To assist you with gaining an understanding about HMA and its versatility, please find some answers to general questions about asphalt.
What is Hot Mix Asphalt and How is it Made?
Hot Mix Asphalt (HMA) is a combination of stone, sand or gravel bound together by asphalt binder. HMA pavement refers to any paved road surfaced with asphalt. Liquid asphalt is heated, combined and mixed with aggregates at a HMA facility in either a batch or drum mix plant. The sized stone and sand are held in bins.
What is RAP and When is It Used?
RAP (Reclaimed Asphalt Product), often integrated into the manufacturing of HMA, is a resource rich in asphalt and aggregates. High capacity manufacturing operations can integrate 30% or more of RAP.The HMA industry has been recycling on a large scale since the 1970’s making asphalt pavement America’s most recycled material.
The benefits of RAP are more evident than ever before. By increasing % of RAP in asphalt mixes, we can free up landfill space and conserve precious natural resources.
What are the Benefits of HMA Pavements?
HMA is safe, economical and it is the most long-lasting and durable paving material. Of the 2.27 million miles of paved road in the US 94% is surfaced with asphalt. Asphalt tends to be the pavement of choice by most designers and specifiers because of its lower construction cost, reduced time of construction, ease of maintenance, and benefits related to improved smoothness, reduced pavement noise, and resistance to deformation in colder climates and higher elevations.
Are HMA pavements safe?
Smooth HMA roads have superior road contact and high skid resistance. They have distinct advantages over other paving materials when driving in inclement weather. HMA pavements are impervious to de-icing salts and chemicals and are unaffected by winter road safety maintenance. HMA pavements can be designed so that water drains through the surface layer of the pavement, thus reducing splash and tire spray and increasing tire-road contact during wet weather.
What impact does the production and use of HMA have on the environment?
In many respects Hot Mix Asphalt (HMA) is the environmentally friendly paving material. First, HMA materials are 100% recyclable. Virtually all of the Reclaimed Asphalt Pavement (RAP) that is removed from existing streets and highways is recycled into new HMA. Because recycling of HMA is economical it occurs without the need for government mandates or subsidies. HMA also has been shown to consume less energy than other materials and systems. A study done by the Asphalt Institute indicated that a comparably designed HMA pavement required only about half the total energy to construct as a comparable Portland cement concrete pavement.
Improvements in technology have been steadily reducing the airborne emissions from the production and placement of HMA. Dust from the drying of aggregates is the major emission and is now almost totally captured and recycled. Other emissions are primarily combustion products from the burning of fuel to heat the aggregates and fumes from hot asphalt itself. Fuel burners are now much more efficient, resulting in very complete combustion. Studies to date by the government and industry have shown emissions levels to be very low and have not identified any health hazard associated with exposure to asphalt fumes. Nevertheless, the industry continues to develop improved technology for reducing emissions and minimizing exposure.
N.B.: Much of the information provided on this page was extrapolated from various industry sites including numerous state asphalt assocation websites, printed material from trade journals and industry publications.