When and Where Concrete Should Be Used
When it comes to paving, “there is a place for asphalt and a place for concrete,” notes Bill Davenport, vice president of communications for the American Concrete Pavement Association.
“Concrete is indicated any time the owner wants durability and strength and other properties like sustainability and resiliency.”
Industry experts say that while using concrete as paving material can cost more in the short term, its resiliency provides long-term benefits.
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Stephen Bullock, vice president of sales and marketing for Power Curbers and Power Pavers—manufacturers of concrete paving equipment—says the decision to use concrete or asphalt typically lies within transportation departments or engineers’ specifications.
“As far as the overall picture of asphalt versus concrete, we would point toward life-cycle costs that concrete—although a little more expensive, initially—typically lasts two to four times longer than asphalt,” he says.
Michael Evangelista, owner of E2 Systems, notes that a life-cycle cost analysis “is always a good way to start when trying to determine if you should use concrete or asphalt for a pavement solution.”
Traffic count, traffic loads, soil conditions, and environment are factors affecting the analysis, he adds.
“The more traffic and the heavier the loads, the more likely you will want to specify concrete,” says Evangelista. “Sandy, gravelly soils with better drainage quality may allow for longer-lasting asphalt than clay type soils where concrete would be the preferred material.”
Concrete is the optimal choice for a more permanent structure with a longer lifespan than asphalt, concurs Mark Rinehart, director of sales and marketing for Cemen Tech.
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“With asphalt, you need to go back and maintain it and re-pave over the surface every couple of years,” adds Rinehart.
Larry Eben, regional sales manager for Terex Bid-Well, concurs that life-cycle costs—along with load ratings—underscore the determination on paving with concrete or asphalt comes down to life-cycle costs and load ratings.
“Project owners will look at the cost to maintain over a period of time—20, 30, 40, or more years—and make a financial determination as to whether concrete or asphalt is more economical,” says Eben.
“If a road faces high loads and heavy truck traffic, concrete will most often be the more economical solution,” he adds. “Also, as more public-private partnerships are formed and the contractor has the responsibility to maintain the road for a
set period of years, the longer the maintenance contract, the more likely the selection will be concrete over asphalt.”
Credit: American Concrete Pavement Association
Workers use GPS stations for accurate paving.
In areas such as the Midwest, for example, heavy truck traffic can encounter harsh roadway conditions during snowstorms, points out Rinehart, adding that the roads are also traversed by those driving salt trucks and snow plows.
“That’s the ideal world for concrete because it can withstand that abuse because of the weather and how the roads need to be treated,” he adds. “You see more asphalt in the South in the warmer climates than up in the Midwest.”
Resiliency is currently uppermost on the priority list for many in the industry because of weather events such as hurricanes that strike the East and Gulf coasts, notes Davenport.
“I grew up in a flood-prone area in south Texas, and as a kid, I can remember whole sections of asphalt pavement—20 to 25 feet long by two or three feet wide—being washed off of city streets and deposited up into people’s yards,” says Davenport.
“It was a real mess, and you can imagine with all of these very terrible hurricanes and tropical storms we’re experiencing, resiliency is an increasingly important issue. I’ve seen it happen where the asphalt has become unbonded and sections are being pulled up. It may have been a weak bond on the surface layer.”
In executing concrete paving, Eben notes that before paving and selecting the right paver for the application, a contractor must properly prepare the base material.
“The contractor must prepare the subgrade according to specifications and must have the fine-grade trimmer set to the proper grade,” he says. “Otherwise, concrete yields will increase, which increases the amount and cost of concrete and negatively impacts the bottom line.”
The next step—mixed design—is often overlooked, says Eben.
“Regardless of what material you are paving with, you have to have the proper mix design for the vehicle traffic loads over the life cycle of the road,” he says. “Do you have the right type and content of aggregate? If you target more flexural strength, loading is sacrificed, and vice versa. The proper mix will give you strength and durability plus workability at the right cost.”
Depending on the machine and technology being used, a contractor then sets up the Total Station (GPS) information and the string line or form work for the paver. It must be set to grade according to the paver type, adds Eben.
“Finally, there are a number of paving options, including slipform pavers and Automatic Roller Pavers like Terex Bid-Well pavers,” he adds. “Due to their design, slipform pavers are fairly inflexible when it comes to paving width changes and work most economically in long, straight pours that do not vary in width.
“If you have to make a width change, the paver is often down several hours to a couple of days to make a width change, sacrificing paving days from the schedule.”
Automatic Roller Pavers such as the Terex Bid-Well 2450, 3600, 4800, 5000, and 6500 pavers are designed with a flexible frame aimed to provide cost efficiencies and quick setup.
It also “delivers variable width changes on the fly as well as the ability to quickly make crown changes at any hinge-point on the frame,” notes Eben.
“Recently, a paving contractor in Montana used the Terex Bid-Well 6500 paver to pave in a single pour a section of road that went from a 38-foot width at one end to a 12-foot width at the other,” he points out. “This type of width change is not possible with a slipform paver, and the pour would have had to have been segmented into multiple pours for slipform paving, which is not practical.”
Davenport notes that asphalt is typically placed in two lifts and that the second half of the asphalt—called the wearing course or driving course—is what can de-bond and lift away from unstable tree roots pulling up on it or the “sheer force” of flood waters that penetrate the first layer and de-bond the asphalt.
Pervious or permeable concrete is catching on in some parts of the county, notes Evangelista.
“It is great for low-volume traffic and parking lots,” he says. “Mix designs combining slag cement, fly ash, and cement make for some very durable and long-lasting concrete.”
Permeable concrete is becoming a favored choice for areas like parking lots, and while it can be flooded, it mitigates some of the flooding, says Davenport.
“It does a great job of mitigating some of the stress of wastewater management in terms of easing the stress on retention and detention ponds,” he adds.
Davenport says his organization has taken note of some asphalt contractors transitioning to the use of concrete. Some of those transitions are simple and easy, he adds.
Davenport references a three-level pyramid of concrete-paving applications.
The easiest level is when asphalt-paving contractors are starting to pave with roller-compacted concrete or RCC.
“Roller-compacted concrete has limited uses, but where it can be used, it is used very successfully,” he adds.
Davenport points out that RCC utilizes technology similar to asphalt paving.
“You place the roller-compacted concrete and then you go over it with a vibratory roller or a compaction roller pretty much like asphalt,” he says. “We consider RCC to be a third type of pavement because it draws a little bit from asphalt technology and a little bit from concrete technology.”
It is used for large parking areas such as those in distribution centers and for some city streets and roadways, he adds.
“It really doesn’t have much of an application for highways other than shoulders, but on a relatively smaller scale, lower-volume roadways and parking areas, it is ideal,” says Davenport.
He adds that its surface characteristic is “a little bit different and rougher-looking than concrete pavement and when the owner decides to use RCC, it’s with the understanding that it may not be quite as aesthetically pleasing as concrete pavement. But in terms of performance, it will outlast asphalt significantly. It could be doing the job for 30 or 40 years.”
Next on the pyramid of concrete paving is the use of a slipform paver for streets and roads, says Davenport.
New technology comes into play here.
“A lot of companies are going with 3D or stringless concrete paving, which is guided by lasers and total stations,” says Davenport. “Instead of the old way of putting down the string line or wire that the paver follows for many miles, it uses advanced digital technology to reduce labor and increase productivity.”
Many contractors start with that technology in areas such as streets, roads, curbs, and gutters, he says.
“They could be an asphalt contractor with asphalt equipment placing the road, but then they’ll use the concrete paving equipment to place curb and gutter,” says Davenport. “Once you’ve mastered that curb and gutter work or those low-volume roads, it’s an easier transition.”
At the top of the pyramid is mainline paving such as highways and airports.
“These very large-scale projects tend to be the most complex,” points out Davenport. “It’s not uncommon for a contractor to use their own central mix plants to mix their own concrete very close to the job site. They will have truckers bring the concrete and deposit it in front of the paver.”
There is an investment in equipment that includes slipform paving equipment and accessories to cure and saw-cut the pavement.
Another investment is made in hiring subcontractors to saw-cut the concrete pavement.
“All concrete will crack, so by saw cutting joints into the concrete pavement, we’re controlling the crack, putting it where we want it to ensure the slabs won’t crack themselves organically,” says Davenport.
Consistency is the foundation for concrete paving, notes Evangelista.
The quality of the materials—the cement and additive technologies—is better, says Davenport.
“It all works together to produce a better-quality concrete, and in turn, a better pavement that lasts longer and performs better,” he adds.
Fly ash and fabric interlayers help increase durability, says Davenport.
“When contractors would put concrete pavement down, maybe they would put an asphalt base down, and that’s time-consuming and labor-intensive,” he says. “Now they can drop these fabrics down, pin the fabric, and put more paver over that concrete. We’re seeing a dramatic increase in productivity. At the same time, we’re seeing an increase in quality, too. We’re seeing it happen because of those materials, the value-added product, and the equipment that is used on the grades.”
Credit: E2 Systems
Concrete-paving operations at Tulsa International Airport
Eben concurs, adding that there has been much advancement in the type of additives used in concrete to meet different needs.
“For example, there are additives to improve load strength and flexural strength, as well as to accommodate heat or extremely cold temperatures,” he says. “Also, contractors have available to them additives that prevent rust from forming at the rebar and beams, as well as accelerator additives to quickly reach compressive strength.”
“You must have a uniform grade condition, a subgrade with uniform density, and elevation for a uniform thickness of the pavement. Concrete must have a uniform and consistent slump and a steady flow of material to keep the paving machine at a steady pace,” he adds.
Technological advancements in equipment are helping to make operators’ jobs easier when utilizing concrete.
From a management point of view, the use of the newer technology offers a competitive advantage in that it allows managers to know what their drivers are doing “so they know exactly where the concrete is poured and how much, and allows them to benefit from a scheduling perspective so if someone calls in and needs concrete from somewhere else, they’re aware of what’s going on with their fleet,” says Rinehart. “It allows them to be more efficient, allows the equipment to be operated easier by the operator, and the opportunity for fewer mistakes.”
There have been many significant technological advances in concrete paving “that have made a sea change difference in the placement of concrete pavement,” dating back to 1948 when concrete was placed by hand, notes Davenport.
“It was deposited by a cement mixer that would be out on the grade. But in 1948, the first slipform paving equipment came along, allowing contractors to eliminate rails that were made with metal and wood,” he adds. “They would use this equipment, which actually had tires on it, and placed the concrete pavement.”
Now, contractors are using 3D technology, notes Davenport.
“Staking used to take a great deal of time,” he says. “Now, surveyors can survey the grade and the survey data can be entered into a system. The equipment—which moves up, down, and left and right—will adjust automatically to follow the terrain.”
That results in “exceptionally smooth” concrete pavement, says Davenport, adding that “we talk about smooth as the absence of rough—it’s a smooth ride for motorists.”
The throughput of the application is faster and more efficient, notes Davenport.
“There is a lot of development that has gone into the machine and the digital equipment which has come on stream in the last 10 years,” he says. “There are special devices used to test and validate the quality of concrete pavement.”
Case in point is the testing equipment used to locate the steel dowels in concrete pavement.
“The testing equipment is relatively new and they keep improving it so it can locate where the dowels are to make sure they’re being placed properly,” says Davenport.
Davenport notes that the transition to new technologies in concrete paving has taken a leap in the last 5 to 7 years.
“The machines are made to last,” he says. “Some of the 3D equipment can be retrofitted to 30- or 40-year-old paving equipment.”
For some contractors, investing in the new technology is “a little bit like suspending disbelief,” points out Davenport. “You have to be able to embrace the fact that a machine can tell you what you need to know without relying on cables to guide your machine along.”
A company also needs engineers to load survey data into a system and work with the data sets to produce quality pavements, he adds.
Investing in the new technology offers a competitive edge in that it increases throughput and quality, says Davenport.
As for new technology, “the current buzz is related to GPS technology,” says Bullock, adding that the ability to work with GPS systems has become increasingly popular with contractors seeking to eliminate labor costs in setting up string lines.
GPS is being used for slipform paving, notes Eben.
Evangelista concurs that concrete equipment has become very technically driven, adding that there are GPS paving machines with “very sophisticated directional systems. One simplified tool for placing concrete is the Portable Modular Conveyor material placer.”
It is designed as a cost-effective way for efficiently placing concrete and other materials. It attaches to most front-end wheel loaders equipped to accept attachments and with third-valve control.
The conveyor belt operates with loader hydraulic controls and is powered by a wheel loader. It is designed to place 300 cubic yards of concrete per hour.
Cemen Tech recently released a new concrete mixer integrating a touchscreen in its C Series mobile concrete mixers.
“With the touch of one button, operators can begin pouring concrete that they need,” says Rinehart. “It records all of the information, telling the operator exactly how much of all of the ingredients were dispensed during that pour, and gets that information back to the office via telematics so they can see how operators are doing out in the field, how much concrete they’re pouring, and how much material is left on the truck.
“Ultimately, the project owner can see exactly what is being dispensed. They get a bill that shows everything that was delivered. There’s no guesswork such as, ‘Did I get two yards or four yards?’ All of that information is provided with today’s technology.”
The mixer also has GPS onboard, enabling end-users to identify the truck’s precise location on the job site.
While there is still a learning curve in the industry when it comes to “understanding what your equipment is doing in the field, there are some contractors who have fully embraced the technology and have it on every piece of equipment, whether it’s paving equipment, construction, or excavation equipment,” says Rinehart.
Rinehart explains that “there is some room for additional growth and additional products in that offering to make it easier for contractors to understand the information coming from their machines. That’s been the hang-up at this point. Contractors don’t have time to study and analyze all of this data, and there need to be better solutions to provide them the recommendations on what to do from the use of that data.”
An alternative to slipform pavers is an automatic roller paver, such as those offered by Terex Bid-Well.
They can be used to pave any concrete flatwork paving application, including building slabs, parking lots, roads, highways, airports, and bridge decks, notes Eben.
Contractors strictly doing roadwork would do well to choose the Terex Bid-Well 5000 or the 6500 paver for their heavier design and ability to pave slabs from 8 to 32 inches (203 to 812 millimeters) thick, with paving widths of 68 feet (20.7 meters), he says.
Their standard frame insert offers up to 12 feet (3.7 meters) of travel to each side of the paver, enabling contractors to change paving widths on the fly, notes Dean Johnson, Terex Bid-Well service manager.
For contractors paving a mix of road and bridge work, Terex Bid-Well 2450, 3600, or 4800 pavers are viable options. Truss segments can be removed or added for significant width changes, while the paver offers up to 15 feet (4.6 meters) of leg travel on either side for on-the-fly width changes.
A dual internal vibration system can be added to the paving carriage for concrete flatwork applications. Dual rollers provide initial surface finish. The pavers can be configured for maximum standard paving widths of 56 feet (17 meters) to 116 feet (35 meters) wide, depending on the model.
Crown points can be set at any frame hinge on automatic roller pavers to give contractors the option of paving multiple lanes simultaneously. There is a range of crown adjustments from +6% to -1.9%.
Terex Bid-Well recently introduced new remote control options for operating its pavers. “These new remote control units allow the operator to adjust critical machine functions from ground level while paving, offering more flexibility to quickly fine-tune paver settings,” says Eben.
Power Curbers & Power Pavers offers a variety of options, including curb machines, multi-purpose slipform machines, extruders, molds, slipform pavers, form pavers, placers, spreaders, textures, and curing machines.
In one of Power Pavers’ latest technological advances, “we have traditionally built two-track pavers and in spring 2017, we released our first series of four-track pavers, offering more versatility,” says Bullock.
The actual mixing of concrete, which was once done offsite and brought to the job site, is now being conducted onsite with mobile mixing units.
The mobile mixing plant meets the demand of projects such as tunnels, roads, and airport construction, as well as ready-mix concrete companies that also require mobile mixing plants to react to changing market demands in a timely manner, notes Liebherr spokesperson Klaus Eckert.
Cemen Tech manufactures volumetric concrete mixers enabling contractors to produce concrete onsite.
“Our technology is a batch plant on wheels,” notes Rinehart. “It allows contractors to pour whatever amount of concrete wherever they want, whenever they want.”
The company offers a variety of configurations. Its stationary mixers are usually set up indoors, typically in a pre-cast environment, to pour into forms to make culverts, grease traps, or ornamental concrete.
Mobile units are used on trucks, trailers, or equipment in the field, with pouring done on a job site.
“It can move to the next job site or be out delivering concrete to contractors throughout the day,” says Rinehart.
The company’s cement silos—which are available in both portable and stationary units—enable end-users to buy cement powder in bulk to reduce the total cost of concrete.
Volumetric mixing technology enables end-users to use what essentially operates as a batch plant and mixer in one unit. The mixer is designed to batch, measure, mix, and dispense from one unit to offer precise design mix and quantity.
The units are designed with weight distribution characteristics to maximize the payload, a dual auger cement for accurate delivery of cement powder, and a large hydraulic reservoir to provide continuous operation without overheating. A Pump Master auger ensures consistent homogenous mixing.
Liebherr recently unveiled its mobile concrete mixing plant Mobilmix 2.5, designed to offer flexible operation, easy transport, and setup within two days—advantageous at sites with limited concrete production times or other challenging projects.
The unit is equipped with a new generation of the twin shaft mixer. Innovations incorporated into the series for efficiency include electric motors, gears, hydraulics, mixer gates, central lubrication, and high-pressure cleaning systems placed close together.
For service work on the mixer, only one of the four sides requires access. Hose and cable paths have been shortened and simplified with the reduction of hoses, corners, or edges designed to reduce the cleaning effort.
Gears are equipped with a directed oil rinse to stressed bearing points and a radiator which forces air from the fan blades into the belt pulley. All screws on the wear tiles are accessible directly from the outside.
The newer version of the Mobilmix includes an increased output capacity from 10–110 cubic meters per hour.
A newer feature is a lowered mixer platform. The slight slope to the discharge hopper—as well as improved spatial conditions and accessibility to the mixer system—is designed to simplify cleaning.
The keyless security system on the mixer access hatch is designed to provide easy cleaning. A feed flap on the skip and dust filter systems have been integrated to provide maximum dust protection around the mixer platform.
The design of the skip with parallel-designed running surfaces and plastic rollers aims to ensure comfortable operation with minimum wear and tear. Galvanized assemblies and quality components are designed to improve durability.
The Mobilmix 2.5 plant and in-line silo can be assembled, and the electric connected, all in one day. Its basic elements are positioned on a supporting platform and transported as a whole on a flatbed truck.
A container with a control system is integrated into a module. The base unit with the mixer system, weighing system, and skip is lifted with a crane, unfolded, and bolted in working position. The control container offers optimal spatial conditions and is equipped with Liebherr’s Litronic-MPS microprocessor control system.
Two additional transportation units provide the in-line silo and support unit with dosing valves and weighing belt. Up to 140 cubic meters of aggregates can be stored in four or six chambers in the in-line silo. Feeding is accommodated through a wheeled loader.
On the second day of a job, the cement silos are set up and electrically connected. A maximum of six cement silos can be set up.
While there is a learning curve in using asphalt, Davenport points out that his association, as well as the National Concrete Pavement Technology Center in Ames, provides education.
All of the advancements in technique and technology can only take a contractor’s business further down the road, notes Eben.
“Advancements with practices and technology allow concrete paving to continue in more severe weather, giving the contractor more paving days in the year,” he says. “The Total Station systems for slipform paving have helped those contractors reduce labor and improve quality due to eliminating manmade or human error with setting string lines.”