This paper describes the preliminary results from the Nordic LTPP program. Results deal with the backcalculation of layer and distress modeling using Nordic GPS-1 data. Two different backcalculation methods (Modulus, Elmod) were used to determine layer moduli for comparison purposes. Results indicate that Modulus produces higher moduli values for asphalt concrete layer and lower moduli values for subgrade than Elmod. Tensile strains at the bottom of asphalt layer were calculated with linear elastic program (BISAR) using layer moduli from Modulus as input and also with Elmod program. Results show that tensile strains of asphalt layer and vertical compressive strains on top of subgrade were close to each other were close to each other with both calculation methods. Distress modeling is based on two separate phases. First stage includes modeling time interval from pavement construction to the first sign of distress (probability of crack initiation). Second stage models the progression of cracking conditionally on the fact that cracking has started. Crack initation models show how the time to the appearance of first crack depends on annual traffic loading and other factors such as tensile strains at the bottom of asphalt layer and roughness (IRI-value). Progression of longitudinal cracking is mostly affected by AC modulus, AC thickness and the interaction of tensile strain and the cumulative number of equivalent single axle loads. At this stage of the study there are not enough data to develop reliable models to predict the progresson of alligator cracking. (A)
Abstract