Experimental Study On The Effect Of Composite Nano-SiO₂ And Fly Ash On The Mechanical Properties And Durability Of Concrete

With the rapid development of global industries and science,concrete as the main material in civil engineering materials which general use and irreplaceability.However,concrete also exposes relevant issues about polluting environment which waste of resources and energy,so it is especially critical about how to use concrete.Industrial waste fly ash has the characteristics of large production,low-cost and optimized internal grading of concrete.But it will reduce the early compressive strength of concrete.Nano-SiO₂ has excellent high pozzolanic activity,nucleation induced effect,filling effect as a new material.It can improve the compressive strength of concrete at all ages and the resistance to salt freeze-thaw performance.But it will reduce the fluidity of concrete.Therefore,carrying out the test research about the compressive strength and durability of NF-C,making up for the negative effects caused by join separately,at the same time,it achieves the green concept of waste recycling,also can further reach benefit of economic and performance.This study mainly explores NF-C from both mechanics and durable performance.Comprehensive analysis has obtained the optimum compounding ratio and damage deterioration mechanism,using Weibull theory to carry out the service life of concrete in the Salt Lake Region in Northwest Inner Mongolia.To supplement the blank part of the study,the main conclusions are as follows:（1）The compressive strength of NF-C showed a trend of first increasing and then decreasing with the increase of mineral blending materials,of which the fly ash is 20%,and the nano-SiO₂ is 3%（F20NS3）.The pressure intensity is the highest,indicating that the inside of the concrete is most intimate under this dosage.（2）The porosity of NF-C has a huge decline in the hydration age of 3-7D,and the rate of decline is slowed from 7-28D,and the internal consistency was mainly based on the inner fluid saturation.The F20NS3 group is porosity and the T₂ spectrum area is the lowest;while SEM and TG-DTA association analysis can be seen that the relative content of CH in the F20NS3 group is the lowest.The relative content of C-S-H gelatin is the highest,comprehensive analysis shows that concrete mechanical performance system is optimal.（3）Through the establishment of the gray joint entropy analysis and the GM（1,4）model,0-0.01μm aperture,0.01-0.1μm aperture accounting and restraint of fluid saturation is the main factor.The prediction model of the compressive strength GM（1,4）,the average relative error of the predicted value and the experimental value is 3.58%（3D）,4.37%（7d）and 2.88%（28D）,which have better precision.（4）NF-C is excellent in high salt（Na Cl）concentration,using Weibull theory to predict the service life of concrete in Western Inner Mongolia,all of concrete under high salt concentration（Na Cl）solution,actual working condition service the life is more than 20 years,of which the F20NS3 group service is 33.6 years.