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Volume 21, Issue 1
(June 1999)
ISSN: 0149-6123
Early Shrinkage Development in a High Performance Concrete As autogenous shrinkage in low water/binder concrete starts to develop almost as soon as portland cement hydrates it is very important to start shrinkage measurement just after the dormant period. One simple way to do it is to insert a gage and a thermocouple at the center of the concrete sample to monitor early shrinkage. Vibrating wire gages having a low rigidity modulus can be used to monitor at the same time length and temperature changes. It is then possible to evaluate separately the actual total deformation while concrete is hydrating at a temperature which is not constant, and autogenous shrinkage in isothermal conditions. Early shrinkage measurements in a 0.30 water/binder ratio concrete beam (250 by 250 by 900 mm) are presented. It is shown that during the first 50 h due to the temperature increase of concrete the actual total shrinkage is much smaller than the autogenous shrinkage, occurring in isothermal conditions particularly during the first 24 h. Moreover a slight swelling of concrete has even been measured from 4 to 16 h. Relative humidity inside the concrete sample was measured using a special probe placed close to the vibrating wire gages. This probe was inserted just after initial setting, 6 h after casting. The initial reading indicates a (RH) relative humidity of 97% and after 28-days the measured RH was still 93%.
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Paper ID: CCA10505J | ||
