FEASIBILITY OF METAKAOLIN AND LIME MATERIAL AS A BINDER MIXTURE FOR CONCRETE THE CASE OF BALENGOU CLAY IN WEST CAMEROON AND THE LIME OF FIGUIL NORTHERN CAMEROON

6907 Revue Internationale de la Recherche Scientifique (Revue-IRS) ISSN: 2958-8413 Vol. 3, No. 6, November 2025 This is an open access article under the CC BY-NC-ND license. FEASIBILITY OF METAKAOLIN AND LIME MATERIAL AS A BINDER MIXTURE FOR CONCRETE THE CASE OF BALENGOU CLAY IN WEST CAMEROON AND THE LIME OF FIGUIL NORTHERN CAMEROON Pr. GOUAFO Casimir University of Dschang (Cameroon) Pr. DEFO Célestin University of d’Ebolowa (Cameroon) Pr. NDONGO Barthélémy University of Dschang (Cameroon) Dr. KOUGOUM GOUAFO Géraldine University of Dschang (Cameroon) M. ZOYEM GOUAFO MATHURIN University of Dschang (Cameroon) Abstract: Diverse complexities and challenges are faced during cement production processes especially the Portland cement. The process requires huge amounts of energy and these fossils fuels when burnt at up to 1450°C released excessive greenhouse gases such as CO2 which contributes to the calamity called global warming. All these facts, in addition to the low economic growth of countrys, and the expensive price of construction materials, reduce the availability of a liveable, ecological and sustainable shelter house for the middle classes. It is in this line that we thought of valorising the calcined clay from Balengou by studying the feasibility of making a binder by mixing it with lime from Figuil as this could help to partially cover some domains done by Portland cement, to improve the lime mortar properties, to reduce the construction cost, and to reduce the degradation of the ozone layer. In this work, Hallosysite clay from Balengou was calcined at 750°C, mixed with lime and the effects of it at metakaolin percentage substitution to lime (10 %, 15 %, 20 %, 25% to 90 %.) were examined on their physico-mechanical properties such as Consistency, water absorption, pozzolanicity etc. In the limemetakaolin mixture with metakaolin from Balengou’s clay, as we increase the percentage of metakaolinin the paste, the setting duration reduces. The proportion of pure lime improves the plasticity of the paste while the metakaolin at its optimum percentage (20%) increases the strength of the paste to 6908 its maximum value at about 28 days. The low energy consumption during the manufacturing process and the CO2 absorption during the carbonation process reduce the environmental impact and cost of lime-metakaolin mixture. Also, the aesthetic appearance of that paste makes it adequate for internal pointing and plastering. At 20% of metakaolin in the paste, the pozzolanicity is at the highest point and the paste gains good plasticity and perspiration with optimum resistance. Lime-metakaolin mixture is good for works where the need of breathability and lower strength is of great importance. Then, we do not recommend it for works with high strength structural elements. Key words: metakaolin, pozzolanicity, Balengou clay, Figuil, lime-metakaolin, binder Mots clés : métakaolin, pouzzolanicité, argile de Balengou, Figuil, chaux-métakaolin, liant Digital Object Identifier (DOI): https://doi.org/10.5281/zenodo.17775902 1. INTRODUCTION For centuries now, Lime was used in both mortars and concrete until it was replacing by Portland cement, due to faster hardening, higher strength and apparent longevity. However, for the production of cement, massive extraction of limestone is done in quarries so much so that it gradually become scarce and consequently expensive. Also, cement has a considerable environment impact due the fact that its manufacturing contributes to greenhouse gases both directly through production of CO2 when calcium carbonate is thermally (900°C) decomposed, producing lime and Carbone dioxide, and also through the use of energy, particularly from the use of fossil fuels (from 900°C to 1450°C for the combination of lime, alumina and Silica). Looking at that environmental impact of cement (creating up to 5% of worldwide emission of CO2) and also it non breathable characteristic for walls and slabs, many researchers nowadays, are coming back to the use of lime for Ecological construction. Indeed, Lime is the most sustainable binder due to lower production energy needed, lower CO2 during emission and CO2 absorption by carbonation. Lime mortar is softer than cement mortar, allowing brickwork a certain degree of flexibility. It is considered breathable in that it will allow moisture to freely move through and evaporate from the surface; allows moisture to escape through evaporation and keeps the wall dry. The only problem with lime mortar is its strength which is not high enough. However, the addition of fly ash, calcined clays or any material with natural or artificial pozzalanic properties, has the ability to improve the strength and lifelong of binders made up of lime (Mertens et al., 2009), particularly the addition in binder of calcined clay (with a high content in SiO2 and Al2O3) at 750°C with an appropriate percentage has an upswing in the construction field. Hallosite clay from balengou is calcined at 750°C (Métakaolin). The feasibility of a binder made up of lime and metakaolin at different percentage were examined on the pozzolanicity, consistency, setting time, compressive strength, water absorption, flexibility, aesthetic and ecological properties such as the fight against humidity and its breathable conditions for civil engineering structures. 6909 2. STATEMENT OF THE PROBLEM As the consumption of cement undergoes an annual increase of 7.9% in Africa in year 2016 (Global cement report) with 2.8 million tons of cement per year in Cameroon (Nimpa, 2016), the growing population will be always in need for shelter constructions. Looking at the damages caused by global warming such as floods, climate change, skin cancers and heart illness, there is an urgent need to come out with ecological materials for construction. People are now called to choose construction materials not only focused on the resistance (for the project owner) and the cost (for the middle class); but also on their ecological aspect in order to respect our ecosystems. The main problem that we are facing is to come out with construction materials which are ecologic, resistant and economic. 3. PURPOSES OF THE STUDY The main objective of this work is to study the feasibility of a binder made up lime and metakaolin. Specifically, this will consist of evaluating the physico-mechanical properties of lime mortar by addition of metakaolin from Balengou hallosyte at different percentages in the lime from Figuil, studying the ecological behavior of that new binder within the house and its effect on the environment, making some recommendation in a bid to delimitated the scope that new binder can cover in Civil Engineering projects for sustainable, ecologic and economic constructions. 4. SIGNIFICANCE OF THE STUDY Pozzalanic materials such as fly ash, calcined clay are known for their strength and long life term improvement (Pandey, 2003). And for centuries, lime has been always known for its good ecological effect on the environment through carbonation. Thus, studying the possible combination of lime and clay, could be helpful in valorizing local materials as the kaolinite clay from Balengou and Lime from Figuil. This will also help us reducing the effect of global warming caused by Portland cement manufacturing. To reduction the amount of cement produced due to its partial replacement with lime-metakaolin mixture. This obviously lead to the reduction of construction cost and to low impact on the environment. 5. VARIABLES • The calcination temperature of hallosyte clays from Balengou; 750°C • The mass percentage of S750 in the blended mixture 10%,15%, 20%, 25%, 35%,50%, 65%, 75%, 80%, 85% • CO2 emission, CO2 absorption, heat effects (dependent variables) 6. Lime as Building Construction Materials Lime used in building materials is broadly classified as "pure", "hydraulic", and "poor" lime; can be natural or artificial; and may be further identified by its magnesium content such as dolomitic or magnesium lime. Uses include lime mortar, lime plaster, lime render, lime-ash floors, tabby concrete, whitewash, silicate 6910 mineral paint, and limestone blocks which may be of many types. The qualities of the many types of processed lime affect how they are used. The Romans used two types of lime mortar to make Roman concrete, which allowed them to revolutionize architecture, sometimes called the Concrete revolution. 7. Clay Definition Clays are defined according to the state of knowledge at the time and their uses. As universal materials they cannot be limited to only one definition. The Word “clay”, a generic universal name is that of “earth”, associated with qualifying names such as potter‟s clay, fire clay, or green clay. The term “clay” comes from the Greek word argilla, the root of which, argos signifies“white”. The relation to purity was quickly established with color even though most clays are not white. Clays are not made up of a definite a unique material but they are composed of complex associations of materials, hydrated silicates and aluminats of a leaf like structure called phylisilicatrs (Tchamo, 2015). There is no uniform definition for clay or clay minerals, however the clay mineral society recommend the use of the following definition: “Clay is a natural occurring material composed primarily of fine grained minerals, which is generally plastic at appropriate water contents and will harden when dried or fired”. a) Mineralogical Properties Clays from Balengou is made up essentiallu of hallosite, Al2Si2O5(OH)4. 2H2O associated to other elements such as quartz, hematite and muscovite. X-ray analasis of calcined metahalloite clays are characterized by the absence of hallosite and other impurities. This simply confirms that the thermal treatment has destroyed the crystalline nature of the original clay minerals (Sabir et al., 2001). The minereal composition of hallosite clay is given in the following table. Table 1: The mineral composition of Hallosite clay Mineral Hallosite Quartz Gibbsite Hermatite Feldpath Anatase Undertermned % 70.41 18.04 4.69 3.19 0.53 0.41 2.36 The determination of the mineralogical phases contained in this material was carried out by Zangue 2016 which consisted in mineral analysis by the X-ray diffraction Method. (XRD).Clays materials and associated minerals have been identified. It is revealed that these clays consist of Hallosite/Kaolinite, quartz, smectite, vermicule, gibbsiten goethite and hematite. Quartz and hallosite are dominant and highly represented in all the five samples (ZA0: ZA1; ZA2; ZA3; ZA4 and ZA5) drawn from the pits. 6911 Figure 1: X-ray diffraction results for the Hallosite clay from Balengou (Zangue, 2016) 6912 b) Chemical composition Hallosite is a naturally occurring clay with kaolinite being the main component having a chemical composition of Al2Si2O5(OH)4. Halloysite is when heated at temperatures between 100 and 200 there is loss of interlayer water to produce metahallosite. This loss of mass explains the procedure of pre-dehydration and the formation of metahalloysite (Minato and Aoki, 1979) according to the equation. Al2Si2O5(OH)42H2O → Al2Si2O5(OH)4 +2H2O Halloysite metahalloysite + water It has a layered silicate structure, where oxygen atoms links in an octahedral sheet of alumina with a tetrahedral sheet of silica. When metahalloysite is calcined at elevated temperatures between 450°C and 750°C, dehydroxylation occurs which collapses the crystal structure to produce amorphous metakaolin (Al2Si2O7), according the folloxing proposed reaction scheme: Al2Si2O5(OH)4 → Al2Si2O7+2H2O↑ Metahalloysite metakaolin+ water The thermal transformation of metakaolin above 1000°C first produces either a Al-Si spinel phase or a aluminosilicate phase which transform into mullite and above 1150°C cristobalite (c-SiO2) is formed. The thermal transformation of kaolin has been the subject of numerous studies, which reported on how the different heating conditions influence the dehydroxylation process. At temperature below 400°C, a dehydroxylation process takes place, upon cooling the hydroxle peaks reappear in the infrared spectra. Above temperature of 400°C irreversible moss of hydroxyls groups occur. The temperature at which the highest rate of dehydroxylation occurs is dependant on the original structural state of the kaolin, the particle size, density of packing, the water pressure.  DTA curves for kaolinic clays Differential thermal Analysis for halloysite type clay minerals shows that they are characterized by a sharp endothermic reaction between 500°C and 600°C and by a very abrupt exorthermic reaction at about 950°C. hydratedhalloysite shows an additional sharp endothermic reaction about 100°c and 200°C. the following diagram emanates from the works of (Tchamo, 2015), representing the DTA curves of kaolin and halloysite. Figure 2: DTA curves of K and H (Kaolin and Hallosite respectively) (Tchamo, 2015) 6913  Clay Activation and Optimum Calcinations Temperature Clay needs to be activated by modifying its original crystallinestructure so as to achieve good pozzalanic properties. This is achieved either by chemical, mechanical or the thermal activation methods, among which thermal activation is the best (Elert et al., 2008). An endothermic reaction occurs during the conversion of hallosite to metakaolin due to the large amount of energy require to remove the structural bound water whereby the clay structure is modified and a less ordered phase is created. This phenomenon is referred to us as the dehydroxylation of clay minerals. The optimal calcination temperature is influenced by the mineralogy of chemical composition of the clay. In order to produce a pozzolan, nearly complete dihydroxylation must be attained without the clay being burnt because overheating or high calcination temperature above 900°C can lead to recrystallization of high temperature phases and additional sintering resulting in a decrease in the pozzolanic reactivity of the material. Several researchers have studied the pozzolanic activity and the optimal calcination temperature for pure clays.The optimal activation temperature depends mainly on the type and structure of the clay mineral. An overview of these studies and the most important conclusions drawn are given in the table below. Table 2: Calcination temperatures for the different clay types (Taylor-Langr et al., 2015) The opti mu m acti vati on tem pera ture of clay is the Te mpe ratu re at whi ch that clay start s to modify its original crystalline structure so as to achieve good pozzolanic properties. Author Ye ar Clay type Calcination T (°C) Optimum act. (°C) Pozzolanic activity Ambroise 19 84 Kaolinite 750 750, 5h High Montmorillonite Low Illite Low Lateritic soils Medium Kaolinite 600, 650, High Martin-calle 19 89 700, 750, 700, 24h Brick clay (illite/kaolinite Medium 800, 850 19 95 Kaolinite 550, 650, 650 High 800, 950 He Na-montmorillonite 740, 830, 920 830 Low Ca-montmorillonite 730, 830, 920 830 Medium Illite 650, 790, 930 930 Low Sepiolite 370, 570, 830 830 Low Mixed layer mica560, 760, 960 960 Low smectile Kaolinite 500, 600, 700 700-800 High Chakchouk 20 06 Illite/montmorillonite clay 500, 700, 800 - Low Kaolinite 600 High Fernandez 20 13 Illite 600, 800 800 Low/Inert Montmorillonite 800 Medium Kaolinite 650, 830, 930 650 High TaylorLange 20 15 Kaolinite – Ca930 Medium montmorillonite Kaolinite – Namontmorillonite 830 Medium to high 6914 Mejía de Gutiérrez et al. (2008a), carried out a test to show the influence of the calcination temperature of kaolin and they conclude that the optimum eating temperature for the kaolin in between 700 and 800°C. Summarily, most reported optimal activation temperature for kaolinites and hallosyte cluster between 650 and 750°C, we can therefore conclude that the optimum calcination temperature for hallosyte clay is very close to 750°c, where by the metakaolin produced has a very high pozzolanicity. c) The Metakaolin from Balengou Halloysite Clay Metakaolin is produced when Halloysite or kaolinite clays are calcined. It is used as supplement in cementitious material and calcination conditions is one of the most important factors influencing the pozzolanic property. It is produced by the calcination of kaolin clay within a define temperature range. The temperature range depends on th kaolin characteristics such as degree of crystallinity and particle size. The heating parameter such as temperature, heating rate and time, as well as cooling parameters (cooling rate and ambient conditions), significantly influence the heating process, the heating temperature range from 550°C to 850°C, but can still change depending on the nature of the kaolin. The appropriate temperature to obtain metakaolin from the Balengouhalloysite clay is 750°C (SADO NJIKE, 2017). The heating process drives off water from the mineral kaolin cly and collapses the material structure, resulting in an amorphous alumino silicate metakaolin. Below is a simple representation of metakaolin. Figure 3: Metakaolin from Balengou (Sado, 2017) Metakaolin is usually a white mineral material of aluminosilicate (Kimberly, 2011). The formula of metakaolin chemistry is Al2O3Si2O2 (Lilla et al., 2013). The grain size of metakaolin is between cement and microsilica and the specific surface is about 15000 m²/ Kg. it‟s a supplementary cementing materials, these are materials used to replace part of the clinker in a concrete. Since it contains pozzolana which contributes to the amelioration of both fresh and hardened concrete properties.Metakaolin is neither the by-product of an industrial process nor is it entirely natural. It is derived from naturally occurring mineral and is manufactured specially for cementing applications. The following table elaborates the physical and chemical composition of metakaolin. 6915 Table 3: Physical and chemical composition of metakaolin (Sanjay et al., 2013). Chemical compsition (% by mass) Physical properties Si2O2 54-53% CaO <0.2% specific density 2.40 to 2.60 Al2O3 42-44% MgO <0.10% Physical form powder White, Buff Gray Fe2O3 <2.20% Na2O <0.050% Color TiO2 <3.0% K2O 0.4% brightness 80-82 SO4 <0.5% L.O.I <0.50% Specific surface 8-15 m²/g 8 METHOD OF TESTING POZZOLANICITY. a) Direct methods.  The Chapelle Test The principal is based on mixing a pozzolanic material in the presence of lime in water at a temperature of (85+-5°c) for 16 hours. The residunis filtered and reacted with hydrochloric acid to determine the quantity of lime that reacted with the material (Melissa and Ndigui., 2005)  The Frattini Test The procedure is specified by EN 196-5 norm : 2011. The pastes are prepared with 80% cement and 20% of the pozzolanic material. After preparation, the samples are conserved in scraped plastics for 8 days at 40°c. The pastes obtained are filtered at room temperature. The filtrate is then reacted either with hydrochloric acid or with E.D.T.A. (Ethylene DammineTetraacetic acid) (Bich, et al.,2009). The EN 196-5 norm evaluates the reduction in the amount of Ca2+ and OHin a satured solution of lime at a temperature of 40 °C and in contact with the pozzolanic material. This solution of lime at a temperature of 40°C and in contact with the pozzolanic material. This solution is then titrated with E.D.T.A. solution or hydrochloric acid. (Ndigui et al., 2008). b) Indirect methods.  Different Thermal Analysis. This method is based on the measurement of residual pick of DTA of Calcium hydroxide on the powders of pastes done with a mixture of percentages of cement and pozzolanic material. The pastes are demolded after 24 hours, ground and sieved to obtain particles less than 100 micro meter. The powder is submitted to the ATD and the pozzolanic activity is determined (Bich et al., 2009).  Mechanical Measurements It is focused in the determination of the material reactivity it is calculated by the ratio between resistances to compression of mortars made with pozzolans those made with pozzolan after 28 days (Cyr et al., 2012). For various decades these materials were mixed with limestone to produce binders with high 6922 done on blended mixture of lime and calcined clay at different percentage. That is 10%, 15%, 20%, 25%, 35% and 50% of calcined clay. The method aimed at determining the amount of Calcium hydroxyde fixed by the material in well stated conditions. The material is placed in excess calcium hydroxide for 16 hours at a temperature of 90°C. After filtration, the residue constituted of Calcium hydroxide which has not been fixed is made to react with an aqueous solution of 0.1 M of hydrochloric acid. The figures below demonstrate the Chappelle test execution. Figure 12: Assembly of the modified Chappelle test equipment 11. PRESENTATION AND INTERPRETATION OF RESULTS Here, we display the results we obtained from the various laboratory test carried out. These results are based on the influence of the partial substitution of metakaolin to the lime at different percentage on the texture, consistency, initial and final setting time, apparent density of the solid mixture paste, water absorption, compressive strength and the Chappelle test of the calcined clays samples. 11.1 The Texture The texture of the clay under study is evaluated by itscolor change as the firing temperature increases from 0° to 750° C. Figure 13: HallosyteBalengou clay at it raw state and at 750°C after crushing. 6923 The color change is cleary noticed with metakaolin fired at 750°C. It moves from the White to the Light-Orange. This phenomenon is explained by the high concentration of the hallosite clay in Iron II oxide which gradually gets oxidized to Iron III as the temperature increase. On the blended cement mixture (lime+metakaoline), as the percentage of metakaolin increases, the blended mixture‟s color changed. The color moves from the extremely white to the brown. This is due to the color of the calcined clays. 11.2 Apparent Density Table 5 : APPARENT DENSITY Sample Mass of can Mass of can + sample Mass of can + water Apparent Density S10 31,37 145,46 303,62 0,419 S15 31,37 146,46 303,62 0,423 S20 31,37 150,64 303,62 0,438 S25 31,37 151,71 303,62 0,442 S35 31,37 158,04 303,62 0,465 S50 31,37 158,44 303,62 0,467 S65 31,37 169,36 303,62 0,507 S75 31,37 176,66 303,62 0,534 S80 31,37 177,01 303,62 0,535 S85 31,37 178,36 303,62 0,540 Lime and metakaolinmixures at different percentage (10%, 15%, 20%, 25%, 35% and 50%, 65%, 75%, 80% and 85%) were passed through a 100µm sieve. And the absolute densities of those pozzolanic mixtures are given by the figure below; Figure 14: Apparent density of lime-metakaolin mixture at different percentage 6924 The general observation of the graph shows that, as the percentage of metakaolin increases in the mixture, the apparent density of the blended cement also increases. This is due to the fineness of the particles contained in the metakaolin; finesness caused by its calcination. And also, that calcination increases the apparent density of hallosyte clay from 0,53at 0°C to 0,638 g/cm3 (638 kg/m3) at 750°C. 11.3 The Consistency and the Workability Table 6 : CONSISTENCY TEST RESULTS An increase in the amount of metakaolin, limits the penetration of the Vicat Needle. Water is then added again into the mixtures until the normal penetration of the Vicat plunger is reached (5mm ± 1mm) and the total amount of water added is noted as a ratio to the original mass of pozzolanic mixture as shown below. Figure 15 : Partial substitution by metakaolin in % Sample Added water Consistency (%) L 0.00 100 S10 2.00 90 S15 7.00 90 S20 11.00 87.5 S25 20.00 85 S35 2.00 82.5 S50 8.00 82.5 S65 12.00 80 S75 18.00 75 S80 7.50 75 S85 68.00 72.5 6925 Looking at this diagram, the consistency of mortar reduces with quantity of metakaolin, this is link to the high demand of metakaolin in water which reduce the fluidity and plasticity of the mortar. As the demand in water for optimum plasticity reduces with the quantity of metakaolin, it affects negatively the workability. Increases in metakaolin to the mixture leads then to the loose of its workability.Whereas at low percentage of metakaolin substitution, the longer the final mixing time the more workable the mortar will be. 11.4 Setting – Time Setting time is one of the most important property of a binder. The results obtained during the setting time experiment are presented in the following table. Table 7: Initial and Final setting time Samples Initial setting / min Final setting / min Setting duration Lime 237 357 178 S10 150 220 160 S15 145 210 172 S20 123 203 175 S25 133 158 171 S35 133 158 140 S50 97 124 90 S65 95 121 65 S75 58 103 50 S80 55 99 37 S85 50 85 20 Figure 16 : Adjustment of the setting duration of the mixture metakaolin +Lime 6926 It can be seen that initial and final intake are delayed by all samples. Samples containing metakaolin increase the duration of socket of the dough. A more stable structure is found with the formation of metakaolin at 750 °C Figure 17: Definition of setting time curves for blended mixtures Setting duration of the mixture paste up to 20% after which it drops. This increase is due to the increasing level of pozzolanic reactions taking place, residual lime originally liberated by the mixture which consequently reduces the degree of pozzolanic reactions and setting duration. Increase in the setting duration provides a greater time for the manipulation of the binder mortar paste during construction before hardening. 11.5 Water Absorption The water contents of the cylindrical solid of our various binders were done and the results are presented in the table 9 to 11. The influence of the pastes when immersed in water for 24 hours after curingand drying in the oven for 24 hours are presented in the figure below. The metakaolin reacts with the calcium hydroxide liberated by lime hydratation to form strong calcium aluminium silicates. Due to the formation of calcium alumino silicate hydrate precipitates (CASH), the ports of metakaolin become closed and absorb less water. Less water absorption is observed at 20% substitution. At this percentage, the structures build with lime + metakaolin mixture will maintain its shape and strength when exposed to water. Figure 18: Water absorption 6927 11.6 Pozzolanic Activity in the Solution An acid-base reaction occured between 0.1 M of HCl and Ca(OH)2. Assuming that all the OHjobs are obtained from the dissociation of Ca(OH)2 which constitute the main constituent of lime, the following table is obtained. Table 8: Summary of the results obtained from the Chappelle test. Samples Concentration of Ca(OH)2 in filtrate (mol/l) Concentration of Ca(OH)2 in filtrate (g/l) Quantity if Ca(OH)2 consumed (g/l) Percentage of Ca(OH)2 consumed (%) 2.5 g metakaolin 0.0023275 0.17575 0.78625 81.73 10 g metakaolin 0.001 0.074 0.888 92.31 15 gmetakaolin 0.000625 0.04625 0.91575 95.19 20 gmetakaolin 0 0 0.962 100 Lime 0.013 0.926 0 0.00 Percentage of Ca(OH)2 consumed 120 100 80 60 40 20 0 0 10 20 30 40 50 60 mass of metakaolin in the mixtures (in grams) Figure 19: Percentage of Ca(OH)2 consumed with as metakaolin is added. The test indicate that thermally activated clay at 750°c absorb Ca(OH)2 in solution at 20g. This is corresponding to the blended lime + metakaolin mixture S20. This is explained by the fineness of clay at 750°c and its greater specific surface which absorb a lot. The specific surface is therefore decisive for the pozzalanic activity, observable for materials comprising of phases in which silica and alumina are amorphous or mobilized. Crystalized forms such as quartz, cristobalite, trydimite and corridon do not participate in pozzalanic reactions. 11.7 Compressive Strength The crushing of the samples was done after 7, 14 and 28days in University Technology Institute Bandjoun by using an electric compressive machine. For each type of binders, 3 samples of cylindrical paste were crushed and the average determine. The diagram below shows the compressive strength of various binders at different percentages of substitution http://www.revue-irs.com 6928 Figure 20: Compressive Strength chart Table 9 : WATER ABSORPTION AND COMPRESSIVE STRENGTH IN MPA AT 7 DAYS Sample Dry mass Wet mass % H 2 O absorption Effort (N) Compression (MPa) S10 16,8 20,12 19,74 224 0,50 S15 14,34 17,23 20,13 556 1,23 S20 11,65 14,23 22,13 2233 4,94 S25 9,18 11,37 23,86 2816 6,23 S35 10,85 13,87 27,86 2395 5,30 S50 14,72 19,32 31,25 2036 4,50 S65 15,87 21,01 32,4 1730 3,83 S75 17,02 22,73 33,55 1473 3,26 S80 18,17 24,47 34,7 1249 2,76 S85 19,32 26,25 35,85 1065 2,36 Table 10 : WATER ABSORPTION AND COMPRESSIVE STRENGTH IN MPA AT 14 DAYS Sample Dry mass Wet mass % H 2 O absorption Effort (N) Compression (MPa) S10 15,23 17,55 15,23 1474 3,26 S15 16,41 19,05 16,07 4404 9,74 S20 10,36 12,30 18,72 4487 9,92 S25 11,78 14,00 18,83 5389 11,91 S35 11,20 14,20 26,83 4338 9,59 S50 18,84 24,62 30,69 3427 7,58 S65 19,99 26,35 31,84 4545 10,05 S75 21,14 28,11 32,99 4396 9,72 S80 22,29 29,90 34,14 5104 11,28 S85 23,44 31,71 35,29 6423 14,20 Revue Internationale de la Recherche Scientifique (Revue-IRS) - ISSN : 2958-8413 http://www.revue-irs.com 6929 Table 11 : WATER ABSORPTION AND COMPRESSIVE STRENGTH IN MPA AT 28 DAYS Sample Dry mass Wet mass % H 2 O absorption Effort (N) Compression (MPa) S10 14.00 14,44 3,17 5111 11,30 S15 14,53 14,82 2,01 7302 16,14 S20 10,57 10,72 1,45 11251 24,87 S25 10,39 10,81 4,03 10483 23,17 S35 11,26 12,16 8,03 7458 16,49 S50 16,30 18,06 10,82 6605 14,60 S65 17,45 19,54 11,97 4545 10,05 S75 18,60 21,04 13,12 4396 9,72 S80 19,75 22,57 14,27 4098 9,06 S85 20,9 24,12 15,42 3740 8,27 Figure 21: Compressive strength curves at different days. The development of strength of the blended binder (lime-metakalon) depends on the pozzolanic activity of the calcined clays added at different percentage. At 7 days all the samples have a slightly lower compressive strength, not more than 7 MPa. This early low strength is probably due to the early reaction of pozzolanic materials. The mechanical resistances gradually increase at 14 days; it is observed that metakaolin, represented in red in the Figure 21, increases the mechanical strength of lime-metakaolin mixture. But finally at 28 days, when the strength starts to stabilize, the compressive strength highly Revue Internationale de la Recherche Scientifique (Revue-IRS) - ISSN : 2958-8413 http://www.revue-irs.com 6930 increases till its maximal value at 20% of metakaolin substitution. This is due to the precipitation of C-SH phases as a result of the reaction between the silica and the Ca2+ ions and the amount mainly depends on the Si/Al ration of the starting material. High alumina concentration will enhance the uptake of alumina in the C-S-H structure and C-A-S-H will additionally precipitate. The most common C-A-S-H for metakaolin is stratlingite. Although the pozzolanic (metakaolin) addition increases the mechanical strength of the mixtures from the 14 days of curing as seen on Figure 21, this did not occur anymore when on the 28 days of curing; the metakaolin percentage passes 20%. The compressive strength drastically decreases. A possible explanation for this is that the surplus of metakaolin is not partaking in the lime-metakaolin reaction. In fact, taking into account the Volumic mass of lime (430 kg/m3), of metakaolin (638 kg/m3) and the fact that some of the lime will be used by carbonation and some by pozzolanic reaction, some of the pozzolan will not be involved in pozzolanic reaction due to lack of lime. It will directly lead to the cracking and crumbling of the surplus metakaolin, which reduices the mechanical strength of the paste after some days. 12. Conclusion, Scientific Relevance and Recommendations 12.1 Conclusion We have studied the feasibility of metakaolin and lime as a binder mixture in Civil Engineering construction projects: case of Balengou clay. The hypothesis of this study are that Lime-metakaolin mixture as a binder in Civil Engineering is feasible, that Lime plus metakaolin binder affects the environment lower than normal cement‟ and that it is cheaper than the normal cement and can cover some domains in Civil Engineering projects.‟ The literature review presented the generalities on hydraulic lime and calcined clays as pozzolans, the research methodology presented the materials and the various test to be done and the methodology displayed the presentation and discussion of results. From the investigation, the following conclusion can be drawn: 12.1.1 On the feasibility of lime-metakaolin as a binder mixture  The calcination of clay at 750°C activates its reactivity with lime in a reaction called: pozzalanic reaction. At 20% of metakaolin substitution, that reaction is at its optimum state.  Addition of Hydrated Lime improves the mix plastic properties but reducethe mortar strength designation. Whereas addition of metakaolin reduce the plasticity, Permeability, capillary, porosity and increases the strength of the paste.  at 20% of metakaolin substitution, we obtain a maximum compressive strength of 24.87 MPa at 28 days, a good consistency at 90 % of water content.  The setting duration reduce as we increase the metakaolin. 12.1.2 On the low impact of lime-metakaolin binder on the environment as compare to normal cement. Revue Internationale de la Recherche Scientifique (Revue-IRS) - ISSN : 2958-8413 http://www.revue-irs.com 6931  The use of lime mortars is a contribution towards sustainability, due to lower temperatures (900°C) used in the production process and lower CO2 emissions; additionally, during the carbonation process, CO2 is absorbed from the atmosphere.  At the optimum percentage of metakaolin for correct pozzalinicity reaction, the carbonation process still occurs as in the pure lime. Because They also have some free lime available for carbonation.  Lime-metakaolin mortar can manage humidity and allow moisture to evaporate, helping to keep building free of damp and create healthier internal environment.  With the respiration of slabs permitted with the perspiring property of lime, capillary effects on walls are reduced.  The humidification of walls through condensation process in the house is reduced. This is because the wall can breathe due to the air permeability property of lime-metakaolin mixture. 12.1.3 On the domains that could be cover by lime-metakaolin mixture in civil engineering  Metakaolin is an adequate pozzolanic addition for lime mortars, providing adequate mechanical and water behaviour characteristics for application in internal Pointing with soft masonry, plastering, tiling, Bedding, Flooring, or chimney flaunching.  Lime-metakaolin is cheaper because it needs less energy consumption for its production  Lime-metakaolin has a good appearance. And so, it can be used for aesthetical and decorative works. For instance, its white color and its plasticity which reduces cracking and spalling on pointing works, could be the advantages for the interior decorations. 12.2 Scientific Relevance The use of greater percentages of pozzolan in a mortar doesn’t necessarily imply improved characteristics. For each particular pozzolanic product there are specific formulations that produce better results for the application that is being considered. 12.3 Recommendations Following the results obtained in this work, the following recommendations are made for a future use of the Balengou Hallosyte clay and a new approach on the utilization of lime.  Lime-metakaolin is viable with good physical properties such as plasticity, high strength, and breathability at 20% of metakaolin.  Use lime-metakaolin binder for internal Pointing with soft masonry, plastering, Bedding, Flooring, rendering. but not for high structural works.  Use Lime-metakaolin only for works where the need for breathability and lower strength is outweighed by the desire for an earlier and harder set such as working on bedding hard masonry, wall copings, chimneys and slate floors.