Massachusetts Unrestricted Construction Supervisor License Practice Test

What causes portland cement to harden when mixed with water?

1. Heat of hydration

2. Cooling effect

3. Molecular bonding

4. Air exposure

The correct answer is: Heat of hydration

Portland cement hardens when mixed with water due to a chemical process known as hydration. During hydration, water reacts with the compounds found in the cement, leading to the formation of various hydrated products, such as calcium silicate hydrate (C-S-H) and calcium hydroxide. This chemical reaction releases heat, known as the heat of hydration, which is essential for the hardening process. The heat generated during this reaction not only helps to speed up the curing process but also contributes to the strength of the hardened cement. It allows the cement to achieve its structural integrity as it continues to hydrate and develop over time. Other options, like cooling effect, molecular bonding, or air exposure, do not primarily drive the hardening of Portland cement. While all these factors can play a role in the larger context of concrete mixing and setting, the fundamental reason for the hardening of Portland cement specifically hinges on the heat produced during hydration, making this the correct choice.