What is a typical effect of high heat of hydration in large pours?

• A. Temperature rise can cause thermal cracking.
• B. It has no impact on cracking risk.
• C. Measures to control temperature include using Type II cement or cooling the mix.
• D. It shortens the curing period.

Answer: (A)

When cement hydrates, heat is released. In a large pour, this heat raises the interior temperature and creates a thermal gradient between the hot interior and cooler exterior. As the concrete later cools and contracts, restrained layers develop tensile stresses that can exceed the concrete’s strength, leading to thermal cracking. That temperature rise causing cracking is the typical effect.

Measures to control temperature, like using Type II cement or cooling the mix, address the problem but are not the immediate effect itself. The idea that high heat has no impact is incorrect, and while temperature can influence curing nuances, the primary concern in large pours is cracking from thermal stresses.