纳米SiO2粉煤灰混凝土抗压强度影响及灰熵分析

为探究纳米SiO₂粉煤灰混凝土孔隙结构对抗压强度的影响,取纳米SiO₂掺量分别为1%,3%,5%和7%,粉煤灰掺量分别为10%,20%和30%,水胶比为0.35,将两者复掺进行试验.测定混凝土3 d,7 d和28 d立方体抗压强度.利用核磁共振技术、场发射扫描电镜和差热-热重技术,综合分析研究孔隙结构及微观形貌特征,通过灰关联熵分析法找出影响混凝土抗压强度的主、次因素,并建立GM(1,4)灰色预测模型.结果表明:两者复掺在混凝土发育阶段起到正耦合作用,宏微观关联分析可知,粉煤灰掺量20%、纳米SiO₂掺量3%为最优;建立了混凝土抗压强度与(0,0.01］ μm孔径占比、(0.01,0.10］ μm孔径占比和束缚流体饱和度的灰色预测模型.GM(1,4)模型3,7和28 d的预测值与试验值的平均相对误差分别为3.28%,4.00%和2.64%,利用孔隙结构预测混凝土抗压强度有较好的精度.该研究可为纳米SiO₂和粉煤灰在混凝土工程中的应用提供一定参考.

Influence of nano-SiO2 fly ash on compressive strength of concrete and grey entropy analysis

To explore the influence of pore structure of nano-SiO₂ fly ash concrete on compressive strength, the content of nano-SiO₂ additional rate 1%, 3%, 5% and 7% and fly ash additional rate 10%, 20% and 30%, respectively, the water to binder ratio was 0.35, and the two are mixed together for the test. Determine the cube microstructure compressive strength 3 d, 7 d and 28 d. The pore structure and micro morphology were comprehensively analyzed and studied by nuclear magnetic resonance technology, field emission scanning electron microscope and differential thermal gravimetric technology. The primary and secondary factors affecting the compressive strength of concrete are found out by gray correlation entropy analysis, and the GM(1, 4)gray prediction model is established. The results show that the nano-SiO₂ and fly ash can promote the hydration of concrete, and improve the early compressive strength of concrete, meanwhile its optimal mix proportion when the mass fraction of fly ash and nano-SiO₂ are 20% and 3%. The main factors affecting the compressive strength are(0,0.01］μm pore size ratio,(0.01,0.10］μm pore size ratio and bound fluid saturation to establish a GM(1, 4)gray model. The average relative errors between the predicted values of 3, 7 and 28 day and the experimental values are 3.28%, 4.00% and 2.64%, respectively. Using the pore structure to predict the compressive strength of concrete has better accuracy. This study can provide reference for the application of nano-SiO₂ and fly ash in concrete engineering.