INFLUENCE OF CEMENT TYPE IN THAUMASITE FORMATION

摘要

The many uncertainties surrounding the main variables involved in thaumasite formation warrant a careful study of their role in this process. The chief aim of the present study was to establish the impact of different variables on thaumasite formation. A relationship was also drawn between this process and mechanical strength and porosity of cement. Cement mortar samples were prepared and stored at 0-5°C in a number of different water-base solutions. The variables studied were: a) Type of cement (CEM IA 42.5 SR; CEM IIIA 42.5 SR and CEM IVA 32.5 SR); and b) storage media (distilled water, ASTM sea water and saturated gypsum solution]. The samples were analyzed by FTIR at different ages -1, 3, 6, 8, 10, 12, 20, 23 and 40 months - to ascertain whether thaumasite had formed. Mechanical strength and porosity of the samples were also determined at the above ages and selected samples were studied using SEM/EDX. Thaumasite formation prompted no material change in mechanical strength at the ages studied. More thaumasite was found to form in saturated gypsum than in sea or distilled water. The worst durability was observed for mortars made with CEM IIIA 42.5 SR immersed in the gypsum solution, which presented TSA-mediated surface cracking at corners and around the edges from 20 months onward.