128 / 2022-04-27 21:56:13

Flow-induced steel fiber alignment for improving mechanical performance of UHPC

UHPC,Flow-induced casting,Fiber alignment,Flexural properties,Dynamic properties

Steel fibers in UHPC cast by conventional method showed random orientation, and the orientation of a large number of fibers does not match the direction of principal tensile stress, resulting in fiber underutilization. Considering the highly flow-dependent characteristics of fiber orientation, this paper developed a flow-induced casting method using a L-shape device to favor fiber alignment during UHPC placement. The alignment of fibers during flow of UHPC mixture was simulated using the Smoothed Particle Hydrodynamics (SPH) method, showing limited deviation compared to the image analysis results. Experimental results indicated that the fiber orientation coefficient was increased from 0.4-0.6 to 0.6-0.8 with the use of flow-induced method, leading to the maximum improvements of 65% and 80% in flexural strength and toughness, respectively. This can enable 50% reduction in fiber volume, given the similar flexural properties. Such fiber alignment also resulted in significant enhancement in impact resistance of UHPC tested by the Spilt Hopkinson Pressure Bar (SHPB). Dynamic compressive strength, peak strain, and energy absorption capacity were enhanced by 20%, 55%, and 95%, respectively, compared to those with random fiber orientation.