Control of asphalt cracking using grids

Control of asphalt cracking using grids

Fatigue Cracking

In an un-reinforced asphalt layer, strain is not evenly distributed but develops in peaks located at weak spots in the asphalt which can lead to the development of cracks. In reinforced asphalt, the grid will delay fatigue and reflective cracking mainly by providing a confinement that prevents strain build-up at these weaker spots.

Thermally induced reflective cracking

Reflective cracking in pavements is caused by peaks in strain centred over the crack or joints from lower layers. Independent research at the University of Nottingham has demonstrated that grid reinforcement eliminates peak strains, preventing thermally induced reflective cracking. The University of Nottingham thermal crack simulation apparatus was used in this investigation. The machine is composed of two concrete slabs, each 1 metre long by 200mm width, mounted on a mechanical device allowing for variable displacement between the slabs. The asphalt layer to be tested is built directly on the concrete frame. Thermal cracking is simulated by driving the two slabs apart from each other, therefore inducing tensile stress into the overlaying asphalt. In this test, strain gauges were positioned with or without AR1 reinforcement. Testing was carried out at -5 degrees C and a crack movement amplitude of 2mm.

Traffic induced reflective cracking

Overlays over fractured surfaces will fail prematurely due to the traffic induced reflective cracking. Tests conducted at the University of Nottingham showed that Tensar grids control traffic induced reflective cracking, greatly extending the life of the pavement. A cyclic bending test was used to estimate resistance of an asphalt layer to repeated bending focused on a cracked substrate. The crack was simulated by mounting the asphalt slab onto two plywood boards, themselves resting on a rubber pad. A cyclic load is then applied on the top of the asphalt layer and crack development recorded versus the number of loading cycles.

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