基于核磁共振法的纳米TiO_(2)混凝土抗冻性能研究

Frost Resistance of Nano-TiO_(2) Concrete Based on Nuclear Magnetic Resonance Method

孔结构演化对混凝土抗冻性能至关重要,为研究纳米TiO_(2)对混凝土孔结构及抗冻性能的影响,本文选取替代率分别为0%、1%、3%、5%(质量分数,下同)的纳米TiO_(2)混凝土为研究对象,进行了快冻法试验、抗压强度试验、核磁共振试验及扫描电子显微镜试验。通过纳米TiO_(2)混凝土冻融循环前后质量、动弹模量、抗压强度、孔结构及微观形貌的变化,评估-18~5℃条件下的冻融损伤并分析纳米TiO_(2)对混凝土性能的改善机理;同时建立抗压强度、相对动弹模量、自由水饱和度及裂缝占比响应模型以确定纳米TiO_(2)的最佳掺量。结果表明:适量的纳米TiO_(2)可有效改善混凝土微观形貌,增加混凝土微孔及中孔的比例,减小大孔及裂缝的比例,过量的纳米TiO_(2)会使混凝土中大孔和裂缝的比例增大,不利于混凝土抗冻性能的提高;纳米TiO_(2)掺量为1%时,混凝土抗冻性能最佳。基于抗冻性能指标与孔隙测试结果建立响应模型,确定纳米TiO_(2)最佳掺量接近1%,这与试验结果相符合。

The evolution of pore structure is very important to the frost resistance of concrete.In order to study the effect of nano-TiO_(2) on pore structure and frost resistance of concrete,the nano-TiO_(2) concrete with substitution rates of 0%,1%,3%,5%(mass fraction,the same below) were selected as research object,and the quick freezing test,compressive strength test,nuclear magnetic resonance test and scanning electron microscope test were carried out.The changes of mass,dynamic elastic modulus,compressive strength,pore structure and micro-morphology of nano-TiO_(2) concrete before and after freeze-thaw cycle were analyzed to evaluate the freeze-thaw damage at-18~5 ℃ and to analyze the improvement mechanism of nano-TiO_(2) on concrete properties.At the same time,the response models of compressive strength,relative dynamic modulus,free water saturation and crack ratio were established to determine the optimum content of nano-TiO_(2).The results show that an appropriate content of nano-TiO_(2) effectively improves the micro-morphology of concrete,increases the proportion of micropores and medium pores of concrete,and reduces the proportion of macropores and cracks,while excessive nano-TiO_(2) increases the proportion of macropores and cracks in concrete,which is not conducive to the improvement of frost resistance of concrete.When the content of nano-TiO_(2) is 1%,the frost resistance of concrete is the best.Based on the frost resistance performance index and pore test results,the response model is established,and the optimal content of nano-TiO_(2) is close to 1%,which is consistent with the test results.