Use of maturity method to estimate compressive strength of mass concrete

• The maturity method was used to predict in-place compressive strength of 6-ft cubes.
• Activation energies for four concrete mixtures for the cubes were determined.
• The core strength of the 6-ft vertical cores was found to increase with depth.
• The predicted strength values were comparable to the core strength at the center position.
• The predictions were higher than the core strength at the top and lower at the bottom position.

In this study, maturity method was used to estimate in-place strength of large concrete placements. Four 6-foot (1.8 m) cube concrete blocks were constructed in four different locations, and the strength development curves for these concrete mixtures were established using 6 by 12 inch (150 by 300 mm) cylinder specimens collected from the construction site. Activation energy values for the concrete mixtures were determined in the laboratory and used for equivalent age calculations. Sacrificial temperature sensors embedded throughout the depth of the concrete cubes were used to monitor temperature histories in specific locations up to 28 days. Equivalent age was employed to estimate in-place concrete strength based on the collected temperature histories. Four inch (10 cm) diameter core samples, with 6-foot (1.8 m) in length, were taken from the cubes at 4, 28 and 56 days after construction and the core strengths were compared with the predicted strengths using maturity relationships. Results show that the predicted in-place concrete strength is always higher than the actual core strength on top surface locations. Results from three different cubes show that core compressive strength from mid-section were within ±15% of the predicted values and core results from the bottom section were generally higher than the predicted values.