Fall
2004
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.
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