Rheological properties of sprayable ultra-high performance concrete with different viscosity-enhancing agents

A sprayable ultra-high performance concrete (SUHPC) with ultra-high strength, low shrinkage and rapid construction characteristics has been developed in this research. Considering the rheological requirements of pumping and spraying, three kinds of viscosity-enhancing agents (VEAs) including hydroxypropyl methyl cellulose (HPMC), polyacrylic acid and welan gum were selected to adjust the rheological properties of SUHPC. Determine the most suitable VEA and carry out field spray tests, to obtain spraying parameters. The thixotropy and viscoelasticity of SUHPC were measured and analyzed, and discussed the connections and differences between slump-flow, static and oscillatory rheology. The main results reveal that HPMC was the most suitable for SUHPC, and the field sprayed thickness could be up to 50 mm when the dosage of HPMC was 0.7‰, which meets the mechanical requirements of repair or lining. A functional relationship between slump-flow, static and oscillatory rheological parameters was revealed and established a simple functional model, beneficial to comprehensively understand the rheological behaviors of SUHPC materials. Finally, VEAs can be adsorbed on the surface active groups of cement particles, and competitive adsorption between polycarboxylate superplasticizer and VEAs was found based on zeta potential.