Graduate Thesis Or Dissertation
 

Synergistic Effects of Alkali Silica Reaction (ASR) and Fly Ash on the Corrosion Characteristics of Reinforced Concrete Systems

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  • Alkali silica reaction (ASR) and corrosion of reinforcement are two deterioration mechanisms in reinforced concrete (RC) structures. These deterioration mechanisms can significantly damage a RC structure and reduce its service life. Supplementary cementitious materials (SCMs) are commonly used to improve the durability of RC systems containing reactive aggregate that are exposed to chloride environments. Fly ash is commonly used to decrease the chloride transport rate in concrete. This reduction can result in longer times to corrosion initiation and longer service lives. Significant research has also been conducted on the effects of fly ash on ASR. The literature indicates that inclusion of fly ash in concretes that contains reactive aggregate can reduce the expansion and damage. Although significant research has been conducted to investigate ASR and corrosion separately, little research has been done to quantify the synergistic effects of ASR and fly ash content on corrosion performance of RC systems. The research presented here investigates the synergistic effects of aggregate reactivity (e.g., ASR) and fly ash content on corrosion performance of RC specimens. Specimens containing different fly ash contents (0, 20, and 40%) with and without reactive aggregate were exposed to wetting and drying cycles exposed to a 100 °F (38 °C) and >95% relative humidity environment. Expansion of the specimens, corrosion potential, and macrocell current were measured at monthly intervals until the embedded reinforcement began to actively corroded. Apparent diffusivity was measured when the corrosion initiation occurred in the specimens. Results show that increasing fly ash content in specimens with non-reactive aggregate results in lower Da values and lower CT values in concrete. Lower Da values are beneficial for extending time to corrosion initiation whereas lower CT values are not. Results from this research indicate that the benefits from the lower Da values are more significant than the disbenefits from the reduction in CT when assessing time to corrosion initiation. Results for specimens containing reactive aggregates indicate that inclusion of 20% fly ash exhibits the longest time to corrosion initiation. Results indicate that the formation of small amounts of ASR gel in specimens containing 20% fly ash with reactive aggregate can fill the ITZs and cracks. EDX analyses of the ASR gel indicate that chlorides are not present in the gel. This indicates that the transport rate of chlorides through ASR gel is significantly lower than the hcp. The results from this research indicate that the ASR gel can reduce the Da of the overall concrete system and increase the time to corrosion initiation.
  • Keywords: Chloride Threshold, Diffusivity, Alkali-Silica Reaction, Interfacial Transition Zone, Fly Ash, Corrosion
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