Rational Structural Design of Highway/Airport Pavements
New EVAPAVE, the Strongest & Toughest Paving Material
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14 RATIONAL STRUCTURAL DESIGN OF HIGHWAY PAVEMENTS “When theory and practice blend, the result is exciting and formidable” When there are rational solutions, the art and science of design becomes exciting. Not only is it simpler, but it inspires the engineer to attain the highest quality product, with engineering efficiency and business economy. 14.1 Flexible Pavements For flexible pavements fatigue in bending of the surface course is the dominant feature. All suitable materials should be tested and the associated costs of the materials delivered to the site should be estimated. Certain minimum requirements should be met. For the subgrade, the undrained shear strength and the compressibility are required. Usually the absolute minimum undrained shear strength of 5 psi and a minimum dry density of 100 pcf are required. For a suitable subbase, the permeability should be at least 100 ft./day (beach sand) with a modulus of at least 20,000 psi. For the base course the dynamic modulus E* should be at least 40,000 psi. 14.2 Concrete Pavements Plain concrete pavements can be built on almost any type of subgrade. The subgrade must be uniform and free of sulphates that attack concrete chemically and organic material should be less than that specified by ASTM ignition test. All non-uniformities should be excavated and replaced by compacted fill, or treated to make them satisfactory. Typical joint spacing is about 15 -19 ft. (4.6 m). If the spacing of the joints is greater than 19 ft. two transverse cracks may develop simultaneously. According to CALTRANS, the most prevalent problem in PCC pavements is faulting at the joints. For the design of dowelled joints the reader is referred to their respective State DOT manuals.
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About the Book
Rational design theories for highway and airport pavements are presented together with an invention of a much superior paving material, comprising recycled Ethylene Vinyl Acetate (EVA) mixed and compacted with graded aggregates. EVA is the binder (cheaper than asphalt), and the new paving material, called EVAPAVE, is four times stronger and tougher than asphalt concrete, and twice as strong and tough as high quality cement concrete. Fracture mechanics is used for determining the fatigue life of the pavement AC surface, while the stress-dilatancy theory is used for the rutting of the pavement. The theories are then combined to obtain the interaction of fatigue and rutting. Several examples are presented to illustrate the design methodology. The new pavement will not require joints and will not have bumps or depressions and will be the smoothest riding pavement, with huge savings in construction and maintenance and in vehicular fuel and maintenance costs, estimated to exceed $10 billion per year in the U.S. alone. Its fatigue life will outlast any other pavement by more than seven times.
About the Author
Dr. Ramsamooj’s fields of specialization are fracture mechanics, geotechnical engineering and pavement design. He has published the pioneering papers on the prediction of fatigue cracking and reflection cracking in pavements, and a theoretical solution for predicting the rutting of flexible pavements. He also developed a theory for the interaction of fatigue cracking and rutting in flexible pavements and a new method of stress analysis for multilayered pavements with cracks and joints which is faster than finite element. As a consultant to the U. S. Navy, he developed a new analytical model for fatigue of metals and composites in the feasibility design of the rigid connectors of the U. S. Navy Mobile Offshore Base. These theories have been validated by 594 published concrete beam tests, 53 different mixes for AC and 39 different metals. Top-down cracking (TDC) in fatigue of AC surfaces has been a mystery all over the world, until Dr. Ramsamooj (2010) discovered the reason for TDC. It occurs whenever the shear stress in the upper 1/3 of the AC layer close to the tire wall exceeds the bending stress at the bottom of the AC layer directly under the wheel load. Recently he invented a new material for highway and airport pavements, EVAPAVE, which is the strongest and toughest paving material. The new material comprises Ethylene Vinyl Acetate (EVA) plus Paraffin wax and aggregates. The tensile strength is four times stronger than asphalt concrete and twice as strong as high-quality cement concrete. It exhibits an insignificant amount of rutting and a fatigue life of over ten times that of asphalt concrete and seven times that of cement concrete. The significance of his research lies in the originality and depth of penetration, the combination of theory and practice and the importance to the nation’s infrastructure.