Predicting the performance of SAMI systems

Abstract

This paper presents a method of predicting the resistance to reflective cracking of an overlay system incorporating a Stress Absorbing Membrane Interlayer (SAMI). The method is based on simulation of crack growth, both top-down and bottom up, over a joint or crack in an underlying layer, utilizing a strain-based crack propagation law. It uses an incremental system such that the strain in the region of a crack has to be re-calculated after each increment of crack growth. Its simplified nature means that the method is suited to being incorporated into a spreadsheet. In support of this method of crack prediction, a series of laboratory tests are described. These comprise wheel track tests on rubber-supported beams representing a scaled-down pavement construction-a cracked lower layer, a SAMI (where present) and an overlay. The data from these tests is input into an adapted version of the crack prediction system as the first step in the process of validation. Validation is then taken a step further by making reference to a particular case study that compares a concrete pavement overlaid with and without a SAMI, and shows the pavement with a SAMI to outperform that without. The magnitude of the improvement, though as yet not fully quantified since failure of the SAMI system has not yet occurred, is compatible with the predictions made. Finally the prediction method is applied to selected design cases and the types of pavement that lend themselves to SAMI usage are identified and approximate performance benefits estimated.