The use of UHDC for the repair and strengthening of elements in compression

Abstract

The development of concrete as a repair and retrofitting confinement technique on degraded structures due to physical, chemical and mechanical process took a new turn through the innovative application of UHDC. In this study, through the use of an optimised self-compacting fibre-reinforced concrete mix, an investigation was carried out to analyse the performance of confined cylindrical and square columns with a 20 mm UHDC confinement. Surface preparation before the casting of the UHDC jacket consisted of sandblasting treatment of 20 specimens, of which half had a coat of bonding agent applied onto the sandblasted surface. The other half was left without any bonding agent and an additional two specimens were used as unconfined control specimens. The behaviour of the confined specimens was also tested by varying the application of the axial load between, over the NSC core only or the whole cross-sectional area. The final variable investigated in this study was the effect of chamfered corners of square columns while confined with UHDC. UHDC confinement on NSC columns exhibited an increase in compressive strength as high as twice the original compressive strength without jacketing. Improved monolithic effect between the two layers of concrete was demonstrated to be more effective without any application of bonding agent. Signs of recovery in strength were exhibited by those specimens which were loaded axially on the NSC core after the ultimate stress capacity of the core has been surpassed. Confined columns with UHDC resulted in a higher modulus of elasticity and compressive toughness index when compared to the unconfined NSC columns. In addition, profilometry results on the surface treated with sandblasting proved beneficial in quantifying the level of roughness achieved.