ABSTRACT
In order to elucidate changes of the value of Relative Humidity (R.H.) related to understanding of the behavior of ASR expansion within massive concrete bodies, humidity within relatively large ASR-affected concrete cylinders (φp450 mm × 900 mm) placed in a natural environment as well as in atmospheres whose temperature and humidity had been precisely controlled, was pursued by measuring R.H. values for long periods. When changes in R.H. value with time in the concrete with ASR cracks which had been placed in dry atmospheres were followed by the re-saturation in an atmosphere of >95% R.H., the humidity up to the depth of 100 mm from surfaces increased in early stages after the beginning of re-saturating process, but a sudden rise of environmental R.H. to >95% was considerably delayed at the depth of 200 mm. It is found that permeability of near-surface regions in the concrete cylinder with reactive aggregate was increased by the formation of ASR cracks. When the concrete was exposed to natural environments whose humidity changed from 20 to 80% throughout a year, humidity within the concrete changed very slowly. R.H. values in surface near portions up to 50 mm were smaller than 80%, but humidity in the portions deeper than 50 mm was maintained at greater than 90% R.H. From a drying-re-saturating repetition tests in the laboratory, the permeability of the portions up to the depth of 50 mm was found to have decreased during the first drying-re-saturating process. The reduction in the permeability of near-surface layers thinner than 50 mm may be due to the impregnation of micro-cracks with ASR gels in the first drying- re-saturating process.
