冻融循环下混凝土力学性能及孔隙损伤劣化研究

Study on the mechanical properties and pore damage deterioration of concrete under freezing-thawing condition

研究了不同水灰比(w/c=0.45和0.55)混凝土在冻融循环作用下的力学性能退化规律和微观孔隙结构损伤。采用低场核磁共振技术对冻害后的混凝土内部微观孔隙结构演变进行了表征。基于核磁共振试验结果,建立了孔隙率损伤模型,定量评估了混凝土的超声波速与力学性能的劣化规律。结果表明:0.55水灰比组混凝土的冻害程度要明显高于0.45水灰比组的混凝土冻害程度。随着冻融循环次数的增加,混凝土的相对动弹性模量、超声波波速和力学性能均呈下降趋势;劈裂抗拉强度与孔隙率损伤变量D之间呈指数函数关系,超声波波速与孔隙率损伤变量D呈线性关系。研究结果可为寒区水工混凝土结构的抗冻设计理论和耐久性寿命预测提供试验参考。

The degradation law of mechanical properties and microscopic pore structure damage of concrete with different water cement ratios(w/c=0.45 and 0.55)under freeze-thaw cycles were studied.Low-field nuclear magnetic resonance(LF-NMR)technology was used to evaluate the micro pore structure of concrete after frost damage.Based on the results of LF-NMR tests,a damage model of porosity was established to quantitatively evaluate the degradation law of ultrasonic pulse velocity(UPV)and mechanical properties of concrete.The results show that the frost damage of concrete with the w/c=0.55 group is significantly higher than the w/c=0.45 group.With the number of freeze-thaw cycles increases,the relative dynamic elastic modulus,UPV,and mechanical properties of concrete showed a decreasing trend.There was an exponential function relationship between the splitting tensile strength and the porosity damage variable D,and the UPV was linearly related to the porosity damage variable D.The results can provide experimental reference for the frost resistance design theory and durability life prediction of hydraulic concrete structures in cold regions.