Role of non-freezing pore water in freeze-thaw damage of concrete mortars

Title: Role of non-freezing pore water in freeze-thaw damage of concrete mortars
Author(s): Vesa Penttala
Paper category : conference
Book title: 2nd International RILEM Symposium on Advances in Concrete through Science and Engineering
Editor(s): J. Marchand, B. Bissonnette, R. Gagné, M. Jolin and F. Paradis
Print-ISBN: 2-35158-003-6
e-ISBN: 2351580028
Publisher: RILEM Publications SARL
Publication year: 2006
Nb references: 9
Language: English

Abstract: A novel theory to explain the mechanism of freeze-thaw damage in concrete mortars is presented. The theory takes into consideration the density changes of ice and unfrozen pore water during cooling and warming phases of the freeze-thaw cycle. Two mortar sample types having 25 MPa compressive strengths were produced for the tests. The other mortar type was air-entrained while the other was produced without admixtures. Half of the test samples were cured in a sodium chloride solution before the water curing regime. During the freeze-thaw tests the temperature cycle in a low-temperature calorimeter decreased from +20 to -70 oC and back to 20 oC. The strains of the mortars were measured by strain gauges and the evolved ice amount was calculated from the calorimeter data.
The volumes of ice, non-freezing pore water, and air-filled pore space were calculated during the freezing cycle. In the salted mortars the total pore space was filled with ice and non-freezing water quite soon after the initial freezing temperature. Thereafter the expansion of non-freezing water caused water to be squeezed out of the samples and to be frozen on the surface of the test prisms. Also the total pore space of the non-air-entrained unsalted mortar was filled with ice and unfrozen pore water but only at the temperature of -57 oC. About 15 % of the pore volume of the air-entrained unsalted mortar was air filled at the lowest temperature.
The pressures due to the expansion of non-freezing pore water causing large tensional stresses into the test mortars is proposed to be counterbalanced by a larger negative pore water pressures originating from the entropy difference between the surface of ice and the non-freezing pore water. The theoretical negative pore water pressure due to the entropy difference between unfrozen pore water and ice on the surface of the prisms was calculated to be nearly 150 MPa and the positive pore water pressure caused by water expansion was estimated to be below 50 MPa in the non-salted mortar prisms.

Keywords: freeze-thaw, damage, concrete, mortar, non-freezing water, mechanism, ice

Online publication: 2006-08-02
Classification: 3.1 Theme 1: Numerical Models: from Microstructure to Transport Properties and Durability
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2351580028.042