'Mass concrete' (large dams, pile caps, thick rafts) uses special measures to control:
Choose the correct answer
Low compressive strength
Thermal cracking — heat of hydration raises core temperature, surface-to-core temperature differential causes tensile cracks
Insufficient workability for pumping
Excessive shrinkage from low water content
Correct Answer
B. Thermal cracking — heat of hydration raises core temperature, surface-to-core temperature differential causes tensile cracks
Why is this the answer?
Mass concrete: large volume where heat of hydration (cement reactions generate heat) creates thermal gradients → temperature differential between core (hot) and surface (cooler) → tensile stresses on surface → thermal cracks. Control: (1) Low heat cement (LHC) or GGBS/fly ash partial replacement; (2) Chilled water/ice for mixing; (3) Pre-cooling aggregates; (4) Post-cooling pipes (water circulated through embedded pipes); (5) Limit pour thickness; (6) Insulate formwork surface. IS 14268 covers mass concrete.
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