Kinetic and morphological differentiation of Ettringites in plain and blended Portland cements using Metakaolin and the ASTM C 452-68 test. Part I: kinetic differentiation

Abstract

In this first part of the study, the results obtained in prior research with XRD and SEM, as well as the Le Chatelier-Ansttet test were confirmed with the ASTM C 452-68 test. To this end, 20%, 30% and 40% metakaolin (MK) was added to ten Portland cements, six OPCs and four SRPCs. Both the ten plain PCs and the 30 metakaolin (MK) blends were tested for two years under ASTM C 452-68 specifications, determining not only the percentage increase in length, ΔL(%), of the specimens, but also the sulphate content in the curing water. Other parameters studied included: chemical analysis of the cementitious materials used and specific properties of some of the cements tested.The experimental results, ΔL(%) versus time, re-confirmed that the formation rate of ettringite from the reactive alumina, Al2O3r-, present in the pozzolan must be substantially higher than the formation rate of ettringite from the C3A present in the PC. This was verified by the variation of the sulphate content in the specimen curing water throughout the test. In light of those findings, in this article these two types of ettringite are denominated rapid forming ettringite or ett-rf, and slow forming ettringite or ett-lf.