Technology

What full automation can do for asphalt plants

Imagine a future where asphalt pavement production is entirely automated. By James Careless.

CONJURE UP self-driving trucks hauling raw materials to a fully-automated asphalt plant; unloading them in sensor-monitored, weight measurement holding areas. Think of the materials and fluids stored in these areas being constantly monitored by sensors tracking their humidity, temperatures, and other vital characteristics; with all this data being fed into and analysed by the plant’s asphalt mixing control software in real-time.

When it is time to make asphalt – as called up by an operator from a set of mix formulas on file – the appropriate ingredients are conveyed into the mixer, including RAP (Recycled Asphalt Pavement) and RAS (Recycled Asphalt Shingles). Everything is mixed precisely, with the control system constantly keeping the asphalt mix at the most optimum temperature.

Once ready, the mixed asphalt is loaded into more self-driving trucks – each with their customer and destination logged into their onboard computers – and sent down the road to job sites, for automated transfers into asphalt paving equipment.

Futuristic? Definitely. But with the exception of self-driving trucks, the degree of automation sophistication outlined above is not far from being within the asphalt pavement industry’s grasp. The current state of hardware and software in modern asphalt plants could elevate their process control to this level.

“You can automate just about everything,” says Peter Ensch, CEO of WEM Automation in Milwauke, USA, a maker of automation-control systems for the asphalt industry. “It really depends on how far you want to go.”

This said, “I have never seen a ‘fully automated’ plant,” notes Malcolm Swanson. He is president of Astec, a maker of fully-automated portable and stationary asphalt plants. “I have seen extensively automated plants, which are about 70 percent automated,” he explains.

“But 100 percent automation is probably possible.”

One thing appears certain: “In the past five years, all of the major manufacturers that build asphalt plant automation systems have moved towards an extensive automation model,” says Terry Young, president of the asphalt industry consulting firm T2ASCO. “That’s how much progress has been made in marrying modern information technology to asphalt plant management.”

This said, many asphalt pavement plants are still using relay-based, push button manual control systems that require real-time human intervention at all times. This is because “most asphalt plants are fairly simple to operate”, says Malcolm. “They do not have the driving need for automation that an electrical power plant does, where a human operator couldn’t stay on top of their job without the support of automated systems.

“Blending of materials such as aggregates, asphalt, RAP, and RAS is about the only thing an asphalt plant does that must necessarily be automated,” he adds. “For that reason, that is the only automation that many plants have. Most of the other equipment and processes have either remote manual control or single loop automation rather than integrated automation.”

The benefits of full automation

Even though it can be costly to fully automate a ‘mainly manual’ asphalt plant, the results justify the cost. “There is a good return on investment due to improvements in throughput and quality,” says Peter Ensch. This is because a fully automated plant requires far fewer employees to create consistent hot mix and warm mix asphalt products.

“We have customers who are operating fully-automated asphalt plants with three people,” Peter says. “They are able to do everything they need to do with this level of staffing.”

For instance, full automation allows human operators to specify which asphalt mixes they want made; using the plant’s computer-controlled systems to get the recipe right every time. “Full automation also checks to make sure all required motors are operating properly, all feed ingredients are flowing properly, and can even start motors that need to be started that the operator has forgotten, or can warn or even shut down the operation if certain upset conditions occur,” says Terry Young. “Full automation can also track and trend historical data to help diagnose plant and mix problems.”

Automation can save money by “minimising out-of-tolerance mixes between mix changes”, Terry adds. “As well, it reduces the ramp-up/ramp-down times of production and heating equipment; cutting energy consumption while improving the quality and consistency of mixes.”

The possibilities for automating an asphalt plant also include elements that don’t directly affect the mix, but do have an impact on the bottom line. For instance, putting bar codes or RFID (radio frequency identification) tags on incoming trucks, their site access can be managed by machine-based scanning systems that control inventory receipt and management, for instance; no human input required.

“Even plant safety systems can be improved using automation; for instance, by using sonar sensors to detect the location of trucks under a bank of silos ensures mix cannot be dropped anywhere but in the truck box,” says Gerry Huber. He is associate director of research at the Heritage Research Group, which works with asphalt plants owned by the Heritage Group in Indianapolis.

Looking ahead

Astec’s Malcolm Swanson is impressed by the current station of asphalt plant automation. But as he noted earlier, much, much more can be done.

A case in point is the moisture levels of outdoor-stored aggregates and RAP, which affect the quality of an asphalt mix. Currently, most plants take occasional moisture readings on individual feeder belts before injecting liquid asphalt into a belt, then use these captured values as if they were constants in formulating that specific mix.

“The real moisture contents of the materials are constantly changing throughout the day due to a number of different causes,” says Malcolm. “If we can set up real-time belt sensors to monitor aggregate/RAP moisture levels during conveyance, such data will eliminate the moisture-related variations that force every contractor on the planet to inject a little more liquid asphalt than is called for in the specification just to be sure he is never out of spec, due to injecting too little asphalt.”

Similar automation-based solutions could keep up with the variable liquid asphalt content of RAP, he adds, and adjusting burner fire rates based on real-time temperatures to reduce energy usage.

These are just some of the present and future benefits of extensive automation for asphalt plants. Collectively, they are revolutionising the very nature of asphalt production – and paving the way towards asphalt plants achieving full automation in the foreseeable future.

This article first appeared in Contractor December 2017.

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