://doi.org/10.1061/9780784482780.057CrossRefGoogle Scholar
Taha, M. (2018). Recent developments in nanomaterials for geotechnical and geoenvironmental engineering. MATEC Web of Conferences, 149. https://doi.org/10.1051/matecconf/201814902004CrossRefGoogle Scholar
Tan, X., Liu, F., Hu, L., Reed, A. H., Furukawa, Y., & Zhang, G. (2017). Evaluation of the particle sizes of four clay minerals. Applied Clay Science, 135, 313–324. https://doi.org/10.1016/j.clay.2016.10.012CrossRefGoogle Scholar
Torraca, G. (1988). Porous Materials Building: Materials Science for Architectural Conservation. ICCROM. https://books.google.com.tr/books?id=Il9oQgAACAAJGoogle Scholar
Tringham, R., & Stevanović, M. (eds) (2012). Last House on the Hill: BACH Area Reports from Catalhoyuk, Turkey. Cotsen Institute of Archaeology Press at UCLA. JSTOR. https://doi.org/10.2307/j.ctvdmwx1jCrossRefGoogle Scholar
TS (2017). Methods of testing soils for civil engineering purposes in the laboratory – Part 1: Determination of physical properties (TS 1900-1/T3:2017). Turkish Standards Institution, Ankara, Turkey.Google Scholar
TS EN (2016). Methods of testing cement – Part 1: Determination of strength (TS EN 196-1:2016). Turkish Standards Institution, Ankara, Turkey.Google Scholar
TS EN (2020). Methods of test for mortar for masonry – Part 11: Determination of flexural and compressive strength of hardened mortar (TS EN 1015-11:2020).Google Scholar
TS EN ISO (2016). Hygrothermal performance of building materials and products – Determination of water vapour transmission properties – Cup method (TS EN ISO 12572:2016).Google Scholar
TS EN ISO (2018). Geotechnical investigation and testing – Identification and classification of soil – Part 1: Identification and description (TS EN ISO 14688-1:2018). Turkish Standards Institution, Ankara, Turkey.Google Scholar
Tucker, M. E. (2001) Sedimentary Petrology: An Introduction to the Origin of Sedimentary Rocks. Wiley. https://books.google.com.tr/books?id=Yebzay3a0FwCGoogle Scholar
Türkmen, İ., Ekinci, E., Kantarcı, F., & Sarıcı, T. (2017). The mechanical and physical properties of unfired earth bricks stabilized with gypsum and Elazığ Ferrochrome slag. International Journal of Sustainable Built Environment, 6, 565–573. https://doi.org/10.1016/j.ijsbe.2017.12.003CrossRefGoogle Scholar
Uddin, F. (2008). Clays, nanoclays, and montmorillonite minerals. Metallurgical and Materials Transactions A, 39, 2804–2814. https://doi.org/10.1007/s11661-008-9603-5CrossRefGoogle Scholar
Velde, B., & Meunier, A. (2008). The Origin of Clay Minerals in Soils and Weathered Rocks. Springer, Berlin. ISBN: 978-3-540-75633-0 (vol. 418). https://doi.org/10.1007/978-3-540-75634-7CrossRefGoogle Scholar
Vilane, B. R. T. (2010). Assessment of stabilisation of adobes by confined compression tests. Biosystems Engineering, 106, 551–558. https://doi.org/10.1016/j.biosystemseng.2010.06.008CrossRefGoogle Scholar
Volz, H., Vogel, S., Necker, C. T., Roberts, J., Lawson, A., Williams, D., Daemen, L., Lutterotti, L., & Pehl, J. (2006). Rietveld texture analysis by neutron diffraction of highly absorbing materials. Powder Diffraction, 21, 114–117. https://doi.org/10.1154/1.2204058CrossRefGoogle Scholar
Walker, P. (2001). The Australian Earth Building Handbook. Standards Australia International. https://books.google.com.tr/books?id=-RD4AAAACAAJGoogle Scholar
Widder, L. (2017). Earth eco-building: textile-reinforced earth block construction. CISBAT 2017 International ConferenceFuture Buildings & Districts – Energy Efficiency from Nano to Urban Scale, 122, 757–762. https://doi.org/10.1016/j.egypro.2017.07.392Google Scholar
Yazarloo, R., Katooli, F. A., Golestani, M., Asadi, M., & Ebrahimi, S. (2017). Adding Calcite and Nanocalcite to Improving the Plastic Properties of the Lean Clay. Proceedings of the 3rd World Congress on New Technologies (NewTech’17). https://doi.org/10.11159/icnfa17.106CrossRefGoogle Scholar
Zainuddin, A. N., Norullain, S., Mukri, B., Azizah, N., & Che Lat, D. (2015). Nano kaolinite as additives in kaolinite clay to develop new clay liner design in landfill. International Journal of Applied Engineering Research, 10, 95.Google Scholar
Figure 0

Table 1.The required levels for compressive and flexural strengths, capillary-water absorption, and water-vapor permeability of adobe according to various codes/standards and literature dataTable 1. Long description.

Figure 1

Figure 1.Location map of the soil resources, indicating the city and village names, geographic coordinates, and sample codes (top), and the three sets of adobe samples and their corresponding sample codes (bottom).Figure 1. long description.

Figure 2

Table 2.Laboratory tests and sample sets summarizing the analyses related to method developmentTable 2. long description.

Figure 3

Figure 2.Dispersion methods of clay-mineral layers: mixing using a magnetic stirrer or laboratory mixer (top), ultrasonic treatment (sonication) for dispersion of clay mineral layer (middle), and a schematic illustration of the sonication-induced dispersion of flocculated clay mineral layer (bottom).Figure 2. long description.

Figure 4

Figure 3.CEC values showing the optimum mixing durations for the magnetic stirrer and ultrasonic bath that yielded the highest clay particle content in the three soil resources (top), the optimum mixing durations for the laboratory mixer and ultrasonic bath for the Konya Küçükköy soil resource (bottom left), and the optimum soil:water ratio for preparing treated adobe samples from the three soil resources (bottom right).Figure 3. long description.

Figure 5

Figure 4.Preparation of the treated (top) and untreated (bottom) adobe samples.Figure 4. long description.

Figure 6

Figure 5.Flexural strength testing of prismatic adobe samples and compressive strength testing of the broken sample halves using a manual testing machine (left); water vapor permeability testing of adobe samples by the dry-cup method in a test chamber (right).Figure 5. long description.

Figure 7

Figure 6.Test configuration for the capillary water absorption experiment.Figure 6. long description.

Figure 8

Table 3.The mineralogical compositions of three soils in terms of <4 μm particle content, clay content, clay-sized CaCO3, and pozzolanic activityTable 3. long description.

Figure 9

Figure 7.XRD traces of the Konya Küçükköy, Çorum Karapınar and Çorum Kınık soil resources (C = calcite; CH = chlorite; I-MI = illite-mica; K= kaolinite; M = montmorillonite).Figure 7. long description.

Figure 10

Figure 8.Laser diffractometry particle size distributions (PSDs) of the soil resources before and after ultrasonic treatment.Figure 8. long description.

Figure 11

Figure 9.Casagrande plasticity chart showing the liquid limit (LL) and plasticity index (PI) of the untreated and treated soil samples relative to the recommended consistency limits for adobe soils (yellow shaded area: PI = 16–33% and LL = 31–50%) (top), and the linear shrinkage (LS) ratio values of the untreated and treated soil samples (at bottom).Figure 9. long description.

Figure 12

Figure 10.Bulk density (dry density), particle density, and porosity of the adobe samples.Figure 10. long description.

Figure 13

Figure 11.SEM images of adobe samples produced from Konya Küçüköy and Çorum Karapınar soil resources.Figure 11. long description.

Figure 14

Figure 12.Compressive and flexural strengths of the adobe samples relative to the minimum requirements specified in national and international standards (Table 1) (top), and the correlation between compressive strength and clay content (bottom).Figure 12. long description.

Figure 15

Figure 13.Minimum and average compressive strengths of the untreated and treated adobe samples in relation to the strength classes defined by the DIN standards (DIN, 2018).Figure 13. long description.

Figure 16

Figure 14.Water vapor diffusion resistance factor (μ) and SD2.5 cm values of the adobe samples determined by the dry cup method.Figure 14. long description.

Figure 17

Figure 15.Capillary water absorption coefficient (A-value) of the adobe samples.Figure 15. long description.