ICE FORMATION AND PORE WATER REDISTRIBUTION DURING 2-CYCLE FREEZING AND THAWING OF CONCRETE MORTARS

摘要

The strains and ice formation of four mortar types were measured in a low-temperature calorimeter. Mortars had compressive strengths of 25 and 40 MPa, one mortar type of each strength class was air-entrained. The test mortars were cured in four different environments, under water and in 87, 91, and 97% relative humidity. The test started from +20℃ and the temperature dropped linearly to -35℃ and then increased to +5℃. In the second freezing and thawing cycle temperature dropped again linearly to -35℃ and thereafter increased to +20℃. The first freezing temperature of the pore water during the first freezing cycle was lower compared with the corresponding freezing temperature at the second freezing cycle. The reason for the increase of the first freezing temperature during the second freezing and thawing cycle is proposed to be the redistribution of pore water in the pore system during the first cycle. The residual strains seem to have a minimum value when mortars have been cured in relative humidity of 97-98%. Residual expansion was noticed when mortar samples were cured in water and also when they were cured at relative humidity of 95% or below if the temperature of the test prism was low enough to cause pore water to freeze during the test.