The development of the fracture process zone associated with subcritic
al crack growth in a three-point bend concrete specimen with an off-ce
ntered single-edged precrack was monitored with moire interferometry.
The applied load and the crack opening and sliding displacements toget
her with a finite element model of the concrete specimen were used to
determine the crack closing stress due to aggregate bridging. Under th
is mixed-mode fracture, aggregate interlocking increased the crack clo
sing 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.