This publication deals with the results of a study to establish whether the deleterious effect on strength development of micro silica in very high grade concrete also occurred in lower grades. In very high grade concrete containing micro silica, there is a loss of flexural strength of about one-tenth relative to the 28-day value, at age 1 year. This study showed that the severity of the retrogression decreases as the grade is decreased. It was also found that the strength retrogression observed in the very high grade concrete with micro silica did not worsen at age 3 years. Price includes VAT