Effect of metakaolin utilization ratio and loop method-pre-shearing process variation on rheological properties of cementitious systems having different C3A content

Abstract

Thixotropic behavior, which directly affects the fresh state properties of cementitious systems such as pump -ability, compressibility and hydrostatic mold pressure, is determined by applying the loop method, step change and constant shear rate. This behavior is seriously affected by parameters such as the type, amount and fineness of the binder and the process applied in rheological measurements. In this study, the effect of cement C3A content, metakaolin utilization ratio, resting time of the mixture, pre-shear rate and applying pre-shear rate on the thixotropic behavior of the mixtures at the beginning and 20th-minutes were investigated. For this purpose, 4 types of cement having different C3A contents (2.13%, 3.60%, 6.82% and 9.05%) were used. By testing each of the 4 cements (2.13%, 3.60%, 6.82% and 9.05%) for 5 conditions (no metakaolin, 3%, 6%, 9% and 12% met-akaolin), a total of 20 mixtures were prepared. For each cement type, 0, 3, 6, 9 and 12% of the total binder volume was replaced with metakaolin. The loop method was used to determine the rheological parameters. According to the results, irrespective of all parameters examined, the structural build-up area values were higher than the structural breakdown ones in the mixtures and the structure formation that occurred after 20 min was mostly reversible. It was determined that rheological parameters, structural build-up area value and rate of reversible structure formation increased with the increase in cement C3A content and metakaolin utilization rate. The increase in the initial dynamic yield stress values of the mixtures with the increase of the cement C3A ratio was more pronounced in the case where the measurement is made without waiting immediately after the pre -shear application. The effect of C3A content on dynamic yield stress and viscosity values was more pro-nounced with an increasing pre-shear rate. The opposite was observed for the structural build-up area values.