Micro-mechanism of static and dynamic strengths for saturated concrete

The existing experimental data indicate that free water in saturated concrete has different effects on mechanical properties of concrete under different strain rates.Comparing with dry concrete,the static compressive strength of saturated concrete may decrease,but the dynamic compressive strength will increase remarkably.A model based on the elastic fracture mechanics is established to analyze the mechanism of these changes of concrete strength due to saturation.In the model,the interaction between micro cracks and different effects of pore water are taken into account.The analysis shows that when loading rate is slow the free water in crack may reach the tip and the wedge effect of water accelerates the expansion of the crack causing the reduction of concrete strength.Whereas,when loading rate is fast the free water in crack will not be able to reach the tip.Due to the combined positive of pore water pressure,viscous of water and Stefan Effect the dynamic compressive strength of concrete will be enhanced.The calculation result is in good agreement with the experimental data.