A method for strengthening recycled coarse aggregate

Abstract

The present invention discloses a method for strengthening recycled coarse aggregate, which is obtained by sequentially immersing the recycled coarse aggregate in an inorganic polymer slurry and a waterproof material under negative pressure, performing an immersion treatment, heating and curing, and drying. The present invention adopts an inorganic-organic strengthening mechanism and further combines a step-by-step curing method, which can significantly reduce the water absorption rate of the recycled aggregate while effectively improving the strength of the recycled aggregate, and can provide a new idea for the efficient application of recycled aggregate in the surface layer; and the strengthening method involved is relatively simple and low in cost, and is suitable for promotion and application.

Description

Technical Field

[0001] The invention belongs to the field of road engineering materials, and in particular relates to a method for strengthening recycled coarse aggregate from construction waste. Background Art

[0002] The development of highway construction consumes a lot of stone materials, and the increasing depletion of natural stone materials has greatly increased the cost of highway construction. Therefore, finding alternative materials for natural stone materials and reducing the consumption of natural stone materials is a major problem that needs to be solved in highway construction. On the other hand, with the continued urbanization process, the renovation and demolition of old houses will generate a large amount of construction waste. If it is not disposed of, the construction waste will not only occupy a large amount of land, but also be buried on the spot, which will also pollute the soil. This is another major problem that needs to be solved urgently.

[0003] By treating construction waste appropriately, recycled aggregates of different particle sizes can be produced; if recycled coarse aggregate can replace natural coarse aggregate and be used in road surface layers, it will not only reduce the consumption of natural stone in highway construction, but also solve the problem of the difficulty in reusing recycled coarse aggregate from construction waste to a certain extent.

[0004] At present, recycled aggregate is often used in the base layer of asphalt pavement. Compared with the pavement base layer, the renovation frequency of the asphalt pavement surface layer is usually higher. If recycled aggregate can be used in the paving of the surface layer, a large amount of recycled coarse aggregate can be consumed. In the current "Technical Specifications for Highway Asphalt Pavement Construction" (JTG F40-2004), the requirements for coarse aggregate used in the surface layer of highways include: stone crushing value ≯26%, Los Angeles abrasion loss ≯28%, apparent relative density ≮2.6, and water absorption rate ≯2.0%. However, since recycled aggregate is mainly a multiphase composite material composed of aggregate and cement mortar, the attached mortar layer causes its surface morphology to be rough, heterogeneous, and has a large number of pore structures, making it difficult for the performance indicators of recycled aggregate to meet the current surface layer specification requirements, which greatly limits the application of recycled coarse aggregate. Strengthening treatment of recycled aggregate is an important way to solve the above problems.

[0005] Patent CN113896456A discloses a process for preparing recycled asphalt mixture using recycled aggregate from construction waste, mechanically strengthening the recycled coarse and fine aggregates, removing the cement mortar attached to the surface of the recycled coarse aggregate, and grinding off the edges and corners on the surface of the recycled coarse aggregate; however, this solution only uses mechanical strengthening means, which will damage the recycled aggregate while removing the cement mortar and grinding the edges and corners, forming cracks and reducing the mechanical properties of the recycled aggregate. Patent CN114716211A discloses a method for strengthening recycled coarse aggregate, which mainly uses silica ash slurry to coat the recycled coarse aggregate. The strengthening effect involved is limited, and the prepared recycled aggregate still faces the problem of easy breakage. In addition, since the silica ash slurry itself is porous, the high water absorption rate of the recycled aggregate cannot be solved after coating; applying it to asphalt pavement will not only increase the amount of asphalt and increase the cost, but also reduce the strength of the asphalt pavement and reduce the service life of the pavement. Summary of the invention

[0006] The purpose of the present invention is to address the problems and shortcomings of the prior art and solve the problem of low strength of existing recycled coarse aggregate at a relatively low cost. The recycled aggregate is reinforced with inorganic polymers and organic polymers in turn in the form of a combination of inorganic and organic materials to achieve a composite reinforcement effect and significantly reduce the water absorption rate of the recycled aggregate, so as to achieve efficient application in the surface layer.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A method for strengthening recycled coarse aggregate comprises the following steps:

[0009] 1) Under negative pressure, the recycled coarse aggregate is added into an inorganic polymer slurry for a soaking treatment, and after being taken out, the recycled coarse aggregate is heated and cured, and dried to obtain a reinforced modified recycled aggregate; the inorganic polymer slurry is a geopolymer slurry;

[0010] 2) Under negative pressure conditions, the primary reinforced modified recycled aggregate is added into a waterproof dispersion (water-emulsion type) for secondary immersion treatment. After being taken out, it is heated and cured for a second time and dried to obtain the reinforced recycled coarse aggregate.

[0011] In the above scheme, the recycled aggregate is obtained by crushing, screening, washing and grinding construction waste, and the particle size of the recycled aggregate is greater than 2.36 mm.

[0012] In the above scheme, the negative pressure condition is 1 to 5 kPa.

[0013] In the above scheme, the components in the geopolymer slurry and their weight percentages include: 100 parts of water, 10-50 parts of aluminosilicate minerals, and 10-50 parts of composite alkali; wherein the composite alkali includes sodium hydroxide and sodium silicate.

[0014] In the above scheme, the silicon-aluminum ratio in the geopolymer slurry is controlled to be 1.0-3.0; wherein the silicon-aluminum ratio is the mass ratio of the total silicon element to the aluminum element introduced into the geopolymer slurry.

[0015] In the above scheme, the modulus of the sodium silicate is 1.5 to 3.5.

[0016] Furthermore, the geopolymer slurry is obtained by mixing an aluminosilicate mineral suspension with a reaction alkali solution; wherein the aluminosilicate mineral suspension is obtained by mixing an aluminosilicate mineral, part of sodium hydroxide and part of water; and the reaction alkali solution is obtained by mixing sodium silicate, remaining sodium hydroxide and water; wherein the modulus of the reaction alkali solution is 1.0 to 1.8.

[0017] In the above scheme, the material with pozzolanic activity includes one or more of metakaolin, fly ash, slag, etc., and its size is 800-2000 mesh.

[0018] In the above scheme, the time of the first immersion treatment is not less than 30 minutes, so that the inorganic polymer can fully penetrate into the recycled aggregate.

[0019] In the above scheme, the waterproof material needs to have the characteristics of strong permeability, good film-forming effect, and good adhesion to stone and cement mortar. Specifically, one or more of polyvinyl acetate, acrylate, polyurethane, and silicone rubber emulsion can be selected.

[0020] In the above scheme, the secondary immersion treatment time is not less than 30 minutes, so that the waterproof material can fully penetrate into the recycled aggregate.

[0021] In the above scheme, the primary heating curing temperature is 40-60°C and the time is more than 8 hours.

[0022] Furthermore, the health-preserving time is 8 to 12 hours.

[0023] In the above scheme, the secondary heating curing temperature is 40-60°C and the time is more than 8 hours.

[0024] Furthermore, the health-preserving time is 8 to 12 hours.

[0025] In the above scheme, the temperature used in the drying step is 100-120° C. and the time is more than 4 hours.

[0026] The recycled aggregate prepared according to the above scheme has a crushing value of 15-25%, a Los Angeles abrasion loss of 18-26%, an apparent relative density of 2.6-2.7, and a water absorption rate of 0.5-1.8%.

[0027] The principle of the present invention is:

[0028] The present invention firstly infiltrates geopolymer slurry into recycled aggregate under negative pressure conditions, and heats and cures the slurry to fill and repair holes and cracks therein, and can react chemically with cement mortar and the like in the recycled aggregate to generate CSH gel, thereby realizing effective combination of the geopolymer and the recycled aggregate and the like; and then further immerses the geopolymer in a highly permeable water-emulsifiable waterproof dispersion under negative pressure conditions, and continues to heat and cure the slurry to further fill cracks and holes generated when the geopolymer loses water and solidifies, and forms a membrane through processes such as approach, contact, and deformation of solid particles, thereby solving the problems and shortcomings of high water absorption of the recycled aggregate after one-time strengthening, and enhancing the bonding effect between the geopolymer and the recycled aggregate, significantly improving the crushing value, and improving the wear resistance and the like.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The present invention adopts an inorganic strengthening-organic modification mechanism and further combines a step-by-step curing method, which can effectively improve the strength of the recycled aggregate and significantly reduce the water absorption rate of the recycled aggregate, providing a new idea for the efficient application of recycled aggregate in the surface layer;

[0031] 2) The geopolymer of the present invention can be prepared from solid waste with volcanic ash activity, which can achieve the recycling of fly ash, slag and other materials while solving the problem of resource utilization of recycled aggregate solid waste, and has significant economic and environmental benefits;

[0032] 3) The strengthening process adopted by the present invention is relatively simple and low in cost, and is suitable for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 2) are the XRD patterns of the recycled aggregate before and after strengthening in step 2) of Example 1. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with some embodiments, rather than all embodiments.

[0035] In the following examples, the recycled aggregate used was obtained by crushing, screening and mechanically grinding waste concrete in the laboratory.

[0036] In the following examples, the water glass used is industrial grade water glass with an initial modulus of 2.6 and a water content of 48%; the alkali used is sodium hydroxide with a purity of ≥98%.

[0037] In the following examples, the volcanic ash active material used is metakaolin with a mesh size of 1250 meshes, and its main chemical components and their mass percentages include: Al2O3 42.6%, SiO2 51.3%, and CaO 2.8%.

[0038] In the following examples, the water-emulsion waterproof material used is an organic silicone resin emulsion provided by Hubei Huanyu Chemical Co., Ltd., the product model is HY-1005, and the solid content is 30%.

[0039] Example 1

[0040] A method for strengthening recycled coarse aggregate comprises the following steps:

[0041] 1) 100 parts (by weight, the same below) of water, 46.8 parts of water glass, and 11.8 parts of sodium hydroxide were mixed to prepare a reaction base solution with a modulus of 1.5;

[0042] 100 parts of water, 50 parts of metakaolin and 11.8 parts of sodium hydroxide are mixed evenly to prepare a uniform suspension containing aluminosilicate mineral components;

[0043] The reaction alkali solution and the suspension containing aluminosilicate mineral components are uniformly mixed in a mass ratio of 1:1.8 to prepare a geopolymer slurry with a silicon-aluminum ratio of 1.5;

[0044] 2) 1000mL of geopolymer slurry and 1kg of recycled coarse aggregate are placed in a negative pressure container, and the negative pressure in the negative pressure container reaches 3.7kPa±0.3kPa within 2 minutes. The vibration device and vacuum are started at the same time, and the container is continuously vacuumed for 45 minutes. The container is then taken out and placed in an oven at 60°C for curing for 12 hours, and finally placed in an oven at 105°C for 12 hours to dry the recycled aggregate, thereby obtaining a primary reinforced modified recycled aggregate;

[0045] 3) 500 mL of silicone resin emulsion and 500 mL of water are mixed evenly to obtain a waterproof dispersion with a solid content of 15%; the mixture is introduced into a negative pressure container, and 1 kg of the primary reinforced modified recycled coarse aggregate is added. The negative pressure in the negative pressure container reaches 3.7 kPa ± 0.3 kPa within 2 minutes. At the same time, the vibration device and vacuum are started for 45 minutes. The mixture is then taken out and placed in an oven at 60°C for curing for 12 hours, and finally placed in an oven at 105°C for 12 hours to fully dry the recycled aggregate to obtain the reinforced recycled aggregate.

[0046] Example 2

[0047] A method for strengthening recycled coarse aggregate, the specific steps are roughly the same as those of Example 1, except that in step 1), a reaction alkali solution with a modulus of 1.5 and a suspension containing aluminosilicate mineral components are respectively prepared, and a geopolymer slurry is prepared at a silicon-aluminum ratio of 2.0; the specific formula requirements of the reaction alkali solution and the suspension are as follows (the mass ratio of the two is determined according to the designed silicon-aluminum ratio): 100 parts of water, 23.4 parts of water glass, and 6 parts of sodium hydroxide are mixed evenly to prepare a reaction alkali solution with a modulus of 1.5; 100 parts of water, 37 parts of kaolin, and 6 parts of sodium hydroxide are mixed evenly to prepare a uniform suspension containing aluminosilicate mineral components; the reaction alkali solution and the suspension containing aluminosilicate mineral components are mixed evenly to obtain a geopolymer slurry.

[0048] Example 3

[0049] A method for strengthening recycled coarse aggregate, wherein the specific steps are substantially the same as those of Example 1, except that, in step 1), an alkali solution with a modulus of 1.5 and a suspension containing aluminosilicate mineral components are respectively prepared, and a geopolymer slurry is prepared at a silicon-aluminum ratio of 2.5; the specific formula requirements of the reaction alkali solution and the suspension are as follows: 100 parts of water, 46.8 parts of water glass, and 11 parts of sodium hydroxide are mixed evenly to prepare a reaction alkali solution with a modulus of 1.5; 100 parts of water, 50 parts of kaolin, and 11.8 parts of sodium hydroxide are mixed evenly to prepare a uniform suspension containing aluminosilicate mineral components; the reaction alkali solution and the suspension containing aluminosilicate mineral components are mixed evenly at a mass ratio of 5:3 to obtain a geopolymer slurry.

[0050] Comparative Example 1

[0051] A method for strengthening recycled coarse aggregate, according to the preparation method in Example 1, only the geopolymer slurry modification described in step 4) is performed (one-time strengthening and modification of recycled aggregate).

[0052] Comparative Example 2

[0053] A recycled aggregate strengthening method is provided, according to the preparation method in Example 1, except that the silicone resin emulsion modification described in step 5) is performed.

[0054] Comparative Example 3

[0055] A method for strengthening recycled coarse aggregate, the specific steps are roughly the same as those of Example 1, except that in step 1), an alkaline solution with a modulus of 1.5 and a suspension containing aluminosilicate mineral components are prepared separately, a geopolymer slurry is prepared at a silicon-aluminum ratio of 3.5, and the mass ratio of the reaction alkaline solution and the suspension is determined according to the designed silicon-aluminum ratio.

[0056] Comparative Example 4

[0057] A method for strengthening recycled coarse aggregate, the specific steps are roughly the same as those of Example 1, except that in step 1), an alkaline solution with a modulus of 1.5 and a suspension containing aluminosilicate mineral components are prepared separately, and a geopolymer slurry is prepared at a silicon-aluminum ratio of 0.6; the mass ratio of the reaction alkaline solution and the suspension is determined according to the designed silicon-aluminum ratio.

[0058] Comparative Example 5

[0059] A recycled aggregate strengthening method, the specific steps are substantially the same as those of Example 1, except that the curing temperature in step 2) and step 3) is set to 80°C.

[0060] Comparative Example 6

[0061] A recycled aggregate strengthening method, the specific steps are substantially the same as those of Example 1, except that the curing temperature in step 2) and step 3) is set to 20°C.

[0062] The recycled aggregate, inorganic polymer slurry and metakaolin before and after strengthening in step 2) of Example 1 were subjected to XRD testing. The results are shown in Figure 1 .Depend on Figure 1 The results show that when the alkaline reaction solution is mixed with the suspension containing aluminosilicate, inorganic polymers are produced. In addition, when the recycled aggregate is immersed in the inorganic polymer slurry, the inorganic polymer can react with the cement mortar to generate CSH gel, which can fill the pores of the recycled aggregate, reduce the water absorption rate of the recycled aggregate, and effectively improve the mechanical strength of the recycled aggregate.

[0063] The recycled aggregates obtained in Examples 1 to 3 and Comparative Examples 1 to 6 were respectively subjected to aggregate performance tests such as crushing value, wherein the original recycled aggregate was further used as a blank group. The specific test results are shown in Table 1.

[0064] Table 1 Performance test results of the reinforced recycled aggregates obtained in Examples 1 to 3 and Comparative Examples 1 to 6

[0065]

[0066]

[0067] The above results show that: by adopting the composite strengthening process of the present invention, the mechanical properties of the obtained recycled aggregate are significantly improved, the water absorption rate is significantly reduced, and the technical indicators meet the requirements of pavement specifications.

[0068] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A method for strengthening recycled coarse aggregate, characterized in that: The following steps are involved: 1) Under negative pressure, the recycled coarse aggregate is added into an inorganic polymer slurry for a soaking treatment, and after being taken out, it is heated and cured, and dried to obtain a reinforced modified recycled aggregate; the inorganic polymer slurry is a geopolymer slurry; 2) Under negative pressure, add the primary reinforced modified recycled aggregate into the waterproof dispersion for secondary immersion treatment. After taking it out, perform secondary heating and curing, and dry it to obtain the reinforced recycled coarse aggregate; The components in the geopolymer slurry and their weight percentages include: 100 parts of water, 10-50 parts of aluminosilicate minerals, and 10-50 parts of a composite alkali; wherein the composite alkali includes sodium hydroxide and sodium silicate; The silicon-aluminum ratio in the geopolymer slurry is 1.0-3.0; The primary heating curing temperature is 40-60°C and the time is more than 8 hours; The secondary heating curing temperature is 40-60°C and the time is more than 8 hours; The crushing value of the reinforced recycled coarse aggregate is 15~20.1%, the Los Angeles abrasion loss is 18~24.8%, the apparent relative density is 2.6~2.7, and the water absorption is 0.5~1.4%.

2. The strengthening method according to claim 1, characterized in that: The recycled aggregate is obtained by crushing, screening, washing and grinding construction waste, and its particle size is greater than 2.36 mm.

3. The strengthening method according to claim 1, characterized in that: The negative pressure condition is 1~5kPa.

4. The strengthening method according to claim 1, characterized in that: The modulus of the sodium silicate is 1.5-3.

5.

5. The strengthening method according to claim 1, characterized in that: The aluminosilicate minerals include one or more of metakaolin, fly ash and slag, and the size thereof is 800-2000 mesh.

6. The strengthening method according to claim 1, characterized in that: The waterproof component in the waterproof dispersion is one or more of ethylene-vinyl acetate copolymer, acrylate, polyurethane, and silicone resin; the solid content is 5-20%.

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