In the construction sector, enhancing the thermomechanical attributes of building materials is of significant importance. This research is centered on examining kaolin-enhanced rammed earth bricks, which are augmented through an alkaline solution to facilitate geopolymerization, creating a synergy between geopolymer and soil. Physico-chemical analysis methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR), differential thermal and gravimetric analysis (DTA-GTA) and particle size analysis were used to characterize the properties and reactive potential of studied materials. The chemical composition analysis revealed that the soil and kaolin contained substantial amounts of Calcite (32.2%), Quartz (26.5%), Muscovite (15.44%), Nimesite (18%), and in kaolin, Quartz (68.3%) and Illite (30.1%) were predominant. Samples with different kaolin-geopolymer ratios (0%, 3%, 4%, 5% and 6%) were designed and prepared for both mechanical (compressive and tensile strength) and thermal testing. The results obtained indicate a significant improvement in the structural integrity of earth bricks with increasing kaolin-geopolymer content when combined with an alkaline solution. However, this improvement is accompanied by a reduction in thermal resistance after 28 days.
Research Article
Assessment of the mechanical and thermal properties of local building materials stabilized by the synthesis of kaolin geopolymers and alkaline solution
https://doi.org/10.21203/rs.3.rs-4013938/v1
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Clay bricks
Thermomechanical properties
Stabilization
Kaolin
Alkaline solution.
One of the major concerns of the population in semi-arid regions is the heating of dwellings, which is linked to high insolation due to environmental destruction and climate change [1]. The climate change context requires more and more energy-efficient building systems [2]. A deterioration of the building can be observed, due to the increase in interior temperature and cracks in the walls. An alternative solution must be found to reduce the effect of these phenomena [3]. In the building sector, it is often desirable to use local materials to reduce the cost and carbon footprint of construction. However, many local materials have insufficient properties to meet construction requirements, mainly in areas of strength and stability, often, Ordinary Portland Cement (OPC) is used to reinforce the thermomechanical of earth bricks [4]. In addition, OPC is the most commonly used binder in industry, and the clinker required for its production is almost entirely imported due to the shortage of raw materials and the high energy consumption involved in its production. The production of OPC also generates large quantities of CO2, which has a negative impact on the environment by contributing to global warming [5,6]. Geopolymerization technology is a solution that has been proposed to meet the need for housing in developing countries. It involves using aluminosilicate materials such as calcined clay, fly and volcanic ash, industrial and municipal waste and an activating solution (alkaline or acidic) to carry out a polymerization/polycondensation reaction at ambient or slightly elevated temperatures. This technology has received a considerable amount of attention in several recent years from a number of scientific researchers [7–11]. Previous work has examined the effectiveness of geopolymers in stabilizing clay soils and improving their mechanical properties. P. Ghadir et al. [12] explored various factors impacting soil stabilization through a VA-based geopolymer. They focused on aspects such as curing conditions, vertical confinements, binder quantities, and the properties of the alkaline activator. Their findings indicated enhancements in shear strength and binder content of treated samples, along with increased curing time and reduced moisture. A. Arulrajah et al. [13] examined principal geotechnical aspects of geopolymer-stabilized mixtures incorporating polyethylene terephthalate plastic and construction and demolition waste (PET/C&D) for pavement purposes. Their goal was to minimize landfill usage and quarry material demand, and they observed notable improvements in strength and rigidity of PET/C&D blends post-stabilization with geopolymers. H. Zhou et al. [14] compared mechanical properties and microstructure of marine soft soil stabilized with low-calcium and high-calcium geopolymers versus ordinary Portland cement. The study revealed that the strength development was positively influenced by factors like the activator/precursor ratio and NaOH concentration. H.H. Abdullah et al. [15] investigated the behavior of different types of clay soils treated with geopolymers made from fly ash. In particular, they examined the effect of soil characteristics and mineral composition on soil behavior. The researchers observed that adding more geopolymer made the clay stronger and stiffer. B. Chowdary et al. [16] investigated the mechanical and durability performance of soil using geopolymers based on industrial by-products and the addition of fibers. Their results showed improved strength and durability properties with increasing geopolymer content. L. Mahtout et al. [17] examined the mechanical properties of kaolin-based materials in the field of geopolymers, using alkaline solutions such as (sodium, potassium and a mixture of alkali). The authors revealed that the addition of alkaline solutions gave good mechanical properties when tested at the 7th day of elaboration. Y. Luo et al. [18] reported on the feasibility of Metakaolin-based geopolymer for the treatment of silty clay foundations. The strength of unconfined soil compression was tested. Their results showed that stabilization with Metakaolin-based geopolymers increases unconfined compressive strength compared with samples stabilized with lime and ordinary Portland cement. E. Adeyanju et al. [19] assessed the mechanical properties of natural subgrades using geopolymers from rice husk ash and cement kiln waste. Their results indicated that these geopolymers enhanced soil's geotechnical and mechanical strength, with cement kiln waste showing superior performance. J. Wu et al. [20] investigated the factors that affect soil stiffness and strength, these factors encompassed the ratio of silicon to aluminum, the mass ratio of solid NaOH to raw materials, and the water/binder ratio. The results obtained showed that the silicon-aluminium proportion, the mass ratio between solid NaOH and raw material, and the water-binder ratio have a significant influence on the stiffness and strength development of soft clay stabilized with alkali-activated geopolymer under one-dimensional compressive loading. In addition, the mechanical performance of clay soil stabilized using geopolymer based on volcanic ash and ordinary Portland cement was examined by P. Ghadir et al. [21]. The authors assessed the dominant factors in the stabilization process, such as curing conditions, curing time, and binder content. Soil stabilization with geopolymer based on volcanic ash revealed a 200% improvement in compressive strength compared to samples based on ordinary Portland cement corresponding to dry conditions. H.Y. Leong et al. [22] developed a brick geopolymer using waste fly ash and soil, along with residual soil. Several factors affecting the compressive strength of the fly ash/soil geopolymer were investigated. H.Y. Leong et al. [22] developed a brick geopolymer using waste fly ash and soil, along with residual soil. Several factors affecting the compressive strength of the fly ash/soil geopolymer were investigated. They found that large quantities of alkaline activators enhanced the strength of earth-ash geopolymer compared with conventional fly-ash geopolymers. N. Ranjbar et al. [23] examined the combined impact of temperature and hot-pressing polymerization duration on the kinetics and mechanical characteristics of hot-pressed geopolymer employing alkaline activators. The outcomes indicated a positive correlation between elevated temperature, prolonged time, and the dissolution of a reactive portion of the aluminosilicate precursors.
The present study focuses on stabilizing soil bricks using a geopolymeric binder made from kaolin, combined with an alkaline solution. The study also explores how different amounts of geopolymeric binder (ranging from 0–6% of the soil's weight) and curing temperature (ambient temperature) affect the bricks' mechanical and thermal properties. A thorough analysis of the earth soil was carried out to assess its suitability as the main material for earth brick production. The results of this research are expected to offer valuable insights for future studies on using an environmentally friendly alternative binder to stabilize Compressed Earth Blocks (CEB) for construction purposes, especially in semi-arid regions.
2.1. Raw materials
2.1.1. Soil studied
The soil used comes from the Errachidia region in southeastern Morocco, and is considered a very fine material. This soil is often used in construction operations, because it has properties that make it ideal for some types of structure (Fig. 1). In addition, the soil of Errachidia is known for its ability to absorb water, which makes it highly resistant to temperature fluctuations. This property is particularly useful in regions where temperatures can vary considerably over the course of the day or season.
2.1.2. Geopolymer based on Kaolins
Kaolin is a beige, friable, refractory clay, mainly composed of kaolinite, aluminum silicates. It can play an important role in construction as an additive in plasters and mortars, reinforcing the structure of bricks and tiles, and improving moisture resistance and breaking strength. Figure 2 shows that the type of kaolin selected for the present study which was extracted in the Taghzoute region of southeastern Morocco. It is first crushed, then ground and sieved to obtain a homogeneous sample ready for use.
2.1.3. Activator solution (alkaline solution)
The alkaline solutions are known as activator solutions and are used in the creation of geopolymers, which include commercially available solutions such as sodium bicarbonate (NaHCO3), lime (Ca(OH)2) and sodium hydroxide (NaOH), as shown in Fig. 3. These solutions are essential for starting the geopolymerization process and contribute to the formation and development of the geopolymer matrix. Sodium bicarbonate acts as an alkaline source, while lime provides calcium ions and sodium hydroxide serves as a strong alkali. The unique properties of each solution introduce variability into the geopolymerization reaction, influencing the final characteristics of the synthesized geopolymer.
2.2. Characterization methods
2.2.1 X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-Ray Analysis (EDX), and Combined Differential Thermal and Gravimetric Analysis (DTA-GTA).
In this study, a range of methods was applied to examine and describe materials such as soil and kaolin. Crystalline structures and the presence of clay minerals were determined using X-ray diffraction. This method consists to evaluate the wavelengths of the scattered X-rays in order to determine the atomic structure of the material. A PANalytical X'pert Highscore diffractometer, equipped with a copper anti-cathode and a copper line Kα, was used to obtain a wavelength of 1.5405980 Å. In addition, Fourier Transform Infrared (FTIR) spectroscopy was used to study chemical bonding at the soil surface. This involved recording the vibrational excitation of atoms in the bonds across a range of 4000 − 400 cm− 1. Soil samples underwent 64 scans at a 4 cm− 1 resolution, whereas kaolin samples were scanned 101 times at the same resolution, with a 2 mm/sec scanning speed, within the same spectral range. The study also included analysis of the morphology and chemical composition of soil and kaolin through a QUATTRO S-FEG-Thermofisher scientific scanning electron microscope (SEM) coupled with an energy dispersive X-ray (EDX) spectrometer. To characterize the structure and composition of studied samples, the SEM used in this study was operated at 20 KV in a low-vacuum mode, with pressure maintained between 0.9 and 1.04 mbar. Then, EDX provided a microanalytical resolution of 133 eV. Thermogravimetric (TGA) and thermodifferential (TDA) analyses were carried out using an analyzer equipped with a DTG-60H detector. This procedure involved heating a 17.755 mg sample of kaolin to 1000°C at a heating rate of 15°C/min, which allowed to measure mass loss and temperature fluctuations during heating.
2.2.2. Granulometric analysis
The granulometric analysis of soils was carried out in accordance with two French standards: NF P94 056 [25] and NF P94 057 [26]. The first standard concerns the granulometric analysis of soil elements larger than 70µm, while the second concerns granulometric analysis by sedimentation. To carry out the particle size analysis, the sample was soaked in water for 24 hours, then sieved by wet sieving, while the remaining elements were dried at 100°C until a constant mass was obtained. The residue of sample from each sieve was weighed. For particle size analysis, the particles suspended in a test tube were deposited at the bottom of the tube according to their diameter. In addition, the density was measured periodically using a hydrometer, and the proportion of particles of each diameter was calculated. These proportions were recorded in tabular form and then used to assess a granulometric graph. These data were used to provide precious information on the particle size composition of the soil sample, and to determine the sample's relevance for later analysis.
2.2.3. Mixing preparation and block manufacture
The method used in this study is based on the preparation of mixtures of a quantity of sieved raw earth and quantities of geopolymers (Kaolin/Alkaline Solution) according to the desired percentage. The mixture is placed in a tub and mixed by hand until homogenized. This operation takes around 5 to 10 min to avoid loss of reactivity between the geopolymer solution and the soil. The prepared sample mixtures are stored in airtight containers to reduce water loss. The bricks are then shaped using the molds used for briquette manufacture, with geopolymer percentages ranging from 0 to 6% by weight. The dimensions of the briquettes are 24×24×4 cm3 (for thermal tests), and cylindrical bricks with a diameter of D = 10 cm and a height of H = 20cm (for mechanical tests) (Table 1).
Table 1: Composition ratios of different earth bricks stabilized with geopolymers and test types
2.2.4. Handling process and drying of bricks after demoulding
After demolding, the bricks are taken carefully by hand, avoiding touching the edges due to their fragility. They are then stored in the laboratory at room temperature and relative humidity for 28 days until the bricks have dried out, to avoid rapid drying out.
2.2.5. Thermal conductivity
To determine the thermal conductivity of the different types of brick studied, an experimental device based on the Heat Insulation House PHYWE was used [30]. This technique has been used in several research studies [27,28] with an uncertainty of less than 10%. The studied brick is placed in a 210×210 mm² square opening for characterization. The experimental device comprises four walls measuring 400×400 mm², each insulated by a cover made of a 5 cm thick layer of polystyrene. At the center of this insulated chamber, a 100 W bulb, placed in a black box to minimize the effects of radiation, serves as a heat source (Fig. 5). Then, the bulb is connected to a thermostat, which is regulated to maintain the indoor air temperature at 50°C. The outside temperature is controlled to around 24°C by an air-conditioning system. For all bricks tested, the inside and outside surface temperatures are recorded every minute using type K thermocouples with an uncertainty of +/-0.7°C are placed at different locations to monitor temperature fluctuations inside and outside the thermal house. These data are collected via a Data-Logger GL840 acquisition system, which also features a PC connection interface. The system uses specialized software to display the data and save it in Excel format. Once a steady state has been reached (around 6 hours after the start of each test), the temperature results are analyzed to determine thermal conductivity.
To measure thermal conductivity, it is necessary to take into account the conservation of heat flow that occurs by convection between the inside air and the inside wall surface. In addition, convection between the outside air and the outer wall surface, as well as conduction through the sample, are also taken into account and are described by Eq. (1). This equation describes the different mechanisms by which heat is transmitted, and contributes to understanding the overall thermal behavior of material.
$${\phi }={\text{h}}_{\text{i}\text{n}\text{t}}\times \left({\text{T}}_{\text{l}\text{o}\text{c}}-{\text{T}}_{\text{i}\text{n}\text{t}}\right)\times \text{S}=\text{S}\times {\lambda }\times \frac{{\text{T}}_{\text{i}\text{n}\text{t}}-{\text{T}}_{\text{e}\text{x}\text{t}}}{\text{e}}={\text{h}}_{\text{e}\text{x}\text{t}}\times \left({\text{T}}_{\text{e}\text{x}\text{t}}-{\text{T}}_{\text{a}\text{m}\text{b}}\right)\times \text{S}$$
1
with :
- hint : inside convection coefficient
- hext : outside convection coefficient
- Tint : inside wall temperature
- Text : outside wall temperature
- Tloc : air temperature inside high insulation houses
- Tamb : ambient temperature
- e : wall thickness
The thermal conductivity value (λ) was figured out using specific equations (Eq. (2) and Eq. (3)), along with a hint coefficient of 8.1 W/m2.K provided by the manufacturer PHYWE [28, 29]. To measure the thermal conductivity of the samples, PHYWE's recommended procedure was followed, employing their thermal control support and a set of thermocouples to track temperature changes inside and outside the thermal house [30]. the temperatures were recorded when the thermocouples stabilized to make sure the system reached equilibrium, typically after 8 hours of measurement.
with
- e = 0.04 m.
2.2.6. Mechanical resistance
Two types of tests were carried out to determine the material's behavior under compression and traction. Firstly, a 500 KN hydraulic press type FORM TEST SEIDNER D79400 (Fig. 6) was used to perform a uniaxial compression test on cylindrical specimens. The specimens were 20 cm high and 10 cm in diameter. These tests allowed to understand how the material reacts when compressed from all sides. In addition, a split traction test on similar cylindrical specimens was carried out to examine how the material behaves when pulled apart. These tests were essential to determine the material's mechanical properties and its response to different types of force.
3.1. XRD, EDX, ATD and ATG analysis
The mineral composition of the soil was examined using X-ray diffraction analysis (see Fig. 7). This technique is based on the analysis of diffraction patterns into d-spacing values, which are distinctive for each mineral, thereby facilitating their identification. The analysis revealed that the soil sample contained calcite and quartz, as indicated by the high peaks in the sample spectra. Additionally, the soil sample exhibited significant dolomite presence: dolomite with the chemical formula (CaMg(CO3)2). Finally, XRD analysis indicated the presence of muscovite (H2KAl3Si3O12) in the soil, as documented in Table 2.
|
Compound Name |
Chemical Formula |
Sample and mineral percentages (%) |
|---|---|---|
|
Calcite |
Ca(CO3) |
43.33 |
|
Quartz |
SiO2 |
36.51 |
|
Dolomite |
CaMg(CO3)2 |
16.18 |
|
Muscovite |
H2KAl3Si3O12 |
3.98 |
The X-ray diagram of kaolin is shown in Fig. 8. From the analysis (XRD), it was observed that kaolin powder is composed mainly of Quartz low (SiO2) and Illite [(K,H3O) Al2Si3Al O10 (OH)2]. Moreover, there is a small amount of Clinochlore, ferrien [(Mg,Fe,Al)6 (Si,Al)4 O10 (OH)8]. Table 3 presents a summary of the results of DRX analysis.
|
Compound Name |
Chemical Formula |
Sample and Mineral percentages (%) |
|---|---|---|
|
Quartz low |
Si O2 |
68.3 |
|
Illite |
(K, H3 O) Al2 Si3 Al O10 (O H )2 |
30.1 |
|
Clinochlore, ferrien |
( Mg, Fe, Al )6 ( Si, Al )4 O10 ( O H )8 |
1.6 |
The analysis of infrared (IR) spectra is particularly important to complete the physicochemical characterization of the samples studied. Based on the data in Fig. 9 and [31], an absorption band was observed between 3200 and 3800 cm− 1, which was associated with the stretching vibrations of the internal hydroxyl (OH) groups. In the soil sample studied, the absorption band is located at a wave number of 3400 cm− 1. The OH bond is found in both Muscovite and Dolomite, while the Si-O bond indicates the presence of quartz. Additionally, the Si-O-Al bond is present in Muscovite and Calcite. These findings reveal the presence of different elements and compounds within the soil samples, which contribute to their distinct spectral features.
In Fig. 10, different parts are observed. The first part shows bands from 3623 cm− 1 to 3393 cm− 1, these bands are due to vibrations of the O-H bonds of the hydroxyl groups in the sample [32]. In the second part, four bands of absorption were oberserved, the bands from 1643 cm− 1 to 1385 cm− 1 originate from the vibrations of Si-O bond in kaolin. In addition, the bands from 1069 cm− 1 to 1024 cm− 1 are due to symmetrical and asymmetrical stretching of the Si-O-Si bonds, respectively [32]. In the third part, bands from 795 cm− 1 to 692 cm− 1 correspond to different vibrations of Si-O-AlIV bonds (Al is four times coordinated) [33]. In the fourth part, two absorption bands with vibrations from 529 cm− 1 to 469 cm− 1, these vibrations are linked to Si-O-AlVI (Al is six times coordinated) and deformed Si-O-Si bonds, respectively [33].
SEM (Scanning Electron Microscope) images of the Errachidia soil studied are shown in Fig. 11.
The presence of randomly dispersed clay sheets was observed, which appeared in various forms such as elongated or rolled shapes, as well as in the form of sticks. Additionally, a few aggregates were also noted, and these may have resulted from impurities present in the clay.
The composition of a soil sample studied was examined using energy dispersive X-ray (EDX) analysis. The results revealed that the sample contained mainly silicon (Si), calcium (Ca), oxygen (O) and aluminum (Al) (Fig. 12). These results are consistent with the findings of X-ray diffraction (XRD) analysis, which showed the presence of quartz (SiO2) and calcite (CaCO3) in the soil sample. In addition, the detection of various other elements, including Al, K, Mg, Fe, Cl, O, C, Ca, Si, Ti and Na, in different concentrations in the soil samples, confirms the idea that the region concerned by the study is rich in a diverse range of muscovite type materials. The results of EDX analysis are presented in Table 4.
|
Element |
Weight % |
Atom % |
|---|---|---|
|
C |
5.01 |
8.26 |
|
O |
54.47 |
67.45 |
|
Na |
0.40 |
0.34 |
|
Mg |
1.93 |
1.57 |
|
Al |
5.79 |
4.25 |
|
K |
1.78 |
0.90 |
|
Ti |
0.47 |
0.19 |
|
Fe |
3.66 |
1.30 |
|
Ca |
14.00 |
6.92 |
|
Cl |
0.10 |
0.06 |
|
Si |
12.41 |
8.75 |
|
Total |
100.00 |
100.00 |
Figure 13 shows EDX results for kaolin powder and the corresponding spectra for the nine peaks. The main elements detected in the sample are silicon, aluminum, carbon and oxygen, and some magnesium. EDX peaks of the kaolin sample indicate that kaolin contains just nine elements, namely C, O, Mg, Al, Si, Ti, Na, K, Fe, with contents of 17.39%, 50.09%, 0.61%, 8.80%, 17.11%, 0.48%, 0.54%, 1.84% and 1.13%, respectively. EDX results are summarized in Table 5.
|
Element |
Weight % |
Atom % |
|---|---|---|
|
C |
10.74 |
17.39 |
|
O |
42.83 |
52.09 |
|
Na |
0.64 |
0.54 |
|
Mg |
0.77 |
0.61 |
|
Al |
12.21 |
8.80 |
|
Si |
24.70 |
17.11 |
|
K |
3.70 |
1.84 |
|
Ti |
1.18 |
0.48 |
|
Fe |
3.24 |
1.13 |
|
Total |
100.00 |
100.00 |
Figure 14 shows the scanning electron microscope (SEM) images of the kaolin powder. In order to visualize the internal morphology of the kaolin powder under the SEM microscope, a grayed background was observed. This amorphous background shows a few very fine particles, indicating the presence of a small quantity of Clinochlore.
The differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were performed on the kaolin sample. The obtained DTA and TGA thermograms for the kaolin fraction are presented in Fig. 15. The TGA thermogram reveals three thermal phenomena:
- The endothermic peak around 60°C is caused by the departure of absorbed water located between the kaolin sheets [34].
- The exothermic peak observed at 448°C is characterized by the dehydroxylation of structural water, which is eliminated by a diffusion mechanism resulting in the formation of a new amorphous material, metakaolin [34]. The third exothermic peak observed at 622°C indicates the recrystallization of metakaolin [35].
- The ATG thermogram of this material shows two thermal phenomena: the first is mass loss (approx. 0.42%) corresponding to the evaporation of absorbed water. The second is mass loss (approx. 2.64%) which continues beyond 846°C, dehydroxylation due to the presence of Illite [36].
3.2. Granulometric distribution effect
The granular composition of the soil was determined using a particle size analysis, whose results are presented in Fig. 16. The granulometric curve indicates that the soil studied is classified as a fine soil, exhibiting a close granulometric distribution ranging from 0.002 to 0.65 mm. This analysis provides valuable information on the physical characteristics and composition of the soil, which allows us to better understand its properties.
The analysis of the studied soil involves a thorough examination of the clay component to determine its consistency states, commonly referred to as Atterberg limits. These limits include the liquid limit (WL), the plastic limit (WP) and the plasticity index (PI = WL - WP), and their specific values (Table 6). This comprehensive analysis of the soil's clay properties gives crucial information on its behavior under different moisture conditions, which allows a better understanding of its technical characteristics.
|
WL (%) |
WP (%) |
IP (%) |
Soil Plasticity |
Swelling potential |
Recommended Technique |
|---|---|---|---|---|---|
|
39 |
23 |
16 |
Medium |
Medium |
CEB/A |
| - CEB : Compressed Earth Brick, | |||||
| - A : Adobe | |||||
3.3. Thermal conductivity analysis
The bricks' thermal properties were assessed using the high insulation house method, as illustrated in Fig. 4. To meet the experimental criteria, thermal conductivity measurements were conducted four times. Table 7 presents the thermal conductivities and resistances of the stabilized bricks, demonstrating how they vary with the percentage of geopolymers derived from kaolin.
|
Rate of geopolymer % |
0 |
3 |
4 |
5 |
6 |
|---|---|---|---|---|---|
|
Thermal conductivity λ (W/m.K) |
0.702 |
0.723 |
0.764 |
0.788 |
0.801 |
|
Thermal resistance R(m².K/W) |
0.0569 |
0.0553 |
0.0523 |
0.0507 |
0.0499 |
An increase in thermal conductivity as a function of the percentage of geopolymer in the mixture was observed. This increase is due to the decrease in porosity in the earth matrix and the increase in geopolymer content. In fact, the pure earth matrix is very dense because the earth particles and geopolymer particles are very fine. The increase of geopolymer percentage in the mixture reduced the volume of voids between the earth and geopolymer particles, which contributes to an increase in thermal conductivity (Fig. 17). Thermal resistance is inversely proportional to thermal conductivity, and depends on material thickness. It has therefore been observed that an increase in conductivity leads to a decrease in thermal resistance. Consequently, a high percentage of geopolymer in the earth matrix results in a very low thermal resistance of the stabilized brick (Fig. 18).
3.4. Mechanical strength of stabilized bricks
The measurement results for tensile and compressive strength are shown in Table 8.
|
Pourcentage de géopolymère (%) |
Rt en MPa |
Rc en MPa |
|---|---|---|
|
0 |
0.114 |
0.892 |
|
3 |
0.132 |
1.146 |
|
4 |
0.285 |
1.273 |
|
5 |
0.413 |
2.675 |
|
6 |
0.624 |
4.076 |
According to the results presented in Fig. 19 and Fig. 20, both tensile and compressive strength increase with an increase in the percentage of geopolymer in stabilized bricks. when the geopolymer content is at 6%, the bricks exhibit a remarkable increase in mechanical robustness. The compressive strength, represented by Rc(6% GP), is found to be 4.56 times the strength of bricks without geopolymer content [Rc(0%GP)], reflecting a 356% increase in the ability of the material to resist crushing loads. Similarly, the tensile strength, denoted as Rt(6%GP), reaches a value that is 5.47 times that of the non-geopolymerized bricks [Rt(0%GP)], indicating a 447% enhancement in resistance to tension. These multiplicative factors are not merely incremental but signify a substantial amplification in strength, suggesting that the geopolymer contributes significantly to the soil matrix's cohesion and overall durability. Moreover, these results may imply that geopolymers could be a viable alternative to traditional binders, offering enhanced mechanical properties that could be beneficial for sustainable construction practices. The increased strength with geopolymer addition could lead to the use of less material for the same structural requirements, reducing the environmental footprint.
The geopolymer contains elements such as silicon, aluminum, calcite and oxygen, which can reinforce the earth matrix and improve its tensile and compressive strength. In addition, the crystalline structure of the geopolymer contributes to a better cohesion of the earth and geopolymer particles, which can also reinforce the mixture and improve its mechanical strength. It is also possible that the porosity of the mixture has an impact on its tensile and compressive strength. Indeed, an earth matrix with higher density and lower porosity may be more resistant to mechanical stress than one with higher porosity. Indeed, as the addition of geopolymer to the earth mixture reduces the porosity of the mixture, this could also contribute to better mechanical strength.
The present study contributes to the evaluation of geopolymer binders based on kaolin and alkaline solutions as an effective method for stabilizing earth bricks. Various characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR), and differential thermal and gravimetric analysis (DTA-GTA), were employed to assess the properties of the stabilized products. The results revealed substantial improvements in the compressive and tensile strengths of earth bricks after incorporation of geopolymer. The compressive strength increased from 0.892 MPa to 4.076 MPa and tensile strength increased from 0.114 MPa to 0.624 MPa. However, thermal conductivity also increased from 0.702 W/m.K to 0.801 W/m.K at ambient temperature, which indicates a slight reduction in thermal resistance. These results confirm that kaolin and alkaline solutions are suitable geopolymeric binders to stabilize earth bricks. Besides improving mechanical properties, these geopolymeric binders also offer advantages in terms of durability and energy efficiency, providing a sustainable material that contributes to reducing carbon footprints and to preserving natural resources. In conclusion, kaolin and alkaline solution-based geopolymer binders present a promising solution for stabilizing earth bricks, providing improved mechanical properties and an eco-friendly approach. These results pave the way for new possibilities in sustainable construction and the conservation of natural resources.
Author Contribution
Mohamed CHAR : Conceptualization, Methodology, Software, Investigation. Amine TILIOUA : Data curation, Writing- Original draft preparation, Visualization, Investigation, Supervision, Validation, Writing- Reviewing and Editing.
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No competing interests reported.