Study On Alkali-Activated Material Slurry Modified Recycled Aggregate Technology

With the continuous advancement of the’carbon peak and carbon neutrality’strategy,the task of resource utilization of industrial solid waste and construction waste is urgent.As the main consumption method of industrial solid waste and construction waste,recycled concrete is gradually applied in practical engineering construction.However,there are many micro cracks and residual mortar on the surface of recycled aggregate after multi-stage treatment such as crushing and screening,which makes its basic physical properties such as apparent density,water absorption and crushing index worse than natural aggregate.In order to improve the performance of recycled concrete,it is necessary to modify the recycled aggregate before preparing concrete.In this study,the alkali-activated material slurry was used to modify the recycled aggregate,fill the micro-cracks of the recycled aggregate,and generate a shell film structure on the surface to improve the performance of the recycled aggregate.The influence of the interaction of different slurry components on the strength of recycled concrete was studied by single factor test,response surface design method and BP-GA neural network model optimization,and the mix ratio of alkali-activated material slurry for slurry modification was optimized with high precision.Through two-dimensional image processing technology and three-dimensional scanning technology,the variation law of morphological parameters of slurry-modified recycled aggregate was studied from different dimensions,and the morphological comprehensive indexes such as texture factor（F₁）,morphology factor（F₂）and angular factor（F₃）were constructed by factor analysis method.Through multiple regression analysis,the correlation between the morphological comprehensive index and the regression coefficientsαa andαb in the Bowromi formula is established,and theα_a（F₁,F₂,F₃）andα_b（F₁,F₂,F₃）reflecting the morphological characteristics of the aggregate are obtained,and then a new mathematical model for calculating the water-binder ratio is constructed,which lays a theoretical foundation for the mix design of recycled concrete with slurry-modified aggregate.The main conclusions are as follows:（1）Based on the response surface database,BP-GA neural network is used to optimize the mix ratio of alkali-activated material slurry for slurry modification with high precision.The relative error is within±1%.When the activator system in the slurry of different alkali-activated materials is cement clinker-chlorine salt and cement clinker-sulfate,the interaction between activators has the most significant effect on the 28 d strength of recycled concrete.Among the three kinds of slurry-modified aggregate recycled concrete,the strength of recycled concrete is the highest when the slurry excitation system is cement clinker-silicate.（2）Conventional morphological parameters such as roundness（R）,axial coefficient（K_A）,angular coefficient（A_U）,roughness（R_C）,fractal dimension（D）,sphericity（DS）,flat coefficient（FER）,shape factor（SF）contain more repetitive information.The texture factor F₁,morphology factor F₂ and angle factor F₃ obtained by factor analysis can more clearly and concisely quantitatively characterize the macroscopic morphology,microscopic angular and microscopic texture of the modified recycled aggregate.（3）Compared with the original recycled aggregate,the surface roughness of the recycled aggregate after slurry modification is reduced,the morphology is closer to the spherical shape,and the surface is relatively reduced.With the change of particle size,the change trend of recycled aggregate morphology after different slurry coating modification is the same.Among them,after the recycled aggregate is coated with the alkali-activated material slurry prepared by the cement clinker-sulfate activator system,compared with the slurry of cement clinker-chloride salt and cement clinker-silicate as activator,the surface of the modified recycled aggregate is less rough and the morphology is closer to the spherical shape,and the concave and convex edges are reduced.（4）When the replacement rate of slurry-modified recycled aggregate in recycled concrete is 30%～50%,the concrete performance is the best.The morphological comprehensive index had a significant linear relationship withα_a and a significant nonlinear relationship withα_b.Based on the regression modelα_a（F₁,F₂,F₃）andα_b（F₁,F₂,F₃）established by morphological comprehensive index,a new mathematical model for calculating water cement ratio is constructed.The relative error range of recycled concrete mix design using this mathematical model is within±5%,which has high accuracy.