Effect of Different Strengthening Techniques on the Structural Behaviour of Continuous Two-Way Slabs with Partially Corroded Reinforcement at Internal Support

Abstract

This research studies the combined effects of partial corrosion of the negative reinforcement in two-way continuous slabs (two spans) with a construction joint at the internal support and investigates the efficiency of the proposed strengthening methods to overcome these effects. The partial corrosion in reinforcement comes from exposure to the corrosive outdoor environment due to an unplanned stoppage in concrete pouring for a long-time which left part of the negative reinforcement without protection. The construction joint formed at the internal support after resume the concrete pouring later. Three types of strengthening are proposed to overcome those effects. The study adopted an accelerated corrosion technique which is running an electrical current in the steel bars partially immersed in a 5% salt solution (elect-chemical cell). The proposed strengthening was: NSM CFRP bars, CFRP strips, and steel plates. All applied to the top face in the tension zone at the internal support. Six two-way continuous (two spans) concrete slabs were cast (2200, 1000, and 100 mm). The strengthening was: four strips of CFRP had 50 mm width, four of 6 mm CFRP bars applied using the NSM technique, and four steel plate 50 mm width and 5 mm thickness. All the strengthening extended to the third of span length and was aligned with the slab continuity axis. The specimens were tested and the deflection, first positive and negative crack width, and failure mode were recorded. Numerical analysis and comparison with the experimental results were conducted to verify the numerical model. The study found that the construction joint and corrosion had a clear influence on the structural behavior of the slab. Those effects were on the ultimate load, deflection, and the negative cracks. The proposed treatments were highly effective and efficient in increasing the ultimate load, delay the appearance of cracks, and reduction of deflection under the load points.