Cement selection for mass concrete — best choice for a massive dam When constructing a massive gravity dam where heat generation and thermal cracking risk are critical, which type of cement should be selected?

Introduction / Context:
Mass concrete elements, such as gravity dams, experience significant temperature rise from cement hydration. The resulting thermal gradients can cause cracking if the temperature rise is excessive or rapid. Selecting an appropriate cement type is central to thermal control and durability in such structures.

Given Data / Assumptions:

• Very large section thicknesses and slow heat dissipation.
• Primary concern: limiting peak temperature and differential thermal strains.
• Conventional placement with temperature control measures (e.g., cooling pipes, lift thickness control) may be used.

Concept / Approach:
Low heat cement is specifically formulated (reduced C3A and moderate C3S) to lower the rate and amount of heat evolved during hydration. This mitigates thermal cracking risk. Rapid hardening cement is unsuitable due to high early heat. OPC generates more heat than low heat cement. Blast furnace slag cement can reduce heat relative to OPC and is often beneficial; however, when a single best choice is requested for a massive dam, the textbook answer is low heat cement, purpose-designed for mass concrete applications.

Step-by-Step Solution:

Verification / Alternative check:
Historic dam projects and specifications commonly cite low heat cement or blended systems designed for low heat evolution as preferred binders for mass concrete.

Why Other Options Are Wrong:

• OPC: higher heat of hydration.
• Rapid hardening: very high early heat; risk of thermal cracking.
• Blast furnace slag cement: helpful but not as targeted as low heat cement when a single best answer is sought.
• White cement: selected for colour, not thermal performance.

Common Pitfalls:
Ignoring placement temperature, lift thickness, and cooling strategies; assuming admixtures alone can offset high-heat cements.

Final Answer:
Low heat cement