Rapid test method for water-binder ratio of fresh concrete

Abstract

The invention discloses a fresh concrete water-binder ratio rapid test method, which comprises: S1, screening to remove coarse aggregate to obtain mortar: screening fresh concrete, and taking out the coarse aggregate to obtain two parts of mortar; s2, calculating the mass percent W of water and the mass percent S of sand in the mortar: S21, calculating the mass percent W of the water in the mortar: for the first mortar, adding a water absorbent and drying at high temperature: adding the water absorbent into a mortar sample of which the moisture content is to be tested, and drying the mortar at high temperature; s22, calculating the mass percent S of sand in the mortar: adding a hydration stopping agent into the second mortar, fully stirring, washing off particles with the particle size of less than 0.075 mm and the hydration stopping agent to obtain particles with the particle size of more than 0.075 mm, and drying the wet sand in a drying oven; s3, calculating the mass percent B of the cementing material in the mortar, wherein B = 1-W-S; and S4, calculating the water-binder ratio: Q = W / B. The method does not need to wait for several hours, and is good in reproducibility and wide in application range.

Description

Technical Field

[0001] The invention relates to the technical field of fresh concrete water-binder ratio testing, in particular to a fresh concrete water-binder ratio rapid testing method. Background Art

[0002] Concrete is a building material made by mixing raw materials such as cementitious materials (cement, fly ash, slag powder, etc.), water, sand and gravel aggregates, admixtures, etc. in a certain proportion. Among them, the mass ratio of water to cementitious materials (i.e., water-to-cement ratio) is a key parameter that determines the various properties of concrete. Generally speaking, when other conditions remain unchanged, the larger the water-to-cement ratio, the higher the fluidity of the fresh concrete, and the lower the strength of the hardened concrete at a certain age. However, due to factors such as aggregate water absorption and deviations in the metering system, the actual water-to-cement ratio of the concrete delivered to the construction site is not completely consistent with the designed water-to-cement ratio. Therefore, concrete users have an urgent need for the water-to-cement ratio of fresh concrete. However, the existing water-to-cement ratio testing technology takes a long time and consumes a lot of energy.

[0003] In the prior art, the specific method of measurement is: (1) sieve the fresh concrete, remove the coarse aggregate, and obtain mortar; (2) divide the mortar into two parts, one part is tested for water content in the mortar by drying method, and the other part is tested for sand content by screening, washing and drying method; (3) subtract the mass of water and sand from the mass of mortar to obtain the mass of cementitious material; (4) finally, divide the mass of water by the mass of cementitious material to obtain the water-cement ratio.

[0004] The existing technology puts the concrete into a blast drying box that has been heated to 105±5℃ in advance and dries it to constant weight; constant weight means that when the interval between two consecutive weighings is greater than 3h, the difference between the two weighings is less than the weighing precision required for the test; it takes an average of 1.5 hours at this temperature for the moisture to dissipate. However, 1.2 hours is difficult to meet the needs of the construction site, because the site often needs to quickly analyze the fresh concrete and decide whether the batch of concrete is usable, and the concrete usually has initial setting after 1.5 hours. For this reason, we propose a rapid test method for the water-cement ratio of fresh concrete. Summary of the invention

[0005] The purpose of the present invention is to provide a method for quickly testing the water-cement ratio of fresh concrete, so as to solve the problem that the testing efficiency in the prior art is difficult to meet the needs of the construction site.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for quickly testing the water-cement ratio of fresh concrete, comprising the following steps:

[0007] S1. Screening and removing coarse aggregate to obtain mortar: Screening the freshly mixed concrete, removing the coarse aggregate, and obtaining two portions of mortar;

[0008] S2. Calculate the mass percentage of water W and the mass percentage of sand S in the mortar:

[0009] S21. Calculate the mass percentage W of water in the mortar: For the first mortar, add a water absorbent and dry at high temperature: After adding a water absorbent to the mortar sample to be tested for moisture content, raise the temperature to a higher level in a short period of time, and dry the mortar at high temperature;

[0010] S22. Calculate the mass percentage S of sand in the mortar: add hydration stopper to the second mortar, stir thoroughly, and then sieve and wash under clean water to remove particles below 0.075 mm and hydration stopper, obtain particles above 0.075 mm, and place the wet sand in an oven to dry;

[0011] S3. Calculate the mass percentage of cementitious material in mortar: B = 1-WS;

[0012] S4. Calculate the water-to-binder ratio: Q = W / B.

[0013] Preferably, the specific steps of adding a water absorbent and drying at high temperature in S2 are:

[0014] S201, adding a water absorbent to the mortar;

[0015] S202, stirring thoroughly;

[0016] S203, raise the temperature from room temperature to 180°C within 5 minutes and maintain it for 15 minutes to obtain the accurate moisture content.

[0017] Preferably, the stirring is performed by using an automatic stirrer or a manual tool to fully mix the water absorbent and the mortar to ensure that the water absorbent is evenly distributed throughout the sample.

[0018] Preferably, in S3, the mixed mortar is placed in an electric oven preheated to 180° C., and the temperature is maintained at 180° C. for 15 minutes, so that the water absorbent fully absorbs the moisture in the mortar and all free water and part of the bound water are completely evaporated.

[0019] Preferably, the water absorbent is a super absorbent resin or sodium silicate; the amount of the super absorbent resin is 0.1%-0.2% of the mass of the mortar, and the particle size of the super absorbent resin is 10-100 microns.

[0020] Preferably, in S1, a sieve with a diameter of less than 4.75 mm is used to screen the fresh concrete.

[0021] Preferably, the calculation process of W is: if the mass of the first mortar (before drying) is m11, and the mass after drying is m12, then W = (m11-m12) / m11×100%

[0022] The calculation process of S is: assuming that the mass of the second mortar is m21 and the mass of the dried sand is m22, then S = m22 / m21×100%.

[0023] Preferably, the stopper in S22 is isopropyl alcohol, and the amount used is 5% of the mass of the second mortar; the temperature of the wet sand placed in the oven for drying is 100-180°C.

[0024] Compared with the prior art, the beneficial effects of the present invention are: the present invention does not need to wait for several hours, and the deviation is no more than 3% compared with the design value, and the results are stable, reproducible and applicable to a wide range; the present invention has a fast test speed and low energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0028] See also Figure 1 In an embodiment of the present invention, a method for quickly testing the water-cement ratio of fresh concrete comprises the following steps:

[0029] S1. Screening to remove coarse aggregate to obtain mortar: Screen the fresh concrete to remove coarse aggregate to obtain mortar; use a sieve with a mesh size of no more than 4.75 mm to screen the fresh concrete to obtain two mortars with the same components but different masses;

[0030] S2. Calculate the mass percentage of water W and the mass percentage of sand S in the mortar:

[0031] S21. Calculate the mass percentage W of water in the mortar: For the first mortar, add a water absorbent and dry at high temperature: After adding the water absorbent to the mortar sample whose moisture content is to be tested, raise the temperature to a higher temperature in a short time, and dry the mortar at high temperature; the water absorbent is a super absorbent resin or sodium silicate; the amount of super absorbent resin is 0.1%-0.2% of the mass of the mortar, and the particle size of the super absorbent resin is 10-100 microns; the water absorbent must have two major characteristics: ① It can capture water from cement at room temperature; ② The captured water will evaporate at high temperature, ③ Ensure that the selected water absorbent will not react with cement, resulting in; ④ Before and after the test, the mass change rate of the water absorbent itself is known (for example, the mass remains unchanged, or it is completely volatilized). The calculation process of W is: If the mass of the first mortar (before drying) is m11, and the mass after drying is m12, then W = (m11-m12) / m11×100%.

[0032] S22. Calculate the mass percentage S of sand in the mortar: Add hydration stopper (isopropyl alcohol is recommended, the amount is 5% of the mass of the second mortar) to the second mortar, stir it thoroughly, and then sieve it under clean water to wash away particles below 0.075 mm and hydration stopper, and obtain particles above 0.075 mm (that is, wet sand). Place the wet sand in an oven for drying (temperature: 100-180°C). The calculation process of S is: Assuming that the mass of the second mortar (before sieving and washing) is m21, and the mass of the sand after drying is m22, then S = m22 / m21×100%.

[0033] S3. Calculate the mass percentage of cementitious material in mortar: B = 1-WS;

[0034] S4. Calculate the water-binder ratio: Q = W / B;

[0035] The specific steps of adding water absorbent and high temperature drying in S2 are:

[0036] S201, adding a water absorbent to the mortar;

[0037] S202, stirring fully, wherein the stirring uses an automatic stirrer or a manual tool to fully mix the water absorbent and the mortar to ensure that the water absorbent is evenly distributed in the entire sample;

[0038] S203. Raise the temperature from room temperature to 180°C within 5 minutes and maintain it for 15 minutes to obtain accurate moisture content; put the mixed mortar into an electric oven preheated to 180°C, reach 180°C, and maintain this temperature for 15 minutes to allow the water absorbent to fully absorb the moisture in the mortar and allow all free water and part of the bound water to evaporate completely.

[0039] 1. The amount of water-absorbing resin used is generally about 0.1-0.2% of the mass of the mortar. (For example, 500g of mortar, 0.5g-1g)

[0040] 2. Super absorbent resin is white particles, and the particle size should be between 10 and 100 microns. If the particles are too large and the distance between the particles is too far, the water absorption effect will be poor.

[0041] The comparison of the measurement error and time of the present application and the prior art is as follows. All tests use super absorbent resin with a particle size of 10 to 80 microns as the absorbent. The advantage is that it completely decomposes itself under the above heating system and does not interfere with the calculation of the moisture content in the mortar.

[0042]

[0043]

[0044] The energy consumption comparison between this application and the prior art is as follows:

[0045]

[0046] The working principle of the present invention is: fresh concrete is screened, coarse aggregate is taken out, and mortar is obtained; a sieve with a diameter of less than 4.75 mm is selected to screen the fresh concrete; two mortar samples are obtained, which are respectively used to test the mass percentage of water and the mass percentage of sand in the mortar, and the mass percentage of cementitious material is obtained through algebraic operation; finally, the mass percentage of water is divided by the mass percentage of cementitious material to obtain the water-cement ratio.

[0047] For step S21 (testing the mass percentage of moisture in mortar), it is easy for the public to think that increasing the heating temperature will accelerate the dissipation of moisture and improve the test efficiency. However, high temperature will accelerate the hydration of cement in mortar, making it impossible for the water in the mortar to fully dissipate. Therefore, simply increasing the heating temperature can improve the efficiency of testing the mass percentage of moisture in mortar, but the accuracy is very poor. Compared with the existing technology, the contribution of the present application is: a water absorbent is discovered, which is used to pre-treat the mortar to ensure that the high-temperature drying process does not accelerate cement hydration, thereby ensuring the accuracy of the mass percentage test in the mortar.

[0048] Another contribution of the present application is that in step S22 (test of the mass percentage of sand in mortar), the mortar is pre-treated with a hydration stopper, which further ensures the accuracy of the test results. This is because, if not treated, the screening and washing process will promote the contact between cement and water, increase the hydration rate, and cause cement to generate hydration products and expand in volume, so that some cement particles cannot pass through the 0.075mm sieve holes that they could have passed through, and are thus mistaken for sand, resulting in an overestimation of the S value, an underestimation of the B value, and an overestimation of the Q value.

[0049] This application no longer requires waiting for 1.5 hours, and compared with the design value, the deviation is no more than 3%, and the results are stable, reproducible, and applicable to a wide range; this application has a fast test speed and low energy consumption.

[0050] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for quickly testing the water-cement ratio of fresh concrete, characterized in that: The following steps are involved: S1. Screening and removing coarse aggregate to obtain mortar: Screening the freshly mixed concrete, removing the coarse aggregate, and obtaining two portions of mortar; S2. Calculate the mass percentage of water W and the mass percentage of sand S in the mortar: S21. Calculate the mass percentage W of water in the mortar: For the first mortar, add a water absorbent and dry at high temperature: After adding a water absorbent to the mortar sample to be tested for moisture content, raise the temperature to a higher level in a short period of time, and dry the mortar at high temperature; S22. Calculate the mass percentage S of sand in the mortar: add hydration stopper to the second mortar, stir thoroughly, and then sieve and wash under clean water to remove particles below 0.075 mm and hydration stopper, obtain particles above 0.075 mm, and place the wet sand in an oven to dry; S3. Calculate the mass percentage of cementitious material B in mortar: B = 1-WS; S4. Calculate the water-to-binder ratio: Q = W / B.

2. A rapid test method for water-binder ratio of fresh concrete according to claim 1, characterized in that: The specific steps of adding water absorbent and high temperature drying in S2 are: S201, adding a water absorbent to the mortar; S202, stirring thoroughly; S203, raise the temperature from room temperature to 180°C within 5 minutes and maintain it for 15 minutes to obtain the accurate moisture content.

3. A rapid test method for water-binder ratio of fresh concrete according to claim 2, characterized in that: The stirring is performed by using an automatic stirrer or a manual tool to fully mix the water absorbent and the mortar to ensure that the water absorbent is evenly distributed in the entire sample.

4. A method for rapid testing water-binder ratio of fresh concrete according to claim 2 or 3, characterized in that: In S3, the mixed mortar is placed in an electric oven preheated to 180° C., and the temperature is maintained at 180° C. for 15 minutes, so that the water absorbent fully absorbs the moisture in the mortar and all free water and part of the bound water are completely evaporated.

5. A rapid test method for water-binder ratio of fresh concrete according to claim 1 or 2, characterized in that: The water absorbing agent is super absorbent resin or sodium silicate; the dosage of the super absorbent resin is 0.1%-0.2% of the mass of the mortar, and the particle size of the super absorbent resin is 10-100 microns.

6. A rapid test method for water-binder ratio of fresh concrete according to claim 1, characterized in that: In S1, a sieve with a diameter of less than 4.75 mm is used to screen the fresh concrete.

7. A method for rapid testing water-binder ratio of fresh concrete according to claim 1, characterized in that: The calculation process of W is: if the mass of the first mortar (before drying) is m11, and the mass after drying is m12, then W = (m11-m12) / m11×100%. The calculation process of S is: assuming that the mass of the second mortar is m21 and the mass of the sand after drying is m22, then S = m22 / m21×100%.

8. A method for rapid testing water-binder ratio of fresh concrete according to claim 1, characterized in that: The stopper in S22 is isopropyl alcohol, and the amount used is 5% of the mass of the second mortar; the temperature of the wet sand placed in the oven for drying is 100-180°C.

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