Research Of Properties And Hydration Mechanisms Of Portland Cement And Calcium Aluminate Cement Compound System

This paper stresses the investigation in the physical performances of a series of composite cement systems composed of Calcium aluminate cement and Portland cement in different proportions. XRD, DSC-TG, SEM and ESEM are used to determine hydrated products of composite cement systems, through which hydration mechanism is preliminary discussed. Furthermore, lime and gypsum are added to composite cement systems and the influence of them on the setting time, mechanical properties, dry shrinkage and hydration of composite cement systems is studied.The test results reveal that blends of calcium aluminate cement and Portland cement exhibit different setting behavior, strength development and dry shrinkage characteristics with that of each of two binders. Portland cement in some range added to calcium aluminate cement can retard the setting of the cement, and only in minor amounts of Portland cement slightly increase the compressive strength without losing strength afterwards. While some dose of Calcium aluminate cement blended to Portland cement can accelerate setting of the system, even cause the composite cement to instant setting. In minor amounts of calcium aluminate cement, unfavorable influence on strength is limited without losing strength over period of time. The dry shrinkage of Portland cement and calcium aluminate cement composite cement system trends towards enlarger.Adding hydrated lime to the Calcium aluminate cement and Portland cement composite cement system, improve the early strength, accelerate setting and reduce dry shrinkage to some extent. Unslaked lime improves the long-term strength, accelerates setting and reduces dry shrinkage of the composite cement limitedly. Anhydrite will raise the early and long-term strength, accelerate setting and reduce dry shrinkage of the system, but if excessive amount of it will product disadvantageous expansion. Dehydrate gypsum will raise the early and long-term strength of the system, reduce dry shrinkage, and if excessive amount of it willproduct disadvantageous expansion either, but will prolong the setting time.Adding both hydrated lime and dehydrate gypsum to the composite cement system can improve the early and long-term strength largely, shorten the setting time, and make the dry shrinkage of the four contents is smaller than that of Portland cement, and doesn't cause the strength of the composite decrease with time increase.