Laterite-based building material

Abstract

The present invention relates to a binder composition for building materials comprising laterite, sand, lime, rice husk ash, an alkaline silicate solution, and bamboo fibers. Figure for the abstract: Fig. 1.

Description

Title of the invention: Laterite-based building material technical field

[0001] This disclosure relates to the field of construction. More specifically, this disclosure concerns a laterite-based construction 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 that forms through the weathering of rocks in tropical climates. In a broader sense, 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 countries. 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] In parallel, soil stability is an important criterion in the field of construction. 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 construction 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 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] [Fig. 1] schematically represents a process for producing soda from laterite and NaNO3.

[0009] [Fig.2] schematically represents a process for the production of NaNO3 from HNO3 and Ca(OH)2.

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

[0011] [Fig.4] schematically represents the method of calculating the plasticity index of a binder conforming to the invention. Description of the invention

[0012] In the context of the present invention, the expression "between A and B" includes the values ​​A and B.

[0013] In the context of the present invention, "ambient temperature" means a temperature of approximately 20 ± 5°C.

[0014] The different embodiments described below can be combined.

[0015] According to one aspect, the present invention relates to a binder composition for a construction material 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; - about 3% to about 35% of an alkaline silicate solution with a molar ratio SiO2 / M2O (M = Na or K) in the range of about 1 to about 3; and - 0% to about 1% of bamboo fibers; - water qsp 100%; the above percentages being mass percentages expressed in relation to the total mass of the binder composition; the binder composition having a liquid / solid mass ratio (L / S) within the range of about 20 to about 75.

[0016] 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; - about 5 to about 30% of an alkaline silicate solution with a molar ratio SiO2 / M2 O (M = Na or K) in the range of about 1 to about 3; and - about 0.1 to about 0.6% of bamboo fibers; - water qsp 100%.

[0017] 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.

[0018] 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 sieve with an opening of 1 mm, and storage for example in a propylene bag.

[0019] The binder composition comprises > 0% to about 12% of rice hull ash, advantageously about 1% to about 10%, about 2% to about 9% or about 3% to about 7% of rice hull ash.

[0020] 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 qm sieve.

[0021] The binder composition may comprise up to about 1% bamboo fibers, advantageously about 0.1% to about 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.

[0022] In certain embodiments, the bamboo fibers are obtained by extraction from cut bamboo immersed in a NaOH or KOH solution, with a concentration between approximately 0.25 and approximately 0.50 mol / L, preferably equal to approximately 0.375 mol / L.

[0023] In some embodiments, the bamboo fibers have a length between about 5 mm and about 40 mm.

[0024] The binder composition comprises about 8% to about 15% sand, advantageously about 10% to about 15%, or about 10% to about 12% sand.

[0025] The binder composition comprises > 0% to about 8% of lime, advantageously 0.1% to about 7%, about 0.5% to about 6%, or about 0.5% to about 5% of lime.

[0026] The binder composition for a building material according to the invention can be prepared by first dry-mixing laterite, sand, lime, rice husk ash, and, when 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 2, and the mixture is thoroughly mixed until a homogeneous blend 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 the 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.

[0027] In some embodiments, sodium or potassium silicate can be prepared by dissolving rice hull ash in a sodium hydroxide or potassium hydroxide solution.

[0028] 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.

[0029] In some embodiments, soda or potash can be produced by an environmentally friendly process via nitrate (NaNO3 or KNO3) directly from laterite, as illustrated in [Fig.1]. 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) → [Na2FeO4 (s) and / or Na2Fe2O4 (s) + NO2 (g)] + kaolin (s) [Na2FeO4 (s) and / or Na2Fe2O4 (s)] + kaolin (s) + H2O → NaOH (1) + 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 (1) + Fe2O3(s) + kaolin (s)

[0030] In certain 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 + 2NaCl------> Na2SO4 (s) + 2NH4C1 Na2SO4 + Ca(NO3)2-------> 2NaNO3 + CaSO4 **** 2HNO3 + Ca(OH)2 — -> Ca(NO3)2 + 2H2O KC1 + Ca(NO3)2-------> KNO3 + CaCl2 it being understood that CaSO4 and CaCl2 are "ecological" products which can therefore be disposed of without harming the environment.

[0031] 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.

[0032] The binder composition according to the invention can be used to prepare building materials of various shapes, for example bricks.

[0033] Another aspect of the invention therefore relates to a construction material obtained from the binder composition described herein. The binder composition is molded or compacted depending 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 plasticity limit of the sample studied according to the formula PI = WL-Wp (see [Fig. 4]).

[0034] Once the binder composition has been molded, for example in the form of 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 strength is 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 about 3 MPa, greater than about 4 MPa, greater than about 5 MPa.

[0035] 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)).

[0036] 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#: KNO3 preparation

[0037] 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 under continuous stirring. After cooling to 5°C, 38 g of KNO3 precipitated and were collected.

[0038] Example 2: preparation of alkaline ferrate or ferrite

[0039] 16.7 g of laterite (equivalent to 5 g of Fe2O3 contained in the laterite) and 15.8 g of KNO3 was mixed and heated for 60 minutes at 650°C. After dissolution in water, potash formed and iron oxide precipitated with kaolinite residues. Analysis of the resulting KOH yielded 95% ferrite and ferrate from fusion. Example 3#: Preparation of bamboo fibers

[0040] Cut bamboo was immersed in a NaOH solution with a concentration of 0.375 mol / L, and the fibers were extracted from this solution.

[0041] Examples 4-10: preparation of a binder composition

[0042] Laterite, sand, lime, rice husk ash, and, where applicable, bamboo fibers were mixed dry. Then, a sodium silicate solution and mixing water were added, and the mixture was kneaded until a homogeneous blend was obtained. The proportions of the different components of the mixture, expressed as percentages by mass, are shown in Table 1.

[0043] [Tables 1] Example Laterite (%) Sand (%) Lime (%) CBR (%) Sodium silicate (%) Bamboo fibers (%) Water (%) 4 50.0 10.0 5.0 6.0 17.0 0.0 12.0 5 42.0 10.0 5.0 10.0 20.0 0.0 13.0 6 38.0 10.0 5.0 10.0 25.0 0.0 12.0 7 32.8 10.0 5.0 10.0 30.0 0.2 12.0 8 32.6 10.0 5.0 10.0 30.0 0.4* 12.0 9 32.6 10.0 5.0 10.0 30.0 0.4** 12.0 10 32.6 10.0 5.0 10.0 30.0 q 4*** 12.0 CBR = rice hull ash § molar ratio SiO2 / Na2O = 2 Fiber length = 20 mm (*) / 14 mm (**) / 22 mm (***)

[0044] Example 11: Preparation and characterization of bricks

[0045] The homogeneous mixture obtained in Examples 4 to 10 was placed in a parallelepiped mold 16 cm long, 4 cm wide, and 4 cm high. Each sample was then compacted manually (using a 1 kg hammer (30 blows)). Each compacted sample was left to air dry for approximately 24 hours, after which the resulting brick was 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.

[0046] [Tables2] Example Rc (MPa) dry state Rc (MPa) wet state 4(scale 8) 4.52 4.20 5(scale 10) 4.18 3.28 6(scale 19) 10.65 8.47 7 (scale 25) 7.42 6.56 8 (scale 27) 9.55 6.32 9(scale 33) 5.22 4.64 10 (scale 36) 9.20 6.28

Claims

Demands

1. Construction material binder composition comprising: - 30% to 85% laterite; - 8% to 15% sand; - > 0% to 8% lime; - > 0% to 12% rice husk ash; - 3% to 35% of an alkaline silicate solution with a molar ratio SiO2 / M2O (M = Na or K) in the range of 1 to 3; and - 0 to 1% bamboo fibers; - water qsp 100%; the above percentages being mass percentages expressed in relation to the total mass of the binder composition; the binder composition having a liquid / solid mass ratio (L / S) in the range of 20 to 75.

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 molar ratio SiO2 / M2O (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 any one of the preceding claims, having a liquid / solid mass ratio (L / S) in the range of 20 to 70, 20 to 65, 20 to 60, 20 to 55, 20 to 50, 20 to 45, 20 to 40 or 20 to 35.

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

5. A process according to claim 4, wherein rice husk ash is obtained by incinerating rice husk at a temperature between 600°C and 700°C; grinding of the resulting ashes; and sieving of the ground ashes.

6. A process according to claim 4 or claim 5, 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.

7. Process according to claim 6, wherein NaOH is obtained by reaction of laterite with NaNO3, followed by treatment of the reaction product with H2O.

8. Process according to claim 7, wherein NaNO3 is obtained by (i) reaction of HNO3 with Ca(OH)2 to form Ca(NO3)2, (ii) separately reaction of (NH4)2SO4 with NaCl to form Na2SO4, and then (iii) reaction of the products obtained in (i) and (ii).

9. A process according to claim 6, wherein KOH is obtained by reaction of laterite with KNO3, followed by treatment of the reaction product with H2O.

10. A process according to claim 9, wherein KNO3 is obtained by reacting HNO3 with Ca(OH)2 to form Ca(NO3)2, and then reacting Ca(NO3)2 with KC1.

11. Construction material obtained from the binder composition according to any one of claims 1 to 3.

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