5 resultados para 658.314 M686c

em Iowa Publications Online (IPO) - State Library, State of Iowa (Iowa), United States


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Iowa's secondary road network contains nearly 15,000 bridges which are less than 12 m (40 ft) long. Many of these bridges were built several decades ago and need to be replaced. Box culvert construction has proven to be an adequate bridge replacement technique. An alternative to box culverts is the Air-O-Form method of arch culvert construction. The Air-O-Form method has several potential advantages over box culvert construction. The new technique uses inflated balloons as the interior form in the construction of an arch culvert. Concrete is then shotcreted onto the balloon form to complete the arch culvert. The objective of the research project was to construct an air formed arch culvert to determine its applicability as an alternative county bridge replacement technique. The project had the following results: (1) The Air-O-Form method can be used to construct a structurally sound arch culvert; and (2) The method must become more economical if it is to compete with box culverts.

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To conserve natural resources and energy, the amount of recycled asphalt pavement has been steadily increasing in the construction of asphalt pavements. The objective of this study is to develop quality standards for inclusion of high RAP content. To determine if the higher percentage of RAP materials can be used on Iowa’s state highways, three test sections with target amounts of RAP materials of 30%, 35% and 40% by weight were constructed on Highway 6 in Iowa City. To meet Superpave mix design requirements for mixtures with high RAP contents, it was necessary to fractionate the RAP materials. Three test sections with actual RAP materials of 30.0%, 35.5% and 39.2% by weight were constructed and the average field densities from the cores were measured as 95.3%, 94.0%, and 94.3%, respectively. Field mixtures were compacted in the laboratory to evaluate moisture sensitivity using a Hamburg Wheel Tracking Device. After 20,000 passes, rut depths were less than 3mm for mixtures obtained from three test sections. The binder was extracted from the field mixtures from each test section and tested to identify the effects of RAP materials on the performance grade of the virgin binder. Based on Dynamic Shear Rheometer and Bending Beam Rheometer tests, the virgin binders (PG 64-28) from test sections with 30.0%, 35.5% and 39.2% RAP materials were stiffened to PG 76-22, PG 76-16, and PG 82-16, respectively. The Semi-Circular Bending (SCB) test was performed on laboratory compacted field mixtures with RAP amounts of 30.0%, 35.5% and 39.2% at two different temperatures of -18 and -30 °C. As the test temperature decreased, the fracture energy decreased and the stiffness increased. As the RAP amount increased, the stiffness increased and the fracture energy decreased. Finally, a condition survey of the test sections was conducted to evaluate their short-term pavement performance and the reflective transverse cracking did not increase as RAP amount was increased from 30.0% to 39.2%.

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Iowa's secondary roads contain nearly 15,000 bridges which are less than 40 feet (12 m) in length. Many of these bridges were built several decades ago and need to be replaced. Box culvert construction has proven to be an adequate bridge replacement technique. Recently a new bridge replacement alternative, called the Air-0-Form method, has emerged which has several potential advantages over box culvert construction. This new technique uses inflated balloons as the interior form in the construction of an arch culvert. The objective of research project HR-314 was to construct an air formed arch culvert to determine the applicability of the Air-O-Form technique as a county bridge replacement alternative.

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Newsletter for Economic Development

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City Audit Report