Manufacturing method a type of green ultra-lightweight concrete block with high compressive strength

Abstract

Abstract This invention develops the manufacturing method a type of high-strength ultra- lightweight concrete block with water resistance, sound and thermal insulation, and anti-flammability properties. To manufacture it, cost-effective, cheap, and environmentally friendly processes and materials were used. Generally, the impact of each of the effective and weight-lightening factors of concrete as well as its manufacturing methods were investigated separately, and then in a general and interrelated manner, it was exactly designed and engineered so that the complexities of the process were properly analyzed and assessed so that a reasonable and simple solution can be offered to produce the green ultra-light concrete block with all the expected desirable characteristics. Finally, the block (CPZ-B1) with a density of 498 kg / m3 and a compressive strength of 2.5 MPa was prepared. This green ultra- light concrete block can compete with autoclaved aerated concrete (AAC) and non- autoclaved aerated concrete in terms of characteristics.

Description

Manufacturing Method a type of Green Ultra-lightweight Concrete Block with High Compressive StrengthTechnical Field

[0001] The technical field of this invention relates to the manufacturing of non- structural (Non-autoclaved) ultra-lightweight concrete block.Background Art

[0002] Mohsen Mohammadi et aL, (2017) conducted experimental research on the properties of non-autoclaved aerated concrete (NAAC) mixtures. Also, they developed a new method to determine the density and air percentage of NAAC mixtures. The results indicated that there is an optimal aluminum percentage of approximately 0.0934% from the point of view of mini slump diameter and compressive strength. As the percentage of aluminum increases compared to the optimal percentage, the diameter and compressive strength decline (the compressive strength declined from 8.5 to 0.5 MPa). Scanning Electron Microscopy (SEM) images of NAAC showed that the air voids were formed as artificial porosity. The results showed that with the increasing amount of aluminum powder, density decreases (density decreased from 1600 to 1020 kg / m3). It was found that as the aluminum percentage increased from 0.0934 to 0.1869, the maximum percentage of air increased. Also, as the water-cement ratio increased, the compressive strength was decreased [1].

[0003] Razia Begum et aL, (2014) investigated the effects of rice husk ash on the non-autoclaved aerated concrete. This paper describes the investigation of using rice husk ash in combination with cement to produce non-autoclaved aerated concrete based on rice husk ash cement. Rice husk ash was used as an aggregate with different replacement ratios, i.e. 0%, 20%, 30%, 40%, 50%. This study aimed to determine the effect of the composition of rice husk ash on the properties of the final product such as compressive strength, water absorption, and density. According to the results, the addition of rice husk ash to the formulation of aerated concrete has reduced the weight of the produced aeratedconcrete for all replacement ratios of rice husk ash and the compressive strength and water absorption of the sample containing rice husk ash were higher than those in ordinary Portland cement aerated concrete. The optimal replacement ratio of ordinary Portland cement with rice husk ash is 30% [2],

[0004] Aurelie Fabien et al., (2019) investigated the effect of several parameters on the non-autoclaved aerated concrete and the use of recycling waste perlite. The used pure perlite or waste is characterized by a volume replacement (30% / 30%) of sand with a lower density that allows the concrete to swell under non-autoclave conditions. All elements were tested to evaluate their effect on thermal insulation properties. The presence of recycled products reduced the mechanical strength but improved the thermal insulation properties. When 2% cement was added, the mechanical resistance increased by 21%. Hence, this study facilitated the development of a repeatable swelling process to produce cellular concretes with a density range of 500 and 600 kg / m3, a compressive strength of about 0.2 MPa, and a thermal conductivity of 0.176 W / m.K [3].

[0005] S. Geetha et al. ,(2023) reported the role of nano-silica in enhancing the properties of aerated concrete. This study aimed to optimize the mix ratio for lightweight concrete through the incorporation of nanomaterial to improve strength and durability. Aluminum powder was used as an aeration agent and foundry sand was used as a substitute for sand. Gypsum up to 5% was used to improve the strength of non-autoclaved aerated concrete. Nano silica was effective up to 7.5%, beyond which there was not much improvement in strength and durability. The produced concrete has a density of 1180 to 1620 kg / m3, which is much lower than ordinary concrete. This is the main advantage of this material, which can reduce the dead load of the structure. The compressive strength and bending strength were 25.2 MPa and 1 .4 MPa, respectively [4],

[0006] 1. Mohsen Mohammadi, Ali Akbar Shirzadi Javid, Mehdi Divandari , “Introducing a Method to Determine Nonautoclaved Aerated Concrete Air content Based on Packing Theory” , Journal of Materials in Civil Engineering, 30(3) (2018) 04017312-1 -04017312-7.

[0007] 2. Razia Begum, Ahsan Habib, Shah Mostafa, “Effects of Rice Husk Ash on the Non Autoclaved Aerated Concrete”, International Journal of Engineering Innovation & Research, 3(1 ) (2014) 116-121.

[0008] 3. Aurelie Fabien, Nassim Sebaibi, Mohamed Boutouil, “Effect of several parameters on non-autoclaved aerated concrete: use of recycling waste perlite”, European Journal of Environmental and Civil Engineering, 26 (2019) 58-75.

[0009] 4. S. Geetha, M. Selvakumar, “Role of nano silica in enhancing the properties of aerated concrete”, Materials Today: Proceedings, In Press, 2023.Technical Problem

[0010] To manufacture low-density high-strength concrete and at the same time get other properties including water resistance, thermal and sound insulation, and anti-flammability, common materials and expensive processes (for example, using an autoclave is not only non-cost effective, but also it is not energyefficient) is used and in addition, the processing and curing of concrete requires a long time. Also, the overutilization of cement in construction results in environmental pollution due to the generation of greenhouse gases and the emission of carbon dioxide gas, and at the same time, the extensive use of cement has made it an unstable material because the raw materials (limestone and clay) used in the cement production are running out over time and it is nonrenewable. Additionally, the production of cement from its raw materials is an energy-intensive process whose energy is supplied by burning fuel in furnaces.

[0011] As a whole, the main objective is to manufacture ultra-light concrete. The ultra-lightweight concrete in this invention is prepared by adding a foaming agent into the concrete (in non-autoclaved condition) and 100% replacement of lightweight aggregates (expanded perlite) with natural aggregates (sand and sand) (it is worth noting that this method preserves natural resources). These methods are economically cost-effective and are more efficient in saving energy consumption. Generally, the impact of each of the effective and weight-lightening factors of concrete as well as its manufacturing methods were investigated separately, and then in a general and interrelated manner, it was exactly designed and engineered so that the complexities of the process were properlyanalyzed and assessed so that a reasonable and simple solution can be offered to produce the green ultra-light concrete block with all the expected desirable characteristics. Ultimately, it should be noted that by selecting the appropriate method and effective and environmentally friendly raw materials, this ultra-light green concrete block can compete with autoclaved aerated concrete (AAC) and non-autoclaved aerated concrete in terms of characteristics. It should also be noted that the design and manufacturing technology of this concrete is entirely new and innovative.Solution to Problem

[0012] In this invention, the goal was to design and manufacture ultra-lightweight concrete block with high strength, water resistance, sound and thermal insulation, and flame retardant. In this regard, an attempt was made to use cost-effective, effective and environmentally friendly methods and materials that made concrete more porous and lighter, and also are environmentally friendly or green (the word "green" has nothing to do with the color of concrete and is attributed to the importance of environment conservation in the manufacturing this concrete) were used. In this regard, azodicarbonamide or Fuku powder was used as a foaming agent.

[0013] When exposed to heat, this material decomposes into several gases and creates many pores, thus, it reduces the weight of concrete and improves its antiflammability properties. Also, it was used thanks to its favorable dispersion, high volume of gas, and its non-toxic, odorless, and non-polluting properties. The concrete produced using Fuku powder because of its good dispersion and high distribution potential, has higher uniform volume and high appearance quality.

[0014] Another material that was used is expanded perlite, which improves the compressive and bearing strength of concrete, reduces the weight of concrete, and also improves sound and thermal insulation, and anti-flammability properties. In this invention, expanded perlite was sieved and granulated and by the appropriate granulation size and model, high compressive strength and low density given its porosity and low weight were obtained. In addition, another material used to reduce density, increase compressive strength, and water resistance and other ions is rice husk ash (made from rice husk, which is themost important agricultural residue). It is a porous pozzolanic material with a particle size of 4-75 pm and a surface area of 50-100 m2 / g, and it acts as a microfiller, pozzolanic material, and viscosity modifying admixture in concrete.

[0015] When a small amount of rice husk ash was added, the compressive strength of concrete was increased and its density was decreased. Another issue is environmental pollution. As mentioned, a higher amount of cement is used in concrete production, and this causes a lot of greenhouse gas emissions, and at the same time, the cement manufacturing process requires high energy consumption, and in addition, using huge amounts of cement reduces natural resources.

[0016] To this end, to obviate these issues, the amount of cement was reduced and hence rice husk ash was added. Also, using the appropriate materials and the engineered concrete mix design, good compressive strength at early ages, and as a result, the blocks were cured in a short time and even though it is ultralightweight and non-autoclaved concrete, it does not disintegrate or become a paste when it is exposed to water, and at the same time it maintains its strength and resistance.

[0017] In this invention, first, the expanded perlite with appropriate sizes was sieved and granulated, which is explained in detail later, then, to prepare a suitable ash with maximum pozzolanic activity and excellent quality, rice husk was added at a suitable temperature inside of the electric furnace, so that it reaches a temperature of 600°C with a slope of 10 °C / min, then it was calcined at a temperature of 600 °C for 6 hours. It is worth noting that at this temperature, enough oxygen is provided for burning, carbon dioxide and disturbing gases are removed, and finally, white and light ash containing very little carbon and a very high amount of amorphous silica is obtained.

[0018] While burning rice husk, enough air should enter the furnace instead of carbon dioxide resulting from the burning of rice husk ash, so that the manner of silica deposition can be set favorably. If the temperature reaches below 600°C, the resulting ash is amorphous crystals, and if the temperature rises above 600°C, it will have a negative effect on the performance of rice husk ash. Another point is that the color of the produced ash will be whiter and brighter as the burningtemperature increases. Of course, if there is not enough air at the time of burning and also, if the burning temperature is low, the color of the ash is darker and contains a high carbon content.

[0019] The obtained rice husk ash should be ground and used in a ground form in the mix design. The reasons behind not using it in unground mode are as follows:

[0020] 1) the coarser particles in rice husk ash have less tendency to disperse uniformly over large areas in the wet mixture than the finer particles, as a result, the distance between the particles in the cement increases and the homogeneity of the mixture decreases.

[0021] 2) The particle size distribution of unground rice husk ash lies in a wide range, and hence, it is necessary to grind them finer to maintain uniformity in size and shape and to ensure consistency in material performance.

[0022] 3) Mixtures containing unground rice husk ash have low compressive strength and this is probably due to insufficient pozzolanic reaction as well as additional porosity created by larger rice husk ash grains.

[0023] Next, various mix designs were created to reduce the density and increase the compressive strength of concrete. In these mix designs, the foaming agent was used as this foaming agent is new in concrete blocks, and due to its behavior, a method was designed. First, two methods were designed to manufacture concrete. In the first method, all materials were mixed on a heater with a mechanical stirrer.

[0024] During heating, azodicarbonamide was decomposed into several gases, and the resulting gases were emitted and created porosity, but then the mixture was poured into a mold for molding and pressed, because of this, the swelling of the specimen was reduced and the concrete lightening was less. In the second method, all the materials were mixed with a mechanical stirrer and then molded, and then placed inside the oven for 10 minutes at a temperature of 170 °C.

[0025] Then, azodicarbonamide was decomposed into several gases and the resulting gases were emitted, and in this way, the volume increased, and because this foaming and swelling occurred uniformly, the weight of concrete block was reduced to a large extent. It should be noted that this process occursunder non-autoclaved conditions. Therefore, in this invention, the second method was used.

[0026] Functional tests and evaluation of characteristics were performed on ultralightweight concrete, including density and compressive strength. Density was calculated based on the mass-to-volume ratio using the formula p=m / V. The density measurement is as follows:

[0027] First, the prepared concrete is weighed, so that the weight is measured with a scale with a precision of 10-4g, then the volume of the mold is taken into account to calculate its volume. In this invention, a cube mold with dimensions of 5 x 5 x 5 cm was used.

[0028] The compressive strength test of prepared concrete was performed according to ASTM C109 standard. The specifications of the device are as follows: precision: 1 Kg, speed: 1 ml / min, load capacity: 3 tons, jack for determining compressive and tensile strength with Abzarazmayesh Arvin brand.Advantageous Effects of Invention

[0029] The advantages of manufacturing ultra-lightweight green concrete compared to similar products include the following:

[0030] 1- The manufacturing process of the concretes prepared in this invention is simple and cost-effective compared to autoclaved aerated lightweight concrete (AAC) and is energy-efficient as it is manufactured in a non-autoclaved manner. The prepared concretes have a very low weight, and this is attributed to the addition of a foaming agent (azodicarbonamide). Under heating, this foaming agent is decomposed into several gases, which can create many porosity, and in this way, these concretes are lighter due to the created porosity, and also they acquire good anti-flammability properties. Hence, by choosing the appropriate method and effective and weight-lightening raw materials, good results can be achieved, which can compete with autoclaved aerated lightweight concrete (AAC).

[0031] 2- The concrete manufactured in this invention (CPZ-B1 ) can compete with non-autoclaved aerated concrete. The concrete manufacturing was designed so that ultra-lightweight and high-strength concrete can be prepared, which is at the same time water-resistant, flame retardant, and sound and thermal-insulated. Ingeneral, in the preparation of concrete, expanded perlite was used instead of sand, and due to its porosity and low density, it facilitates the swelling process and provides excellent sound and thermal insulation as well as excellent antiflammability. Also, by using it in pores of concrete, the weight of the structure is reduced, and as a result, it reduces the density of the specimen, then, by using the appropriate size and granulation, the compressive strength increases. Also, rice husk ash was used as a porous pozzolanic material. Rice husk ash acts as microfiller, pozzolanic material, and viscosity-modifying admixture in concrete. Also, given its remarkable pozzolanic activity and creating chemical reactions with calcium hydroxide, it reduces the porosity and increases the durability and strength of concrete, as well as reducing the permeability of concrete against water, acids, chlorides, and sulfates. Additionally, suitable raw materials (azodicarbonamide) were used, which decompose into several gases due to heat and create high porosity, thus making the concrete lighter. As a whole, these concretes were manufactured in non-autoclaved conditions.

[0032] 3- As mentioned in the previous sections, a higher volume of cement is used in a concrete manufacturing process, which emits greenhouse gases and causes environmental pollution. So, the amount of cement was reduced and, in this way, a small amount of rice bran husk replaced a lot of cement. In this invention, a small amount of rice husk ash (0.4 grams) replaces 50% of the cement, hence, the density decreased by about 39% and the compressive strength decreased by about 38% (comparing CPZ-B1 specimen (containing 4 grams of cement) ) with CP25 specimen (containing 8 grams of cement).

[0033] 4- In addition, using the suitable materials and the engineered mix design, good compressive strength at an early curing age was achieved and as a result, the specimen was cured in a short time, although it is ultra-lightweight and is prepared without using an autoclave, it does not disintegrate or become a paste when it is placed in water, and at the same time, it maintains its strength and resistance.Brief Description of Drawings

[0034] Figure (1 ): formulas of expanded perlite granulation

[0035] Figure (2): The first mode of granulation of expanded perlite

[0036] Figure (3): The second mode of granulation of expanded perlite

[0037] Figure (4): The third mode of granulation of expanded perlite

[0038] Table 1 . Density and compressive strength of CP specimens

[0039] Table 2. Mix design of CPZ-B1 specimen

[0040] Table 3. Density and compressive strength of CPZ-B specimensDescription of Embodiments

[0041] The manufacturing process of an ultra-lightweight concrete laboratory specimen

[0042] CPZ-B specimens: dry materials (cement, expanded perlite, rice husk ash, azodicarbonamide) were stirred for 2 minutes with a mechanical stirrer at 520 RPM at room temperature. Then water was slowly added to the mixture for 3 minutes and stirred simultaneously.

[0043] The material was poured into the mold in several stages. Then the mold was placed in the oven for 10 minutes at a temperature of 170 °C (in this step the azodicarbonamide decomposes into several gases under heating and thus, when the produced gases are released, it causes an increase in the volume of concrete and more reduction in concrete weight.).

[0044] The specimens were left at room temperature for one day to harden and remove from the mold. After removing the specimens from the mold, they were dried at 80°C for 13 hours. Then, their density was measured and they were placed in drinking water. After being immersed in drinking water at room temperature for 7 and 28 days, the compressive strength test was carried out.

[0045] Sieving of expanded perlite:

[0046] This granulation is performed according to the formulas in Figure 1 , and this is because the pores of the concrete are filled with sieved expanded perlite particles to achieve the appropriate density and compressive strength. If the empty spaces of concrete are filled with cement, the density will increase, and if it is filled with water or air, the compressive strength will decrease. Therefore, to achieve lowdensity and high compressive strength, expanded perlite granulation was performed according to the formulas in Figure 1 . Cc and Cu values range from 1 - 3 and 4-6 respectively.

[0047] Based on the Cc and Cu values, three granulation models were proposed. In the first model shown in Figure 2, the value of Cu is 4.46 and Cc is 2.55. In the second model shown in Figure 3, the value of Cu is 5.29 and Cc is 3.02. In the third model, as shown in Figure 4, the values of Cu and Cc are 4 and 1 respectively.

[0048] Among these models, the third model was chosen because the objective is to produce ultra-lightweight concrete with high compressive strength. With this model, it was possible to do different mix designs in order to achieve low density at the same time with good compressive strength, but with other models, desirable results were not achieved.

[0049] The effect of the size of expanded perlite with the mentioned granulation and the amount of cement was investigated to reduce the density and improve the compressive strength of concrete. For this purpose, first samples named CP were prepared, which was a mixture of cement with different percentages (with the symbol C) and expanded perlite (with the symbol P) with the said size and granularity. The compressive strength test was performed on these specimens after 7 days of processing. Table 1 presents the density and compressive strength of CP specimens.

[0050] A Mesh size: 30 (Expanded perlite with size of 1 -3 mm)

[0051] B Mesh size: 16 (Expanded perlite with size of 5-8 mm)

[0052] C Mesh size: 8 (Expanded perlite with size of 5-8 mm)

[0053] D Mesh size: 4 (Expanded perlite with size of 5-8 mm)

[0054] As the size of the expanded perlite particles enlarges, the density and compressive strength increase, for this reason, we used a larger amount of expanded perlite with larger size in the mix designs and used a smaller amount of cement to reduce the density (4 grams). In general and according to Table 1 , as the amount of cement decreases, the bond strength between cement andmaterials decreases, and the compressive strength of the specimens and the density decreases. On the other hand, this granulation, which uses a larger amount of expanded perlite with a larger size and a smaller amount of expanded perlite with a smaller size, improves the compressive strength.

[0055] Then, various amounts of the foaming agent (azodicarbonamide) (to reduce density and weight) were added to the CP23 specimen which was previously investigated and the optimal amount is given in this invention. It is worth noting that as the amount of A increases, the density and compressive strength of concrete decreases, which is because the higher the value of A, the more gas is produced and the porosity increases, and as a result, lighter specimens are produced. In some cases, as the amount of A increases, the density and compressive strength increase, because by this granulation of expanded perlite, the particles sank into each other and formed strong networks, and although the amount of substance A increased, but did not decompose completely and remains inside the created voids and porosity and has a negative effect on the density. Different percentages of material B were added and these specimens were named as CPZ-B. A compressive strength test was conducted on these specimens after 7 days of curing.

[0056] The density and compressive strength of CPZ-B specimens (from 1.18% (CPZ-B05%) to 3.45% (CPZ-B2) of material B) were investigated and among them CPZ-B1 specimen contains 2.33% of material B (the mix design of specimen CPZ-B1 is given in Table 2 (values have been multiplied by 4 because they were placed in a mold with dimensions of 5 x 5 x 5 cm)) which had the best density and compressive strength. Table 3 presents the density and compressive strength of CPZ-B specimens. (Note: rice husk ash is represented by symbol B and azodicarbonamide is represented by symbol A).

[0057] As shown in Table 3, in the lower percentages of material B (CPZ-B05% and CPZ-B08% specimens), the density has increased by about 10% and the compressive strength has decreased (compared to the CPZ-B1 specimen, the compressive strength of the CPZ-B05% specimen and the CPZ-B08% specimen is reduced by about 37% and 60%, respectively,), because the amount of material B, which has pozzolanic properties, is low, and as a result, the amount ofCSH gel is reduced, therefore, it has a negative effect on compressive strength and the strength and durability of concrete decreases.

[0058] As the percentage of material B (CPZ-B1 ) increases, the density decreases and the compressive strength increases, the reason behind this is that the material has a high percentage of SiO2 (silica) and also has very fine and porous particles. It fills the holes and pores of concrete, in other words, it reduces the porosity, and on the other hand, by creating pozzolanic reactions and creating CSH gel, which is due to the high surface area and the presence of cellular structure, the permeability of concrete can be reduced, and as a result, the durability and the strength of concrete is improved.

[0059] At the same time, this material acts as an accelerator in cement and reduces setting time. This process is performed through the absorption of water around the particles, and the amount of water decreases and causes the pores in the structure to shrink, this issue ultimately causes a decrease in the permeability of concrete against acids, chlorides, and sulfates. Also, it is worth noting that when 0.4 grams of rice husk ash replaces 50% of cement, the density decreases by about 39% and the compressive strength decreases by about 38% (comparing the CPZ-B1 specimen(with 4 grams of cement) with the CP25 specimen (with 8 grams of cement)). In the CPZ-B2 specimen, upon an excessive increase in the percentage of material B, the density increased slightly and its compressive strength decreased by about 60% compared to the CPZ-B1 specimen, which is because when the percentage of material B increases beyond a certain limit, the spontaneous contraction of concrete and its cracking potential increases, and as a result, it has a negative effect on the compressive strength and the strength and durability of concrete decreases.

[0060] As mentioned, the CPZ-B1 specimen was the best in terms of density and compressive strength, and after 7 days of curing, its compressive strength was measured and its value is given in Table 3. Then it was decided to check the curing of the best specimen at the age of 28 days. After the completion of the curing time, the compressive strength test was performed. Its compressive strength at the age of 28 days is 0.824 MPa (Table 3). The compressive strength value of the specimen at the age of 28 days is much lower than the compressivestrength value of the specimen at the age of 7 days (2.5 MPa) and the compressive strength decreased a lot (about 67%). The reason is that at an early age, the rapid reaction of the cement hydration mechanism occurs and that the reaction of non-hydrated cement grains may not continue from the age of 7 days onwards days and the cement hydration process may not have been completed well.

[0061] Another specimen of CPZ-B1 was manufactured, which was tested for resistance immediately after drying and without being immersed in water. Its compressive strength is 0.56 MPa and it decreased a lot compared to the age of 7 days (about 77%). This indicates that the manufactured specimen must be placed in water and cured to complete the cement hydration process and thus increase the strength and compressive strength.Examples

[0062] The manufacturing process of an ultra-lightweight concrete laboratory specimen .Firstly, expanded perlite with appropriate sizes was sieved and granulated (as it was described in the previous sections). Subsequently, to prepare suitable ash with maximum pozzolanic activity and excellent quality, rice husk was exposed to air at a suitable temperature inside the electric furnace so that it reached a temperature of 600 °C with a slope of 10 °C / min, then it was calcined at a temperature of 600 °C for 6 hours. The obtained rice husk ash should be ground and used in a ground form in the mix design.

[0063] Then, various mix designs were created to reduce the density and increase the compressive strength of concrete. In these mix designs, the foaming agent was used as this foaming agent is new in concrete blocks, and due to its behavior, a method was designed. First, two methods were designed to manufacture concrete. In the first method, all materials were mixed on a heater with a mechanical stirrer.

[0064] During heating, azodicarbonamide was decomposed into several gases, and the resulting gases were emitted and created porosity, but then the mixture was poured into a mold for molding and pressed, because of this, the swelling of the specimen was reduced and the concrete lightening was less. In the secondmethod, all the materials were mixed with a mechanical stirrer and then molded, and then placed inside the oven for 10 minutes at a temperature of 170 °C. Then, azodicarbonamide was decomposed into several gases and the resulting gases were emitted, and in this way, the volume increased, and because this foaming and swelling occurred uniformly, the weight of concrete block was reduced to a large extent.

[0065] It should be noted that this process occurs under non-autoclaved conditions. Therefore, in this invention, the second method was used. Functional tests and evaluation of characteristics were performed on ultra-lightweight concrete, including density and compressive strength. Density was calculated based on the mass-to-volume ratio using the formula p=m / V.

[0066] The density measurement is as follows: First, the prepared concrete is weighed, so that the weight is measured with a scale with a precision of 10-4g, then the volume of the mold is taken into account to calculate its volume. In this invention, a cube mold with dimensions of 5 x 5 x 5 cm was used. The compressive strength test of prepared concrete was performed according to ASTM C109 standard. The specifications of the device are as follows: precision: 1 Kg, speed: 1 ml / min, load capacity: 3 tons, jack for determining compressive and tensile strength with Abzarazmayesh Arvin brand.

[0067] CPZ-B specimens: dry materials (cement, expanded perlite, rice husk ash, azodicarbonamide) were stirred for 2 minutes with a mechanical stirrer at 520 RPM at room temperature. Then water was slowly added to the mixture for 3 minutes and stirred simultaneously.

[0068] The material was poured into the mold in several stages. Then the mold was placed in the oven for 10 minutes at a temperature of 170 °C (in this step the azodicarbonamide decomposes into several gases under heating and thus, when the produced gases are released, it causes an increase in the volume of concrete and more reduction in concrete weight.).

[0069] The specimens were left at room temperature for one day to harden and remove from the mold. After removing the specimens from the mold, they were dried at 80°C for 13 hours. Then, their density was measured and they wereplaced in drinking water. After being immersed in drinking water at room temperature for 7 and 28 days, the compressive strength test was carried out.Industrial Applicability

[0070] This invention is used in non-structural (non-load-bearing) components of the building, including separation walls (internal and external), flooring, and roof sloping (pitched slope).

Claims

Claims

1. A manufacturing method of green ultra-lightweight concrete block with high compressive strength which comprising: a. Rice husk ash - 2.33 % w / w; b. Expanded Perlite - cc: 1 and cu: 4; c. Cement -23.32 % w / w; d. Azodicarbonamide- 0.58 % w / w; e. Water- 37.32 % w / w; wherein the rice husk ash, expanded perlite, cement, and azodicarbonamide are mixed at the amount mentioned for 2 minutes by a mechanical stirrer with 520 RPM at room temperature, and then water is gradually added to it for 3 minutes and stirred and then the following steps are taken:1- Molding;2- Placement of the molds in the oven for 10 minutes at a temperature of 170 °C;3- Separation of the blocks from the mold and drying them at 80 °C for 13 hours;4- Curing the blocks in drinking water at room temperature for 7 and 28 days;

2. The manufacturing method of rice husk ash for incorporation in the ultralightweight concrete manufacturing process so that according to claim 1 , rice husk is calcined at a temperature of 600 °C for 6 hours in an electric furnace under air and then the produced rice husk ash is ground.

3. The manufacturing method of concrete block according to claim 1 , so that the amount of 1 .18-3.45 %W / W rice husk ash is used to manufacture CPZ-B specimens.