Performance prediction of Louisiana accelerated loading facility test sections

Using the accelerated loading facility (ALF), the Louisiana Transportation Research Center recently conducted an accelerated pavement test of nine test sections that consisted of the same asphalt wearing course but had different types and thicknesses of crushed stone and soil cement bases and subbases. One of the aims of the project was to compare observed field performance with that predicted with use of the VESYS 3A-M mechanistic prediction model, which predicts the development of rutting, cracking, and roughness, along with serviceability [present serviceability index (PSI)] over time. It was found that VESYS provided a reasonable prediction of observed rutting and PSI-albeit an underestimation-but a poor estimate of surface cracking. This was probably related to the fact that the observed cracking was due to shrinkage of the soil cement rather than fatigue cracking under the load, and also to the fact that VESYS is generally used to model unbound granular materials that have a modulus no greater than 690 MPa (100 ksi). The modulus of soil cement material tested by ALF was 105 MPa (150 ksi) and its behavior under load would be different from that of an unbound granular material. More research is needed into the behavior of soil cement bases, their influence on the cracking of asphalt surfacings, and the most appropriate input into VESYS to model this behavior.