Roman conquest did not introduce slavery and brutality to the world; there was plenty to go around before Rome rose to power. What the Romans did bring to countries such as England was travel and trade with the rest of the world over paved roads that made wheeled traffic something better than a bone-jarring ordeal.
The next great revolution in roadbuilding had to wait about 1,400 years for the work of John Loudon McAdam. Born in 1756 in Ayr, Scotland, McAdam lived before Roads & Bridges began its 100 years of publishing, but his story is fascinating nonetheless.
His method, named “macadamization” after its creator, specified that a proper road should be constructed of crushed stone bound up with gravel on top of a solid base of larger stone. It also should have a camber to ensure that water drains off the road instead of penetrating and damaging the base. McAdam emphasized the use of “angular fragments” of rock, which would form a stone-on-stone structure that was very stable, hard and nearly impenetrable to water. He preferred hand-broken, 6-oz stones to natural stones of the same weight, because they had sharper edges that would create a more solid, interlocking structure.
The first macadam road to be built in North America was the National Road (see Fabled in story and song about America’s top all-time roads, Roads & Bridges, July 2006, p 26).
McAdam’s influence is still felt in modern asphalt, which is made up of crushed rock of various sizes bound together with an oil-based asphalt that is a liquid at high temperature.
The first rock-asphalt road was constructed by accident, according to “Paving the Way: Asphalt in America,” by Dan McNichol, published last year by the National Asphalt Pavement Association (NAPA). A load of naturally asphalt-impregnated rocks fell out of their overloaded carts in Switzerland in the early 1800s. Wagon wheels compacted the asphalt-bearing limestone rocks into the surface of the macadam road.
The accidental asphalt-macadam pavement proved to be quiet, dust- and mud-free and easier to clean of animal waste.
It was a turning point. In time, the paving industry switched from naturally asphalt-laden rock to pure asphalt collected from natural deposits and finally to man-made, or “artificial,” asphalt refined from petroleum.
“The transition from using rock asphalt to liquid petroleum was a very big move,” Mike Acott, president of NAPA, told Roads & Bridges. “Without that the asphalt industry would not have developed. If it had been left to importing rock asphalt or mining it in the U.S., just the cost to do that and bring that to market in the quantities that would have been needed would have been a severe limitation.”
The first successful asphalt roadway that was not constructed with naturally asphalt-impregnated rock came in 1870. It was designed by Edward J. DeSmedt and laid in front of City Hall in Newark, N.J. DeSmedt received patents for his mixes, which consisted of stone, sand-powdered limestone and natural asphalt taken from Pitch Lake, a volcanic lake in Trinidad.
The earliest magnate in laying asphalt pavement was Amzi Lorenzo Barber. He was the Andrew Carnegie of asphalt. By his wheeling and dealing in the late 19th and early 20th centuries, Barber dominated the market for asphalt paving with his company, Barber Asphalt Paving Co., and paved many miles of the city streets of Washington, D.C. The tale of how Barber and his colleague Gen. Francis Vinton Greene plundered first Trinidad and later Venezuela for their natural deposits of asphalt is worthy of consideration alongside tales of their more famous fellow industrialist robber barons. Eventually, a revolution in Venezuela, known as the Asphalt War, left Venezuela in control of the Lake of Pitch, Barber’s asphalt empire broken up and Barber defending himself in a U.S. government investigation of his role in the Asphalt War and the private army his company had assembled to protect its investment in Venezuela.
Demand rose fast for asphalt in the early 20th century, about the same time that oil production was increasing to keep pace with the growing popularity of automobiles. Also about that time, chemists figured out how to process crude oil into asphalt.
Another major course correction for the industry was the oil crisis of the 1970s. With the price of oil soaring, many paving contractors took an interest in recycling. The introduction of milling machines and drum-mix plants made the time ripe for adding recycled asphalt pavement to the virgin mix.
The late 20th century brought innovations such as Superpave, stone-matrix asphalt and perpetual pavement to asphalt road construction.
The speed of laying asphalt increased by 50% when the Griffith Paving Co. first used an automated paving machine in 1927 in Orange County, Calif. Griffith found using a concrete paver to spread asphalt produced pavement that was more uniform in density, smoother and faster to roll.
As with asphalt, the pioneer of concrete pavement also lived before the start of Roads & Bridges, but not by much. George Bartholomew was the driving force behind the first concrete-paved street in America, in Bellefontaine, Ohio, and is credited with inventing concrete pavement, according to Wikipedia.
Bartholomew proposed the first concrete pavement to the city officials of Bellefontaine in 1889. In his laboratory, Bartholomew produced a cement that he was convinced would form a hard, durable concrete surface. He spent the next two years promoting his idea for a concrete pavement and finally persuaded the city officials to let him build it, but only after he offered to donate all of the materials and agreed to a $5,000 bond guaranteeing that the pavement would last for five years. That pavement is still in use.
Concrete roads came along at exactly the right time. The automobile was catching on in the U.S. Ford introduced the first mass-produced automobile, the Model T, in 1908. Americans were hitting the road in increasing numbers, for leisure and for commerce, challenging the road builders to keep up with their demand for good roads.
In the early years of the 20th century, concrete was trucked as separate materials to the paving site, mixed on the site, spread on the grade between forms and screeded and consolidated with vibrating strike-off machines.
When states began using salts to melt snow and ice on roads in the 1930s, they started noticing surface scaling on their concrete pavements. Engineers started learning about the freeze-thaw cycle’s effect on concrete. The story on the American Concrete Pavement Association’s (ACPA) website has it that the Portland Cement Association, started in 1916, tested various samples and found that one of them had better freeze-thaw resistance. Microscopic examination revealed that the sample contained billions of tiny air bubbles.
After being initially stumped about where the air bubbles came from, the researchers visited the plant that supplied the cement and found out the operator was using beef tallow as a grinding aid. The beef tallow was producing the bubbles. Purely by accident, the cement producer had invented air-entrained concrete, which resisted freeze-thaw action. The concept caught on and nearly eliminated surface scaling.
A major advancement in concrete paving came in 1946 with the invention of the slipform paving machine. James W. Johnson and Bert Myers got the idea and built a simple prototype in their laboratory. The next year, the two slip formed a sidewalk section. The Iowa Highway Department slip formed the first roadway in 1949 with a 9-ft-wide, 6-in.-thick slab of county road.
Slipform pavers quickly grew wider and more powerful. Quad City Construction Co. built a self-propelled, track-mounted slipform paver in 1955 that would pave a 24-ft-wide slab up to 10 in. thick.
The development had a profound effect on the concrete pavement industry.
“It made the paving process a lot faster. I think it also helped with the consistency. I think it improved the quality by making a much more consistent process,” Bill Davenport, vice president of communications and policy at the ACPA, told Roads & Bridges.
The concrete paving industry was well positioned for the kickoff of the interstate highway system the next year. When the 41,000-mile system was substantially complete a couple of decades later, 60% of it was concrete.
Other innovations in concrete pavement construction of the past 100 years include sawed instead of hand-formed joints for a smoother ride, electronic controls on slipform pavers, tied concrete shoulders for improved structural durability and sensors that monitor the strength of fresh concrete to determine exactly when it can be opened to traffic.
Now, with a mature highway system, concrete pavers face the challenges of repairing, resurfacing or reconstructing roadways.
After all the investigation and invention of the past century, both asphalt and concrete have become highly technical. Add global positioning, laser guidance systems and sophisticated mathematical models, and paving seems almost like rocket science.
Maybe in the next 100 years, paving will combine with rocket science, and contractors will be paving roads joining habitats on the Moon.