Experimental studies and modeling of creep of UHPC

The ultra-high performance concrete (UHPC) mixed with normal coarse aggregate is a promising material due to its excellent mechanics, durability performance and relatively lower cost. To verify the applicability of the current creep prediction models on this concrete with ultra-high strength grade, the creep behaviors of the specimens with different steel fiber contents of 0%, 1% and 2% and two water-to-binder ratios of 0.16 and 0.22 were examined. The results show that the creep coefficient with 1% and 2% ultra-fine steel fibers exhibits remarkably decline of 25.4% and 13.4% after 180 days of loading in comparison to that without steel fibers. The rise of W/B has a negative effect on creep behavior of UHPC. While the specimens with similar compressive strength have different creep coefficients. The test results are compared with the values simulated by the common prediction models (fib MC2010, ACI 209-08, B4 and simplified B4, GB 50010-2010 and JTG D62-2004 models). By substituting the experimental compressive strength with the calculated compressive strength derived from the elastic modulus of UHPC, the modified creep prediction model based on fib MC2010 functions is applicable for the concrete with higher strength grade and more complicated components. In the meanwhile, the creep mechanism of UHPC was discussed based on the mesoscopic and microscopic analyses determined by X-ray computer tomography (CT) and scanning electron microscope (SEM) techniques.