Scope of Work
This scope of work is similar to the work done in 1999 and 2010 on the deck with the addition of the epoxy overlay.
The unsound and delaminated concrete in the deck was removed, the corroded reinforcement bar was sand blasted, and a new silica fume overlay was placed. After the silica fume was cured adequately, an epoxy overlay was placed. The epoxy overlay adds water resistance to the deck, strength, and provides a higher friction wear surface.
While the overpass was closed, broken concrete paving in the intersection of 4th Street and Gurley Avenue were replaced.
Structural Evaluation and Development of Scope
In the development of the scope of this repair work, Structural Dynamics performed a thorough evaluation of the deck condition, sounding (chaining) the entire deck for delaminated concrete. During this process, deck spall developed on the north span. The deck was cored at 10 representative locations to gain an understanding of the depth of the delaminations. Additionally, Structural Dynamics investigated Wyoming Department of Transportation statistics to help refine estimates of the proportion of deep repairs vs shallow repairs. This information was used to develop the quantities for the bidding document.
Wyoming Department of Transportation specifications and bid items were used in the bid documents.
Additional Damage
The extent and depth of damaged concrete was substantially more than estimated. The initial area of unsound concrete was estimated to be approximately 14% of the deck surface. The actual extent of unsound concrete involved nearly 40% of the deck surface. Additionally, the pay item for unsound concrete, deeper than 1/2 the deck thickness, exceeded the original estimate by nearly 10 fold. The corresponding volume also caused the volume of silica fume placed to nearly double.
The sounding and coring that was performed, to map the extent and depth of damage prior to the work, provided to be inadequate to accurately determine the actual extent and depth of the damage. The proportions of deep removals to shallow removals exceeded averages available from WYDOT. The age of this structure and the rate of progression of damage may be factors in the misinterpretation of the extent of the damage.
Due to the additional work, 31 working days were added to the 60 working day contract for a total of 91 contract working days.
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