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📅 Wed March 15, 2017 - Southeast Edition #6
By Giles Lambertson
Heavy highway pavement-making equipment has evolved in the last hundred years from primitive to awesome. Modern pavers, compactors, and millers (or cold planers) have turned the surfacing phase of road-building and reclamation into an efficient, productive work. And the evolution continues.
This is what a highway paving machine looked like at the turn of the 20th century: It stood just under six feet tall with a strong back, sturdy biceps and well-muscled legs. Asphalt or concrete was dumped on a prepared path and this machine, otherwise known as a laborer, raked the material, roughly flattening it out between pre-set forms, and then ran a wooden screed across the surface to smooth it.
The hardened roadway thus produced worked well enough. Before long, photos and newsreels of automobiles mired to their bumpers in rutted, muddy roads became something to laugh about instead of something for a traveler to endure.
Concrete road-paving started to mechanize in 1903 when Chester and Charles Foote, a pair of brothers living in New York State, took a concrete mixer of their own design and incorporated it into a steel-wheeled distribution machine. The “No. 3 Continuous Mixer” received concrete materials in front, mixed them in the middle, and discharged the mix from the rear where it was laboriously formed into a slab of pavement. The mixer then was pulled forward and another batch readied.
In 1905, this concrete paving rig got an engine of its own and, in 1918, crawlers or tracks were subbed for the wheels, giving the heavy machine some flotation as it moved along the prepared bed. In 1931, the company created a subsidiary manufacturing enterprise called Adnun Engineering, which produced the first self-propelled asphalt paver that didn't move on forms. Despite this innovation, Foote went out of existence in 1948 when it was acquired by Blaw-Knox Co.
In the 1920s, Jacob Blaw and Luther Knox had combined their manufacturing expertise in the Northeast U.S. In 1929, they bought a company that was making concrete finishers. This equipment, which was branded Ord, grew into a full line of Blaw-Knox form-riding concrete spreaders and asphalt finishers. Eventually, Blaw-Knox changed hands in corporate transactions and today is a brand name in the Volvo Construction Products portfolio.
Developing the paving equipment industry concurrently with Foote and Blaw-Knox were two Illinois mechanical engineers, Harry Barber and William Greene. In 1930, Barber invented an asphalt mixing and spreading machine that he believed held great promise. Shortly thereafter, the two asphalt functions were separated into asphalt production and asphalt paving equipment. In 1936, several features of the machine were patented, including a tamper that evenly dispersed material and a floating screed that smoothly finished it.
Thus protected by patents, Barber Greene engineers began to dominate the paving equipment market with their machines. Over the next several decades, they followed their early inventive solutions to asphalt paving by introducing the first paver on rubber crawlers, the first hydraulic paver, and the first hydrostatic paver.
An early asphalt paver that solidified Barber Greene's presence in the industry was Model 879. The crawler-mounted paver had features that become commonplace. Hot asphalt was dumped in the front hopper of the simply designed machine and conveyed to the rear where it was spread by a screw conveyor, tamped by a rapidly vibrating bar and finished by a screed. This machine and an upgraded model introduced a few years later became the industry standard for asphalt paving.
Like Blaw-Knox, Barber Greene was subsequently absorbed into larger companies. First, Astec (maker of the Roadtec line of pavers) acquired it and then Caterpillar did, the Barber Greene designs becoming the basis for the Cat line of asphalt pavers.
In 1949, concrete paving lost its forms. Three years earlier, an Iowa Highway Commission engineer and assistant lab chief, Jimmy Johnson, watched a demonstration of paving with concrete. He went away convinced that a more cement-rich concrete could be poured and vibrated into place under a moving paving machine and keep its shape with moveable forms. He and two other commission members began experiments to test his theorem.
Finally, when a bid to construct several miles of highway for the state was rejected, the commission decided to give their “slipform” apparatus a tryout. For the next several years, the new technology was successfully tried, producing generally acceptable but imperfect 10-foot-wide lanes not quite abutting one another. Finally, in 1955, an Iowa construction company manufactured its own version, the Quad City Paver, and the slipform industry was born. Within a few years, concrete pavement 40-feet-wide was being slipformed.
Among makers of slipforming concrete equipment was an Iowa company that soon emerged and would become dominant. An innovative construction contractor, Harold Godberson, started his company in 1938, expanded it in 1946, and in 1965 spun off and incorporated a mechanically inventive division that had created a double-oscillating screed concrete finisher. Thus was born GOMACO.
A continuing string of industry-changing machines followed from the company. Some of them included a cone drum finisher developed in the 1960s that eventually was upgraded to the familiar C-450 model, and an effective slipform curb and gutter machine, the GT 6000, introduced the next decade. A method of introducing dowel bars to a concrete slab was first employed by GOMACO in 1983, and a slipform paver capable of pouring 50-ft.-wide (15 m) airport runway slabs in 1984. Among the 1990s achievements was stringless paving using a laser guidance system to true the work. A patented “Smoothness Indicator” for surface readings of both wet and cured concrete and asphalt slabs came along in 2003 and digital controls in 2007.
Today, GOMACO manufactures more than 50 machines for concrete paving and related equipment. It is not alone. Other familiar concrete and asphalt paving brands include Roadtec, Cedarapids and Dynapac.
The Caterpillar AP1055E is a representative model of the industry in 2016. It is a 22-ton (19.9 t) asphalt paver 12 ft. (3.7 m) high and 22 ft. (6.7 m) long with a hopper capacity of 250 cu. ft. (7 cu m) of mix that the paver can spread into a slab ranging in width from 8 ft. to 26 ft. (2.4 to 7.9 m).
Powered by a 225-hp Cat engine, the AP1055E carries 90 gal. (340 L) of fuel, and features a ventilation system that draws asphalt fumes away from the operator, who sits on a moveable platform with an array of diagnostic screens and operational controls. The platform can swing out over the side of the machine for greater visibility below. The entire paver rides on a tracked undercarriage controlled by a hydrostatic system.
So the pavement industry continues to evolve — and the enabling machinery along with it. For example, roller-compacted concrete was used in Virginia last year for something besides parking lots. RCC is a cement mix laid with asphalt pavers and compacted with vibratory rollers. No reinforcement bars are incorporated and the process is faster and cheaper than either asphalt or concrete paving, yet smoothness is problematic so highway use is discouraged. But an RCC-asphalt combination is being considered to smooth out and advance the process — and a new line of equipment may result.
In the beginning was the horse, of course, or maybe oxen. These beasts pulled weighted cylinders to produce relatively smooth and firm roadways. But midway through the 19th century, horses were put out to pasture and steam-powered rollers were seen on the streets of New York. A leading builder was a British firm begun by an agricultural engineer, Thomas Aveling. He went from steam engine-powered plows, tractors and other farm implements to introducing in 1865 with his business partner the Aveling & Porter steamroller. The A&P roller became the market leader.
One of the virtues of the steamroller over horse-drawn ones was that it was heavy. Heavy is good when it comes to compaction. Beyond this elemental principle, the compaction industry expanded its understanding of the compaction process. Single-cylinder steam-powered rollers were employed to tighten the base of roadways and smoother-running two-cylinder engines introduced early in the 20th century to smoothly compact hot-mix surfaces. The Iroquois Macadam (Three-Wheel) Roller weighed 12 tons (10.9 t) and was powered by a double-cylinder steam-powered engine with a Massachusetts Standard boiler, the smokestack up front and three-quarters of its engine and operator area shielded from the sun by a canopy with canvas-rolldown sides.
Steam lost some cache when engines were introduced that operated on low-grade gasoline and kerosene. The Austin (of Austin-Western) rollers were advertised as “the future” of self-propelled compactors. After all, according to a 1914 construction publication article, “the roller will run from daylight to dark without stopping, if desired, and its economy in operating costs is so great that road builders figure they can do at least 25 percent more work each day with an Austin Roller at from 30 to 70 percent less cost, compared with any steam machine…” A photo of the Austin Two-Cylinder roller shows a remarkably streamlined, imposing machine — with an operator in suit and tie.
Besides switching from steam to kerosene to, eventually, diesel fuel, compactor machines evolved their technology of compacting and smoothing earth and pavement. Drums continued to produce finished smooth pavement, but rollers with projecting rows of “padfeet” proved effective in tightening substrate soils by driving thousands of punches into the earth. Static steel drum rollers that relied on tonnage to compress pavement have been augmented and, in some cases, replaced by pneumatic rollers and vibrating rollers.
Bopparder Maschinenbau-Gesellschaft mbH, more popularly known as Bomag, entered the market in 1957 in Germany when Karl Heinz Schwamborn developed an all-drum drive vibratory roller. Within five years, he was selling 7-ton double vibratory rollers. Today the company, having changed ownership several times, produces single- and tandem-drum vibratory rollers and pneumatic rollers, among other pieces of heavy equipment.
Bomag's BW190AD-4 AM is a state-of-the-art tandem roller, with a Tier III Deutz engine and hydrostatic drive, crab steering, two-amplitude-two-frequency individual-drum automatic vibration systems and pressurized water-spray outlets. The machine can travel fast enough (up to 7 mph) to require a speedometer on its dash.
The buzzword (or phrase) “Intelligent Compaction” summarizes the current state of construction rolling. It is modern technology applied to the work of packing down an optimum density either dirt or asphalt pavement. The technologies employed include a finely-tuned measurement system, computerized reporting, a Global Positioning System, and optional feedback controls for real-time adjustments.
The feedback controls analyze the response of paving material to the passing roller and determine if another pass is required. They adjust the force of the roller to the material beneath it. The analysis even determines when a segment of pavement is not responding to roller treatment and recommends against further compaction. Volvo's intelligent compaction feature a “with Direct Density” system actually analyzes density, instead of extrapolating the metric from stiffness calculations.
In short, roller operators have given all they need to know to produce best-quality pavement while burning less fuel. Today's compactors are light years from their deadweight predecessors.
Milling (Cold Planing)
Numerous reasons exist to chew up old asphalt pavement and spit it out into dump trucks. Some of the reasons are raveling, rutting, washboarding, “bleeding” and potholes—the conditions of stressed pavement that bring aggravation to drivers and new business to tire and shock absorber shops. Bad roads beg for chewing up and spitting out.
But the early 1970s oil embargo and sky-high (for the period) prices for oil products hastened the movement to mill up old asphalt pavement and recycle it. Cold planers were developed to strip entire stretches of highway of its upper layer of asphalt and prepare the remaining pavement for a new, smooth overlay. Sometimes all the asphalt in a stretch of roadway is removed and the segment entirely repaved. Today, recycling of asphalt is a principal, rather than auxiliary, reason for highway stripping.
Before milling machines, asphalt and concrete pavements were more apt to be broken into chunks with pile drivers, scooped up and hauled away to a ditch. The first milling machines simply mounted a revolving spindle on tracks and fastened hardened teeth to it, not unlike machines used in mining. The earliest models conveyed the planed material out the back end for trucking away, but later models put the conveyors in front for handier trucking and more thorough cleanup of the planed surface.
Pavement milling is a predictably loud and rough process, a thoroughly destructive one that nevertheless produces consistently-sized aggregate suitable for recycling. This is possible by advances in the machines and in their chewing teeth.
Cold planers were heavy machines to begin with and have grown larger. The Wirtgen W250i weighs 47 tons (42.6 t) and in a single pass can plane up a section of pavement 7 ft. (2 m) wide and 13 in. (35 cm) deep. Early milling machines could carve just 2 to 3 in. (5 to 7.6 cm) into the pavement. The W250i creeps along on four hydraulically propelled tracks powered by a Cummins diesel. It spins a cutting-tool drum almost 4 ft. (1.2 m) in diameter that can discharge aggregated pavement at a rate of 870 cu. yds. (665 cu m) an hour.
In short, these are big machines that not only can rip away, but can lay down a desired slope and grade while doing it and leave behind a variety of surface textures. On the other hand, some smaller planer models are amazingly nimble, neatly circling a manhole and cutting away the asphalt that surrounds it. Some models (Roadtec) can reverse the rotation of the cutting drum for cases where up-cutting the pavement is not as effective as down-cutting it.
Where the teeth meet the road, today's planers can perform any of several tasks depending upon how they are set up. Early milling machines had teeth welded to the drum. Changing out meant shutting down for extended periods. Now teeth are held in housings bolted to the drum and can be more quickly changed out.
The teeth are carbide-tipped for everyday milling. Specialty milling applications include carving rumble strips into new pavement. Diamond-tipped teeth are utilized for finer grinding, especially of concrete pavement, when the aim is to repair rather than replace a section of roadway. The diamond-tipped blades of the planer are closely set and effectively smooth out irregularities in old pavement, leaving behind a serrated surface.So, old pavement is not old news. It is good news. Recycled concrete pavement is part of the 140 million tons of concrete recycled each year in the United States. In 2014, recycled asphalt pavement totaled 72 million tons. All of that is the product of today's cold planers that are helping turn old into new.—CEG