'Alkali-Silica Reaction' (ASR) in concrete causes:
Choose the correct answer
Rapid early strength gain
Expansive silica gel from alkali-silica reaction causing map cracking and disintegration of concrete
Improved bond of reinforcement
Reduced setting time
Correct Answer
B. Expansive silica gel from alkali-silica reaction causing map cracking and disintegration of concrete
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ASR: alkalis (Na⁺, K⁺) from cement react with reactive silica in aggregate (opal, flint, volcanic glass) in presence of moisture → hygroscopic silica gel forms → expands → map cracking (crazing), disintegration. Prevention: (1) Low-alkali cement (< 0.6% Na2O_eq); (2) Fly ash/slag (consumes alkalis); (3) Lithium salts; (4) Non-reactive aggregate. Takes years to manifest. IS 383 classifies reactive aggregates.
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