Constitutive Design Criteria for a Fiberglass Grid: The Mechanical Performance and Bottom-Up Crack Propagation Retardation Mechanism of a Grid-Reinforced Asphalt Concrete System

Asphalt reinforcement is used to extend the service life of pavements while taking into account the increasingly rapid growth in traffic volume. This paper presents constitutive design criteria for a semi-rigid, resin-impregnated fiberglass grid that enhances the mechanical performance of the asphalt concrete overlay and provides a mechanism to retard crack propagation. The structure of the grid is formed by stitching warp and weft strands at their intersections such that the design allows the formation of interlocking columns of the asphalt mix. An acrylic polymer resin covers the fiberglass strands, thus making their viscoelastic nature compatible with the asphalt materials as well as protecting the glass fibers from corrosion in a roadway environment. The remarkable temperature susceptibility of the resin is observed in a high shear modulus profile over an extensive range of material temperatures using time-temperature superposition. The grid tensile strength of 100 kN/m was qualified using standard measurements. Three-point bending and cyclic fatigue loading mechanical tests affirm the retardation performance of the grid-reinforced system in terms of crack propagation. The retardation mechanism is effected by synchronizing the cracking pattern with the flexural stress-strain profile through image analysis. The bottom-up crack propagation at the grid interface exhibits a time delay until the upward fracturing process is resumed at a slower rate. Fracture toughness quantitatively represents the effects of crack retardation. Laboratory fatigue testing results indicate a nearly seven times longer life for the grid-reinforced specimen than that of the non-reinforced one. A National Center for Asphalt Technology (NCAT) full-scale road testing program provides comparative assessments of the grid-reinforced pavements. After trafficking 20 million ESALs, longitudinal and transverse cracks appeared only in the non-reinforced area. A visual inspection of the grid extracted from the reinforced area showed fair condition of the pavement.