Fall 2004

Alkali-Silica-Reaction (ASR) Induced Expansion of Concrete Beams with Different Restrained Conditions: Results till 1150 Days of Exposure

  Md. Zakir Ahsan
Shamima Roushan Ara

 A detailed experimental investigation was carried out to understand alkali-silica reaction (ASR) induced expansion of concrete beams with various restrained conditions as well as the change in mechanical properties of concrete with the progress of ASR. For this, beam specimens of size mm and cylinder specimens of diameter 100 mm and length 200 mm were made with and without reactive aggregates. Additional NaOH was added to raise the total Na2O equivalent alkali content to 6 kg/m3 in concrete. Beam specimens were made with and without reinforcements. Various restrained conditions were provided inside the specimens by the reinforcements. The specimens were submerged in seawater of temperature 40oC for 612 days. Lateral and longitudinal surface strains over the specimens were measured frequently. Strain gauges were fastened over the steel bars before casting concrete and the strains were measured once a day through a data logger automatically. After 612 days, the specimens were shifted to a marine splash exposure, where seawater was automatically splashed over the specimens twice a day.

Young’s modulus of concrete drops significantly due to ASR, particularly immediately after cracking, but later stabilizes. The reduction of 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 restrained condition has a significant influence on the surface strain as well as steel strain, i.e., ASR induced stress in the bars. Linear relationships between the surface strain and the strain over the steel bars for various restrained conditions in concrete are found, especially for the cases with a higher degree of restrained conditions. The expansion process is divided into three remarkable periods, such as incubation period, cracking period, and stabilized period.