A method for producing recycled concrete using waste slurry and recycled water from a mixing plant and recycled concrete

Abstract

The application discloses a method for preparing recycled concrete from waste slurry and recycled water in a mixing station, wherein the recycled concrete comprises the following components in parts by weight: 150-220 parts of waste slurry, 110-180 parts of cement, 1-4 parts of nano calcium carbonate, 30-60 parts of coal cinder, 20-40 parts of silica fume, 800-1100 parts of fine aggregate, 700-1000 parts of coarse aggregate, 0.1-0.5 parts of a retarder, 5-12 parts of an additive, 25-60 parts of recycled water and 80-115 parts of water. The method of the application reuses the waste slurry and recycled water in the mixing station, improves the cementitious activity of the concrete by combining the hydration micro-mechanism of the components, endows the recycled concrete with higher strength, and is green and low-carbon in the preparation of the recycled concrete, thereby fully responding to the 'double carbon' policy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building materials, in particular to a method for preparing recycled concrete by using waste slurry and recycled water of a mixing station and the prepared recycled concrete. BACKGROUND

[0002] In recent years, the continuous rise of infrastructure projects in China has promoted the development of the commercial mixing station industry. During the production and use of commercial concrete, a large amount of waste slurry and recycled water is generated, which mainly comes from the cleaning of mixers, transport vehicles, transport buckets, and site cleaning. According to research reports, about 0.03 m 3 of wastewater is generated per cubic meter of concrete produced, and the total wastewater generated by concrete mixing stations nationwide will exceed 0.75 billion m 3 per year. The alkalinity of this wastewater is high, and it cannot be directly discharged. It needs to be recovered and stacked first and then treated, which requires a certain amount of manpower, material resources, and financial resources.

[0003] There are still a certain amount of unhydrated cement particles, cement hydration products, mineral admixtures, and residual admixtures in the waste slurry. With the in-depth study of construction solid waste, it is found that the waste slurry of the mixing station can also be used as part of the concrete for recycling.

[0004] However, the mixing station recycled water contains a large amount of soluble and insoluble substances and a large amount of chloride ions, which will inevitably affect the concrete. The activity of the products in the waste slurry is low, and direct use will not be able to fully play its cementitious role. Therefore, effective measures need to be taken to solve the above problems. The solution to this problem not only effectively alleviates the shortage of resources and reduces environmental hazards, but also reduces carbon emissions and contributes to the "double carbon" goal. SUMMARY

[0005] In order to achieve the above technical purpose, the present application provides a method for preparing recycled concrete by using waste slurry and recycled water of a mixing station and the recycled concrete prepared by the method. The technical purpose of the present application is achieved by the following technical scheme:

[0006] The present application first provides a method for preparing recycled concrete by using waste slurry and recycled water of a mixing station, which comprises the following implementation steps:

[0007] Step 1: Put the waste slurry into an oven for drying to form a dry intermediate, then spray recycled water on the surface of the dry intermediate, so that the water content of the dry intermediate after spraying reaches 3% to 4%, forming a water-containing intermediate;

[0008] Step 2: the aqueous intermediate formed by the waste slurry is placed in a carbonization box for carbonization, and the carbonization requires a CO2 concentration of 98%±2%, a relative humidity of 80%±2%, a temperature of 22℃±2℃, and a carbonization time of 24h;

[0009] Step 3: then step 2 is repeated to obtain the final carbonized waste slurry after carbonization;

[0010] Step 4: the waste slurry after carbonization obtained in step 3 is placed in a ball mill to obtain waste slurry powder with a particle size of not more than 60 microns;

[0011] Step 5: 0.1-0.5 parts of a retarder is added to 25-60 parts of recycled water collected from the sedimentation tank of the mixing station, ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution A;

[0012] Step 6: 1-4 parts of nano calcium carbonate is added to 80-115 parts of water, ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution B;

[0013] Step 7: 150-220 parts of waste slurry powder, 110-180 parts of cement, 800-1100 parts of fine aggregate, 700-1000 parts of coarse aggregate, 30-60 parts of coal cinder, and 20-40 parts of silica fume are first placed in a mixing pot for stirring, then the mixed solution A and the mixed solution B are added respectively, and finally 5-12 parts of an additive is added, the stirrer is uniformly stirred at a constant speed for 3 to 5 minutes to obtain the recycled concrete.

[0014] In the method for preparing recycled concrete from waste slurry and recycled water in a mixing station according to the application, the waste slurry in step 1 is taken from the bottom of the sedimentation tank, the waste slurry does not contain coarse aggregate, and the waste slurry taken is in the form of a solid agglomerate with a pH of 11.0.

[0015] In the method for preparing recycled concrete from waste slurry and recycled water in a mixing station according to the application, further, the recycled water in step 1 is the upper or middle layer water in the sedimentation tank that has been standing for 24 hours or more, has a pH of 12.2, a soluble matter content of ≤3000mg / L, and an insoluble matter content of ≤3000mg / L, wherein:

[0016] Ca 2+ ≤880mg / L,

[0017] Na + ≤160mg / L,

[0018] K + ≤180mg / L,

[0019] Cl - ≤250mg / L,

[0020] SO4 2 ≤90mg / L.

[0021] The application also provides the recycled concrete prepared by the preparation method.

[0022] 150-220 parts of waste slurry;

[0023] 110-180 parts of cement;

[0024] 1-4 parts of nano calcium carbonate;

[0025] 30-60 parts of coal cinder;

[0026] 20-40 parts of silica fume;

[0027] 800-1100 parts of fine aggregate;

[0028] 700-1000 coarse aggregate;

[0029] 0.1-0.5 parts of retarder;

[0030] 5-12 parts of additive;

[0031] 25-60 parts of recycled water;

[0032] 80-115 parts of water.

[0033] In the recycled concrete prepared by waste slurry and recycled water in the mixing station, the retarder is boric acid, potassium phosphate and glycerol, and the ratio is 6-5:4-3:2-1.

[0034] In the recycled concrete prepared by waste slurry and recycled water in the mixing station, the cement is P. II 52.5 Portland cement, the total mass ratio of silicon dioxide, calcium oxide and aluminum oxide in the cement is not less than 80%, the specific surface area of the cement is 380 m 2 / g, the apparent density is 3020 kg / m 3 , and the 28d strength is greater than or equal to 55 MPa.

[0035] In the recycled concrete prepared by waste slurry and recycled water in the mixing station, the fine aggregate is river sand or machine-made sand, the fineness modulus is 2.5, the bulk density is 1400 kg / m 3 , the apparent density is 2654 kg / m 3 , the stone powder content is 1.8%, and the water absorption is 1.4%.

[0036] In the recycled concrete prepared by waste slurry and recycled water in the mixing station, the coarse aggregate is one of basalt, limestone and andesite gravel with a particle size of 5-20 mm and a continuous gradation, the crushing index is 4.7%, and the dry apparent density is 2700-2950 kg / m3 , the bulk density is 1430kg / m 3 .

[0037] In the recycled concrete prepared from the waste slurry of a mixing station and recycled water, the average particle size of the nano calcium carbonate is 40±5nm, the density is 2.46g·cm -3 , the specific surface area is 480m 2 / g, the pH is 9.0, and the purity is ≥98%.

[0038] In the recycled concrete prepared from the waste slurry of a mixing station and recycled water, the coal cinder is a coal cinder discharged by a thermal power plant, is sieved through a 190-mesh sieve after ball milling, and mainly contains 59.6% SiO2, 20.45% Al2O3, 5.84% Fe2O3 and 3.21% CaO.

[0039] In the recycled concrete prepared from the waste slurry of a mixing station and recycled water, the composition of the silica fume contains 95.33% SiO, 0.43% Al2O3, 0.43% Fe2O3 and 0.20% CaO, the density is 2.15g / cm 3 , the specific surface area is 22m 2 / g, and the loss on ignition is 0.67%.

[0040] In the recycled concrete prepared from the waste slurry of a mixing station and recycled water, the additive is a polycarboxylic acid type high-performance water reducing agent, the water reducing rate is >25%, the solid content is 23%, and the density is 1030kg / m 3 .

[0041] Based on the above technical solution, compared with the prior art, the beneficial effects of the present application are as follows:

[0042] 1. In the recycled concrete of the present application, nano calcium carbonate is added. Due to the surface effect, the surface stability of nano particles is poor, and ultrasonic dispersion is used for dispersion treatment, which is beneficial to further play the role of nano. Nano calcium carbonate can improve the nucleation site of hydration products, can fill the pores between cement particles, and can improve the interface transition zone of cement-based materials. However, nano calcium carbonate hydrates too fast in the early stage, which is not conducive to the complete hydration in the later stage. The addition of a retarder solves the problem of fast early hydration of cement slurry. Secondly, nano calcium carbonate promotes the generation of C-S-H, and in this process, C-S-H gel can physically adsorb a large amount of chloride ions in recycled water, reducing the influence of free chloride ions in cement slurry on the performance of concrete.

[0043] 2. In the preparation of recycled concrete of the present application, recycled water is used, which contains abundant calcium ions, and the waste slurry contains a large amount of hydration products such as calcium hydroxide, C-S-H, ettringite, etc. After spraying with recycled water, carbonation can promote the formation of more calcium carbonate, gypsum and other products. The main form of generated calcium carbonate is calcite. The carbonized micro powder after ball milling has high cementitious activity. These products can provide nucleation sites in the cement-based material, and further hydration reaction can generate hydrated calcium aluminate, C-S-H, etc., improving the utilization efficiency of waste slurry. And the carbonation process will consume a large amount of free water, providing an appropriate amount of free water after spraying on the surface of the waste slurry block, which can deepen the carbonation depth.

[0044] 3. The coal cinder and silica fume used in the recycled concrete of the present application are high-activity silico-alumina materials containing SiO2, Al2O3 and a small amount of CaO, which can be used as an alkali activator for waste slurry. The recycled water has high alkalinity, which improves the alkaline environment of the cement-based material. The amorphous silicon and aluminum gel inside the coal cinder and silica fume can be hydrated with calcium hydroxide, which is beneficial to the further activation of waste slurry and produces certain hydraulicity.

[0045] 4. The materials used in the present application are prepared by reasonable mix proportion design and preparation method. The prepared slurry can be used to prepare various types of recycled concrete, etc., providing an effective utilization way for the large amount of waste slurry and recycled water produced by the mixing station, relieving resource shortage, reducing environmental pollution, and contributing to the corresponding double carbon policy. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a flowchart of the method for preparing recycled concrete from waste slurry and recycled water of the mixing station. DETAILED DESCRIPTION

[0047] The technical solutions of the present application will be further described below in combination with specific embodiments:

[0048] The present application provides a recycled concrete prepared from waste slurry and recycled water of a mixing station, which comprises materials configured in weight fractions as follows:

[0049] 150-220 parts of waste slurry, 110-180 parts of cement, 1-4 parts of nano calcium carbonate, 30-60 parts of coal cinder, 20-40 parts of silica fume, 800-1100 parts of fine aggregate, 700-1000 parts of coarse aggregate, 0.1-0.5 parts of retarder, 5-12 parts of additive, 25-60 parts of recycled water, and 80-115 parts of water.

[0050] The waste slurry is taken from the bottom of the sedimentation tank in the mixing station and does not contain coarse aggregate. The waste slurry is in the form of solid agglomeration, and the pH is 11.0.

[0051] The recovered water is the upper or middle layer water in the sedimentation tank after standing for 24 hours or more, with a pH of 12.2, a soluble matter content of ≤3000 mg / L, an insoluble matter content of ≤3000 mg / L, wherein Ca2+ is ≤880 mg / L, Na+ is ≤160 mg / L, K+ is ≤180 mg / L, Cl- is ≤250 mg / L, and SO42- is ≤90 mg / L, meeting the “Water Standard for Concrete” (JGJ63-2006). The recovered water contains rich calcium ions, and the waste slurry contains a large amount of hydration products such as calcium hydroxide, C-S-H, ettringite, etc.

[0052] The cement is P. II 52.5 Portland cement, the total mass percentage of silicon dioxide, calcium oxide and aluminum oxide in the cement is not less than 80%, the specific surface area of the cement is 380 m 2 / g, the apparent density is 3020 kg / m 3 , and the 28d strength is ≥55 MPa.

[0053] The fine aggregate is river sand or machine-made sand, the fineness modulus is 2.5, the bulk density is 1400 kg / m 3 , the apparent density is 2654 kg / m 3 , the stone powder content is 1.8%, and the water absorption rate is 1.4%.

[0054] The coarse aggregate is one of continuous gradation basalt, limestone and andesite gravel with a particle size of 5-20 mm, the crushing index is 4.7%, the dry apparent density is 2700-2950 kg / m 3 , and the bulk density is 1430 kg / m 3 .

[0055] The average particle size of the nano calcium carbonate (CaCO3) is 40±5 nm, the density is 2.46 g·cm -3 , the specific surface area is 480 m 2 ·g -1 , the pH is 9.0, and the purity is ≥98%. Due to the surface effect, the surface stability of the nano particles is poor, so it is necessary to disperse the nano particles by ultrasonic dispersion, which is beneficial to further play the nano effect. In the recycled concrete, the nano calcium carbonate can improve the nucleation site of the hydration product, can fill the pores between the cement particles, and can improve the interfacial transition zone of the cement-based material.

[0056] The added nano calcium carbonate is too fast in the early hydration reaction, which is not conducive to the later hydration. The addition of the retarder solves the problem of too fast early hydration of the cement slurry. In the present application, the retarder is a mixture of boric acid, potassium phosphate and glycerol, and the mixing ratio is 6-5:4-3:2-1.

[0057] Coal slag is coal slag discharged by thermal power, and is sieved through a 190-mesh screen after ball milling, and mainly comprises 59.6% SiO2, 20.45% Al2O3, 5.84% Fe2O3 and 3.21% CaO. The composition of silica fume comprises 95.33% SiO, 0.43% Al2O3, 0.43% Fe2O3 and 0.20% CaO, and the density is 2.15 g / cm 3 , the specific surface area is 22 m 2 / g, and the loss on ignition is 0.67%. The coal slag and the silica fume are high-activity siliceous and aluminous materials, contain SiO2, Al2O3 and a small amount of CaO, can be used as alkali activators of waste slurry, the recycled water has high alkalinity, the alkalinity of the cement-based material is improved, the amorphous silicon and aluminum gel in the coal slag and the silica fume can be hydrated with calcium hydroxide, and the waste slurry is further activated to have certain hydraulicity.

[0058] The admixture is a polycarboxylic acid type high-performance water reducing agent, has a water reducing rate of >25%, a solid content of 23%, and a density of 1030 kg / m 3 .

[0059] The application further provides a method for preparing the recycled concrete.

[0060] Step 1: the waste slurry is placed into an oven to be dried to form a dry intermediate, and then recycled water is sprayed on the four peripheral surfaces of the dry intermediate so that the water content of the dry intermediate after spraying is 3%-4%, and a water-containing intermediate is formed;

[0061] Step 2: the water-containing intermediate formed by the waste slurry is placed into a carbonization box to be carbonized, and the carbonization is required to be performed at a CO2 concentration of 98%±2%, a relative humidity of 80%±2% and a temperature of 22℃±2℃ for 24 hours;

[0062] Step 3: then, step 2 is repeated to obtain the finally carbonized waste slurry after carbonization;

[0063] Step 4: the waste slurry after carbonization obtained in step 3 is placed into a ball mill to obtain waste slurry powder with a particle size of not greater than 60 microns;

[0064] Step 5: 0.1-0.5 parts of a retarder are added into 25-60 parts of recycled water collected from a sedimentation tank of a stirring station, and ultrasonic dispersion is performed for 2 minutes to obtain a mixed liquid A;

[0065] Step 6: 1-4 parts of nano calcium carbonate are added into 80-115 parts of water, and ultrasonic dispersion is performed for 2 minutes to obtain a mixed liquid B;

[0066] Step 7: 150-220 parts of the waste slurry micro powder, 110-180 parts of cement, 800-1100 parts of fine aggregate, 700-1000 parts of coarse aggregate, 30-60 parts of coal cinder, 20-40 parts of silica fume are put into a stirring pot for stirring, then mixed liquid A and mixed liquid B are added respectively, finally 5-12 parts of an additive is added, and the stirring machine is stirred at a uniform speed for 3 to 5 minutes to obtain the recycled concrete.

[0067] In steps 1 to 3, the waste slurry is sprayed with recycled water and then carbonized, which can promote the formation of more calcium carbonate, gypsum and other products, and the generated calcium carbonate is mainly calcite, and the carbonized micro powder after ball milling has high cementitious activity, and these products can provide crystal nucleus sites in the cement-based material, and the waste slurry can be used again to improve the efficiency of the waste slurry. And the carbonization process consumes a large amount of free water, which provides an appropriate amount of free water after spraying on the surface of the waste slurry block, which can deepen the carbonization depth.

[0068] In step 6, nano calcium carbonate is added, and due to the surface effect, the surface stability of nano particles is poor, so ultrasonic dispersion is used for dispersion treatment, which is beneficial to further play the role of nano. Nano calcium carbonate can improve the nucleation site of the hydration product, can fill the pores between the cement particles, and can improve the interface transition zone of the cement-based material. However, the nano calcium carbonate reacts too fast in the early stage of hydration, which is not conducive to the complete hydration in the later stage. The retarder added in step 5 is used to solve the problem of too fast hydration of the cement slurry in the early stage. Secondly, nano calcium carbonate promotes the generation of C-S-H, and in this process, a large amount of chloride ions in the recycled water can be physically adsorbed by C-S-H gel, reducing the influence of free chloride ions in the cement slurry on the performance of the concrete.

[0069] In order to better understand the present application, the following examples and comparative examples are provided:

[0070] Example 1

[0071] This embodiment is a specific method for preparing recycled concrete, which comprises the following steps:

[0072] Step 1: The waste slurry is put into an oven for drying to form a dry intermediate, and then recycled water is sprayed on the surface of the dry intermediate to make the water content of the dry intermediate after spraying reach 3%-4%;

[0073] Step 2: The waste slurry is put into a carbonization box for carbonization, and the carbonization requires CO2 concentration of 98%, relative humidity of 80%, temperature of 22℃, and carbonization time of 24h;

[0074] Step 3: Then step 2 is repeated to obtain the final carbonized waste slurry.

[0075] Step 4: Put the waste slurry obtained in step 3 into a ball mill to obtain waste slurry micro powder with particle size not greater than 60 microns, and take 180 parts.

[0076] Step 5: 0.3 parts of a retarder is added to 32 parts of recycled water collected from a settling tank of a mixing station, ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution A.

[0077] Step 6: 2.1 parts of nano calcium carbonate is added to 100 parts of water, ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution B.

[0078] Step 7: 180 parts of waste slurry micro powder, 140 parts of cement, 900 parts of fine aggregate, 800 parts of coarse aggregate, 40 parts of coal cinder, and 25 parts of silica fume are put into a mixing pot for stirring, then the mixed solution A and the mixed solution B are added respectively, finally 6 parts of an additive is added, and uniform stirring is performed for 5 minutes to obtain high-performance recycled concrete.

[0079] Comparative Example 1

[0080] Step 1: The waste slurry is put into an oven at 80℃ for drying, and the time is 48h.

[0081] Step 2: The dried waste slurry is put into a ball mill to obtain waste slurry micro powder with particle size not greater than 60 microns, and 180 parts is taken.

[0082] Step 3: 0.3 parts of a retarder is added to 32 parts of recycled water collected from a settling tank of a mixing station, ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution A.

[0083] Step 4: 2.1 parts of nano calcium carbonate is added to 100 parts of water, ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution B.

[0084] Step 5: 180 parts of waste slurry micro powder, 140 parts of cement, 900 parts of fine aggregate, 800 parts of coarse aggregate, 40 parts of coal cinder, and 25 parts of silica fume are put into a mixing pot for stirring, then the mixed solution A and the mixed solution B are added respectively, finally 6 parts of an additive is added, and uniform stirring is performed for 5 minutes to obtain high-performance recycled concrete.

[0085] Comparative Example 2

[0086] Step 1: The waste slurry is put into an oven for drying to form a dry intermediate, then recycled water is sprayed on the surface of the dry intermediate, so that the water content of the dry intermediate after spraying is 3% to 4%;

[0087] Step 2: The waste slurry is put into a carbonization box for carbonization, and the carbonization is required to be performed at CO2 concentration of 98%, relative humidity of 80%, and temperature of 22℃ for 24h.

[0088] Step 3: Then step 2 is repeated to obtain the final carbonized waste slurry.

[0089] Step 4: Put the waste slurry obtained in step 3 into a ball mill to obtain waste slurry micro powder with a particle size of not more than 60 microns, and take 180 parts.

[0090] Step 5: 0.3 parts of a retarder is added to 32 parts of recycled water collected from the settling tank of the mixing station, and ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution A.

[0091] Step 6: 180 parts of waste slurry micro powder, 140 parts of cement, 900 parts of fine aggregate, 800 parts of coarse aggregate, 40 parts of coal cinder, and 25 parts of silica fume are put into a mixing pot for stirring, and then mixed solution A, 100 parts of water, and finally 6 parts of an additive are added to obtain recycled concrete.

[0092] Comparative Example 3

[0093] Step 1: Put the waste slurry into an oven to dry to form a dry intermediate, and then spray recycled water on the surface of the dry intermediate to make the water content of the dry intermediate after spraying reach 3% to 4%;

[0094] Step 2: Put the water-containing intermediate formed by the waste slurry into a carbonization box for carbonization, and the carbonization requires CO2 concentration of 98%, relative humidity of 80%, and temperature of 22℃, and the carbonization time is 24h;

[0095] Step 3: Then repeat step 2 to obtain the final carbonized waste slurry.

[0096] Step 4: Put the waste slurry obtained in step 3 into a ball mill to obtain waste slurry micro powder with a particle size of not more than 60 microns, and take 180 parts

[0097] Step 5: 0.3 parts of a retarder is added to 32 parts of recycled water collected from the settling tank of the mixing station, and ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution A.

[0098] Step 6: 2.1 parts of nano calcium carbonate is added to 100 parts of water, and ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution B.

[0099] Step 7: 180 parts of waste slurry micro powder, 140 parts of cement, 900 parts of fine aggregate, and 800 parts of coarse aggregate are put into a mixing pot for stirring, and then mixed solution A and mixed solution B are added, and finally 6 parts of an additive are added to obtain recycled concrete.

[0100] Comparative Example 4

[0101] Step 1: Put the waste slurry into an oven to dry to form a dry intermediate, and then spray recycled water on the surface of the dry intermediate to make the water content of the dry intermediate after spraying reach 3% to 4%;

[0102] Step 2: the aqueous intermediate formed by the waste slurry is placed in a carbonization box for carbonization, with a CO2 concentration of 98%, a relative humidity of 80%, a temperature of 22℃, and a carbonization time of 24h;

[0103] Step 3: then step 2 is repeated to obtain the final carbonized waste slurry.

[0104] Step 4: the waste slurry obtained in step 3 is placed in a ball mill to obtain waste slurry powder with a particle size of not more than 60 microns, and 180 parts

[0105] Step 5: 2.1 parts of nano calcium carbonate are added to 100 parts of water, and ultrasonic dispersion is performed for 2 minutes to obtain a mixed solution A.

[0106] Step 6: 180 parts of waste slurry powder, 140 parts of cement, 900 parts of fine aggregate, 800 parts of coarse aggregate, 40 parts of coal cinder, and 25 parts of silica fume are placed in a stirring pot for stirring, then mixed solution A is added, and finally 6 parts of an additive is added to obtain recycled concrete.

[0107] The experimental results of all the above examples are shown in Table 1.

[0108]

[0109] Through comparison of the parameters in the table, it can be seen that the recycled concrete in this embodiment has considerable advantages, which are analyzed as follows:

[0110] Comparing Example 1 with Comparative Example 1, it can be seen that carbonizing the waste slurry can enrich the cementitious material products and strengthen the concrete strength.

[0111] Comparing Example 1 with Comparative Example 2, it can be seen that the addition of nano calcium carbonate can fill the internal pores of the concrete and enhance the strength of the concrete.

[0112] Comparing Example 1 with Comparative Example 3, it can be seen that the coal cinder and silica fume can further activate the waste slurry, enhance the hydraulicity, and improve the strength of the concrete.

[0113] Comparing Example 1 with Comparative Example 4, it can be seen that the retarder can reduce the rapid hydration of the internal concrete in the early stage, reduce the hydration and strength growth of the concrete in the later stage, and the addition of recycled water promotes the formation of more calcium carbonate, gypsum and other products, thereby enhancing the strength of the concrete.

[0114] In summary, the method for preparing recycled concrete from waste slurry and recycled water provided by the present application uses reasonable material components, optimizes the hydration process of waste slurry reuse through the cement-based hydration micro-mechanism, improves the cementitious activity, and enhances the compressive strength of the recycled concrete.

[0115] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement or improvement made in the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for producing recycled concrete using waste slurry from a mixing plant and recycled water, characterized in that, The method includes the following implementation steps: Step 1: Place the waste slurry into an oven to dry it and form a dry intermediate. Then, spray recycled water on the surface of the dry intermediate to make the moisture content of the dry intermediate reach 3%~4% after spraying, thus forming a water-containing intermediate. Step 2: Place the water-containing intermediate formed from the waste slurry into the carbonization box for carbonization. The carbonization requirements are CO2 concentration of 98%±2%, relative humidity of 80%±2%, temperature of 22℃±2℃, and carbonization time of 24h. Step 3: Then repeat step 2 to obtain the final carbonized waste slurry; Step 4: Put the carbonized waste slurry obtained in Step 3 into a ball mill to obtain waste slurry powder with a particle size of no more than 60 micrometers; Step 5: Add 0.1-0.5 parts of retarder to 25-60 parts of recycled water collected from the sedimentation tank of the mixing plant, and ultrasonically disperse for 2 minutes to obtain mixture A; Step 6: Add 1-4 parts of nano-calcium carbonate to 80-115 parts of water, and ultrasonically disperse for 2 minutes to obtain mixture B; Step 7: First, put 150-220 parts of waste slurry powder, 110-180 parts of cement, 800-1100 parts of fine aggregate, 700-1000 parts of coarse aggregate, 30-60 parts of coal ash, and 20-40 parts of silica fume into a mixing pot and stir. Then, add mixture A and mixture B respectively, and finally add 5-12 parts of admixture. Stir the mixture at a uniform speed for 3 to 5 minutes to obtain recycled concrete.

2. A method of producing recycled concrete from waste slurry and recovered water at a mixing plant according to claim 1, characterized in that, The waste slurry mentioned in step 1 is taken from the bottom of the sedimentation tank. The waste slurry does not contain coarse aggregates. The waste slurry taken out is in the form of solid agglomerates and has a pH of 11.

0.

3. A method of producing recycled concrete from waste slurry and recovered water at a mixing plant according to claim 1, characterized in that, The recycled water mentioned in step 1 is water taken from the upper or middle layer of a sedimentation tank that has been left to stand in a sedimentation tank for 24 hours or more, with a pH of 12.2, a soluble content ≤3000 mg / L, and an insoluble content ≤3000 mg / L. Ca 2+ ≤ 880 mg / L, Na + ≤ 160 mg / L, K + ≤ 180 mg / L, Cl - ≤ 250 mg / L, SO4 2 ≤ 90 mg / L.

4. Recycled concrete prepared by the method according to any one of claims 1 to 3, characterized in that The recycled concrete consists of materials configured according to parts by weight: 150-220 parts of waste slurry; 110-180 parts cement; 1-4 parts of nano calcium carbonate; 30-60 parts coal slag; 20-40 parts silica fume; 800-1100 parts fine aggregate; 700-1000 coarse aggregate; 0.1-0.5 parts of retarder; 5-12 parts of admixture; 25-60 parts of recycled water; 80-115 parts water.

5. A recycled concrete prepared from waste slurry and recycled water of a mixing plant according to claim 4, characterized in that, The retarder is boric acid, potassium phosphate and glycerol, in a ratio of 6-5:4-3:2-1.

6. A recycled concrete prepared from waste slurry and recycled water of a mixing plant according to claim 4, characterized in that, The cement is P.Ⅱ52.5 silicate cement, and the total mass percentage of silica, calcium oxide and alumina in the cement is not less than 80%. The specific surface area of ​​the cement is 380 m² / g, the apparent density is 3020 kg / m³, and the 28-day strength is ≥55 MPa.

7. A recycled concrete prepared from waste slurry and recycled water of a mixing plant according to claim 4, characterized in that, The fine aggregate is river sand or manufactured sand, with a fineness modulus of 2.5, a bulk density of 1400 kg / m³, an apparent density of 2654 kg / m³, a stone powder content of 1.8%, and a water absorption rate of 1.4%.

8. The recycled concrete prepared from waste slurry and recycled water from a mixing plant according to claim 4, characterized in that, The coarse aggregate is one of the continuously graded basalt, limestone, and andesite crushed stone with a particle size of 5-20 mm, a crushing index of 4.7%, a dry apparent density of 2700-2950 kg / m³, and a bulk density of 1430 kg / m³.

9. The recycled concrete prepared from waste slurry and recycled water from a mixing plant according to claim 4, characterized in that, The average particle size of the nano calcium carbonate is 40±5 nm, the density is 2.46 g·cm -3 , the specific surface area is 480 m 2 / g, the pH is 9.0, and the purity is ≥98%.

10. The recycled concrete prepared from waste slurry and recycled water from a mixing plant according to claim 4, characterized in that, The coal slag is coal slag discharged from thermal power plants. After ball milling, it is passed through a 190-mesh sieve. Its main components are 59.6% SiO2, 20.45% Al2O3, 5.84% Fe2O3, and 3.21% CaO.

11. The recycled concrete prepared from waste slurry and recycled water from a mixing plant according to claim 4, characterized in that, The silica fume composition contains 95.33% SiO2, 0.43% Al2O3, 0.43% Fe2O3, 0.20% CaO, density 2.15 g / cm 3 , specific surface area 22 m 2 / g, 0.67% loss on ignition.

12. The recycled concrete prepared from waste slurry and recycled water from a mixing plant according to claim 4, characterized in that, The admixture is a polycarboxylic acid type high performance water reducing agent with water reducing rate > 25%, solid content 23%, density 1030 kg / m 3 .

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