Of all the components that compose a highway bridge, the bridge deck usually deteriorates the most quickly and requires the most maintenance and repair because of its exposure to detrimental conditions. Several preventive maintenance techniques are available to retard bridge deck deterioration and thus prolong service lives. Of these techniques, types of bridge deck overlays are investigated. As preventive maintenance, an overlay provides a protective layer between the bridge deck and the detrimental conditions that promote deterioration. In general, this protection enhances the material properties of the overlay, which may include low permeability and resistance to chemical attack as well as added thickness. The overlay procedures used for bridge decks in Tennessee are investigated from information about overlay types and their usage obtained through several sources, including interviews with Tennessee Department of Transportation personnel who are experienced in bridge maintenance. Four types are identified: asphalt, reinforced portland cement concrete, nonreinforced polymer-modified concrete, and thin bonded overlays. Each overlay is described and typical applications, bridge deck preparation, general construction techniques, special considerations, expected service lives, and average costs are discussed. Expected service lives ranged from 15 to more than 30 years, and average costs ranged from $30 to more than $100 per square yard. All overlay types are useful and appropriate under different situations.
Bridge decks, concrete or otherwise, represent one of the most heavily deteriorated components of typical highway bridges. Bridge construction continues to proceed at high volume, and in the past, bridge repair, rehabilitation, and replacement increased as well. Enormous amounts of funding are required to support initial construction and repairs as needed. This national trend is also evident within the Tennessee bridge inventory, which currently numbers approximately 20,000, with a majority of the structures utilizing concrete cast-in-place decks. Because of the increasing volume of work and limited funding, efficient methods of constructing and repairing concrete bridge decks have been of interest during the past decades. Durable, high-quality bridge decks have been constructed in Tennessee with three primary forming systems: temporary forms and falsework and stay-in-place form systems consisting of precast concrete panels and permanent steel forms. Each of these form systems is discussed, with a description of typical applications and estimation of the frequency of use. Currently, cast-in-place decks in Tennessee represent approximately 60% of the inventory and are predominantly (90%) cast by using permanent steel forms. The effects of stay-in-place forms on finished cast-in-place decks were investigated as well as form durability and inspection and repair considerations. This information was obtained through review of Tennessee Department of Transportation specifications and standard drawings and interviews of department personnel.
The objective of the research was to determine if fly ash not meeting ASTM C618 can be used successfully in an aggregate-lime fly ash-stabilized base course (ALFASB). The Tennessee Dept. of Transportation (TDOT) Specification 312 for ALFASB includes hydrated lime, fly ash, and TDOT grading C limestone in percentages by dry weight of the total mix of 3.5, 11, and 85.5, respectively. The moisture content of the mix was determined by AASHTO T99. Hydrated lime is required to meet ASTM C977. Fly ash is required to meet ASTM C593 with several exceptions. TDOT grading C limestone was produced by blending No. 57 and limestone screenings. TDOT 312 requires an average compressive strength of 6.5-MPa (950-psi) for three specimens and no individual compressive strength less than 5.5-MPa (800-psi) after 28 days of curing at 37.8°C (100°F). Two different fly ashes were obtained: the control had a loss-on-ignition (LOI) of 1.6 %; the variable had an LOI of 8 %. Twenty-four (8 × 3) compressive strength specimens were fabricated for each set of materials. The only differences were fly ash and optimum moisture contents. The average compressive strength and coefficient of variation were 8.71-MPa (1263-psi) and 5.7 % for the control and 8.41-MPa (1219-psi) and 3.2 % for the variable, respectively. Each individual specimen met the compressive strength requirement for each fly ash. Sixteen (8 × 2) modulus of elasticity specimens were fabricated for each set of materials. The average static modulus of elasticity (estimated with ASTM C469) was 20.68-GPa (3000-ksi) and 15.81-GPa (2294-ksi) for the control and variable, respectively. These results indicate that a very high LOI fly ash can be useful as a stabilizing agent when used in combination with hydrated lime.
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