About Macadam The original system involved a triple layer of stone. The bottom two layers were comprised of hand-broken rocks laid to a depth of 8 in (20.3 cm) over a formation level called a subgrade. The top layer was much smaller rocks, made to be no more than 2 in (5 cm) thick. The entireroad was then compacted and crushed together by use of an enormous roller. In addition, macadamized roads had a slightly convex shape, so that water would run off into drains on eitherside, rather than collecting on the road. The paving process became popular throughout the world, particularly in the quickly expanding American Northeast. The first American macadamized road was a remade 10-mile (16-km) section of unpaved road that connected the Maryland towns of Boonsboro and Hagerstown. The Boonsboro Turnpike was completed in 1823, using McAdam’s specific directions. In 1830, work was completed on the 73-mile (117.5-km) National Road, which remains one of the only roads in America to still contain macadam sections. These roads were initially created for use with carriages and horse-powered travel. With the advent of automobiles, the process underwent a variety ofchanges to meet new challenges posed by the vehicles. Dust thrown up by automobile wheels became a serious problem for travelers, leading to the invention of tar-bound macadam ortarmac. The new process used a layer of taron the subgrade and bound the rock layers together during rolling with sand and tar. Many early airports used tarmac pavement around the terminals, leading to the modern usage of the term for the disembarking area around a plane. Advances in road construction l ead to the gradual phase-out of macadam in industrialized nations. Replacements, such as concrete and asphalt, became popular as technology and synthesized materials became available to aid production. In America, the passage of the 1956 Federal Highways act lead to the modernization of most of the country’s major roads, mostly eliminating macadamized constructions. Some developing nations still use the process, and a few remaining areas of such road are protected as historical sites in some American town s. Water-bound macadam McAdam's road building technology was applied to roads by otherengineers.One of these engineers was Richard Edgeworth, who filled the gaps between the surface stones with a mixture of stone dust and water, providing a smoothersurface for the increased traffic using the roads. This basic method ofconstruction is sometimes known as water-bound macadam. Although this method required a great deal of manual labour, it resulted in a strong and free- draining pavement. Roads constructed in this manner were described as "macadamized." Tar-bound macadam With the advent ofmotor vehicles, dust became a serious problem on macadam roads. The area of low air pressure created under fast-moving vehicles sucks dust from the road surface, creating dust clouds and a gradual unravelling of the road material. This problem was approached by spraying taron the surface to create tar-bound macadam. On March 13, 1902 in Monaco, a Swiss doctor, Dr. Ernest Guglielminetti, came upon the idea of using tar from Monaco's Gasworks for binding the dust. Later a mixture ofcoal tarand ironworks slag,patented by Edgar Purnell Hooley astarmac, was introduced. A more durable road surface, modern mixed asphalt pavement, sometimes referred to in the US as blacktop, was introduced in the 1920s. This pavement method mixed the aggregates into the asphalt with the binding material before they were laid. The macadam surface method laid the stone and sand aggregates on the road and then sprayed it with the binding material. While macadam roads have now been resurfaced in most developed countries, some are preserved along stretches of roads such as the United States' National Road. Due to uses of macadam as a road surface in former times, roads in some parts of the United States (as parts ofPennsylvania) are often referred to as macadam, even though they might be made of asphalt orconcrete. Similarly, the term "tarmac" is sometimes colloquially misapplied to asphalt roads oraircraft runways. Tar-bound macadam Dry-bound macadam– Crushed aggregates laid in two separate sizes, coarse and fine, compacted dry by rolling and/or vibration to a dense layer (Smith and Collis 1993). Water-bound aggregate, or water-bound macadam– Usually a road base or sub-base in which a layer of aggregate has sand watered in to fill the voids (Smith and Collis 1993).
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Diagram aliran daur ulang limbah perkerasan aspal pada Pabrik Pengolahan
(source: OCAJI, The Overseas Construction Association of Japan, Inc.)
Present Serviceability Index
The present serviceability index (PSI) is based on the original AASHO Road
Test PSR. Basically, the PSR was a ride quality rating that required a panel of
observers to actually ride in an automobile over the pavement in question.
Since this type of rating is not practical for large-scale pavement networks, a
transition to a non-panel based system was needed.
To transition from a PSR serviceability measure (panel developed) to a PSI
serviceability measure (no panel required), a panel of raters during 1958 to
1960 rated various roads in the states of Illinois, Minnesota, and Indiana for
PSR. This information was then correlated to various pavement measurements
(such as slope variance (profile), cracking, etc.) to develop PSI equations.
Further, the raters were asked to provide an opinion as to whether a specific
pavement assessed for PSR was “acceptable” or “unacceptable” as a primary
highway (see PSR). Thus, although PSI is based on the same 5-point rating
system as PSR it goes beyond a simple assessment of ride quality. About one-
half of the panel of raters found a PSR of 3.0 acceptable and a PSR of 2.5
unacceptable. Such information was useful in selecting a “terminal” (or failure)
serviceability (PSI) design input for empirical structural design equations. It is
interesting to note that the original AASHO Road Test rater opinions are basedon car ride dynamics; it is unclear whether such levels are acceptable for trucks.
Pavement performance can then be defined as “The serviceability trend of a …
(pavement segment) with increasing number of axle applications” (Highway
Research Board, 1972). Figure 1 further demonstrates this concept.
Concept of pavement performance using Present Serviceability Index (PSI)