Batch plants, which produce HMA in individual batches, tend to be smaller-volume output plants than drum mix plants. However, they offer greater flexibility in the amounts of a particular mix they can produce, the variety of materials that can be incorporated into one batch, and their ability to produce small batch sizes. Typical batch quantities range from 2.0 to 5.5 metric tons of HMA, running at production capacities of up to 350 metric tons per hour, with each batch taking 15 to 45 seconds to make.
Hot Mix Asphalt (HMA) Manufacturing
The basic purpose of a hot mix asphalt (HMA) plant is to properly proportion, blend, and heat aggregate and liquid asphalt cement to produce an HMA that meets the requirements of the job mix formula (JMF) (Roberts et al., 1996). Modern HMA plants also have the ability to incorporate reclaimed asphalt pavement (RAP), mineral filler, fibers, and anti-stripping agents, and will have advanced environmental systems to limit noise and dust emissions.
There are two basic types of HMA plants commonly in use today: the batch plant, and the drum mix plant. Batch plants produce HMA in individual batches while drum plants produce HMA in a continuous operation.
How HMA Is Made
Hot mix asphalt (HMA) is produced in a manufacturing plant that proportions, blends, and heats aggregate and liquid asphalt cement to produce a material that conforms to the specific product mix design and job mix formula (JMF). The JMF ensures that the HMA produced will provide the designed performance characteristics of that particular mix (durability, stability, rut resistance, skid resistance, and so on).
There are two basic types of HMA plants commonly in use today: batch plants and drum mix plants. As their name implies, batch plants produce HMA in individual batches, whereas drum plants produce HMA in one continuous operation. Both types of production plants produce the same HMA, and a mix produced in one will perform the same as a mix produced in the other. The choice of a batch or drum mix plant depends upon on business factors such as purchase price, operating costs, production requirements, and the need for flexibility in local markets.
Hot Mix Asphalt - The Sustainable Solution
Lafarge Asphalt supports sustainability in construction through material conservation, reduced energy costs, water preservation, noise reduction, and long-life pavements.
Hot Mix Asphalt Is Sustainable
Asphalt is widely recognized as one of the most recyclable construction materials in use on the planet today. Lafarge North America typically incorporates up to 30 percent of reclaimed asphalt pavement (RAP) back into new asphalt production, reducing total life-cycle greenhouse gases by 10 percent. Hot Mix Asphalt (HMA) pavement is the most recycled material in the United States; each year more than 100 million tonnes of asphalt pavement is reused or recycled into new pavements.
Lafarge asphalt operations do not just recycle RAP but our mixes utilize waste material from other industries, with roofing shingles, tire rubber, glass, and spent rail ballast all being incorporated into new asphalt production.
Currently, 100 percent of the asphalt supplied can be recycled. Even more important, it can be recycled at the highest point in the asphalt value chain-back into new asphalt construction-without detriment or compromise to the quality of the finished product.
Sustainable construction is a growing concern for all stakeholders, from state governments with major highway projects to parking lots for grocery chains that also want to demonstrate a commitment to the green agenda.
Lafarge is promoting and driving sustainability on five fronts: