|July 16th, 2016, 10:41 PM||#1|
Joined: Jan 2016
Asphalt is mans oldest engineering material, having been used since the dawn of civilization. About 6000 B.C in Samaria, there existed a thriving shipbuilding industry that produced and used asphalt. Asphalt was used for mortar in building the ziggurats-the Tower of Babel being one of many ziggurats. A thriving asphalt production existed near the cities of Sodom and Gomorrah. Asphalt was used by the Egyptians as a waterproofing material as early as 2600 B.C. From the Persian word for asphalt, mummy, we derive the word mummy. In the ancient world, asphalt was widely used as mortar for building and paving blocks, as caulking for ships, and as waterproofing in numerous applications.
The early asphalt occurred naturally. They were found in geologic strata as soft, readily workable “mortars” and as hard, friable black veins of rock formations. The soft asphalt material is typified in the Trinidad Lake depository on the island of Trinidad, in Bermudez Lake in Venezuela, and in extensive “tar sands” throughout western Canada. These soft asphalt products, called natural asphalts, were used extensively until the early part of the twentieth century.
In the early 1900s, the discovery of a method of refining asphalt from crude petroleum-as well as increasing demand for better roads because of the overwhelming popularity of the automobile-created an expanding industry. Asphalt appeared to be a cheap and inexhaustible resource for smooth, modern roads and numerous other applications.
As the asphalt paving industry blossomed, the physical properties and character of asphalt needed to be determined. To ensure that asphalt roadways were durable and reliable, numerous tests and procedures were developed in the early 1900s. Probably the first scientific approach to designing asphalt paving mixes was to determine asphalt content based on aggregate voids.
In order for design samples to represent field performance, compacted samples had to contain the desired void and asphalt cement contents. In the mid-1920s, Prevost Hubbard and F.C Field of the Asphalt Institute developed one of the earliest methods of evaluating the physical properties of a compacted asphalt mixture. The empirical Hubbard-Field test indicated the stability of a mix by a punching-shear type of failure.
In the 1930s, Francis Hveem, while working for the California Department of Highways, developed a test that ensured that compacted asphalt pavement mixtures were stable and did not bleed excessive asphalt. The principles of the Hveem method are based on triaxial compression and an estimate of asphalt content is determined by the surface area of the aggregate. The Hveem method is still in use.
Also in the 1930s, Bruce Marshall who was an engineer with the Mississippi Highway Department developed an asphalt mix design method that could be used to determine the desired density and asphalt content. With the advent of World War II the U.S Army Corps of Engineers at the Waterways Experiment Station refined and expanded Mr.Marshalls work for use in the development of the mix design for HMA to use on airfields being exposed to heavy aircraft wheel loads. After World War II the Marshall method continued to be refined for heavier aircraft loads and for use in the design of heavy truck loads. These test procedures continue to be used for the design and quality control of hot mix asphalt (HMA).
In the early 1990s, Super pave was introduced as the result of the research conducted as a part of the Strategic Highway Research Program (SHRP). It has now become the prevailing procedure for the design of HMA mixtures used by the various United State Departments of Transportation
Last edited by greg1313; August 2nd, 2016 at 08:25 PM.
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