Effect of loading rate on crack velocities in HSC

This paper presents the recent results of an experimental program aimed at disclosing the loading rate (loading-point-displacement rate) effect on the crack velocity in high-strength concrete (HSC). Eighteen three-point-bend tests were conducted using either a servo-hydraulic machine or a self-designed drop-weight impact device. Four strain gauges mounted along the ligament of the specimen were used to measure the crack velocity. Six different loading rates were applied, from 10(-4) mm/s to 10(3) mm/s (average strain rate from 10(-6) to 10(-1) s(-1)), i.e., a low loading-rate range (5.50 x 10(-4) mm/s, 0.55 mm/s and 17.4 mm/s) and a high loading-rate range (8.81 x 10(2) mm/s, 1.76 x 10(3) mm/s and 2.64 x 10(3) mm/s). At low loading rates, the crack propagates with increasing velocity. Under high loading rates, the crack propagates with slightly decreasing velocity, though the maximum crack speed reached up to 20.6% of the Rayleigh wave speed of the tested HSC. In addition, the loading-rate effect on crack velocities is pronounced within the low loading-rate regime, whereas it is minor under the high loading-rate range. (C) 2009 Elsevier Ltd. All rights reserved.