Effects of sodium tripolyphosphate on the rheology and hydration rate of Portland cement pastes

The aim of this study was to evaluate the effect of sodium tripolyphosphate (STPP) on the early-age behaviour of cementitious matrices. Different concentrations of STPP were considered (1–50 g/l). Rheological tests, setting time measurements, microcalorimetry and compressive strength tests were performed on Portland cement pastes. The main results showed that the effect of STPP on the early-age cement paste properties strongly depends on its concentration. Rheological tests showed an increase of viscosity for the higher STPP dosage. Microcalorimetric measurements revealed an increasing delay in early-age cement hydration as the STPP concentration increased. This delay was also recorded on setting times for the lower STPP dosages. The effect was inverted in the case of the higher STPP concentrations, for which a false set phenomenon was observed. In spite of the delay on hydration rate, the differences recorded between the compressive strength values of the different mixtures remained low.