STUDIES ON EFFECTS OF ACTIVATORS ON PROPERTIES AND MECHANISM OF HYDRATION OF PORTLAND CEMENT

摘要

The need for a concrete with sufficient strength at a very early age has led to the use of various admixtures such as the calcium chloride which has been, for some time, the most widely used set accelerator in this field. However, the presence of chloride causes serious problems regarding steel corrosion in reinforced and prestressed concrete members. This concern has led to the development of a number of chloride-free admixtures. The purpose of this work is to investigate the effect of using the calcium nitrate alone or combined to the triethanolamine on the setting and hardening process of cement pastes at 20℃ temperature. Tests were performed on specimens from various mixes considering two types of cements. The results obtained indicate that the calcium nitrate used alone acts as a setting accelerator and improves the compressive strength at 24hrs. However, in the long term, its strength increase is not significant so as to be considered as a hardening accelerator. In return, the use of calcium nitrate in combination with triethanolamine leads at very early age to significant results with respect to both setting and hardening acceleration, and to a continuous compressive strength increase with time. The results regarding mechanical strength were also confirmed by an analysis of the materials hydration kinetic.