McAdam's road cross section was made out of a compacted subgrade of crushed granite or greenstone meant to carry the weight, which was topped by a light stone surface to absorb wear and tear and shed water into drainage ditches. In contemporary macadam construction, crushed stone or gravel is used on the compacted foundation course. The top layer is usually asphalt pavement.
The term "macadam" is derived from John Macadam, who in 1825 published A Treatise on Roads and Streets, in Which Are Described and Proposed Improvements Made By Him After That Name. This work greatly influenced Thomas Jefferson when he designed his own roads around Charlottesville, Virginia. The book included detailed instructions on how to make a road with a macadamized surface that could withstand heavy traffic loads.
In America, the first highways were built with earth turned up on each side of the path to make it less slippery when wet and more resistant to erosion. But soon there were problems with this method: the soil would wash away during rainstorms, leaving potholes that could cause cars to crash. So the Maryland General Assembly passed an act in 1815 authorizing the state highway department to pay a contractor $100,000 (about $1.5 million in today's dollars) to build a road between Baltimore and Ellicott City. The road was to be made of stones set in mortar and covered with a mixture of gravel and clay.
Macadam is a kind of pavement designed in the 18th century by John McAdam of Scotland. The road maker would lay out courses of stones as large as possible (up to 4 feet across) and then compact the soil between them to make a flat surface.
McAdam's roads were improved upon by Thomas Telford who added turnings to many of the main roads around Edinburgh so that horses could be driven into town instead of being pulled by teams of men. These roads are still in use today. Macadam's road fell out of favor when steel beams were introduced into construction projects in the 1850s. By the 1890s, all new roads had been paved with asphalt, which is a mixture of petroleum products and limestone or clay. This type of pavement is still used today in countries where oil prices remain high enough to make asphalt profitable.
When McAdam first proposed his idea for a road system based on using stone for the base and breaking it up into small pieces for traction, people thought he was crazy. He built one road using his method and it turned out very well. So he decided to publish a book describing his ideas so that others could learn from his experience. The book became a success and spread McAdam's knowledge about making better roads that last longer.
ROAD STONE is a type of aggregate made up of shattered chunks of Ordovician Dolomitic limestone mixed with a certain proportion of limestone particles. Because the material is a mix of bigger and fine particles, it compacts quite effectively. It is used as a surface dressing on roads and other surfaces where a hard-wearing, non-slip surface is required.
Limestone is the most common mineral form of calcium carbonate (CaCO3). It is found in many different places all over the world. When exposed to heat and pressure, limestone can transform into dolomite, which is an important constituent of sedimentary rocks such as shales and sandstones. Dolomite is also used as a roadstone because of its hardness and durability.
Calcium carbonate has a high density so when broken down into smaller pieces, it makes for an efficient road base. The mixture of limestone and dolomite is called "grit". This term is usually applied to rock fragments less than 2mm in diameter but any size down to 0.6mm or even smaller can be used instead.
The word "grit" comes from the Dutch word "grut", which means "small bits of rock".
Limestone is present in most sedimentary rocks formed from waterlogged environments that are subjected to heat and pressure over time.
The granite was utilized in the caissons, anchorages, and towers, while the steel was used for the web truss, which made it six times stronger and more stable, preventing it from collapsing into the East River. The use of different materials to build a bridge of such length was innovative at the time.
The Brooklyn Bridge is one of the oldest bridges still in use today. It was completed in 1883 by John A. Roebling's son, Washington J. Roebling. The elder Roebling had died the previous year, but he was survived by his wife, who took charge of the project's financial affairs. She also supervised the work of their two sons, who were responsible for all aspects of construction. The younger Roebling chose as his professional office a site near the end of the job where he could watch his son John Jr.'s electric lights illuminate up and down the river at night.
When it was finished, the Brooklyn Bridge was the longest suspension bridge in the world. It connected Brooklyn with its neighbor across the East River, Manhattan, and provided a vital link between the city's industrial centers. The opening ceremony was held on February 20, 1883, and hundreds of thousands of people attended. The New York Times described it as "the greatest illumination this city has ever known."
The bridge was an immediate success.
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