Examples Of Reflective Cracking

Reflective Cracking in Pavements: State of the Art and Mitigation Practices

Abstract

Reflective cracking is usually caused by the discontinuities or cracks present in the bottom layers of pavement which propagates through the Hot Mix Asphalt (HMA) layer due to traffic wheel loads on the cracks. Excessive seasonal thermal variations and movements of cement-treated base layer may also result in shrinkage cracking, which extends to the pavement surface to cause reflection crack. Reflective cracking leads to premature failure of the overlay and allows moisture ingression through the cracks, which causes stripping in HMA layers and weakening and / or deterioration of the base and / or subgrade layers. Recent and past studies suggest various mitigation

Horizontal movement associated with temperature or moisture changes in the old pavement induces tensile stress in the overlay or live load flexural stress in the overlay, which tends to concentrate directly over discontinuities. Abe et al. (2000) stated that cracking was caused by the movement of the pavement and traffic load on the surface of the overlay at an early stage. Von Quintus et al. (2007) reported three causes for reflective cracking, the major being horizontal movements from the expansion and contraction of the base pavement that is caused by temperature changes; the differential vertical deflections across transverse cracks, which create shear stresses; and the curling of cement concrete slabs during colder temperature, when the HMA overlay is stiff and brittle. Palacios et al. (2008) reported that cracks propagate to new overlays due to vertical movement of the underlying pavement layer which may be due to traffic loading, frost heave and consolidation of the subgrade soils and/or the horizontal movement of the pavement upper layers due to temperature changes. But, in case of flexible pavements with expansive subgrade, the shrinkage cracks are initiated in the subgrade layer, when the shrinkage induced tensile stress is more than the tensile strength of the material. These cracks are propagated due to the

Thermal induced stresses in older pavements developed on the crack tip as a result of daily/seasonal temperature variation. Thermal induced horizontal stresses in the upper new layers due to seasonal temperature variation. Shrinkage induced cracks originated from cemented bases. Shrinkage induced cracks originated from expansive soil subgrades.

Lytton (1989) described the mechanism of reflective cracking based on the fracture mechanics theory and Nunn (1989) pointed out the three mechanisms that start the reflection cracking as shown in Fig. 1. Fig. 1(a) shows that the cracking is due to thermal action (which produces expansion and contraction movements in the old layer), Fig. 1(b) shows cracking caused by the action of traffic and Fig. 1(c) shows the cracking due to thermal shrinkage (because of the thermal gradient variations throughout the