Evaluation Of Asphalt Overlays Anti-cracking System Over Existing Cracked Asphalt Pavements

The overlay design procedures which are available nowadays are based on reducing the stresses and strains in the existing pavements. However, If the pavement shows too much cracking, these cracks rapidly make their way through the new overlay before design life has been reached. The fast deterioration of the asphalt overlays over old cracked pavements becomes a serious problem year after year. Recovering the old pavement by simple asphalt overlay is not an effective solution; the cracks tend to propagate up to the new asphalt overlay, which leads to what is called reflective cracking problem.This paper analyses and determines crack resistance and propagation characteristics for asphalt concrete mixes in general, and for reinforced asphalt concrete over old cracked asphalt pavements in particular. It also provides an analysis of cracking propagation mechanism in flexible pavements. Several Anti-cracking systems are proposed, where the glass fibers materials are used.Two different reinforcing methodologies are applied. First: Modification of the overlay characteristics by adding chopped glass fibers to the Hot Mixture Asphalt (HMA) to form Glass Fibers Reinforced Asphalt Concrete (GFRAC). Second: with Glass Grid Reinforced Asphalt Concrete (GGRAC). The theory of Fracture Mechanics (FM) has been employed to determine crack growth rates of the suggested anti-cracking overlay systems. Asphalt mixture designing tests, three points bending tests and fatigue crack propagation tests were carried out. The concept of the potential fracture energy is introduced, The Critical Stress Intensity Factors (K_IC) are determined for plain and reinforced asphalt concrete. Depending on the fatigue crack propagation, the crack growth rate is determined for each type of anti-cracking systems. The cracking process is also analyzed.One of the significant points in this study is the attempt to give a better understanding of the crack propagation for multilayer asphaltic overlay or what herein is suggested as Composite Structure Anti-cracking Overlay Systems. Therefore fatigue crack propagation tests are carried out for three different composite structure overlay anti-cracking systems; plain composite structure overlay anti-cracking system (AK/AC), glass fiber reinforced composite structure anti-cracking system (AK/GFRAC), and grid reinforced composite structure anti-cracking system (AK/GGRAC).Calculations of the stress intensity factor in the vicinity of the crack tip are performed using simulation of the specimens by means of the Finite Elements Method (FEM). Combining experimental measurements of the crack growth rate and the numerical...