Influence of insufficient early-age strength of UHPFRC on rehabilitation of OSDs

Recently, an UHPFRC overlayer was employed for the rehabilitation of orthotropic steel bridge decks. To minimize the interruption on operation, the strengthened bridges were reopened to traffic only a few days after casting. As a result, the traffic loads may generate a stress in UHPFRC with a magnitude higher than the early-age cracking strength. Therefore, this study focuses on assessing the influences of applying load at early age on the performance of OSDs overlaid with UHPFRC based on a 3-dimensional finite element method. In this method, the elastic, strain-hardening and strain-softening domains of the stress to strain relation of UHPFRC under tension are considered with a smeared crack model. The cracking and ultimate tensile strengths are reduced to different levels to simulate the insufficient strength development in the early age. It is found that the UHPFRC overlay which should be intact if the designed strengths can be developed may crack due to applying load at early age, and the cracked region exhibits a clear enlarged trend with the increasing reduction rate of the tensile properties. As the degradation rate of fiber reinforced cementitious material increases remarkably after cracking, all the observations emphasize the significance of considering the early-age strength of UHPFRC in engineering applications. However, attributed to the high tensile strengths and the strain-hardening behavior after cracking, the cracks propagate in a relatively speed along the depth direction, which makes UHFPRC more superior to other cementitious materials, e.g. concrete, steel fiber reinforced concrete (SFRC), and engineering cementitious composites (ECC).