Research On Anti-carbonization Performance And Prediction Model Of Concrete Using Super Absorbent Polymer(SAP) As Internal Curing Agent Modified By Nano-silica(NS)

The curing methods of concrete are divided into two types:external curing and internal curing.As a new type of curing method,Internal Curing has a better curing effect than external curing.At present,Super Absorbent Polymer（SAP）is commonly used as internal curing material of concrete.It has strong water absorption and water retention,and is widely used in internal curing concrete.Nano-Silica（NS）has ultra-fine particle size and extremely high volcanic ash activity,which makes the microstructure of concrete denser,and opens up a new way to improve the carbonization resistance of curing concrete in SAP.With the support of the National Natural Science Foundation of China project"Research on Technology and Design Theory of Durability Improvement of Offshore Prestressed Concrete Structure（51778272）",the anti-carbonization performance of concrete materials and components using super absorbent polymer as internal curing agent modified by NS through experiments was studied through experiments,and the anti-carbonization performance of concrete was predicted by using multivariate nonlinear model,BP and RBF neural network.The main contents are as follows:1、Study on the anti-carbonization performance of concrete using SAP as internal curing agent modified by NS.From the perspectives of the depth of carbonization,the compressive strength of the concrete before and after carbonization,and the microstructure,the modification effect of NS on the concrete cured in SAP is studied.The results show that:1)the incorporation of SAP can increase the carbonation depth of concrete.Adding an appropriate amount of NS can effectively reduce the carbonation depth of concrete,and the carbonation depth of concrete mixed with 0.16%SAP and 1.0%NS can be reduced by15.5%.2)The compressive strength of concrete carbonated with 0.16%SAP and 1.0%NS for 28 days is 5.52%higher than that of the benchmark group,and the compressive strength of concrete mixed with 0.16%SAP and 1.0%NS is 10.62%higher than that of uncarbonized concrete.3)The wave velocity of concrete carbonized with 0.16%SAP and1.5%NS increases by 2.6%for 28 days.4)It can be seen from the micro-morphology map that the hydration microstructure of the concrete using SAP as internal curing agent modified by NS is rougher and denser,which is beneficial to improve the anti-carbonization performance of concrete.2、Study on the anti-carbonization performance of the concrete supporting beam using SAP as internal curing agent modified by NS.Through 16 concrete corbel beams using super absorbent polymer as internal curing agent modified by NS are designed to be poured,and the 42d rapid carbonization test and 42d indoor exposure test are carried out under constant load.The results show that:1)the elastic modulus of concrete decreases with the increase of SAP content.The addition of NS increases the elastic modulus of concrete.The elastic modulus of concrete mixed with 0.16%SAP and 1.0%NS increases by 8.3%.2)Under the conditions of accelerated carbonization and indoor exposure,the half-cell potential value of intact concrete components mixed with 0.16%SAP and 1.5%NS is the largest,and the corrosion of the steel bars in the concrete is the smallest.The half-cell potential value of the steel bar at the cracked part is significantly lower than the half-cell potential value of the intact part,and the half-cell potential value of the cracked concrete members mixed with 0.16%SAP and 1.0%NS is the largest.3)In the case of accelerated carbonization,the carbonization depths of the 21d and 42d concretes in the intact parts of the mixed with 0.16%SAP and 1.0%NS are reduced by 2.64%and 9.63%,respectively,and the carbonation depths of the concrete at the cracking site are reduced by12.56%and 7.96%respectively for 21d and 42d.3、Study on the prediction model of carbonation depth of the concrete using SAP as internal curing agent modified by NS.The results show that:1)the carbonation depth of concrete increases with the increase of water-cement ratio,temperature and SAP content,and the influence of water-cement ratio is significant and directly proportional to the carbonation depth.The depth of concrete carbonization decreases with the increase of compressive strength,CO₂ concentration,relative humidity and NS content.2)The average relative error between the multivariate nonlinear prediction model and the test value measured by carbonization 28d is 5.18%.The model value and the test value of the carbonization depth have a small error,and the two are in good agreement.3)By comparing the prediction results of the BP and RBF neural networks with the experimental results,the R² of the BP and RBF neural networks are 0.956 and 0.617,respectively,and the relative errors of the carbonization depth are 1.95%and 4.74%,respectively.Therefore,a carbonization depth model suitable for NS modified SAP concrete is established,and the predicted value is in good agreement with the experimental value.This paper analyzes the impact of SAP and NS on the anti-carbonization performance of concrete materials and loaded concrete beams,and uses multivariate nonlinear models,BP and RBF neural networks to predict the depth of concrete carbonation.The research results show that the incorporation of NS and SAP can improve the anti-carbonization performance of concrete,and the concrete carbonation depth prediction model provides a theoretical basis for structural durability evaluation and life prediction.