Date

2006-09-01

Author

Bektas, F.
Turanlı, Lutfullah
Ostertag, C. P.

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Alkali–silica reaction (ASR) is a chemical reaction between the alkali and hydroxyl ions produced by portland cement hydration and certain types of silica present in the aggregate. The stages that are involved in causing damage due to ASR are shown schematically in Fig. 1. The alkali ions and hydroxyl ions in the pore solution of the hydrated cement paste react with amorphous or poorly crystalline silica in the aggregates to form alkali silica (AS) gel. The AS gel expands by imbibing water and the resulting pressure exerted onto the surrounding mortar matrix causes extensive cracking and strength loss. The traditional approach to prevent ASR has focused on either preventing the ASR or reducing the expansion of the gel by modifying the chemical environment in which the ASR takes place. Examples are: (i) avoiding reactive aggregates, (ii) using low alkali cement, or (iii) either adding mineral admixtures [1–4] or lithium salts [5, 6]. Avoiding reactive aggregates and limiting the alkali content in cement seem to be the easiest way to prevent damage in concrete due to ASR. Unfortunately, since costs dictate that aggregates and cement be produced locally, this apparently simple solution can be rather challenging. Furthermore, quarries with adequate aggregates are being depleted and using non-ideal aggregates may be a necessity in the future. Influencing the reaction chemistry by adding mineral admixtures to concrete had mixed results in terms of its effectiveness in reducing the expansion and hence damage associated with ASR. The mixed results are because of the wide variety of reactive aggregate types and sizes and cement types, and because of variations in chemical compositions [7] and agglomerations [8, 9] of mineral admixtures. Therefore, it is of interest to investigate alternative forms of mitigating ASR. This paper reports on mitigating the damage associated with ASR by controlling crack formation. Since strength reduction associated with ASR is due to cracking utilizing fibers to control and minimize crack formation seems to be a promising alternative. Cracks initiate in close vicinity to the reactive aggregates and need to be influenced at onset before they become dominant macrocracks. Therefore steel fibers of relatively small diameters are utilized in this study since they are more effective in interacting with these small cracks than conventional steel fibers commonly used in fiber-reinforced concrete.

Subject Keywords

EXPANSION, ADMIXTURES

URI

https://hdl.handle.net/11511/56646

Collections

Graduate School of Natural and Applied Sciences, Article