Quality Control/Quality Assurance Testing for Joint Density and Segregation of Asphalt Mixtures
Longitudinal joint quality control/assurance is essential to the successful performance of asphalt pavement and it has received considerable amount of attention in recent years. The purpose of the study is to evaluate the level of compaction at the longitudinal joint and determine the effect of segregation on the longitudinal joint performance.
Five paving projects are selected for sampling and evaluation in Iowa with each one representing a typical longitudinal joint construction technique. The first two joint construction methods use the tradition butt joint placed with hot mix asphalt (HMA) and warm mix asphalt (WMA). Another three construction methods paved with HMA are the butt joint with an infrared heat treatment, edge restraint by milling method and a modified butt joint with the first pass of rolling 6 inches away from the joint (hot pinch). For each project, joint quality is compared with regard to the “center” of the pavement mat (2 ft right of the joint). Field densities using a PaveTracker 2701 non-nuclear gauge and permeability using an NCAT Permeameter were made. Cores at both the longitudinal joint and 2 ft right of joint were obtained for subsequent lab permeability, AASHTO T166 and AASHTO T331 density, and indirect tensile (IDT) strength testing. Asphalt content and gradations were also obtained by ignition oven method to determine the joint segregation.
In general, this study finds that the minimum required joint density should be 90.0% of theoretical maximum density based on the AASHTO T166 method. The restrained-edge by milling and butt joint with infrared heat treatment construction methods all create joint density values higher than the proposed 90.0% limit. The traditional butt joint paved in both HMA and WMA exhibits lower density and higher permeability than the aforementioned limit. In addition, all of the projects appear to have segregation at the longitudinal joint except for the one using the edge-restraint by milling method. Based on various mix design and joint construction methods, the joints show differences in asphalt content and types of segregation (via gradation) as compared to the job mix formula. Results of this study indicate that lower density of the longitudinal joint is a combination of segregation (gradation), asphalt content variation and insufficient density.