Construction methods · Shallow foundations, cofferdams and dewatering

Mass concrete and thermal control

Footings, caps and pylon bases are thick enough that the heat of hydration cannot escape; the core can reach 70 C while the surface cools, and the difference cracks the concrete. Thermal control is part of building a foundation, not an optional extra.

How bridges get built · Shallow foundations, cofferdams and dewatering · Mass concrete and thermal control

Also called: thick pour, thermal cracking control, cooling pipes

Mass concrete and thermal control — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Limit the placing temperature (chilled water, ice, night pours) and the cement content; use slag or fly ash.
Embed cooling pipes at 1-1.5 m spacing in pours over about 1.5 m thick; circulate water for 1-3 weeks.
Insulate the surfaces so the core-to-surface difference stays below about 20 C; monitor with thermocouples.
Plan lift heights and joints so each pour can be controlled.

Where it fits

Any pour thicker than about 1 m: pile caps, pylon bases, cofferdam seals, arch springings.

Where it does not

Pouring a 3 m cap in the desert afternoon without a plan.

Plant, pace and money

PlantChillers or ice plant, cooling pipe network and pumps, thermocouples and loggers.

ProductivityUnchanged for placing; adds 1-3 weeks of monitoring per pour.

CostUSD 10-30 per m3 extra.

Risks and controls

What goes wrong

Through cracks that let chlorides into the reinforcement; delayed ettringite formation if the core exceeds 70 C.

Quality assurance

Thermal analysis before the pour, thermocouple records, crack mapping after stripping.

Examples

Pylon bases of sea bridges in the Gulf are routinely cooled for two to three weeks.