Relation between Strain on Surface and Strain over Embedded Steel Bars in ASR Affected Concrete Members

Abstract

A detailed experimental investigation was carried out to understand the change in mechanical properties of concrete, surface strain over the specimens and the steel bars embedded in concrete, crack growth, and change in mechanical properties of steel bars under sustained stress induced by the Alkali-Silica Reaction (ASR) in concrete. Also, chloride diffusion in concrete, corrosion over the steel bars, investigation on ASR gel at the porous matrix region by SEM, and visual examination of the ASR gel on the cut surface of the specimens were carried out. For this, beam specimens of size 250x250x600 mm and cylinder specimens of diameter 100 mm and length 200 mm were made. Beam specimens were made with and without reinforcement. Various restrained conditions by the reinforcement were provided. Additional NaOH was added to raise total Na₂O equivalent alkali content to 6 kg/m³ in concrete. The specimens were submerged in seawater at temperature 40°C in a closed container. The investigation was carried out for 383 days.
Young's modulus of concrete drops significantly due to ASR immediately after cracking. However, it becomes stable later. The reduction in compressive strength was not as significant as Young's modulus. Internal restraint provided by the steel bars results in the reduction of surface strain in the restraint direction. The degree of restraint has a significant influence on the surface strain as well as strain over the bars. A good linear relation between the surface strain and the strain over the steel bars is found, especially for the cases with highly restrained conditions. Less surface strain is observed if the steel bars are placed near the concrete surface, however, the strain over the bars is increased for this arrangement. Placing longitudinal steel bars near the surface also results in the significant lateral surface strain as well as higher strain over the stirrups, if any.