Interactions between Portland cements and carboxylated and naphthalene-based superplasticizers.

摘要

The objective of this study is to explore the interactions between Portland cements and superplasticizers. The dispersing behaviors of cement pastes with carboxylated and naphthalene-based superplasticizers were determined using small amplitude dynamic rheological technique.; Cement pastes with superplasticizers had a wide range of the dispersing behaviors, from dispersion to gelation. Incompatibilities were identified in some combinations, in which both elastic modulus and yield stress were increased by the addition of superplasticizers. Subsequent experiments showed that the incompatibilities between cement pastes and SNF were associated with the increased ettringite formation, which was considered to bridge the cement particles. The ettringite formation was reduced by additional alkalis and the high-alkali cement did not show incompatibility with SNF.; Promising solutions to the compatibility problems are proposed in this study. The incompatibilities in cement-admixture combinations can be mitigated by delayed superplasticizer addition, changes in shear history, and addition of alkalis. The mechanisms behind these protocols are discussed.; In the final part of this study, the relation between the concrete slumps and the paste rheology is established. However, concretes required much less superplasticizer than paste to be dispersed. The differences in the shear history between the concretes and the pastes possibly explain such discrepancies in admixture dosages.