Pave the way

by Clair David Urbain

Vee-Jay Cement Contracting Co., Inc. uses 3-D screeding to achieve complex slopes, yet maintain concrete flatness on a variety of jobs at the Lambert St. Louis International Airport.

The Lambert St Louis International Airport is undergoing a $1.109 billion metamorphosis. More than 1,500 acres of developed property has been purchased, and the airport authority is adding another runway that will increase its size and capacity by almost 50 percent. The changes will allow planes to land simultaneously in all types of weather.

To make room for the new runway, almost 2,000 residences and 70 businesses were purchased and nine major roads in the area are being rerouted. One cemetery was totally relocated and enough soil to fill in Busch Stadium three times over – 8 million cubic yards – will be moved using state-of-the-art earthmoving equipment that almost eliminates the need for traditional surveyor’s stakes.

The first highway tunnel built in Missouri will move traffic on Lindbergh Avenue underneath the new runway, and the road reconfiguration will straighten many roads, improving capacity and highway safety.

New roads, new construction methods
With the area’s highway infrastructure getting a big makeover, the Missouri Department of Transportation (MODOT) has set some high standards to assure the new roads will drain well, offer a smooth ride and last a long time.

“MODOT now requires very flat road work, holding tolerance to 1/8" in 10' for non-profilograph pavement. Their thinking is with a smoother road and fewer bumps, there will be less shock force as traffic goes over the road,” says David Barnes, who handles safety, quality control and mix designs at the St. Louis-based Vee-Jay Cement Contracting Co., Inc.

Vee-Jay has several subcontracts on the airport project. In 2003, the contractor was involved with four major jobs taking place at the same time. With heavy rains last spring, the work crews lost about 40 days of work time. “But the completion dates didn’t change. You can’t make up for that much lost time, but we have managed to stay close to schedule,” he says.

To meet the demands of the tighter specifications and timeframes, Barnes says the company has taken a next-generation strategy with equipment, and the strategy is working.

The work Vee-Jay is doing at Boeing’s new Phantom Works plane assembly facility requires even tighter tolerances than other jobs. The FAA specifications require a straight-edge test of 1/8" in 10' in all directions on the apron.

“We are pouring all of the concrete outside of the assembly hangers as well as the paint booths and hush houses, where assembled airplanes are strapped down and taken up to flying speed for testing before they are commissioned to fly. FAA spec requires the areas to have less than one percent of slope because it is so easy for the airplanes to roll. Still, the water must be able to drain off, which meant that many parts of the apron had to be sloped in two directions to get the proper run-off,” he says.

What first looked like a job that would require intensive forming for alternate paving lanes, the staff at Vee-Jay got together and explored some cutting-edge technology that could significantly cut labor and maintain accuracy.

“When we bid on jobs, especially difficult ones, our estimators call in labor foremen, screed operators and riding bosses to discuss the job to come up with a competitive bid. We have been seeing increasingly complex jobs with very tight specs. We researched the equipment out there, made our purchases based on the jobs we were bidding, and it has worked in our favor. We are able to complete more complex jobs faster than what we could have with our present equipment,” he says.

A 3-D view
In their research, Vee-Jay employees came upon the Somero S-240 laser screed. The unit has a 12'-wide head mounted to a 20' telescopic boom. The 12' head can produce an 8 to 10' strip.

The four-wheel, all-steer unit takes its orders from an on-board computer that gets its information from a Trimble AST-600 Series geodimeter that communicates with the prism placed on the right-hand mast on the screed. A sonic tracer mounted on the left-hand side of the screed uses sound waves to follow the edge of the poured concrete.

“We first plot the site, then work through the job layout on the laptop, setting up the slope needed across the job. The computer automatically figures what adjustments must be made to the screed to get the slope and flatness we need. It can be accurate to 3 mm. It will even warn you if you are about to make a mistake,” Barnes says.

Vee-Jay put the unit into service early this year. Somero reports it has a capacity of laying up to 50,000 sq. ft. of concrete a day.

“We have been using the unit on pours from 14,000 to 42,000 sq. ft. a day, depending on the job. When we first got the unit, we used it more as a regular screed, but as we became familiar with the unit, we use it more and more in its 3-D mode. This machine has opened up new avenues to do things we used to do by hand and it gives us a better quality product,” he says.

The screed has electro-hydraulic controls that direct its movements. The laptop computer takes the signals it receives from the geodimeter and translates them into height and directional changes needed to accomplish the flatness and the slope required. “The hydraulic control system is a continuous-flow spool so we get smooth, fluid speed changes. On our older screeds, speed changes are jerky and it shows up in the pour, but not with this unit,” Barnes says.

For long and relatively simple portions of a paving job, Vee-Jay crews use a Whiteman 52' super-screed to lay down concrete. “We then use the 3-D screed next to these long pours to fill in. The unit also has zero clearance, so we are able to get up next to buildings. It has reduced the amount of hand screeding we must do,” he says.

The unit effectively works in any pour shape, and it doesn’t matter if you change the direction of the pour in relation to your plotted area. “The 3-D system is very flexible. On the Boeing job, our crews laid down strips of concrete with a rolling screed, then came back and filled in the perimeter with the 3-D screed. The unit matches existing concrete easily because it takes its reading off the sonic tracer and matches it up with the geodimeter reading to produce the right slope while maintaining flatness,” he says.

Tricks of the trade
In a trained operator’s hands, the 3-D screeding unit is easy to operate, and with experience, Vee-Jay and their screed operators are pushing it to new limits. With experience under their belt, Vee-Jay offers a few insights:

Have good operators. “The key is to have good screed operators from the start and to put them through training. Somero requires a training class at their facility. Trainees should have some computer knowledge and be familiar with working with slopes,” Barnes says.

Take advantage of training. Somero mandates the three-day training session be taken at their location. According to its Web site, the away-from-work training gets operators away from normal work routines so they can concentrate on learning everything about the system. Near the end of the training, instructors “sabotage” the machine, giving the newly trained operators a chance to put what they have learned into practice.

When plotting, watch for information overload. “The more information you put into the 3-D Profiler System, the more accurate the pour. However, you can over-plot sites and give it too much information,” says Barnes.

Watch your speed. In most cases, the slower you go, the more precise the screeding will be.

“Every pour is a learning experience because every job is so different. Our operators are very helpful because they know what the machine can and can’t do.

“We have found the Trimble 600 ATS series geodimeter and Somero’s 3-D Profiler System are very user-friendly.

“The software lets you double-check cross-sections and concrete thicknesses before the pour begins. We can change it on the computer before we pour or right in the field. Most changes we make are on the Z axis (thickness) but we can also adjust the X and Y axes if there is a problem,” he says.

“This is a real simple program to use, but for a total screeding system that costs nearly $400,000, you need a lot of jobs for it. Larger contractors shouldn’t have a problem keeping a unit like this busy,” he concludes.

Published in the January/February 2004 issue of Contractor Tools and Supplies magazine.

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