Concrete kept at a temperature of 50 degrees Fahrenheit for one day will usually reach what compressive strength to prevent damage from freezing?

Concrete kept at a temperature of 50 degrees Fahrenheit for one day will usually reach what compressive strength to prevent damage from freezing?

• A. 400 psi
• B. 500 psi
• C. 600 psi
• D. 700 psi

Answer: (B)

The main idea is early strength to resist freezing damage. When concrete is exposed to freezing temperatures, water inside the pores can expand as it freezes and create internal stresses. If the concrete hasn’t gained enough early strength, those stresses can crack the paste and aggregate, leading to freeze-thaw damage. Reaching about 500 psi in the 24 hours after placement at 50°F shows the mix has developed enough cohesive strength to withstand those expanding forces without cracking excessively. This early strength level is a practical target: it balances the slower cure at 50°F with a level of resistance that helps protect against freezing, without requiring unrealistically high early strengths. Values around 400 psi would be weaker and more vulnerable to damage, while 600 or 700 psi would indicate unusually rapid early strength gain and isn’t the standard benchmark for preventing freeze damage after one day.

The main idea is early strength to resist freezing damage. When concrete is exposed to freezing temperatures, water inside the pores can expand as it freezes and create internal stresses. If the concrete hasn’t gained enough early strength, those stresses can crack the paste and aggregate, leading to freeze-thaw damage. Reaching about 500 psi in the 24 hours after placement at 50°F shows the mix has developed enough cohesive strength to withstand those expanding forces without cracking excessively. This early strength level is a practical target: it balances the slower cure at 50°F with a level of resistance that helps protect against freezing, without requiring unrealistically high early strengths. Values around 400 psi would be weaker and more vulnerable to damage, while 600 or 700 psi would indicate unusually rapid early strength gain and isn’t the standard benchmark for preventing freeze damage after one day.