Final answer:
Type IV Portland cement is the appropriate choice for massive concrete placements such as gravity dams due to its low heat hydration properties, which prevent thermal cracking.
Step-by-step explanation:
The type of Portland cement that should be used in a massive concrete placement such as a gravity dam, specifically for low heat hydration, is Type IV. Type IV Portland cement is also known as Low Heat (LH) cement, and it is formulated to release heat at a slower rate during the curing process, which minimizes the risk of thermal cracking in large concrete pours. This characteristic makes it an ideal choice for massive structures like gravity dams, where control of temperature is essential to ensure structural integrity.
In contrast, Type III cement, also known as High Early Strength cement, is designed to reach higher strengths more quickly and would not be appropriate for massive placements due to the rapid heat generation during hydration. Similarly, Type V cement is formulated for high sulfate resistance and is not specifically designed for low heat hydration characteristics.