Prevention of Reflection Cracks in Asphalt Layers Polyester Reinforcement Grids demonstrate most effective results

Cracks (even micro-cracks) in an existing asphalt layer continue to cause problems when these existing layers of roads or airfields are resurfaced.

As a result of daily temperature variations, but especially due to the frost-dew cycles, existing cracks in an old asphaltic layer reflect through to the surface of the newly applied layer of asphalt. Time and again this results in costly, and at the same time unnecessary, reconstruction work. The existing cracks which very quickly propagate through to the new layer of asphalt are called reflection cracks.

By installing a polyester asphalt reinforcement grid, the development of reflection cracks can be substantially slowed down, or even completely avoided.

In order to simulate thermally induced reflective cracking, the Belgium Road Research Center (BRRC) developed a test method at the beginning of the 90’s (see diagram 2) investigating the effect an asphalt reinforcement has on the reduction of cracks.

For the test, a 65 mm thick layer of asphalt is installed over a pre-cracked surface. The simulated crack is 4 mm wide and is widened by 1 mm per cycle then returned to a 4 mm width. The opening of the crack by one mm per cycle corresponds to the expansion volume of water which exists in the crack. The exact widening of the crack is achieved by means of a control liquid which freezes and then thaws.

This test method has now become so well established that nearly all products and systems which are available on the market have been tested. The reinforcement products differ mainly by the choice of the raw material and the use of a bituminous coating. The tested products which are available on themarket consist of glass, carbon, polypropylene (PP), steel and polyester (PET). Several results are shown in table 1.

The reference test without interlayer (0) shows that the crack rose to the surface after very few cycles. The asphalt interlayer systems clearly show differences in their effectiveness, with HaTelit^® (6, 7) completely preventing reflection cracks. Even after completion of the tests, no cracks had been initiated, whereas all other systems made from synthetics, carbon or glass indicated cracks, many of which soon reached the surface.

This clearly demonstrates, that reinforcement stiffness must be matched to the total asphalt package (i.e. if the reinforcement is too stiff it will not interact with the surrounding asphalt matrix).

The polyester used in HaTelit^®‘s manufacture shows that it is the ideal raw material for asphalt reinforcement. It consists of a special, high modulus polyester  covered with a protective bituminous coating. Furthermore this special coating ensures  a high bond, considered to be an important parameter. Only when a good bond is obtained with the surrounding asphalt layers can the tensile forces be considered to  be transferred to the reinforcement.

In the case of cracked asphalt surfaces, under heavy use, HaTelit^®‘s effective mobilisation of tensile forces, through good bond and excellent system performance, provides a highly effective solution.

The results also confirm the, more than, 35 years of experience, of HaTelit® substantially extending maintenance intervals.