Freezing induced stresses in concrete-steel composite beams and effect of air voids
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The thermal expansion match between concrete and steel is lost when freezing occurs, owing to enhanced shrinkage caused by cryosuction in the pore solution and the high coefficient of thermal expansion (CTE) of ice. Freezing dilatometry performed on steel and on well-cured mortar samples with and without air entrainment showed a sharp transition to damage by very slight increase of water content, and revealed how cryosuction increased the CTE of air entrained mortar after nucleation. Freezing-induced warping was measured on mortar-steel composite beams. After nucleation, beam warping in both directions (concave down or up) was observed depending on whether the mortar was air entrained or not. Comparison of beams with different quality of mortar-steel bond shows loss of bond and internal damage to various degrees for non-air entrained mortar, whereas air entrainment protected the bond while preventing internal frost damage. Poromechanical modelling of the bi-material and hydrodynamic effects could simulate most of the pre-freezing warping, whereas post-freezing modelling is still in progress.