A method for preparing reinforced waste concrete recycled aggregate and recycled concrete.

Abstract

This invention discloses a method for preparing reinforced waste concrete recycled aggregate and recycled concrete. 5-10 parts of waste diatomaceous earth filter aid, 2.5-5 parts of water glass, 50 parts of water, and 85-92.5 parts of ordinary silicate cement are mixed to form a reinforcing slurry. This reinforcing slurry is then coated onto the waste concrete recycled aggregate to obtain the reinforced waste concrete recycled aggregate. (1) Recycled concrete is prepared using 306-360 parts of ordinary silicate cement, 1150-1200 parts of the reinforced waste concrete recycled aggregate as described in claim 5, 700-750 parts of natural river sand, 1.8-2.88 parts of polycarboxylate superplasticizer, 18-54 parts of waste diatomaceous earth filter aid, and 140-180 parts of water. Compared with ordinary waste concrete recycled aggregate, the reinforced waste concrete recycled aggregate has lower water absorption and crushing index, and the modified recycled concrete has better mechanical properties and durability. The method for preparing recycled concrete of this invention has the advantages of reinforcing waste concrete recycled aggregate, improving the mechanical properties of recycled concrete, and enhancing its resistance to chloride ion erosion.

Description

Technical Field

[0001] This invention relates to a method for preparing concrete, and more particularly to a method for preparing reinforced waste concrete recycled aggregate and recycled concrete. Background Technology

[0002] The optimal way to dispose of construction waste concrete is through effective recycling. Crushing waste concrete to obtain recycled aggregate, which is then used to prepare recycled aggregate concrete, is a method of "not discarding" waste concrete and reusing it. However, recycled aggregate from waste concrete has micro-cracks and loose, porous old mortar adhering to its surface. Compared to natural coarse aggregate, it has lower density, lower strength, and higher porosity and water absorption. Therefore, recycled concrete made by directly replacing natural aggregate with recycled aggregate from waste concrete often has poor workability, mechanical properties, and durability, making it difficult to meet the needs of actual engineering projects.

[0003] Based on the above analysis, this invention proposes a method for strengthening recycled aggregate from waste concrete and improving the performance of recycled concrete. Utilizing the characteristic that diatomaceous earth filter aids discarded after a period of use in pharmaceutical factories, food factories, and breweries contain a large amount of amorphous silica, it is used as a silica source. The waste diatomaceous earth is pretreated with water glass, and the pretreated diatomaceous earth solution is mixed with a certain amount of cement to generate hydrated calcium silicate gel. This gel is then used to coat the recycled aggregate from waste concrete, strengthening the surface of the recycled aggregate with old mortar, thereby significantly reducing the water absorption and crushing index of the recycled aggregate. Recycled concrete is prepared using the strengthened recycled aggregate from waste concrete, and waste diatomaceous earth is further added to replace part of the cement as an auxiliary cementitious material. Utilizing the porous structure of diatomaceous earth and its large amount of amorphous silica, a nucleation effect and a certain pozzolanic effect are achieved, allowing for more complete cement hydration in the new mortar of the recycled concrete, thereby improving the mechanical properties and durability of the recycled concrete. Summary of the Invention

[0004] To address the above technical problems, the primary objective of this invention is to provide a method for preparing reinforced waste concrete recycled aggregate and recycled concrete.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A reinforced waste concrete recycled aggregate is prepared by mixing 5-10 parts of waste diatomaceous earth filter aid, 2.5-5 parts of water glass, 50 parts of water, and 85-92.5 parts of ordinary silicate cement to form a reinforcing slurry. The reinforcing slurry is then coated onto the waste concrete recycled aggregate to obtain the reinforced waste concrete recycled aggregate.

[0007] Furthermore, the recycled aggregate from waste concrete is recycled aggregate obtained by crushing and screening construction waste concrete, with a particle size range of 4.75mm to 31.5mm, a micro powder content of no more than 1.9%, an old mortar content of 11.5% to 13.2% by weight, a water absorption rate of no more than 6%, and a crushing value index of no more than 15%.

[0008] Furthermore, the water glass is a solid with a solid content of 100%, a modulus of 1, and is white and granular.

[0009] Furthermore, the waste diatomaceous earth is a powdered material obtained by drying waste diatomaceous earth filter aids used in the food and pharmaceutical industries at 100°C and sieving it. The mesh size ranges from 200 to 400 mesh, and its amorphous SiO2 content is ≥70wt%, organic matter content is ≤11wt%, heavy metal content is <0.005wt%, and moisture content is 10wt% to 30wt%.

[0010] Furthermore, the specific preparation process of the reinforced waste concrete recycled aggregate is as follows:

[0011] (1) Thoroughly wash the recycled aggregate from waste concrete in water to reduce the content of surface mud, sand and fine powder, then soak it thoroughly, and then wipe the surface of the soaked recycled aggregate from waste concrete dry, which can be done with a waste cloth. This yields recycled aggregate from waste concrete in a saturated, surface-dry state.

[0012] (2) Weigh each component of the strengthening slurry according to claim 1 and set aside;

[0013] (3) Put cement and waste diatomaceous earth into a mortar mixer and dry mix evenly. Then add water glass to the weighed water and stir thoroughly to make the solid water glass completely dissolve in the water. Add the water glass solution into the mixer and stir. Stir and mix evenly to obtain the reinforced slurry.

[0014] (4) The prepared reinforcing slurry is poured into the aggregate treatment tank. A screen containing the recycled aggregate obtained in step (1) is repeatedly immersed in the reinforcing slurry to ensure it fully coats the surface of the recycled aggregate. The aggregate is then dried to a saturated surface-dry state to obtain reinforced waste concrete recycled aggregate. The water absorption rate of the reinforced waste concrete recycled aggregate is 2.72%–2.91%, and the crushing index is 14.1%–15.4%. The 28-day cubic compressive strength of the test blocks made from the recycled concrete is 31.7 MPa–53.6 MPa, the splitting tensile strength is 2.37 MPa–5.23 MPa, and the rapid chloride ion penetration coefficient is (2.1–11.5).

[0015] ×10 -12 m 2 / s.

[0016] This invention also discloses a method for preparing recycled concrete, the method comprising the following steps:

[0017] (1) Weigh and prepare materials according to the following proportions: 306-360 parts of ordinary silicate cement, 1150-1200 parts of the reinforced waste concrete recycled aggregate as described in claim 5, 700-750 parts of natural river sand, 1.8-2.88 parts of polycarboxylate superplasticizer, 18-54 parts of waste diatomaceous earth filter aid, and 140-180 parts of water.

[0018] (2) Put the cement and waste diatomaceous earth into the mixer and mix until fully combined;

[0019] (3) Mix the polycarboxylate superplasticizer with the weighed water evenly and pour half of the mixture into the mixer, then add it to the mixture from step (2).

[0020] Mix the dry powders together thoroughly;

[0021] (4) Add the remaining water and polycarboxylate superplasticizer mixture, the reinforced waste concrete recycled aggregate, and natural river sand into a mixer and mix thoroughly to obtain a concrete mixture.

[0022] (5) The concrete mixture obtained in step (4) is molded and demolded one day later. It is then placed in a standard curing room for curing until the specified age to obtain the recycled concrete.

[0023] Furthermore, the cement is PO 42.5 type ordinary Portland cement; the waste diatomaceous earth is a powdered material obtained by drying waste diatomaceous earth filter aids used in the food and pharmaceutical industries at 100°C and sieving, with a mesh size range of 200 to 400 mesh, an amorphous SiO2 content ≥70wt%, an organic matter content ≤11wt%, a heavy metal content <0.005wt%, and a moisture content of 10wt% to 30wt%.

[0024] The mechanism of this invention is as follows: the main component of waste diatomaceous earth filter aid is amorphous silicon dioxide, which can activate the silicon dioxide in waste diatomaceous earth in water glass solution, generating a large amount of SiO4 in the solution. 2- After adding cement to supplement the calcium source, ions can generate more hydrated calcium silicate gel. After surface treatment of the recycled aggregate in the above slurry, the hydrated calcium silicate gel will adhere and bond to the old mortar on the surface of the recycled aggregate, filling the pores and micro-cracks on the surface of the old mortar, thus improving the performance of the old mortar. On the other hand, when preparing recycled aggregate concrete, after adding diatomaceous earth to replace cement, the diatomaceous earth will exert a pozzolanic effect, undergoing a secondary hydration reaction with the cement hydration product CH, generating more CSH; diatomaceous earth can act as a nucleation site for cement hydration products, thereby promoting hydration and generating more CSH.

[0025] The beneficial effects of this invention are as follows: The waste diatomaceous earth used in this invention has a certain pozzolanic activity and possesses the potential to be dissolved and activated by strong alkalis. Using waste diatomaceous earth as a silicon source, it is pretreated with water glass solution to convert it into sodium silicate solution. The pretreated diatomaceous earth solution is then mixed with a certain amount of cement to generate hydrated calcium silicate gel. This gel is used to coat recycled waste concrete aggregate with old mortar to strengthen the surface of the recycled waste concrete aggregate, significantly reducing the water absorption and crushing index of the recycled waste concrete aggregate. Compared with ordinary recycled waste concrete aggregate, the strengthened recycled waste concrete aggregate has lower water absorption and crushing index, and the modified recycled concrete has better mechanical properties and durability. In the recycled concrete preparation method of this invention, adding waste diatomaceous earth during the mixing of recycled concrete allows it to exert a nucleation effect and a certain pozzolanic activity during cement hydration, generating more hydration products. This method has the advantages of strengthening recycled waste concrete aggregate, improving the mechanical properties and resistance to chloride ion erosion of recycled concrete.

[0026] Compared with the prior art, the present invention also has the following advantages:

[0027] (1) This invention uses waste diatomite as a raw material for the treatment of waste concrete recycled aggregate, and at the same time as a concrete admixture to modify recycled concrete, making full use of the potential value of waste diatomite, turning waste into treasure, which is in line with my country's sustainable development policy.

[0028] (2) The recycled aggregate and recycled concrete performance improvement process involved in this invention has low cost and significantly improves the mechanical and durability properties of recycled aggregate concrete while reducing the amount of cement used, thereby expanding the use of recycled aggregate in high-performance concrete. Attached Figure Description

[0029] Figure 1 This is a flowchart of the method for preparing recycled aggregates and recycled concrete from reinforced waste concrete.

[0030] Figure 2 This is the SE diagram showing the effect of diatomaceous earth incorporating pozzolanic material;

[0031] Figure 3 This is a SE diagram showing the formation of dense hydration products from diatomaceous earth in the slurry under strong alkali activation. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to embodiments, such as... Figure 1 As shown, a method for preparing reinforced waste concrete recycled aggregate and recycled concrete is disclosed. The method for preparing the reinforced waste concrete recycled aggregate is as follows:

[0033] (1) Wash the recycled coarse aggregate of waste concrete thoroughly in water to reduce the content of mud and fine powder on the surface, then soak it for 1 day, and then wipe the surface of the soaked recycled aggregate of waste concrete dry to obtain the recycled aggregate of waste concrete in a saturated surface-dry state.

[0034] (2) Weigh each component of the strengthening liquid according to the example;

[0035] (3) Add cement and waste diatomaceous earth filter aid into the mortar mixer and dry mix evenly. Then add water glass to the weighed water and stir thoroughly to make the solid water glass completely dissolve in the water. Add the water glass solution into the mixer and stir. Stir and mix evenly to obtain the reinforced slurry.

[0036] (4) Pour the prepared reinforcing slurry into the aggregate treatment tank, and immerse the screen containing saturated surface-dry recycled coarse aggregate in the slurry multiple times to ensure that the reinforcing slurry fully coats the surface of the recycled coarse aggregate. Then, dry the aggregate to a saturated surface-dry state to obtain reinforced waste concrete recycled aggregate.

[0037] Furthermore, the method for preparing recycled concrete is as follows:

[0038] (1) Weigh and prepare each component of recycled concrete according to the example;

[0039] (2) Put the cement and waste diatomaceous earth into the mixer and mix for 1 minute;

[0040] (3) Mix the water-reducing agent with the weighed water evenly and pour half of the mixed solution into the mixer, and mix it with the dry powder for 1 minute;

[0041] (4) Add the remaining water and water-reducing agent mixture, reinforced waste concrete recycled aggregate, and sand into the mixer and stir for 2 minutes to obtain concrete mixture.

[0042] (5) The obtained freshly mixed recycled concrete mixture is molded, and the mold is removed one day later. It is then placed in a standard curing room for curing until the specified age to obtain the finished recycled aggregate concrete.

[0043] Example 1:

[0044] To prepare recycled concrete, the following raw material components were prepared by weight: 324 parts of PO 42.5 type ordinary Portland cement, 1154 parts of recycled aggregate from reinforced waste concrete, 708 parts of natural river sand, 36 parts of waste diatomaceous earth, 180 parts of water, and 2.52 parts of polycarboxylate superplasticizer. The raw material components for preparing the reinforced grout were: 50 parts of water, 92.5 parts of PO 42.5 type ordinary Portland cement, 5 parts of waste diatomaceous earth, and 2.5 parts of water glass. The waste diatomaceous earth used in this example had a SiO2 content of 94.07 wt%, an average particle size of 32.26 μm, and a density of 2060 kg / m³. 3Specific surface area 488.1 m² 2 / kg. The final recycled concrete was prepared, and the performance test results are shown in Table 1.

[0045] Example 2:

[0046] To prepare recycled concrete, the following raw material components were prepared by weight: 324 parts of PO 42.5 type ordinary Portland cement, 1154 parts of recycled aggregate from reinforced waste concrete, 708 parts of natural river sand, 36 parts of waste diatomaceous earth, 180 parts of water, and 2.52 parts of polycarboxylate superplasticizer. The raw material components for preparing the reinforced grout were: 50 parts of water, 85 parts of PO 42.5 type ordinary Portland cement, 10 parts of waste diatomaceous earth, and 5 parts of water glass. The waste diatomaceous earth used in this example had a SiO2 content of 94.07 wt%, an average particle size of 32.26 μm, and a density of 2060 kg / m³. 3 Specific surface area 488.1 m² 2 / kg. The final recycled concrete was prepared, and the performance test results are shown in Table 1.

[0047] Example 3:

[0048] To prepare recycled concrete, the following raw material components were prepared by weight: 342 parts of PO 42.5 type ordinary Portland cement, 1154 parts of recycled aggregate from reinforced waste concrete, 708 parts of natural river sand, 18 parts of waste diatomaceous earth, 180 parts of water, and 2.16 parts of polycarboxylate superplasticizer. The raw material components for preparing the reinforced grout were: 50 parts of water, 92.5 parts of PO 42.5 type ordinary Portland cement, 5 parts of waste diatomaceous earth, and 2.5 parts of water glass. The waste diatomaceous earth used in this example had a SiO2 content of 94.07 wt%, an average particle size of 32.26 μm, and a density of 2060 kg / m³. 3 Specific surface area 488.1 m² 2 / kg. The final recycled concrete was prepared, and the performance test results are shown in Table 1.

[0049] Example 4:

[0050] To prepare recycled concrete, the following raw material components were prepared by weight: 306 parts of PO 42.5 type ordinary Portland cement, 1154 parts of recycled aggregate from reinforced waste concrete, 708 parts of natural river sand, 54 parts of waste diatomaceous earth, 180 parts of water, and 2.88 parts of polycarboxylate superplasticizer. The raw material components for preparing the reinforced grout were: 50 parts of water, 92.5 parts of PO 42.5 type ordinary Portland cement, 5 parts of waste diatomaceous earth, and 2.5 parts of water glass. The waste diatomaceous earth used in this example had a SiO2 content of 94.07 wt%, an average particle size of 32.26 μm, and a density of 2060 kg / m³. 3 Specific surface area 488.1 m² 2 / kg. The final recycled concrete was prepared, and the performance test results are shown in Table 1.

[0051] Comparative Example 1:

[0052] In this comparative example, the recycled aggregate from waste concrete was not pretreated with grouting liquid, and the recycled aggregate concrete was not mixed with diatomaceous earth.

[0053] To prepare recycled concrete, the following raw material components were prepared in parts by weight: 360 parts of PO 42.5 ordinary Portland cement, 1154 parts of untreated recycled aggregate, 708 parts of natural river sand, 180 parts of water, and 1.8 parts of polycarboxylate superplasticizer. The recycled concrete was then prepared, and the performance test results are shown in Table 1.

[0054] Comparative Example 2:

[0055] In this comparative example, the recycled aggregate from waste concrete was not pretreated with grouting liquid, and 10% diatomaceous earth was added to the recycled concrete.

[0056] To prepare recycled concrete, the following raw material components were prepared by weight: 324 parts of PO 42.5 type ordinary Portland cement, 1154 parts of untreated recycled aggregate, 708 parts of natural river sand, 36 parts of waste diatomaceous earth, 180 parts of water, and 2.52 parts of polycarboxylate superplasticizer. The waste diatomaceous earth used in this comparative example had a SiO2 content of 94.07 wt%, an average particle size of 32.26 μm, and a density of 2060 kg / m³. 3 Specific surface area 488.1 m² 2 / kg. The final recycled concrete was prepared, and the performance test results are shown in Table 1.

[0057] Comparative Example 3:

[0058] In this comparative example, the recycled aggregate from waste concrete was pretreated with a coating liquid, and the recycled aggregate concrete was not mixed with diatomaceous earth.

[0059] To prepare recycled concrete, the following raw material components were prepared by weight: 360 parts of PO 42.5 type ordinary Portland cement, 1154 parts of recycled aggregate from reinforced waste concrete, 708 parts of natural river sand, 180 parts of water, and 1.8 parts of polycarboxylate superplasticizer. The raw material components for preparing the reinforced grout were: 50 parts of water, 92.5 parts of PO 42.5 type ordinary Portland cement, 5 parts of waste diatomaceous earth, and 2.5 parts of water glass. The waste diatomaceous earth used in this comparative example had a SiO2 content of 94.07 wt%, an average particle size of 32.26 μm, and a density of 2060 kg / m³. 3 Specific surface area 488.1 m² 2 / kg. Finally, recycled concrete was prepared. Performance test results are shown in Table 1.

[0060] The water absorption rate and crushing index of recycled aggregate from waste concrete were determined according to the standard "Recycled Coarse Aggregate for Concrete" (GB / T 25177-2010); the compressive strength and splitting tensile strength of the modified recycled concrete obtained in Examples 1-4 and Comparative Examples 1-3 were determined according to the test methods specified in the standard "Test Methods for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50081-2009); and the durability index of the concrete was determined according to the standard "Test Methods for Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082-2009). The test results are shown in Table 1.

[0061] Table 1. Performance indicators of recycled aggregates and recycled concrete in the examples and control group.

[0062]

[0063] As shown in Table 1, the compressive strength and splitting tensile strength of the recycled concrete obtained in Examples 1-4 and Comparative Examples 2-3 are significantly improved, and the rapid chloride ion diffusion coefficient is reduced. The recycled concrete of this invention exhibits excellent performance. (Appendix) Figure 2 This indicates that when diatomaceous earth is incorporated into recycled concrete, CSH gel, potentially formed through a secondary hydration reaction between amorphous silica in the diatomaceous earth and CH produced during cement hydration, adheres to the diatomaceous earth walls. This gel exerts a pozzolanic effect, making the overall spatial structure more compact. Furthermore, the porous structure of diatomaceous earth provides more favorable sites for CSH growth, thus promoting cement hydration through a nucleation effect. (See attached image) Figure 3 This indicates that after the recycled aggregate from waste concrete is treated in the strengthening slurry, the strengthening slurry enters the surface of the old mortar. The diatomaceous earth in the strengthening slurry reacts under strong alkali activation to generate dense hydration products that adhere to the surface of the diatomaceous earth. Therefore, after the strengthening slurry hardens, it will form a dense protective layer on the surface of the recycled aggregate from waste concrete. Thus, after the recycled aggregate from waste concrete is coated with this strengthening slurry, its water absorption rate and crushing index can be effectively reduced.

[0064] The above provides a detailed description of the recycled concrete and its preparation method provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

[0065] The above content is only used to illustrate the technical solution of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing reinforced recycled aggregate from waste concrete, characterized in that: A strengthening slurry is prepared by mixing 5-10 parts of waste diatomaceous earth filter aid, 2.5-5 parts of water glass, 50 parts of water, and 85-92.5 parts of ordinary silicate cement. The strengthening slurry is then coated onto the waste concrete recycled aggregate to obtain the strengthened waste concrete recycled aggregate. The specific preparation process of the reinforced waste concrete recycled aggregate is as follows: (1) Wash the waste concrete recycled aggregate thoroughly in water to reduce the content of mud and powder on the surface, then soak it thoroughly, and then wipe the surface of the soaked waste concrete recycled aggregate dry to obtain saturated surface-dry waste concrete recycled aggregate. (2) Weigh each component of the strengthening slurry according to the predetermined weight and set aside; (3) Put cement and waste diatomaceous earth into a mortar mixer and dry mix evenly. Then add water glass to the weighed water and stir thoroughly to dissolve the solid water glass completely in the water. Add the water glass solution into the mixer and stir. Stir and mix evenly to obtain the reinforced slurry. (4) Pour the prepared reinforcing slurry into the aggregate treatment tank, and immerse the reinforcing slurry multiple times on the screen containing the recycled aggregate obtained in step (1) so that the reinforcing slurry fully coats the surface of the recycled aggregate. Then, dry the aggregate to a saturated surface-dry state to obtain reinforced waste concrete recycled aggregate.

2. The method for preparing reinforced waste concrete recycled aggregate according to claim 1, characterized in that: The recycled aggregate from waste concrete is recycled aggregate obtained by crushing and screening construction waste concrete. The particle size range is 4.75mm to 31.5mm, the micro powder content is not higher than 1.9%, the old mortar content by weight is 11.5% to 13.2%, the water absorption rate is not higher than 6%, and the crushing value index is not higher than 15%.

3. The method for preparing reinforced waste concrete recycled aggregate according to claim 2, characterized in that: The water glass is a solid with a solid content of 100% and a modulus of 1, and is white and granular.

4. The method for preparing reinforced waste concrete recycled aggregate according to claim 3, characterized in that: The waste diatomaceous earth is a powdered material obtained by drying waste diatomaceous earth filter aids used in the food and pharmaceutical industries at 100°C and sieving it. The mesh size ranges from 200 to 400 meshes. Its amorphous SiO2 content is ≥70wt%, organic matter content is ≤11wt%, heavy metal content is <0.005wt%, and moisture content is 10wt% to 30wt%.

5. A method for preparing recycled concrete, characterized in that: The preparation method includes the following steps: (1) Weigh and prepare materials according to the following proportions: 306-360 parts of ordinary silicate cement, 1150-1200 parts of the reinforced waste concrete recycled aggregate as described in claim 4, 700-750 parts of natural river sand, 1.8-2.88 parts of polycarboxylate superplasticizer, 18-54 parts of waste diatomaceous earth filter aid, and 140-180 parts of water. (2) Put the cement and waste diatomaceous earth into the mixer and mix until fully combined; (3) Mix the polycarboxylate superplasticizer with the weighed water evenly and pour half of the mixed solution into the mixer, and mix it thoroughly with the dry powder from step (2); (4) Add the remaining water and polycarboxylate superplasticizer solution, the reinforced waste concrete recycled aggregate, and natural river sand into a mixer and mix thoroughly to obtain a concrete mixture. (5) The concrete mixture obtained in step (4) is molded and demolded one day later. It is then placed in a standard curing room for curing until the specified age to obtain the recycled concrete.

6. The method for preparing recycled concrete according to claim 5, characterized in that: The cement is P.O 42.5 type ordinary Portland cement; the waste diatomaceous earth is a powdered material obtained by drying waste diatomaceous earth filter aids used in the food and pharmaceutical industries at 100℃ and sieving, with a mesh size range of 200~400 mesh, an amorphous SiO2 content ≥70wt%, an organic matter content ≤11wt%, a heavy metal content <0.005wt%, and a moisture content of 10wt%~30wt%.

Images