Chloride Permeability of Lightweight Concretes Subjected to Freeze-Thaw Cycles
Mitsuru SAITO, Shingo TANAKA and Hiroshi ISHIMORI
Abstract:It is known that lightweight concretes made with fully-saturated expanded shale aggregates exhibited an extremely high chloride permeability, when they were subjected to freezing and thawing. In order to improve the chloride permeability of lightweight concretes under freezing and thawing, the effect of absorbed moisture of expanded shale aggregates and mix proportions on this property of the concretes was investigated by using the AASHTO T277 chloride permeability test method. The results showed that the chloride permeability of lightweight concretes increased conspicuously with the repeated cycles of freezing and thawing up to about 10 cycles at both curing periods of 28 days and 3 days, when the levels of absorbed moisture of a expanded shale sand and a expanded shale coarse aggregate were higher than 9 % and 27 %, respectively. It was found that at the moisture levels of at most 5 % and 2 % for the sand and 14 % and 7 % for the coarse aggregate at 28 days and 3 days, respectively, the lightweight concretes showed an almost constant chloride permeability up to 34 cycles of freezing and thawing. The test results also indicated that air entrainment up to about 11 % and decrease in water-cement ratio from 55 % to 45 % were little effective in suppressing an increase in the chloride permeability of lightweight concretes exposed to freezing and thawing at the age of 28 days but yielded great benefit in terms of the chloride permeability of the concretes which had undergone freezing and thawing at the age of 3 days. Key Words:Chloride permeability, Freezing and thawing, Lightweight concretes, Expanded shale aggregates, Absorbed moisture, Air entrainment, Water-cement ratio