Experimental investigation of hydration of ternary blended cement paste

In this paper, ternary and binary blended cement pastes as well as pure Portland cement paste were prepared by Portland cement, ground granulated blast-furnace slag (GGBFS), limestone powder and water, which were then hydrated from 1 to 91 days at 20 °C in a sealed environment. At each curing age, the hydration kinetics of cement and slag was determined by XRD/Rietveld and selective dissolution method (EDTA), respectively. The content of CaCO3 (limestone) was quantified by Thermogravimetric analysis (TGA) technique. The degree of hydration of cement clinker was distinctly accelerated by the single addition of slag or limestone within 91 days of hydration. The coexistence of slag and limestone in ternary blended cement accelerated the hydration of cement clinker within the first 14 days of hydration, but lowered the degree of hydration of cement clinker after 91 days of hydration compared with other pastes. The degree of reaction of slag in blended cement pastes was about 8% and 35% after 1 and 91 days of hydration, respectively, which was almost not influenced by the addition of limestone powder. A small amount of limestone, i.e. around 2% of the total solid raw materials, was reacted in pastes, and mainly occurred at the early age. Based on the experimental investigation, the results show that the hydration of calcium silicate phases of cement in pastes was enhanced by the presence of limestone, but hampered by slag. The hydration of calcium alumina phases of cement was greatly accelerated by the addition of slag, and also enhanced by the presence of limestone powder in binary blended limestone cement paste at early age. However, the coexistence of limestone with slag in ternary blended cement paste restrained the hydration of calcium alumina phases of cement.