Effects of sodium tripolyphosphate addition on early-age physicochemical properties of cement pastes

Sodium tripolyphosphate (STPP) is generally employed as a dispersing agent in ceramic processing and could be a low-cost plasticizer for cement-based materials. The aim of the present work was to evaluate the effect of STPP on the early-age behavior of cementitious matrices. Different concentrations of STPP were considered (0 g/L to 50 g/L). Rheological tests, setting time measurements, microcalorimetry and compressive strength tests were performed on Portland cement pastes with W/C ratios equal to 0.30 and 0.40. The main results showed that the effect of STPP on early-age cement paste properties was dependent on its concentration. The rheological results showed a pronounced increase of viscosity for the higher STPP dosage, immediately after the end of mixing. Microcalorimetric measurements revealed an increasing delay in early-age hydration of cement pastes as the concentration of STPP increased. This delay was also recorded on setting times for the lower STPP dosages. The effect was inverted in the case of higher STPP concentrations, for which faster setting of cement pastes was observed. In spite of the delay on the early-age hydration rate due to STPP, no significant difference was recorded between the 28 day-compressive strength values of the different mixtures investigated. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11