Michael I. Hammons

Application of Artificial Neural Networks to Concrete Pavement Joint Evaluation

Application of the principles of dimensional analysis has recently led to the development of a robust method for assessing the deflection and stress load transfer efficiencies of concrete pavement joints and for backcalculating joint parameters. The new method eliminates the need to make a priori assumptions since pertinent inputs can now be experimentally determined using the falling weight deflectometer. A data base has been generated using numerical integration of Westergaard-type integrals and has been used to train a backpropagation neural network algorithm for joint evaluation. The resulting computer program is simple, efficient, and precise and can be used on site for immediate results. Its predictions are verified by comparisons with closed-form and finite-element solutions pertaining to data collected at three major civilian airports in the United States, including the new Denver International Airport. Also discussed is the role of dimensional analysis in the generation of the training set for a ...

WESTERGAARD-TYPE SOLUTION FOR EDGE LOAD TRANSFER PROBLEM

On the prominent issue of edge load transfer in portland cement concrete pavements, common understanding has been that Westergaards last contribution was the very cursory treatment contained in his 1948 paper. A recent examination of the archives at the U.S. Army Engineer Waterways Experiment Station, however, has brought to light a consulting report that Westergaard submitted to the Corps of Engineers in 1949 containing a detailed examination of the edge load transfer problem, prepared by his associate M. S. Skarlatos. To expedite dissemination of this information, the results of an investigation that sought to extend and refine the edge load transfer solution by Skarlatos using modern computational tools are presented. A comparison of this solution to earlier finite element solutions is also presented. Following the same approach as Skarlatos and Westergaard, closed-form equations are derived for the maximum deflection and maximum bending stress occurring on the unloaded side of an edge capable of load...

Detection of Stripping in Hot-Mix Asphalt

Damage mechanisms that lead to stripping significantly affect the dynamic modulus and tensile strength of hot-mix asphalt (HMA). When stripped HMA is unexpectedly encountered below the planned milling depth during routine mill and overlay rehabilitation projects, it must be removed and replaced; this causes significant cost overruns and delays. A procedure was developed to identify the extent and depth of stripping in in-place HMA pavement sections. Several nondestructive survey methods were analyzed to determine their capability to locate areas of stripping, either by themselves or in various combinations. Cores were extracted and used to calibrate the methods. Visual inspections of the cores and laboratory tests on selected cores were used to validate the results. The procedure involved observation of surface distresses, complete ground penetrating radar survey, seismic testing of selected areas, limited coring, and laboratory testing of selected cores. With these procedures, areas with stripping can be distinguished so that effective rehabilitation strategies can be developed.

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.

Validation of Three-Dimensional Finite Element Modeling Technique for Joints in Concrete Airport Pavements

A rational, three-dimensional (3D) finite element modeling technique was developed to predict the structural response of a jointed concrete airport pavement system. Model features include explicit 3D modeling of the slab continua, load transfer capability at the joint, explicit 3D modeling of the base course continua, load transfer capability across the cracks in the base course, and contact interaction between the slabs and base course. Environmental effects were not explicitly included in the model development. The model was applied to predict the response of an instrumented pavement at the Denver International Airport (DIA) to a test vehicle driven over the instrumented pavement under day and night conditions. The DIA pavement was modeled as a three-layer system with the presence of cracking in the base course as well as a variety of interface conditions between the slabs and base course considered. Complex response patterns caused by environmental factors were observed in the data from DIA, making separation of load-induced and environmentally induced response difficult. The general shape and form of the deflection- and stress-based load transfer efficiency predictions from the finite element models match those observed at DIA. Model predictions of stress-based load transfer efficiencies were generally more accurate than predictions of deflection-based load transfer efficiency. The model developed represents a significant advancement in the state of the art and features innovations that are compatible with the FAA’s advanced pavement design model requirements.

Highway Construction Quality Index for Florida

The Florida Department of Transportation (FDOT) is developing strategies to improve the quality of transportation infrastructure while coping with changes in business models and reductions in agency personnel. Nationwide, policy is changing more quickly than ever, and every policy change reinforces the need for contractors who perform high-quality work. There have been several initiatives in the past to develop some kind of rational, objective system of rating the quality of highway construction projects. There have also been initiatives to utilize these ratings for substantial issues such as contractor qualification and bidding purposes, but not one state uses their quality ratings for anything more substantial than setting contractors’ bidding ceilings. Some states do not use these ratings at all and some states do not even rate the quality of their projects. One of the chief complaints against current systems is their subjectivity. The construction quality index, developed through a grant from FDOT, is a rating of the quality of materials and workmanship on highway projects that, unlike current quality rating models used by state highway agencies, is totally objective. Under limited validation testing, the model assigned quality index values consistent with the owners level of satisfaction with the project.

Recommended Practice for Identifying Vibration-Sensitive Work Zones Based on Falling Weight Deflectometer Data

In recent years, larger vibratory rollers have been implemented because of their improved efficiency. An unfortunate consequence is that greater ground motion caused by these larger vibratory rollers might damage adjacent infrastructure, particularly in or near urban areas. Various federal, state, and foreign agencies have proposed vibration limit criteria; some are intended to mitigate damage to structures while others are based on limiting human annoyance. Two of these existing criteria (U.S. Office of Surface Mines blasting level criteria and German DIN 4150 standard level for human annoyance) were selected to form the basis of a recommended practice for limiting vibratory compaction in critical work zones. These criteria are used to differentiate three zones on a plot of peak particle velocity versus vibratory roller frequency. A square-root scaling law of ground motion is used to predict the ground motions from vibratory compaction equipment based on falling weight deflectometer (FWD) data. With this predictor, a potentially vibration-sensitive portion of a resurfacing project can be identified using displacement time histories from the FWD obtained during routine preconstruction testing. Detailed knowledge of the layering of the pavement structure or the geology of the surrounding site is not required. It is demonstrated that this predictor can successfully be used to restrict vibratory compaction near sensitive structures, including fragile buried infrastructure.