硫酸盐环境下再生混凝土抗冻耐久性及界面微观结构研究

Study on Frost Resistance Durability and Interface Microstructure of Recycled Concrete in Sulfate Environment

为了研究硫酸盐侵蚀和冻融循环两者耦合作用下再生混凝土的耐久性能,设计硫酸盐环境下冻融循环试验,测定再生骨料取代率分别为0、30%、60%混凝土的质量损失、相对动弹性模量等力学指标,并利用核磁共振(NMR)、扫描电镜(SEM)等技术探究骨料取代率对再生混凝土耐久性损伤过程及微观结构发展规律的影响.结果表明:在冻融循环试验中,再生骨料取代率为60%的混凝土和普通混凝土抗冻性能及抗硫酸盐侵蚀性能相近.掺入再生骨料增加了小孔(d<10nm)、中孔(d为10~50nm)及大孔(d为50~1 000nm)的孔隙数量,有利孔隙数量增大,且未冻融前有利孔隙数量排序:R60>R30,再生骨料取代率为60%时可以有效减少冻胀裂缝,内部孔隙结构扩展不明显;再生骨料取代率为30%的混凝土内部孔隙扩展情况更为显著,其T2谱曲线总面积变化率为162.46%.扫描电镜结果可以看出界面过渡区与裂缝是再生混凝土中较薄弱的环节,在硫酸盐冻融环境下混凝土内部孔隙处生成的钙矾石晶体和石膏晶体是后期混凝土裂缝发展的直接原因.

In order to study the durability performance of recycled concrete under the coupling effect of both sulfate attack and freeze-thaw cycle,the freeze-thaw cycle test in sulfate environment was designed,the mass loss and relative dynamic elastic modulus of concrete with replacement rates of recycled aggregate of 0,30%and 60%were measured,and to investigate the effect of aggregate replacement rate on the durability damage process and microstructure development pattern of recycled concrete using nuclear magnetic resonance(NMR)and scanning electron microscope(SEM)techniques.The results show that in the freeze-thaw cycle test,the frost resistance and sulfate resistance of concrete with 60%replacement rate of recycled aggregate and ordinary concrete are similar.The addition of recycled aggregate increases the number of pores in small holes(d<10nm),medium holes(10~50nm)and large holes(50~1000nm),and the number of favorable pores increases.The order of the number of favorable pores before freeze-thaw is R60>R30.When the replacement rate of recycled aggregate is 60%,it can effectively reduce frost heave cracks,and the expansion of internal pore structure is not obvious.The internal pore expansion of concrete with 30%replacement rate of recycled aggregate is more significant,and the total area change of its T2 spectrum curve is 162.46%.The SEM results show that the interface transition zone and cracks are the weaker links in the recycled concrete.The ettringite crystals and gypsum crystals formed in the pores of concrete under sulfate freeze-thaw environment are the direct reasons for the development of concrete cracks in the later stage.