Yield shear stress of cementitious mortar for self-compacting concrete

Abstract

Abstract: Self-Compacting Concrete (SCC) is extensively used in modern constructions as it consolidates under its own weight without requiring any other compactive effort, whilst maintaining homogeneity. SCC is a thick suspension, and its rheology can be characterized by Bingham model, in terms of yield shear stress (τy) and plastic viscosity (μ).The main objective of this study is to explore variation of consistence of the mortar fraction, in terms of τy, when high-range water-reducing admixtures (HRWR), fly-ash and river sand are present in mortar. As SCC is a suspension of coarse aggregates in mortar, the research focuses on τy of grout and mortar. In this study, τy of pastes that contain different quantities of HRWR, fly-ash and sand was measured. Combined effects of the constituents on τy were observed for two common w/c ratios using concentric rheometer and mini slump cone with the view to determine the optimum compositions. Results suggest to maintain HRWR and fly-ash contents around 1.0L/100 kg, and 25%-30% by mass of cement, respectively, and sand content below 40% by the total volume of the mix. Moreover, the study validates an analytical model derived to evaluate τy by using slump spread diameter and also develops and empirical formula linking τy to the slump spread diameter of cement paste. The findings pave way to use mini slump test as simple tool to judge the adequacy of the consistence of mortar and grout in proportioning of SCC, minimizing the repetitive trials.