Peat soil curing agent prepared based on rice hull material and preparation method of peat soil curing agent

Abstract

The invention discloses a peat soil curing agent prepared based on a rice hull material and a preparation method thereof, and belongs to the technical field of soil curing. The peat soil curing agent prepared based on the rice hull material is prepared from the following components in percentage by mass: 30% of ordinary Portland cement, 5-30% of fine rice hull ash, 0-4% of modified rice hull fiber and distilled water which is 0.7 time of the mass of the ordinary Portland cement, and the particle size distribution in the fine rice hull ash is controlled to be d50lt; 29mu m, d90lt; and 50 [mu] m. Compared with pure cement, the strength of the cured peat soil is obviously improved after the ground rice hull ash and the modified fibers are added. When the mixing amount of the cement is 30% and the mixing amount of the rice hull ash is 25%, the pressure reaches 295 kPa, and the strength is improved by 146.66% compared with that of pure cement. On the basis, the strength of the cured peat soil added with 2% of Ca (OH) 2 solution modified rice hull fibers reaches 361.9 kPa.

Description

Technical Field

[0001] The invention discloses a peat soil solidifying agent prepared based on rice husk material and a preparation method thereof, belonging to the technical field of soil solidification. Background Art

[0002] Peat soil brings many challenges in engineering construction due to its low strength, high water content, high organic matter content, significant compressibility and large porosity. For example, in construction projects involving peat soil, common problems include foundation pit instability, uneven foundation settlement and landslides. At present, cement is mainly used as a cementitious material for the reinforcement of peat soil foundations, and admixtures such as kaolin, lime, and fly ash are added as auxiliary reinforcement agents. However, excessive use of these admixtures is inconsistent with the concept of sustainable development. At present, the annual output of solid waste in my country has exceeded 3 billion tons, which is mainly disposed of by landfill and incineration. Both treatment methods have environmental problems. Landfill occupies tight land resources, and incineration produces polluted gases.

[0003] Rice husk is one of the main by-products produced during rice processing. It is an abundant resource, with an annual output of about 40 million tons in my country alone. Rice husk is often regarded as a solid waste. Rice husk ash is the product of high-temperature combustion of rice husk. Because it is rich in silica, it is regarded as a volcanic ash material and is often used as an auxiliary cementitious material to partially replace cement in concrete. The fibers intersect and aggregate with each other in the soil to play a reinforcing role, which can improve the strength of the soil. Since rice husk fiber is low-cost and renewable, using it for soil reinforcement is considered an effective and economical soil improvement technology. Summary of the invention

[0004] In view of the problems and shortcomings of the above-mentioned prior art, the present invention provides a peat soil solidifying agent prepared based on rice husk material and a preparation method thereof. The materials used in the present invention are easily available, which is a resource utilization of solid waste, has no pollution to the environment, and has a simple production process.

[0005] The technical solution of the present invention is:

[0006] A peat soil curing agent prepared based on rice husk material, calculated by the mass percentage of cement-containing peat soil, is mixed with 30% of ordinary Portland cement, 5% to 30% of fine-grained rice husk ash, 0% to 4% of modified rice husk fiber and distilled water 0.7 times the mass of ordinary Portland cement, wherein the particle size distribution of the fine-grained rice husk ash is controlled to be d 50 <29um, d 90 <50um.

[0007] The specific surface area of ​​the ordinary Portland cement (PO42.5) is 340m2 / kg, and the oxide components mainly include CaO, SiO2, Fe2O3 and Al2O3, accounting for more than 86% of the total mass, and the Ca / Si ratio is 2.6.

[0008] The preparation method of the fine-grained rice husk ash is as follows:

[0009] (1) The rice husk fiber is placed in a muffle furnace and burned at a high temperature of 550°C to 650°C for 2 hours to generate rice husk ash;

[0010] (2) The rice husk ash was placed in a planetary ball mill at 600 r / min and ground for 5 to 10 min. During the grinding process, a small amount of ethanol was added as a dispersant to prevent the rice husk ash from agglomerating during the grinding process and to improve the uniformity and efficiency of the grinding. After screening, the particle size distribution was d 50 <29um, d 90 Fine rice husk ash <50um, fine rice husk ash specific surface area greater than 2000cm 2 / g.

[0011] The modification method of the modified rice husk fiber is:

[0012] (1) Prepare 2% NaOH solution and saturated Ca(OH)2 solution respectively;

[0013] (2) The rice husk fiber is added to the NaOH solution and the Ca(OH)2 solution respectively, and mixed and stirred for 4 to 5 minutes, and then stirred for 2 to 4 minutes every hour. After soaking for 12 hours, the fiber is taken out, air-dried for 12 hours, and then dried to obtain the modified rice husk fiber.

[0014] The rice husk fiber has a length of 6 mm to 10 mm and a bulk density of 96 to 120 kg / m 3 , surface area 130cm 2 / g. Rice husk fiber is commercially available or conventionally prepared.

[0015] A method for preparing a peat soil solidifying agent based on rice husk material,

[0016] (1) 30% cement, 5% to 30% fine rice husk ash, and 0% to 4% modified rice husk fiber are fully mixed according to the mass percentage of cement-containing carbon soil to obtain a solid phase mixture;

[0017] (2) Add distilled water in an amount of 0.7 times the mass of cement to the solid phase mixture obtained in (1), put it into a JJ-5 cement mortar mixer, set the initial speed of the mixer to 100±5rpm, and perform preliminary stirring for 5 minutes to ensure that the water is fully distributed; then, increase the stirring speed to 200±10rpm, and continue stirring for 5 minutes until a uniform paste is obtained, thereby preparing a peat soil solidifier based on rice husk material.

[0018] The present invention uses rice husk ash for the following reasons: (1) rice husk ash is rich in highly active amorphous SiO2, and the particle size distribution of the fine rice husk ash after grinding is controlled to be d 50 <29um, d 90 <50um, which optimizes its fineness and increases its specific surface area, allowing it to more quickly come into contact with calcium hydroxide generated by cement hydration to react with volcanic ash (Ca(OH)2+SiO2+H2O→CSH), generating more cementitious substances. (2) The particle size distribution is d 50 <29um, d 90 Rice husk ash particles <50um can fill in between soil particles to increase density. As the amount of rice husk ash increases, the filling effect becomes more significant. (3) Particle size distribution is d 50 <29um, d 90 Rice husk ash <50um also has a certain water absorption capacity and can absorb moisture in the soil, which can achieve the effect of water supply during the volcanic ash reaction. (4) The use of rice husk ash as a solid waste for engineering applications is a green and sustainable measure.

[0019] The reasons for using modified rice husk fiber in the present invention are: (1) The surface of the modified fiber is rougher, which can effectively rub and interlock with cement, rice husk ash and soil particles, thereby improving the bonding force between particles and helping to improve the compressive strength of the material. (2) Rice husk fiber has certain tensile strength and toughness. The fiber is distributed in the solidified soil, which can reduce stress concentration and delay the development of cracks. (3) Peat soil is an acidic environment. Fibers treated with alkali can be more resistant to corrosion and degradation, thereby improving the durability of the fiber. (4) Rice husk fiber is low in cost and abundant. The use of rice husk fiber is a green treatment of waste.

[0020] The beneficial effects of the present invention are:

[0021] (1) Compared with pure cement content, the strength of solidified peat soil increased significantly after adding ground rice husk ash and modified fiber. When the cement content was 30% and the rice husk ash content was 25%, it reached 295 kPa, which was 146.66% higher than the strength of pure cement. On this basis, the strength of solidified peat soil after adding 2% Ca(OH)2 solution modified rice husk fiber reached 361.9 kPa.

[0022] (2) Rice husk is one of the most abundant waste materials in China. Whether it is rice husk fiber or converting rice husk into rice husk ash and then using it in engineering practice, it not only helps to treat solid waste sustainably but also is low-cost.

[0023] (3) The raw materials are easy to obtain and the preparation is simple. It can be used in areas where rice is grown and where peat soil engineering is involved. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily without conflict.

[0025] In the following embodiments, peat soil was taken from a project in Gongjia Village, Guandu District, Kunming City. The underground of this area is a typical peat soil layer. The peat soil was taken from a depth of 10m underground. After testing, the natural moisture content of peat soil was as high as 230%, the liquid limit was 286.15%, the plastic limit was 142.49%, and the density was 1.08g / cm 3 , porosity 4.6, pH value 6.4. The main chemical components are: SiO2 content accounts for 26.38%, Al2O3 accounts for 13.88%, CaO accounts for 9.39%, and Fe2O3 accounts for 5.492%.

[0026] Embodiment 1:

[0027] The peat soil curing agent prepared based on rice husk material comprises, based on the mass percentage of the peat soil containing cement, 30% of ordinary silicate cement, 5% to 30% of fine-grained rice husk ash, 0% of modified rice husk fiber and distilled water of 0.7 times the mass of ordinary silicate cement, wherein the particle size distribution of the fine-grained rice husk ash is controlled to be d 50 <29um, d 90 <50um.

[0028] The specific surface area of ​​ordinary Portland cement (PO42.5) is 340m2 / kg, and the oxide components mainly include CaO, SiO2, Fe2O3 and Al2O3, accounting for more than 86% of the total mass, and the Ca / Si ratio is 2.6.

[0029] The preparation method of fine rice husk ash is as follows:

[0030] (1) The rice husk fiber was placed in a muffle furnace and burned at 550°C for 2 h to generate rice husk ash (the chemical composition content of fine rice husk ash is shown in Table 1);

[0031] Table 1: Chemical composition of fine rice husk ash (wt%)

[0032]

[0033] (2) The rice husk ash was placed in a planetary ball mill at 600 r / min and ground for 5 min. During the grinding process, a small amount of ethanol was added as a dispersant to prevent the rice husk ash from agglomerating during the grinding process and improve the uniformity and efficiency of the grinding. After screening, the particle size distribution was d 50 <29um, d 90 Fine rice husk ash <50um, fine rice husk ash specific surface area greater than 2000cm 2 / g.

[0034] The preparation method of the peat soil solidifying agent prepared based on rice husk material,

[0035] (1) 30% cement, 5% to 30% fine rice husk ash, and 0% modified rice husk fiber are fully mixed according to the mass percentage of cement-containing carbon soil to obtain a solid phase mixture;

[0036] (2) Add distilled water in an amount of 0.7 times the mass of cement to the solid phase mixture obtained in (1), put it into a JJ-5 cement mortar mixer, set the initial speed of the mixer to 100±5rpm, and perform preliminary stirring for 5 minutes to ensure that the water is fully distributed; then, increase the stirring speed to 200±10rpm, and continue stirring for 5 minutes until a uniform paste is obtained, thereby preparing a peat soil solidifier based on rice husk material.

[0037] Comparative Example 1

[0038] Comparative Example 1 uses unground rice husk ash added to cement-solidified peat soil. Comparison with Example 1 shows that the fine-grained rice husk ash used in the present invention has a better reinforcement effect on peat soil.

[0039] Comparative Example 2

[0040] Comparative Example 2 is to grind the particles to a particle size distribution of d 90 The addition of rice husk ash with a particle size of <15 um into cement-solidified peat soil and the comparison with Example 1 show that the fine-grained rice husk ash used in the present invention has a better reinforcement effect on peat soil.

[0041] The peat soil curing agent obtained in Example 1 and Comparative Examples 1 and 2 was added to the peat soil and stirred to mix; the peat soil mixed with the curing agent was filled into a 70.7mm×70.7mm×70.7mm cubic mold three times, and then the cubic test mold was fixed on a vibration table and vibrated for not less than 2 minutes. After vibration, the excess mixture on the top of the test mold was scraped off and immediately covered with plastic wrap to prevent moisture evaporation to ensure that the sample was not damaged or deformed. The mold was demolded after 24 hours.

[0042] All samples were placed in a standard curing room (temperature controlled at 20±2℃, relative humidity 95±2%) for 28 days. The cured samples were tested according to the unconfined compressive strength test method in GB / T 50123-2019; the mass of the cured samples was weighed, the density was calculated, and the moisture content was tested; the samples after compression failure were crushed and sieved through a 0.5mm sieve, and the solution concentration required by JTG 3430-2020 was made for pH testing.

[0043] Table 2: Unconfined compressive strength of stabilized peat soil with rice husk ash as a control

[0044]

[0045] As shown in Table 2, when the cement content is 30%, the optimal content of fine rice husk ash is 25%, and the unconfined compressive strength is 295.5 kPa, which is 146.1% higher than that of pure cement soil. 50 <29um, d 90 Fine-grained rice husk ash <50um can significantly improve the strength of peat soil better than unground or over-fine rice husk ash.

[0046] Example 2

[0047] The peat soil curing agent prepared based on rice husk material comprises, based on the mass percentage of the peat soil containing cement, 30% of ordinary silicate cement, 25% of fine rice husk ash, 0.5-4% of modified rice husk fiber and 0.7 times of distilled water by mass of ordinary silicate cement, wherein the particle size distribution of the fine rice husk ash is controlled to be d 50 <29um, d 90 <50um.

[0048] The specific surface area of ​​ordinary Portland cement (PO42.5) is 340m2 / kg, and the oxide components mainly include CaO, SiO2, Fe2O3 and Al2O3, accounting for more than 86% of the total mass, and the Ca / Si ratio is 2.6.

[0049] The preparation method of fine rice husk ash is as follows:

[0050] (1) The rice husk fiber was placed in a muffle furnace and burned at 550°C for 2 h to generate rice husk ash (the chemical composition content of fine rice husk ash is shown in Table 1);

[0051] Table 1: Chemical composition of fine rice husk ash (wt%)

[0052]

[0053] (2) The rice husk ash was placed in a planetary ball mill at 600 r / min and ground for 5 min. During the grinding process, a small amount of ethanol was added as a dispersant to prevent the rice husk ash from agglomerating during the grinding process and improve the uniformity and efficiency of the grinding. After screening, the particle size distribution was d 50 <29um, d 90 Fine rice husk ash <50um, fine rice husk ash specific surface area greater than 2000cm 2 / g.

[0054] The modification method of the modified rice husk fiber is as follows:

[0055] (1) Prepare a 2% NaOH solution;

[0056] (2) Rice husk fiber (rice husk fiber length 6mm ~ 10mm, bulk density 96 ~ 120kg / m 3 , surface area 130cm 2 / g) were added to the NaOH solution and stirred for 5 minutes, followed by stirring for 2 minutes every hour, and then taken out after soaking for 12 hours, air-dried for 12 hours and then dried to obtain the modified rice husk fiber. The modified rice husk fiber was named RHF2.

[0057] The preparation method of the peat soil solidifying agent prepared based on rice husk material,

[0058] (1) 30% cement, 25% fine rice husk ash, and 0.5-4% modified rice husk fiber are fully mixed according to the mass percentage of cement-containing charcoal soil to obtain a solid phase mixture;

[0059] (2) Add distilled water in an amount of 0.7 times the mass of cement to the solid phase mixture obtained in (1), put it into a JJ-5 cement mortar mixer, set the initial speed of the mixer to 100±5rpm, and perform preliminary stirring for 5 minutes to ensure that the water is fully distributed; then, increase the stirring speed to 200±10rpm, and continue stirring for 5 minutes until a uniform paste is obtained, thereby preparing a peat soil solidifier based on rice husk material.

[0060] Example 3

[0061] The peat soil curing agent prepared based on rice husk material comprises, based on the mass percentage of the peat soil containing cement, 30% of ordinary silicate cement, 25% of fine rice husk ash, 0.5-4% of modified rice husk fiber and 0.7 times of distilled water by mass of ordinary silicate cement, wherein the particle size distribution of the fine rice husk ash is controlled to be d 50 <29um, d 90 <50um.

[0062] The specific surface area of ​​ordinary Portland cement (PO42.5) is 340m2 / kg, and the oxide components mainly include CaO, SiO2, Fe2O3 and Al2O3, accounting for more than 86% of the total mass, and the Ca / Si ratio is 2.6.

[0063] The preparation method of fine rice husk ash is as follows:

[0064] (1) The rice husk fiber was placed in a muffle furnace and burned at 550°C for 2 h to generate rice husk ash (the chemical composition content of fine rice husk ash is shown in Table 1);

[0065] Table 1: Chemical composition of fine rice husk ash (wt%)

[0066]

[0067] (2) The rice husk ash was placed in a planetary ball mill at 600 r / min and ground for 5 min. During the grinding process, a small amount of ethanol was added as a dispersant to prevent the rice husk ash from agglomerating during the grinding process and improve the uniformity and efficiency of the grinding. After screening, the particle size distribution was d 50 <29um, d 90 Fine rice husk ash <50um, fine rice husk ash specific surface area greater than 2000cm 2 / g.

[0068] The modification method of the modified rice husk fiber is as follows:

[0069] (1) Prepare saturated Ca(OH)2 solution;

[0070] (2) Rice husk fiber (rice husk fiber length 6mm ~ 10mm, bulk density 96 ~ 120kg / m 3 , surface area 130cm 2 / g) were added to the Ca(OH)2 solution and stirred for 5 minutes, followed by stirring for 2 minutes every hour, and then taken out after soaking for 12 hours, air-dried for 12 hours and then dried to obtain the modified rice husk fiber. The modified rice husk fiber was named RHF2.

[0071] The preparation method of the peat soil solidifying agent prepared based on rice husk material,

[0072] (1) 30% cement, 25% fine rice husk ash, and 0.5-4% modified rice husk fiber are fully mixed according to the mass percentage of cement-containing charcoal soil to obtain a solid phase mixture;

[0073] (2) Add distilled water in an amount of 0.7 times the mass of cement to the solid phase mixture obtained in (1), put it into a JJ-5 cement mortar mixer, set the initial speed of the mixer to 100±5rpm, and perform preliminary stirring for 5 minutes to ensure that the water is fully distributed; then, increase the stirring speed to 200±10rpm, and continue stirring for 5 minutes until a uniform paste is obtained, thereby preparing a peat soil solidifier based on rice husk material.

[0074] The specific parameters of each embodiment and comparative examples 1 to 3 are shown in Table 3.

[0075] Table 3: Proportions of rice husk ash and rice husk fiber for reinforcement of peat soil.

[0076]

[0077]

[0078] Table 4: Unconfined compressive strength of peat soil stabilized by different modified rice husk fibers

[0079]

[0080] Table 4 shows that when the dosage of the three types of fibers increases from 0.5% to 2%, the strength of the solidified peat soil shows an upward trend. Among them, RHF3 modified by calcium hydroxide solution shows the highest strength, reaching 361.9 kPa; RHF2 treated with sodium hydroxide is second, reaching 342.8 kPa; and the untreated RHF1 has the weakest strength, which is 317 kPa. After that, the strength begins to decrease with the increase of fiber dosage. The Ca2+ ions in Ca(OH)2 can cross-link with functional groups such as carboxyl and hydroxyl groups in the fiber, thereby enhancing the toughness and elastic modulus of the fiber. The strong alkalinity of NaOH can effectively remove the wax layer and other organic impurities on the surface of rice husk fiber, improve the surface roughness of the fiber, and help to form a stronger mechanical intercalation between the fiber and the peat soil matrix. In contrast, the mild alkaline environment provided by Ca(OH)2 is more effective in maintaining the integrity of the fiber structure, mechanical properties, and improving the interfacial bonding. Therefore, rice husk fibers modified by Ca(OH)2 immersion perform better than NaOH-treated fibers in improving the strength of peat soil. However, as the number of fibers increases excessively, too many fibers aggregate and contact each other in the soil, and there is no friction between the fibers and they will slide against each other, so too many fibers are not conducive to the growth of strength.

[0081] Table 5: Moisture content of the samples of Example 1 after curing for 28 days (%)

[0082]

[0083] Table 6: Moisture content of samples of Examples 2 to 3 and Comparative Example 3 after curing for 28 days

[0084]

[0085] Table 7: Density of the sample of Example 1 after curing for 28 days (g / cm 3 )

[0086]

[0087] Table 8: Density (g / cm2) of the samples of Examples 2 to 3 and Comparative Example 3 after curing for 28 days 3 )

[0088]

[0089] It can be seen from Tables 5 and 7 that with the increase in the amount of fine rice husk ash, the moisture content of the solidified peat soil decreases and the dry density increases. This is because the fine rice husk ash promotes the volcanic ash reaction and effectively fills the pores between soil particles. It can be seen from Tables 6 and 8 that the modified rice husk fiber has a small effect on improving the density of the sample and has a limited effect on the moisture content.

[0090] Table 9: pH value of the sample of Example 1 after curing for 28 days

[0091]

[0092] Table 10: pH values ​​of samples of Examples 2-3 and Comparative Example 3 after curing for 28 days

[0093]

[0094] Table 9 shows that the pH value of the solidified peat soil increased under the action of fine-grained rice husk ash. Rice husk ash itself is usually not alkaline, but when it works with cement, the silica in the rice husk ash reacts with calcium hydroxide to produce more cementitious materials and release more OH- ions, thereby further increasing the pH value of the solidified peat soil. Rice husk fiber itself has little effect on the pH value because its main component is organic fiber, which is not alkaline or acidic. However, since RHF2 and RHF3 are modified in alkaline solution, the fibers may contain a small amount of alkaline substances. Therefore, Table 10 shows that the addition of modified rice husk fiber has a slight effect on the overall pH value.

[0095] In Example 3, the addition of 30% cement, 25% fine-grained rice husk ash, and 2% rice husk fiber modified with Ca(OH)2 solution is the optimal peat soil reinforcement solution after comprehensively considering the strength, moisture content, density and pH value of the solidified soil.

[0096] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A peat soil solidifier prepared based on rice husk material, characterized in that: According to the mass percentage of cement-containing carbon soil, the ordinary silicate cement with a dosage of 30%, the fine-grained rice husk ash with a dosage of 5% to 30%, the modified rice husk fiber with a dosage of 0% to 4% and the distilled water with a mass of 0.7 times of the ordinary silicate cement, wherein the particle size distribution of the fine-grained rice husk ash is controlled to be d 50 <29um, d 90 <50um.

2. The peat soil solidifying agent prepared based on rice husk material according to claim 1, characterized in that: The specific surface area of ​​the ordinary Portland cement is 340m2 / kg, the oxide components mainly include CaO, SiO2, Fe2O3 and Al2O3, accounting for more than 86% of the total mass, and the Ca / Si ratio is 2.

6.

3. The peat soil solidifying agent prepared based on rice husk material according to claim 1, characterized in that: The preparation method of the fine-grained rice husk ash is as follows: (1) The rice husk fiber is placed in a muffle furnace and burned at a high temperature of 550°C to 650°C for 2 hours to generate rice husk ash; (2) The rice husk ash was placed in a planetary ball mill at 600 r / min and ground for 5 to 10 min. During the grinding process, ethanol was added as a dispersant to improve the uniformity and efficiency of the grinding. After screening, the particle size distribution was d 50 <29um, d 90 Fine rice husk ash <50um, fine rice husk ash specific surface area greater than 2000cm 2 / g.

4. The peat soil solidifying agent prepared based on rice husk material according to claim 1, characterized in that: The modification method of the modified rice husk fiber is: (1) Prepare 2% NaOH solution and saturated Ca(OH)2 solution respectively; (2) The rice husk fiber is added to the NaOH solution and the Ca(OH)2 solution respectively, and mixed and stirred for 4 to 5 minutes, and then stirred for 2 to 4 minutes every hour. After soaking for 12 hours, the fiber is taken out, air-dried for 12 hours, and then dried to obtain the modified rice husk fiber.

5. The peat soil solidifying agent prepared based on rice husk material according to claim 4, characterized in that: The rice husk fiber has a length of 6 mm to 10 mm and a bulk density of 96 to 120 kg / m 3 , surface area 130cm 2 / g.

6. A method for preparing a peat soil solidifying agent based on rice husk material according to any one of claims 1 to 5, characterized in that: (1) fully mixing 30% cement, 5% to 30% fine rice husk ash, and 0% to 4% modified rice husk fiber according to the mass percentage of cement-containing carbon soil to obtain a solid phase mixture; (2) Add distilled water in an amount 0.7 times the mass of cement to the solid phase mixture obtained in (1), set the initial stirring speed to 100±5rpm, and perform preliminary stirring for 5 minutes; then, increase the stirring speed to 200±10rpm, and continue stirring for 5 minutes until a uniform paste is obtained, thereby preparing a peat soil solidifier based on rice husk material.

Images