Mass Concrete

Mass concrete is concrete placed in sections large enough that the heat generated by cement hydration, and the resulting temperature differentials, must be managed to avoid thermal cracking — typically rafts, large pile caps, transfer girders, dam blocks and thick foundations. As the interior heats and the surface cools, the temperature gradient (and later the differential contraction as the core cools) induces tensile stresses that crack the concrete if the core-to-surface differential is not limited (commonly kept within about 20 °C, with placing temperature controlled).

Control measures, guided by IS 456 Cl. 8.2.1 and IS 14591 (temperature control of mass concrete for dams), include low-heat cements/high SCM replacement (fly ash, GGBS), reducing cement content, pre-cooling aggregates/mix water (chilled water or ice), embedded cooling pipes, pour-height/lift limits with delay between lifts, insulating surfaces to slow cooling, and continuous thermocouple monitoring with a thermal-control plan. The objective is a structurally sound, crack-controlled monolith, not merely meeting cube strength.