Evaluation of the Maturity Method to Estimate Concrete Strength

Abstract

The strength of a newly constructed concrete structure or roadway is critically important to contractors and engineers who must decide when to safely allow construction loads, prestressing operations, or opening to traffic loads. The maturity method allows the user to estimate concrete strength at any given time using the structure’s unique temperature history. The purpose of this project was to analyze the effectiveness and accuracy of the maturity method to estimate concrete strengths for a variety of commonly used mixtures. The mixtures were chosen to show the effects of using various types of cements, various types and doses of supplementary cementing materials, and various water-to-cementitious materials ratios. Each mixture was batched at three different temperatures selected to span the entire range of expected conditions;with average batch temperatures of 55°F, 70°F, and 101°F. Concrete cylinders were prepared and cured under various temperature histories. Compressive strength versus age data was examined. Mixtures were evaluated based on the amount of long-term strength loss or gain due to curing temperatures and the amount of “temperature sensitivity.” The time-temperature histories were then converted to maturity using the Nurse-Saul and Arrhenius maturity functions. Compressive strength versus maturity data were then analyzed to determine the accuracy of estimating strengths using the maturity method. It was found that the maturity method was inaccurate for estimating concrete strengths beyond 7 days of equivalent age, especially for mixtures with severe long-term strength loss due to high curing temperatures. The results of this study indicated that the Nurse-Saul maturity function using a datum temperature of 32°F (0°C) was the most effective and practical method for estimating concrete strengths of all mixtures studied. However, if the Arrhenius function will be used, a temperature sensitivity function is recommended to allow for a higher temperature sensitivity at low curing temperatures and a lower temperature sensitivity at high curing temperatures.