Outcomes of the RILEM round robin on degree of reaction of slag and fly ash in blended cements

Working group 2 of the RILEM TC 238-SCM undertook a comparison of laboratories and techniques for the quantification of the degree of reaction of supplementary cementitious materials in blended cements. A common set of binary pastes of Portland cement with two slags, a calcareous and a siliceous fly ash was tested in seven laboratories. The results obtained by selective dissolution produced were quite scattered and seemed to underestimated the degree of reaction. The analysis of portlandite consumption was found to significantly underestimate the reaction unless additional data from XRD and electron microscopy was gathered to complete the corrections. Despite limited access to electron microscope among the participants and thus only a small data set being collected, this technique appeared as one of the most consistent. XRD-PONKCS gave considerable scatter, due mainly to a lack of a strict protocol and excessive overlap of slag and C–S–H signals. Overall, the study indicated that the precision of determination of the degree of reaction of SCMs in cement pastes is rather low and at best ±5%.