Early-age shrinkage characteristic of UHPC in strengthening stone masonry arch: Influence of restraint from arch structure

Abstract

Ultra-high performance concrete (UHPC) is frequently employed in strengthening existing bridges, due to its extremely high mechanical qualities and exceptional durability. Nevertheless, the early shrinkage of UHPC layer restrained by the arch structure may result in the risk of cracking, when used for strengthening masonry arch bridges. This paper aimed to investigate the shrinkage and cracking potential of ultra-high-performance concrete (UHPC) at early age under restraint from masonry arch structure. For that, different types of masonry model arches were respectively strengthened by using UHPC and then the shrinkage behaviors of UHPC layer were tested. The effects of four different strengthening modes, i.e., F-hoop (wrapping for four sides), T-hoop (wrapping for three sides), Intrados and Extrados, three different rise-span ratios, i.e., 1/5, 1/4, 1/2 and two different arch ring widths, i.e., 0.42 and 0.15 m, were considered. Results indicate that the shrinkage strain time-varying curve of UHPC layer was not only related to the material characteristics, but also negatively related to the change in external environment temperature. For different strengthening methods, the final shrinkage strain of UHPC layer follows: F-hoop < T-hoop < Intrados < Extrados. The shrinkage strain was unaffected by different strengthening modes along the thickness and arch axis directions. The shrinkage effect of UHPC generates the maximum tensile stress value (1.0–2.0 MPa) at the arch top of the strengthening layer, which was significantly less than the tensile strength of UHPC during the same risk period. The arch foot is the most complex area under stress and should be taken seriously.