Two-stage Model And Crack Development In Reinforced Concrete Structures With Rebar Corrosion

To change the extensive mode of production in construction industry to a relatively more sustainable one, one way is to improve the durability of concrete structures, and the other way is to reduce the emissions of construction waste by applying recycled aggregates concrete in structures. Steel corrosion is one of the most predominant deterioration mechanisms in reinforced concrete structures. The corrosion of reinforcing steel in concrete will induce a pressure on the surrounding concrete, thus inducing cracks in the concrete cover. As a result, corrosion of the steel is accelerated, leading to serious damages like spalling of the concrete cover. As for the recycled aggregates concrete, the use of recycled coarse aggregates brings more complicated interfacial transition zone (ITZ) and microcracks in coarse aggregates, which will have complex influence on the corrosion-induced cracking progress in concrete. This paper focuses on the mechanism of corrosion-induced cracking progress in concrete and recycled aggregate concrete by experimental studies and analytical studies. The main work in this paper can be summarized as follows:(1) A reinforced concrete specimen that had deteriorated in an artificial environment for two years is investigated. Samples with different degree of steel corrosion and damage are made from the specimen and the steel/concrete interface and corrosion-induced cracks are observed by SEM operated in BSE mode. Thicknesses of corrosion-filled paste (CP) along with that of corrosion layer (RL) are measured, and the rust distributions in cracks are studied.(2) Instead of the widely accepted three-stage model, a two-stage model is proposed to describe the concrete cracking process induced by steel corrosion, according to the findings from the above experiments. The previous analytical model for corrosion-induced concrete cracking process is revised to make it closer to the real situation, and then improved so it can predict the crack development after surface cracking of concrete cover. Based on this model, crack development behavior and mechanism in concrete cover due to steel corrosion are discussed. (3) An improved electrochemical method is used to accelerate the corrosion of reinforced concrete specimens with0%,33%,67%and100%of coarse aggregates from recycled sources. The thickness of the rust layer and the total crack width at the surface of the concrete cover are measured for slices cut from the specimens, and the crack development path in recycled aggregate concrete was studied. The experimental results have been compared to the calculation results of the proposed model. Mechanism of crack development and engineering application of recycled aggregate concrete are discussed.