The Future FORWARD BRIDGES -section 5 -- revised 6-10-02

BACK FORWARD THE FUTURE Material properties, such as corrosion resistance, fire resistance and durability are being continuously improved and exploited. These inherent qualities of precast prestressed concrete and its considerable design flexibility also make it ideal for a wide variety of other applications: poles, piles, culverts, storage tanks, retaining walls, sound barriers and even railroad ties. BACK FORWARD

BACK FORWARD THE FUTURE The benefits of High Performance Concrete are already beginning to be applied. These include reduced initial construction costs that result from wider girder spacing and longer spans as well as reduced long-term costs due to fewer replacements and fewer repairs. High Performance Concrete is being increasingly specified for the nation’s bridges and structures. BACK FORWARD

BACK FORWARD THE FUTURE One form of HPC is high strength concrete. A strength of 14,000 psi was specified here for the beams of the Louetta Road Bridge, a demonstration project, located in Houston, Texas. High strength concrete was also used in this bridge for the stay-in-place deck panels, the cast-in-place concrete deck and precast segmental piers. BACK FORWARD

BACK FORWARD THE FUTURE The Giles Road Bridge in Sarpy County, Nebraska also was constructed using High Strength Concrete. Completed in 1996, it is another example of a bridge with 12,000 to 14,000 psi concrete girders and a 5,000 to 8,000 psi concrete deck. The Federal Highway Administration, together with PCI and several states, continues to promote the use of High Performance Concrete in bridge applications. For the precast industry, High Performance Concrete often involves higher than average compressive strength. BACK FORWARD

BACK FORWARD THE FUTURE However, other factors, such as low permeability and resistance to freeze-thaw – not just strength – may be features of High Performance Concrete depending on the geographic location of the bridge and the component for which it is used. Lightweight aggregate concrete with strengths in the 7,000 to 10,000 psi range is also being used on some newer bridges. Lightweight concrete provides reduced dead-loads and seismic forces. BACK FORWARD

BACK FORWARD THE FUTURE Strands of larger diameters and higher strengths are becoming more common as higher strength concretes are used and the demand for higher tensile force increases. When 0.6 inch diameter strands are used in conjunction with high strength concrete, in the 10,000 to 12,000 psi range, standard I-beams and other products are able to reach significantly longer spans never thought possible before. Even larger and stronger strand are on the horizon. Corrosion-resistant steels and coatings promise unlimited durability. Corrosion-resistant coatings Stainless-clad Corrosion-resistant steel 0.7"? BACK FORWARD

BACK FORWARD THE FUTURE Nonmetallic reinforcement such as glass, carbon and aramid fiber composites will be increasingly used for special applications. A recent demonstration project has shown the compatibility of carbon fiber strands for prestressing a bridge girder. Both, internally bonded prestressing and external unbonded prestressing systems are used. BACK FORWARD

BACK FORWARD THE FUTURE Synthetic, organic and steel fibers have been shown to improve toughness and shrinkage cracking. Recent developments in high performance fiber-reinforced concrete hold promise in terms of performance and cost-effectiveness. BACK FORWARD

BACK FORWARD THE FUTURE Reinforcing steel corrosion Initiation Migration of chlorides, H20 and O2 into the concrete, no corrosion and no damage to concrete Corrosion of the steel reinforcement and cracking and/or spalling of concrete Initiation Propagation (corrosion) Degree of Corrosion Critical chloride threshold I Time BACK FORWARD

BACK FORWARD THE FUTURE Corrosion mechanism of steel Corrosion Mechanisms Can be Minimized By Avoiding Microgalvanic Cell Formation Present in Conventional and Micro-Alloyed Steels BACK FORWARD

BACK FORWARD THE FUTURE MMFX is not a stainless steel but Step 1 of its production adds chromium and reduces the carbon content. Benefits of adding chromium to reduce the steel’s corrosion rate. BACK FORWARD

Prior Austenite Grain Boundary THE FUTURE Prior Austenite Grain Boundary 2 –Dislocated Laths (Martensite) 1 – Untransformed Nano Sheets of Austenite 1 2 The Second Step to Achieving Microstructure Steel MMFX approach to altering the micro-structure of the steel: Produce a Microcomposite Steel that Eliminates Formation of Microstructural Galvanic Cells BACK FORWARD

Chloride Threshold (lb/yd3) THE FUTURE Reinforcement Type Low Cost installation High Chloride Threshold (lb/yd3) Propagation (years) Black Steel $0.38 $0.53 1 6 Epoxy Coated Steel $0.50 $0.66 20 Stainless Steel $2.75 $2.91 12 MMFX 2 Steel (4 X) $0.70 $0.85 4 MMFX 2 Steel (6 X) BACK FORWARD

Time to Initiation (Years) Total Life Cycle Cost ($/ft2) THE FUTURE Reinforcement Type Installation Cost Initial Cost ($/ft2) Time to Initiation (Years) Time to First Repair (Years) Total Life Cycle Cost ($/ft2) MMFX 2 Steel (4 X) HIGH $15.01 90 >100 MMFX 2 Steel (6 X) Epoxy Coated Steel $14.93 44 64 $19.02 Black Steel $14.42 50 $21.31 Stainless Steel $23.75 BACK FORWARD

BACK FORWARD THE FUTURE Self Consolidating concrete is an extremely cohesive and flowable material capable of being placed without vibration. It can be placed very fast at a very dramatic reduction in noise. BACK FORWARD

BACK FORWARD THE FUTURE The cohesion of the fresh concrete and no negative effects from vibration will result in a more homogeneous surface layer. This reduces permeability, increases resistance to chloride ingress, carbonation and other chemical attack BACK FORWARD

BACK FORWARD THE FUTURE Another development has been the use of precast deck panels. Used as stay-in-place forms, the panels reduce labor for field placement of reinforcing steel and concrete for bridge decks, resulting in considerable savings. The panels become composite with the field-placed concrete for live loads. They’re made of high-quality, plant-produced concrete and contain the primary tensile reinforcement between beams. They remain crack-free, protecting this important reinforcing steel. BACK FORWARD

BACK FORWARD THE FUTURE Full-depth precast deck panels promise to provide the solution for extended closings due to deck replacement. The technique applies to new construction as well. Precast highway paving panels are being demonstrated in Texas to speed lane widenings and reduce traffic closures and detours. Refined materials and methods are making these solution an exciting new part of the designers tool box. BACK FORWARD

BACK FORWARD THE FUTURE Another innovation is the development of horizontally curved precast concrete bridges which is creating exciting new options in contemporary bridge designs. This technique involves post-tensioning precast elements together in the plants before shipment or in the field after erection. BACK FORWARD

BACK FORWARD THE FUTURE Spliced girders give Prestressed concrete girders the ability to reach further and longer BACK FORWARD

BACK FORWARD THE FUTURE And yet another solution for curved structures is segmental construction. Working together with the American Segmental Bridge Institute (ASBI) and the AASHTO Bridge Subcommittee, PCI has endorsed a family of standard shapes for segmental bridges that is intended to reduce the cost of segmental bridges for smaller structures such as urban grade separations. BACK FORWARD

BACK FORWARD THE FUTURE Prestressed concrete got its start as the original composite material and further developments by the industry and its suppliers have continued to refine the performance of the product for the bridge market. BACK FORWARD

BACK FORWARD THE FUTURE Today, it still gives the public extremely good value for its money. The reputation of the precast prestressed concrete industry has been built on the strength, imagination, consistency and integrity of its people and products alike. In the future, it will continue to be the solution of choice. BACK FORWARD

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