The freezing strains of mortar prisms were measured by strain gauges during a freezing run in a low-temperature calorimeter. Test samples comprised of normal strength mortars of which the other type was produced by using an air-entraining agent. Before the freezing test both mortar types were stored in two different climate rooms having 96-98% and 90-92% relative humidity, respectively. During a freezing run from +20 to -70℃ and a subsequent thawing back to +20℃ the ice formation in the wet samples was calculated by using a dry reference sample in the comparison chamber. The runs were performed with two freezing rates of 3℃/h and 10.5℃/h. When the slower freezing rate was applied remarkable expansion was noticed in the samples stored in 96-98% relative humidity compared to the dry samples. With the faster freezing rate the wet samples behaved quite differently and during ice formation the mortars contracted compared to the dry samples. The measured ice amounts of the mortars which were run at the faster freezing rate of 10.5℃/h were about half of the induced ice amounts in the mortars which were frozen at the slower rate. The mortar prisms stored in the relative humidity of 90-92% contracted always during ice formation in the freezing test but the contraction differences due to the different freezing rates were much smaller than with the mortars stored in the higher relative humidity.
展开▼
