ASPIRE Summer 08 - Aspire - The Concrete Bridge Magazine

Designers on theSoutheast CorridorTransportationExpansion Project(T-REX), the largesttransportationcontract in Coloradohistory, reconfiguredthe interchange tomove light-rail trainsfrom the highestlevel to the lowest.The changes resultedin significant costsavings, aestheticimprovements, andenhanced temporarytraffic control.Photo: Parsons andColorado Departmentof Transportation.New Techniques ContinueDesigners expect the dominance ofconcrete in their projects to continue,especially as new engineering techniquesare unveiled. The Woodrow WilsonBridge, for instance, used lightweightconcrete on the deck slabs for its movablespan. “When moving a big mass like that,it makes a lot of sense to use lightweightmaterials wherever possible,” says Shafer.“We used lightweight concrete combinedwith normal weight mixtures to create anefficient system that took advantage ofthe best properties of both.” Weight alsobecomes a concern for large componentsthat must be transported and lifted underchallenging conditions, he notes.Low water-cementitious materials ratiosalso are being used more often, he says.“We can achieve a nice, low permeabilitymix by using a lower ratio and improvedcuring techniques. These help providebetter durability, which is in demandtoday.” High-performance concrete (HPC)also helps meet challenging goals, headds. “We’re using HPC more and more,because it provides strength that cancreate longer spans and eliminate piers.But it’s also being used more often for itsdurability, which helps when the clientwants a 100-year service life.”The designers also are intrigued by theadvancements being made in reinforcingsteel. Stainless-steel strand, such asused on the Woodrow Wilson Bridge,is becoming more popular, along withgalvanized and epoxy-coated options.“The idea of stainless-steel reinforcement,both in solid forms and as a claddingover a carbon steel core, creates realpossibilities,” says Shafer. “They arerelatively new technologies that arestill not readily available or always costeffective,but we expect to see themmore and more.”As their volume increases, the prices willcome down, adding more demand—which will increase volume and helpdrop the price further. Adds Goryl,“There is a lot of research going on withreinforcement in concrete. We sometimesget into complex designs that push thelimits, and we like to see new techniquescome out.”As those techniques arrive, Parsons willwork with local contractors and concretesuppliers to find the most efficientsolution. “We always look at what localconcrete producers are accustomed toproviding,” says Shafer. “We ask if theyhave experience with certain techniquesto ensure we are specifying somethingthat can be built in the local businessclimate.”That approach ensures the design createsthe most efficient approach possible, saysShafer. “New techniques and growingfamiliarity with them in new areas go along way toward giving owners whatthey want, which is something that willlast a long time and save them money inthe long run.”For more information on this or otherprojects, visit www.aspirebridge.org.ASPIRE, Summer 2008 | 13