纳米碳酸钙改性再生混凝土疲劳性能

为研究纳米改性再生混凝土的疲劳性能,对其疲劳寿命进行估计并建立疲劳方程。以不同再生骨料取代率(0%、30%、50%,质量分数)与纳米CaCO₃掺量(0%、1%,质量分数)为主要影响因素,设计了不同应力水平(0.75、0.80、0.85)下的疲劳循环加载试验。结果表明:混凝土的弹性模量随再生粗骨料取代率的增大而减小,掺入纳米CaCO₃可以提高混凝土的弹性模量并优化破坏形态,有效提升整体性;循环荷载下的疲劳寿命随最大应力水平增大而快速缩短,1%的纳米CaCO₃改性可以使疲劳寿命延长60%;以双对数S-N(应力水平-疲劳寿命)曲线建立疲劳寿命方程,并推导出考虑寿命概率的P-S-N曲线,得到的相关系数随再生粗骨料取代率的增加而快速减小,经纳米改性后有所增大;再生混凝土的疲劳应变演化基本符合三阶段应变曲线发展规律,提出新方程描述再生混凝土第二阶段应变曲线,并建立变形量与循环比的关系式。

Fatigue Performance of Nano-CaCO3 Modified Recycled Concrete

To study the fatigue performance of nano-modified recycled concrete, the fatigue life was estimated and fatigue equations were developed. Fatigue cycle loading tests at different stress levels (0.75, 0.80, 0.85) were designed with different recycled aggregate replacement rates (0%, 30%, 50%, mass fraction) and nano-CaCO₃ content (0%, 1%, mass fraction) as the main influencing factors. The results show that the elastic modulus of concrete decreases with the increase of recycled coarse aggregate replacement rate, and incorporation of nano-CaCO₃ can improve the elastic modulus, optimize the damage pattern of concrete and effectively enhance its integrity. The overall fatigue life under cyclic load decreases rapidly with the increase of maximum stress level, and 1% nano-CaCO₃ modification can increase the fatigue life by 60%. Establish the fatigue life equation with a two parameters S-N (stress level-fatigue life) curve, and deriving the P-S-N curve considering the life probability. The correlation coefficient obtained decreases rapidly with the increase of recycled coarse aggregate substitution rate and increases after nano-modification. The fatigue strain evolution of recycled concrete basically conforms to the three-stage strain curve development law. A new equation is proposed to describe the second-stage strain curve of recycled concrete, and the relationship equation between deformation volume and cycle ratio is established.