Hesham Mahgoub

INVESTIGATION OF RECYCLED CONCRETE MADE WITH LIMESTONE AGGREGATE FOR A BASE COURSE IN FLEXIBLE PAVEMENT

The research objectives were to investigate the feasibility of using recycled concrete aggregate (RCA) as a base course material in asphalt pavement, to evaluate the physical properties of RCA, and to develop practical and reliable guidelines and specifications. The tasks included literature review, sample collection, laboratory testing, accelerated performance testing and pavement distresses monitoring, falling weight deflectometer (FWD) test, theoretical analysis of pavement, and development of guidelines and specifications for the use of Florida RCA. Three test sections of asphalt pavement were constructed at the University of Central Florida’s circular accelerated test track. Two sections of different thicknesses were constructed with RCA base and one section with limerock (LR) base. A total of 362,198 load repetitions were applied to the test sections. This is equal to 811,324 repetitions of the 18-kip (80-kN) equivalent single-axle load. The pavement distresses of rutting, cracking, and settlement were monitored during the course of the performance testing. The FWD test was performed on the pavement test sections to backcalculate the in situ resilient moduli of RCA and LR for theoretical analysis of life expectancy. The findings support the hypothesis that RCA can be used effectively as a base course when appropriate quality control techniques are used. On the basis of the information obtained, a set of specifications for the use of RCA as a base course in flexible pavements was developed.

Local Rural Road Safety Audit Guidelines and Case Studies

The main goal of this study was to improve the safety performance of local rural roads in South Dakota by promoting road safety audits (RSAs) and by providing a toolbox of low-cost safety improvement strategies to county highway superintendents and local highway agencies. The study conducted RSAs at 12 selected sites along county highways, city streets, and township roads. RSA projects were selected through South Dakota Local Transportation Assistance Program promotion and commitments from South Dakota local agencies. The study exposed local governments to the concept and practices of road safety analysis. The study also provided a good opportunity for local highway agency staff members to participate and gain experience by working with road safety teams. This paper reports on the procedures and the results of the rural road RSAs and identifies guidelines to conduct RSAs on local rural roads to help local agencies identify, prioritize, and implement safety improvements.

Infrared Thermography for Asphalt Crack Imaging and Automated Detection

A research project evaluated the application of infrared thermography for the detection of asphalt cracking. Such detection has generally relied on image processing of pictures and videos of asphalt produced by analog and digital cameras that operate in the visual range of light. The presence of shadows, poor light conditions, white cracks, and a variety of other problems have presented serious challenges to automated crack identification and detection in this frequency region. The research reported here is primarily aimed at testing the hypothesis that asphalt cracks cause changes to surface conditions and emissivity, leading to perceived temperature differentials that can be exploited by infrared detectors in cameras. The research involved the production of tens of images from both conventional and infrared cameras. Several parameters were evaluated for both flexible and rigid pavements, including choice of infrared detection range, various lenses, and exposure during day and night hours. Under the right conditions, infrared thermography can yield superior results and allow the identification of tiny cracks about 1 mm in width, which are virtually impossible to detect with conventional cameras.

Percent Within Limits for Hot-Mix Asphalt on Low-Volume Agricultural Roads in Egypt

Replacement of traditional, method-based specifications, which use average deviations to determine payment for materials, with percent-within-limits (PWL) specifications is essential for highway agencies. The PWL approach recognizes that construction material properties follow a normal distribution. When the appropriate standard deviations for each material property are known, then upper and lower test limits can be set around the target value of the material property. The contractors payment is then based on the percentage of the test results that fall within these upper and lower limits. The main goal of this research study was to investigate the potential of developing a PWL specification system for low-volume agricultural roads in Egypt that included the selection of the material properties used for payment, the frequency of testing for these properties, development of the standard deviations and specification limits, and development of a payment system. The proposed system is capable of providing guidelines for determining acceptable quality level, rejectable quality level, and appropriate sampling frequency with operating characteristic curves based on known standard deviation to achieve the recommended risk levels. Field data were used to evaluate the implications of implementing PWL and the risk between PWL and the current specifications.

Analysis of Factors Causing Corrugation of Gravel Roads

Gravel and unpaved roads are viable and important components of the road transportation network throughout the world. In the United States, gravel and unpaved roads still make up close to 50% of road miles. Motorists traveling on a gravel road will encounter the problem of corrugation. Corrugation, or washboarding, is a problem with many causes and no long-term solutions, requiring continual maintenance to control its appearance. Several factors have been researched and found to contribute to corrugation, such as traffic volumes, vehicle speeds, subgrade characteristics, harmonic vibration of the vehicles suspension system, and gravel properties. This study examines the causes of corrugation by using variables previously considered by other researchers as well as new variables added by the studys research team. The objective of this study is to develop a comprehensive prediction model that can identify the potential occurrence of corrugation at a specific location. The model calculates corrugation height and wavelength. One significant and considered new conclusion is that corrugation is affected by the amount of natural soil placed between the gravel layer and the natural subgrade material. This natural soil is placed on the road surface during the original construction of the road and comes from formation of the side ditches. Another conclusion is that the moisture content of the subgrade, the ratio of the thickness of the surface gravel to the depth to the subgrade, and traffic speeds are the most significant influencing factors in the formation of corrugation.

PAVEMENT RESPONSES DUE TO HARD LANDINGS OF HEAVY AIRCRAFT

The effects on airport runways of impact loads induced by hard landings of heavy aircraft have been investigated. A hard landing is defined as a landing in which the angle of landing by a single-wheel impact load is greater than the static load for the same aircraft, with inclusion of the effects of the shock-absorption system. A numerical model, based on some earlier work by others, was developed to define the impact load for any given landing angle. With the impact-load values calculated from the model, theoretical stresses and strains were computed by existing elastic-layer and finite-element computer programs. The results indicated that tensile strains at the base of the asphalt layer and compression strains at the top of the subgrade could be up to 10 times as high under impact loading than under static loading. The study concluded that impact loads caused by angles of landing between 0.2° and 0.8° above horizontal were not greater than the static load of the aircraft (upon which current design standards are based). However, at angles of landing greater than about 0.8°, the fatigue cracking and permanent deformation of airport runway pavements increased exponentially with an increase in landing angle. As a result of this study, the effects of impact loads due to hard landings were demonstrated to be sufficiently significant to be considered in the design of airport runway pavements.