Today, there is uncertainty about how much the results differ when drying concrete
at 20, 50 and 105 °C prior to saturation of concrete in order to determine the
degree of saturation and hydraulic conductivity. Micro-cracks occur when concrete is
dried at higher temperatures and causes increased hydraulic conductivity. Further, the
concrete is believed not to be completely saturated if not all the physically bound
water, so called free water, has been dried out prior to saturation.
This thesis compares the effect of three different drying temperatures on the
possibility to saturate concrete with water. The work was conducted at Vattenfall’s
concrete laboratory in Älvkarleby. The three drying temperatures were +20 °C
(room temperature), 50 °C and +105 °C. The objective was to determine if
differences on the degree of saturation and hydraulic conductivity were non-existent
or negligible. Vacuum saturation after drying at 105 °C is considered to be complete.
The results after drying at 20 °C and 50 °C were compared to those after drying at
105 °C. The results of the tests indicate that the concrete should be dried at +105°C
prior to saturation with water. Then the risk of frost damage to concrete in hydro
power structures can be assessed.
How determination of the hydraulic conductivity is affected by the drying
temperature gave more vague and dubious results. All specimens showed a maximum
hydraulic conductivity after drying at 50 °C, not after 105 °C as expected. It was
believed that the hydraulic conductivity theoretically would increase because of
(more) micro-cracks when being dried at 105 °C. Results from the concrete with vct
1.0 gave results that indicated that the specimens had been damaged by method 1. To
sum up, the results of the tests indicate that further studies on the effects of drying
temperatures should be made.