Shrinkage-induced warping of UHPC overlay cast on hardened NSC substrate under various conditions

Abstract

Ultra-high performance concrete (UHPC) shows very different properties such as high level of autogenous shrinkage and low creep coefficient compared to conventional concrete. One of the problems posed by this is that when UHPC is used as a thin, bonded overlay for concrete bridge decks or pavements, there is limited information regarding the shrinkage-induced warping of the overlay and optimization designs to minimize it. This study conducted a hygro-mechanical finite element analysis to investigate the warping behavior of UHPC overlay cast on mature substrate of normal strength concrete (NSC). The simulation results were validated with the observations from outdoor overlay tests. It is shown that incorporating the shrinkage and creep of UHPC and the bonding behavior of the overlay-to-substrate interface can predict the UHPC overlay's warping deformation in an accurate way. Based on the model, a parametric study was carried out to investigate the influences of sealed curing period, the roughness degree (the bond strength) of overlay/substrate interface, the overlay thickness, the rebar reinforcement inside the overlay, and the amount of total (free) shrinkage of UHPC on the magnitude of the overlay's warping. The findings obtained in this study include the following: (1) The UHPC's shrinkage and the bond strength between UHPC overlay and substrate are two essential factors affecting the overlay's warping behavior, (2) With an increase in UHPC overlay thickness, the calculated overlay's warping deformation is slightly increased, and (3) Internal rebar reinforcement has a limited contribution to reduce the overlay's warping.