Evaluation of the Maturity Method to Estimate Concrete Strength in Field Applications

Abstract

Estimating the strength of concrete is essential to contractors and engineers to allow concrete construction operations to proceed safely and expediently. The maturity method is a technique that allows the in-place concrete strength to be estimated using the time and temperature history of freshly placed concrete. The purpose of this project was to evaluate the accuracy of the maturity method to assess concrete strength under field conditions and develop a specification for Alabama Department of Transportation (ALDOT) to implement the maturity method. The field applications investigated were the construction of a precast prestressed girder and the construction of a bridge deck. For each project the accuracy of the maturity method for estimating the in-place strength of concrete was evaluated. A mock girder and mock bridge decks were constructed to test the in-place strength. The in-place strength was tested with pullout tests, compression testing of cast-in-place cylinders, and compression testing of cores. Also the accuracy of using laboratory-cured specimens versus field-cured specimens for developing the strength-maturity relationship to estimate the in-place strength was evaluated. Seasonal effects on the maturity method were also evaluated during the bridge deck project. The optimum locations of temperature sensors used in estimating the in-place strength were determined in the prestressed girder and bridge deck. Finally the American Society of Testing and Materials (ASTM) Standard ASTM C 1074 recommended procedures for implementing the maturity method were evaluated on the actual bridge decks that were constructed. It was found that the maturity method may only be accurate for estimating the in-place strength of the concrete up to an equivalent age of seven days. The Nurse-Saul maturity function with a datum temperature of 0 °C (32 °F) was found to be the most accurate function for estimating the strength when considering all projects and variables. When comparing the activation energies for the Arrhenius maturity function, an activation energy of 33,500 J/mol was more accurate for the warm-weather concrete placements, and an activation energy of 40,000 J/mol was more accurate for the cold-weather concrete placements. This supports the results of the laboratory study. The maturity method accurately estimated the pullout and cast-in-place cylinder strengths. The ASTM C 1074 recommended procedures were determined to be useful, but some modifications were recommended for implementation for ALDOT projects. A proposed specification is presented in this thesis.