Comparative study of the mechanical and thermal performance of two-clay-Based Compressed Earth Blocks (BTC) for housing building

 Corresponding author: Bamba COULIBALY Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Comparative study of the mechanical and thermal performance of two-clay-Based Compressed Earth Blocks (BTC) for housing building Bamba COULIBALY *, Youssouf BERTHE, Mahamadou ALLASSANE, Kélétigui DAOU, Moumouni CISSE and Amadou DOUMBO National School of Engineering Abderhamane Baba Touré (ENI-ABT) Bamako -Mali. World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 Publication history: Received on 21 August 2025; revised on 01 October 2025; accepted on 03 October 2025 Article DOI: https://doi.org/10.30574/wjarr.2025.28.1.3371 Abstract This study is part of a sustainable construction approach by exploring the mechanical and thermal performance of compressed earth blocks (BTC) made from Dialakoro and Kita clays. BTC measuring 23 x 11 x 8 cm and cylindrical specimens measuring 5 cm in diameter by 10 cm in height were manufactured for the mechanical tests, and rectangular specimens measuring 27 x 27 x 3 cm were used for the measurement of thermal conductivity. The water absorption results by capillary action reveal a low resistance to humidity for the BTC from Kita (caused by rapid degradation in the presence of water) with a coefficient of -8 g/cm²·s¹/², compared to 2 g/cm²·s¹/² for those from Dialakoro, indicating better resistance to humidity. In terms of compressive strength, Dialakoro BTC averaged 6,85 MPa on the 28th day compared to 4,97 MPa for Kita. After 7 days, both types of BTC exceed the minimum permissible compressive strength for BTC, which is 2 MPa according to the NF EN 772-1 standard, with 3,86 MPa for Dialakoro and 2,29 MPa for Kita. Thermal conductivity measurements also show an advantage for Dialakoro’s BTC with 0,86 W/m·K compared to 1,02 W/m·K for Kita’s, suggesting better thermal insulation. These results confirm the superior potential of Dialakoro’s BTC in terms of mechanical performance and thermal efficiency. Keywords: Compressed Earth Blocks (BTC); Capillary Water Absorption; Compressive Strength; Thermal Conductivity; Sustainable Construction 1. Introduction Clay has been the most widely used material on earth for several centuries. The various archaeological sites around the world bear witness to this.[1] •Nowadays, earthen constructions are still visible on different continents. •It is estimated that one-third of the world’s population lives in earthen structures [2]. Despite the contribution of other resistant and durable materials (cement, lime, bitumen, steel, etc.) for construction through economic and technological development, the problems of global warming have forced man to use healthy materials that do not emit greenhouse gases. This has encouraged the return of earth in construction. The first reason is the availability of land and its proximity to the construction site. The implementation, which is relatively easy, does not require heavy materials and equipment, let alone advanced technology. The earth material does not require energy for its implementation and it has excellent thermal inertia due to its high density. This thermal inertia makes it possible to have a cool home in summer and warm in winter. On the other hand, the earth material also has disadvantages such as low mechanical strength and high sensitivity to water. Man has always thought about finding solutions to the inadequacies of the earth material using several means of stabilization, such as mechanical, chemical and physical, World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 337 which allowed the invention of the different earth products, these are: adobe; cob; rammed earth; terracotta bricks, and compressed earth block (BTC). Among the various raw earth building material products, BTC is the recent version of adobe, which has the advantage of limited shrinkage, high strength, low water sensitivity and a well-erect shape with straight edges. , [1][2] The building trade accounts for a significant share of global energy consumption and greenhouse gas (GHG) emissions. Faced with growing environmental and economic challenges, the optimization of building materials is becoming an essential lever to promote more sustainable and eco-responsible architecture. The use of local, minimally processed materials with a low environmental impact is therefore a priority in the search for alternative solutions to conventional materials such as concrete or fired bricks, which require highly energy-intensive manufacturing processes. In this context, compressed earth blocks (BTC) appear to be a promising solution. Used for centuries in traditional construction, these blocks are now being re-evaluated from a modern perspective thanks to technological advances and new building standards. They are distinguished by their low carbon footprint, their ability to naturally regulate indoor humidity and their thermal performance that contributes to the comfort of the occupants. Compressed earth blocks are building blocks obtained by mechanical compaction of a mixture of earth and water, with or without the addition of stabilizers such as lime or cement. [3] The effectiveness of BTC depends largely on the properties of the clay used. The Dialakoro clays (located in the Sikasso region of Mali) and Kita (located in the region of the same name in Mali), two regions known for the richness and quality of their clay soils, have mineralogical and particle size compositions that can influence the mechanical and thermal characteristics of the blocks. The comparative study of these two types of clays will therefore make it possible to assess their potential as sustainable building materials and to identify their advantages and limitations according to the requirements of the building sector. The main objective of this study is to evaluate and compare the mechanical and thermal performance of BTC made from Dialakoro and Kita clays, in order to determine their suitability for use as sustainable building materials. In this context, the central question of this research is the following: How are the mechanical and thermal characteristics of BTCs that are made from the clays of Dialakoro and Kita different, and what implications might this have for their use in sustainable construction? 2. Methodology The methodology adopted for this study is based on four (4) main parts: • The presentation of the materials used, • The presentation of the specimens produced, • The geotechnical characterization of the basic materials (Dialakoro and Kita clays), • The mechanical and thermal characterization of BTC. 2.1. Presentation of the materials used The materials used for the production of our test tubes are: Dialakoro and Kita clays and drinking water provided by SOMAGEP-SA. 2.2. Presentation of the specimens produced We have produced: • Cylindrical specimens of diameter and height intended for capillary water absorption and compression tests;𝜙 = 5𝑐𝑚𝐻 =10 𝑐𝑚 • BTC dimensions for compression testing;23 𝑥 11 𝑥 8 𝑐𝑚 • Rectangular specimens of dimensions intended for the measurement of thermal conductivity.27 𝑥 27 𝑥 3 𝑐𝑚 World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 338 Cylindrical test pieces BTC Bricks : Rectangular test tubes Figure 1 Test tube and brick products 2.3. Geotechnical characterization of the base materials 2.3.1. Particle size analysis by sieving Purpose of the Experiment It determines the distribution of grains by weight of the elements of a material according to their size. Principle of the Experiment Sieving is carried out for elements of dimensions greater than or equal to 0.08mm on a series of sieves.[4] Figure 2 Experimental set-up for particle size analysis by dry sieving 2.3.2. Atterberg Limits Purpose of the Trial The aim is to characterise the consistency of a soil as a function of water content. Three conventional physical constants are defined: • Liquidity limit WL: Transition from liquid to plastic. • WP plasticity limit: transition from plastic to solid state. • WS shrinkage limit : Transition from solid state without shrinkage to solid state with shrinkage. Principle of the Experiment The principle of the trial is as follows: • Finding the liquidity limit using the CASAGRANDE device. • Search for the plasticity limit by making rolls of 3mm in diameter. World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 339 Liquidity Limit The WL liquidity limit is the water content (expressed in %) of a reworked soil characterizing the transition from a liquid state to a plastic state that corresponds to a 25-shock closure. The Atterberg limit is applied to fine soils whose elements pass through the 0.4mm sieve .[5] The test was carried out in accordance with the NF P94-051 standard. Figure 3 Liquidity Limit Trial Set-up Plasticity limit The plasticity limit consists of determining the water content of a moist soil in the form of a roll, diameter (Փ = 3 mm) and length (L = 10 to 15 cm) when it passes from the plastic to the solid state.[5] The test was carried out in accordance with the NF P94-051 standard. Figure 4 Experimental device of the plasticity limit Plasticity index The plasticity index is the difference between the values of the liquidity limit and the plasticity limit. 𝑰𝒑= 𝑾𝑳− 𝑾𝑷 (1) 2.3.3. Absolute density The density of solid soil particles in 𝝆𝒔 (g/cm3) is the ratio of the mass of these solid particles (Ws) to their absolute volume (Vs). The density of our sample is measured in accordance with the standard NF P 94-054 with a water pycnometer. This method uses solid soil particles that are not larger than 2 mm in diameter.[6] World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 340 Figure 5 Pycnometer test experimental set-up 2.3.4. Normal Proctor Purpose of the Experiment The purpose of the Proctor test is to determine the optimum water content () and maximum dry density by means of a standard compaction (of known intensity) or for a given compaction energy 𝝎𝒐𝒑𝒕(𝜸𝒅 𝒎𝒂𝒙) . Principle of the Experiment Samples of the same soil with different water contents are compacted in a normal mould (or standard mould) in the same way. The dry densities obtained vary with the water content of the samples at the time of compaction. This density passes through a maximum which is obtained for an optimum water content.[7] The test was carried out in accordance with the NF P94-093 standard. Figure 6 Proctor Normal trial investigational device 2.4. Characterization of compressed earth blocks (BTC) 2.4.1. Physical characterization Water absorption capacity by capillary action The capillary water absorption test is essential to evaluate the porosity and the ability of a material to absorb moisture. It is particularly relevant for building materials such as BTC, as it allows you to appreciate their durability and their behaviour in the face of water. World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 341 Objective of the experiment The objective of this test is to measure the speed and quantity of water absorbed by capillary action of a porous material when it is in contact with a water source. It is used to assess its sensitivity to moisture and its suitability for use in construction. Principle of the experiment The test is based on the phenomenon of capillarity, where water rises in the material through pores and micro-cracks as a result of adhesion and cohesion forces. The amount of water absorbed is measured as a function of time, allowing the coefficient of water absorption by capillary action to be calculated. Procedure ➢ Specimens are selected and put in an oven at 105°C for 24 hours to ensure complete removal of water. ➢ After complete drying, each specimen is weighed (initial dry mass Mi). ➢ They are placed in a tank of water with an immersion limited to 5cm in height (50% of the total height of the individual specimens) and then the stopwatch is started immediately. ➢ After 5 minutes, each of them is gently removed from the water and the surface is quickly wiped with a paper towel or a dry cloth to remove the unabsorbed water and then immediately they are weighed (wet mass Mf). ➢ Calculation of the coefficient of water absorption by capillary action: The coefficient of capillary absorption is calculated by the following formula: 𝑪𝒂𝒃 =𝑴𝒇−𝑴𝒊 𝑺∗√𝒕 (2) With: 𝑪𝒂𝒃 : Capillary absorption coefficient (g/cm²·s¹/²). 𝑴𝒊: Initial dry mass of the specimen (g). 𝑴𝒇: Wet mass of the specimen after immersion (g). 𝑺: Immersion surface (fifth grade) 𝒕: Immersion time (Seconds) Figure 7 Experimental device of the water absorption test by capillary action 2.4.2. Mechanical characterization In this study, we are interested in the determination of the compressive strength of cylindrical specimens and BTC. For each test, three cylindrical specimens and three BTC were tested. The tests were carried out at 7, 14 and 28 days, thus making it possible to monitor the evolution of mechanical strength over time. Compressive strength of cylindrical specimens This test is used to determine the nominal compressive strength of cylindrical specimens. This involves subjecting the specimens to simple compression until they break at 7, 14 and 28 days. World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 342 The manual 60KN CBR press from the Civil Engineering Laboratory of ENI-ABT was used for our test. Procedure ➢ The specimen is placed by centering it on the bottom plate of the press, making sure it is properly aligned with the top plate (piston). ➢ The piston is lowered until it comes into contact with the specimen. ➢ The initial load is checked to be almost zero before starting the test. ➢ The manual press works with a cylinder activated by a lever, which allows the force to be gradually applied to the specimen. The lever is turned slowly and steadily to avoid a sudden shock (application of the load). ➢ The application of the load is continued until the specimen breaks (cracks or collapse). The value of the maximum breaking load is read directly in KN on the press’ pressure gauge. ➢ The compressive strength is obtained by the following formula: 𝑹𝒄=𝟏𝟎 ∗𝑭𝒎𝒂𝒙 𝑺 (3) With: 𝑹𝒄 The compressive strength of specimens in Mpa 𝑭𝒎𝒂𝒙: The breaking load in KN 𝑺: The compression surface of the specimen in fifth grade Figure 8 Experimental device for the compression test on cylindrical specimens Resistance to BTC compression BTC bricks are selected and subjected to the 7, 14 and 28-day compression test. The hydraulic press of the Civil Engineering Laboratory of ENI-ABT was used for our test. Procedure ➢ The BTC is placed in the center of the lower plate of the press to ensure proper axial loading. We make sure that it is well aligned with the upper plate in order to avoid off-center efforts that could distort the results. ➢ The trial involves applying an increasing load until the BTC breaks. The load is applied gradually and continuously at a constant speed. The recommended loading speed is usually 0.5 to 1 Mpa/s ➢ At breakage, the value of the maximum load is directly read in KN on the pressure gauge of the press. ➢ The compressive strength is obtained by the following formula: 𝑹𝒄=𝟏𝟎 ∗𝑭𝒎𝒂𝒙 𝑺 (4) With: 𝑹𝒄 The compressive strength of BTC in Mpa 𝑭𝒎𝒂𝒙: The breaking load in KN 𝑺: The cross-sectional area of BTC in fifth grade World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 343 Figure 9 Experimental setup of the BTC compression assay 2.4.3. Thermal characterization In this study, we are interested in the measurement of thermal conductivity on rectangular specimens. Measurement of thermal conductivity It characterizes the ease with which heat enters the material. It is always positive and corresponds to the density of the heat flux passing through a homogeneous body subjected to a temperature gradient of 1 Kelvin (or 1°C) per metre in a steady state. Thermal conductivity depends mainly on the nature of the material and the temperature. The measurement of thermal conductivity was made using a device set up by the thermal laboratory of ENI-ABT. Thermal Conductivity Measurement Protocol Instrumentation • Thermal conductivity measuring device • Clamp meter (to measure the current of the electric heating resistor) • Voltmeter (to measure the voltage of the electric heating element) • Five (5) T-type thermocouples or any other type available for measuring different temperatures • Conversion table of the thermocouple used (Type K for our test) • Dewar vase containing melting ice (or a thermos) • Autotransformer 0 – 240 V • Air-conditioned room Procedure • Thermocouple Positioning o A thermocouple is fixed in the centre of each side of the specimen, using plaster, a very thin layer, to measure the temperature of the faces of the specimen. We wait for the plaster to dry; o A thermocouple is positioned between the hot plate and the bottom of the plate to measure the temperature of the air on the hot side; o The fourth thermocouple is suspended in the air of the room next to the apparatus, for the measurement of the temperature of the room; o The fifth thermocouple is placed in the melting ice contained in the Dewar mud (or in the thermos) for the measurement of the reference temperature. Measurement process • The room’s air conditioner is turned on at a temperature of no more than 25°C (21°C for our test); • The specimen is placed in the apparatus in the designated place; • The edges of the specimen are insulated to prevent movement between the heating plate and the room; • The autotransformer is adjusted to have an output voltage of less than 60 V to supply the heating element; World Journal of Advanced Research and Reviews, 2025, 28(01), 336-350 344 • Temperature, intensity and voltage measurements are made every 30 minutes to ensure that the temperature gradients are established correctly; • We wait about 10 to 12 hours to resume the measurements mentioned above for 2 hours (the permanent regime should be obtained); • The coefficient of losses is measured; • After the steady state at which the measurements have been made, the voltage is reduced to 30 V; • We hear that the temperatures of the two sides of the specimen are identical, this can take hours; • The measurements are then carried out. Experimental outcomes (Only steady-state values are used) Heating power𝑃 = 𝑈 ∗ 𝐼 = 𝐶 ∗ (𝑇𝑎𝑖𝑟 𝑐ℎ𝑎𝑢𝑑 − 𝑇𝑎𝑖𝑟 𝑙𝑜𝑐𝑎𝑙) Hence the loss coefficient: (in 𝐶 = 𝑈∗𝐼 𝑇𝑎𝑖𝑟 𝑐ℎ𝑎𝑢𝑑 − 𝑇𝑎𝑖𝑟 𝑙𝑜𝑐𝑎𝑙W/°C) (5) The net power passing through the specimen: 𝑃 𝑒𝑝 = 𝑃 − 𝐶 ∗ (𝑇𝑎𝑖𝑟 𝑐ℎ𝑎𝑢𝑑 − 𝑇𝑎𝑖𝑟 𝑙𝑜𝑐𝑎𝑙)=𝜆 ∗ 𝑆 ∗ ∆𝑡 𝑒 Hence the thermal conductivity coefficient: 𝝀 = 𝑷𝒆𝒑 ∗ 𝒆 𝑺 ∗ ∆𝒕 (6) Where: = thickness of the specimen;𝑒 𝑆 = surface area of the specimen; ∆𝑡 = 𝑇𝑓𝑎𝑐𝑒 𝑐ℎ𝑎𝑢𝑑𝑒 − 𝑇𝑓𝑎𝑐𝑒 𝑙𝑜𝑐𝑎𝑙𝑒= temperature difference between the two sides of the specimen. Figure 10 Experimental device for measuring thermal conductivity