Screening method of water reducing agent

Abstract

The invention relates to a screening method of a water reducing agent, and relates to the technical field of building materials. The compatibility of the high-flowability mortar is detected by utilizing the influence of different water reducing agents on the initial flowability and the flowability after 1h when the solid dosage of the water reducing agents is the same, and the water reducing agent variety with good compatibility with certain granite chips or machine-made sand can be quickly selected from various water reducing agents; the method provided by the invention has the advantages of capability of comprehensively reflecting the compatibility between the granite chips or the machine-made sand and the water reducing agent, low experimental workload, high experimental efficiency and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and specifically to a screening method for water reducing agents. Background Art

[0002] More and more granite chips and granite manufactured sand have become substitutes for river sand and are gradually used in engineering to prepare concrete. Different from traditional river sand, granite chips and granite manufactured sand contain more stone powder, and their adsorption capacity for water reducing agents is relatively large. When granite chips and manufactured sand are used in actual engineering, the compatibility between the water reducing agent and the chips and manufactured sand is poor. Some types of water reducing agents cannot be used, and some types of water reducing agents require excessive dosages.

[0003] To test the compatibility between granite chips and manufactured sand and water reducing agents and to preferably select water reducing agent varieties with good compatibility with a certain type of granite chips or manufactured sand from different water reducing agents, currently in engineering, the performance of different water reducing agents is usually tested through concrete experiments, which involves a large amount of work and a lot of material waste. Therefore, there is an urgent need to develop a method that can quickly detect the compatibility between granite chips and manufactured sand and water reducing agents, so as to achieve the purpose of quickly selecting water reducing agent varieties with good compatibility with a certain type of granite chips or manufactured sand from different water reducing agents.

[0004] Regarding the compatibility between granite chips and manufactured sand and water reducing agents, currently only the stone powder fluidity ratio in the standard "Aggregates for High Performance Concrete" (JG / T 568 - 2019) can be used as a reference. The stone powder fluidity ratio refers to the ratio of the flow table fluidity of the mortar containing stone powder (replacing 30% of the binder) to the reference cement mortar under the conditions of adding a water reducing agent and a water - binder ratio of 0.40, and is an index for judging the adsorption performance of stone powder on the water reducing agent.

[0005] However, when using it to detect the compatibility between granite chips and manufactured sand and water reducing agents, the following problems are found: (1) It only uses stone powder for detection and does not use larger - sized granite chip and manufactured sand particles. Granitic chips and manufactured sand particles larger than 0.075 mm also have a relatively large adsorption effect on water reducing agents. Therefore, it can only be used to reflect the compatibility between stone powder and water reducing agents and cannot comprehensively reflect the compatibility between chips or manufactured sand and water reducing agents.

[0006] (2) For each water reducing agent, a comparative mortar experiment needs to be carried out, and the dosage of the water reducing agent in the comparative mortar is determined through multiple experiments. The experimental workload is large, and it consumes a lot of manpower and material resources.

[0007] (3) The fluidity of its mortar is relatively low (compared with the flow table fluidity of the reference mortar of 180 mm ± 5 mm, the flow table fluidity of the experimental mortar with stone powder is even lower), and it can only detect the difference in the initial fluidity between different water reducers and the same kind of stone powder; however, due to the large adsorption amount of granite stone powder on the water reducer, its fluidity after 1 h is relatively low, and it is difficult to effectively distinguish the influence of different water reducers on the fluidity performance after 1 h.

[0008] Due to the above-mentioned many problems in the detection methods of the compatibility between granite chips, manufactured sand and water reducers in the prior art, it is difficult for people to quickly select a water reducer variety with good compatibility with a certain granite chip or manufactured sand from a variety of water reducers. SUMMARY OF THE INVENTION

[0009] Aiming at the problems existing in the prior art, the object of the present invention is to provide a screening method for water reducers, by which a water reducer variety with good compatibility with granite chips or manufactured sand can be quickly selected from a variety of water reducers.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions: A screening method for water reducers, comprising the following steps, Step 1, preparing a granite chip or manufactured sand sample: (1) Taking dry stone chips or manufactured sand and screening out particles larger than 4.75 mm; (2) Using the stone chip or manufactured sand sample prepared in (1), sampling the stone chips or manufactured sand by the splitter method or the manual quartering method according to the GB / T 14684 standard, adding a 0.075 mm sieve, measuring its particle size distribution, and calculating the content of stone powder and sand therein, wherein the particle size of the stone powder is less than 0.075 mm, and the particle size of the sand is 0.075 - 4.75 mm; (3) Calculating the mass of each graded sand between 0.075 - 4.75 mm and the mass of the stone powder according to the mass of the sand being 800 - 1350 g, preferably 1200 g; (4) Using the stone chip or manufactured sand sample prepared in (1), sampling and screening by the splitter method or the manual quartering method according to the GB / T 14684 standard, and preparing multiple sand and stone powder samples for use according to the mass of each graded sand and stone powder obtained in (3); Step 2, conducting a mortar fluidity experiment: Prepare the mortar raw materials. Among them, the powder materials include cementitious materials and stone powder. The water-powder ratio of the mortar is 0.50, the sand-powder ratio is 2.0 - 3.0. The dosage of stone powder is calculated according to the ratio of stone powder to sand in the particle size distribution. The solid admixture content of the water reducer is the mass ratio of the solid of the water reducer to the powder materials. The water-powder ratio is the mass ratio of water to the powder materials, and the sand-powder ratio is the mass ratio of sand to the powder materials. The mass of sand required for each experiment is 800 - 1350 g, preferably 1200 g. The initial solid admixture content of the water reducer is taken as 0.10 - 0.15%. Conduct the mortar fluidity test with different water reducers. The steps are as follows: Put the cement mortar mixer in a standby state. Then add the mixture of the water reducer and water into the mixing pot, and then add the powder materials weighed according to the test ratio. Immediately start the machine to stir, and add the weighed sand into the mixing pot and continue to stir. Use a cement mortar fluidity tester to test the mortar fluidity. Among them, the bottom plate uses a glass bottom plate and does not perform jolting. Adjust the dosage of the water reducer to make the initial fluidity of some mortar between 180 - 220 mm. After testing the fluidity, collect all the mortar, put it into a sample cylinder wiped with a wet cloth, cover the container, let it stand for 1 h and then pour it out. Use the cement mortar mixer to stir at a low speed and measure the fluidity after 1 h. Step three, select the preferred water reducer type: Calculate the difference between the initial fluidity and the fluidity after 1 h, and compare it with the initial fluidity, that is, obtain the 1 h time-dependent change rate of the fluidity. The water reducer with a larger initial fluidity of the mortar and a smaller 1 h time-dependent change rate of the fluidity is the preferred water reducer variety.

[0011] Furthermore, when the used water reducer is in liquid form, calculate the liquid dosage of the water reducer according to the solid content of the water reducer, and deduct the water content in the water reducer from the total water volume.

[0012] Furthermore, the machine stirring in step two is carried out according to the automatic program, including stirring at a low speed for 30 s first, then manually adding the weighed sand evenly into the mixing pot at the beginning of the second 30 s, stirring at a high speed for another 30 s, then stopping stirring for 90 s, and scraping the mortar on the blades and the pot wall into the mixing pot with a trowel within 15 s, and then continuing to stir at a high speed for 60 s.

[0013] Furthermore, when testing the mortar fluidity, if the fluidity of all the water reducer samples is lower than 180 mm or higher than 220 mm or segregation occurs, appropriately adjust the solid dosage of the water reducer, re-conduct the mortar stirring and fluidity test to make the initial fluidity of some mortar between 180 - 220 mm.

[0014] Furthermore, the timing of the 1 h standing of the mortar in the sample cylinder starts from the time when the water is added to the powder materials and stirring begins.

[0015] Further, the workability is characterized by the initial fluidity, and the workability retention ability is characterized by the time-dependent change rate of the 1h fluidity. A variety of water reducers are respectively used for detection. According to the initial fluidity of the mortar and the time-dependent change rate of the 1h fluidity when different water reducers are used, water reducer varieties with good compatibility are preferably selected from a variety of water reducers.

[0016] Further, the judgment criterion for a water reducer having good compatibility with granite chips or manufactured sand is that the initial fluidity of the mortar is not less than 180 mm, and the time-dependent change rate of the 1h fluidity does not exceed 25.0% of the initial fluidity.

[0017] Further, the cementitious material is a reference cement, or a 42.5 (R) grade ordinary Portland cement or Portland cement.

[0018] Further, the cementitious material adopts the variety and proportion of cement and admixture in the actual project.

[0019] Further, in step (4) of the first step, the prepared chip or manufactured sand sample is directly sampled by the splitter method or the manual quartering method according to the GB / T14684 standard without screening, and multiple sand and stone powder mixed samples are respectively prepared for use. At this time, the addition time of the stone powder in the second step is changed to be manually added to the mixing pot at the same time as the sand.

[0020] Generally speaking, the present invention has the following advantages: (1) Using the particles below 4.75 mm in the sand for the experiment can comprehensively reflect the compatibility between granite chips or manufactured sand and the water reducer, rather than just the compatibility between stone powder and the water reducer.

[0021] (2) Using the fluidity instead of the vibrating table fluidity to characterize the fluidity of the mortar, the initial fluidity of the mortar is higher, and its 1h fluidity is also higher, so as to effectively distinguish the compatibility between different water reducers and granite chips or manufactured sand.

[0022] (3) For different water reducers, experiments are carried out with a unified solid dosage of the water reducer, and there is no need to carry out comparative mortar experiments, greatly reducing the experimental workload.

[0023] (4) The unscreened and ungraded chip or manufactured sand can be directly used, and after sampling, the experiment is carried out. There is no need to screen the chip into each particle size grade, greatly reducing the experimental workload and improving the experimental speed.

[0024] (5) Using the method of the present invention to respectively detect the compatibility of a variety of water reducers, according to the initial fluidity of the mortar and the time-dependent change rate of the 1h fluidity when different water reducers are used, water reducer varieties with good compatibility can be quickly preferably selected from a variety of water reducers. Specific embodiments

[0025] The following is a further detailed description of the present invention.

[0026] A screening method for water reducing agents, comprising the following steps: Step 1, preparing a granite chip or granite manufactured sand sample; (1) Taking representative chips or manufactured sand, drying them in an oven at 105 °C, and screening out particles larger than 4.75 mm.

[0027] (2) Using the chip or manufactured sand sample prepared in (1), sampling by the splitter method or the manual quartering method according to the GB / T 14684 standard, adding a 0.075 mm sieve, and determining its particle size distribution. According to the experimental results, calculate the content of stone powder (less than 0.075 mm) and sand (0.075 - 4.75 mm) in the chip or manufactured sand.

[0028] (3) The mass of sand in the mortar mix is 800 - 1350 g. At this time, the dosages of other materials are calculated according to the selected sand - powder ratio and water - powder ratio based on the mass of sand. Preferably, according to the sand mass (m s , with a particle size of 0.075 - 4.75 mm) being 1200 g, calculate the mass of each graded sand between 0.075 - 4.75 mm and the mass of stone powder (m f ).

[0029] (4) Using the chip or manufactured sand sample prepared in (1), sampling and screening by the splitter method or the manual quartering method according to the GB / T 14684 standard, and preparing multiple sand and stone powder samples for use according to the mass of each graded sand and stone powder obtained in (3).

[0030] Step 2, conducting a mortar fluidity experiment; (1) The water - powder ratio of the mortar is 0.50, and the sand - powder ratio is 2.0 - 3.0, preferably 2.0. The powder material includes a cementitious material and stone powder. The dosage of stone powder is calculated according to the ratio of stone powder to sand in the particle size distribution. The solid admixture content of the water reducing agent is the mass ratio of the solid of the water reducing agent to the powder material, the water - powder ratio is the mass ratio of water to the powder material, and the sand - powder ratio is the mass ratio of sand (with a particle size of 0.075 - 4.75 mm) to the powder material.

[0031] (2) When the sand - powder ratio is 2.0, prepare raw materials according to the mix ratio in Table 1: Table 1 Mortar Mix Ratio

[0032] When the water reducing agent is in liquid form, the liquid dosage of the water reducing agent should be converted according to the solid content of the water reducing agent, and the water content in the water reducing agent should be deducted from the total water volume.

[0033] (3) Conduct mortar fluidity tests for different water reducing agents. The specific test steps are as follows: ① Put the cement mortar mixer in a standby state, and then operate according to the following procedures: Add the mixture of water reducer and water into the mixing pot, and then add the powder materials (including cement, admixture and stone powder, pre-mixed evenly by hand) weighed according to the test mix ratio; Then start the machine immediately and stir for 4 minutes according to the automatic program, specifically: After stirring at low speed for 30 seconds, add the weighed sand evenly at the same time as the start of the second 30 seconds (manually add it to the mixing pot, not pre-add it to the sand tank), and stir at high speed for another 30 seconds. Stop stirring for 90 seconds, and use a trowel to scrape the mortar on the blades and the pot wall into the pot within the first 15 seconds, and then continue to stir at high speed for 60 seconds.

[0034] ② According to GB / T 2419 "Test Method for Fluidity of Cement Mortar", use a cement mortar fluidity tester (a truncated cone mold with an upper inner diameter of 70 mm, a lower inner diameter of 100 mm, and a height of 60 mm) to test the fluidity of the mortar, but use a glass bottom plate for the bottom plate and do not perform jolting.

[0035] ③ If the fluidity of all water reducer samples is lower than 180 mm or higher than 220 mm or segregation occurs, appropriately adjust the solid dosage of the water reducer, remix the mortar and test the fluidity again to make the initial fluidity of part of the mortar between 180 - 220 mm.

[0036] ④ After testing the fluidity, collect all the mortar, put it into a sample cylinder wiped with a wet cloth, cover the container, and let it stand for 1 h (calculated from the start of stirring after adding the powder materials into the water), then pour it out, stir at low speed with a cement mortar mixer for 30 seconds, and measure the fluidity after 1 h.

[0037] Step 3, Optimize the type of water reducer (1) Calculate the difference between the initial fluidity and the fluidity after 1 h, and compare it with the initial fluidity to obtain the time-dependent change rate of the fluidity. Use the initial fluidity to characterize the working performance, and use the time-dependent change rate of the 1 h fluidity to characterize the working performance retention ability.

[0038] (2) According to the initial fluidity of the mortar and the time-dependent change rate of the 1 h fluidity when using different water reducers, optimize the water reducer varieties with good compatibility.

[0039] (3) The judgment criteria for a water reducer with good compatibility with granite chips or manufactured sand are: the initial fluidity of the mortar is not lower than 180 mm, and the time-dependent change rate of the 1 h fluidity does not exceed 25.0% of the initial fluidity.

[0040] (4) The water reducer with a larger initial fluidity of the mortar and a smaller time-dependent change rate of the 1 h fluidity is the preferred water reducer variety. Examples

[0041] The raw materials used in the experiment are as follows: Cement: Portland cement of grade 42.5R; Granite chips: the maximum particle size is 4.75 mm, and the content of stone powder (the ratio of stone powder to the total mass of chips) is 12.5%. After screening, multiple groups of chip sands (1200 g per group) and stone powders (171 g per group) are prepared for use.

[0042] Three different water reducers: namely water reducer A, water reducer B, and water reducer C, all of which are powders.

[0043] Weigh the materials according to Table 2, prepare the mortar, and measure its initial fluidity and fluidity after 1 h, as shown in Table 3.

[0044] Table 2 Mortar Mix Ratio

[0045] Table 3 Mortar Properties

[0046] As can be seen from Table 3, the compatibility between water reducer A and granite chips is the worst, the compatibility between water reducer C and granite chips is the second, and the compatibility between water reducer B and granite chips is the best. Water reducer B is preferably selected.

[0047] The present invention detects the compatibility of different water reducers with the initial fluidity and the time-dependent change rate of fluidity after 1 h of high-fluidity mortar when using the same solid dosage of water reducer, and quickly selects the water reducer variety with good compatibility with a certain granite chips or manufactured sand. The method proposed by the present invention has the advantages of being able to comprehensively reflect the compatibility between granite chips or manufactured sand and water reducer, low experimental workload, and high experimental efficiency.

[0048] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for screening a water reducing agent, characterized in that: The following steps are included: Step 1: Prepare granite chips or machine-made sand samples: Take dry stone chips or machine-made sand, and sieve out particles larger than 4.75 mm; add a 0.075 mm sieve, measure its particle size distribution, and calculate the content of stone powder with a particle size less than 0.075 mm and sand with a particle size of 0.075-4.75 mm; prepare multiple sand and stone powder samples according to the particle size distribution for later use; Step 2: Conduct mortar fluidity test: Prepare mortar raw materials, including powder materials, sand, water reducer and water. Powder materials include cementitious materials and stone powder. The water-powder ratio of mortar is 0.50, the sand-powder ratio is 2.0-3.0, the amount of stone powder is calculated according to the ratio of stone powder to sand in the particle grading, and the initial solid content of water reducer is 0.10-0.15%; The mortar fluidity test of different water reducing agents is carried out as follows: Use a cement mortar mixer to mix the mixture of water reducer and water, powder material and sand according to the test ratio evenly; test the initial fluidity and 1h fluidity of the mortar, where the bottom plate uses a glass bottom plate and does not bounce; Step 3: Select the water reducing agent type: Calculate the change rate of fluidity over 1 hour; select the water-reducing agent with good compatibility from a variety of water-reducing agents based on the initial fluidity and change rate over 1 hour of different water-reducing agents.

2. The method for screening a water reducing agent according to claim 1, characterized in that: The solid dosage of water-reducing agent is the mass ratio of water-reducing agent solid to powder material, the water-powder ratio is the mass ratio of water to powder material, and the sand-powder ratio is the mass ratio of sand to powder material; the mass of sand required for each experiment is 800~1350g; when the water-reducing agent used is liquid, the amount of water-reducing agent liquid is converted according to the solid content of the water-reducing agent, and the water content in the water-reducing agent is deducted from the total water content.

3. The method for screening a water reducing agent according to claim 1, characterized in that: The machine stirring in step 2 is stirred according to an automatic program, including stirring at a low speed for 30 seconds, then manually adding the weighed sand into the stirring pot evenly at the beginning of the second 30 seconds, stirring at a high speed for another 30 seconds, then stopping stirring for 90 seconds, and scraping the mortar on the blades and the pot wall into the stirring pot with a spatula within 15 seconds, and then continuing stirring at a high speed for 60 seconds.

4. The method for screening a water reducing agent according to claim 1, characterized in that: When testing the fluidity of mortar, if the fluidity of all water-reducing agent samples is lower than 180 mm or exceeds 220 mm or segregation occurs, the amount of water-reducing agent solids should be appropriately adjusted, and the mortar mixing and fluidity test should be repeated so that the initial fluidity of some mortars is between 180 and 220 mm.

5. The method for screening a water reducing agent according to claim 1, characterized in that: After testing the fluidity, all the mortar is collected and placed in a sample tube wiped with a wet cloth. The container is covered and poured out after being left to stand for 1 hour. It is stirred at low speed with a cement mortar mixer and the fluidity is measured after 1 hour. The timing of the mortar being placed in the sample tube and left to stand for 1 hour is calculated from the time when stirring starts after the powder material is added to the water.

6. The method for screening a water reducing agent according to claim 1, characterized in that: The initial fluidity is used to characterize the working performance, and the time-dependent change rate of the 1h fluidity is used to characterize the ability to maintain the working performance. According to the initial fluidity and time-dependent change rate of the mortar when using different water reducers, the water reducer with good compatibility is selected from a variety of water reducers.

7. The method for screening a water reducing agent according to claim 1, characterized in that: The criteria for judging whether the water-reducing agent is compatible with granite chips or machine-made sand is that the initial fluidity of the mortar is not less than 180 mm, and the rate of change of fluidity over 1 hour does not exceed 25.0% of the initial fluidity.

8. The method for screening a water reducing agent according to claim 1, characterized in that: The cementitious material is standard cement, or 42.5 (R) grade ordinary Portland cement or Portland cement.

9. The method for screening a water reducing agent according to claim 1, characterized in that: Cementitious materials adopt the types and proportions of cement and admixtures used in actual engineering projects.

10. The method for screening a water reducing agent according to claim 1, characterized in that: The stone chips or machine-made sand samples prepared in step 1 are directly sampled according to GB / T 14684 standard using the divider method or manual quartering method without screening, and multiple sand and stone powder mixed samples are prepared for standby use. At this time, the stone powder addition time in step 2 is changed to manually adding it to the stirring pot at the same time as the sand.

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