| The comprehensive application of recycled aggregate concrete(RAC)can promote the resource reuse of construction solid waste.It is an important way to realize the coordinated development of resources and environment.It is of great significance to promote the construction of a green and sustainable development society and the realization of the "double carbon" goal.The investigation and application of RAC technology have become a topic of common concern of all countries in the world,as well as one of the hot and cuttingedge issues of engineering and academic circles at home and abroad.The chloride corrosion on RAC is the core cause of the durability degradation of the coastal structure.The chloride migration behavior in RAC is investigated,which has important theoretical significance and engineering application value for service life prediction and long-term performance improvement of infrastructure.With the support of the National Natural Science Foundation of China(No.51509084),the effect of characteristic factors of RAC on chloride migration behavior was analyzed,and the chloride migration law in cracked RAC was deeply studied by using the research method of combining macroscopic physical experiment and micro-and meso-scopic numerical modeling.The primary study details and gains are as below:(1)The macroscopic mechanics and impermeability of RAC were studied.Through chloride wetting-drying cycles test,the chloride migration law in RAC under different water-binder ratios and recycled coarse aggregate content was studied.The results show that the increase of water-binder ratio and volume fraction of recycled coarse aggregate would reduce the mechanical properties of fully recycled coarse aggregate concrete,but enhance chloride migration performance.When the water-binder ratio was expanded from 0.4 to0.55,the chloride diffusivity increased by 107.4%.When the content of recycled coarse aggregate increased from 0% to 50%,the diffusivity increased by 94.2%.The content and migration depth of chloride were positively correlated with wetting-drying cycle periods.(2)A five-phase meso-model of convex polygonal aggregate for RAC was developed.Based on Monte-Carlo theory,a meso-analysis model of RAC was established by selfprogramming,which can achieve the three-random objectives of recycled coarse aggregate shape,particle size and position,and has stronger authenticity.By comparing the physical experimental data with the numerical model calculation results,it is found that the fivephase convex aggregate meso-model can effectively predict the chloride migration behavior in RAC.(3)The influence of characteristic factors of recycled aggregate on chloride migration behavior was analyzed.The results show that the increase of recycled coarse aggregate volume fraction would strengthen the chloride migration behavior.When the thickness of the interface transition zone increased from 25 μm to 100 μm,chloride migration depth and diffusion coefficient increased by 13% and 37%,respectively.The increase of old adherent mortar would significantly reduce the chloride permeability of RAC.When the adherent rate of old mortar increased from 0.1 to 0.4,and chloride ion diffusion coefficient increased by 18.2%.New and old interface transition zone and old adherent mortar are the fundamental factors affecting the chloride penetration resistance of RAC.(4)A seven-phase micro-and meso-scopic numerical model was developed to evaluate chloride migration in cracked RAC.The effect of crack and damage zone characteristic parameters on chloride migration behavior of cracked RAC was studied at micro-scale.The numerical results show that the presence of the damage zone can accelerate the chloride migration behavior in cracked RAC.Chloride migration in cracked RAC is faster,especially around the crack area.Compared with crack width,crack length is more critical on chloride migration behavior.In this study,the multi-phase and multi-scale numerical analysis method of recycled convex polygonal coarse aggregate concrete was proposed,which can develop a novel research way for the simulating calculation of long-term performance of RAC,and provide theoretical support for the engineering application of RAC. |
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