The alkali-silica reaction (ASR), known as "concrete cancer" is a deleterious swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (i.e., non-crystalline) silica found in many common aggregates, given sufficient moisture. What are the emerging repair and prevention techniques for ASR?.
Utilization of pozzolanic materials in concrete prevents alkali silica reaction by controlling and limiting lime (calcium hydroxide) content through pozzolanic reaction to produce more calcium silicate/aluminate hydrates (CSH or CAH).
Generally alkalis present in cement react with amorphous silica from aggregate in presence of moisture to form ASR gel which is expansive in nature. The ratio of Ca2+ to the alkalis ( Na+ and K+ ) in the gel determine its nature. Higher the Ca2+ lesser expansive will be the ASR gel. The different way to protect the ASR is as follows:
1. Use mineral admixture (mainly Silica fume) which reduce the penetration of water by producing highly compact microstructure. Moreover, ASR gel that forms in mineral admixture have high Ca2+ content and thus not very expansive.
2. Use of low alkali content cement (less than 0.6% equivalent of Na2O).
3. Use of Lithium salt as chemical admixture(Ex- LiNO3 and LiOH). Lithium has higher reactivity than Na+ and K+ . So Lithium bind with reactive silica into a non-expansive product.
4. Use Silane coating or water proofing agent, which does not permit water to come into concrete.
Well I do agree with above given answers, but here I would like add one point that by making cement free from unnecessary extra retarders and admixtures we can help in preventing ASR.
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