Athar Saeed

Use of Recycled Concrete as Unbound Base Aggregate in Airfield and Highway Pavements to Enhance Sustainability

This research evaluated the use of recycled concrete aggregate (RCA) from airfield and highway pavements to enhance sustainability based on engineering, economic, and environmental criteria. The objective was to develop evaluation and construction guidelines by defining the minimum standards for RCA as unbound base. The research approach included contacts with industry representatives, technical assessments, site visits, and performance review of airfield pavements with unbound RCA layers. RCA can be used as unbound base material if produced from uncontaminated PCC. All virgin aggregate tests and their limits are applicable to RCA except the sulfate soundness test, which is waived for RCA due to the incompatibility of PCC components with the chemical reactants used in the test. RCA should not be used where there is a potential for sulfate exposure from subgrade soils, ground water, or other external sources. RCA from ASR-distressed PCC can be used considering site conditions. RCA is not a hazard to the environment. An economic analysis can be conducted by considering initial material and construction costs for both RCA and virgin aggregate.

Expedient Spall Repair Methods and Equipment for Airfield Pavements

Selected equipment and procedures were evaluated to expedite repair of spalls with rapid-setting materials. The objective was to develop one or more methods to excavate and prepare a 2-ft2 × 4-in. deep spall for placement of a rapid-setting repair material in 15 min or less. A secondary objective was to correlate various excavation methods with a relative life expectancy of the repair. For five excavation methods, 2-ft2 × 4-in. deep spalls were excavated in triplicate. The spalls were subsequently repaired with a commonly used rapid-setting spall repair material. The efficacy of the repair methods and equipment were evaluated on the basis of petrographic examination of the substrate excavation, production rate, total production rate, in situ tensile pull-off strength, direct shear bond strength, and performance under simulated F-15E wheel loading. Each of the methods evaluated had a significant improvement in production rate over the 30-lb jackhammer, the standard Department of Defense spall repair excavation method. The most efficient method was a cold planer, which, on average, was approximately 58% more efficient than the jackhammer. Of the methods evaluated, only the cold planer could meet the requirement of excavating a 2-ft2 × 4-in. deep spall in no more than 15 min.

PERFORMANCE MONITORING OF ULTRA-THIN WHITETOPPING AT A GENERAL AVIATION AIRPORT

The first ultra-thin whitetopping (UTW) project in the United States on a general aviation (GA) airport runway was built at the Savannah-Hardin County Airport (SNH) in Tennessee. The asphalt concrete (AC) surface at SNH Runway 18-36 was aged and had significant amounts of cracking. Existing surface conditions were assessed using the pavement condition index procedure and pavement structural capacity was estimated using the falling weight deflectometer and dynamic cone penetrometer; insitu and laboratory CBR tests were also conducted. Current pavement conditions, structural capacity, and subsurface soil conditions were evaluated to determine pavement design parameters. UTW deflection and bending stresses (estimated using 2-D ILLI-SLAB code), because of FAA C-2 classification aircraft, were used in the Portland Cement Association fatigue law to determine the allowable number of load repetitions. A 100-mm thick UTW on top of the existing AC surface with a 1220-mm joint spacing was recommended. Strain gages were installed near the surface and bottom of the Portland cement concrete (PCC), and on the top of the milled AC surface for performance monitoring by determining if the UTW is completely bonded, completely unbonded or partially bonded to the milled AC surface. Strains were measured in the winter and summer seasons during both morning and afternoon hours using a loaded dump truck. A paper presented at the 2001 ASCE Airfield Pavement Specialty Conference in Chicago, Illinois, described the UTW design process and the results of the field-testing conducted during the summer months. This paper provides results of winter and summer testing and compares the summer and winter test results. Analysis of both summer and winter field test data indicated that the UTW is performing satisfactorily and is adequately bonded to the existing AC surface.

Airport Rubber Removal: A Comparison of Ultra-High Pressure Water Runway Rubber Removal Systems

Runway rubber removal is a maintenance function employed to ensure safe landing areas for aviation operations. Rubber deposits accumulate on runway areas where aircraft tires touchdown and braking occurs. This tire rubber build up occludes pavement microtexture and macrotexture, causing a significant loss in available skid resistance during wet conditions. Reduction of available pavement microtexture in a wet environment prevents the development of adhesional friction, which can result in viscous hydroplaning. Reduction of pavement macrotexture prevents the removal of bulk water from the tire-pavement contact area and also prevents the development of the hysteresis frictional component. To restore friction to safe levels for aircraft operations, rubber must be periodically removed. Several techniques for rubber removal are available. Waterblasting is a proven surface decontamination technique which employs the use of high or ultra-high pressure water (UHPW) to blast rubber deposits from the runway surface. This effort provides a performance-based comparison between three commercially available UHPW waterblasting systems. The evaluation was conducted on an ungrooved Portland Cement Concrete (PCC) runway with heavy rubber contamination along the touchdown and breaking zones. Several testing equipment such as Circular Track Meter (CTM) and Dynamic Friction Tester (DFT) were used to characterize the surface properties of the runway before and after rubber removal. The measurements were used for statistical pairwise comparative analysis of International Friction Index (IFI), speed constant and Mean Profile Depth (MPD). Treatment effect analysis of pre-measured and postmeasured data revealed that UHPW systems improved the surface texture properties by at least 40% regardless of the decontamination equipment.