ASPIRE Spring 08 - Aspire - The Concrete Bridge Magazine

The new multiple-span Benicia-Martinez Bridge traverses theCarquinez Strait between theCity of Benicia in Solano Countyand the City of Martinez inContra Costa County, California.The cast-in-place, segmentalbridge is built to be a “lifelinestructure,” remaining open toemergency traffic after a majorearthquake.he adds. For instance, the firm hasworked with the Colorado Departmentof Transportation on one of seven bridgesthe department has developed using acurved, spliced-girder system. “They’vepioneered this design and led the way,which is really an interesting approach.Owners are definitely sold on concreteconcepts and are leading its use.”Lightweight ConcreteEvolvingConcrete mixtures that have led to morelightweight concrete also are changingdesign concepts, he says. “Lightweightconcrete is fast becoming a standard,and it has a tremendous influence ondesign.”An example can be seen in the company’swork in a joint venture with T.Y. LinInternational on the Benicia-MartinezBridge in California. The project used“sand-lightweight” prestressed concretebox girders constructed primarily by thesegmental, balanced cantilever, cast-inplaceconstruction method. The sandlightweightconcrete uses normal weightsand and lightweight coarse aggregate toproduce concrete that is lower in densitythan normal weight concrete. (For moreon this project, see the Summer 2007issue of ASPIRE.)“We needed to use concrete that waslightweight but that also offered otherproperties related to modulus of elasticityand creep,” he explains. “We stretchedthe capabilities in that design, and that ishappening more often all the time.”The design for the new 3175-ft-longconcrete crossing of the Fraser Rivernear Vancouver, British Columbia,Canada, features a much lower profiledue to the concrete material and a newfoundation design, which uses largediameterbored piles to provide costeffectiveconstruction in the deep layersof soft silt. The project also features anemphasis on aesthetics, using decorativeeagles as a recurring theme on bridgetowers and other locations.Self-consolidating concrete also is beingused more often, most usually to aidcontractors in speeding constructionrather than for design purposes.Showers notes. He also has great hopesfor a variety of new reinforcementmaterials, such as fiber reinforcedplastics or carbon fibers.“A number of states have createddemonstration projects with thesematerials, and there is some work beingdone in Europe,” he says. “I haven’tseen a massive breakthrough yet, butthere could be one in the next fewyears. It would be ideal if the materialcould be put into slabs and wouldn’tcorrode. An indefinite service life wouldbe the Holy Grail.”As concrete producers work with CH2MHill toward that goal, the firm willcontinue to improve on its own designand construction processes, as wellas their integration, to help cut costsand create designs that meet the morediverse, specialized, and challengingneeds of all types of bridge clients.ASPIRE, Spring 2008 | 13