Aging infrastructure facilities, particularly those made of reinforced concrete (RC), are currently deteriorating at a rapid rate—faster than they are being repaired, rehabilitated, or replaced. A major cause of concrete deterioration is corrosion of the reinforcing steel in the structure resulting from chloride penetration or carbonation. This project focused on the development of high performance cement-based composites and their application in RC structures for enhanced durability against reinforcement corrosion and deterioration by corrosive substances. This work presents a new direction for tackling the problem of durability of reinforced concrete structures . The approach adopted is based on the concept of functionally-graded concrete (FGC) where part of the concrete, which surrounds the main flexural reinforcement in a RC member, is strategically replaced with a cementitious composite material with high strain-capacity and fracture resistance.

The material development part of this research was guided by a micromechanical model based upon fracture mechanics and deformation mechanisms taking into account the effects of hybrid fibres. The model was later used to design two types of strain-hardening materials. The first was a hybrid fibre reinforced cement paste composite exhibiting strain-hardening behaviour and multiple-cracking under uniaxial tensile loading. This material is referred to as an Engineering Cementitious Composite or ECC for short. Engineering cementitious composites are characterised by their high tensile strain capacity, fracture energy and notch insensitivity, making them ideal materials for numerous applications such as: impact-resistant structures, blast-resistant structures, seismic-resistant structures and ductile RC connections. The second type of material is a hybrid fibre reinforced cement mortar exhibiting strain-hardening behaviour and multiple-cracking under flexural loading. This material is referred to as Ductile Fibre Reinforced Cementitious Composites (DFRCC).

The FGC concept was adopted to prepare a series of FGC beams where a layer of DFRCC material was used around the main longitudinal reinforcement for corrosion protection. The effectiveness of the DFRCC material in retarding the corrosion of steel reinforcement in RC beams and reducing the tendency of the concrete cover to delaminate was then evaluated. The effects of steel loss and corrosion damage on the flexural response of the RC beams were also evaluated. The FGC concept using DFRCC material was found in this study to be very effective in preventing corrosion-induced damage in RC beams (Figure 1) and minimising the loss in the beam’s load and deflection capacities.

Figure 1: Photographs showing extensive corrosion damage in ordinary Portland cement concrete (OPCC) beam (left) and minimal corrosion damage in Functionally-Graded Concrete (FGC)induced damage in RC structures beams (right).

Figure 2: Concrete embeddable Fibre Optics Sensor (FOS) used to detect and measure corrosion-induced damage in RC structures

The proposed fibre optic sensing technique (Figure 2) was found to be useful for measuring and monitoring tensile strains (Figure 3) in the concrete resulting from the corrosion-induced expansion of the reinforcing steel. It can also be used to detect any crack forming in concrete due to corrosion where visual inspection is not possible.

Figure 3: Strain output from FOS used to track development of delamination/spalling resulting from expansion of corroding steel bars.

Our research team comprises Assoc Prof M Maalej, Prof P Paramasivam and Mr SFU Ahmed.