In modern commercial concrete, concrete admixtures have been widely used. Its use greatly saves corporate costs and also gives concrete excellent properties. Therefore, it is accepted by many concrete suppliers. However, due to the current use of concrete admixtures in my country, Most of the additive manufacturers are medium and small-scale enterprises, and the quality of the additives they produce fluctuates greatly, which requires the concrete mixing station to test every batch of additives entering the factory. Through summary and experiments, it was found that there is a certain relationship between the water consumption of the standard consistency of cement slurry and the water consumption of the standard consistency of cement slurry mixed with admixtures. This relationship can be expressed as the water reduction rate of concrete admixtures.
With the advancement of science and technology, concrete admixtures have become the fifth essential material in addition to cement, coarse and fine aggregates, admixtures and water. As an important indicator for detecting admixtures, water reduction rate plays an important role in determining the quality of admixtures. Category determination is made based on statistical analysis of test data, errors of measuring instruments, and actual conditions of the instrument and equipment itself. Through uncertainty evaluation, synthesis, and expansion of each factor, the uncertainty of the water reduction rate of the admixture is finally obtained. The credibility of the water reduction rate test results has guiding significance and provides a strong guarantee for objective and fair evaluation of the quality of admixtures.
The technical indicators of concrete admixtures include water reduction rate, bleeding rate ratio, air content, setting time difference, compressive strength ratio, shrinkage ratio, etc. Among all these technical indicators, water reduction rate is the key factor for preparing concrete. is the first thing to consider. The mechanism of water reduction is that there is a surfactant in the admixture, which diffuses, lubricates, and moistens the cement particles, so that the cement particles are evenly distributed, thereby reducing water consumption, lowering the water-cement ratio, saving cement, and The purpose of improving work performance. Therefore, the detection of water reduction rate is more important. This article briefly talks about the method of using cement slurry fluidity to detect water reduction rate:
The cement slurry fluidity test is generally used to measure the dispersion effect of admixtures on cement slurry. It uses cement slurry within a certain period of time. Indicates the maximum diameter of the paste flowing freely on the glass plane. Use the fluidity of cement slurry to detect the water reduction rate. The method is to prepare two cement slurries. When the fluidity of the cement slurries is basically the same, the difference between the water consumption with and without admixtures is the same as the water consumption without admixtures. The percentage of the amount is the water reduction rate.
For different types of cement, the fluidity of cement slurry mixed with admixtures is different, and the workability of the mixed concrete is different. This is the compatibility of cement and admixtures, so when choosing admixtures Pay attention to compatibility with cement.
Various factors causing uncertainty
Testing of water reduction rate of concrete admixtures, in accordance with the specifications of GB8076-2008 "Concrete Admixtures", using standard cement, fineness modulus For medium sand with a particle size of 2.6 to 2.9 and aggregate with a particle size of (5 to 10) and (10 to 20) mm, the admixture detection uses a mix ratio and is calculated according to the absolute volume method. Mix two types of concrete without admixture (A) and with admixture (B) respectively. The slump of the two concrete mixtures meets the requirements of (80±10) mm. According to the unit water consumption of the two concrete mixtures , calculate the detection results. The main factors that affect the uncertainty of the compressive strength of concrete cubes include: the standard uncertainty introduced by measurement personnel performing repeated measurements under the same conditions; the standard uncertainty introduced by measuring equipment.
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