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Good Rideability Starts With Accurate Trimming

Wed September 02, 2009 - Midwest Edition
Construction Equipment Guide

Two total stations are used on the project — one controls the 9500 trimmer while the other one is used for grade accuracy checks.
Two total stations are used on the project — one controls the 9500 trimmer while the other one is used for grade accuracy checks.

The I-64 project in St. Louis, Mo., is unique in several aspects. It’s the first design/build project in the St. Louis area and it completely shuts down 4 mi. (6.4 km) of interstate while it’s being rebuilt. In total, 8 mi. (12.9 km) will be reconstructed, with the next half of the project completed in 2009.

The project is being built by a consortium called Gateway Contractors, which involves Granite Construction, Fred Weber and Millstone-Bangert. Millstone-Bangert is responsible for all of the mainline paving on the project and it is using a GOMACO paving train with a four-track GHP-2800 paver.

Project smoothness specifications require a reading of less than 30 on the zero-blanking band. Millstone-Bangert is consistently running between 10 and 12. Smoothness, according to Ron Dibler, Millstone-Bangert’s paving superintendent, begins with the base.

“Good ride is a process that begins from the ground up,” Dibler said. “You have to have good string, consistent mix and try to keep the paver moving with minimum stops. Most important though, is a good solid trimmed base to pave on and run the paver’s tracks.”

The grade for the I-64 project consists of 10 in. (25.4 cm) of 6 in. (15.2 cm) minus rock, capped with 2 in. (5.1 cm) of Type 5 rock. The top layer is trimmed to final, accurate grade with a GOMACO 9500 with an 18-ft. (5.5 m) trimming head.

On the first phase of the project, the company has trimmed 5 mi. (8 km) of 100-ft. (30.5 m) wide mainline, plus extra room for the track line. Each lane of highway is 25 ft. (7.6 m) wide, so two passes created a 36-ft. (11 m) wide trimmed area for pavement and trackline.

Millstone-Bangert uses the Leica system on its 9500 to eliminate the need for stringline.

“We have in-house surveyors who make our Leica project models and set our paving hubs,” Dibler said. “We’ve been running the system for four years now and we love it. We run two total stations on our trimming work and we keep them within 500 feet of the trimmer. We’ll set them up in the middle of a 1,000-foot trimming pass and use that total station for multiple passes.”

Production averages 15 to 16 ft. (4.6 to 4.9 m) per minute when trimming through 2 in. (5.1 cm) of material.

“Our Leica equipment is very accurate, user-friendly and great to operate,” Dibler said. “It helps us build a base that’s our first step in achieving smooth ride numbers.”

This story was reprinted from GOMACO World, Vol. 36, No. 3.

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