Study On The Influence Of Nano-silica On The Mechanical Properties Of Early-age Frozen Concret

In the process of engineering construction in cold regions,especially in the concrete hardening stage,if the maintenance is improper,the concrete will be frozen,which will cause irreversible damage to the later strength.Many scholars have proved that the use of nanomaterials under standard curing conditions can optimize the cement hydration reaction to improve the performance of concrete to face various environmental challenges.However,there are few studies on negative temperature curing environment.In this paper,the condition of early negative temperature curing at-10 °C is set up to simulate the early freezing of concrete after pouring.The concrete is improved by adding 0.5%,1%,1.5% and 2% nano-silica with quantitative antifreeze.Considering the water-cement ratio and pre-curing time,the working performance and mechanical properties of concrete are tested.The scanning electron microscope is used to analyze the concrete modification mechanism from the microscopic point of view,and the multivariate nonlinear regression fitting analysis is used to establish the nano-silica early negative temperature concrete-7+28d compressive strength prediction regression relationship.The results are as follows :(1)Under negative temperature curing conditions,the addition of nano-silica does not promote the hydration process of cement materials,but has an adverse effect.(2)When the curing conditions change from negative temperature to standard curing,nano-silica can continue to play a role.The strength of nano-silica concrete under each dosage is higher than that of the blank group,and the strength increase is16 %.Considering all aspects,the optimum content of nano-silica is 1.5 %.In addition,the greater the water cement ratio,the lower the strength of concrete;the longer the pre-curing time,the higher the concrete strength.(3)Through the scanning electron microscope,it can be found that after adding nano-silica,it cannot participate in the cement hydration reaction under the condition of negative temperature curing;after the curing condition is changed to standard curing condition,nano-silica can continue to play a role,the formation of calcium silicate hydrate gel increases,the hydration structure of cement is obviously improved,and the compactness is improved,which is consistent with the results of mechanical properties test.(4)Based on the multivariate nonlinear regression theory,the strength prediction equation of nano-silica negative temperature concrete was established with water-cement ratio,nano-silica content,negative temperature curing temperature and pre-curing time as independent variables.According to the evaluation indexes such as residual diagram,error rate diagram,determinable coefficient and relative error index,the accuracy of the three prediction models is evaluated,and the model 3 has the highest accuracy and meets the test requirements.