Preparation method of biobrick with mechanical property enhanced by admixture

Abstract

The invention discloses a preparation method of a biobrick with mechanical properties enhanced by admixtures, which is characterized in that clay, cementing liquid and bacillus pasteurii liquid are used as main raw materials, active magnesium oxide and fiber materials are used as the admixtures, the fiber materials are polypropylene fibers or basalt fibers, the main raw materials and the admixtures are uniformly mixed to form a mixed material, and the mixed material is used as a raw material for preparing the biobrick with the mechanical properties enhanced by the admixtures. And preparing the biobrick by using the obtained mixed material. According to the preparation method of the biobrick with the mechanical property enhanced by the admixture, the compressive strength and the breaking strength of the biobrick are improved by adding the active magnesium oxide; by adding the polypropylene fiber or basalt fiber, the compressive strength and breaking strength of the biobrick are further improved, the brittleness of the biobrick is improved, and the ductility of the biobrick is improved.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a method for preparing a bio-brick with enhanced mechanical properties using external admixtures. Background Art

[0002] Building materials are a significant factor influencing CO2 emissions. Energy consumption during material production and transportation is directly correlated with greenhouse gas emissions. The embodied energy of buildings can be broadly categorized as direct and indirect. Direct embodied energy refers to the energy consumed during the transportation and installation of building materials, while indirect embodied energy relates to the energy used in acquiring, processing, and manufacturing building materials, including the transportation associated with these processes. Therefore, the proper selection of materials is crucial for conserving energy and reducing CO2 emissions. Natural materials such as soil, stone, wood, or biomass are considered ideal building materials because they contribute to low emissions, have a minimal carbon footprint, and can be recycled and reused. Traditional bricks are made from clay or ordinary Portland cement concrete (OPC) fired in high-temperature kilns. The manufacture of conventional bricks involves the continuous use of natural and energy resources, accompanied by greenhouse gas emissions. Over the past few decades, the development of other materials, such as concrete blocks, fly ash bricks, and stabilized mud blocks, have created viable alternatives to fired clay bricks, but have yet to make a significant impact in displacing the highly polluting fired clay brick industry.

[0003] Microbially induced carbonate precipitation (MICP) is a new technology developed in recent years. In MICP, urea is hydrolyzed under the action of an enzyme in the presence of calcium salts. The urea hydrolysis process produces dissolved ammonium and inorganic carbonates. The resulting carbonate ions react with calcium ions in the calcium-rich environment and precipitate as calcium carbonate crystals. The precipitated calcium carbonate crystals bind soil particles together, thereby improving its geotechnical properties. Microbially induced calcium carbonate precipitation can be used to increase strength and dilatancy, improve liquefaction resistance, reduce hydraulic conductivity, reduce compressibility, increase thermal conductivity, control erosion, inhibit particle disintegration, heal cracks, and enhance pile bearing capacity. Using microbially induced calcium carbonate precipitation, energy-saving and environmentally friendly biobricks can be produced. Biobricks are a new type of brick material with "life" that is not only environmentally friendly but also economically efficient.

[0004] Currently, research on the mechanical properties of biobricks is scarce both domestically and internationally, and many issues remain to be addressed. When applying microbially induced calcium carbonate precipitation (MICP) technology to consolidated soils, the mineralization effect is unstable. In particular, when consolidating small-particle soils, poor consolidation and uneven calcium carbonate formation within the specimens often occur, limiting the application of MICP technology. Research on biobricks has also focused on coarse sand, primarily because the small pores in small-particle soils hinder the free flow of bacterial solution and cementing fluid, thus affecting mineralization results. Biobricks, in particular, are prone to soil particle aggregation due to their high clay content, which in turn affects their mechanical strength. Similar to other cementitious materials, microbial soil-consolidating materials are inherently brittle, with a sharp drop in strength upon failure. This can pose challenges to their long-term performance and safety, as the ductility of biobricks is crucial in addressing certain engineering geological challenges. Therefore, overcoming the technical bottlenecks of biobricks and seeking methods to improve their mechanical properties and mitigate their brittle nature are crucial for promoting green building wall materials and reducing carbon emissions. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing bio-bricks with enhanced mechanical properties by adding external admixtures, so as to solve the technical problems of low mechanical strength and brittle bricks of bio-bricks.

[0006] The method for preparing bio-bricks with enhanced mechanical properties using external admixtures of the present invention uses clay, a binder and a Bacillus pasteurianus solution as main raw materials, and uses active magnesium oxide and a fiber material as external admixtures, wherein the fiber material is polypropylene fiber or basalt fiber. The main raw materials and the external admixtures are evenly mixed to form a mixed material, and the obtained mixed material is used to prepare bio-bricks.

[0007] Furthermore, the binder is a CaCl2 solution with a solute concentration ranging from 0.5 mol / L to 2.0 mol / L, the urease activity of the Bacillus pasteurianus solution ranges from 1 mS / cm / min to 1.2 mS / cm / min; and the volume ratio of the binder to the Bacillus pasteurianus solution is 1:1.

[0008] Furthermore, the concentration ratio of magnesium ions to calcium ions in the biobrick is in the range of 1:4 to 1:2.

[0009] Furthermore, the concentration ratio of magnesium ions to calcium ions in the biobrick is 1:2.

[0010] Furthermore, the length of the polypropylene fiber is 12 mm, and the dosage is 0.2-0.3%.

[0011] Furthermore, the content of the polypropylene fiber is 0.2%.

[0012] Furthermore, the length of the basalt fiber is 6 mm, and the dosage is 0.1-0.2%.

[0013] Furthermore, the content of the basalt fiber is 0.2%.

[0014] Beneficial effects of the present invention:

[0015] The method for preparing biobricks with enhanced mechanical properties using external admixtures of the present invention improves the compressive strength and flexural strength of the biobricks by adding active magnesium oxide; further improves the compressive strength and flexural strength of the biobricks by adding polypropylene fibers or basalt fibers, improves the brittleness of the biobricks, and improves the ductility of the biobricks; the method for preparing biobricks improves the mechanical properties of the biobricks by using external admixtures. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The activity of magnesium oxide is 90. 2+ / Ca 2+ Processing the flexural strength of biobricks.

[0017] Figure 2 Compressive strength of biobricks treated with different magnesium oxide activities.

[0018] Figure 3 Compressive strength of MgO-biobricks treated with different amounts of polypropylene fibers.

[0019] Figure 4 The flexural strength of magnesium oxide-biobricks treated with different amounts of polypropylene fiber.

[0020] Figure 5 Compressive strength of MgO-biobricks treated with different amounts of basalt fiber.

[0021] Figure 6 The flexural strength of MgO-biobricks treated with different amounts of basalt fiber was investigated. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and examples.

[0023] Example 1: The method for preparing bio-bricks with enhanced mechanical properties using admixtures in this embodiment uses clay, binder and Bacillus pasteurianus solution as main raw materials, and active magnesium oxide and fiber material as external admixtures, wherein the fiber material is polypropylene fiber. The main raw materials and the external admixtures are evenly mixed to form a mixed material, and the obtained mixed material is used to prepare bio-bricks.

[0024] In this embodiment, the binder is a CaCl2 solution with a solute concentration ranging from 0.5 mol / L to 2.0 mol / L, and the urease activity of the Bacillus pasteurianus solution ranges from 1 mS / cm / min to 1.2 mS / cm / min; the volume ratio of the binder to the Bacillus pasteurianus solution is 1:1.

[0025] The concentration ratio of magnesium ions to calcium ions in the biobrick is 1:2. Of course, in different embodiments, the concentration ratio of magnesium ions to calcium ions can also be other values ​​within the range of 1:4 to 1:2.

[0026] The length of the polypropylene fiber is 12 mm, and the content of the polypropylene fiber is 0.2%. Of course, the content of the polypropylene fiber can also be other values ​​within the range of 0.2-0.3%.

[0027] Example 2: The difference between Example 2 and Example 1 is that the fiber material is basalt fiber, the length of the basalt fiber is 6 mm, and the basalt fiber content is 0.2%. Of course, in different embodiments, the basalt fiber content can also be other values ​​within the range of 0.1-0.2%.

[0028] The following compression test and flexural test are used to verify the effect of the admixture of the present invention on enhancing the mechanical properties of the biobrick:

[0029] 1) Flexural strength test

[0030] The flexural strength of biobricks refers to their ability to resist fracture under bending forces. It is a key indicator of brick quality and performance and plays a crucial role in ensuring the safety of building walls. According to ASTM C67-05, cured biobricks are tested for flexural strength using a universal testing machine at a loading rate of 1 mm / min and a span of 100 mm. Loading is stopped after the specimen fails, and the maximum failure load is taken. The flexural strength of the biobrick is calculated using the following formula.

[0031]

[0032] Where: R c is the flexural strength of the biobrick, MPa;

[0033] P is the maximum failure load, N;

[0034] L is the support span, mm;

[0035] b is the width of the biobrick, mm;

[0036] h is the height of the biobrick, mm.

[0037] 2) Compressive strength test

[0038] Compressive strength is a key mechanical property that measures a material's ability to resist failure under pressure. It directly impacts the safety and stability of a structure and is an essential parameter in design, construction, and quality control. According to ASTM C67-05, biobricks are cut into two halves and stacked with their fractures facing each other. A cement paste is applied between the fractured ends of the two halves to bond them together. The thickness of the cement paste should not exceed 3.18 mm. A thickness of approximately 2 mm is applied to both the top and bottom surfaces of the biobrick. After the specimens are allowed to rest for at least 48 hours, they are placed on a universal testing machine for compressive strength testing. During the test, load is applied at a rate of 1 mm / min. Loading is stopped after the specimen fails, and the maximum stress recorded during loading is used as the compressive strength of the specimen.

[0039] 1) Experimental verification of the effect of adding active magnesium oxide on improving the mechanical properties of biobricks:

[0040] Preparation of biobricks: (1) Weigh the clay that has been dried after passing through a 2mm sieve and mix it evenly with active magnesium oxide; (2) At a temperature of 30±2℃, add 150ml of a mixture of Bacillus pasteurianus liquid with a urease activity of about 1.2mS / cm / min and 150ml of a 0.5mol / LCaCl2 solution to the mixed clay, stir evenly, and prepare biobrick test blocks with a size of 120mm×50mm×25mm in a mold; (3) After the preparation of the biobrick test blocks, place the biobrick test blocks in a temperature environment of 30±2℃ and let them stand for 24h, then remove the mold; (4) After removing the mold, use a spray bottle to spray 10ml of bacterial solution on each test block, spray 10ml of bonding liquid after 6h, and spray 10ml of bacterial solution again after 18h. Repeat this step (4) 5 times and then place it in a 100℃ oven to dry to constant weight.

[0041] Test conditions

[0042] This test used 75ml of 0.5mol / L CaCl2. 0-0 was a test block without activated magnesium oxide. Test blocks with different magnesium ion to calcium ion concentration ratios were divided into seven groups. Test blocks were prepared by adding activated magnesium oxide at magnesium ion to calcium ion ratios of 0, 1 / 4, 1 / 3, 1 / 2, 1, 2 / 1, 3 / 1, and 4 / 1. The activity of the activated magnesium oxide was 30, 60, 90, and 120. Three parallel samples were prepared for each group. The specific experimental plan is shown in Table 1.

[0043] Table 1 Test conditions

[0044]

[0045]

[0046] The flexural strength test results are as follows Figure 1 ,from Figure 1 It can be seen that when a small amount of active magnesium oxide is added, the flexural strength of the test block is enhanced better, but when the active magnesium oxide continues to increase and the active magnesium oxide is excessive, the flexural strength of the test block is inhibited. When the concentration ratio of magnesium ions to calcium ions is greater than or equal to 1 / 2, the flexural strength of the test block is inhibited by magnesium oxide with an activity of 30; when the concentration ratio of magnesium ions to calcium ions is greater than or equal to 1 / 1, the flexural strength of the test block is inhibited by magnesium oxide with an activity of 60; when the concentration ratio of magnesium ions to calcium ions is greater than or equal to 1 / 1, the flexural strength of the test block is inhibited by magnesium oxide with an activity of 90; when the concentration ratio of magnesium ions to calcium ions is greater than or equal to 1 / 1, the flexural strength of the test block is inhibited by magnesium oxide with an activity of 120. It was found that when the active magnesium oxide is added in excess, it has an inhibitory effect on microbial consolidation of clay.

[0047] When the magnesium ion to calcium ion concentration ratio varies between 1 / 4 and 1 / 2, the biobrick's flexural strength is positively correlated with the ratio. This result is due to the fact that a higher magnesium ion to calcium ion ratio results in a higher magnesium ion concentration in the biobrick, which consumes the carbonate produced by urease generated by microorganisms. This allows more carbon dioxide to remain in the solution, resulting in a more complete solidification reaction and enhanced soil integrity, leading to higher flexural strength.

[0048] Overall, as the concentration ratio of magnesium ions to calcium ions increases, the flexural strength of the test block first increases and then decreases. When the concentration ratio of magnesium ions to calcium ions is 1 / 2, the flexural strength of the test block is the highest, and the effect is the best. Therefore, it can be seen that the above embodiment, which optimizes the concentration ratio of magnesium ions to calcium ions in the biobrick to 1:2, has a significant effect on improving the strength of the biobrick.

[0049] The compressive strength test results are as follows Figure 2 As shown, from Figure 2 It can be seen that when a small amount of active magnesium oxide is added, the compressive strength of the specimen is enhanced to a greater extent. However, when the active magnesium oxide is continuously increased and the amount of active magnesium oxide is excessive, the compressive strength of the specimen is inhibited. When the magnesium ion to calcium ion concentration ratio of 30 and 60 is greater than or equal to 2 / 1, the compressive strength of the specimen is inhibited. When the magnesium ion to calcium ion concentration ratio of 90 and 120 is greater than or equal to 3 / 1, the flexural strength of the specimen is inhibited.

[0050] When the magnesium ion to calcium ion concentration ratio ranges from 1 / 4 to 1 / 2, the compressive strength of the biobrick is positively correlated with the magnesium oxide content. This result is due to the cementing agents, such as hydrated magnesium carbonate and calcium carbonate, formed by the magnesium and calcium ions within the brick. These precipitates effectively bind loose clay particles together, filling the clay pores, enhancing its integrity, and increasing the density of the biobrick. As the magnesium ion to calcium ion concentration ratio increases, when the ratio ranges from 1 / 3 to 4 / 1, the compressive strength of the specimen decreases.

[0051] In general, as the concentration ratio of magnesium ions to calcium ions increases, the compressive strength of the specimen first increases and then decreases. When the concentration ratio of magnesium ions to calcium ions is 1 / 2, the compressive strength of the specimen is the highest.

[0052] 2) Experimental verification of the effect of external fiber addition on improving the mechanical properties of biobricks:

[0053] Sample preparation: (1) Weigh and dry clay that has been passed through a 2mm sieve, magnesium oxide with an activity of 90 and a magnesium ion to calcium ion concentration ratio of 1 / 3, and polypropylene fiber or basalt fiber and mix them evenly; (2) At a temperature of 30±2℃, add 150ml of a mixture of a bacterial solution with an activity of about 1.2mS / cm / min of urease and 150ml of a 0.5mol / L binder to the mixed clay, stir evenly, and then put it into a mold for compaction; (3) After the preparation of the biobrick specimen is completed, place the biobrick specimen in a temperature environment of 30±2℃ and let it stand for 24h, then remove the mold; (4) After removing the mold, use a spray bottle to spray 10ml of bacterial solution on each specimen, spray 10ml of binder after 6h, and spray 10ml of bacterial solution again after 18h. Repeat this step (4) 5 times and then place it in a 100℃ oven to dry to constant weight.

[0054] Test conditions

[0055] This test uses 75ml, 0.5mol / L CaCl2, 90-1 / 3 means that only active magnesium oxide is added with an activity of 90 and Mg 2+ / Ca 2+ =1 / 3 test blocks were added with polypropylene fiber and basalt fiber, respectively. The test blocks with different fiber dosages were mainly divided into four groups: 0.1%, 0.2%, 0.3%, and 0.4%. Polypropylene fibers of 6mm, 12mm, and 19mm lengths were added to the magnesium oxide-biobrick test blocks, and basalt fibers of 6mm, 12mm, and 18mm lengths were added to the magnesium oxide-biobrick test blocks. Three parallel samples were prepared for each group. The specific experimental plan is shown in Table 2.

[0056] Table 2 Test conditions

[0057]

[0058]

[0059] Effect of polypropylene fiber treatment on the compressive strength of magnesium oxide-biobricks:

[0060] from Figure 3 It can be seen that: for the polypropylene fiber with a dosage of 0.1%, as the length of the polypropylene fiber increases, the compressive strength of the biobrick specimen has been increasing, and the compressive strength is highest when the polypropylene fiber length is 19 mm; for the polypropylene fiber with a dosage of 0.2%, 0.3%, and 0.4%, as the length of the polypropylene fiber increases, the compressive strength of the biobrick specimen first increases and then decreases, among which the compressive strength is highest when the polypropylene fiber length is 12 mm.

[0061] For 6 mm long polypropylene fibers, the compressive strength of the biobrick specimens has been increasing with the increase of polypropylene fiber content, and the compressive strength is highest when the polypropylene fiber content is 0.4%; for 12 mm long polypropylene fibers, the compressive strength of the biobrick specimens first increases and then decreases with the increase of polypropylene fiber content, and the compressive strength is highest when the polypropylene fiber content is 0.3%; for 19 mm long polypropylene fibers, the compressive strength of the biobrick specimens first increases and then decreases with the increase of polypropylene fiber content, and the compressive strength is highest when the polypropylene fiber content is 0.2%.

[0062] In summary, the compressive strength of biobricks first increases and then decreases with increasing fiber content. The optimal fiber content for polypropylene is 0.3%, resulting in the highest compressive strength and the best results. Therefore, the compressive strength of biobricks is highest when the polypropylene fiber length is 12 mm and the fiber content is 0.3%. The compressive strength increases by 20.6% compared to the test blocks without polypropylene fiber and by 141% compared to the test blocks without activated magnesium oxide.

[0063] Effect of polypropylene fiber treatment on the flexural strength of magnesium oxide-biobricks:

[0064] from Figure 4 It can be seen that: for 6 mm long polypropylene fibers, with the increase of polypropylene fiber content, the flexural strength of the biobrick specimen has been increasing, among which the flexural strength is the highest when the polypropylene fiber content is 0.4%; for 12 mm and 19 mm long polypropylene fibers, with the increase of polypropylene fiber content, the flexural strength of the biobrick specimen first increases and then decreases, among which the flexural strength is the highest when the polypropylene fiber content is 0.2%.

[0065] Overall, the flexural strength of biobricks first increased and then decreased with increasing fiber content. The optimal fiber content for polypropylene was 0.2%, resulting in the highest flexural strength and the best results. The highest flexural strength was achieved when the polypropylene fiber length was 12 mm and the fiber content was 0.2%. The flexural strength increased by 124.7% compared to samples without polypropylene fiber and by 235.7% compared to samples without activated magnesium oxide.

[0066] Effect of basalt fiber on the compressive strength of MgO-biobricks:

[0067] from Figure 5 It can be seen that for 6 mm long basalt fiber, with the increase of basalt fiber content, the compressive strength of the biobrick specimen has been increasing, among which the compressive strength is the highest when the fiber content is 0.4%; for 12 mm long basalt fiber, with the increase of basalt fiber content, the compressive strength of the biobrick specimen first increases and then decreases, among which the compressive strength is the highest when the fiber content is 0.3%; for 18 mm long basalt fiber, with the increase of basalt fiber content, the compressive strength of the biobrick specimen first increases and then decreases, among which the compressive strength is the highest when the fiber content is 0.2%.

[0068] In summary, the compressive strength of biobricks first increases and then decreases with increasing fiber content. The optimal basalt fiber content is 0.3%. Therefore, the compressive strength of biobricks is highest when the basalt fiber length is 12 mm and the fiber content is 0.3%, increasing by 178.9% compared to the test blocks without activated magnesium oxide. Given the inherent high strength and high elastic modulus of basalt fiber, it significantly improves the rigidity and compressive strength of the composite material. However, due to its relatively low strength and modulus, the maximum compressive strength of biobricks treated with polypropylene fiber only increased by 141% compared to the test blocks without activated magnesium oxide.

[0069] Effect of basalt fiber on flexural strength of MgO-biobrick:

[0070] from Figure 6 The data shows that for 6mm and 12mm long basalt fibers, as the basalt fiber content increases, the flexural strength of the biobrick specimen first increases and then decreases, among which the flexural strength is highest when the basalt fiber content is 0.2%; for 18mm long basalt fibers, as the basalt fiber content increases, the flexural strength of the biobrick specimen continues to decrease, among which the flexural strength is highest when the basalt fiber content is 0.1%. However, the flexural strength of the basalt fiber with the largest content is still higher than the flexural strength of the biobrick specimen without fiber.

[0071] In summary, the flexural strength of biobricks first increases and then decreases with increasing fiber content. The optimal basalt fiber content is 0.2%. Therefore, the flexural strength of biobricks is highest when the basalt fiber length is 12 mm and the content is 0.2%. The flexural strength increases by 96.1% compared to the test blocks without basalt fiber and by 193% compared to the test blocks without active magnesium oxide.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing biobricks with enhanced mechanical properties by using external admixtures, characterized by: Clay, cementing liquid and Bacillus pasteurianus liquid are used as main raw materials, active magnesium oxide and fiber material are used as external admixtures, and the fiber material is polypropylene fiber or basalt fiber. The main raw materials and the external admixtures are evenly mixed to form a mixed material, and the obtained mixed material is used to prepare bio-bricks.

2. The method for preparing bio-bricks with enhanced mechanical properties using external admixtures according to claim 1, characterized in that: The binder is a CaCl2 solution with a solute concentration ranging from 0.5 mol / L to 2.0 mol / L, and the urease activity of the Bacillus pasteurianus solution ranges from 1 mS / cm / min to 1.2 mS / cm / min; the volume ratio of the binder to the Bacillus pasteurianus solution is 1:

1.

3. The method for preparing bio-bricks with enhanced mechanical properties using external admixtures according to claim 2, characterized in that: The concentration ratio of magnesium ions to calcium ions in the biobrick is in the range of 1:4 to 1:

2.

4. The method for preparing bio-bricks with enhanced mechanical properties using external admixtures according to claim 3, characterized in that: The concentration ratio of magnesium ions to calcium ions in the biobrick is 1:

2.

5. The method for preparing biobricks with enhanced mechanical properties using external additives according to any one of claims 1 to 4, characterized in that: The length of the polypropylene fiber is 12 mm, and the content is 0.2-0.3%.

6. The method for preparing bio-bricks with enhanced mechanical properties using external admixtures according to claim 5, characterized in that: The content of the polypropylene fiber is 0.2%.

7. The method for preparing biobricks with enhanced mechanical properties using external additives according to any one of claims 1 to 4, characterized in that: The length of the basalt fiber is 6 mm, and the mixing amount is 0.1-0.2%.

8. The method for preparing bio-bricks with enhanced mechanical properties using external admixtures according to claim 7, characterized in that: The content of the basalt fiber is 0.2%.

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