Repair corroded reinforced concrete columns using alkali-activated slag ferrocement

A new method for repairing corroded reinforced concrete columns using alkaliactivated slag (“AAS”) ferrocement is proposed. Ten full-scale column specimens were prepared and seven of them suffered artificial accelerated corrosion at a mass loss of main reinforcement of 8.9 %. Three corroded specimens were subsequently strengthened. This is achieved by replacing concrete cover by AAS ferrocement jackets with two layers of stainless steel wire meshes (“SSWM”). The specimens were tested under axial, small and large eccentric compression, respectively. Experimental results have shown the corroded columns suffer loading capacity losses from 21 to 30 % as compared with the control specimens. AAS ferrocement jacket can enhance the loading capacity of corroded columns by 18 to 38 %. Confinement effect of AAS ferrocement is observed on specimens under axial and small eccentric compression. INTRODUCTION Old reinforced concrete structures in coastal areas are found to exhibit different extents of defects caused by reinforcement corrosion, such as spalling of concrete and deteriorative loading capacity, which have posed a serious threat to structural safety. Kashani et al. [1] indicated that corroded reinforcements with mass loss of 15.5 % experienced a reduction of 78 % in elongation compared with control ones. Corrosion also weakened the buckling capacity of reinforcements. In addition, expansion stress due to corrosion of reinforcement can result in cracks and spalling of concrete which exposes reinforcements to aggressive environment and aggravates their corrosion [2, 3]. Ferrocement has been successfully used to strengthen reinforced concrete structures because of its outstanding mechanical performance, fire resistance and low cost [4-6]. Ganesan and Anil [6] investigated the strength of RC columns confined by ferrocement under axial compression. Increases of 8 %, 29 %, and 42 % in strength were achieved by confinement of ferrocement with 2, 3, and 4 layers of meshes.Compared with Portland cement, slag is regard as a more environmentally friendly material which reduces energy consumption by 90 % in production [7]. It can be activated in alkaline environment and has higher strength than cement [7-9]. Moreover, AAS presents strong resistance to chemical attack because of dense microstructure and a low calcium silicon ratio in hydration products ensuring chemical stability in corrosive environment [7]. In this paper, a new type of ferrocement, comprising of AAS mortar, is proposed to strengthen corroded reinforced concrete columns. 11th International Symposium on Ferrocement and Textile Reinforced Concrete 3rd ICTRC