Evolution of the mechanical behaviour of limestone subjected to freeze–thaw cycles

The frost weathering of three French limestones [Lens (LS), Migne (MI) and Savonnieres (SA)], with different physico-mechanical properties, during the freeze–thaw cycles was studied. The weathering evolution in stone samples undergoing the freeze–thaw cycles was monitored by measurement of following properties: total porosity, P-wave velocity, static elastic moduli, uniaxial compressive strength and toughness. The thermo-mechanical behaviour of stones was also studied by measurement of the strain and temperature (in surface and centre of sample) during one freeze–thaw cycle. These results, mainly the weathering observed for SA(73) with a degree of saturation of 73 % and a lack of weathering for LS with a degree of saturation of 90 %, show that it is impossible to define a unique critical degree of saturation for different stones and this varies from stone to stone. The shrinkage and (or) the expansion of samples during the crystallization phase were determined. The shrinkage is related to the migration of water away from tiny pores towards larger cavities where ice has already formed. The expansion is attributed on the one hand to the rise in pressure that comes from the water which flows towards the ice front and on the other hand to the relatively important quantity of ice formed when thermal contraction and the contraction due to migration dominate. The elastic moduli (static moduli and dynamic moduli) was found to be affected the most by frost weathering and is a real sensor of first micro-crack initiation, whereas the uniaxial compressive strength and the porosity were found to be affected the least.