Making Asphalt: A Conversation with Solterra’s Pat Weaver
How did you start in the asphalt industry? As a lab technician with Speedie and Associates in Phoenix. I later worked for APAC Southeast/Preferred Materials (a CRH-Oldcastle Company) in Florida, Vulcan Materials, New West Materials, CalMat (all in Arizona and New Mexico), and Gallagher and Burke in Oakland, California.
How did Solterra Materials start in 2018? It was a merger between Sunland Asphalt and Grey Mountain Construction. Grey Mountain’s asphalt plant in Coolidge was combined with a plant in Buckeye bought by Sunland. I was recruited to bring the pieces together to develop an agile and responsive commercial HMA business, where people, products, and processes form our core foundation.
What’s the basic process of asphalt production? Crushed rock and sand separated into specific sizes are precisely proportioned through the plant's cold feed system. Mineral admixture is then blended with the moist aggregates through a pugmill and then conveyed across a weighbridge into the drier-drum. As the drum turns, the aggregate mixture is heated and dried by a 100 million BTU per hour low combustion and noise emissions burner. Hot liquid asphalt cement is metered into the drum and mixed with the dry aggregate mixture. Reclaimed/recycled asphalt pavement (RAP), fibers, and some other additives are added at this point in the mixing process when specified.
The hot blended mixture falls into the drag slat conveyor where the product is lifted into the hot storage silos. The mix is now ready to be weighed and loaded into trucks to be delivered to the job site. The entire process requires particle emissions control technology in the form of a baghouse, which ensures that the dust created by this process is contained and reused via augers back into the plant. This form of asphalt production is considered continuous and is computer-controlled. Some plants batch small proportions at a time, but that conversation is for another day.
Solterra Materials - Buckeye Plant
What maintenance is involved in your operations? Safety is our #1 business foundation since this is dangerous work. We employ full-time maintenance technologists at each facility to ensure that the plant remains operational. These folks know every aspect of the plant, including electrical troubleshooting, mechanical engineering, fluid dynamics, thermal dynamics, airflow, combustion principles, proper lubrication principles, computer troubleshooting, and metal fabrication. They work at heights, in confined spaces, around hot liquids, and open flames. Our products are precisely engineered for each application; they understand that we are in business to make great products, not just to make mix and fix things.
What are the advantages of new asphalt plants? The most significant difference is in the plant control systems. Most old plants used buttons, switches, and relays systems to control each aspect of the plant. Newer plants use PLCs which are fully controlled by computers. Older plants may even have the burner on the drum's front end (parallel flow), while newer plants have the burners at the end (counter flow). Baghouses have improved, mixing flights have evolved, burners have improved yielding lower combustions and noise emissions. The good news for older plants is the new technology can be added via individual components from several manufactures and are virtually plug-n-play.
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This article originally appeared in the bimonthly Arizona Contractor & Community magazine, Sept/Oct 2020 issue, Vol. 9, No. 5.