Fibre reinforced polymer rehabilitation of alkali aggregate reaction damaged concrete structures

Abstract

It is well known that Reinforced Concrete (RC) structures are vulnerable to a number of factors that can cause deterioration, such as excessive loading, fire and harsh environmental exposure. To counter deterioration and extend the life span of deteriorated structures, the Fiber Reinforced Polymer (FRP) strengthening method has become a popular choice for structural repair. Due to the increased use of this strengthening method, design provisions have been developed for the repair of deteriorated concrete structures. Whilst FRP has been successfully applied to concrete structures where deterioration has been caused by external factors, the application of FRP to concrete structures damaged by internal factors such as Alkali Aggregate Reaction (AAR) is very limited. AAR is a chemical reaction which occurs in the concrete between the non-crystalline silicon oxide found in aggregate with the highly alkaline cement. The result of this reaction is expansion and then cracking starts deep within the concrete cement paste. The reaction is slow but progressive. When the expansion exceeds the tensile strain capacity of the concrete, cracks occur and the concrete loses its initial mechanical properties. Since the discovery of AAR by Stanton in 1940, many research studies have been carried out to develop understanding of how the reaction occurs, to establish guidelines to assess the reactivity of the aggregate, and to evaluate the effect of AAR on the mechanical properties of the concrete. Research on AAR is quite challenging due to the uncertainty of the reaction, as it is affected by factors such as type and amount of aggregate, the nature of the cement and environmental conditions. It is important to treat the concrete structures damaged by AAR in effective ways so that the expansion can be delayed and the life-span of affected structures can be extended. This thesis concerns the effectiveness of using FRP to repair RC structures damaged by AAR. The thesis begins with the assessment of the mechanical properties of concrete at various expansion levels. To relate to real phenomena, medium-scale RC columns were prepared and treated with FRP under two types of conditions: active and passive confinement. In active confinement, it was assumed that the expansion in the columns was continuing while in passive confinement it was assumed that the expansion had ceased. The residual strength of the columns after repair was evaluated and compared against other column properties. Furthermore, the effectiveness of FRP confinement to restrain expansion was monitored and analysed. A new strength model has been developed based on the experimental results. Evaluation of residual strength was compared against existing models, which were found to be ineffective for the prediction of the strength of damaged columns after repair. In addition, FE models were also developed to provide understanding of the behavior of AAR concrete, and to estimate the load-carrying capacity of the repaired columns.