Polycarboxylate and Polyether Admixture Compatibility with Different Cement Com positons

摘要

The use of polycarboxylate (PC)- and polyether (PE)-based superplasticizers often generates segregation, inadequate flowability or similar problems due to the incompatibility between the cements and admixtures used. In light of the widely varying composition of these admixtures, not all cement- and superplasticizer-related factors which could affect compatibility have been defined to date. In this study, therefore, rheological trials were conducted with a rotational viscometer and adsorption tests were conducted in a total organic carbon (TOC) analyzer to explore the compatibility between different PC - PE admixtures and cements employed in a variety of compositions and additions.Three admixtures (PC1, PC2, and PC3) with different carboxylate (CA) and polyether (PE) group contents were used, along with seven standard cements whose chemical and mineralogical compositions and active additions varied.The structural characteristic of the admixtures affecting compatibility most intensely was found to be the carboxylate (CA) to polyether (PE) group ratio. In cements with no active additions, characteristics such as fineness and the C A to calcium sulphate and C3S to C3A ratios were also observed to have marked effect on compatibility. On the other hand, in cements with limestone or fly ash additions, no fundamental differences were identified with respect to a standard CEM I 42.5R cement in terms of admixture compatiblity.In calcium aluminate cement (CAC) the fluidizing effect of polycarboxylate superplasticizers led to very significant declines in yield stress.