Investigation of anionic group characteristics of PCEs on the behaviour of fly ash cementitious systems

The compatibility of polycarboxylate-based water-reducing admixtures (PCEs) having different carboxylate, phosphate and sulfonate anionic groups with paste and mortar mixtures containing fly ash (FA) was investigated. It was found that, with an increase in the FA content of the mixtures, the PCE requirement for the target flow decreased and the consistency retention performance was improved due to the decrease in the amount of hydrated cement. An improvement in rheological parameters was observed with an increase in FA content from 15% to 30%. However, increasing the FA replacement level beyond 30% caused stability problems in the mixtures. This problem was eliminated with the addition of PCE. In the paste and mortar mixtures, regardless of the FA substitution ratio, the best performance was obtained with PCEs containing 7% and 5% phosphate and sulfonate, respectively. The most suitable FA replacement ratio in terms of rheological parameters and 28-day compressive strength was 30% and 15%, respectively. It was observed that the PCE anionic group content did not have any significant effect for all FA substitution ratios.