HARDENING AND EXPANSION PROCESSES IN C_3S-(CA+C S H_2)-H SYSTEM

摘要

Blended expansive cements consisting of Portland cement as matrix binder and an expansive addition, which is able to form ettringite (C_3A.3C S .H_(31)), represent binders having good expansive properties. The composition of the binders and the dosage of the components can control their expansion. The expansive additions consist of an aluminate material (high aluminate cement, sulphoaluminate clinker, Portland high aluminate clincher) and gypsum. Taking into account that C_3S is the main compound of the Portland cement the processes that are going on during their hardening in the presence of sulphate-aluminate additions (CA, C_4A_3 S, C_3A) should be interesting. The present paper brings information about the hardening and expansive processes in the binding system C_3S-(CA+C S H_2)-H. The content of the expansive additions (CA+C S H_2) in the binding mixes was of 10-30%. CA and C S H_2 were dosed corresponding to an Al_2O_3/SO_3 molar ratio of 1/3. The content of the expansive addition in correlation with the humidity of the curing environment exerted a significant influence on the ettringite formation and on the expansion. This was as greater as the amount of the expansive addition and the humidity of the environment were higher. In the case of the binder with 30% (CA+C S H_2), in humid atmosphere, the expansion was so great that the hardening structure formation was hindered (the samples disintegrated). The best binding behaviour presented the composition that had a content of 10% expansive addition. This composition has developed good mechanical strengths and a relative low expansion, compensating the shrinkage. A relative good correlation between the ettringite formation and the expansion has been pointed out.