Water reducing agent is an admixture that can be added before or during the mixing process to reduce or greatly reduce the water used for concrete mixing.
Adding water-reducing agent to concrete can effectively improve the workability and fluidity of concrete, improve the structure of concrete, and increase its strength. It can also save a lot of cement while maintaining the strength of concrete. Therefore, water reducing agent has become an indispensable admixture for preparing commercial concrete.
Seeing that the water-reducing agent can increase the degree and save a lot of cement, the construction personnel mistakenly believe that when preparing the commercial concrete and using the water-reducing agent, the higher the water-reducing rate, the better, and the higher requirements are even when preparing low-grade concrete. The water reduction rate. Under normal circumstances, as the water reduction rate increases, the strength of concrete will become higher and higher. For concrete with high water glue, the reduction in water consumption will reduce the drying shrinkage of the concrete, which is of course very beneficial to increase the strength of the concrete and reduce the shrinkage and cracking of the concrete.
But at present, the general design of concrete construction has a low water-to-binder ratio.
Since auto-shrinkage cannot be ignored, if the water consumption is greatly reduced, the internal drying shrinkage of the concrete will be increased, thereby increasing the auto-shrinkage of the concrete.
In addition, the preparation of commercial concrete is generally mixed with retarder, because the hydration is slow, the concrete does not set for a long time, and the concrete surface loses water seriously, which increases the risk of shrinkage and cracking of the concrete. Of course, some people think that we can prevent concrete from drying and shrinking by watering and curing, but the extremely low water glue is denser than concrete, and the water seldom can penetrate into the concrete, and it is difficult to achieve the purpose of supplementing the lack of water. .
Someone has tested the high water reducing rates of three commonly used water reducing agents
molasses, wood calcium, and naphthalene-based water reducing agents, which were 6%, 8%, and 20% respectively. Although the naphthalene-based water reduction rate is high, the concrete shrinkage value after adding the above-mentioned water-reducing agent is higher than that of the naphthalene-based product, while the low water-reduction rate of molasses is low. It is a common habit to reduce the amount of cement by reducing water and increasing the degree. However, if the amount of cement is drastically reduced and the amount of cement is too small, because the cement layer is too thin, micro-cracks are more likely to occur, the ultimate elongation of concrete is reduced, and the tensile strength of concrete is reduced. Excessive reduction of the amount of cementitious material will increase the elastic modulus of concrete When the same shrinkage deformation and temperature deformation are the same, the deformation stress increases, and the concrete is prone to cracking.
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