Adjustment of concrete mix proportion
I. small scale adjustment
When the properties of raw materials change little, for convenience, usually only a single parameter is adjusted, while other parameters are kept as constant as possible. The advantage of this method is simple and easy to operate. However, after adjustment, the comprehensive performance of the concrete in the concrete mixing plant may deviate from the optimum. In other words, the adjusted concrete mix proportion is not necessarily the optimal mix proportion. However, due to the small adjustment range, after adjustment, the deviation between the mix ratio of concrete and the optimal mix ratio will not be too large.
II. Adjustment of concrete water consumption
When the fineness or particle size distribution of cement changes, or the water demand ratio of mineral admixture changes, or the water reduction rate of superplasticizer changes, the water consumption of concrete may change. Commercial concrete is produced by slump control. When the actual water consumption of concrete changes, if not properly adjusted, it will cause the change of the actual water binder ratio, which will lead to the change of concrete strength.
This method is used to adjust the mix proportion of the concrete mixing plant. Because the water binder ratio is kept unchanged, and the composition of the cementitious material is not changed, the strength of the concrete is basically unchanged. However, due to the change of the total amount and water consumption of cementitious materials, the heat release and shrinkage deformation of concrete will change accordingly.
III. adjustment of concrete strength
When the strength of cement changes, the strength of concrete will also change. There are two parameters that affect the strength of concrete, one is cement strength, the other is water cement ratio. Therefore, the strength of concrete can be kept unchanged. According to the actual strength of cement to be used at present, the water cement ratio can be recalculated, and the amount of each kind of cementitious material can be calculated with this water cement ratio and the water consumption of concrete.
By using this method to adjust the mix proportion of concrete, the workability of fresh concrete will not change significantly because of the constant water consumption of concrete. Of course, after the amount of cementitious material is adjusted, the heat release of concrete will also change, and the heat release rate may also change due to the change of retrograde water.
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