磷酸盐和氟盐对水泥凝结特性的影响及作用机理

为揭示磷酸盐与氟盐延缓水泥水化的作用机理,向硅酸盐水泥中分别掺入易溶性和难溶性的磷酸盐和氟盐,利用XRD、微量热仪等微观测试手段,研究了不同胶凝体系的凝结特性和水化特性。试验结果表明,P₂O₅与氟当量掺量在0.5%~1.5%范围内时,易溶性的Na₂HPO₄,Na₃PO₄与难溶性的CaF₂会显著延缓水泥的凝结时间,而难溶性的CaHPO₄,Ca₃(PO₄)₂与易溶性的NaF则不会产生明显的缓凝,甚至还会出现速凝。微观测试表明,易溶性的Na₂HPO₄,Na₃PO₄和难溶性的CaF₂是通过延长水泥的水化诱导期导致凝结时间延长。其中,Na₂HPO₄,Na₃PO₄主要通过降低液相pH值、形成铝相水化产物以及硅酸盐固溶体等多重效应叠加,CaF₂则是通过与水泥颗粒表面水化产物的H⁺形成氢键产生的吸附效应,延缓水泥的水化。

Influence of Phosphate and Fluoride on Cement Setting and Its Working Mechanism

Soluble and insoluble phosphate and fluoride were incorporated into cement respectively,and setting and hydration of pastes were investigated by using XRD and micro calorimeter.The results indicate that,when equivalent content of P2 O5 or F varies from 0.5% to 1.5%,setting time of cement is significantly increased by blended soluble phosphates such as Na2 HPO4 and Na3 PO4 and insoluble CaF2 ,whereas insoluble phosphates such as CaHPO4 and Ca3 (PO4 )2 and soluble NaF have not obvious retarding effect on cement setting,even flash setting is seldom ob-served.Microscopic analysis on soluble phosphate and insoluble fluoride discloses that they retard cement setting due to lengthened induction period.As for soluble Na2 HPO4 and Na3 PO4 ,they can decrease PH value,produce hy-dration products of aluminum phase and yield silicate solid solution,whereas insoluble CaF2 retards hydration of ce-ment by absorption effect of hydrogen bond,which comes from the combination of CaF2 with H + of hydration prod-ucts located on surface of cement particles.