What is the minimum age requirement for concrete specimens before testing for compressive strength?

The minimum age requirement for concrete specimens before testing for compressive strength is 28 days. This timeframe is significant because concrete continues to cure and gain strength over time due to the hydration process of the cement. While concrete might gain some strength shortly after placement, the majority of its strength development occurs between the 7-day and 28-day marks.

Testing at 28 days provides a more accurate representation of the concrete's potential compressive strength under typical conditions, as this is the standard curing period used in most specifications and design practices. Factors such as mixture design, environmental conditions, and curing methods also influence strength development, but the 28-day criterion serves as a reliable benchmark for assessing structural integrity and performance in construction applications.

Although concrete does gain strength before reaching 28 days—for example, it may reach around 70% of its strength at 7 days—testing at this earlier age may not provide a reliable indication of the concrete's ultimate strength, which is why 28 days is the widely accepted standard in the industry.