Quality control at your HMA plant

Quality control at your HMA plantBy Timothy R. Murphy, P.E. and Amanda L. Murphy

Understand Your Production Facility
Transportation in North America has evolved from simple dirt and gravel market roads to asphalt interstate roads that are part of an elaborate infrastructure traveled by millions of passengers annually. Technological advances like Superpave, stone matrix asphalt, high RAP mixtures, porous asphalt, recycling roof shingles and warm mix asphalt have created a revolution in the transportation industry.

As transportation needs have changed over time, our road building and manufacturing abilities have adapted, and now over 94 percent of all roadways in the United States are paved with hot mix asphalt (HMA). Since good inputs will yield good outputs at the hot mix plant, today it is more essential than ever to improve your plant.

Whether you own and operate a stationary or a portable drum, continuous, or batch plant, success starts with a comprehensive Production Facility Checklist (see below) to ensure that these various mixtures are produced in a quality-driven, efficient manner to optimize overall value for production and for clients.

Production Facility Checklist

  • Safety manual
  • Aggregate stockpiles
  • Front end loader operator training
  • Schedule equipment calibrations
  • Thermometric equipment
  • Checking flights, dams, and targets in the drum are set for robust heating and drying
  • Dust collection system well calibrated to reduce particulate emissions and to control minus #200 in the mix
  • Liquid asphalt storage and control
  • Scales for belts and trucks
  • HMA storage and loading
  • QC and agency inspection, sampling, and testing facilities.

It is crucial to understand the relationship of plant layout and circuitry. More movements mean increased costs, larger potential for segregation of the aggregates, potential safety problems, material contamination and waste.

You may need to retrofit and redesign your plant layout to accomplish these items, but this long term investment will begin to pay dividends immediately in cost savings, safety enhancements and quality control simplification. If your trucks are spending too much time getting from place to place, find ways to streamline your operation to improve quality and efficiency while cutting down expenses.

Manage Your Material Inputs
Quality aggregates and asphalt make HMA pavements last. After ordering materials from the quarry, ensure that aggregates are properly handled and stored when they arrive at the hot plant. Proper stockpile management leads to zero percent waste of product.

Many contractors find that posting signs at the stockpiles is the simplest way to control stockpile resupply and inventory. The same is true for the liquid asphalt being used for a specific job, especially when polymerized asphalts are being stored and used at the hot plant.

After purchasing customer-specific quality materials, it is imperative to manage those materials. Ensuring that visual identification of segregation and other problems can be dealt with by everyone in the manufacturing process requires walking the yard and talking about challenges, areas for improvement and potential yard layout changes to accomplish these goals.

Management of material inputs will maximize plant efficiency and is facilitated with computer systems. “Full plant control is critical to allow instant diagnostics and historical trending of data of all plant devices for optimum maintenance scheduling,” says James Phillips, Vice President of Construction and Aggregates at WEM Automation, Inc.

“More importantly it allows the operator to focus on productivity and the activities in the yard. The system will function on ‘cruise control’ and let the operator know when there is a problem. The use of off-the-shelf components is also very critical,” Phillips adds.

“In the event there is a hardware problem you need to be able to buy parts locally to get you up and going quickly. The use of custom boards and other components leaves you vulnerable and dependant on a single source. Lastly, open architecture software is crucial in communicating with remote information systems such as billing and project management software.”

These systems should:

  • Increase productivity
  • Minimize downtime
  • Provide complete control of motors, pressures, temperatures, sensors, and all other components of the plant
  • Eliminate outdated push buttons
  • Provide instant plant alarming
  • Minimize plant troubleshooting.

Full plant controls can provide complete control and monitoring of an entire facility on any type of plant. Each system must be customized to your exact plant layout and specifications for optimum ease of use and efficiency.

Analyze, Adjust, and Anticipate (Triple A)
Successful Quality Control (QC) managers are capable of gathering, measuring, and acting on relevant information and data. “The most successful QC managers and, therefore, the most successful hot mix asphalt manufacturer, will pay attention to the needs of the customer and react accordingly based on what their internal process control tells them,” states Philip J. Peters of P. Flanigan & Sons, Inc.

From year to year, aggregates may change slightly. However, looking back to improve going forward requires a diligent and complete review of QC results from past years to improve on the next year’s HMA production.

Production Efficiencies Analysis Checklist
Triple A behavior implies that:

  • Mix designs include aggregate ‘breakdown’ to anticipate degradation through the plant
  • Multiple products are used to allow for re-proportioning to maintain volumetric properties
  • Audits of sampling and testing personnel and equipment occur frequently to ensure process control competency
  • Product cost analysis occur ongoing based on fluctuating materials cost and the ability to produce and place HMA at maximum quality and pay.

Your goals will change from year to year, and that is as it should be, but you should prepare a back-up plan just in case. This Production Efficiencies Analysis needs to be undertaken on an ongoing basis as part of your back-up plan. Quality and quantity can and must co-exist to ever increase the hot mix asphalt market share.

Recycle, Recycle, Recycle
Just as with virgin aggregates, we need to sample and test RAP on an on-going basis for gradation and asphalt content. Monitoring moisture content, checking the crush, and following the fundamental principles for the sizing, stockpiling, and balancing of recycled inventory leads to:

  • More consistent HMA product
  • Higher utilization of RAP
  • Increased savings.

Retrofitting the plant may include installing a vent retrieval system in the slat elevator that returns it to the burner area thus reducing ‘blue smoke.’ Recycling will reduce waste, impress clients and save money while improving the environment.

Warm mix asphalt has the potential of allowing additional recycling at reduced production temperatures, thus significantly reducing fuel use and emissions. We are still in the proving stages yet all signs are pointing in a favorable direction.

Silos, Trucks, and Trucking Coordination
Coordinating the efforts of your trucks can be a major time and money saver. Having multiple storage silos allow for increased product production and more efficient load-out. But multiple silos also require coordination. Stagger start times; use two scale lines – one for commercial and one for project trucks. Multiple silos can cause problems if the surge isn’t properly timed, if silo segregation occurs, and/or if timing switches aren’t closely monitored by the plant operator.

Educating the truck drivers about the importance of staying in the truck leads to a win-win for everyone as fewer accidents occur and higher productivity is achieved. Improving cleanliness and safety, as well as rewarding better drivers, will lead to more efficient and cost-effective use of time on and off the truck.

Equipping drivers with maps to and from job sites, having a back-up plan for congested traffic and promoting driver training will all result in saving time, effort, and money, as well as improving services to your client.

Tim Murphy is president of Murphy Pavement Technology, Inc. Amanda Murphy is a technical writer for Applied Pavement Technology, Inc.