不同替代率风积砂混凝土冻融损伤特性

Freeze-thaw Damage Characteristics of Aeolian Sand Concrete with Different Replacement Ratios

为探讨风积砂混凝土冻融损伤特性,对替代率为0%、20%、40%、60%、80%、100%的风积砂混凝土,开展冻融循环试验,结合扫描电镜(SEM)、核磁共振(NMR)等表征手段,从宏观、微观及细观角度多尺度分析风积砂混凝土冻融损伤劣化规律。研究发现:风积砂混凝土质量损失率、相对动弹性模量、抗压强度损失率随冻融循环次数的增加分别呈现先减小后增大、不断减小和逐步增大的趋势;随着风积砂替代率的增加,呈现总体下降、不断上升和小幅降低的趋势,表明混凝土抗冻性增强,当达到100%时,其抗冻性最佳。从微观角度分析,随着冻融循环次数的增加,风积砂混凝土界面过渡区(ITZ)结构劣化明显。随着风积砂替代率的增加,骨料与砂浆基质剥离程度减小,水化产物由密变疏,高硫型水化硫铝酸钙(AFt)、封闭小孔隙增多,抑制冻融损伤作用增强。从细观角度分析,随着冻融次数的增加,风积砂混凝土内部孔隙结构经历着新孔隙生成、大孔隙向小孔隙转换的复杂过程。随着风积砂替代率的增加,T 2谱小孔隙峰值逐渐增大,孔隙结构劣化程度减小,混凝土抗冻性增强。

In order to investigate the freeze-thaw damage characteristics of aeolian sand concrete,the freezethaw cycle tests were carried out on aeolian sand concrete with replacement rates of 0%,20%,40%,60%,80%and 100%.Combined with scanning electron microscope(SEM),nuclear magnetic resonance(NMR)and other characterization methods,the law of freeze-thaw damage and deterioration of aeolian sand concrete was analyzed from macroscopic,microscopic and mesoscopic perspectives.The results show that the mass loss rate,relative dynamic elastic modulus and compressive strength loss rate of aeolian sand concrete showed the trend of decreasing first then increasing later,decreasing and gradually increasing respectively with the increase of freeze-thaw cycles.With the increase of aeolian sand replacement rate,it shows a trend of overall declining,rising and slight decreasing,which indicates that the frost resistance of concrete is enhanced.When it reaches to 100%,the frost resistance is the best.From the microscopic point of view,with the increase of the number of freeze-thaw cycles,the interface transition zone(ITZ)structure of aeolian sand concrete deteriorates obviously.With the increase of aeolian sand replacement rate,the stripping degree of aggregate and mortar matrix decreases,the hydration products change from dense to sparse,AFt and closed small pores increase,and the effect of inhibiting freeze-thaw damage increases.From the mesoscopic point of view,with the increase of freeze-thaw times,the internal pore structure of aeolian sand concrete undergoes a complex process of new pore formation and large pore to small pore transformation.With the increase of aeolian sand replacement rate,the peak value of small pores in T2 spectrum increases gradually,the deterioration degree of pore structure decreases,and the frost resistance of concrete increases.