Effect of chemical structure of high range water reducing admixture on properties of cementitious systems containing fly ash

In this study, the effects of the chemical structure of polycarboxylate-based high range water reducing admixture on the adsorption performance, setting time, fresh state properties, rheological properties and some hardened state properties of fly ash substituted cementitious systems were investigated. In the first stage of the study, 3 admixtures with different main chain lengths, 3 admixtures with different side chain lengths in the second stage, 3 admixtures with constant molecular weight and different chain lengths in the third stage, and in the fourth stage 5 admixtures with different anionic monomers were synthesized. According to the test results, regardless of the use of fly ash, the substitution of the admixture anionic monomer with phosphate and sulfonate and the admixture main chain and side chain lengths higher or lower than a certain value positively affected the fresh state properties, rheological properties and time-dependent fluidity performances of paste and mortar mixtures. However, it did not have a significant effect on the compressive strength and water absorption capacity of the mixtures. It was determined that the effect of the admixture was similar in all fly ash substituted mixtures. In addition, the rheological properties and time-dependent flow performances of the mixtures were adversely affected and the water absorption rate decreased by the increase in the fly ash replacement ratio, independent of the water reducing admixture. In addition, while the early compressive strengths decreased, strength at later ages were positively affected by the use of fly ash.