Crack width control is important in many reinforced concrete structures. A solid concrete structure is likely to fail if gaps are not bridged and protected. Furthermore, when the concrete structure in question acts as a containment vessel of fluids, leakage must be minimized or eliminated altogether depending on use and purpose.
In plain concrete, crack bridging is provided by aggregate locking action. When fibers are added to concrete, an additional bridging action is brought into effect, super imposing on the aggregate bridging effect. The combined bridging action in a fiber-reinforced concrete (FRC) can be very beneficial to increase the stress carried across the crack, and it’s important to test it for effectiveness.
Therefore, Crack bridging test is done to measure the joint bridging ability and durability of the fiber/watertight covering used.
The test can easily be performed on a Tinius Olsen 50K-T tension compression testing machine using QS4531 grip; a four point bend test grip. The test is done on a reinforced concrete sample 200 x 300 mm to EN1062-72004 Annex C.
After the test specimen is prepared and loaded in a bending test apparatus as shown in figure below, the test specimen is bent by applying a constant force until a crack appears on the uncovered sides of the concrete surface. The crack will appear on both sides of the concrete, close to the edge of the watertight material. The crack is measured for a width 0.4, 0.75 and 1.5 mm resp. The test is passed, if 24hr after fixing the crack in the substrate no perforation has occurred in the watertight covering.