Across the vast landscape of Texas, billions of dollars are being spent to expand and repair bridges and roadways. Although U.S. states are struggling to maintain driveable roadways with dwindling budgets, infrastructure construction is going strong in Texas, thanks to bonds for highway improvements approved by taxpayers in 2003 and 2007. The Texas Department of Transportation (TxDOT) is also exploring public-private partnerships to pay for even more major highway projects in the Houston and Dallas metro areas.
The boom has not caught precast/prestressed concrete producers offguard. “Concrete is the material of choice for bridge design in Texas, and every precaster in the state has a heavy workload right now,” says Chris Lechner, executive director of the Precast Concrete Manufacturers’ Association of Texas (PCMA). He estimates 96 percent of the bridge market is precast/prestressed concrete, with the exception of extremely long spans. He notes that gap is closing with advances in technology such as spliced precast/prestressed girders.
Off the top of his head, Lechner can name multi-billion dollar projects under construction across the state using every conceivable precast product: mechanically stabilized earth (MSE) walls on the I-635 Dallas/Fort Worth connector; hundreds of concrete pilings supporting the Campano Bay bridge; a precast pavement test strip south of Waco; and bridge beams, decks, and sound walls rebuilding the I-35 corridor from Dallas-Fort Worth to San Marcos.
Precasters also have their eyes on exit ramps. TxDOT is exploring test projects using curved precast girder sections that are cast in forms adjusted to a specific radius. The Colorado DOT estimates it has been able to save $1 million per exit, using steel reinforced curved girders.
Potential roadblocks ahead
But road construction in Texas may not continue full speed ahead for much longer. Unless the state legislature approves more taxes or registration fees to fund roadwork by 2014, TxDOT could go into maintenance mode.
“Right now the focus is on water infrastructure, after several years of experiencing the worst drought we’ve seen since the 1950s,” he says. Some precast producers could actually be involved in that construction as well, supplying pipes, culverts, and panels.
Although Texas precasters have benefited from forward-thinking investment in infrastructure, they are bound by the same uncertainty faced by other parts of the country — and the concrete industry. “The total use of concrete in Texas is increasing, especially for pavements,” says Lechner, citing comparable costs of concrete and asphalt. “Concrete delivers a better value for longevity, hands down. But we’re not out of the woods yet. There are so many variables right now; it’s hard to keep track of where the economy is going to go.
“What impresses me about precasters is that they are always innovating,” says Lechner. “The industry is constantly improving.” This restlessness has served producers well during economic downturns, and it may be what keeps them afloat through tough times in the future.
Here, we highlight three Texas precast producers and the ways in which they are meeting the challenges of their competitive infrastructure market with creativity, quick thinking, and a dedication to high-quality products.
Sylvan Avenue Bridge
Looking out over the site of the new Sylvan Avenue Bridge in Dallas, Jorge Hinojosa, P.E. sees the future of precast concrete. “The precast industry has taken, and will continue to take, a larger piece of the steel girder market over the next five years,” says the general manager of Bexar Concrete Works.
For 35 years, the Dallas precast/prestressed producer has specialized in making concrete elements for highways. Currently, Bexar is casting girders for the Sylvan Avenue Bridge, which will connect downtown and west Dallas when it opens early 2014. The 3500-foot, six-lane bridge replaces a flood-prone two-lane road and three separate bridges that cross two levees and the Trinity River.
The City of Dallas calls it a “vital project [that] will provide a new bridge across the last of the Dallas streets low water crossings.” The project will raise the elevation of Sylvan Avenue to eliminate the frequent flooding and closures experienced on the current road. The public will also benefit from new bike lanes, sidewalks on each shoulder, and a ramp for pedestrian access to a park.
In January, Bexar began casting the 150-foot girders it will supply for the bridge, including standard 28-, 54-, and 82-inch prestressed girders, as well as spliced precast/prestressed girders to span 250 feet. The project consists of 23 spans, 14 of which are typical 82-inch prestressed girders and nine that are divided in three units of three spliced, post-tensioned girders.
With higher-strength concrete and significantly more steel reinforcement than a typical prestressed element, the spliced girders essentially span longer. The girders are shipped in shorter sections and spliced on the bridge by post-tensioning to obtain a longer span. Bexar’s 82-inch-high, 8500 psi spliced girders allow the Sylvan Avenue Bridge to cross the 250-foot mid-span of the Trinity River with fewer bridge piers. Bexar has worked closely with TxDOT to overcome the challenges posed by the large amount of mild steel in the girders. “It’s easy to draw it on paper, but a different story when it’s for real,” says Hinojosa.
Controlling the curing temperature has also put the producer to the test. “The specification allows a maximum curing temperature of 170 degrees F, but to increase production you need to add as much Type III cement as possible without exceeding the allowable temperature,” he explains. “Fortunately, the weather has cooperated so far.”
The sheer size of the elements Bexar is producing is impressive. “The trend in precast infrastructure is longer and bigger concrete girders,” says Hinojosa. “This means the prestress forces are larger so the fabrication beds and trucking equipment need to be larger.” He describes the production process as very similar to casting standard precast/prestressed concrete girders, but with more pieces to the puzzle.
Because the modified TxDOT 82-inch girders are wider than standard TxDOT girders, the forms had to be designed with a wider soffit. Fort Worth-based Hamilton Form Company configured the special formwork so the soffit could be cut down after the Sylvan Avenue Bridge job and used to cast typical 82-inch girders.
The formwork package includes 7- and 10-foot-long end blocks for the 85-foot girders. Two 8 1/2-foot end blocks are used back-to-back at the center of each beam to create a blister, or the thickened section, that forms the interior diaphragm that bears on a pier.
Hamilton Form also produced bearing and embed plates for the $42 million project. The 35- by 60-inch embedded plates are 1 inch thick; each has forty 6- by 7/8-inch steel studs and weighs 620 pounds. The larger beams use 55- by 44-inch beveled, galvanized steel bearing plates that are 2 inches thick and weigh 1850 pounds a piece.
Hinojosa sees the experience as an investment in Bexar’s future. “The infrastructure market is competitive,” he says. “It requires a high degree of quality control.” By working through the challenges of producing more complex precast and prestressed elements, the producer is determined to keep concrete at the forefront of Texas infrastructure.
Northeast Tarrant County (NTE) 183 Extension
Before 2012, Fort Worth precast producer Speed Fab-Crete had never produced a sound wall panel. But when a subcontractor asked for help producing 170,000 square feet of precast sound walls for the $2.5 billion North Tarrant Express (NTE) 183 extension project, a new product line was born.
The contractor had never worked with precast, so Speed Fab-Crete worked with the engineer to develop the best system for the job. They decided on a series of panel sizes varying from 10 to 18 feet high, and up to 18 feet long.
The panels are produced with two 4-unit battery forms, designed by Hamilton Form, that can be adjusted to accommodate the different sizes of panels needed. Each wall panel has an integral column cast on one end.
One battery form is designed with the columns across the top of the form. The wall panels will be shipped to the jobsite in this orientation, and then rotated 90 degrees for installation. This allows for panels up to 18 feet tall to be produced.
The other form casts the column in its normal vertical position at the end of the panel, producing panels up to 18 feet long. Both battery molds are designed with internal headers to accommodate casting up to four panels at a time.
Panels are 6 inches thick. The integral column is 18 by 18 inches; a void centered in the outer edge allows for the adjacent wall panel to lock into place.
Interior sideforms are fixed in place on a sleeper system. The outer sideforms are split into two 21-foot sections that roll back on wheel carriages and tracks. A catwalk between the two interior sideforms allows access to the top of the mold. The mold’s top ties are welded into a single assembly for each panel cavity for quick installation and removal.
In addition to its flexibility for production, the mold design has an aesthetic benefit. “The system produces many wall height and width variations,” says co-owner Carl Hall. “It reduces the cookie-cutter look.” This system also has the benefit of building walls set to a radius. Speed Fab-Crete uses formliners to create a one-sided decorative finish per project specifications.
With the right mold design in place, the precasters went to work tackling some other logistical issues. “We were out of space in the main plant,” explains Hall. “So we relocated the inventory from a small storage area across the road. This allowed us to make space for casting the sound walls.”
The owners reassigned a product manager — a lifelong precaster — and hired extra labor to focus on the sound wall project. Even with the right personnel in place, “it was a pretty big learning curve,” says Hall. “Early on, because of the size of the molds, we had problems with vibration and trying to get a good finish.” The precasters worked out a sequence of external and internal vibration to eliminate bug holes and achieve surface finishes that met the strict standards of the North Texas Tollway Authority. In addition to maintaining a high level of quality, working on large infrastructure projects requires patience. “With roadway projects you are dealing with traffic, utilities, and very busy areas,” Hall says. “You have to be flexible to handle schedule changes or you’ll go crazy.”
For the NTE 183 extension, Speed Fab-Crete constantly coordinates its production schedule with the project plans to reduce the number of mold changes. The team tries to pour as many panels of each mold as possible before changing it out, while keeping up with the different panel sizes required for each phase of the project.
When the project is completed in the middle of 2015, the 13.5-mile Interstate Highway 820 and State Highway 121/183 (Airport Freeway) corridor in Northeast Tarrant County will be rebuilt, relieving traffic congestion along one of the busiest highway corridors in the Dallas-Fort Worth region.
Clearfork Main Street Bridge
Precast concrete was the ideal material for an innovative bridge design that meets both the floodway requirements of the U.S. Corps of Engineers and the lifestyle needs of Fort Worth citizens. Architects Freese and Nichols chose precast for the $11 million-$13 million, four-lane, split bridge with suspended pedestrian bridge beneath.
The 550-foot vehicular bridge carries four lanes of traffic, with a center span of 220 feet. It is built using a system of precast concrete beam segments that are spliced together using post-tensioned steel strands to form a streamlined structure. Walkers, cyclists, wheelchair users, and others have a separate level of access underneath, with scenic overlook spots and ramps that connect with trails on either side of the Trinity River.
Precast girders offered designers a solution to both aesthetic and practical concerns, creating a sleek look for less than the cost of steel. Likewise, innovative formwork helped meet the precast producer’s needs for producing the unique bridge elements.
Texas Concrete Partners produced the precast haunch girders and Type 6 modified beams for the bridge in two locations. At its Victoria headquarters, the precaster produced specialty haunch beams, including a massive 96-foot-long, 10-foot-deep haunch girder that tapers to 6 feet at the ends.
Hamilton Form fabricated formwork for the girders. The haunch girder formwork included an arched soffit and 10-foot, 4-inch sideforms. The soffit was formed with a 200-foot radius on one side and a 185-foot radius on the other.
The producer did not want to tie up one of its main beds to cast the limited number of specialty beams, so Hamilton Form provided a solution. The abutment at the bed they used was generally used for smaller beams, and did not have the capacity to resist the required amount of prestress force (480 kips) 10 feet in the air. To accommodate this setup, the formwork supplier designed sideforms with stressing bars to resist the prestress force in their upper flanges.
“The ends of the beams were congested with steel,” says Jeff Sexton, production manager for Texas Concrete Partners. Post-tensioned haunch beams have three 3 1/2-inch ducts to accommodate steel strand that is added onsite, post-tensioned, and filled with grout.
In Waco, Texas Concrete Partners produced Type 6 modified beams, which are similar to a Type 4 beam at the bottom, but with the wider flange of a Texas Bulb-T beam at the top. They cast three beams at a time, every third day. Like the haunch girders, these beams required self-consolidating concrete, which slightly reduced the amount of manpower needed during each pour.
The producer began casting bridge elements began in August 2011, and finished in Spring 2012. TCP
Longer, Leaner Beams Give Precast an Advantage
Many state DOTs are collaborating with industry associations and experts to develop bridge beams that are more efficient for both bridge designers and precast producers. The widespread adoption of these new designs has given precast producers a competitive edge.
The Florida Department of Transportation worked in collaboration with the Florida Prestressed Concrete Association and Dr. Maher Tadros of the University of Nebraska to develop the Florida I-Beam (FIB). First produced by Standard Concrete Products in Tampa in 2009, the beams feature a constant top and bottom flange with a variable web to facilitate the use of fillers in casting various beam sizes.
The FIB shape accommodates more strand than the old Florida Bulb-T beam design. The increased strand allows for longer beams, which means bridges can be designed with fewer beams and spans.
New FIBs have a wider bottom flange and lower center of gravity than the AASHTO beams, making them more stable in shipping, handling, and placement. The FIBs also have a fully predesigned reinforcement option that significantly reduces fabrication time.
In 2009, the Texas DOT (TxDOT) also replaced AASHTO Type 4 I-beams a new Texas I-Girder. The new beam features a thinner vertical section, thinner flange, and more bulbous bottom than the AASHTO design. Although it uses less material, the I-Girder is stronger so it can be designed in longer lengths, and bridges can be built with fewer beams.
The Precast Concrete Manufacturers’ Association of Texas (PCMA) consulted on the I-Girder design, with suggestions to make it easier for precasters to pour. Although its adoption meant precasters had to purchase new forms, the PCMA reports they have ultimately received more orders with the I-Girder,even with fewer beams being used per bridge.