粉煤灰对高强混凝土力学性能及孔隙结构影响

Effect of fly ash on mechanical properties and pore structure of high-strength concrete

为探究粉煤灰替代水泥比例对机制砂高强混凝土(MSC)和天然砂高强混凝土(NSC)的强度影响以及内部孔隙结构变化,设计粉煤灰替代水泥比例分别为0,10%,15%,20%和25%配制C80高强混凝土,借助核磁共振技术(NMR)分析混凝土孔隙演变规律,利用X射线衍射(XRD)、差热-热重综合仪、场发射扫描电镜(SEM)技术分析胶凝材料水化产物形态和微观形貌.结果表明:MSC工作性能略低于NSC,各龄期下MSC强度均高于NSC,前期强度随粉煤灰掺量的增加而降低,后期10%粉煤灰混凝土强度最高;10%粉煤灰促进水泥水化进程,填充凝胶孔隙,降低裂隙生成,从而优化混凝土内部结构孔隙,提升混凝土整体密实度;考虑细骨料形貌参数及粉煤灰掺量对混凝土强度的影响,基于可压缩堆积理论建立了粉煤灰混凝土28 d抗压强度预测模型,模型精度良好.研究可为粉煤灰高强混凝土高质量应用提供一定参考.

To investigate the impact of fly ash replacement cement ratios on the strength and internal pore structure changes of manufactured sand high-strength concrete(MSC)and natural sand high-strength concrete(NSC),C80 high-strength concrete was designed with fly ash replacement cement ratios of 0,10%,15%,20%,and 25%,respectively.Nuclear magnetic resonance(NMR)technology was used to analyze the evolution of concrete pores,and X-ray diffraction(XRD),diffe-rential thermal gravimetric analysis(DTA),as well as field emission scanning electron microscopy(SEM)technology were used to analyze the morphology and microstructure of hydration products in cementitious materials.The results show that the strength of MSC is higher than that of NSC at all ages,and the initial strength decreases with the increase of fly ash content.In the later stage,the strength of 10%fly ash concrete is the highest;10%fly ash promotes the hydration process of cement and fills gel pores to reduce the generation of cracks,thus optimizing the internal structural pores of concrete and improving the overall compactness of concrete.Considering the influence of fine aggregate morphology parameters and fly ash substitution rate on concrete strength,a 28-day compressive strength prediction model for fly ash concrete is established based on the compressible stacking theory with good accuracy.The research can provide some reference for the high-quality application of fly ash high-strength concrete.