As the raw material of concrete, sand is a natural resource formed in the long-term process of nature, and the more it is used, the less it is used. Although we have been used to the application of river sand, it will soon become history, and the application of machine-made sand will soon come. But now, it is in a stage of green and yellow, the variety of sand is miscellaneous, the index is not reasonable and fluctuates greatly, which affects the quality of concrete.

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砂子质量波动，主要是颗粒形状与级配不合理导致的比表面积、孔隙率、流变性的变化。混凝土中的水，一是用于胶材水化产生强度、二是对固体材料表面润湿并填充其空隙使之产生流变方便施工。水在混凝土中的存在方式有三种：结合水、吸附水、自由水。

The fluctuation of sand quality is mainly caused by the change of specific surface area, porosity and rheological property caused by unreasonable particle shape and gradation. The water in concrete is used to produce strength by hydration of glue material, and to wet the surface of solid material and fill its gap to make it rheological, which is convenient for construction. There are three existing ways of water in concrete: combined water, adsorbed water and free water.

自由水受体系的电性吸附力小，若混凝土拌合物的密实度差则空隙通道粘滞阻力小而使自由水容易泌出。通常的办法，一是增加细砂用量、二是增加掺合料用量。现在的问题就是细砂紧缺、需水量少的粉煤灰同样紧缺。

If the compactness of the concrete mixture is poor, the viscosity resistance of the gap channel is small and the free water is easy to secrete. The common solution is to increase the amount of fine sand and admixture. Now the problem is that fine sand is in short supply, so is fly ash, which needs less water.

离析，不仅影响施工、更影响了混凝土的匀质性。混凝土的离析，是浆骨分离导致的。浆骨分离，一是漏浆就如同泌水是因为骨料的孔隙率太大，二是因为浆骨之间不黏连导致浆体泌出。

Segregation not only affects the construction, but also affects the homogeneity of concrete. The segregation of concrete is caused by the separation of mortar and bone. There are two reasons for the separation of pulp and bone. One is that the leakage of pulp is like bleeding because the porosity of aggregate is too large; the other is that the non adhesion between pulp and bone leads to the bleeding of pulp.

泌浆现象通常是因为聚羧酸盐系外加剂过掺造成的。聚羧酸盐系外加剂是一个系列，不同的分子结构性能差距会很大，也包括减水率差距很大，可能在20%—35%之间波动。

The bleeding phenomenon is usually caused by the over mixing of polycarboxylate additives. Polycarboxylate series admixtures are a series, and different molecular structures and properties will vary greatly, including water reduction rate, which may fluctuate between 20% and 35%.

我们在配合比设，希望随着外加剂掺量的提高减水率线性增大，但忽略了其饱和掺量。一旦超过饱和掺量，混凝土拌合物中的部分水会被排出浆体，浆体与骨料分离，浆体本身又板结黏底造成泌浆现象。

In the design of mix proportion, we hope that the water reducing rate will increase linearly with the increase of admixture content, but we ignore its saturated content. Once the saturated content is exceeded, part of the water in the concrete mixture will be discharged from the slurry, and the slurry will be separated from the aggregate, and the slurry itself will harden and stick to the bottom, resulting in bleeding.

所以，如何把适当的自由水留在浆体以及拌合物体系中，是克服现阶段砂子质量以及聚羧酸盐系外加剂质量对混凝土匀质性影响的重要因素。

Therefore, how to keep proper free water in the slurry and mixture system is an important factor to overcome the influence of sand quality and polycarboxylate admixture quality on concrete homogeneity.