Concrete brings longevity and strength in so many places
Written by Paul Hull
The concrete path that comes to my front door from the sidewalk showed a crack this summer, and I was annoyed, thinking such features of a residence should never fail. Then I realized that the little path had already lasted, untended, untreated, battered by months of snow and ice each year, for almost 60 years. It makes those wonder products of today with a 90-day warranty look rather pathetic, doesn’t it? It seems there is so much good concrete around us that we take little notice of it. We take concrete for granted because it lasts so well.
Smile, concrete contractors, and that includes those who want to expand their construction work by undertaking concrete contracts. We’ve heard so many stories of the lingering death of construction projects that to hear well-founded optimism in our industry is wonderful. As the summer of 2012 was ending, Terex Roadbuilding celebrated the 40th anniversary of its Advance Mixer truck by restarting its new truck assembly in response to improving market conditions. A large ready-mix concrete producer that operates in several Midwestern states has placed a substantial order for new trucks. “The initial order is for 65 trucks built with various axle configurations to meet market requirements and production starts in the fourth quarter of 2012,” advises David Rinas, director of sales and marketing for Terex Roadbuilding. “Several other loyal customers have begun reserving production slots for both the last quarter of 2012 and the first quarter of 2013.” Hiring has begun for new workers, and they will be producing a revamped front discharge mixer truck design. “We began the redesign with a comprehensive customer outreach program to identify and prioritize enhancements,” adds Rinas. The fourth quarter of 2012 sees full-scale truck production. “Ready mix concrete producers are operating with aging truck fleets, and repair costs are escalating to keep these older trucks on the road. Customers are at the beginning of a major fleet replacement cycle, which will require both new trucks and glider products.” The Terex glider program allows customers to upgrade existing trucks by recycling major components, such as the engine and transmission, rather than purchasing new trucks.
I’ll say this a few times in this article. Nothing in the concrete world gets done well without an efficient delivery of concrete to the correct site. Getting the right mix, the right slump, the right amount, at the right time, is the very base of concrete projects, and ready-mix trucks have always played a great part in getting that done.
People notice concrete when it is being placed on highways and streets but seldom know what the concrete is achieving for road users and taxpayers. When Interstate 70 in western Kansas needed treatment, the state wanted something to last longer than the previous treatment, asphalt that lasted five to seven years in different locations. The state chose a 6-inch bonded concrete overlay. There were 1.45 million square yards of it. Koss Construction milled out 6 inches on a stretch of just over 15 miles of four-lane interstate. Including the shoulders, the projects totaled 725,000 square yards and cost $20.1 million. That is the kind of project where everybody notices concrete.
Koss used a Guntert & Zimmerman S850 Quadra four-track paver to pave 30 feet wide, with excellent smoothness in the final result. The contractor averaged just 8.5 inches per mile on a zero blanking band. On every section of concrete pavement last year, Koss earned a smoothness incentive from the state. The overlay is sawed into panels that are 6 feet square; similar overlays have been most successful in Colorado, with 10 to 12 good years on heavily traveled roads. “Kansas expects to get 20 years from a 6-by-6-by-6 overlay,” comments Andrew Gisi, geotechnical engineer with the Kansas DOT. “There may be some panel replacement at midlife.” He adds that the road really needed reconstruction but the state could not afford that, so it chose to use the overlay.
“These pavers are easy to set up and easy to train people on,” says Robert Kennedy, quality control manager at Koss Construction. “We averaged about 1,800 square yards per hour, or maybe a little better.” Two belt placers spread concrete in front of the Gunter & Zimmerman S850 paver and that helped boost production because they could dump two trucks at once. Each Koss project last year had its own batch plant and, typically, 15 trucks hauled concrete to the site. Another advantage to the milling and concrete overlay process was that the contractor could correct roadway slopes and transitions into and out of curves. With so many asphalt treatments over 40 years, the slopes had lost accuracy. “We could go in there and pave back to the exact slope and correct all of those geometric issues,” adds Kennedy.
Airports are other sites where the public (peeping patiently from little plane windows) may notice concrete paving in progress, and airports offer their own challenges to the paving crews. Production is complicated by the many irregularly shaped pieces of pavement that must be done at the same time. For Dallas Love Field Airport, contractor MCM (with a local office in Irving, TX) had the contract to remove concrete, grade the subgrade and base, relocate the necessary utilities, and place almost 300,000 square yards of new concrete pavement. Most of it is 17-inch jointed plain concrete with no steel. A number of gates must remain open at the airport during the four years of construction, which is scheduled to finish in 2015. MCM bought a new Gunter & Zimmerman S850 slipform paver for this major project; it was fitted with a stringless control package from Leica Geosystems. “We have had some amazing results with that,” comments Luis Munilla, business operations manager for MCM in Texas. “Many of our pavements out here are right on plan grade, or within 1 one-hundredth of an inch. The results are just amazing. The stringless controls really help trucking and production.” One of the important aspects of airport paving is the pavement edge. “The edges are sharp and clean with the Guntert & Zimmerman S850,” reports Joe Roundtree, general superintendent for MCM’s Dallas Love Field Airport. “The paver also helps with placing small pieces because the tracks can turn 90 degrees under the paver at the end
of a run.”
The Awkward Parts of Paving
Photo: Gomaco Becco
Making a barrier of variable height went smoothly with Gomaco equipment.
More and more, contractors are discovering that smaller pavers like this one from MBW can get excellent results for curb-and-gutter work.
Concrete paving is not just a matter of slapping down some concrete at a certain depth and width, then walking away. The shoulders of the road are important, and also what is known as curb-and-gutter. What would be the condition of our streets and sidewalks, for instance, if the curbs and gutters were ruined? In some cities, they are! In some rural communities there are few curbs or gutters. That has prompted manufacturers to engineer and develop machines built especially for the placing of curbs and gutters. Those machines can vary from attachments for skid-steer loaders to make curbs and gutters for municipal streets to large units that can place barriers along highways. While the machines themselves are cleverly designed, there is still a large measure of skill required from the operators. All concrete work requires skill. When you are doing slipform paving (because it is so fast and accurate) the management of the grade must be right, the concrete mix must be right, the slump, the air entrainment and the placement of the stringline (or its equivalent if you have advanced to stringless work) must all be right. The machine operators and the crew who finish off the project must be skilled at their appointed tasks.
MBW makes smaller concrete slipform pavers and has them used successfully in more than 25 countries worldwide; the company has been making those pavers for almost 20 years now. The slipform process is the same as for bigger machines, with concrete fed into a hopper and vibrated with hydraulic vibrators, then slipped through a steel mold form. The quality of the finished product is comparable with that of larger pavers, but the initial cost is much less and the operational costs are lower. Operational costs? They would include the essential, but sometimes forgotten, costs of crew size, fuel efficiency, transportation, setup, cleanup, service, and spare parts. It’s difficult to state a paver’s productivity accurately unless you know the efficiency of the concrete delivery to the paving machine. No paver, however sophisticated and accurate, can pour concrete faster than it receives concrete from a transit mixer, and the production rates will also depend on the concrete mix, the grade, and the crew’s proficiency. Experienced crews with an MBW paver can produce 1,000 to 3,000 feet per day of curb and gutter, and 1,000 to 5,000 feet per day of curb over pavement.
All models in the MBW range have proved effective on stable soil or pavement, while the foam-filled tires help maintain consistent machine orientation, get rid of concerns about punctures on the job, and they give good traction. They can handle a 3-foot radius. The C101 slipforms vertical curb to 18 inches high by 12 inches wide. The C101-18 offers profiles to 18 inches high by 18 inches wide. The CG200 slipforms curb, curb and gutter, roll curb, sidewalk, and similar profiles to 18 inches high by 48 inches wide. A 24-inch hopper is the standard, with 30-, 36-, and 48-inch hoppers also available. The C101 is also easily converted to a C101-18 or CG200.
You can steer these smaller pavers in manual or automatic mode. Automatic control is based on a sensor/stringline system and is favored by many contractors on pours over soil. When the slipforming is for curb over pavement, manual control is often preferred. All MBW models can handle drop pours. That’s when you want to slipform curb on a lower grade while the paver runs on the higher grade of adjacent pavement. To do this successfully, you’ll need an optional drop adapter attachment.
More Demands for Precision and Accuracy
Some smaller concrete projects can require accuracy that is there, but not so obvious, on the largest placements. Gomaco is another global leader in concrete machinery and it’s not only for the long, broad highway projects where you have seen Gomaco in action. This company’s range of equipment is genuinely comprehensive and has been successful for years, slipforming highways, streets, airport runways, sidewalks, bridges, canals, recreational trails, parking lots, and curbs and barriers. One Gomaco project that grabbed my attention (and admiration) was a barrier wall of 26,000 feet on US Highway 169 in Tulsa, OK. This barrier was variable, not just a straight length all the same. The contractors were Becco Contractors Inc., who had already slipformed nearly half a million feet of barrier around Oklahoma, but this was their first variable barrier.
I tried to imagine achieving the required results without slipforming and asked myself how anybody had ever done that with the techniques of yesteryear. How long and expensive they must have been! The profiles of wall for this project included a 42-inch-tall safety barrier with continuous No. 5 rebar fed through the front of the barrier mold. The second profile was a variable height safety barrier slipformed over a continuous cage of steel reinforcing. Both walls were 9 inches wide across the top and 24 inches wide on the bottom. The contractors slipformed the wall on a new asphalt surface, within tight working conditions, surrounded by live traffic. Setting stringline and keeping it in place was a difficult challenge and the solution was for the contractors to make their own stringless system for the Gomaco Commander III by using three independent grade-averaging ski systems.
“We used two skis to operate the mold,” explains the Becco crew. “They were the length of the mold and attached directly to the right and left sides of the mold framework. They averaged the exact profile of the asphalt grade, specifically in and out of a superelevation and maintaining those elevations. The third averaging ski was built in two parts, with one attached to the left rear leg barrel extending to 10 feet back. The other part was attached to the left front leg barrel and extended 10 feet forward. They were connected with a common stringline and averaged a length of 50 feet. The left-side machine-control system traced this line, which controlled the top of the wall. The frame-mounted cross-slope sensor kept the top of the wall level. The steering sensors traced off square tubing that was laid on grade and aligned with a prepainted control line.” This invented-for-the-project stringless innovation worked well. Barrier slipforming production averaged between 900 and 1,200 feet per day; that depended, of course, on the wall design. The best production day saw 3,300 feet completed.
The concrete was a fly-ash mix with standard 57 stone. Slump averaged between 0.25 and 0.5 inches. Ready mix trucks carrying 10-cubic-yard loads delivered the concrete to the Gomaco Commander III. As an average, the trucks emptied their loads in 12 minutes onto the paver’s conveyor belt. Slump and delivery timing, those are important factors in all concrete work. The slump of the concrete is always critical. For all paving machines the best slump is consistent because too wet or too dry can be a serious problem. Concrete that is too wet tends to settle at the top and bulge at the sides once it has left the paver; that can slow down the paver. Concrete whose slump is too dry can cause a kind of honeycomb configuration as it leaves the paver and that will mean considerably more manual work to remove defects and finish the pavement well.
In a similar vein, J.D.Abrams LP (a Texas contractor with almost 50 years experience) had the opportunity to do two concrete projects. “One was barrier wall, and the other was side draft paving,” notes Brad Everett, vice president of operations for J.D.Abrams. “With Gomaco’s newest paver, the GP-2400, we are able to take on both of those with one machine.” For the Border Highway in El Paso, the company has been slipforming 10-foot-wide side-mounted shoulder. The scab-on shoulder is 11 inches thick and slipformed over single-mat steel reinforcing. The GP-2400 is not running on stringline for the scab-on shoulder. The contractor uses steer sensors that follow the edge of the existing slab and the paver slipforms locked to grade. “We’re very pleased with our GP-2400,” adds Everett. “Almost every job we’re on has an application for it, whether it’s a barrier, a shoulder, or concrete adjacent to a retaining wall. It has a lot of applications for us and we’re looking forward to giving it a lot more use.”
Concrete Without Machines
There are thousands of concrete projects completed without the help of machines: projects like sidewalk repairs, driveways, paths, and residential improvements. You don’t see many onsite mixers these days, as most contractors seem to rely on a concrete plant to supply the necessary mixtures. Onsite, portable cement mixers are still available and they work well for those smallest jobs a contractor undertakes. Many are powered electrically and some are attachments for standard construction machines like skid steer loaders. They certainly eliminate the backbreaking aspects of mixing concrete. In my teen years I mixed concrete with a shovel on a wooden board and anything that avoids that is a heaven-sent improvement. The machine used most often today is the ready-mix truck, which brings the right mix, with the right slump, at the right time. If you’ve asked your local ready-mix company to be at the job site at eight in the morning, make sure that job site is ready to accept the truck at eight in the morning. The preparations for even the smallest concrete jobs should be as careful and accurate as those for the longest highway. A website that has an enormous amount of useful information for those placing concrete in smaller jobs is ConcreteNetwork.com. There is so much useful information on it, it’s worth a read even by the experienced professional.
You’ll still see wooden forms used in many places. Metal forms are now simple to use and the speed you can gain with them may compensate for any extra cost. Forms are used to produce accurate and attractive curbs, foundations, walls, and steps. Steel forms (which are generally lighter than the equivalent in wood) can be straight, or flexible to design the curves you want. They are strong, reusable, and require fewer stakes than alternatives. On the straight, a steel form will require fewer stakes and they are easy to handle and position. There are special pieces for corners, and most users also use steel division plates for best results in, say, a stretch of sidewalk. The weight and strength of steel forms will, of course, depend on how thick your concrete will be. You can also use plastic forms, both straight and flexible. Plastic forms will last for years and have been used successfully for all kinds of concrete work (both straight and radius) like driveways, paths, and shapely patios at residential or commercial properties.
Rolling to Success
There are signs that the demand for concrete work is growing. That’s wonderful news for our industry after some lean years. When expanding services to offer concrete paving, the first piece of equipment contractors typically have in mind is the concrete slipform paver…often until they look at the price for a new paver. The initial price can easily be $400,000, depending on options and configurations. “Even the price of a low-hour used slipform paver can top $200,000,” says Dean Johnson, service manager for Terex Bid-Well. For less than the cost of some used slipform pavers, contractors can purchase a new automatic roller paver, which offers more flexibility and several advantages not available with slipform pavers. Aren’t those the pavers used exclusively for paving bridges? “Many contractors think initially of paving bridges when it comes to automatic roller pavers,” notes Larry Eben, district manager for Terex Roadbuilding. “The truth is, they pave virtually any concrete flatwork paving application and are just as effective at paving building slabs, parking lots, roads, highway, and airports as they are at paving bridges.” When considering an automatic roller paver for paving roads, Eben recommends that contractors consider carefully the type of paving opportunities available in their market to select the right design.
The Terex Bid-Well 5000 paver is an automatic roller paver designed and equipped specifically for roadwork. It is heavier than similar pavers designed for bridge work. (Roads can carry more than many bridges.) For about one third the cost of a new slipform paver, automatic roller pavers can pave slabs from 8 inches to 24 inches thick, while offering increased flexibility. Mid-range slipform pavers can pave roads from 12 feet to 34 feet wide; the Terex Bid-Well automatic roller paver offers maximum paving widths of 68 feet. The contractor can add or remove truss segments in hours, as opposed to days for traditional pavers. “The standard frame insert of the 5000 paver offers up to 12 feet of travel to each side of the paver, so contractors can change paving widths on the fly to handle additional lanes and flares,” advises Johnson.
For paving roadways, automatic roller pavers will be equipped with an internal vibration system, positioned in front of the paving augers to consolidate the concrete. Some pavers have dual alternating vibrators that allow for vibration right up to the edge of a concrete slab. The Terex Bid-Well 5000 includes the Rota-Vibe vibration system, which delivers up to 5,000 vpm over the roller’s 15.5 feet in length. “This helps to reconsolidate the top 2.5 inches of concrete to deliver a denser and more uniformly consolidated concrete surface,” explains Eben.
There are differences between a dual use automatic paver and one designed strictly for roadwork. The first is weight. Since the 4800 is designed first for paving bridge decks, it will be lighter, as contractors can’t put as much weight on a bridge. Standard engines will be lighter and components to the paving carriage will be smaller, to reduce weight. The paving rollers on a 5000 are 6 feet long contrasted with the 5-foot rollers on the 4800. Johnson recommends careful consideration of how many options are added to the paver to match application needs. Terex Bid-Well offers different engines, longer paving and Rota-Vibe rollers, and power leg raise/lower options for their customers. But keep in mind that a dual-purpose paver should not add too much weight with roadwork options, because the bridges won’t accept too much weight. Another difference is that a standard 4800 can be configured to pave up to 170 feet wide. One contractor had a job that required paving multiple bridges with only a few hundred feet of road in between. He used the same 4800 to pave both the roads and the bridges.
Roller pavers are not new. It is the understanding of their potential uses that makes them so attractive today, especially to contractors who are beginners in the concrete paving field. Isn’t it encouraging, too, that we can consider these new options seriously because the signs of improvement in our markets are so definite and promising? A large measure of contracting success in the next few years will be our ability to benefit from equipment available and our ability to understand what all the equipment, especially in a segment like concrete placement, can do for us. Tomorrow’s successful business cannot be the business-as-usual of yesterday. Concrete work offers us a tremendous opportunity to be so much better than yesterday.
Author Paul Hull writes on technology, finance, and construction safety.