Showing papers in "Concrete international in 2008"

Practical Finite Element Analysis

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Pervious Concrete in Severe Exposures

Abstract: Porous pavement, especially portland cement pervious concrete (PCPC), helps control pollution discharge by allowing rainwater to rapidly infiltrate into an open-graded aggregate subbase and into the ground. Hydrocarbons become attached to the large surface area of the PCPC or the aggregate subbase and are reduced by natural attenuation, either through evaporation or biological degradation. PCPC also mechanically filters out larger pieces of metal or biological material for later collection during routine maintenance. Thus, the majority of first-flush pollutants are removed by the pervious concrete system, preventing the pollutants from entering stormwater collectors and being conveyed to local surface waters. By allowing stormwater to naturally percolate into the soil, PCPC can also reduce or eliminate the need for stormwater retention areas and the infrastructure required to convey the water. This article provides a summary of the authors' work in this area that focused on the durability of PCPC subjected to freeze/thaw cycles.

Pavement System Suiting Local Conditions

Abstract: Since the early 1990s, the Ministry of Transportation of Quebec (MTQ) has placed renewed emphasis on constructing long-lasting concrete pavements suiting local traffic and climatic conditions. In 2000, these efforts led to the installation of Canada's first roadway with continuously reinforced concrete pavement (CRCP). However, 5 years later, concerns were raised about the long-term performance of CRCP, as portions of this initial installation were found to have insufficient cover over the bars, and core samples showed that the longitudinal reinforcement was corroding at transverse cracks. These observations led the MTQ to select galvanized steel as the standard reinforcement for subsequent CRCP projects and to continue investigating other systems with enhanced corrosion resistance. As part of these investigations, the MTQ and the University of Sherbrooke began studying the use of glass fiber-reinforced polymer bars for CRCP in September 2006. A stretch of test pavement has since been constructed on eastbound HW-40 in Montreal. This article summarizes the design concepts, construction details, material properties, early-age behavior, and preliminary monitoring results for this test pavement after 18 months in service.

Cathodic Protection of Historic Bridges

Abstract: In 1936, a project funded by the Oregon Public Works Administration completed the last of 5 major bridges on Oregon Coast Highway route allowing the remaining ferries between the Columbia River and the California border to be taken out of service. Over the following decades, the bridges were attacked by the marine environment of the Pacific Coast. The diffusing into the concrete to the reinforcing bars, chlorides depassivated the steel, provided an effective electrolyte, and allowed formation of galvanic corrosion cells. The resulting corrosion products generated sufficient force to crack and spall the concrete cover. This article describes how the Oregon Department of Transportation began investigating cathodic protection technology during the 1980s to protect these historic spans.

Adhesive Anchor Installation and Inspection

Abstract: Post-installed adhesive anchors, also known as epoxy anchors, chemical anchors, bonded anchors, and adhesive-bonded anchors, have been successfully used to make connections to concrete structures for many years With the failure of adhesive structures in the Boston (Massachusetts) I-90 Tunnel Project, commonly called the Big Dig, the use of these types of anchors has been called into question This article reiterates the proper installation and associated inspections necessary for adhesive anchors to achieve the desired performance

Strengthening by external prestressing

Abstract: Compared with conventional reinforced concrete structures, prestressed concrete structures are assumed to be more corrosion resistant due to the use of high-strength materials and the crack-free nature brought about by precompression. In spite of these advantages, stress corrosion in prestressed concrete structures can result in premature and catastrophic failure even when epoxy-coated reinforcement is used. Further, the deterioration of embedded prestressing reinforcement may not be visible as external distress in the concrete, resulting in degradation that goes undetected and unremediated until becoming severe. When prestressed concrete structures degrade prematurely due to corrosion of the prestressing steel, reliable methods of repair and strengthening must be available to minimize the economic consequences. One such method is the use of external prestressing. In this article, an investigation is described into the effectiveness of this method for various levels of internal prestressing steel deterioration.

Our Aging infrastructure

Abstract: In the 21st century, U.S. transportation infrastructure is clearly showing its age. For many of these structures, especially bridges, aging has been accelerated by corrosion. This is especially true in environments where the conditions are harsh and aggressive, such as coastal marine environments and settings that use deicing salts in the winter months. The corrosion problem is compounded by surface cracks in the concrete that provide a direct path for water and salt (chlorides) to reach the reinforcing steel. The concentration of chlorides and the ability of the reinforcing steel to resist corrosion initiation often become the limiting factors that determine the life cycle of the reinforcing steel bars and subsequently the life of the structure. This article provides an overview of a number of different solutions to deal with structural corrosion, including various coatings on the reinforcing steel, concrete admixtures, impressed current systems, and even bulk anodes. Each method comes with its own unique compromises and drawbacks.

Packing More Value Into the Mix: System Optimizes Concrete Cost and Performance

Abstract: The iCRETE software system allows producers to create concrete mixtures that have up to 25% less portland cement, reduced variability, and better workability than traditional mixtures. iCRETE uses pre-production inputs that include strength and slump target values, unit cost for all consitutents, and particle size and packing density for the cementitious materials and aggregates. The author examines iCRETE-related optimization, specification, performance, and applications. Cost is also discussed.