Influence Of Compounding Chemical Admixtures On Cement Hydration Process

With the wide application of pumping concrete, especially ready-mixed concrete, pumping agents have become a most important compounded chemical admixture widely used. In general, pumping agents contain ingredients of superplasticizers, retarders and air entraining agents. There have been some reports about the influences of superplasticizers, retarders and air entraining agents respectively, but the influences of their compounding application on cement hydration process have been seldom reported from now on. Considering this situation, in this paper, the influences of compounding superplasticizers, retarders and air entraining agents on cement hydration process were investigated systematically.Through the cement paste experiments, the influences of superplasticizers, retarders or air entraining agent, and the compounding of superplasticizers with retarders and the compounding of superplasticizers with retarders and air entrarning agent on cement setting time were investigated. By using the direct thermometry and XRD technique, the influences of superplasticizers, retarders, air entraining agent, the compounding of superplasticizers with retarders, the compounding of superplasticizers with retarders and air entraining agent on cement hydration heat, the temperature peak of hydration, the appearing time of temperature peak, and the quantity of Ca(OH)₂ and ettringite(AFt) at different age were investigated.The obtained result showed that superplasticizers used together with retarders can further postponed the cement setting time because of their cooperating effects; superplasticizers used together with retarders and air entrarning agent has no big change to the the cement setting time when compare to superplasticizers used together with retarders.Compared to superplasticizers and redarders used separately, if superplasticizers used together with retarders, both the dispersing action of superplasticizers and the retarding action of retarders can be strengthened due to their cooperating effects, so the temperature peak can be further postponed, and the temperature peak, the hydration heat and the quantity of Ca(OH)₂ at the time of appearing of temperature peak can be also further decreased; When superplasticizers used together with sodium gluconate, the cooperating effects can be affected by the time of appearing of temperature peak of superplasticizers and sodium gluconate, the bigger time gap, the better work of the cooperating effects.Compared to superplasticizers used with sodium gluconate, if superplasticizers used together with superplasticizers and sodium gluconate, the temperature peak and the hydration heat and the quantity of Ca(0H)2 at the time of appearing of temperature peak can be strengthened because of the cooperating effects; compare with superplasticizers used to sodium gluconate, we can say, the cooperating effects of superplasticizers used with sodium gluconate is the main factor in the three admixtures used together on the cement hydration.The obtained results have a great significance for decreasing cement hydration heat, and the temperature peak of hydration, postponing the time of appearing of temperature peak, so preventing cracks of concrete caused by temperature stress through compounding superplasticizers, retarders and air entraining agents.