Following table shows the strength of concrete at different ages. Age Strength % 7days 65% 14days 90% 28days 99% Compressive strength of different grades of concrete at 7 and 28 days Grade of Cement Minimum compressive strength N/mm2 at 7 days Specified characteristic compressive strength (N/mm2) at 28 days 15 10 15 20 13.5 20 25 17 25 30 20 … Continue reading Strength of concrete at various ages