溶蚀作用下纳米SiO2混凝土的孔隙演变

为探究溶蚀条件下纳米SiO₂混凝土微观特性和宏观性能的规律,采用2M NH₄Cl溶液加速溶蚀试验,通过核磁共振技术、场发射扫描电镜和能谱分析研究孔隙特征、微观形貌及微结构的演变规律,同时采用灰熵法分析研究不同溶蚀龄期与不同NS掺量下混凝土的孔隙结构参数和孔隙半径分布对溶蚀损伤的影响规律,并在此基础上建立混凝土孔隙特征与抵抗溶蚀度的关系模型.在该试验中,水胶比为0.29,纳米SiO₂掺量分别为0,1%,3%和6%.结果表明:纳米SiO₂的掺入显著提高混凝土的抗压强度,在经过溶蚀循环后,<100 nm孔径占比对混凝土抗溶蚀度影响程度最大,灰熵关联度均大于0.999;相对于基准组,纳米SiO₂混凝土溶蚀后有向外辐射的纤维状C-S-H生成,填充因溶蚀作用产生的裂隙,使其抗溶蚀性提高,延缓混凝土的劣化损伤;建立了混凝土抗溶蚀度与孔径占比为<100 nm,100~1000 nm和孔隙度的灰色模型,4组混凝土GM(1,4)模型预测值与试验值的平均绝对误差分别为8.18%,7.03%,7.83%和7.90%.该研究可为纳米SiO₂混凝土在实际工程应用提供理论依据.

Pore evolution of nano- SiO2 concrete under dissolution

In order to investigate the microscopic and macroscopic mechanical properties of nano-SiO₂ concrete under the dissolution condition, the 2M NH₄Cl solution was used to accelerate the corrosion test, the evolution of pore characteristics, microscopic appearance and microstructure of nano-SiO₂ concrete was analyzed by means of nuclear magnetic resonance(NMR)technique, field emission scanning electron microscopy and energy spectrum analysis. Meanwhile, the influence of pore structure parameters and pore radius distribution on the corrosion damage of the different dissolution ages and nano-SiO₂ dosage was studied by using grey correlation entropy analysis. Based on this, the relationship model between concrete pore characteristics and corrosion resistance was established. In the test, the water to binder ratio was 0.29 and the replacement ratios of nano-SiO₂ were 0, 1%, 3% and 6%, respectively. The results show that the incorporation of nano-SiO₂ significantly improves the compressive strength of concrete, <100 nm pore size ratio has the greatest influence on concrete corrosion resis-tance, the grey entropy correlation degree is greater than 0.999. Compared with the reference group, the nano-SiO₂ concrete is formed by the outwardly radiated fibrous C-S-H after dissolution, filling the cracks caused by the dissolution, which improves the corrosion resistance and delays the deterioration of the concrete. A grey model GM(1, 4)is established for the influence of pore radius of <100 nm, 100-1000 nm and porosity on the corrosion resistance of concrete. The average absolute errors between predicted values and experimental values of four concrete GM(1,4)models are 8.18%,7.03%,7.83% and 7.90%, respectively. This study provides a theoretical basis for practical engineering applications of nano-SiO₂ concrete.