After a period of 7 days, concrete typically achieves what percentage of its specified compressive strength?

After a period of 7 days, concrete typically achieves around 70% of its specified compressive strength. This percentage indicates that concrete continues to gain strength after the initial setting and curing phase.

The correct answer aligns and falls within the range described in option B (60-75%). Concrete does not reach its full specified compressive strength until it has been cured for a longer duration, often achieving about 100% strength at 28 days. The rate of strength gain for concrete can vary based on factors including the mix design, curing conditions, and ambient temperature.

The significance of understanding this percentage lies in the planning of construction activities; knowing that concrete is not at full strength after just one week allows for appropriate decision-making regarding loads and usage during this curing period. While various concrete mixtures may deviate slightly, this range is a general guideline used by professionals in the field.