The Strength-Maturity Relationship – The relationship between the concrete temperature and maturity index, which is also called the temperature-time factor, can be calculated using the following formula (E4-2, page 4):

In cases when, in the early stages of curing, concrete strength does not have a linear relationship with temperature, a separate formula is utilized (E4-2, page 5):

A key variable in this equation is the datum temperature T0. Approximate values for the datum temperature are provided in the American Society for Testing and Materials' ASTM C 1074 (E4-2, page 5; E4-15, page 4):