Laterite-based construction material

Abstract

The present invention relates to a binder composition for a construction material comprising laterite, sand, lime, rice husk ash, an alkaline silicate solution and bamboo fibres.

Description

Laterite-based building material Technical Field

[0001] This disclosure relates to the construction industry. More specifically, this disclosure concerns a laterite-based building material. This material enables the manufacture of building components with a low environmental footprint. State of the art

[0002] Laterite is a red or brown rock formed by the weathering of rocks in tropical climates. More broadly, it refers to all materials, loose or hardened, rich in iron or aluminum hydroxides, that constitute soils, surface horizons, and deep horizons of weathering profiles. This natural resource is abundant in tropical countries and offers a valuable alternative to overcome shortages of building materials or excessively high prices in these regions. However, the poor mechanical properties of materials made from this resource limit its use to structures subject to minimal mechanical stress and little or no exposure to water.

[0003] Simultaneously, soil stability is an important criterion in the construction field. Soil stabilization is the process of improving the physical properties of soil in order to enhance its strength, durability, etc. Conventional methods used for soil stabilization include cement stabilization, lime stabilization, bitumen stabilization, and chemical stabilization. A study published in 2016 examined the feasibility of soil stabilization using rice husk ash and coconut fiber (International Journal of Engineering Research & Technology 2017, 6(4), 552-556). Another study, published in 2018, demonstrated the potential of bamboo fibers as a soil stabilization material for volcanic soil from the Kanto region of Japan (International Journal of Environmental and Rural Development 2018, 9(1), 156-161).

[0004] Today, there is a need, particularly in developing countries, for construction materials that can be obtained from local resources and whose properties, especially mechanical properties, are comparable to those of conventional materials. It is with this in mind that the present invention was developed. Summary of the invention

[0005] According to one aspect, the present invention relates to a binder composition for building material comprising: laterite, sand, lime, rice hull ash, an alkaline silicate solution, bamboo fibers and water.

[0006] According to one aspect, the present invention relates to a method for preparing the above-mentioned binder composition.

[0007] According to one aspect, the present invention relates to a construction material obtained from the above binder composition. Description of the figures

[0008] Figure 1 schematically represents a process for producing soda from laterite and NaNO3.

[0009] Figure 2 schematically represents a process for producing NaNO3 from HNO3 and Ca(OH)2.

[0010] Figure 3 schematically represents a process for the production of KNO3 from HNO3 and Ca(OH)2.

[0011] Figure 4 schematically represents the method of calculating the plasticity index of a binder according to the invention.

[0012] Figure 5 represents the conductivity and pH of binders according to the invention. Description of the invention

[0013] In the context of the present invention, the expression "between A and B" includes the values ​​A and B.

[0014] In the context of the present invention, "ambient temperature" means a temperature of approximately 20 ± 5°C.

[0015] The different embodiments described below can be combined.

[0016] According to one aspect, the present invention relates to a binder composition for construction materials comprising: - approximately 30% to approximately 85% laterite; - approximately 8% to approximately 15% sand; - > 0% to approximately 8% lime; - > 0% to approximately 12% rice hull ash; - approximately 3% to approximately 35% of an alkaline silicate solution with a SiO2 / M2O molar ratio (M = Na or K) in the range of approximately 1 to approximately 3; and - 0% to approximately 1% bamboo fibers; - water qsp 100%; the percentages above are mass percentages expressed in relation to the total mass of the binder composition.

[0017] In certain embodiments, the binder composition according to the invention comprises (percentages expressed by mass relative to the total mass of the binder composition): - approximately 33% to approximately 73% laterite; - approximately 10% to approximately 12% sand; - approximately 0.5% to approximately 5% lime; - about 1% to about 10% rice hull ash; - approximately 5 to approximately 30% of an alkaline silicate solution with a SiO2 / M2O molar ratio (M = Na or K) in the range of approximately 1 to approximately 3; and - approximately 0.1 to approximately 0.6% bamboo fibers; - water qsp 100%.

[0018] The binder composition comprises about 30% to about 85% laterite, advantageously about 33% to about 73%, about 35% to about 70%, or about 45% to about 65% laterite.

[0019] In some embodiments, the laterite used in the context of the invention is prepared by extraction of laterite present in the soil, drying (advantageously, at room temperature), sieving advantageously with a 1 mm opening sieve, and storage for example in a propylene bag.

[0020] The binder composition comprises > 0% to about 12% rice hull ash, advantageously about 1% to about 10%, about 2% to about 9% or about 3% to about 7% rice hull ash.

[0021] In some embodiments, rice husk ash is obtained by incinerating rice husk at a temperature advantageously between about 600°C and about 700°C, preferably at a temperature of about 650°C; grinding the ash obtained; and sieving the ground ash, advantageously with a 400 µm sieve.

[0022] The binder composition may include up to approximately 1% bamboo fibers, advantageously from approximately 0.1% to approximately 0.6% bamboo fibers. Within the scope of the present invention, the source of bamboo is not limited; therefore, it is possible to use species originating from tropical, subtropical, or temperate regions.

[0023] In certain embodiments, bamboo fibers are obtained by extraction from cut bamboo immersed in a NaOH or KOH solution, with a concentration between about 0.25 and about 0.50 mol / L, preferably about 0.375 mol / L.

[0024] In some embodiments, the bamboo fibers have a length of between about 5 mm and about 40 mm, preferably between about 10 mm and about 30 mm, for example between about 10 mm and 25 mm.

[0025] The binder composition comprises approximately 8% to approximately 15% sand, advantageously approximately 10% to approximately 15%, or even approximately 10% to approximately 12% sand.

[0026] The binder composition includes > 0% to about 8% lime, advantageously 0.1% to about 7%, about 0.5% to about 6%, or about 0.5% to about 5% lime.

[0027] The binder composition for building materials according to the invention can be prepared by first dry-mixing laterite, sand, lime, rice husk ash, and, where present, bamboo fibers. Then, water is added to the mixture thus obtained, followed by an alkaline silicate solution with a molar ratio of SiO2 / M2O (M = Na or K) between approximately 1 and approximately 3, preferably between approximately 1.5 and approximately 3, or between approximately 1.5 and approximately 2.5, or between approximately 1 and approximately 2, or equal to 2, and the whole is mixed until a homogeneous mixture is obtained.It is important, as far as possible, to maintain the aforementioned molar ratio, as it has been observed that a molar ratio below 1 results in a detergent / corrosive mixture, and a molar ratio above 3 leads to an excess of active silica (from rice husk ash) which does not contribute to the binder's properties. In some embodiments, the mass of water added, also called mixing water, is between approximately 5% and approximately 15% of the total dry mass.

[0028] In some embodiments, sodium or potassium silicate can be prepared by dissolving rice hull ash in a soda or potash solution.

[0029] In some embodiments, the binder composition according to the invention has a liquid / solid mass ratio (L / S) in the range of about 20 to about 75, advantageously about 20 to about 70, for example about 20 to about 65, about 20 to about 60, about 20 to about 55, about 20 to about 50, about 20 to about 45, about 20 to about 40, or about 20 to about 35.

[0030] In certain embodiments, the binder composition according to the invention has a liquid / solid mass ratio (L / S) in the range of approximately 0.20 to approximately 0.75, advantageously from approximately 0.20 to approximately 0.70, for example from approximately 0.20 to approximately 0.65, from approximately 0.20 to approximately 0.60, from approximately 0.20 to approximately 0.55, from approximately 0.20 to approximately 0.50, from approximately 0.20 to approximately 0.45, from approximately 0.20 to approximately 0.40, or from approximately 0.20 to approximately 0.35. In certain embodiments, the binder composition according to the invention has a liquid / solid mass ratio (L / S) in the range of about 0.15 to about 0.35.

[0031] In some embodiments, sodium hydroxide or potassium hydroxide can be produced by an environmentally friendly process via nitrate (NaNO3 or KNO3) directly from laterite, as illustrated in Figure 1. The laterite, supplemented with NaNO3 or KNO3, is heated to a temperature between approximately 400°C and approximately 800°C, preferably between approximately 500°C and 650°C, to generate alkali ferrite or ferrate, which is then dissolved in water to give NaOH or KOH according to the reactions: Laterite (s) + NaNO3(s) — > [NazFeC (s) and / or NazFezC^ (s) + NO2 (g)] + kaolin (s) [NazFeC (s) and / or NazFezC^ (s)] + kaolin (s) + H2O -> NaOH (I) + Fe2O3 (s) + kaolin (s) **** Laterite (s) + KNO3 (s) — -> [K2FeO4(s) and / or K2Fe2O4(s) + NO2(g)] + kaolin (s) [K2FeO4(s) and / or K2Fe2O4(s)] + kaolin (s) + H2O - > KOH (I) + Fe2Û3(s) + kaolin (s)

[0032] In some embodiments, as illustrated in Figures 2 and 3, the nitrous oxide generated during the production of sodium hydroxide or potassium hydroxide can be used to obtain nitric acid HNO3 according to the reaction: NO2 + H2O ----> HNO3 + NO, Nitric acid, which in turn can be transformed into NaNO3 or KNO3 according to the reactions: 2HNO3 + Ca(OH)2- → Ca(NO3)2 + 2H2O (NH4)2SO4+ 2NaCI - > Na2SO4(s) + 2NH4CI Na2SO4+ Ca(NO3)2- > 2NaNO3+ CaSO4 **** 2HNO3 + Ca(OH)2- — > Ca(NO3)2+ 2H2O KCI + Ca(NO3)2- > KNO3 + CaCI2 it being understood that CaSO4 and CaCl2 are "ecological" products which can therefore be disposed of without harming the environment.

[0033] It is therefore possible, within the scope of the present invention, to use raw materials available in the country of operation and / or to prepare and / or recycle the various ingredients of the binder composition. This makes it possible to reduce operating costs while having a positive impact on the carbon footprint of the manufactured construction materials.

[0034] The binder composition according to the invention can be used to prepare building materials of various shapes, for example bricks.

[0035] Another aspect of the invention relates to a construction material obtained from the binder composition described herein. The binder composition is molded or compacted. based on the plasticity index (PI) of the mixture. The plasticity index depends on the amount of clay present in the laterite and is determined by calculating the difference between the liquid limit and the plastic limit of the sample studied, according to formula I P = W L - W P (see figure 4).

[0036] Once the binder composition is molded, for example into bricks, it is allowed to set by air drying, for example for approximately 24 hours. The bricks are then removed from the mold and left to air dry for 14 days, after which their compressive and tensile strengths are determined (in accordance with Standard XP P-13901 (March 2022)). The results obtained with a representative sample of bricks show a compressive and tensile strength greater than approximately 2 MPa, for example greater than approximately 3 MPa, greater than approximately 4 MPa, greater than approximately 5 MPa.

[0037] After 14 days of drying, another part of the bricks is kept in water for 24 h to determine their mechanical resistance to immersion (wet state) (in accordance with standard XP P 13-901 (March 2022)).

[0038] The invention will be better understood with the aid of the following examples, given purely for illustrative purposes. In these examples, the compressive strength (Rc) measurements were carried out as indicated above. EXAMPLES Example 1: Preparation of KNO3

[0039] 65.6 g of a 50% Ca(NO3)2 solution were heated to 70°C. 30.0 g of KCl were added to the hot Ca(NO3)2 solution while stirring continuously. After cooling to 5°C, 38 g of KNO3 precipitated and were collected. Example 2: Preparation of alkaline ferrate or ferrite

[0040] 16.7 g of laterite (equivalent to 5 g of Fe₂O₃ contained in the laterite) and 15.8 g of KNO₃ were mixed and heated for 60 minutes at 650°C. After dissolution in water, potassium hydroxide (KOH) formed, and iron oxide precipitated with kaolinite residues. Analysis of the resulting KOH yielded 95% of the resulting ferrite and ferrate fusion. Example 3: Preparation of bamboo fibers

[0041] Cut bamboo was immersed in a NaOH solution with a concentration of 0.375 mol / L, and the fibers were extracted from this solution. Examples 4-10: preparation of a binder composition

[0042] Laterite, sand, lime, rice husk ash, and, where appropriate, bamboo fibers were mixed together dry. Then, a sodium silicate solution and mixing water were added, and the mixture was kneaded until homogeneous. The proportions of the different components of the mixture, expressed as percentages by mass, are given in Table 1. Table 1 CBR = rice hull ash § SiO2 / Na2O molar ratio = 2 (solids content = 38%) Fiber length = 20 mm (*) / 14 mm (**) / 22 mm (***) Example 11: Preparation and characterization of bricks

[0043] The homogeneous mixture obtained in Examples 4 to 10 was placed in a rectangular mold measuring 16 cm long, 4 cm wide, and 4 cm high. Each sample was then compacted manually (using a 1 kg hammer, with 30 blows). Each compacted sample was left to air dry for approximately 24 hours. The resulting brick was then removed from the mold and left to air dry for 14 days. The compressive strength (Rc) at 14 days was measured. The resulting bricks were then placed in water for 24 hours to determine their mechanical resistance to immersion (wet state). The results are shown in Table 2. Table 2 Examples 12-21: Conductivity and pH of binder compositions

[0043] Different binder compositions were prepared (see Table 3) according to the procedure described for Examples 4-10, and their conductivity and pH were measured according to the protocol below: - dehydration of the composition; - weighing of 5 mg of dehydrated composition; - solubilization of the dehydrated composition in 100 ml of distilled water; - the solution is left to rest for 24 hours; - filtration of the solution through a 0.45 pm filter membrane; - measurement of the conductivity and pH of the filtrate obtained. The results are presented in Table 4 and Figure 5. Table 3 § SiO2 / Na2O molar ratio = 2 (solids content = 38%) * fiber length = 18 mm ** fiber length = 20 mm *** fiber length = 22 mm Table 4

Claims

Demands 1. Binder composition for construction materials comprising: - 30% to 85% laterite; - 8% to 15% sand; - > 0% to 8% lime; - > 0% to 12% rice hull ash; - 3% to 35% of an alkaline silicate solution with a SiO2 / M2O molar ratio (M = Na or K) in the range of 1 to 3; and - 0 to 1% bamboo fibers; - water qsp 100%; the percentages above are mass percentages expressed in relation to the total mass of the binder composition.

2. Binder composition according to claim 1, comprising: - 33% to 73% laterite; - 10% to 12% sand; - > 0% to 5% lime; - > 0% to 10% rice hull ash; - 5% to 30% of an alkaline silicate solution with a SiO2 / M2O molar ratio (M = Na or K) in the range of 1 to 3; and - 0.1% to 0.6% bamboo fibers; - water qsp 100%.

3. Binder composition according to claim 1 or claim 2, comprising from 1% to 10% rice hull ash.

4. Binder composition according to any one of claims 1 to 3, comprising from 0.1% to 0.6% bamboo fibers.

5. Binder composition according to any one of claims 1 to 4, wherein the bamboo fibers have a length between 5 mm and 40 mm.

6. Binder composition according to any one of claims 1 to 4, wherein the alkaline silicate solution has a SiO2 / M2O molar ratio (M = Na or K) between 1.5 and 3, preferably between 1.5 and 2.

5.

7. Binder composition according to any one of claims 1 to 6, having a liquid / solid mass ratio (L / S) in the range of 20 to 75.

8. Binder composition according to any one of claims 1 to 6, having a liquid / solid mass ratio (L / S) in the range of 0.20 to 0.

75.

9. A method for preparing a binder composition as defined in any one of claims 1 to 8, comprising: a) the mixture of laterite, sand, lime, rice husk ash and bamboo fibers; bl) the addition to the mixture thus obtained of water and then of an alkaline silicate solution with a molar ratio SiO2 / M2O (M = Na or K) between 1 and 3; c) Mixing everything together until a homogeneous mixture is obtained.

10. A process according to claim 9, wherein rice husk ash is obtained by incinerating rice husk at a temperature between 600°C and 700°C; grinding the ash obtained; and sieving the ground ash.

11. A process according to claim 9 or claim 10, wherein the bamboo fibers are obtained by extraction from cut bamboo immersed in a NaOH or KOH solution, with a concentration between 0.25 and 0.50 mol / L.

12. A process according to claim 11, wherein NaOH is obtained by reaction of laterite with NaNO3, followed by treatment of the reaction product with H2O.

13. Process according to claim 12, wherein NaNOs is obtained by (i) reaction of HNO3 with Ca(OH)2 to form Ca(NO3)2, (H) separately reaction of (NH4)2SO4 with NaCl to form Na2SO4, then (iii) reaction of the products obtained in (i) and (ii).

14. Process according to claim 11, wherein KOH is obtained by reaction of laterite with KNO3, followed by treatment of the reaction product with H2O.

15. Process according to claim 14, wherein KNO3 is obtained by reaction of HNO3 with Ca(OH)2 to form Ca(NO3)2, then reaction of Ca(NO3)2 with KCl.

16. Construction material obtained from the binder composition according to any one of claims 1 to 8.

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