ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/295658
38 | ASPIRE, Spring 2014 S TAT E T he first recorded bridge built in Hawaii was constructed in 1840. The first concrete bridges in Hawaii's bridge inventory are recorded as being built in 1900 and are still in service. Since then, concrete has been the predominant construction material for bridges. More than 85% of the more than 1160 bridges in the state's inventory (including the counties) are constructed with concrete. In the last 50 years, over 95% of all permanent bridges constructed (not including culverts) have been made of concrete. Recent history shows that about nine out of every 10 bridges constructed in Hawaii are made of precast, pretensioned or post-tensioned concrete elements. Concrete bridges have proven to be a durable, cost- effective solution with lower maintenance concerns compared to timber and steel bridges. Hawaii constructed its first bridges using precast, prestressed concrete girders in 1959. Approximately 30% of the bridges in the state's inventory are constructed using pretensioned or post-tensioned concrete technology. Hawaii's first concrete segmental box girder bridge—constructed by the balanced cantilever method—was the Kipapa Stream Bridge on Interstate Route H-2 on the island of Oahu built in 1975. Recent History Over the last few years, a number of bridges with significant innovative applications have been constructed by the State of Hawaii Department of Transportation, Highways Division (HDOT). North-South Road (Kualakai Parkway) Separation Completed in 2009, the North-South Road (Kualakai Park way) Separation supporting Interstate Route H-1 on the island of Oahu provided some innovative developments of high- performance concrete in drilled shafts and bridge decks. The twin, single-span structures are each 165 ft long with integral abutments. Four 5-ft-diameter drilled shafts support each abutment. A pplication of dr illed sha f t s for Hawaii highway bridges had historically demonstrated several undesirable concrete properties. The aggregate usually segregated from the concrete matrix during placement resulting in lower density concrete at the top of the drilled shaft. In addition, data indicated extremely high concrete temperatures. To overcome these difficulties, the project structural engineer designed a cohesive concrete that did not segregate, remained at temperatures b elow 16 0°F, a nd d i splaye d t e mp er at u r e differentials of less than 35°F during hydration. T he m i x t ure propor tion s, which included polycarboxylate plasticizers and stabilizers, also resulted in a flowable concrete with slumps of about 10 in. This flowable characteristic was maintained throughout the casting process. A low cement content (630 lb/yd 3 ) reduced t h e h y d r a t i o n t e m p e r a t u r e . T h i s w a s accomplished without much loss of compressive strength because a low water-cement ratio was maintained by using a proprietary, synthetic, air-entraining admixture. Bleed water was almost non-existent. The deck concrete materials and proportions were selected to minimize drying shrinkage, enhance fatigue endurance, minimize bleeding, and reduce plastic shrinkage compared with previous deck mixtures. The concrete contained a shrinkage-reducing admixture and synthetic air to improve workability, in combination with water-reducing, hydration-stabilizing, corrosion- inhibiting, and viscosity-modifying admixtures. For increased durability of the riding surface, synthetic fibers were added to the deck concrete to address micro- and macro-cracking. As a result of the success from this project, a number of other bridges have subsequently used similar concrete mixture proportions, especially for the deck concrete. Kealakaha Stream Bridge The Kealakaha Stream Bridge, located on Hawaii Belt Road (Route 19) on the island of Hawaii, was featured in the Summer 2010 issue of ASPIRE. T M It is a 720-ft-long, three- spa n, c ont i nuou s c oncr et e br idge on a n 1800-ft-radius curve with a maximum span of 360 ft. This bridge utilized Washington State Department of Transportation bulb-tee girders that were spliced and made continuous with post-tensioning. HAWAII Concrete bridges dominate the state's bridge inventory by Paul Santo, State of Hawaii Department of Transportation Kahoma Stream Bridge. All photos: KSF Inc. AspireBook_Spr14.indb 38 3/21/14 2:21 PM