Usability of mortar for predicting shear strength development at rest of fresh self compacting concrete

Determining the relationship between the rheological parameters of the model mortar and the rheological parameters of SCC (Self-Compacting Concrete) was the aim of the work. The static yield stress and the thixotropy coefficient AT were determined, which are important due to the development of the shear strength at rest and the formwork pressure generated during SCC casting. Shear strength of SCC reflected as static yield stress gs at rest develops mainly due to a self-compaction ability of SCC. And in the longer term, gs develops due to the progressive hydration of the cement and the disappearance of the HRWR impact (loss of fluidity). The static yield stress gs depends on w/c ratio, the type of HRWR (High Range Water Reducers) and cement. SCCs with a higher w/c ratio develop static yield stress gs faster, but up to 40 min the influence of w/c ratio decreases. The stiffening of SCC due to thixotropy increases the shear strength of SCC, but at the same time, it slows down the self-compaction of concrete. Thixotropy coefficient AT depends primarily on w/c ratio, and with the same w/c, on the type of cement and HRWR. The thixotropy coefficient AT increases in the initial period of SCC being at rest. The SCC with higher w/c ratio are characterized by higher thixotropy coefficient AT but at the same time by lower static yield stress gs. The significance of the thixotropic effect for shear strength disappears in time.