Determination of the strength of in-place concrete is obviously important to contractors. Decisions such as when to strip forms, when to post-tension, when to remove shores or reshores, and when to terminate cold-weather protection are based on reaching a minimum level of concrete strength. The information used to make these decisions is usually obtained from field-cured cylinders, pullout tests, or penetration testing. The maturity method is another technique that can be used to estimate the strength of in-place concrete. THE STRENGTH-MATURITY RELATIONSHIP The maturity method is simply a technique for predicting concrete strength based on the temperature history of the concrete. Strength increases as cement hydrates. The amount of cement hydrated depends on how long the concrete has cured and at what temperature. Maturity is a measure of how far hydration has progressed. MATURITY MEASURING EQUIPMENT To determine maturity, a time-temperature record is kept for the in-place concrete. Temperature sensors placed in concrete and attached to a strip chart recorder provide data that is used to calculate maturity. ESTABLISHING THE STRENGTH-MATURITY RELATIONSHIP To use the maturity method, the concrete mix specified for the job must have a reference maturity curve. Your local testing laboratory can develop a relationship between strength and maturity under known time and temperature conditions. This testing must be done with exactly the same materials and concrete proportions that are used for the project. After the laboratory reference maturity curve is constructed, it is used with field maturity data to estimate compressive strength.