Mustaque Hossain

Evaluation of Superpave Mixtures with High RAP Content

The Kansas Department of Transportation (KDOT) is currently evaluating Superpave mixture performance with higher percentage of reclaimed asphalt pavement (RAP) materials. Hamburg Wheel Tracking Device (HWTD) tests were done on Superpave mixes with high RAP content sampled from a number projects across the state. Each mixture was subjected to 20,000 repetitions or 20-mm rut depth, whichever came first. The HWTD test results were also correlated with the volumetric parameters and other potentially significant factors. The analysis results showed that the rutting performance was significantly affected by the asphalt source and binder grade regardless of RAP content. The surface mixes with higher percentage of RAP material were not significantly susceptible to rutting compared to the mixes with moderate percentage of RAP material. Volumetric mix design parameters of these mixtures, except voids in mineral aggregate (VMA), were not significant in determining rutting performance. The rut depth decreased with increasing percent VMA for the mixes with moderate percentage (25%) of RAP materials.

Effect of Construction Environment on JPCP Performance

Some properties of newly paved Jointed Plain Concrete Pavements (JPCP) are known to influence the long-term performance. The traditional empirical design procedures for JPCP were unable to take into account most of these factors. However, the new Mechanistic-Empirical Pavement Design Guide (MEPDG) accounts for climatic conditions, local materials, selected construction practices, and actual highway traffic distribution. In this study, performance (in terms of International Roughness Index (IRI), faulting, and percent slab cracked) of six typical JPCP pavements in Kansas corresponding to alternative inputs of Portland Cement Concrete (PCC) strength development, PCC shrinkage, and zero-stress temperature has been evaluated using MEPDG. The results show that predicted JPCP roughness (IRI) and faulting by MEPDG are not very sensitive to the PCC strength. However, slab cracking decreases with higher PCC strength. In general, PCC shrinkage does not affect predicted IRI. Higher shrinkage strain results in higher faulting. Long term cracking appears to be fairly insensitive to the shrinkage strain. MEPDG-predicted IRI and percent slabs cracked are fairly insensitive to the zero-stress temperature but the faulting is severely affected except on a JPCP pavement section with widened lane and tied PCC shoulder. Percent slab cracked highly depends on the PCC slab thickness. April and October are the best months for JPCP construction (paving) in Kansas.

Moisture Susceptibility of Superpave Mixtures with Varying Binder Contents

The process control for the hot-mix asphalt mixtures (HMA) by the Kansas Department of Transportation (KDOT) requires each lot of HMA be produced within ±0.6% of the design binder content. Recent reviews indicate that HMA lots are being produced consistently with lower binder contents. This situation has been exacerbated by the use of higher proportion of Reclaimed Asphalt Pavement (RAP) materials in the HMA mixtures. This project evaluated two moisture susceptibility test methods to assess the effect of asphalt content on the moisture resistance of HMA. Two different commonly used mixtures for overlaying and four varying asphalt contents, optimum and lower, were selected. The Hamburg Wheel Tracking Device (HWTD) test was used to predict moisture damage potential of these mixes. All specimens tested were prepared with the Superpave gyratory compacter. Results indicate that within the tested range, deformation decreases as the binder content decreases. This trend was verified by studying the correlation of the number of wheel passes with the asphalt binder film thickness.

Instrumentation Experience at the Kansas Accelerated Pavement Testing Facility

Pavement test section instrumentation changes from laboratory to laboratory and also with the purposes and objectives of each test. There is a need for sharing knowledge of successes and failure in instrumentation of pavement sections. This paper describes the instrumentation from a geocellular system-reinforced pavement experiment at the Civil Infrastructure Systems Laboratory (CISL) of Kansas State University. CISL houses an accelerated pavement testing (APT) machine that is being used to apply 80-kN load on a single axle with dual tire to the test pavement sections. These sections get instrumented with asphalt pavement and other strain gages, earth pressure cells, time domain reflectometry (TDR) probes, and thermocouples. The data collection is done using a new compact data acquisition system (cDAQ). The cDAQ system, manufactured by National Instrument, allows multiple interchangeable modules to be used with an electronic chassis, and a simple USB interface with a personal computer. LabVIEW is used to setup the visual interface to collect and store the data. The paper discusses step-by-step process followed in sensor installation, testing, data collection, and variability analysis in the experiment involving geocellular sytem-reinforced bases. The experience described here will be valuable for those designing and installing new pavement instrumentation.

Investigation of Aged Asphalt Pavement Moduli

Asphalt roadways are typically designed to be resurfaced with an asphalt overlay every ten years. The thickness of an asphalt overlay is related to the structural strength of the existing pavement however, currently there are no methods to accurately determine the in-place structural capacity. This study investigates six Kansas roadways to determine how the pavement modulus can be evaluated nondestructively. Cores were taken from each roadway for Indirect Tension testing in the lab to determine the resilient modulus of each asphalt layer in the pavement. Two in-situ non-destructive tests, Falling Weight Deflectometer (FWD) and Portable Seismic Pavement Analyzer (PSPA), were also conducted on each roadway. The FWD and PSPA tests are much faster and less expensive than the laboratory tests. Therefore, relationships were explored to convert the FWD and PSPA moduli to the resilient modulus obtained by the Indirect Tension test. However, no universal correlation was found but the FWD results would yield the most conservative design.

Innovative Uses of Quarry Waste and Reclaimed Asphalt Pavement

In Kansas, due to processing of soft limestone in the quarries, a large amount of fines are produced. The problem has been exacerbated by the introduction of Superpave system for hot-mix asphalt (HMA) that tends to use coarser aggregates and materials with lower fine content. This has resulted in a large amount of quarry waste being available as a construction material. Again due to binder issues, the uses of reclaimed asphalt pavement (RAP) in Superpave HMA are limited. Geocellular confinement systems (geocells) are 3-dimensional honeycomb-like structures filled with an in-fill of some available materials that vastly improve shear strength of in-fill materials. The objective of this study was to test geocell-reinforced bases with RAP and quarry waste under a thin HMA layer under full-scale traffic loading. HMA pavement test sections with geocell-reinforced bases, with RAP and quarry waste as infill materials, were constructed at the Civil Infrastructure System Laboratory (CISL) of Kansas State University. The sections were paved with a 50-mm Superpave hot-mix asphalt HMA layer and instrumented to measure the stresses on top of the subgrade. The sections were loaded to 50,000 to 70,000 repetitions of an 80-kN single axle load. The calculated and measured responses show that on both test sections, stresses on top of the subgrade exceeded the unconfined compressive strength of the soil. It was concluded that the geocell depth and/or the thickness of the HMA layer need to be increased even for paved low-volume roads.