Structure formation of plasticized cement systems under heat-moisture treatment

Abstract

Reducing the water-cement ratio is successfully achieved using superplasticizers (SP). However, their use can reduce the early strength of concrete and reinforced concrete. Heat-moisture treatment (HMT) is the leading way to accelerate concrete strength. The use of the latest SP based on polycarboxylate esters (PCE) allows adjusting the HMT mode, in particular, to reduce the presteaming period duration. The structure formation of cement pastes was studied depending on PCE modification and the presteaming period duration. The authors show PCE effectiveness in terms of reducing the water-cement ratio and joint action with HMT. It was found that the most effective use of low PCE dosages when using HMT. Increasing the amount of introduced SP to 1.2-2.0 % doesn’t lead to significant changes in initial and final setting times of cement pastes. The results of the study of cement stone compressive strength after HMT and on the 28th day, also the density and capillary porosity revealed a slight deterioration of these physical and mechanical properties (up to 5-10 %) when the presteaming period was abandoned. The results of X-Ray Diffraction analysis indicate no significant differences in the mineralogical composition of cement stone, which hardened at the HMT with the presteaming period of 2 hours and without it. The study of the cement stone microstructure showed that the PCE introduction in cement pastes contributes to the stone structure compaction and reduction of the number of pores. There were no significant changes in the cement stone pore structure, depending on the presteaming period duration. The conducted research shows that it is possible to regulate the HMT modes for the hardening of cement systems with SP.