Cement and Superplasticizer Combinations: Compatibility and Robustness

Abstract

This study highlights the notion of robustness of combinations of cements and superplasticizers. Tests done with various cements and different families of superplasticizers showed that although a combination of a cement and a superplasticizer could be compatible, it is not necessarily robust. Sometimes a little variation in the dosage of the admixture could lead to detrimental side effects, such as segregation, excessive set retardation, or excess air content in the concrete. Results showed that the chemical composition of the cement is critical to ensure good compatibility and adequate robustness of various combinations of cements and superplasticizers. The chemical nature of the superplasticizer also plays a role in the behavior of such combinations. The C3A content, the soluble (alkali) sulphate content, and the fineness of the cement, which influence the adsorption rate of the superplasticizers on the cement particles, are among the key factors that control the compatibility and the robustness of cement-superplasticizer combinations, especially for polysulfonated admixtures. Based on the results of this study, a rough prediction of the compatibility and robustness of cements and superplasticizers could be made by analyzing the chemical composition of the cement and the chemical nature of the superplasticizer.

Effect of specimen composition on the strength development in cemented paste backfill

“…Zeta potential measurements conducted on mine tailings -water mixtures show an increase in the magnitude of the zeta potential from -15 to -40 mV upon the addition of 0.2 mL of a sulphonic-based superplasticizer, supporting the idea that the dispersing effect of these types of superplasticizers is due to electrostatic repulsion (Simon 2004). In addition, the compatibility between the solid particles and the superplasticizer plays an important role in particle dispersion and paste fluidity (Nkinamubanzi and Aitcin 2004). If a large amount of a superplasticizer is adsorbed during the early stages of hydration, it is typically adsorbed onto the aluminate hydrate phase (Ramachandran et al 1981;Kim et al 2000).…”

On the mechanisms of consumption of calcium lignosulfonate by cement paste

“…The main shortcoming of adding this chemical admixture is the retardation it causes to concrete hydration, which limits the maximum dosage usable in practice (Collepardi et al, 1973, Young, 1972. Additionally, incompatibility issues sometimes exist between plasticizer and cement, which can lead, for example, to high consumption of plasticizer by the cement paste, reducing the amount of admixture effective in dispersing the cement paste (Agarwal et al, 2000, Nkinamubanzi et al, 2004. A high dosage of plasticizer might in turn lead to incompatibility phenomena such as severe setting retardation or sudden slump loss.…”

Interaction of polycarboxylate-based superplasticizers with cements containing different C3A amounts

“…Despite numerous research project have been carried out 0958 on the subject cement-superplasticizer interaction, many questions remain unsolved. Certain cement-superplasticizer combinations are incompatible [12][13][14] exhibiting poor flow behaviour, early slump loss, strong retardation or flash set.…”