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In-class surveys have shown that very few of today’s students have any degree of familiarity with construction of any type. They will be unfamiliar with most of these common road construction terms. So, it will be necessary to go over them in some detail.
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•Base Material: In Central Texas it is generally crushed and graded limestone material from one of the Quarries along the Balcones Escarpment. It is generally put on top of the sub-base in 12-inch lifts and compacted to optimum density using a variety of compaction equipment. It is the load bearing structure.
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•Shoot and Chip: Texas practice is to shoot a thin asphalt layer on top of the compacted base course and then spread a layer of chips (pea gravel) over that. This is the wearing surface.
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•Pea Gravel: Is a manufactured, gap graded (.25” to .50”) gravel with most of the fines removed. It can be hard limestone or river gravel. Limestone is preferred because of polishing.
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•Design Profile: The design life of a rural FM Road in Texas is normally 4-years. At that time a shoot and chip seal coat is applied after any major break-up of the base material is repaired. At the end of 7-years the pavement condition is assessed. And the road is resealed or rebuilt as required. Light traffic roads in West Texas seldom need rebuilding. Roads in the fat-clay regions of central and east Texas require constant maintenance because of failure of the sub-base. This causes structural failure of the base course, etc. It would cost $-billions to build FM-Roads to any other design profile. High volume roads are built to higher standards.
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