Compaction and pavement design testing machine and method for testing flexible pavement materials

摘要

A combination kneader/compactor and plane-strain, simple shear testing apparatus for use in testing paving materials by subjecting them to anticipated design stress over a range of temperatures and various rates of shear. The sample is compacted to the ultimate in-place (equilibrium) density that occurs in the pavement structures. This apparatus and method pre-stresses the sample under the actual stress anticipated for the structure and use the anticipated theoretical vertical stress to fully compact the sample followed by a plane strain simple shear test to measure the dimensionally correct shear strength and moduli which are used to calculate the dimensionally correct design parameters. Pertinent variables are displayed on a computer screen during testing followed by print out of a graph and data sheets with relevant design data. Fundamental engineering (stress-strain) measurements including rational shear strength and static as wall as dynamic moduli are obtained which are suitable for use in design calculations in a rational engineering approach to flexible pavement design in lieu of conventional empirical correlations. The optimum bitumen or water content is precisely determined on the basis of the elasto-plastic property response under simulated traffic, independently of conventional empirical correlations with a percentage of voids and empirical shear indices. Precisely controlled cyclic shear deformation is introduced while the sample is subjected to the anticipated design vertical stress, this being analogous to what happens in the pavement beneath a moving vehicle tire. Thus this laboratory testing machine becomes an accelerated traffic simulator.