延缓硫铝酸盐水泥凝结的研究

以硼砂和硫酸铝为主要成分研制成新型硫铝酸盐水泥缓凝剂。实验结果表明，只要合理控制缓解凝剂中硼砂与硫酸铝的比例，在一定的加入量范围可保证水泥适度缓慢，对强度也不利影响，通过对水泥化初期浆体中钙矾石生成量的测定、水泥浆体液组成的分析及XRD，DTA，SEM分析，对这种新型缓凝剂的作用机理进行了系统研究，由于熟料颗粒形状的极度不规则和表现凹凸不平，只有加入足够的硼砂量才能保证熟粒颗粒周围迅速形成严密的硼酸钙包裹层，有效抑制水化；适量硫酸铝的同时引入，可以促使包裹层外部相中析出钙矾石，相当于在包裹层外液相中设置了一个降低液相浓度的机构，迫使水较快向包裹层内渗透，从而达到促使包裹层破裂、避免过度抑制水化的目的。

STUDY ON RETARDING THE SET OF SULPHOALUMINATE CEMENT

A new type of retarder, of which main ingredients are borax and aluminum sulphate, was developed for sulphoaluminate cement (SAC). Experimental results show that as long as the ratio of borax and aluminum sulphate in the retarder and the amount of the retarder added are controlled appropriately, a moderate retardation of hydration of sulphoaluminate cement can be achieved without negative effects on strength. The action mechanism of the retarder was studied by XRD, SEM, DTA with the measurements of ettringite formed and the analyses of the liquid composition of cement pastes at the initial hydration stage. The study indicates that it is the dense calcium borate wrapping layer around the clinker particles, which is formed when enough amount of borax is added, that efficiently retarded the hydration. Adding proper amount of aluminum sulphate promoted the crystallization of ettringite in the liquid phase outside the wrapping layer. As a result, the concentration of the liquid outside the wrapping layer is decreased and the water is forced to permeate into the inside of the layer more quickly. And, the breaking of the wrapping layer is accelerated and the over retardation was avoided.