Microcracking Considerations in Full-Depth Reclamation with Cement

Abstract

Drying shrinkage cracks in pavements rehabilitated using full-depth recycling with cement can reflect through asphalt concrete overlays. The effect of shrinkage cracks on the fatigue life of pavements increases with increasing crack width because of the loss of load transfer across the cracks. Wide shrinkage cracks can also lead to pumping of the subgrade material, leading to faulting of the base, loss of support, and eventual deterioration of the stabilized layer. One method to mitigate drying shrinkage cracks is with microcracking. Microcracking creates a network of hairline cracks in the stabilized layer which serve to relieve initial stresses during early hydration of the cement, thereby limiting the wider and more severe block cracks typical of cement stabilized layers. The process involves applying several passes of a steel drum vibratory roller, at maximum vibration frequency and amplitude settings, over the stabilized layer within a set time window after construction. The effectiveness of microcracking was investigated through regular crack monitoring and deflection testing over a four-month period on a 37-cell test road at the University of California, Davis. The results showed that microcracking does not prevent the development of shrinkage cracks but, in conjunction with selecting a mix design seven-day strength between 2.0 and 4.1 MPa (300 and 600 pounds per square inch), it can mitigate its effects by creating additional, thinner, more closely spaced, shrinkage cracks that are unlikely to reflect through the asphalt concrete surfacing.