CALORIMETRY, RHEOLOGY AND COMPRESSIVE STRENGTH OF SUPERPLASTICIZED CEMENT PASTES

Calorimetry, together with fluidity and compressive strength measureme nts, has been exploited to investigate the hydration kinetics of sever al types of cements in the presence of different poly-beta-naphthalene sulfonate (PNS) superplasticizers for periods up to 20 hours. The hea t flux thermograms show a number of distinct features which vary marke dly with, for example, cement type or superplasticizer composition and concentration. The calorimetric results show that the two sodium-PNS salts investigated (differing in molecular weight) and the calcium-PNS salt exert similar retardation effects (increase of dormant period). The rates of hydration reactions occurring beyond the lag period (set or acceleration period) are however influenced quite differently by Na - and Ca-PNS salts. The influence of Na-PNS is confirmed to be strongl y dependent on the C3A content of the cement. The fluidity results sho w a dependence both on the type of Na-PNS (molecular weight) and the c ounterions (Na, Ca).