The development of the fracture process zone associated with subcritical crack growth in a three-point bend concrete specimen with an off-centered, single-edged precrack was monitored with moire interferometry. The applied load and the crack opening and sliding displacements together with a finite element model of the concrete specimen were used to determine the crack closing stress due to aggregate bridging. Under this mixed-mode fracture, aggregate interlocking increased the crack closing stresses in the fracture process zone and hence the load carrying capacity of the concrete specimen. The dissipated energy rate in the fracture process zone also increased with aggregate interlocking.

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