纳米二氧化硅自密实道路混凝土弯曲疲劳性能研究

Study on Flexural Fatigue Performance of Nano-SiO2 Self-Compacting Road Concrete

目的通过掺入纳米二氧化硅颗粒优化自密实道路混凝土配合比,改善其弯曲疲劳性能.方法以填充性能和28 d抗压强度为评价指标,设计L 9(3^4)正交试验优化混凝土初始配合比,选取4种配合比制备纳米改性自密实混凝土,进行四点弯曲疲劳试验,分别得到50%和95%存活率下基于两参数Weibull分布的概率疲劳方程,并借助SEM观察试件断面微观形貌.结果自密实道路混凝土取得最佳配合比时水胶比为0.26,纳米二氧化硅和硅灰分别占胶凝材料的质量分数为1%、10%;纳米二氧化硅颗粒掺量为1%的试件的疲劳性能最优,达到预估疲劳寿命2.0×10^6次时弯拉强度折减系数增大了1.4%~5.7%,且疲劳寿命对应力水平变化的敏感性降低了2.1%~9.8%;纳米颗粒具有物理填充效应并与水化产物发生二次反应生成低密度水化硅酸钙凝胶,填充内部微孔使结构更为致密.结论纳米二氧化硅能在一定程度上提升自密实道路混凝土的疲劳性能.

The mixing ratio of self-compacting road concrete was optimized by incorporating nano-SiO2 particles to improve its flexural fatigue performance.Taking filling performance and 28 d compressive strength as evaluation indexes,L 9(3^4)orthogonal tests were designed to optimize the initial mix proportion of concrete.Four kinds of mix ratios were selected to prepare nano-modified self-compacting concrete.Four-point bending fatigue tests were carried out to obtain probabilistic fatigue equations based on Weibull distribution with 50%and 95%survival rates,respectively.And observed the microscopic morphology of the specimen cross section with the help of SEM.The results show that when the optimal mix ratio of self-compacted road concrete is obtained,the water-binder ratio is 0.26,nano-SiO2 and silica fume accounted for 1%and 10%of the mass of binder respectively.The fatigue performance of the specimens doped with 1%nano-SiO2 particles are the best.When the fatigue life is estimated 2×10^6 times,the reduction ratio of flexural tensile strength increases by 1.4%~5.7%,and the sensitivity of fatigue life to the change of stress level decreases by 2.1%~9.8%.Nano-SiO2 particles have physical filling effect and react with hydration products to generate low density hydrated calcium silicate gel,filling the internal microporous to make the structure more compact.Nano-SiO2 can improve the fatigue performance of self-compacting road concrete to some extent.