Abstract: Damage tests of concrete specimens were conducted to investigate into the damage evolution law of concrete’s mechanical properties under the actions of freeze-thaw cycles and axial fatigue load. Cyclic freezing and thawing, fatigue loading, fatigue loading after freeze-thaw cycles and freeze-thaw cycles after fatigue loading were applied on concrete specimens respectively. With the deterioration of compressive strength as the damage assessment index, the deterioration of relative dynamic modulus of elasticity and mass were obtained. Results show that under combined actions, the relative dynamic elastic modulus of concrete decreases: 1) under the single action of cyclic freezing and thawing, concrete strength declines gradually as freeze-thaw cycle proceeds; 2) while under the single action of fatigue load, concrete strength grows firstly and then declines as the number of fatigue increases, with the damage degree equals 1.8% when fatigue loading is imposed for 40 000 times; 3) under the combined actions of fatigue loading (with a stress level 0.1 f_c~0.5 f_c for 10 000 times) after freeze-thaw cycles, concrete strength shows a trend of rising; 4) while under the combined actions of cyclic freezing and thawing (for 75 times) after fatigue load (imposed for 5 000 times and 10 000 times respectively), the mechanical properties of concrete deteriorates remarkably as freeze-thaw cycle proceeds, with the damage degree equals to 19% and 24.2%, respectively. This study provides reliable theoretical basis for the design theory of concrete structures consistent with practical engineering.

Key words: concrete, freeze-thaw cycles, fatigue loading, damage test, strength degradation