Environment-friendly anti-freezing pervious concrete for sponge city and preparation method of environment-friendly anti-freezing pervious concrete

Abstract

The invention belongs to the technical field of pervious concrete, and particularly relates to environment-friendly anti-freezing pervious concrete for a sponge city and a preparation method of the environment-friendly anti-freezing pervious concrete. The inventor creatively adds the filtrate and the filter residue obtained after straw powder treatment into the cementing material applied to the pervious concrete in two modes; on one hand, a chitosan composite gel obtained by crosslinking a filtrate containing lignin and hemicellulose and obtained after straw powder treatment and chitosan replaces part of polymer rubber powder to be mixed with a cement base material, the porosity and the water permeability of concrete bricks can be guaranteed, and meanwhile the bonding strength of a gel material is not reduced; on the other hand, filter residues obtained after straw powder treatment are directly mixed with a cement base material, and the compressive strength of the cement material is improved; the gel material and the pervious concrete thereof can ensure the compressive strength and the water permeability of pervious concrete bricks, have good freezing resistance and crack resistance, and are suitable for being applied to sponge city pavements.

Description

Technical Field

[0001] The present invention belongs to the technical field of permeable concrete, and in particular relates to an environmentally friendly, frost-resistant permeable concrete for sponge cities and a preparation method thereof. Background Art

[0002] Permeable concrete is an environmentally friendly building material with high porosity and good permeability, and is widely used in urban construction.

[0003] In the prior art, permeable concrete is mainly composed of coarse aggregate of a single particle size, a cementitious material (such as cement) and a small amount or no fine aggregate, admixtures and additives, etc., to form a porous structure.

[0004] Permeable concrete has a high porosity, which allows rainwater to quickly penetrate the ground, reducing surface runoff and effectively alleviating urban waterlogging. However, substances accumulated in the pores can cause blockages, or the growth of moss or algae, or the growth of plant roots, can also cause blockages, resulting in a decrease in porosity and permeability, affecting the thermal stability and frost resistance of permeable concrete bricks, making them prone to cracking, and thus affecting their service life. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a cementitious material for use in permeable concrete, wherein a method for preparing the cementitious material comprises the following steps:

[0006] Step 1) After removing dust from the straw, the straw is crushed with a crusher to obtain straw powder with a fineness of 500 to 800 mesh;

[0007] Step 2) According to parts by weight, 1 part of the straw powder is mixed with 0.8-1.2 parts of a hydrochloric acid solution with a concentration of 3-8% wt, 5-8 parts of ethylene glycol, and 3-6 parts of water in a reactor, and the mixture is stirred at 150-300 r / min and a temperature of 100-120° C. for 1-2 hours. After cooling, the mixture is filtered to obtain a filtrate and a filter residue, and the filtrate is adjusted to neutral, and the filter residue is washed to neutral and dried;

[0008] Step 3) adding 2-5 parts of chitosan by weight to every 100 parts of the filtrate, mixing uniformly in a reaction kettle to obtain a homogeneous system, then adding 10-30 parts of a 10-30% wt zinc nitrate hexahydrate solution, and stirring at a temperature of 120° C. to 130° C. for 0.5 to 1 hour to obtain a composite gel;

[0009] Step 4) According to weight parts, 20 to 40 parts of the filter residue, 20 to 50 parts of the composite gel and 0.5 to 2 parts of polymer powder are added to every 100 parts of cement and mixed evenly to obtain the cementitious material.

[0010] Preferably, in step 3), the molecular weight of the chitosan falls within the range of 50 to 150 kDa.

[0011] Preferably, in step 4), the polymer powder is selected from polyvinyl ether or polyacrylamide.

[0012] Preferably, in step 4), the cement is ordinary Portland cement with a strength grade of 42.5.

[0013] Preferably, the straw used in step 1) is any one or more of corn, wheat, rice, and reed straw.

[0014] Another aspect of the present invention provides a permeable concrete, wherein the raw materials of the permeable concrete include, by weight, 200-260 parts of coarse aggregate, 150-200 parts of fine aggregate, 160-220 parts of cementitious material and 70-120 parts of water; wherein the cementitious material adopts the above-mentioned cementitious material.

[0015] Preferably, the particle size of the coarse aggregate falls within the range of 5-20 mm, and the particle size of the fine aggregate is less than 4 mm; preferably, the coarse aggregate is crushed stone or a mixture of crushed stone and industrial waste; preferably, the fine aggregate is natural medium sand.

[0016] Preferably, the raw materials of the permeable concrete further include a water reducing agent.

[0017] Another aspect of the present invention provides a permeable concrete brick, wherein the permeable concrete brick is made of the raw materials of the permeable concrete as described above; preferably, the coarse aggregate, fine aggregate and cementitious material are stirred and mixed, and water and an optional water reducer are added while stirring, and the mixture is evenly mixed, and then poured into a mold to prepare the permeable concrete brick.

[0018] The present invention also provides the use of the above-mentioned cementitious material, the above-mentioned permeable concrete or the above-mentioned permeable concrete bricks in urban pavements, preferably, in sponge city pavements.

[0019] The inventors of the present application creatively added the filtrate and filter residue obtained after straw powder treatment into the cementitious material used in permeable concrete in two ways; on the one hand, the chitosan composite gel obtained by cross-linking the filtrate containing lignin and hemicellulose obtained after straw powder treatment with chitosan was used to replace part of the polymer glue powder and mixed with the cement base material, which can ensure the porosity and permeability of the concrete bricks without reducing the bonding strength of the gel material; on the other hand, the filter residue obtained after straw powder treatment was directly mixed with the cement base material to improve the compressive strength of the cement material; by adopting the gel material of the present invention and its permeable concrete technical solution, even if ordinary Portland cement with a strength grade of 42.5 with a lower cost is used, even if the amount of polymer glue powder used is reduced, the compressive strength and water permeability of the permeable concrete bricks can still be guaranteed, and it has good frost resistance and crack resistance, and is suitable for application in sponge city pavements. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail below with reference to the embodiments, but the present invention is not limited to the scope of the embodiments. The process parameters not specified in the examples of this application can be carried out according to conventional methods, and the raw materials used can be obtained through commercial channels.

[0021] Example 1

[0022] The preparation method of the cementitious material applied to permeable concrete in Example 1 is as follows:

[0023] In some embodiments of the present invention, step 1): after removing dust from the straw, crush it with a crusher to obtain straw powder with a fineness of 500 to 800 mesh;

[0024] In some embodiments of the present invention, the straw is any one or more of corn, wheat, rice, and reed straw.

[0025] Specifically, in this embodiment, wheat straw is used as the straw, which is coarsely ground into powder to obtain dry straw powder with a mesh size of about 600.

[0026] In some embodiments of the present invention, step 2): according to weight parts, each part of the straw powder is mixed with 0.8-1.2 parts of a hydrochloric acid solution with a concentration of 3-8% wt, 5-8 parts of ethylene glycol, and 3-6 parts of water in a reactor, and the mixture is stirred at 150-300 r / min and a temperature of 100-120° C. for 1-2 hours. After cooling, the mixture is filtered to obtain a filtrate and a filter residue, and the filtrate is adjusted to neutral, and the filter residue is washed to neutral and dried;

[0027] Specifically in this embodiment, the straw powder obtained in step 1) is mixed with 1 part of a 5%wt dilute hydrochloric acid solution, 6 parts of ethylene glycol and 5 parts of water in a reactor for every 1 part of straw powder. The mixture is stirred and cooked at a temperature of 100-120°C at a stirring speed of about 200 r / min. The reaction time is between 1 and 2 hours. After that, the mixture in the reactor is taken out and cooled, and filtered to obtain a filtrate and a residue.

[0028] Specifically in this embodiment, the filtrate is adjusted to neutrality with a small amount of sodium bicarbonate, the filter residue is washed with hot water to neutrality, and dried to obtain a dry filter residue for use in subsequent steps.

[0029] In step 2) of this embodiment, stirring and cooking are carried out at a specific stirring speed and cooking temperature so that the crude straw powder can fully contact the ethylene glycol solvent and the cellulose swells. Under the treatment of dilute hydrochloric acid, the lignin and hemicellulose in the straw powder are removed to a certain extent, exposing the cellulose molecules embedded therein; the above-mentioned lignin and hemicellulose are dissolved in the obtained filtrate, and the obtained filter residue is crude straw cellulose.

[0030] In some embodiments of the present invention, for corn straw powder and reed straw powder with higher lignin content, higher toughness and strength, the concentration of dilute hydrochloric acid can be appropriately increased, and / or the stirring speed and cooking temperature can be increased. These adjustments can be made by those skilled in the art based on the knowledge of the operating process and parameter conditions of step 2).

[0031] In some embodiments of the present invention, step 3): adding 2-5 parts of chitosan to every 100 parts of the filtrate by weight, mixing uniformly in a reaction kettle to obtain a homogeneous system, and then adding 10-30 parts of a 10-30% wt zinc nitrate hexahydrate solution, stirring at a temperature of 120° C. to 130° C. for 0.5 to 1 hour to obtain a composite gel;

[0032] Specifically in this embodiment, the filtrate adjusted to neutrality obtained in step 2) was mixed with chitosan. About 3 parts of chitosan were added to every 100 parts of the filtrate. After mixing in a reactor to obtain a uniform system, about 20 parts of a 20% wt zinc nitrate hexahydrate solution was added, and the mixture was stirred at a temperature of 120° C. to 130° C. for 0.5 to 1 hour to obtain a composite gel.

[0033] In some preferred embodiments of the present invention, chitosan with a relatively low molecular weight is used, for example, chitosan with a molecular weight ranging from 50 to 150 kDa. Specifically, in this embodiment, the chitosan used was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0034] In step 3) of the present invention, the filtrate obtained in step 2) is mixed with chitosan, and the lignin and hemicellulose in the filtrate are cross-linked with the chitosan to form a chitosan complex having a network hydrogel structure. In addition, a zinc nitrate hexahydrate solution is added to react with the chitosan sol to generate zinc oxide. Specifically, at a temperature of 120° C. to 130° C., the amino and hydroxyl groups of the chitosan promote the conversion of zinc nitrate hexahydrate into zinc oxide, and the generated zinc oxide is contained in the gel network structure of the chitosan complex.

[0035] Zinc oxide is a photocatalytic material that undergoes a photocatalytic reaction under sunlight, effectively degrading pollutants such as organic pollutants. Specifically, in permeable concrete brick applications, it can effectively degrade accumulated materials, such as moss and plant roots, trapped in the brick pores. This effectively resolves the problem of blockage in permeable concrete bricks, improves the pavement's water permeability, and thus ensures the thermal stability and frost resistance of the permeable concrete bricks.

[0036] In some embodiments of the present invention, step 4): according to weight parts, 20 to 40 parts of the filter residue, 20 to 50 parts of the composite gel and 0.5 to 2 parts of polymer powder are added to every 100 parts of cement to mix evenly to obtain the cementitious material.

[0037] In the field of permeable concrete technology, cement can be silicate cement or ordinary silicate cement; however, when it comes to the application of permeable concrete bricks in pavement, cement materials with higher compressive strength grades are generally used, such as strength grades of 52.5 / 52.5R or above (based on the provisions of the national standard GB175-2023 "General Portland Cement").

[0038] However, in some embodiments of the present invention, the cement in step 4) can be ordinary Portland cement, and can be of lower strength grade, which can reduce the cost of cement in specific applications; for example, in this embodiment, ordinary Portland cement with a strength grade of 42.5 is used.

[0039] In some embodiments of the present invention, in step 4), the polymer powder is selected from polyvinyl ether or polyacrylamide. In this embodiment, the polymer powder is polyacrylamide.

[0040] In the field of permeable concrete technology, the use of polymer glue powder can, on the one hand, improve the bonding strength between aggregate and cement matrix, and improve the crack resistance and durability of permeable concrete; on the other hand, it can improve the pore structure of permeable concrete, reduce the total porosity, reduce the number of large pores, increase the number of small pores, and make the surface of concrete bricks denser, which can effectively reduce the chance of dust, soil and other impurities entering the pores and prevent pore blockage; but as a result, the use of polymer glue powder may cause a decrease in porosity and permeability.

[0041] Therefore, in the scheme of the present invention, in order to reduce the amount of polymer glue powder used, ensure the porosity and water permeability of concrete bricks while not reducing the bonding strength of the gel material, and improve the crack resistance of permeable concrete, the inventors of this application creatively added the filtrate and filter residue obtained after straw powder treatment to the gel material in two ways; specifically, on the one hand, the chitosan composite gel obtained by cross-linking the filtrate containing lignin and hemicellulose obtained after straw powder treatment with chitosan is used to replace part of the polymer glue powder and mix with the cement base material, which can ensure the porosity and water permeability of concrete bricks while not reducing the bonding strength of the gel material; on the other hand, the filter residue obtained after straw powder treatment is directly mixed with the cement base material to improve the compressive strength and crack resistance of the cement material (after permeable concrete is formed). Using the scheme of the present invention, even if ordinary Portland cement with a strength grade of 42.5 is used, even if the amount of polymer glue powder used is reduced, the compressive strength of permeable concrete bricks can still be guaranteed, and the porosity and water permeability can be improved, thereby obtaining better permeability and frost resistance.

[0042] Specifically in this embodiment, 30 parts of the filter residue obtained in step 2), 35 parts of the composite gel obtained in step 3) and 1 part of polymer powder were added to every 100 parts of ordinary Portland cement and mixed evenly to obtain the cementitious material of embodiment 1 of the present invention.

[0043] Example 2

[0044] The raw materials of the permeable concrete of Example 2 include, by weight, 200-260 parts of coarse aggregate, 150-200 parts of fine aggregate, 160-220 parts of cementitious material, and 70-120 parts of water; wherein the cementitious material adopts the cementitious material obtained in Example 1.

[0045] In some embodiments of the present invention, the particle size of the coarse aggregate falls within the range of 5-20 mm, and the particle size of the fine aggregate is less than 4 mm. In some preferred embodiments of the present invention, the coarse aggregate is crushed stone or a mixture of crushed stone and industrial waste, and the fine aggregate is natural medium sand.

[0046] Specifically in this embodiment, the coarse aggregate is crushed stone with an average particle size of 10-20 mm purchased from Taiyuan Yangqu Guoxingrong Building Materials Co., Ltd. The fine aggregate is natural medium sand with an average particle size of 0.35-0.5 mm purchased from Shanxi Tongda River Management Co., Ltd.

[0047] In some embodiments of the present invention, the raw materials of the permeable concrete further include a water reducer, for example, a polycarboxylic acid water reducer, a naphthalene water reducer, an aliphatic water reducer, an aminosulfonate water reducer, or a melamine water reducer.

[0048] Specifically, 2 parts of polycarboxylic acid water reducer were added to the raw materials of the permeable concrete of this embodiment. The industrial-grade polycarboxylic acid water reducer was purchased from Shanxi Keteng Environmental Protection New Materials Co., Ltd.

[0049] Specifically in this embodiment, the raw material formula of permeable concrete includes, in parts by weight, 230 parts of coarse aggregate, 160 parts of fine aggregate, 200 parts of cementitious material, 100 parts of water and 2 parts of polycarboxylic acid-based water reducer.

[0050] Application Examples

[0051] According to the raw material formula of permeable concrete in Example 2, the coarse aggregate, fine aggregate and cementitious material are stirred and mixed, water and water reducer are added while stirring, and after mixing evenly, poured into a mold. After conventional production and curing procedures, permeable concrete bricks are obtained after demolding.

[0052] The permeable concrete bricks obtained by the present invention can be used as urban pavement bricks, especially as pavement bricks in sponge cities.

[0053] Comparative Examples 1-3

[0054] The raw material formula of the permeable concrete of Comparative Examples 1-3 includes, in parts by weight, 230 parts of coarse aggregate, 160 parts of fine aggregate, 200 parts of cementitious material, 100 parts of water and 2 parts of polycarboxylic acid-based water reducer.

[0055] Except for the cementitious material, the sources of the coarse aggregate, fine aggregate and polycarboxylic acid-based water-reducing agent in Comparative Examples 1-3 are the same as those in Example 2.

[0056] Preparation of the gel material used in Comparative Example 1: Add 5 parts of polymer glue powder to every 100 parts of ordinary Portland cement and mix well.

[0057] Preparation of the gel material used in Comparative Example 2: 35 parts of chitosan gel and 1 part of polymer powder were added to every 100 parts of ordinary Portland cement and mixed uniformly. The chitosan gel used in Comparative Example 2 was obtained by adding 3 parts of chitosan to every 100 parts of water, mixing uniformly in a reaction kettle to obtain a homogeneous system, then adding approximately 20 parts of a 20% wt zinc nitrate hexahydrate solution, and stirring at 120°C to 130°C for 0.5 to 1 hour to obtain the chitosan gel.

[0058] Preparation of the gel material used in Comparative Example 3: To every 100 parts of ordinary Portland cement, 30 parts of straw powder (wheat straw powder obtained in step 1 of Example 1), 35 parts of chitosan gel (the same as the chitosan gel used in Comparative Example 2) and 1 part of polymer glue powder were added.

[0059] The sources of ordinary Portland cement and polymer powder (polyacrylamide) used in Comparative Examples 1-3 are the same as those in Example 1.

[0060] The permeable concrete of Comparative Examples 1-3 was prepared into permeable concrete bricks according to the method of the above application example (mixing the coarse aggregate, fine aggregate and cementitious material, adding water and water reducer while stirring, mixing evenly, pouring into a mold, and demolding after conventional production and curing procedures).

[0061] Performance Testing

[0062] The permeable concrete blocks prepared in the application examples of this application, as well as the permeable concrete blocks obtained in Comparative Examples 1-3, were tested for compressive strength and water permeability. The testing methods were based on CJJ / T 135-2009, "Technical Specification for Permeable Cement Concrete Pavements" (2023 Edition). The test results are shown in Table 1 below.

[0063] Table 1 Test results of compressive strength and water permeability of permeable concrete bricks

[0064] Test Bricks 7-day compressive strength / MPa 28-day compressive strength / MPa Permeability coefficient / (mm / s) Application examples of this application 23.7 43.6 4.1 Comparative Example 1 25.1 45.2 2.6 Comparative Example 2 21.2 36.8 3.3 Comparative Example 3 23.3 39.7 2.9

[0065] It can be seen from the results in Table 1 that the compressive strength and water permeability of the permeable concrete bricks obtained by the method of the present application are significantly better than those of Comparative Examples 1-3.

[0066] Specifically, the permeable concrete formula of Comparative Example 1 differs from that of Example 2 of the present application only in that the gel material of Comparative Example 1 is prepared using an existing method (5 parts of polymer glue powder (polyacrylamide) are added to every 100 parts of ordinary Portland cement and mixed evenly). As can be seen from the results in Table 1, the permeable concrete bricks prepared using the existing method have good compressive strength but poor water permeability.

[0067] The gel material of Comparative Example 2 uses chitosan gel to replace part of the polymer powder (polyacrylamide). However, the chitosan gel of Comparative Example 2 does not contain the filtrate obtained from the straw powder treatment during its preparation, and the filter residue obtained from the straw powder treatment is not added to the gel material of Comparative Example 2. Based on the results in Table 1, the permeable concrete blocks of Comparative Example 2 have poor compressive strength and average permeability.

[0068] The gel material of Comparative Example 3 uses chitosan gel to replace part of the polymer powder (polyacrylamide), but the filtrate obtained by treating with straw powder is not added during the preparation of the chitosan gel of Comparative Example 3, and straw powder (prepared in step 1 of Example 1 of the present application) is directly added to the gel material of Comparative Example 3.

[0069] From the results in Table 1, it can be seen that compared with Comparative Example 2, the addition of straw powder in Comparative Example 3 can improve the compressive strength to a certain extent, but it is still lower than the compressive strength of the embodiment of the present application; and the water permeability effect of Comparative Example 3 is poor.

[0070] Based on the above results, it can be seen that the combination of general chitosan gel and straw powder to replace part of the polymer glue powder mixed with the cement base material cannot achieve the effect achieved by combining the chitosan composite gel prepared in step 3) of Example 1 of the present application with the filter residue (crude straw cellulose) obtained in step 2, whether in terms of replacing the polymer glue powder to ensure the bonding strength of the gel material or in terms of ensuring the porosity and permeability of the concrete bricks.

[0071] The present invention is not limited to the above-described embodiments. Any changes in shape or structure fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims. Those skilled in the art may make various changes, modifications, substitutions, combinations, and simplifications to these embodiments without departing from the principles and essence of the present invention. All such changes shall be considered equivalent replacements and fall within the scope of protection of the present invention.

Claims

1. A cementitious material used in permeable concrete, characterized in that: The preparation method of the gelling material comprises the following steps: Step 1) After removing dust from the straw, the straw is crushed with a crusher to obtain straw powder with a fineness of 500 to 800 mesh; Step 2) According to parts by weight, 1 part of the straw powder is mixed with 0.8-1.2 parts of a hydrochloric acid solution with a concentration of 3-8% wt, 5-8 parts of ethylene glycol, and 3-6 parts of water in a reactor, and the mixture is stirred at 150-300 r / min and a temperature of 100-120° C. for 1-2 hours. After cooling, the mixture is filtered to obtain a filtrate and a filter residue, and the filtrate is adjusted to neutral, and the filter residue is washed to neutral and dried; Step 3) adding 2-5 parts of chitosan by weight to every 100 parts of the filtrate, mixing uniformly in a reaction kettle to obtain a homogeneous system, then adding 10-30 parts of a 10-30% wt zinc nitrate hexahydrate solution, and stirring at a temperature of 120° C. to 130° C. for 0.5 to 1 hour to obtain a composite gel; Step 4) According to weight parts, 20 to 40 parts of the filter residue, 20 to 50 parts of the composite gel and 0.5 to 2 parts of polymer powder are added to every 100 parts of cement and mixed evenly to obtain the cementitious material.

2. The gelling material according to claim 1, wherein In the step 3), the molecular weight of the chitosan falls within the range of 50 to 150 kDa.

3. The gelling material according to claim 1, wherein In step 4), the polymer powder is selected from polyvinyl ether or polyacrylamide.

4. The gelling material according to claim 1, wherein In the step 4), the cement is ordinary Portland cement with a strength grade of 42.

5.

5. The cementitious material according to any one of claims 1 to 4, characterized in that The straw used in step 1) is any one or more of corn, wheat, rice, and reed straw.

6. A permeable concrete, characterized by: The raw materials of the permeable concrete include, by weight, 200-260 parts of coarse aggregate, 150-200 parts of fine aggregate, 160-220 parts of cementitious material and 70-120 parts of water; Wherein, the gelling material is the gelling material as claimed in claim 5.

7. The permeable concrete according to claim 6, wherein: The particle size of the coarse aggregate falls within the range of 5-20 mm, and the particle size of the fine aggregate is less than 4 mm; preferably, the coarse aggregate is crushed stone or a mixture of crushed stone and industrial waste; preferably, the fine aggregate is natural medium sand.

8. The permeable concrete according to claim 6, wherein: The raw materials of the permeable concrete further include a water reducing agent.

9. A permeable concrete brick, characterized by: The water concrete bricks are made of the raw materials of the permeable concrete according to any one of claims 6 to 8; preferably, the coarse aggregate, fine aggregate and cementitious material are stirred and mixed, water and an optional water reducer are added while stirring, and the mixture is evenly mixed, and then poured into a mold to prepare the permeable concrete bricks.

10. Use of the cementitious material according to any one of claims 1 to 5, the permeable concrete according to any one of claims 6 to 8, or the permeable concrete brick according to claim 9 in urban pavement, preferably in sponge city pavement.