Effect of alkali silica reaction on the performance of hooked bars

Abstract

The Alkali-silica reaction (ASR) is a deterioration phenomenon that causes undesirable expansion and cracking in hardened concrete. This reaction usually occurs between certain types of reactive aggregates and high-alkali cement and is reported in a notable number of reinforced concrete (RC) structures worldwide, for which assessing the residual performance is critical. Many of these structures employ hooked bars to provide anchorage, especially in their joint regions. This paper examines the pull-out behavior of hooked bars in RC beam-column joints affected by ASR to help assist with safety evaluation of RC structures impacted by this reaction. A set of 7 full-scale RC columns was fabricated with concrete containing reactive fine aggregates, which incorporated different hooked bar diameters and amounts of transverse reinforcement. The specimens were subjected to pull-out of their hooked bars either in control conditions or after curing in a relative humidity of 100 % and a temperature of 50°C for up to 303 days to achieve different levels of ASR-induced expansions. Results showed that up to an unrestrained uniaxial expansion level of 0.2 %, the ASR-affected hooked bars showed an increase by up to 22 % in their ultimate pull-out capacity but a notable reduction in their ductility. Despite distributed cracking in ASR-affected specimens, their failure mode was relatively similar to that in the control specimen and remained a combination of side and front failure.