Prediction of fiber orientation and flexural performance of UHPC based on suspending mortar rheology and casting method

Abstract Fiber orientation is an important parameter to model flexural performance of ultra-high-performance concrete (UHPC). This study proposes a novel approach to predict fiber orientation and flexural performance based on the rheological parameters of the suspending mortar and casting method. The plastic viscosity of the suspending mortar was varied from 10 to 65 Pa ⋅ s using welan gum and superplasticizer to maintain mini-slump values of 200 and 270 mm, or yield stress values of 40 and 15 Pa, respectively. A 30° chute and an L-shape device were used to promote fiber orientation when casting flexural prismatic specimens. Test results of fiber orientation and flexural performance of UHPC indicated significant dependency on the rheological properties of suspending mortar and casting method. Semi-empirical models that consider the effect of plastic viscosity for a given level of yield stress and casting method were developed to predict fiber orientation coefficient and probability density function of fiber orientation angle (p(θ)). A micromechanical model that considers the predicted p(θ) was developed to establish the flexural load-deflection response of UHPC. The model was successfully validated using the experimental data. The spread between predicted and experimental results was limited to 10% for flexural strength and toughness.