Bridge to Opportunity
Bridge to OpportunityHigh-Strength Concrete Mixes and High Performance Pumps Help Construct Longest Bridge in Ecuador to Boost Tourism and Trade
STURTEVANT, WI (March 22, 2011) – Building the Bahía-San Vicente Bridge, one of the most important engineering installations and longest bridge in Ecuador, required many detailed construction processes and special high-strength concrete mixes. Selective mixes had to be meticulously designed for pumping concrete long distances up to 2,789 feet (850m), while maximizing the power of Putzmeister trailer-mounted pumps.
The new 1.25 mile (2km) bridge, built in the coastal province of Manabí over the Chone River estuary, is targeted to boost tourism and trade. Previously, it took three hours to cross the estuary; with the bridge that time is reduced to 15 minutes.
This important bridge joins the coastal town of San Vicente and the Pacific resort town of Bahía de Caráquez, where previously small boats or ferries with room for just 12 vehicles were required to cross to the other side. Consequently, real estate and tourism is destined to expand in a picturesque yet underdeveloped coastal region north of the bridge. Plus, the bridge will significantly facilitate the transportation of merchandise to the major port of Manta, just 30 minutes south of the overpass.
Big Bridge, Big Challenge
With modern seismic features that enable the Bahía-San Vicente Bridge to withstand an earthquake of 8.5 magnitude, the project was undertaken by Ecuador's Army Corps of Engineers and built at a cost of $102 million. The bridge consists of a central span from abutment one to abutment two for a total length of 6,510 feet (1,984.5m), which crosses the entire Chone River estuary.
The bridge deck is 30.5 feet (9.3m) wide for vehicular traffic and has a 10-foot (3m) bicycle lane. Entry on to the bridge is via a 682 foot (208m) access ramp from the Bahía span, and a 1,992 foot (607m) access ramp from the San Vicente span.
ECUAEX S.A., the authorized Putzmeister distributor in Quito, Ecuador, coordinated the equipment needs for placing concrete on this high-profile project. To meet the job's challenging requirements, ECUAEX chose two Putzmeister BSA 120-D trailer pumps to handle the bulk of the concrete work during bridge construction. The pumps set up in several unusual locations, on land as well as over water, pumping concrete at high pressures through delivery line stretched long distances, as well as pumping at high outputs for greater efficiency in accommodating many other large volume tasks on the bridge.
To assist the two larger BSA models, a Putzmeister Katt-Kreter® trailer pump, capable of pumping tough concrete jobs at outputs up to 50 yd3/hr (38m3/hr), showed its power and versatility by helping to pump concrete for the reinforced piles supporting the bridge. These piles, in turn, are supported by steel jetty piles, four feet (1.20m) in diameter and averaging 130 feet (40m) in length. The superstructure is supported by four seismic isolators in each of the piles.
The structure of the bridge was designed on the basis of pre-stressed and post-stressed reinforced concrete. The reinforced concrete elements were constructed on site, the pre-stressed beams were prefabricated about 180 miles away in Guayaquil and transported to the project and the post-stressed beams were prefabricated on the Bahía side of the bridge. The framework, including plugs, footings, columns and headers for the infrastructure, was also produced at the construction site on the Bahía side. Later, these frameworks were transported from the dock to the placement span by a crane.
Each of the bridge’s concrete slab spans consist of six beams, and of these, two are directly supported by seismic isolators. As each isolator weighs 1.5 tons, they were transported by barge and hoisted in place by crane. Four steel lifts kept each isolator elevated, leaving a minimum space of two inches (50mm) between its base and the upper part of the header.
Next, a Putzmeister Strobot 401E rotor/stator pump injected grout beneath each isolator. The Strobot model, specifically equipped to handle grout injection, was capable of pumping and spraying up to a 3/16-inch (5mm) grain size at variable outputs from zero to three gallons per minute (11 L/min). It additionally offered pump pressures up to 580 psi (40 bar) and a vibrating grid to filter out unwanted particles. To ensure a strength of 6,969 psi (490kg/cm2) was achieved, six grout samples for each isolator were taken. This construction method resulted in a bridge that is able to withstand strong earthquakes.
The post-stressed beams were built with a high-strength 5,974 psi (420kg/cm2) concrete. This type of concrete had a 10-inch (254mm) slump, achieved with high-range super plasticizing additives.
Tracks were developed to create the bottom of the beam, where the reinforcing steel and ducts were assembled. The formwork was made with metallic casings, and a crane was used to position them in place. Later, a pump and delivery line were needed for placing concrete in the forms.
For the post-stressing process, four cables passed through four ducts with a 2.75-inch (70mm) diameter. Once 80 percent of the strength was attained, they were post-stressed by hydraulic jacks until a total strength of 162 tons per cable was achieved. Then, each beam was transported and positioned above lifts to a height of 2.3 feet (0.70m) so that two Type T footings could later be soldered at each end. This provided a separation from the metal plates of six inches (150mm), through which passed the lower steel elements of the diaphragm. After the post-stressed beams were constructed, a crane loaded from one to three beams on a barge which transported them for placement against the two piles that functioned as their support.
Managing the Impossible
Initially, there was no logical way to place concrete in forms for structural components located at far distances. Therefore, a special concrete mix was needed that possessed a consistency and manageability that could be pumped long distances without plugging the delivery line.
To develop this type of concrete, Portland cement Type IP and aggregates from the mines of Quevedo and Santo Domingo located 100 miles away were used. In addition, super plasticizing additives and setting retardants were used to ensure consistency and workability for long-distance pumping. It became necessary to work with aggregates outside the province of Manabí because the aggregates from the mines near the project were presenting problems in their chemical composition, which made it impossible to achieve a pumpable concrete, even with the use of special additives.
Consequently, the design of a pumpable concrete with an eight-inch (200mm) slump included a combination of Pozzolanic Portland Type IP cement, ¾-inch crushed Quevedo gravel, washed Santo Domingo sand and the additives Rheobuild 716 and Polyheed® RI.
“As a result of the final mix design and the high performance Putzmeister pumps, it was possible to pump concrete the long distance of 2,789 feet (850m), from pile 6 to pile 24,” says Andrés Cruz of ECUAEX.
“In addition to a good concrete mix, it was important that we could count on a pump whose capabilities make long-distance pumping possible,” adds Cruz. “The BSA 120-D trailer pump had the important features we needed on this project, including Free Flow Hydraulics for a smooth output, a powerful 197 hp (147kW) engine and high pressures up to 1,030 psi (71 bar).”
More than Strong
The central span of the superstructure is constructed of post-stressed six-foot (1.85m) high and 121-foot (37m) long concrete beams. To construct 228 post-stressed beams in a short amount of time, it was necessary to strip the beam after 24 hours to reuse the formwork and subject them to maximum post-stressed forces in five days.
These demanding requirements in producing the beams, in turn, required producing a high-strength concrete. As a result, Portland Type I cement was fundamental in the mix, along with a low water-cement ratio that achieved a nine-inch slump (230mm). In addition, the additives selected were a high-range super plasticizer known as Glenium® and a viscosity modifier called Rheomac®. For the aggregates, Guayaquil #57 stone, ¾-inch Quevedo stone, Guayaquil homogenized sand and washed Santo Domingo sand were used.
The strengths developed for the bridge's structural elements did not present any problems over time, because from the very beginning a strict quality control was taken in the selection of materials and in the design of each type of concrete. Based on samples taken from the bridge's structural elements, the beams at three days reached compressive strengths greater than 100 percent.
Began in October 2007, the Bahía-San Vicente Bridge was completed three years later by a crew of 700 directly employed on the project, along with an estimated 1,500 contracted workers. The historical project finished on schedule by its targeted completion date of October 2010.
Putzmeister America, Inc. manufactures a complete line of truck-mounted concrete boom pumps, seperate placing booms, truck-mounted telescopic belt conveyors. ready mix trucks and trailer-mounted concrete pumps as well as mortar, grout, shotcrete, plaster and fireproofing pumps and mixers, industrial pumps, tunneling machinary and pipeline systems. Some of the industry's best known brands, such as Tellebelt, Thom-katt, and Tommy Gun are part of the Putzmeister America family. The company's workforce is dedicated to the hands-on customer support and advancing the industry in design and technical innovation.
Technology that puts you first
General Contractor: Ecuador Army Corps of Engineers
Ready Mix Producer: HORMICONCRETOS—Quito, Ecuador
Concrete Pumping Contractor: ECUAEX S.A.—Quito, Ecuador
Equipment: Putzmeister BSA 120-D trailer-mounted concrete pumps (2), Putzmeister Katt-Kreter® trailer-mounted concrete pump, and Putzmeister Strobot 401E rotor/stator pump