Ayman Ali

Impact of dynamic loading on backcalculated stiffness of rigid airfield pavements

The objective of this paper was to evaluate the deterioration of Portland Cement Concrete (PCC) slabs throughout trafficking. A full-scale accelerated pavement testing at the National Airport Pavement Test Facility (NAPTF) was conducted on Construction Cycle 6 (CC6) on rigid pavements with low, medium and high flexural strengths on both a concrete and asphalt stabilised base. Heavy Weight Deflectometer (HWD) testing was conducted on the test sections to backcalculate the stiffness of the layers. The majority of PCC deterioration occurred roughly within the first 1500–2000 passes of trafficking. On average, the MRS-1 (low flexural strength) PCC elastic modulus was found to decrease by 20%, from 5.0–.4 × 106 (34.5–37.2 GPa) to 4.0–4.3 × 106 psi (27.6–29.7 GPa), whereas the PCC elastic modulus of MRS-2 and MRS-3 was found to decrease by 17% and 22%, respectively. However, neither the MRS-2 nor MRS-3 elastic modulus was found to drop below 5.0 × 106 psi (34.5 GPa) after 15,000 passes.

Estimating fatigue endurance limits of flexible airfield pavements

Abstract In perpetual pavements, damage from bottom-up cracking can be limited to the top surface lift through using a very thick surface layer or a binder-rich intermediate layer. This can be attained by maintaining tensile strains at the bottom of the hot-mix asphalt (HMA) layer below a certain value known as the fatigue endurance limit (FEL). This paper presents a method for estimating a strain-based FEL for flexible airfield pavements. The proposed method is based on the concept that a 50% reduction in HMA layer modulus would indicate initiation of fatigue cracking. Falling weight deflectometer (FWD) testing results, collected from National Airport Pavement Test Facility (NAPTF) flexible pavement sections, were analyzed to determine at which loading pass each section had a 50% reduction in HMA layer modulus (Nf50). NAPTF tensile strain data were also used to determine the tensile strain at Nf50 for each pavement section by averaging the peak tensile strains. The proposed approach was validated by comparing its results to those obtained using a common FEL estimation model known as the rate of dissipated energy change (RDEC) model. To further verify the results of the proposed approach, peak tensile strain was plotted vs. number of loading cycles for all sensors. Using these plots, the peak tensile strain at which the variability in the strain gauge data increased was used as an estimate of a possible FEL. The Nf50 tensile strains estimated using the proposed method were comparable to the values determined from RDEC and variability approaches.

Fuel Resistance Asphalt Binder: Mixing Procedure and Fuel Damage Resistance

Most of the biopolymers are made from animal waste. Animal waste is treated and converted in a form of glue generally known as Hide Glue or Bone Glue (BG), which is prepared from animal protein. This study focusses of developing fuel resistant asphalt using biopolymers i.e. protein based polymers. A procedure to develop fuel resistant asphalt for commercial use and its performance evaluation was conducted in this study. Mixing procedure of BG was evaluated and refined and multiple fuel resistance tests were performed to evaluate the impact of bone glue modification on resistance to fuel of neat binder. It was determined that BG-binder mixing equipment developed in earlier studies was appropriate. Optimum BG dosage to develop FRA was found to be higher than the BG dosage recommended in earlier studies to develop mechanistically better performing asphalt binder. Fuel solubility resistance test was used to select the optimum BG dosage. Fourier Transform Infrared Spectroscopy results proved that water was completely evaporated using the mixing procedure developed for the preparation of FRA. Fuel damage resistance test revealed that BG modification not only improved the intermediate to high temperature characteristics of the neat binder but outperformed the conventional polymer modified asphalt binder in resistance to fuel damage.

Evaluation of Non-nuclear Alternatives to Replace the Nuclear Density Gauge During Compaction Quality Control of Unbound Pavement Layers

Pavement performance is highly dependent on several factors that include: structural adequacy, material properties, traffic loading, and construction quality. The quality of subgrade or base/subbase compaction also significantly affects the performance of pavements; predominantly flexible pavements. In particular, the majority of the distresses in flexible pavements are mainly attributed to the compaction defect in these layers. In current practice, the compaction quality of these layers is usually quantified using the nuclear density gauge (NDG). However, several concerns arise due to the use of the NDG. This study was initiated with the aim of evaluating the sensitivity of the parameters measured using non-nuclear methods/devices to moisture content, compaction effort, testing time after compaction, and aggregate type. To fulfill this objective, a laboratory procedure for compacting large samples was developed. This procedure facilitated testing using three non-nuclear devices: Briaud compaction device (BCD), light weight falling deflectometer (LWD), and dynamic cone penetrometer (DCP). Four types of aggregates, two subgrade soils, one dense graded aggregate, and one recycled concrete aggregates, were selected to comprehensively cover a wide range of subgrade and base/subbase materials. Each device was evaluated for accuracy and repeatability. The sensitivity of the results measured from each device to moisture content, compaction effort applied, and testing time was also evaluated. Based on testing results, it was concluded that the DCP was most sensitive to detecting changes in the measured parameters. In addition, precision of the DCP was similar to other non-nuclear devices.

Heavy Vehicle Simulator and Accelerated Pavement Testing Facility at Rowan University

The use of full-scale accelerated pavement testing is gaining more prominence in recent years due to (1) the several advantages such tests offer and (2) the development of portable and non-portable accelerated pavement testing equipment that facilitate conducting these tests. For instance, conducting accelerated pavement testing offers the advantage to simulate long-term traffic conditions in a short period of time that ranges between three to six months. It can also help in better simulating field conditions simply because full-scale sections are constructed using paving equipment and procedures utilized by contractors in the field. Therefore, it can be argued that full-scale accelerated pavement testing can provide results that are more representatives of field conditions that does laboratory testing. To keep up with current transportation and pavement research trends, Rowan University is currently in the process of constructing an accelerated pavement testing facility. In fact, the mission of the Civil and Environmental Engineering Department at Rowan University is to grow the program to become one of the nationally recognized research programs in the areas of transportation and pavement engineering. To accomplish this mission, the department along with the College of Engineering at Rowan University, the State of New Jersey (NJ), and the United State Department of Defense (USDoD) have established a state-of-the-art transportation research center known as the Center for Research and Education in Advanced Transportation Engineering System (CREATEs). CREATEs houses an AMRL (AASHTO Materials Reference Laboratory) certified Rowan University Construction Materials Laboratory (RUCOM) and the Rowan University Accelerated Pavement Testing Facility (RUAPTF). Therefore, CREATES is envisioned to provide states and local agencies as well as the pavement industry in the northeastern region of the United States (US) with both laboratory and full scale accelerated pavement testing capabilities. This paper documents the design and construction processes currently being implemented for building RUAPTF.

Evaluation of the morphological and rheological impacts of cross-linking agents in polymer modified binders

This study was initiated with the aim of evaluating the relative impact of different cross-linking agents on the rheological and morphological properties of polymer modified asphalt binders. To complete this objective, two cross-linking agents (an aromatic oil and silicon oxide elemental sulfur) were selected for evaluations. The cross-linking agents were then added to a styrenebutadiene-styrene (SBS) polymer modified binder (virgin PG 70-22) at different dosages. The selected cross-linking dosages were 2 and 4% by weight of virgin binder. The SBS, virgin binder, and cross-linking agents were mixed together for 90 minutes using a high shear mixer. The morphology of the modified binder was then tested using a florescent microscope and the rheological properties were evaluated using the dynamic shear rheometer (DSR) to determine the dynamic shear modulus master curves and the multiple stress creep recovery (MSCR) properties of these binders. The results show that with the increase in aromatic oil cross-linking agent dosage, there is a reduction in shear modulus results. In addition, the florescent microscope images show that there seems to be an improvement in the compatibility between the virgin asphalt and SBS in the presence of the aromatic oil extracts.

Development of Pavement Preservation Strategies with Pavement ME Design Software for the State of Rhode Island

The objective of this study was to propose an approach to integrate AASHTOWare Pavement ME Design software into pavement preservation strategies of the Rhode Island Department of Transportation. The use of Pavement ME Design software could assist in the prioritization of mitigation alternatives; this procedure would optimize resources in Rhode Island. Four representative pavement sections on state highways in Rhode Island were selected and then analyzed with the Pavement ME Design software. Weigh-in-motion traffic data also were collected from nine stations in Rhode Island to establish representative state traffic patterns. This information was used as input to Pavement ME Design, and the predicted performance measures (i.e., international roughness index, rutting, longitudinal cracking) were then used to determine when the typical Rhode Island pavement mitigation alternatives [e.g., crack seals; level and overlay; mill and overlay with and without friction course; paver placed elastomeric surface treatment; rubberized chip seals; reconstruction and reclamation; and stress-absorbing membrane interlayer (SAMI)] were triggered. In addition, a cost-based approach and an incremental benefit–cost alternative prioritization method were analyzed to determine the most cost-effective alternatives and the most beneficial alternatives, respectively. On the basis of the analysis, the Pavement ME Design software was found to have potential for use in the enhancement of pavement preservation strategies. Crack seals, rubberized chip seals, and SAMI were found to be the most cost-effective and the most beneficial of all alternatives assessed.