GOMACO World Index --- GOMACO World 30.3 - November 2002
It's a project of gargantuan proportions, the size of which is unheard of in most parts of the world. In Argentina, South America, a consortium of contractors is slipforming 143 miles (230 km) of four-lane highway.
Approximately 461,704 yd3 (353,000 m3) of concrete will be slipformed by the time the project is completed in March 2003. Nineteen new bridges will be built and 5,362,598 yd3 (4,100,000 m3) of earth will be removed or reshaped in the process.
The official name of the project is the Autopista Nacional Nro. 7 (Route 7) Provincia de San Luis. It is a major roadway running across the country of Argentina through the San Luis, Cordoba and Mendoza provinces connecting Buenos Aires to the Andes. Route 7 is also the main connection to roads that lead to Brazil and Chile.
The project entails replacing the old two-lane Route 7 with a new four-lane roadway, two lanes traveling in each direction. The two-lane roads are each 24 feet (7.3 m) wide and 8.27 inches (210 mm) thick.
The consortium, including Alquimac S.R.L., Green S.A., and Rovella Carranza S.A. UTE (Unión Transitoria de Empresas), was new to slipform paving. To help manage a project of this size, the work was divided into four sections, each approximately 37 miles (60 km). The concrete paving is managed separately by a chief paving engineer.
One engineer or sector chief is responsible for the work, completed in his section. Several departments including programming and control, design and technical, labor and subcontracts and administration operate in each section.
When it was time to purchase their paving equipment, the consortium turned to GOMACO and their distributor SAMIT in Buenos Aires for assistance.
Work on the project officially began in May 2001. GOMACO equipment wasn't involved until later when it was time to prepare the subbase. The new roadway is slipformed on a soil-cement base 26 feet (8 m) wide and 4.92 inches (125 mm) thick.
"The construction is done in two fronts using reclaimers and trucks with metered cement discharge," Engineer Leon Zakalik, project manager, said. "Then we bring in our two GOMACO 9500 trimmers for final trimming. This way we obtain a surface with minimum deformation allowing us to control the pavement thickness and facilitate paver movement."
Once the grade is prepared, paving can begin and the consortium's GHP-2800 with IDBI is put to work. Concrete is supplied by a portable batch plant with a capacity of 392 yd3 (300 m3) per hour.
Seven different plant locations will be used to minimize the transport distance. The plant is never more than 11 miles (18 km) away from the paving site.
The concrete mix has an average slump of 1.18 inches (30 mm) plus or minus 0.39 inches (10 mm). Maximum size of the aggregate is 1.5 inches (38 mm) with a cement ratio of 590 lbs/yd3 (350 kg/m3).
"We're also using additives for air incorporation and plastification to diminish water and facilitate the dump truck's discharge," Zakalik explained.
Rear tandem-axle dump trucks supply the concrete to the site. Anywhere from nine to 24 trucks are used to transport the mix, depending on the distance of the batch plant. Each truck carries a 12 yd3 (9 m3) load.
"A major challenge of this project was simply training the personnel on the new equipment," Zakalik said. "GOMACO personnel and local technicians from SAMIT visited our site and were available to answer our questions and show us how to adjust the equipment."
The GHP-2800 with IDBI is paving 24 feet (7.3 m) wide and 8.27 inches (210 mm) thick. The IDBI inserts 24 bars for the transverse joint every 14.8 feet (4.5 m).
The bars are one inch (25 mm) in diameter and 17.7 inches (450 mm) long. They are placed six inches (150 mm) in from the outside edges of the slab and 11.8 inches (300 mm) apart across the length of the joint.
"We decided to purchase the IDBI because of the great length of the project and the daily production required to comply with the job schedule," Zakalik said. "Other considerations were to diminish paver stops to help us obtain the smoothness requirements."
A rear-mounted center bar inserter shoots a 0.5 inch (12 mm) diameter, 27.6 inch (700 mm) bar into the slab every 29.5 inches (750 mm) for the center joint.
All of the bar insertions for both the transverse and center joint are controlled by the IDBI's computer.
"The learning curve with the IDBI was short," Zakalik said. "The IDBI has given us an important level of confidence."
An AutoFloat® behind the GHP-2800 is part of the finishing process. A burlap drag is then applied and a T/C-400 texture/cure machine sprays a resin compound on the slab as part of the curing process.
Production for the first-time slipformers has been outstanding. As part of the project requirements, the consortium has to have an average production of 3281 feet (1000 m) per day. They had already exceeded that average in the first weeks of paving.
In the beginning, their average production was 3937 feet (1200 m). Before long, they broke the mile per day barrier when their peak production in an average 11-hour day was 5912 feet (1802 m). They have had several days of production exceeding the mile mark since then.
They're not just paving for speed either. The consortium has tight rideability requirements that have to be met on the project.
The project requires a smoothness reading of seven inches per mile (180 mm/km) as measured by a Bureau of Public Roads (BPR) roughometer. The BPR roughometer measures the road's "Dynamic Accumulated Roughness" or the vehicular response to pavement roughness.
Measurements are taken in both lanes of the newly paved roadway. The consortium's rideability is under the smoothness specification averaging only six inches per mile (160 mm/km).
"Two factors allow us to achieve high production and maintain quality: a quality mix and limited paver stops," Zakalik said. "You have to have a constant, quality mix, especially with the slump. It is very important to have quality control over the mix. We also try to reduce paver stops. We vary the speed of advance according to the supply of concrete."
"We think production is very good, but we feel we haven't yet obtained the maximum possible," Engineer Carlos Roman, project manager, said. "We have exceeded our expectations and the reliability of the equipment is very high."
The consortium is now in its fifth month of paving. They have already completed approximately 106 miles (170 km) of pavement and used 341,000 yd3 of (260,714 m3) concrete.
They continue to maintain their high production figures with a superior rideability.