All the public sees at the end is the concrete or asphalt. It looks good. It looks neat and travels well. “Today’s machines do such a good job,” say contractors (which they do!), and the public wonders how those contractors do the project so well.
Truthfully, it’s no wonder. The new road is a marvel of good design, products, workmanship, and cooperation. There are many parts and technologies that go into the making of a good road, or the rehabilitation of an old one. They all come together to make the good result. What do we start with? The ground…earth…soil. The route could be destined to cut across country that includes valleys, hills, slopes, and different soils. There’ll be some rocks here and there, some ups and downs that we certainly don’t want in the final appearance, so we need techniques and technologies that will eliminate the potential weaknesses in our new road. Roads are expensive, and we expect them to last several years. One of the greatest challenges for municipalities, counties, and states is that of deciding which sections of road can be built or bettered within the constraints of the budget.
The project starts without equipment or crews, before any grader, dozer, or asphalt paver arrives on the scene. The designers of the road will take into account all the facets of the terrain, all the practical challenges of cost and durability. Designers will have studied past roads, learned about mistakes that may have been made before, seen places where the roads are constantly being repaired, welcomed positive results from similar roads, and now they devise ways to give their clients (i.e., everybody in the community) the best results. Computers, of course, will help our designers achieve the accuracy they want; they should eliminate some mistakes made earlier through lack of accurate information.
Walk around my town’s streets in the early spring, and you’ll see what water can do to the best-planned, best-placed roads. Most of the water might have settled as ice, but it’s still water! One of the most important (and too often shrugged off) aspects of road building is the drainage. If you can build highways, streets, and rural roads so that the water runs off safely and without damage to the pavement itself, you will have achieved a success that is rare and invaluable. Some municipal public works professionals will tell you that poor drainage has caused more problems than anything else for their departments over the years. We can’t stop the rain, snow, or ice, so is there anything we can do?
First, we should do some homework. Look carefully at existing roads and see how the water is coaxed away from the surface. Look to see where there are drainage problems below the top surfaces. Why are there problems? Can they hurt? Yes, they can hurt travelers and taxpayers alike. Potholes are a good indication of water problems to come. If water stands in potholes, it will harm the sub-base of the road, often in an unseen way, until a major deterioration occurs that is obvious to everybody and his vehicle.
The water that needs to drain away from the road can be below the surface; that is why an investigation of the planned route is advisable. Culverts have proved their value over many years, but do remember that culverts need to be cleaned periodically, especially those that are not wide. Smaller culverts (some with only a few inches inside diameter) can be most efficient, but they must be kept clean and clear for the escaping water. This may sound too simple, but do make sure that water drained from your road goes into an area where it can be used beneficially-in a wooded area, among dense brush-but not into barren ground. Enough on drainage! There are whole books on the subject, so some more homework seems required. Even if you don’t want to research deeper, don’t forget the importance of good drainage to a new road, whether it’s an interstate or a little-used rural route.
Clearing the Route
Before bringing in equipment and products to make the sub-base of our roadway, we usually have to clear the path along which everything will run. If you saw many of the photos of graders and dozers in action from some years ago, you’d imagine that all ground was sandy soil and the machines could travel through it happily and without challenge. But we know that is not how the terrain for the new road starts. There will be different types of soil, different levels of wetness, and rocks (some of them a half-ton or more), so it is most likely that our first machines will be excavators, serving as plows to push the way through all obstructions. There are many excavators available, for purchase or rent, and we should have no trouble finding one that seems perfect for our road-building project. Check the brochures and specs (on the Internet, if you want the information immediately) of manufacturers like Liebherr, Komatsu, Caterpillar, Volvo, Kubota, Link-Belt, Hyundai, Case, Terex, Doosan, Hitachi, Sany, and John Deere. Some of those same manufacturers market graders and dozers that you should research. Probably the best advice I can give you today is to check back at an article by Carol Brzozowski in the September/October, 2013, issue of Grading & Excavation Contractor, titled, “Building with the Basics“. It’s excellent, worth reading again, and contains most helpful information.
If there are two aspects of ground preparation that have puzzled me for some years, they would be the apparent unwillingness of many contractors to bring new technologies to their aid and the poor attention that some operators give to new techniques. A few years ago I was talking with a crew working on preparations for road construction in North Dakota. (It turned out extremely well.) There were busy dozers, scrapers, graders, excavators, loaders, and trucks. “Do you have one worker who is better than all the others?” I asked the owner/supervisor of the contracting company. Without hesitation, he pointed to a young man operating a dozer. “He’s the best, and all the others agree.” “Why?” I asked, surprised that best would be the obvious youngest of the crew, not long out of high school. “He takes the trouble to find out how to run a machine before he starts it,” smiled the contractor. In the last couple of decades, there have been many new technologies to help run our earthmoving machines. The operator’s and contractor’s reaction to them should not be “Mmm, that’s nice,” as if they were discussing a new recipe for pizza. We must learn about new technologies, even if we think we can’t afford them this spring.
When you started work in construction, who would have tried fine-grading with a dozer? Leica SP Technology lets you do that, fast and accurately. It gives improved hydraulic control that allows faster (dozer) grading with impressive smoothness at high speeds. Dozers (especially with operators trained to succeed) can now undertake more grading jobs. A more appealing advantage is that contractors can finish projects with less heavy equipment onsite, and they have a good chance of finishing ahead of schedule and under budget. Leica’s technologies can improve stakeout accuracy and productivity; you could choose Builder or RedLine Power Tracker, and the PowerBlade group of systems will help earthmovers especially well. The PowerBlade systems start as simple ways to achieve good formation and subgrade leveling, while PowerGrade 2D and 3D systems for dozers, scrapers, and graders give a contractor ease of use, flexibility, and excellent accuracy at fast speeds. After your preparation work, paving contractors will use Leica Geosystems’ PaveSmart system, a 3D machine control system for mainline concrete pavers. For tens of thousands of customers worldwide, Leica has helped the efficiency of contractors in all areas of earthmoving and site preparation.
With Trimble’s GCS900 grade control system, the data collection helps people onsite to work together more efficiently. The latest version also supports single-point mapping that allows the operator to record most accurate point information from the blade, bucket, or drum focus position. Single-point mapping improves the ability to collect as-built information from the machine and complements the work done by grade checkers. That as-built information can be transferred back to the office over the wireless two-way data synchronization link, using Trimble’s Connected Site solutions in the GCS900 grade control system. The program’s remote switch hardware add-on that can be attached to the excavator joystick for point-and-shoot collection of data points. When its point collection button is pressed, the operator can collect, record, and map individual bucket positions.
From Topcon, a world leader in the machine control arena, we found the X62, another big step forward in excavator grade indication. The system includes four TS-1 360-degree tilt sensors used to measure angles between the cab, stick, boom, and bucket of an excavator. If you include Topcon’s optional LS-B10W laser receiver, you will have one of the most advanced laser indicate systems available. The X62 can create, cut, and check complex designs-from the cab. It can also work with an existing elevation reference or laser, with easy-to-see cut-and-fill indicators. This system will keep the grade checker out of the trench. It’s as simple as selecting your reference and entering a cut and/or slope depth. It’s a system that lets you cut multiple elevation and slopes continuously. Or you could use Topcon’s System Five. It is easy to learn for operators and easy to use, with a control box that is laptop programmable so you can update or revise the software in the field.
As new software and technologies are developed and marketed, it is the whole technique of achieving successful earthmoving that is advancing. The technologies mentioned are just some available. Yes, here I go again. You must do some homework. It will save you-earn you-bucketsful of dollars in future projects.
Helping the Earth Work for Our Benefit
Start with the ground, the earth on which we build everything, road or structure. In a stretch of, say, 5 miles there can be several different types of ground, and they must all carry the same road and the same speeding loads. One of the best technologies to have helped us in this respect is geosynthetics. There are several well known companies with expertise in geosynthetics, among them TenCate, NAUE America, Tensar International, and ACF Environmental. You’ll often see two types mentioned: geogrids and woven geotextiles. They are not the same thing. Both have helped road construction, but you cannot forecast the performance of geosynthetics simply by knowing the properties of the materials used. “There is no correlation between tensile strength and performance in a roadway stabilization application for geogrids,” explains Bryan Gee, product manager at Tensar for the company’s portfolio of products and systems, including those for roadways such as Tensar TriAx Geogrid and the Spectra System. “The only proven way to quantify geogrid performance is full-scale testing and monitoring of installed systems. In other words: performance data. Lots of it.” Gee mentions another important aspect of pavement performance: good drainage. “It is critical that engineers and contractors understand fully how water will be managed in and around the road. Getting water out of the pavement section and away from the road as efficiently and effectively as possible has huge benefits for the road’s long-term performance.”
The Tensar Spectra System uses a mechanically stabilized layer consisting of aggregate stabilized by TriAx Geogrid to form a more robust and stiffer structure. It has been used successfully by municipal and county agencies, by state departments of transportation, and by private owners on projects that range from parking lots and rural roads with low volume and light loads, to high-volume highways and heavy-duty industrial pavements. The Federal Highway Administration and the American Recovery and Reinvestment Act have both approved projects incorporating the Tensar Spectra System. The system can save the contractor and funding authority money, because it will simplify and speed construction, avoid over-excavation, reduce undercut, disposal, and backfill. It has been shown to reduce labor and equipment costs. Perhaps most practical is the evidence that Tensar’s geogrid system will reduce the thickness of the components of the pavement (including the aggregate base course, asphalt, and granular sub-base). With better durability, the whole project will need less maintenance and offer a better life for the owners. As with all construction jobs, the work must be done correctly, with no shortcuts or neglect just to save an hour or two.
Building Up the Base
Like the ingredients of a tasty cake, gravel has several mixtures to suit particular requirements. Size is important and probably specified by the future owners of the road. For some sub-bases, the material may be 1.5 inches to 3 inches, but the mixture of gravels for the base nearest the final surface (the concrete or asphalt) is usually three-quarters of an inch, three-eighths of an inch, or less than one-eighth of an inch. The larger particles of gravel knock together in compaction, and the smaller sizes fill the gaps, so that you end up with a dense layer that is a solid foundation for the road. A good, compacted base will keep out water if you have a crown that encourages the water to run away sideways. This part of the road is most important for its durability. The gravel for a good road base can come from various rocks. Often, you will find that local rocks (such as basalt and limestone) are hard and durable enough. That’s the key: The gravel rocks must be hard and durable.
Good compaction is essential to good results. Soil compactors, usually with padfoot or smooth drums (some with smooth drums to which you can attach padfoot covers), are not new machines. The technologies that have made compaction so much more efficient than it was 20 years ago are most impressive. Ask the manufacturers about the features and benefits of their compactors. These machines can almost tell if they have reached the desired and demanded density without relying on the experience of the operator to know. Some operators who say they can easily do the required compaction in 12 passes would be surprised to learn that they can do it in two. Today’s intelligent compactors will save time more than you could imagine. Some manufacturers you could contact are Volvo, Case, Hamm, Bomag, Dynapac, Terex, Caterpillar, and Sakai. Most of them provide compaction machines for those final parts of the road, too. For strong, solid bases, vibratory soil compactors with smooth drums have proved their worth when dealing with semi-cohesive and granular materials. When the material is cohesive or semi-cohesive, padfoot compactors are favored. Some compactors (like the Volvo SD200) offer dual/variable frequency and dual amplitude capability to match vibration frequency to the natural frequency of the material for the best compaction. A minimum number of passes is the goal of these soil compactors, and that is achieved by an efficient power-to-weight ratio and high dynamic force.
This would be a good time to remind you that recycled materials can make good aggregate for road sub-bases. Aggregate comprises hard fragments of inert mineral materials, such as gravel, sand, crushed stone, slag, and rock dust, and there could be supplies of aggregate in the inert solid waste found everywhere-concrete, asphalt, bricks, and other rubble. Much recycled aggregate will come from other road projects, where there has been rehabilitation or even maintenance of existing roads. It would not be too difficult to have a portable crushing plant at or near the new road project site, to accept loads of concrete and other demolition chunks for grinding down to levels acceptable for sub-base work. That sub-base is not as strong as the base above it (and immediately below the asphalt or concrete top), so it can receive materials like sand, clay, and silt.
Everything I’ve mentioned so far tends to be for road projects that start from the ground itself, but some new roads and rehabilitation start with the milling of existing pavements. This is another area where today’s capabilities have truly progressed from those of yesterday. I’m thinking especially of the accuracy of today’s milling machines. The advances made in the design and performance of milling machines have contributed enormously to the efficiency of resurfacing. Milling used to be a job from which many contractors would shy away. Today’s milling machines have remedied that. Some communities have used fine milling to shape up their roads and streets to remove rutting and areas where asphalt has been shoved by traffic (at busy intersections, for example). Fine milling has been particularly useful when done to prepare for thin overlays.
You have a road base (often called a binder course) and a surface course with almost all asphalt projects, with the binder taking the load and the surface course sealing the top and providing the needed friction for the traffic. The binder mix will have larger aggregate, while the surface mix is thinner, with smaller aggregate, some of it less than a half-inch in size. When you mill for such an overlay, you don’t want a drum with a spacing that will yield peaks and valleys; that would not allow a smooth asphalt surface. Mill with a finer texture drum (like those from Wirtgen) and those peaks and valleys could be half the size, with no negative effect on the top layer at the surface.
The objective of the milling is to produce a pavement surface that is true to line, grade, and cross-section, while maintaining a uniform surface texture. The milling portion is critical because any flaws will compromise the finished surface of the project. As the existing pavement is removed, close attention must be paid to surface pattern, cut depth, grade/slope controls, tooth wear, and ground speed of the machine. “Smooth paving can’t occur without smooth milling,” affirms Kyle Hammon, technical marketing coordinator at Roadtec. “When milling at depths of 1 to 2 inches, the double hit Roadrunner cutter drums from Roadtec have produced excellent surface patterns at high ground speeds. The Roadrunner drums are laced in a way that increases the longitudinal smoothness of the milled surface with fewer teeth than traditional micro drums. Surfaces milled at 1-inch depths with Roadrunner cutter drums have passed the ASTM 965-96 Sand Test at a speed of 100 feet per minute. The ASTM 965-96 is a common quality specification for smoothness of a milled surface.”
The preparation for the concrete or asphalt is critical to the project’s final result, including its durability. As you research the techniques and companies involved, you’ll probably find what I have found. Some of the companies that are directly involved in many aspects of road building, from ground to finished surface, offer equipment for most of the necessary stages. Without prejudice, let me mention the interesting offerings of Volvo, Caterpillar, the Wirtgen Group, Roadtec, Dynapac, the Fayat Group, John Deere, Leica, Trimble, and Topcon.
