Application of surface wetting water absorption in preparation of recycled concrete

Abstract

The invention belongs to the technical field of building materials and concrete preparation, and particularly relates to application of surface wetting water absorption in recycled concrete preparation, in the application, a method for obtaining the surface wetting water absorption comprises the steps that the water absorption W of recycled aggregate in a saturated surface dry state and the water absorption Ww of the recycled aggregate in a water absorption saturated state are tested; the surface wetting water absorption rate is the difference value between W and Ww. According to the surface wetting absorption rate, the water amount required by the recycled aggregate to reach the surface wetting state can be obtained, and the water saturation of the recycled aggregate can be controlled through the water amount for surface wetting; the influence on the performance of the recycled concrete due to overlarge water consumption for wetting the recycled aggregate (for example, the water-binder ratio of the aggregate to a slurry interface is increased due to overlarge water consumption, and the compressive strength of the concrete is reduced) is avoided, so that the mechanical property of the recycled concrete is improved (the recycled concrete prepared by the method has higher compressive strength).

Description

Technical Field

[0001] The invention belongs to the technical field of building materials and concrete preparation, and particularly relates to the application of surface wetting water absorption rate in the preparation of recycled concrete. Background Art

[0002] The different moisture states of recycled aggregate significantly impact the performance of recycled concrete. Based on their water content or degree of saturation, recycled aggregate moisture states can be broadly categorized as completely dry, partially saturated, and saturated surface dry. Recycled aggregates have varying water absorption capacities in different moisture states, which influences their absorption of water from the cement paste during concrete mixing. This impacts the workability of freshly mixed concrete, the interfacial transition zone (ITZ), and the microstructure of the new cement mortar, ultimately affecting the subsequent properties of the hardened recycled concrete.

[0003] In the preparation of recycled concrete, the amount of water required to pre-wet recycled aggregate is typically calculated based on the water absorption rate specified in the national standard "Pebbles and Crushed Stone for Construction" (GB / T 14685-2022). However, this method often results in a pre-wetting state that reaches a saturated surface dry state (where the internal pores are saturated with water but there is no excess free water on the surface), exceeding the actual water requirement for pre-wetting the recycled aggregate. This excessive pre-wetting water increases the water-cement ratio of the recycled concrete, thereby affecting the workability of the concrete in its fresh state. Furthermore, excessive water content can interfere with the interaction between cement and aggregate, potentially reducing the concrete's strength. Summary of the Invention

[0004] The present invention aims to provide an application of surface wetting water absorption in the preparation of recycled concrete. The surface wetting water consumption obtained according to the surface wetting water absorption can control the water saturation of the recycled aggregate, thereby avoiding the impact of excessive water consumption on the performance of the recycled concrete due to the wetting of the recycled aggregate, and improving the compressive strength of the recycled concrete.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides an application of surface wetting water absorption in the preparation of recycled concrete. The method for obtaining the surface wetting water absorption is: Test the water absorption rate W of recycled aggregate in saturated surface dry state and water absorption rate W in water saturated state w ; The surface wetting water absorption rate is W and W w The difference.

[0006] Preferably, the water absorption rate W of the recycled aggregate in a saturated surface-dry state is tested in accordance with 7.15.2 of the national standard "Pebbles and Crushed Stones for Construction" (GB / T 14685-2022).

[0007] Preferably, the water absorption rate W of the recycled aggregate in the water saturated state is w Obtained by weighing using a hydrostatic balance.

[0008] Preferably, the water absorption rate W w The test steps are as follows: put the dry recycled aggregate obtained when testing the water absorption rate W in the saturated surface dry state into a perforated hanging basket and immerse it in a water tank until the water is higher than the surface of the dry recycled aggregate. From the time when the water contacts the dry recycled aggregate, record the reading on the electronic scale for 2 seconds, which is recorded as m w When the reading of the electronic scale no longer changes, record the reading of the electronic scale and record it as m u ; Water absorption rate W w According to formula (2), we can get: w =(m u -m w ) / m g* 100%; formula (2).

[0009] Preferably, the particle size of the recycled aggregate is 5-10 mm or 10-20 mm.

[0010] Preferably, the recycled aggregate is concrete-type construction waste.

[0011] The present invention also provides a method for preparing recycled concrete, comprising the following steps: first mixing surface wetting water and recycled aggregate to obtain wetted recycled aggregate; After a second mixing of the wetted recycled aggregate, cement, design water and polycarboxylic acid admixture, the mixture is molded and cured to obtain recycled concrete; The mass of surface wetting water is calculated according to formula (3); m s =G×W s Formula (3); In formula (3), G is the mass of recycled aggregate in concrete; W s is the surface wetting water absorption rate; The method for obtaining the surface wetting water absorption rate is: Test the water absorption rate W of recycled aggregate in saturated surface dry state and water absorption rate W in water saturated state w ; The surface wetting water absorption rate is W and W w The difference.

[0012] Preferably, the solid content of the polycarboxylic acid admixture is 20%.

[0013] Preferably, the first mixing method is stirring, the stirring speed is 46-48 rpm, and the stirring time is 5-10 s.

[0014] Preferably, the second mixing method is stirring, the stirring speed is 46-48 rpm, and the stirring time is 40-50 s.

[0015] The present invention creatively proposes the concept of surface wetting absorption rate. The amount of water required for surface wetting of the recycled aggregate can be obtained based on the surface wetting absorption rate. The water saturation of the recycled aggregate can be controlled by the amount of water used for surface wetting, thereby avoiding the impact of excessive water used for wetting the recycled aggregate on the performance of the recycled concrete (for example, excessive water consumption will lead to an increase in the water-binder ratio at the interface between the aggregate and the paste, thereby reducing the compressive strength of the concrete), thereby improving the mechanical properties of the recycled concrete (the recycled concrete prepared using this method has higher compressive strength). DETAILED DESCRIPTION

[0016] The present invention provides an application of surface wetting water absorption in the preparation of recycled concrete. The method for obtaining the surface wetting water absorption is: Test the water absorption rate W of recycled aggregate in saturated surface dry state and water absorption rate W in water saturated state w ; The surface wetting water absorption rate is W and W w The difference.

[0017] As an embodiment of the present invention, the recycled aggregate is concrete-type construction waste.

[0018] As an embodiment of the present invention, the water absorption rate W test of the recycled aggregate in the saturated surface dry state can be carried out in accordance with the national standard "Pebbles and Crushed Stones for Construction" (GB / T 14685-2022) 7.15.2.

[0019] Specifically, the test steps are as follows: take the recycled aggregate and place it in a container filled with water, with the water level about 5 mm higher than the sample surface. After soaking for (24 ± 1) hours, take it out of the water and wipe the water on the surface of the particles with a wet towel to obtain a saturated surface dry sample. The mass of the saturated surface dry sample is weighed and recorded as m b ; Place the saturated surface dry sample in an oven at (105±5)℃ and dry it to constant weight, then cool it to room temperature to obtain the dry recycled aggregate. Weigh the mass of the dry recycled aggregate and record it as m g ; The water absorption rate W is calculated according to formula (1): W = (m b -m g ) / m g* 100%; formula (1); As an embodiment of the present invention, the water absorption rate W w The test can be obtained by weighing with a hydrostatic balance; Specifically, the testing steps may be: Put the dry recycled aggregate obtained when testing the water absorption rate W under the saturated surface dry state into a hanging basket with holes and quickly immerse it in a water tank until the water is higher than the surface of the dry recycled aggregate. Count 2 seconds from the time when the water contacts the dry sample and record the reading on the electronic scale, which is recorded as m w When the reading of the electronic scale no longer changes, record the reading of the electronic scale and record it as m u ; Water absorption rate W w According to formula (2), we can get: w =(m u -m w ) / m g* 100%; formula (2); As an embodiment of the present invention, the perforated hanging basket can be a stainless steel density basket.

[0020] In the present invention, the surface wetting water absorption rate test is preferably performed twice, and the arithmetic mean of the two test results is taken, and the result is accurate to 0.1%.

[0021] The present invention provides a method for preparing recycled concrete, comprising the following steps: first mixing surface wetting water and recycled aggregate to obtain wetted recycled aggregate; After a second mixing of the wetted recycled aggregate, cement, design water and polycarboxylic acid admixture, the mixture is molded and cured in sequence to obtain recycled concrete; The mass of the surface wetting water is calculated according to formula (3); m s =G×W s Formula (3); In formula (3), G is the mass of recycled aggregate in concrete; W s is the surface wetting water absorption rate; The method for obtaining the surface wetting water absorption rate is: Test the water absorption rate W of recycled aggregate in saturated surface dry state and water absorption rate W in water saturated state w ; The surface wetting water absorption rate is W and W w The difference.

[0022] The present invention first mixes surface wetting water and recycled aggregate to obtain wet recycled aggregate.

[0023] As an embodiment of the present invention, the first mixing method is stirring; the stirring speed may be 46-48 rpm, specifically 45 rpm; and the stirring time may be 5-10 s.

[0024] After obtaining the wet recycled aggregate, the present invention performs a second mixing of the wet recycled aggregate, cement, design water and polycarboxylic acid admixture, and then sequentially performs molding and curing to obtain recycled concrete.

[0025] As an embodiment of the present invention, the solid content of the polycarboxylic acid admixture can be 20%.

[0026] As an embodiment of the present invention, the components of the recycled concrete are preferably designed with reference to the "Technical Specification for Application of Recycled Aggregate Permeable Concrete" CJJ / T 253-2016; the molding and curing are carried out in accordance with the molding and curing methods specified in the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019.

[0027] As an embodiment of the present invention, the second mixing method is stirring; the stirring speed may be 46-48 rpm, specifically 45 rpm; and the stirring time may be 40-50 s.

[0028] The application of this technology not only improves the overall performance of recycled concrete, but also ensures its reliability and durability in practical applications. Through appropriate pre-wetting moisture and the reuse of recycled aggregate from construction waste, it can effectively promote the sustainable development of recycled concrete and provide a more efficient and environmentally friendly solution for the construction industry.

[0029] In order to further illustrate the present invention, the scheme of the present invention is described in detail below with reference to the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0030] Note: The basic properties of the aggregates in the examples are shown in Table 1. The cement is P·O 42.5 cement; the recycled aggregate is concrete-type construction waste.

[0031] Table 1 Basic properties of aggregates in the examples

[0032] Example 1 Test the surface wetting water absorption of recycled aggregate with a particle size of 5-10mm and a particle size of 10-20mm; The test method is as follows: take the recycled aggregate and place it in a container filled with water, with the water level 5mm higher than the sample surface. After soaking for 24 hours, take it out of the water and wipe the water on the surface of the particles with a wet towel to obtain a saturated surface dry sample. The mass of the saturated surface dry sample is weighed and recorded as m b ; Place the saturated surface dry sample in an oven at 105°C and dry it to constant weight, then cool it to room temperature to obtain the dry recycled aggregate. Weigh the mass of the dry recycled aggregate and record it as m g ; The water absorption rate W is calculated according to formula (1): W = (m b -m g ) / m g*100%; formula (1); Place the dried recycled aggregate in a stainless steel density basket, which is hung on the bottom hook of the electronic scale with a non-elastic steel wire. Use a movable tray to move the constant temperature bath vertically, and quickly immerse the dried recycled aggregate in the water bath until the water is above the surface of the dried recycled aggregate. Record the reading on the electronic scale for 2 seconds from the moment the water contacts the dried recycled aggregate, which is recorded as m. w When the reading of the electronic scale no longer changes, record the reading of the electronic scale and record it as m u ; Water absorption rate W w According to formula (2), we can get: W = (m u -m w ) / m g* 100%; Formula (2); Surface wetting water absorption rate is W and W w The experiment was carried out twice, and the results are shown in Table 2 below.

[0033] Table 2 Calculation of test results

[0034] Application Example 1 The particle size of natural aggregate is 5~10mm, the particle size of recycled aggregate is 5~10mm, and the replacement rates of recycled aggregate are 25%, 50%, 75% and 100% respectively. The mix proportions are designed with reference to the Technical Specification for Application of Recycled Aggregate Permeable Concrete CJJ / T 253-2016, see Table 3.

[0035] Table 3 Mix ratio of each component material in recycled concrete when the aggregate size is 5-10 mm

[0036] The surface wetting water consumption was calculated based on the water absorption rate of the 5-10 mm recycled aggregate in Example 1. The results were as follows: when the recycled aggregate replacement rates were 25%, 50%, 75%, and 100%, the surface wetting water consumption was 11 kg / m 3 , 22 kg / m 3 33kg / m 3 , 45 kg / m 3 .

[0037] Preparation of recycled concrete (prepare raw materials according to the mix proportions in Table 3 and the surface wetting water consumption for different recycled aggregate replacement rates): Surface wetting water and recycled aggregate with a particle size of 5 to 10 mm were stirred at 45 rpm for 10 s to obtain wetted recycled aggregate; The wetted recycled aggregate, cement, design water and polycarboxylic acid admixture were stirred at a speed of 45 rpm for 50 seconds, and then molded and cured in sequence (molding and curing were carried out according to the molding and curing methods specified in the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019) to obtain recycled concrete.

[0038] Application Example 2 The particle size of natural aggregate is 10~20mm, the particle size of recycled aggregate is 10~20mm, and the replacement rates of recycled aggregate are 25%, 50%, 75% and 100% respectively. The mix proportions are designed with reference to the Technical Specification for Application of Recycled Aggregate Permeable Concrete CJJ / T 253-2016, see Table 4.

[0039] Table 4 Mix ratio of each component material in recycled concrete when the aggregate size is 10-20 mm

[0040] The surface wetting water consumption was calculated based on the water absorption rate of the 10-20 mm recycled aggregate in Example 1. The results were as follows: when the recycled aggregate replacement rates were 25%, 50%, 75%, and 100%, the surface wetting water consumption was 8 kg / m 3 , 16 kg / m 3 , 24kg / m 3 , 32 kg / m 3 .

[0041] Preparation of recycled concrete (prepare raw materials according to the mix proportion in Table 4 and the surface wetting water consumption for different recycled aggregate replacement rates): Surface wetting water and recycled aggregate with a particle size of 5 to 10 mm were stirred at 45 rpm for 10 s to obtain wetted recycled aggregate; The wetted recycled aggregate, cement, design water and polycarboxylic acid admixture were stirred at a speed of 45 rpm for 50 s, and then molded and cured in sequence (molding and curing were carried out according to the molding and curing methods specified in the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019) to obtain recycled concrete.

[0042] The compressive strength of the recycled concrete prepared in Application Examples 1 and 2 was tested in accordance with the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019, and the permeability coefficient was tested in accordance with the industry standard "Technical Specifications for Permeable Cement Concrete Pavement" CJJ / T135. The test results are shown in Tables 5 and 6.

[0043] Table 5 Compressive strength and water permeability coefficient of recycled concrete prepared in Application Example 1

[0044] Table 6 Compressive strength and permeability coefficient of recycled concrete prepared in Application Example 2

[0045] Comparative Example 1 Table 7 Mix ratio of each component material in recycled concrete when the aggregate size is 5-10 mm

[0046] According to the mix proportions in Table 7, recycled aggregate with a particle size of 5-10 mm, cement, water without pre-wetting, and polycarboxylic acid admixture were stirred at 45 rpm for 50 s, and then molded and cured in sequence to obtain recycled concrete. Non-pre-wetting water is the sum of the design water and the additional water required for recycled aggregate based on the water absorption rate determined in accordance with 7.15.2 of the national standard "Pebbles and Crushed Stone for Construction" (GB / T 14685-2022). Non-pre-wetting means that pre-wetting of the recycled aggregate is not required. This means that the various components of the recycled concrete are mixed with the non-pre-wetting water.

[0047] Comparative Example 2 Table 8 Mix ratio of each component material in recycled concrete when the aggregate size is 10-20 mm

[0048] According to the mix proportions in Table 8, recycled aggregate with a particle size of 10-20 mm, cement, water, and polycarboxylic acid admixture were stirred at 45 rpm for 50 s, and then molded and cured in sequence (according to the molding and curing methods specified in the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019) to obtain recycled concrete.

[0049] Comparative Example 3 Table 9 Mix ratio of each component material in recycled concrete when the aggregate size is 5-10 mm

[0050] The saturated pre-wetting water absorption rate is tested according to the national standard "Pebbles and crushed stones for construction" (GB / T 14685-2022) Part 7.15.2, and the mass of the saturated pre-wetting water is calculated according to formula (4); m s =G×W Formula (4); In formula (4), G is the mass of recycled aggregate in concrete; W is the saturated pre-wetting water absorption rate.

[0051] According to the mix proportion in Table 9, saturated pre-wetting water and recycled aggregate with a particle size of 5-10 mm were stirred at a speed of 45 rpm for 10 s to obtain saturated wetted recycled aggregate.

[0052] Saturated wetted recycled aggregate, cement, design water and polycarboxylic acid admixture were stirred at a speed of 45 rpm for 50 seconds, and then molded and cured in sequence (molding and curing were carried out according to the molding and curing methods specified in the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019) to obtain recycled concrete.

[0053] Comparative Example 4 Table 10 Mix ratio of each component in recycled concrete when the aggregate size is 10-20 mm

[0054] According to the mix proportion in Table 10, saturated pre-wetting water and recycled aggregate with a particle size of 10-20 mm were stirred at a speed of 45 rpm for 10 s to obtain saturated wetted recycled aggregate; Saturated wetted recycled aggregate, cement, design water and polycarboxylic acid admixture were stirred at a speed of 45 rpm for 50 seconds, and then molded and cured in sequence (molding and curing were carried out according to the molding and curing methods specified in the national standard "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2019) to obtain recycled concrete.

[0055] The compressive strength and water permeability of the recycled aggregate concrete obtained in the comparative example were tested, and the test results are shown in Tables 11 and 12.

[0056] Table 11 Compressive strength and water permeability of recycled concrete prepared in Comparative Examples 1 and 2

[0057] Table 12 Compressive strength and water permeability of recycled concrete prepared in Comparative Examples 3-4

[0058] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. Application of surface wetting water absorption in the preparation of recycled concrete, characterized in that: The method for obtaining the surface wetting water absorption rate is: Test the water absorption rate W of recycled aggregate in saturated surface dry state and water absorption rate W in water saturated state w ; The surface wetting water absorption rate is W and W w The difference.

2. The use according to claim 1, characterized in that The water absorption rate W of the recycled aggregate in the saturated surface dry state was tested in accordance with 7.15.2 of the national standard "Pebbles and Crushed Stones for Construction" (GB / T14685-2022).

3. The use according to claim 1, characterized in that The water absorption rate W of the recycled aggregate in the water saturated state w Obtained by weighing using a hydrostatic balance.

4. The use according to claim 3, characterized in that The water absorption rate W w The test steps are as follows: put the dry recycled aggregate obtained when testing the water absorption rate W in the saturated surface dry state into a perforated hanging basket and immerse it in a water tank until the water is higher than the surface of the dry recycled aggregate. From the time when the water contacts the dry recycled aggregate, record the reading on the electronic scale for 2 seconds, which is recorded as m w When the reading of the electronic scale no longer changes, record the reading of the electronic scale and record it as m u ; Water absorption rate W w According to formula (2), we can get: w =(m u -m w ) / m g* 100%; formula (2).

5. The use according to any one of claims 1 to 4, characterized in that The particle size of the recycled aggregate is 5-10 mm or 10-20 mm.

6. The use according to any one of claims 1 to 4, characterized in that The recycled aggregate is concrete-type construction waste.

7. A method for preparing recycled concrete, comprising the following steps: first mixing surface wetting water and recycled aggregate to obtain wetted recycled aggregate; After a second mixing of the wetted recycled aggregate, cement, design water and polycarboxylic acid admixture, the mixture is molded and cured to obtain recycled concrete; The mass of surface wetting water is calculated according to formula (3); m s =G×W s Formula (3); In formula (3), G is the mass of recycled aggregate in concrete; W s is the surface wetting water absorption rate; The method for obtaining the surface wetting water absorption rate is: Test the water absorption rate W of recycled aggregate in saturated surface dry state and water absorption rate W in water saturated state w ; The surface wetting water absorption rate is W and W w The difference.

8. The preparation method according to claim 7, wherein The solid content of the polycarboxylic acid admixture is 20%.

9. The preparation method according to claim 7, wherein The first mixing method is stirring, the stirring speed is 46-48 rpm, and the stirring time is 5-10 s.

10. The preparation method according to claim 7, wherein The second mixing method is stirring, the stirring speed is 46-48 rpm, and the time is 40-50 s.

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