Compatibility assessment of commercial cements and superplasticizers

Abstract

In spite of the widespread use of superplasticizers, it is still not possible to anticipate the compatibility between these materials and a specific cement. Such lack of knowledge does not restrain the use of admixtures in concrete, but it makes it harder to optimise mixtures and can lead to an unexpected behaviour. Therefore, in order to contribute to the on-going discussion concerning the cement-superplasticizer interaction, a study was conducted where the effectiveness of one naphthalene sulfonate-type and four polycarboxylate-type superplasticizers was assessed against a CEM I 52,5R and a CEM I 42,5R cement supplied from two different sources in Portugal. The results show the impact of the composition of commercial cements and the nature and dosage of commercial chemical admixtures on the cement-superplasticizer compatibility. This translates the difficulties felt by the end users on a day to day basis and stresses out the urgent need of the development of a compatibility indicator that can be straightforwardly utilised by the end user.