Method for testing effective water absorption rate of reclaimed sand suitable for concrete

Abstract

A reclaimed sand effective water absorption testing method suitable for concrete is characterized by comprising the following steps: step 1, fixing the type and dosage of a concrete raw material, preparing concrete from natural sand, adjusting the water consumption to adjust the water-binder ratio so as to adjust the strength of the concrete, and respectively recording the water-binder ratio and the corresponding 28d compressive strength of the concrete. 2, obtaining an optimal linear function relationship between W / B and fC by using a least square method; 3, reclaimed sand with the same mass is selected to replace natural sand, the water consumption and the cementing material consumption are consistent with the natural sand concrete consumption, concrete is mixed, and the 28d compressive strength of the concrete is tested; and 4, calculating the effective water absorption rate of the reclaimed sand. The method is high in pertinence and suitable for regulating and controlling the performance of the recycled sand concrete; the precision is high and reliable; and the method can be widely applied to actual production and application of the recycled sand concrete.

Description

Technical Field

[0001] The invention relates to a method for testing effective water absorption rate of regenerated sand suitable for concrete. Background Art

[0002] Recycled sand is a sand-like material obtained by recycling waste building materials, concrete, etc. Recycled sand has good physical, chemical properties and mechanical strength. It is a high-quality environmentally friendly material and is widely used in various fields.

[0003] In concrete, recycled sand can replace part or all of natural sand, reducing dependence on natural resources. The use of recycled sand can not only reduce construction costs, but also reduce the amount of construction waste and pollution problems.

[0004] Compared with natural sand, regenerated sand has higher water absorption, so it is often necessary to use pre-wetting technology or add additional water to prepare regenerated sand concrete. However, in the actual production process of premixed recycled concrete, the amount of water used in concrete and the amount of admixtures used are not easy to control, which leads to certain fluctuations in the quality of concrete. It is difficult to accurately control the amount of water used with pre-wetting technology. The method of adding additional water requires accurate acquisition of the water absorption rate of regenerated sand. The existing method still uses the test method of saturated surface dry water absorption rate of natural sand or machine-made sand. However, since regenerated sand often has a large amount of mortar and inherent angularity on its surface, the interaction force between particles is different from that of natural sand or machine-made sand. At the same time, regenerated sand generally contains 5-12% of regenerated micropowder, which will inevitably be blown out during the air-drying process using a hair dryer, resulting in errors. Therefore, it is also difficult to accurately test the saturated surface dry water absorption rate. At the same time, the water absorption characteristics of regenerated sand in water are different from those in concrete mortar. In actual production and application, adding too much additional water will reduce the strength and easily cause water seepage during the vibration process, while too little additional water will greatly increase the amount of water reducer, increase the cost, and even cause extremely poor conditions due to too little free water. According to the 100% water absorption rate, additional water is added. After indoor tests and actual applications, it is known that the additional water calculated by the water absorption rate is too much, resulting in water seepage and reduced strength. That is, the amount of additional water is difficult to control according to the visual state in production.

[0005] According to relevant research, when configuring recycled concrete with strength grade C30 and below, the quality of recycled sand has no significant effect on its compressive strength, provided that the amount of recycled sand does not exceed 40% of the total amount of sand, that is, recycled sand from different types of waste concrete does not affect the strength of concrete with strength grade C30 and below. Based on this research result, the effective water absorption index of recycled sand when configuring concrete is determined to guide the amount of additional water added during production.

[0006] At present, the determination method of saturated surface dry water absorption of regenerated sand and regenerated stone needs to be improved. The existing method has poor accuracy and large errors, and the additional water consumption will affect the effective water-cement ratio.

[0007] By adjusting the water consumption, the working performance is kept equivalent with a small effect on the reduction of compressive strength (± 10%). Summary of the invention

[0008] In view of the above problems, the present invention provides a method for testing the effective water absorption rate of regenerated sand suitable for concrete. Based on the relationship between the strength of natural sand concrete and the water-binder ratio, the effective water-binder ratio of the regenerated sand concrete is obtained according to the strength of the regenerated sand concrete, and then the effective water absorption rate of the regenerated sand is calculated.

[0009] The present invention adopts the following technical solution:

[0010] A method for testing the effective water absorption rate of regenerated sand suitable for concrete, characterized by comprising the following steps:

[0011] Step 1: Fix the type and amount of concrete raw materials, prepare concrete with natural sand, adjust the water-cement ratio by adjusting the water consumption, and then adjust the concrete strength, and record the water-cement ratio and the corresponding 28d compressive strength of concrete respectively.

[0012] Step 2: Use the least squares method to obtain W / B and f C The optimal linear function relationship between the two;

[0013] Step 3: Select reclaimed sand of equal quality to replace natural sand, use the same amount of water and cementitious materials as natural sand concrete, mix the concrete and test its 28d compressive strength;

[0014] Step 4: Calculate the effective water absorption rate of regenerated sand.

[0015] In step 2, the least squares method is used to obtain W / B and f C The optimal linear function relationship between the two is W / B = k·f C +b, determine the fitting coefficients k and b, where W / B is the water-binder ratio, f C is the concrete strength.

[0016] Step 4: Calculate the effective water absorption rate of regenerated sand by formula (1):

[0017]

[0018] Among them, m S is the mass of regenerated sand, m W is the water consumption, m B is the amount of cementitious material used, f C ' is the 28d compressive strength, β is the effective water absorption.

[0019] The concrete prepared in step 1 is of strength grade C30 and below, and in order to ensure the reliability and accuracy of the regression fitting results, there are no less than 5 groups of water-cement ratio and strength data.

[0020] In step 3, the mass ratio of the regenerated sand replacing the natural sand is not higher than 40%.

[0021] Beneficial effects:

[0022] 1. Highly targeted, suitable for performance control of recycled sand concrete.

[0023] 2. High precision and reliability.

[0024] 3. It is highly practical and can be widely used in the actual production and application of recycled sand concrete. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific embodiments.

[0026] A method for testing the effective water absorption rate of regenerated sand suitable for concrete, characterized by comprising the following steps:

[0027] Step 1: Fix the type and amount of concrete raw materials, prepare concrete with natural sand, adjust the water-cement ratio by adjusting the water consumption, and then adjust the concrete strength, and record the water-cement ratio and the corresponding 28d compressive strength of concrete respectively.

[0028] Step 2: Use the least squares method to obtain W / B and f C The optimal linear function relationship between the two is W / B = k·f C +b, determine the fitting coefficients k and b, where W / B is the water-binder ratio, f C is the concrete strength.

[0029] Step 3: Select reclaimed sand of equal quality to replace natural sand, use the same amount of water and cementitious materials as natural sand concrete, mix the concrete and test its 28d compressive strength;

[0030] Step 4: Calculate the effective water absorption rate of regenerated sand by formula (1).

[0031]

[0032] Among them, m S is the mass of regenerated sand, m W is the water consumption, m B is the amount of cementitious material used, f C ' is the 28d compressive strength, β is the effective water absorption. Calculate the effective water absorption of the regenerated sand.

[0033] The concrete prepared in step 1 has a strength grade of C30 or below, and in order to ensure the reliability and accuracy of the regression fitting results, there are no less than 5 groups of water-cement ratio and strength data.

[0034] In step 3, the mass ratio of the regenerated sand replacing the natural sand is not higher than 40%.

[0035] Example 1

[0036] In order to ensure the reliability and accuracy of the regression fitting results, 5 sets of water-cement ratio and strength data were used for calculation. The specific steps are as follows:

[0037] Step 1: Fix the type and amount of concrete raw materials, use natural sand to prepare concrete, adjust the water-binder ratio (W / B) by adjusting the amount of water, and then adjust the concrete strength (f C ), and recorded the water-cement ratio and the corresponding 28d compressive strength of concrete, for a total of 5 groups of data, namely (0.75, 17.9), (0.68, 23.2), (0.6, 27.5), (0.51, 33.6), and (0.47, 38.5).

[0038] Step 2: Use the least squares method to obtain W / B and f C The optimal linear function relationship between the two is W / B = k·f C + b, determine the fitting coefficients k = -0.0141, b = 0.9995, R 2 =0.9884 (goodness of fit is high).

[0039] Step 3: Select the mass of regenerated sand (m S =350kg / m 3 ) to replace natural sand with the same quality, water consumption m W =193kg / m 3 , cementitious material dosage (m B =331kg / m 3 ) is consistent with the amount of natural sand concrete, mix the concrete and test its 28d compressive strength (f C '=35.1MPa).

[0040] Step 4: Calculate the effective water absorption rate (β) of the regenerated sand using formula (1).

[0041]

[0042] It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

Claims

1. A method for testing the effective water absorption rate of regenerated sand suitable for concrete, characterized in that: The following steps are involved: Step 1: Fix the type and amount of concrete raw materials, prepare concrete with natural sand, adjust the water-cement ratio by adjusting the water consumption, and then adjust the concrete strength, and record the water-cement ratio and the corresponding 28d compressive strength of concrete respectively. Step 2: Use the least squares method to obtain W / B and f C The optimal linear function relationship between the two; Step 3: Select reclaimed sand of equal quality to replace natural sand, use the same amount of water and cementitious materials as natural sand concrete, mix the concrete and test its 28d compressive strength; Step 4: Calculate the effective water absorption rate of regenerated sand.

2. A method for testing effective water absorption of regenerated sand suitable for concrete according to claim 1, characterized in that: In step 2, the least squares method is used to obtain W / B and f C The optimal linear function relationship between the two is W / B = k·f C +b, determine the fitting coefficients k and b, where W / B is the water-binder ratio, f C is the concrete strength.

3. The method for testing effective water absorption of regenerated sand suitable for concrete according to claim 1, characterized in that: Step 4: Calculate the effective water absorption rate of regenerated sand by formula (1): Among them, m S is the mass of regenerated sand, m W is the water consumption, m B is the amount of cementitious material used, f C ' is the 28d compressive strength, β is the effective water absorption.

4. The method for testing effective water absorption of regenerated sand suitable for concrete according to claim 1, characterized in that: The concrete prepared in step 1 is of strength grade C30 and below, and in order to ensure the reliability and accuracy of the regression fitting results, there are no less than 5 groups of water-cement ratio and strength data.

5. The method for testing effective water absorption of regenerated sand suitable for concrete according to claim 1, characterized in that: In step 3, the mass ratio of the regenerated sand replacing the natural sand is not higher than 40%.

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