ABSTRACT
I. INTRODUCTION In 1988, there were approximately 4 million miles of roads in the United States of America, of which 2.3 million miles were surfaced with asphalt or concrete. Of the surfaced roads, approx imately 96%, or 2.2 million miles, had asphalt pavements [1]. More than 95% of the 2 trillion vehicle miles traveled each year occur on asphalt-paved roads. In 1988, expenditures for high ways amounted to over $68 billion at all levels of government [1]. During 1988, 500 million tons of hot mix asphalt (HMA) was produced and placed, and about 250 million tons of HMA was used for construction, rehabilitation, and maintenance of the highways [1]. The HMA in dustry directly employs 300,000 people and indirectly accounts for an additional 600,000 jobs [1] . The hot mix asphalt concrete consists of a combination of aggregates blended and uni formly mixed, coated with asphalt cement, and compacted into a dense material. The materials in HMA consist of (1) coarse aggregates with sizes ranging from 1.5 in. to U.S. sieve No. 4, (2) fine aggregate or sand with sizes passing U.S. sieve No. 4 and retained on U.S. sieve No. 200, (3) mineral filler such as crushed stone dust or lime passing U.S. sieve No. 200, and (4) asphalt cement. A typical HMA composition consists of 50% coarse aggregates, 40% fine ag gregate, 5% mineral filler, and 5% asphalt cement.
