Fatigue Performance of Double-Layered Asphalt Concrete Beams Reinforced with New Type of Geocomposites

Abstract

The reinforcement of asphalt layers with geosynthetics has been used for several decades, but proper evaluation of the influence of these materials on pavement fatigue life is still a challenging task. The presented study investigates a novel approach to the reinforcement of asphalt layers using a new type of geogrid composite, in which square or hexagonal polypropylene stiff monolithic paving grid with integral junctions is bonded to polypropylene non-woven paving fabric. The laboratory fatigue tests were performed on large asphalt concrete beams reinforced with the new type of geocomposite. Unreinforced samples were used as reference. Test results were analysed in several aspects, including the standardised approach based on stiffness reduction, but also using energy dissipation. The effect of reinforcement on pavement fatigue life was also estimated. Based on the obtained final results of fatigue life calculations, it can be concluded that the evaluated geogrid composites have an evident positive effect on pavement performance and have a significant potential to extend the overall pavement life, especially in the case of hexagonal grid.

Keywords: fatigue of asphalt pavements; four-point bending test; geogrid reinforcement; reflective cracking.

Figure 1

View of the AR-GN composite, square geogrid bonded to non-woven geotextile.

Figure 2

View of the AX5-GN composite, hexagonal geogrid bonded to non-woven geotextile.

Figure 3

View of the successive steps of specimen fabrication. Step 1—completely assembled wooden mould. Step 2—compacted lower layer AC 11 W. Step 3—application of bitumen emulsion C 69 B3 PU. Step 4—application of geogrid composites. Step 5—compacted upper layer AC 16 W. Step 6—cut testing beam from compacted specimen.

Figure 4

Four-point bending apparatus: (a) scheme of the 4PB test configurations (all dimensions in mm), (b) view of the test equipment outside the climatic chamber, (c) close-up of the beam cross-section.

Figure 5

Example plot of stress and strain versus time/cycle number.

Figure 6

The area within the hysteresis loop in a given period (50th cycle) of the fatigue test, reflecting the energy dissipated in this cycle.

Figure 7

Shearing strength (a) and shearing stiffness (b) of systems without reinforcement, with hexagonal geogrid and with square aperture geogrid reinforcement.

Figure 8

Comparison of the initial stiffness obtained at different load frequencies for double-layered asphalt concrete beams reinforced with square and hexagonal geogrids, as well as for reference samples without reinforcement.

Figure 9

Comparison of the initial stiffness obtained at different strain values for double-layered asphalt beams: without reinforcement and reinforced with square and hexagonal geogrids.

Figure 10

The change in stiffness modulus of double-layered asphalt beams: (a) without reinforcement, (b) with square grid reinforcement and (c) with hexagonal grid reinforcement.

Figure 10

The change in stiffness modulus of double-layered asphalt beams: (a) without reinforcement, (b) with square grid reinforcement and (c) with hexagonal grid reinforcement.

Figure 11

The change in the energy parameter R_ε of double-layered asphalt concrete beams: (a) without reinforcement, (b) with square grid reinforcement and (c) with hexagonal grid reinforcement.

Figure 12

Fatigue model chart for double-layered asphalt beams.

Figure 13

Comparison of critical strain ε₆ and its relative change after introduction of reinforcement.

Figure 14

Accumulation of dissipated energy in consecutive test cycles for double-layered asphalt concrete beams: (a) without reinforcement, (b) with square grid reinforcement and (c) with hexagonal grid reinforcement.

Figure 15

A comparison of the cumulative dissipated energy at failure (N_f load cycles).

Figure 16

Estimated relative increase in fatigue life due to application of asphalt layer reinforcement at chosen levels of strain.