Slow Dynamics for Concrete Strength Evaluation

Abstract

This study explores the use of slow dynamics behavior to estimate the compressive strength of concrete. Slow dynamics, a nonlinear elastic phenomenon observed in heterogeneous materials like concrete, involves stiffness reduction under conditioning followed by a logarithmic recovery over time. Concrete specimens with compressive strengths of 32, 40, 49, and 56 MPa were tested. Each was subjected to a 6 kN load while ultrasonic signals were monitored to track relative velocity changes (dv/v) during recovery. Higher strength specimens showed larger velocity drops and faster recovery. The 56 MPa samples had dv/v drops that were 2.23, 1.80, and 1.37 times greater, and recovery rates that were 2.09, 1.84, and 1.37 times faster, than those of the 32, 40, and 49 MPa groups. In contrast, ASR damaged specimens exhibited greater sensitivity to conditioning but recovery rates that did not scale with the velocity drop, unlike the proportional behavior observed in intact samples.