Estimation of In-situ Concrete Flexural Strength using Maturity

Abstract

Concrete maturity is being recognized as a viable test method to measure in-situ strengths of early age concrete and to assist agencies in making informed decisions on construction schedules. This increased interest is partly due to improved data collection technology in recent years coupled with a better understanding of the effects of construction and curing temperature on early age and long term performance of rigid pavements. The “maturity index”, which is correlated to strength gain in a concrete mixture, is determined from the time-temperature history of the mixture. This paper presents a study conducted by Caltrans to evaluate the accuracy of this technology in predicting both flexural and compressive strength. The study involved a comprehensive laboratory study using two mix designs cured under four different temperature regimes. The test results indicate that calibration regression equations developed from samples cured in standard room temperature conditions are sufficient to predict concrete strengths associated with both cooler (~10OC) and warmer (~37OC) curing temperatures with reasonable accuracy. Further, actual field-measured maturity from a recent paving project, using the same mix design as the present study, yielded similarly accurate in-situ concrete strength predictions. The importance of proper curing for accurate strength predictions is demonstrated in the project.