Why Do Civil Engineers Test Compressive Strength of Concrete at 28 Days?

Viewing the table, you can discover that concrete gains 16 percent strength in one day, 40 percent in 3 days, 65 percent in 7 days, 90 percent in 14 days and 99 percent strength in 28 days.

As per IS 456 and BS CP 114 concrete gains 120 % -124 % strength in one year. This is a pretty long time to test concrete and commence the project. Hence the principle of the ‘ Law of Averages’ ( LOA) is adopted.

Thus by Statistical principle the 28 day compressive strength of Concrete is relied upon by The Art of Conjecturing, propounded by Jacob Bernoulli.