Study of self-consolidating concrete robustness containing limestone powder based on rheological parameters

One of the major obstacles to development of self-consolidating concrete (SCC) on the industrial scale and various applications is the high sensitivity or very low robustness of this concrete to conventional concrete. From this, in the present study, a total of eight SCC mixes have been produced and their rehology parameters were tested. A control mix (C) was the initial target and, seven series of mixes were developed with variations of each of the principal properties (i.e. filling and passing ability and segregation resistance) or using of AEA and VMA admixture.In order to evaluate the robustness of each mixture, in addition to the mixture with amount of water content, four mixtures were made that the water content of each mix was changed ±3% and ±6% relative to the base water content and then the rheological properties of each mixture were determined. The rheology parameters (yield stress, plastic viscosity) values were determined by a coaxial rhometer. This automated rheometer is a rate-controlled rheometer that was employed to carry out rheological measurements 10 minutes after the initial contact between water and cement. It consists of a four-bladed vane that is immersed into the concrete and rotated at various speeds while the torque acting on the vane is measured. the objective of using rheology measurements is to provide scientific parameters that are capable of describing multiple aspects of workability. This fact are true especially for self consolidating concrete that has several properties in fresh state. So, it is required to perform several tests to evaluation of these properties that in addition to increase the quality control time, it also raises the costs and reduces the accuracy. Therefore, it seems logical to determine rheological parameters that are an accurate test with high sensitivity Instead of measuring multiple properties of fresh state through different workability tests for achieving to a proper robustness index for SCC. Therefore a good approximation of the fundamental rheological quantities for cement based material can be obtained in terms of yield stress (τ0) and plastic viscosity (μ). In this study a rheograph is defined as a graph that X axis is yield stress (τ0) and Y axis is plastic viscosity (μ). This graph that to that has been named “rheograph” is a convenient and essential tool to compare different concrete batches and examine the behavior relative to changed constituents, quantities of constituents, and/or relative to different times from water addition (and so forth). Thus rheograph is a systematical way to reveal the effects of slight decrease and increase in mixing water. The results of the study show that a slight increase in the amount of water increase the yeild stress of SCC, but decreasing water content in some concrete increase and in some concrete reduce the yeild stress. In contrast, in plastic viscosity of SCC, a slight decrease in the amount of water content increases the viscosity and a slight increase in the amount of water reduces the plastic viscosity of SCC. An appropriate index for estimating the robustness of SCC is the area enclosed between the rheological properties of concrete in changing the water content by ± 3% or ± 6%. According to this index, the addition of air entraining admixture to SCC improves robustness and reduces the amount of paste volume resulting in a severe reduction of robustness.