Direct effects of thermal cracks on pavement roughness

The direct effect of the deterioration of thermal cracks on pavement longitudinal roughness was investigated. To evaluate the transverse crack influence on IRI (International Roughness Index), thermal cracks that occurred in asphalt concrete pavements at MnROAD were transferred into longitudinal profiles with no transverse cracks. The cracks used in this study were collected by the Automated Laser Profile System (ALPS). The baseline profiles for crack transfer were selected from the low volume roadway at MnROAD. The cracks were sampled in accordance with the sampling frequency of the baseline profiles. Three cracks in a cell were transferred into four profiles with IRI values ranging from 1.0 to 4.0 m/km. IRI values for the modified profiles with three cracks were then computed. The three thermal cracks increased roughness across the overall range of IRI. IRI increments ranged from 0.06 to 0.2 m/km and from 0.01 to 0.1 m/km for the profiles with 1.20 and 4.33 m/km initial IRI, respectively. The amount of IRI increment due to the transverse cracks was relatively greater for the profiles with lower IRI values. Relatively larger cracks (more than 0.5 cm in depth) produce greater IRI increase. For three cells with 16, 27 and 32 transverse cracks, respectively, the actual numbers of observed cracks were transferred into the four baseline profiles. This resulted in significant increases in IRI, varying from 0.15 to 1.10 m/km. Impacts on vehicle operating costs were briefly evaluated, and were found to be significant. The range of annual cost increases, from $14,000/km to $97,000/km, provides additional information for maintenance and construction decisions.