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本文用胶体化学的理论分析和讨论了水泥浆絮凝现象的本质和减水剂的作用机理。提出:不掺外加剂的新拌水泥净浆的絮凝及流变性主要受浆体中颗粒间的范德华引力和以ζ电位表征的静电斥力之间的矛盾支配;减水剂的作用机理应从多种作用的共同结果考虑,高效减水剂以产生较高的双电层静电斥力为主,木钙虽也产生一定的双电层静电斥力,但以产生大分子保护作用为主;高效减水剂先掺时其作用可概括为“近程吸附——部分电荷中和”,后掺时为“远程吸附——ζ电位迭加”。本文还提出:随着硅酸盐水泥熟料中 C_2A、C_4AF 的增加,阴离子高效减水剂对水泥的作用效果变差。为此,可用后掺法加入高效减水荆,或用复合使用法,即先掺少量具有大分子保护作用的木钙,隔一定时间再掺高效减水剂。后一方法也适用于解决流态混凝土中坍落度损失加快的问题。
In this paper, the theory of colloidal chemistry is used to analyze and discuss the nature of the flocculation phenomenon of cement slurry and the action mechanism of water-reducing agent. It is suggested that the flocculation and rheological properties of fresh cement paste without additives are mainly dictated by the contradiction between the van der Waals attraction between the particles in the slurry and the electrostatic repulsion expressed by the ζ potential; the mechanism of action of the water reducer should be from a variety of The common effect of the action considers that the high-range water-reducing agent is mainly responsible for the higher electrostatic repulsive force of the electric double layer, while the wood calcium has a certain electrostatic repulsion of the electric double layer, but it mainly produces macromolecular protection; the high-efficiency water-reducing agent The role of the first blending can be summarized as “proximity adsorption - partial charge neutralization” and after doping is “remote adsorption - superposition of zeta potential”. This article also proposes that: With the increase of C2A, C_4AF in Portland cement clinker, the effect of anionic superplasticizer on cement becomes worse. For this purpose, the post-doping method can be used to add a high-efficiency water-reducing agent, or use a compound method, that is, first add a small amount of wood calcium with a macromolecular protective effect, and then add a superplasticizer at a certain time. The latter method is also suitable for solving the problem of accelerated slump loss in the flow of concrete.