Properly heating asphalt and preparing food have more in common than you might think. Since I began reporting on the asphalt industry in 1998, I’ve embraced our penchant for using food analogies. Designing a mix is like baking a cake. Pneumatic-tire compaction action is like kneading dough. More recently, Travis Mick, vice president of CWMF Corp., Waite Park, Minnesota, used another cooking example for today’s heating discussion.

“If you cook a pizza in the oven per the instructions for 15 minutes at 425 degrees, it comes out properly cooked,” Mick said. “Alternately, if you cook the same pizza in the oven for 10 minutes at 525 degrees, the outside may get done or even burnt, but the center of the pizza could still be cold.”

“Oxidation of HMA is linear with time, but exponential with temperature.”—Greg Renegar

This relates directly to our topic of dwell time. As Carlos O. Cardenas, the Midwest area sales manager for Ammann America Inc., Orlando, suggested, “Too much retention time can overheat your mix, increase fuel usage and age the binder unnecessarily. Too little, and the materials may exit the drum under-dried or uncoated. The real value lies in the ability of the operator or control system to adjust and balance that time to fit each job’s demands.”

We see the analogy relates directly to the removal of internal and external moisture. Greg Renegar, the vice president of customer success for Astec Industries, Chattanooga, shared, “The primary reason to change the residence time of aggregate in a rotary dryer is to enhance heat transfer.”

Renegar included education about the entrained moisture concept in his “What An Aggregate Dryer Does” presentation, sharing that internal moisture trapped in the coated aggregate not only affects mix temperature, but also affects storability, or the absorption of binder while mix rests in the silo. Producers want to remove internal moisture before liquid binder is introduced to the process, and that may require taking a look at retention times.

“An effective dwell time is not simply about how long material remains in the drum, but how efficiently that time is used to transfer heat, remove moisture and achieve uniform mixing.”—Steve Elam

“Another reason to make the aggregate spend more time in the dryer is moisture removal,” Renegar said. “External aggregate moisture is easy to remove, but internal moisture removal takes time. Time is required for the heat to soak into the aggregate and drive the internal moisture out.”

Hervé Riche, the business development manager for ADM/FAYAT Group, Huntertown, Indiana, shared, “When it comes to asphalt production, increasing dwell time in the dryer drum mixer plays a crucial role in ensuring the mix is both high quality and road-ready.”

Riche listed thorough drying of aggregates, better heat transfer, improved coating efficiency, consistent mix quality and consumption control as benefits of lengthening dwell time. He explained, “Especially for high-spec pavements (like airport runways or highways), consistency is everything. Extra time allows for better homogenization of aggregates, additives and bitumen. Oddly enough, a well-optimized dwell time can actually reduce consumption, by giving the lowest exhaust gas temperature but keeping [gas temperatures] high enough to be above the dew point in the gas ductwork.”

“The real value lies in the ability of the operator or control system to adjust and balance that time to fit each job’s demands.”—Carlos O. Cardenas

“As the asphalt industry advances, the heat transfer and coating challenges of different mix designs and technologies make understanding the fundamentals of heat transfer and coating an important topic,” Renegar said.

Multiple sources agreed increasing the time materials spend in the dryer drum can increase efficiency—but you must do it right. Most asphalt applications depend upon time and temperature, so let’s dive into the effects of time and temperature on mix quality.

The Right Retention

“In asphalt production, retention time refers to how long aggregate and other materials such as recycled asphalt pavement (RAP) and filler spend inside the dryer drum,” Cardenas said. “And getting that timing right is critical. While it’s common to focus on increasing retention time to improve drying or coating, there are also times when decreasing it can benefit plant performance.”

He emphasized controlled flexibility and defined that as the ability to “tune” retention time up or down depending on the material, production rate and environmental conditions.

“In my opinion, dwell time has always been critical for mix quality,” said Mike Mauzy of Reliable Asphalt Products Inc., Shelbyville, Kentucky. “I believe, like so many other areas of improvement over the years, it has been a learning process. RAP, and specifically higher RAP percentages, have highlighted the issue of poorly performing pavements. ‘Stiff mix’ has been an issue with RAP mixes.”

Mick listed additional benefits of increasing dwell time for producers, showing that increasing the dwell time, thus efficiency, offers fewer British thermal units (BTUs) per ton. “It allows the opportunity for optimal heat transfer from the burner into the materials,” Mick said. “It allows more time for virgin and RAP materials to comingle, optimizing heat transfer and potentially reducing excessive fuel energy from the burner. You get better moisture removal in the RAP with longer dwell times. Additional dwell time allows aged RAP binder to activate and blend with the new binder. And you get reduced emissions with reduced BTUs.”

Steve Elam of Stansteel Hotmix Parts & Service, Louisville, Kentucky, shared: “An effective dwell time is not simply about how long material remains in the drum, but how efficiently that time is used to transfer heat, remove moisture and achieve uniform mixing. Optimal lifter flight design creates a consistent veiling pattern for maximum heat transfer, while in counterflow drums and dryers, maintaining adequate exhaust temperatures above dew point is critical to protect the baghouse.”

Elam continued, “Dwell time should be considered in two parts: material exposure in the drying/heating zone (which includes the combustion zone), where efficient and consistent veiling is key; and the mixing zone, where longer duration improves coating, blending and allows for higher recycle content. Ultimately, dryer drum performance depends on balancing residence time with flight design, temperature and exit gas control, and mixing strategies to produce high‑quality, homogenous output. When we maintain focus on the quality of the final hot-mix product, we may work backwards through the existing equipment of any individual asphalt plant and determine what is required to achieve this outcome, including critical dwell times.”

How to Retain for Profit & Quality

After considering the reasons for lengthening mix dwell time, producers may wonder how to effect this change at the plant. It’s not as simple as slowing down the drum’s rotation and expecting everything to magically blend more perfectly. Depending on your flight pattern, slowing the drum’s rotation may cause a failure of material to veil properly, resulting in uneven heat distribution.

Mick shared that changing the dwell time on an existing application will have an impact on load in the drum. “This could result in high amps on the drive motors, which could impact starting the drum up from a hot stop.” Mick recommended recording data before and after any changes.

“This can also affect your AC inject timing,” Mick shared. He suggested, if an additional load in the drum causes material to leak or backfill out of the inlet, you may need to make tweaks to the flighting.

A Flighting Discussion

“Flight design has played a large part in retaining aggregates in the drying portion of the drum,” Mauzy agreed. “Utilizing restrictor dams to hold material in longer has been a common practice. More recently, variable frequency drives have been installed on dryers as a means to control dryer rotation speed, thereby holding material in the dryer commensurate with the percentage of RAP in the mix.”

Elam elaborated on drum modifications—both inside and in alignment. “The flight configuration can be a myriad of different designs based on specific production and condition demands. Flight pattern, number and size of flights, and placement of flights inside the drum determines how aggregates are lifted and showered, which promotes even exposure to hot gases and effective energy transfer as well as impacting material throughput travel. Maintaining the correct aggregate bed depth (live load) in the drum at veiling zones is also critical; an insufficient material pool can disrupt veiling, elevate exit gas temperatures, and cause premature flight wear, especially at lower production rates.

“Drum slopes and rotational speed matter,” Elam continued. “As an example, short drums with steep slopes operating at low RPM, or longer drums with shallow slopes at high RPM, may produce similar dwell times but differ in heat efficiency and wear implications.”

A spokesperson for an original equipment manufacturer (OEM) in the southeast, cautioned against making internal modifications to a drum without careful research and engineering, preferring a lengthened drum instead.

Mick also mentioned longer drums as an element some producers are putting into practice. “Traditional lengths are 50 feet long,” Mick said. “It is not uncommon to see 54- and 60-foot-long drums today. Changing the angle of the drum is another way to play with retention/dwell time. This is a bit easier to do on portable applications versus stationary.”

ADM/FAYAT Group’s Riche agreed the increased drum length offers more axial space for a longer material path, thus more time for drying and mixing. He shared this is best for new plant designs or major retrofits and cautions producers to watch out for the obvious cost and space constraints, but also to maintain proper heat gradients across the longer chamber.

Elam suggested, when reviewing drums for dwell times and efficiency, pay close attention to any drum shell deformations in the central combustion area. (These might be hidden by insulation.) Deformations could be mitigated by proper flame adjustment/shaping, proper combustion flight design and integrity, the use of proper materials capable of withstanding high temperatures from varying fuels, and so on.  Avoid catastrophic failure in the drum by monitoring for drum shell deformation. With winter maintenance season coming on, you have the perfect opportunity to assess this vital plant component.

Ammann’s Cardenas also discussed the importance of monitoring flight patterns within the drum. “Flights control how material flows inside the drum,” he said. “Replacing or modifying worn or poorly performing flights can dramatically change retention time and heat transfer, whether you need more or less retention.”

“Changing flight arrangement can be one of the most cost-effective and impactful upgrades for increasing dwell time and improving efficiency,” Riche agreed. “From my vantage point, the drying zone is the most advantageous section to target.”

Riche reminded producers that the drying zone, or front end, of the counterflow drum is where aggregates enter with high moisture content. “Flight design here directly impacts veiling. Optimized veiling equals faster, more uniform drying, which allows for gentler downstream temperatures. Upgrading to ‘high-lift’ or ‘shower-type’ flights here can vastly improve heat exchange, reducing required peak temps and enabling more control over residence time.”

Veiling = the cascading curtain of material that maximizes surface area for heat transfer

“Every showering flight design requires some fill level of aggregate to ‘sprinkle’ or shower the aggregate through the hot burner gases,” Astec’s Renegar said. “If the aggregate is not showered uniformly across the cross-sectional area of the drum, some of the hot gases will escape the drum without giving up enough of their heat. This energy (heat) that bypasses the aggregate becomes wasted energy as it exits the fan stack into the atmosphere. It is also possible for some of the aggregate to retain moisture if this occurs.

How to Change Drum Flights

“Getting the right level of aggregate in the drum showering flights sometimes requires increasing or decreasing the residence time (or level) of the material in the drum,” Renegar continued. “This can be done by adding or removing showering flights, advancing or slowing down the aggregate by other mechanical means (easy), changing the slope of the dryer (difficult), increasing the length of the drum (rarely an option), or using variable frequency drive (VFD) technology to change the rotational speed of the dryer (best).”

“Using a VFD to control drum speed gives you real-time flexibility,” Cardenas agreed. “Slow it down to increase retention time for wet materials or RAP-heavy mixes. Speed it up for drier aggregates or when running warm mix…But if you’re over-drying, you may benefit from smoother, faster-release flight designs. Combined with a variable speed drum, the right flight design can provide for the best control of material retention.”

Over-drying = adding unnecessary heat to the aggregate that does not add value to the mix

Another area where a producer might consider altering flighting is the combustion zone, and Riche offered some cautions about this. “This zone is where the burner flame directly interacts with incoming aggregates (in a counterflow setup), and it’s critical for initial moisture removal and heat transfer,” Riche said. “But it’s also where things can go very wrong if not managed properly, especially when playing with dwell time. It’s risky to tinker too much here because lots of times, the combustion zone length is minimized, but it is a critical choice. This area with a high density of energy and highest temperature spot needs to be properly designed to give enough space for a proper combustion on the whole range of burner capacity.”

Keep Asphalt Drum Maintenance Safety in Mind

He suggested if the combustion chamber design is too small for the burner size, equipment could be damaged, emissions could be heightened or other problems with efficiency could arise quickly. But he offered some smart ways to optimize the combustion zone without overexposure:

• Tune burner settings, adjusting flame shape, length and position to avoid direct flame impingement on aggregates while delivering high radiant heat;
• Refine flight design in the combustion zone; and
• Segregate mixing from combustion and if you’re increasing dwell time elsewhere, ensure the liquid AC is introduced far downstream from the combustion zone.

“While the combustion zone isn’t the primary level for extending dwell time, optimizing it ensures that any downstream gains aren’t undone by scorching material too soon,” Riche said.

Stack temperatures and emissions are early indicators of combustion zone misbehavior. A sudden rise in either could indicate over-drying or incomplete combustion.

An area where a producer can often slow the forward progress slightly, giving binder more time to coat without increasing exposure to flame or oxidation, is the coating/mixing zone downstream. “While not the best target for increasing dwell time per se, the coating zone is still worth attention,” Riche said. “Installing paddle-style or scoop-type flights helps with thorough mixing of bitumen and additives, preventing segregation.”

Change Out a Drum

Craft a Recipe for Success

Riche suggested the plant operator is engaged in the fine art of mix craftsmanship. While dwell time is important, the temperature is vital to monitor.

“Longer dwell time only benefits the mix if temperature is properly controlled,” Riche shared. “Avoid the overheating conditions trap: overheat will cause binder oxidation.”

Renegar spoke to this craftsmanship in detail. “Every asphalt plant has a section or external device that coats the hot, dry aggregate with liquid asphalt. If the time of passage is too short, insufficient coating of the aggregate can occur. On the other hand, excessive time can theoretically oxidize the mix. The optimum situation is to make adjustments that provide sufficient coating in the minimal amount of time.

Address Your Drum Interior Now

“A little-known fact is that the ‘quality’ of mix improves with time in a storage silo,” Renegar continued. “While in the silo in contact with each other, the aggregate particles, large and small, come to the same internal and external temperature, and the film of asphalt equalizes on all particles. Yes, some oxidation occurs with the air in the voids, but that will happen regardless. The most important thing to remember when storing mix is to make the mix at as low a temperature as possible.

“Oxidation of HMA is linear with time, but exponential with temperature, so if one is concerned about oxidation, managing the mix temperature will have a much greater effect than changing the mixing time by a few seconds. That is one reason warm mix is so advantageous; the oxidation reaction slows down significantly. This is good whether the WMA goes from the plant straight to the road, or if it is stored in a silo.”

Oxidation = hardening of the binder in HMA

As discussed in the August issue’s “Avoid Explosions and Oxidation when Preheating RAP,” adding RAP adds complexity. Cardenas said: “Imagine you’re running a high-RAP mix. You might need more residence time to ensure proper blending and to bring the RAP up to temperature. Reducing the drum speed helps accomplish this without needing to oversize the burner or intensely overheat the virgin materials.

“The optimal drum speed is a balance that ensures enough time to dry and mix materials thoroughly, efficient use of fuel and burner energy, allows for proper handling of recycled materials (like RAP), and has minimal wear and environmental impact,” Cardenas continued. “Having too little or too much drum speed can have different effects on production. Finding the right speed is crucial for the best performance.”

Cardenas reminded producers, “The most common mistake is making drum speed changes without adjusting the rest of the system. For example, slowing the drum without considering burner output or flight action can create bottlenecks or hotspots. Speeding it up too much can allow under-dried aggregate to pass through to the mixing zone.” You guard against this by monitoring stack temperatures and the discharge moisture content. “Make small adjustments and give the system time to respond.”

Address Drum Exteriors Now to Prevent a Breach During Production

Reliable Asphalt Products’ Mauzy said, “Even more recently, I believe the industry is understanding the benefit of longer dwell time for mixing the RAP and virgin aggregates prior to injecting liquid asphalt. In most conventional counterflow drum mixers, there is very little time between the RAP inlet to liquid injection. Two issues regularly surface. One, the RAP is not completely dry prior to coating the mix with liquid AC, which traps moisture in the mix. Two, the RAP AC and virgin liquid AC are less likely to mix at the differing viscosity. Several producers have figured out that increasing aggregate dwell time by utilizing flight modification, aggregate dams and dryer VFDs has resulted in better quality.”

One of the challenges Mauzy has seen and wanted to warn against is neglecting to achieve proper mix quality with dry enough or hot enough RAP when favoring a higher production rate.

CWMF’s Mick reminded producers that location affects the timing and temperature, too. “Efficiency equals profitability,” Mick said. “Your baghouse exhaust stack temperature is the measuring stick of efficiency. The closer you can keep this temperature to 212 degrees, the better. Given the multitude of mix designs, specifically at stationary plants, a VFD is a fantastic way to adjust dwell times and temperatures to achieve optimal efficiency. Plant results vary from one geographical location to the next. Achieving optimal efficiency takes some trial and error.” He recommended producers take the time to experiment to bring all the elements together.

“In the real hot-mix world, no asphalt plant operates at a single production rate (TPH), fixed moisture content, constant recycle usage percentage and single mix design,” Elam said. “Production demands fluctuate, materials vary and production requirements change daily. That’s why designing for flexibility and performance is not just preferred—it’s essential.”

Ultimately, you’re mixing a specific measure of time, heat, motion and material inputs. The best plant operators treat that process like a MICHELIN-star restaurant recipe with each ingredient (flights, valves, burner, controls, slope and speed of the drum) blending in harmony.

A primer for the handling and use of polymer-modified asphalts and highly modified asphalts

Authors’ Note: This article is based on the Association of Modified Asphalt Producers training workshop. The original presentation was developed by Ron Corun and edited by Bob Kluttz. No AI was used in writing this article.

Currently up to 20% of all paving asphalt is polymer modified. The most common polymer-modified asphalt (PMA) binders are in the range of PG64-28 to PG76-28. Key for all modified asphalts is to be safe and follow the manufacturers’ recommendations.

Assess the Air System at Your HMA Plant

Handling and Storage

PMAs are not all created the same way. Mixing modified asphalts from different suppliers can cause the mixture to fail to meet the performance grade (PG) requirements.

Some guidelines help reduce contamination at the terminal. Make sure that the tanker trunk is empty before loading, then make sure to load from the correct loading arm. It is important to minimize the heel in both trucks and tanks. As little as 6 inches of residue in a tank can cause up to 10% contamination by a different grade.

At the asphalt mixing plant, use dedicated tanks, if at all possible. If a dedicated tank is not available, empty the tank as much as possible from the previous material and then add two or three loads to fill the tank before testing. Diluting PMA may cause the PG grade to fail.

Vertical tanks are optimum as they provide more efficient agitation. Most PMAs today do not require agitation to prevent separation, the exception being ground tire rubber (GTR). Horizontal tanks work fine for most PMAs but it’s important to circulate to achieve uniform temperatures above and below the heating coils.

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For proper circulation it is important that the product should be pumped out of one end of the tank with the return to the other end of the tank. If the circulation is all at one end of the tank the other half of the tank will be a dead zone. It is also important to ensure that the return line goes into the tank below the liquid level. Otherwise, you are spraying liquid asphalt through the remaining air in the tank and essentially running RTFO on your virgin binder.

As mentioned above, beware of mixing modified asphalts from different suppliers as not all PMAs are created with the same components by the same process and may not be fully compatible. Direct fire heating is not desired. Direct fire heat tubes will have hot spots, which cause two problems. Hotspots will damage the polymer network and lead to loss of PG grade and/or undesired viscosity rise. Hot spots can also lead to coking, which effectively insulates the line requiring ever increasing heat to maintain temperature.

Highly modified asphalt (HP or HiMod) is increasing in use around the United States. Handling and storing HiMod is not much different than handling and storing conventional PMA. The same general guidelines apply, but shelf life of a HiMod may be substantially shorter than a standard PMA. Check with your supplier to get his recommendations.

An ideal tank storage temperature is 320-330°F. A key point for HiMod as well as all PMA is do not overheat it. Overheating can cause the HiMod to further shorten the shelf life. The hotter the temperature, the more rapidly aging can take place in the binder, so it is important to keep the temperature as low as comfortably possible for easy pumping.

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Long-term storage of PMA is feasible, but cooling is required. For 60 days or longer, the heat must be turned down or completely off. When bringing back up to temperature, do it slowly. The tank contents must heat up uniformly through conduction and convection until the material is pumpable. Use increments of 20°F over three to four days to get the material back up to circulation temperature.

Mix Production

Pay attention to optimum mixing and compaction temperatures for PMA. The classic rule of rotational viscosities at 135 and 165°C does not apply to PMA. The low shear rotational viscosity of conventional asphalt is similar to the viscosity at high shear—mixing and compaction. PMAs, however, are shear thinning. The apparent viscosity in a drum is much lower than that from a rotational viscometer. Consequently, rotational viscosity will yield a much higher temperature than is actually recommended. Again, your provider should recommend ideal temperatures for their product.

Ensure that all plant equipment is in good condition and suitable for PMA. PMAs tend to be higher in viscosity so they will draw higher amperage at the pump. The pump should be calibrated and the strainer likely will require larger than standard holes—you want a minimum of 1/8-inch holes.

At startup, circulate unmodified asphalt first. Once everything is hot, switch to PMA and circulate again before starting production. Switch back to unmodified asphalt after the shutdown of the shift to leave unmodified asphalt in the pump and the strainer.

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The slat conveyor must be properly sized and in good condition. PMA will increase the amperage draw on the conveyor. It’s good practice to start out at reduced tonnage with unmodified mix to get everything up to temperature.

Again, not much is different with HiMod. The ideal mixing temperature is dependent on the mix as always, but 325 to 340°F is generally good. Check with your supplier on recommended warm-mix additives and again start up a little hotter and slower to heat up the whole system, slat conveyor, silos and trucks, to make sure every point in your process is allowed to get up to good operating temperature. On overnight modified asphalt storage there is varying guidance. If you are new at this, or if you have older storage systems, it is probably unwise to store overnight. If you’re well experienced with modified asphalts, if your silos in particular are in excellent condition, well insulated and well maintained, it may be quite feasible to store overnight.

Construction and More Thoughts on HiMod

When transporting to the paver, make sure as always that the truck bed is smooth and clean. Use of release agents is recommended, but do not use hydrocarbons. Tarping is a very good thing and probably required in your state. These same practices apply for general PMA and for HiMod. Placing hot-mix asphalt (HMA) generally requires no modifications to equipment. Handwork likely will be more difficult, depending on the mix. The ambient temperature guideline recommended by the Association of Modified Asphalt Producers is 50°F and rising.

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Compaction equipment, again, is normal. Keep the mix temperature high enough for good compaction, but no higher. Every 10°F increase doubles the amount of fumes and the higher temperature can damage the PMA polymer structure. Keep the roller up right behind the screed. If available, direct temperature and density measurement is great. Compacting PMAs may actually be easier than unmodified asphalts as it’s been noted that PMA may help reduce or eliminate a tender zone.

There is not much different when placing HiMod. Aim for the temperature behind the screed to be about 300°F. Hotter is not better as it can lead to shoving. Keep the breakdown roller close to the paver. The only significant caveat, and this is an important one, is cooling. HiMod mixes are not any stiffer at operating temperatures than conventional PMA mixes. The cooling rate is about the same. However, the HiMod mix will stiffen up faster than a conventional PMA so your working time on the mix is shorter. This applies to cleanup as well.

Best practices from some states that regularly use HiMod have shown laydown of HiMod binders does not pose a significant problem as reported so far but keep in mind general good construction practices. Prevent end of load segregation. HiMod binders may magnify poor construction practices. Balance your production rate, plant to truck to paver to rollers. Keep the mix moving. Delays will add to cooling of the material, which will give you an increase in viscosity and difficult handling.

Be ready when the trucks arrive on the project as temperature is critical for the mix. Keep compactors tight with the paver. Adjust the rolling pattern as needed to maintain target density. Plant storage may be somewhat different as previously noted. HiMod binders do have a limited shelf life, so scheduling and frequent communication with the binder supplier and the agency is important. Do not store indefinitely. Follow supplier specific handling guidelines, storage temperature, storage time and circulation. Recommended best practices may vary with suppliers, so as with all modified asphalt follow your supplier’s advice.

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Some final comments:

• Do not overheat. High temperature accelerates viscosity rise. Monitor viscosity daily.
• Warm-mix additives are good.
• Unused high polymer binder can readily be diluted to a PG76-22 or -28.
• Repeat—do not overheat.

A good quality control plan is as important or more so with PMA than it is with conventional unmodified asphalt. Especially if the plant uses both unmodified and PMA, all of your materials, all your tanks, pumps, valves, sampling points, all need to be well labeled. Establish standard procedures and hardware settings for asphalt flow into the storage and into the HMA plant. In summary, PMA improves the performance of asphalt pavements. Understand the product that you’re using and treat it with respect. Follow supplier’s recommendations and use best practices.

Stansteel Hotmix Parts & Service shares best practices to inspect the exhaust fan and ductwork

Assessing components at the hot-mix asphalt (HMA) plant is only one step in the overall picture of plant health. The continuous drum mix plant has its best chance at optimum, clean production when all components and electronics are functioning properly without signs of wear or damage. If a duct, bin, flight, bag or other component develops a shiny surface, small leak or other problem, more than production suffers. This month, let’s assess the exhaust areas of the asphalt plant for maintenance purposes.

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Safety Notes

The first step with any plant maintenance is to make sure all inspections, markings or repairs happen while using proper OSHA Lockout/Tagout procedures. Ensure you have complete power disengagement before performing any inspections or repairs. For observations that require fans, motors or other components to be operating, listen or watch for vibration and noises from a safe distance or rely on your controls system to provide feedback on specific parameters. In this situation, you will observe and document, but do not touch the operating equipment.

For this series on assessing your asphalt plant for repairs and to avoid unplanned downtime, plant owners are reminded that only fully trained personnel should be allowed to conduct work on or around the equipment. For safety’s sake, the worker(s) should be fully trained on and act in accordance with all federal, state, county and local laws and regulations, and that includes OSHA and MSHA laws. You want your workers to be familiar with and act in accordance with the equipment specifications and manuals as well as your site-specific safety rules and regulations.

Workers have to take responsibility for their own actions, inactions, consequences and results, but you can ensure the best possible outcome for their safety and your operation’s success when you take the time to train and educate each worker who has access to the equipment and material at your facility.

How to Inspect the Dryer at Your Asphalt Batch Plant

Before You Power Down

While the exhaust fan is still running, from a safe distance, observe the following:

• Is there excess vibration?
• Do you smell any unusual odors?
• With the exhaust fan running, visually inspect it for vibration (If you see vibration, locate a professional fan balancing company to inspect and balance the fan.)
• Are the drive belts shaking excessively?
• Upon startup, do the drive belts squeal until the fan is up to speed?
• When you start the exhaust fan, is there visible dust coming from the stack (dust will cause excessive wear on fan)?
• What AMPS are the motor or motors drawing?

If you said yes to any of these items, a full inspection is needed to ensure the fan is operating correctly. Now is also a good time to inspect the air system to ensure there are no further issues that will inhibit maximum efficiency and production.

With the fan running, compressed air operating and timer engaged, note the action of the filter tubes. You should note a momentary short expansion in each row of filter tubes as they are pulsed.

Lockout, Tagout, Inspect

Start by inspecting the fan outside.

• Are the bearings in good shape? Clean off any excessive grease and see if the fan wheel turns easily.
• Check drive belts for tightness, wear and cracks. Are the V’s polished and running deep in the sheaves?
• Check sheave alignments, wear, proper tightening of taper locks.
• Check V belt alignment and guards.
• Check fan housing where it is secured to concrete or base plates.
• With V belts removed, spin motor shafts to see if bearings sound and feel smooth.
• Do not overtighten V belts. This will damage motor and fan shaft bearings.

Inspect the fan itself.

• Check for leaks at all locations.
• Does the fan rotate correctly and freely without friction?

Look at fan wheel alignment.

• Ensure wheels are positioned on the shaft so there is minimum running clearance near the inlet.
• Ensure the fan wheel is concentric with the inlet.
• Check for any vibration.
• Check the fan strike-off plate.

Open the inspection door on fan housing.

• Check fan impeller edges, welds for wear, wash areas, cracks.
• Spin by hand and check if the impeller runs true.
• Check the fan housing for wear, holes, debris inside.
• Check inlet funnel for wear and alignment with impeller (check OEM specifications).
• Inspect fan strike-off plate for wear, cracks (located in the fan housing).

Best Practices for Pugmill Inspection

Look at the V-belt drive alignment, checking and adjusting the following:

• Fan and motor shafts must be parallel. Adjust and shim the motor as required.
• Fan and motor sheaves must be aligned.
• Adjustable motor sheave grooves must have no eccentricity.
• Fan and motor sheave balance should be checked when there is any vibration.
• Belts must be tight enough to avoid slippage. Do not over-tighten, which loads bearings and causes vibration and unnecessary wear. Follow the drive manufacturer’s recommendations for the type of drive being used.

For direct-drive systems, check the couple alignment. Couplings, particularly gear type, require careful alignment for smooth operation and long life.

The exhaust fan has the critical function to move air throughout the system. Often, many infrequent users do not realize that air has weight and volume, and all this must be taken into consideration when properly sizing and maintaining the fan. The “air” has elevated temperatures, steam, moisture, products of combustion, along with dust-laden air including various particle sizes.

The exhaust fan should be tested at least once per year, depending on volume and material processed.

It’s important to have a baseline and establish the design parameters when the fan is originally installed and the air system was permitted. The annual inspection air volume test should show that it is performing within 5% of the original design. Air volume below design will significantly affect the plant’s ton per hour production rate.

Check Components

Each component in the process should have an original baseline for pressure drop.  Example: The primary knockout box, ductwork, baghouse or other pollution control devices.

Each baghouse—or other air filtration—manufacturer has guidelines for operation and performance and those should be followed.  What some typical guidelines should include:

• Verification that there’s no build-up inside the primary collector and baffles or cyclone impact components are operating originally as designed and installed.
• Ductwork should be inspected for signs of uneven air flow or temperature. If the paint or wear patterns can potentially indicate improper combustion/improper flighting, please note and remove dust build-up and verify proper air velocity.
• Baghouse common checkpoints include verifying the internal baffle plate is intact and the bags are not being worn or sandblasted from lack of air stream diversion.
• Check each pulse valve or poppet cycle to make sure they’re functioning properly and no clean compressed air is applied to the bags.
• At least once per year, perform a fluorescent powder and blacklight test to check for leaks in the bags, top seals, top seal connection and weld joints, especially between the clean air plenum and the dust release area of the baghouse. Often, the top door seals are neglected, but any bleed-in or tramp air will cut plant production performance.
• Verify that all ancillary components, such as rotary air locks, air flow control dampers and safety bypass diverters are functioning as designed.

If you have comments on any of the elements you’ve inspected, make those notes for your ground crew or mechanic and set a date by which you’ll check back on the progress of repairs. Well-maintained and properly functioning exhaust fan and ductwork is integral to the success of your plant. Keeping it in good working order keeps your operation safe as well as efficient.

Here’s how bringing RAP up to mixing temperature can solve problems at the asphalt plant

When the oil embargo of 1973 caused a spike in liquid asphalt cement (AC) prices, our industry rallied around ways to reuse existing asphalt pavements and their constituent parts. Everyone from state departments of transportation (DOT) engineers to contractors experimented with up to 100% recycled asphalt pavement (RAP). You can look up the research papers to learn field trials took place in pioneering states like Pennsylvania and Florida. There were even some lane miles tested in the Los Angeles area of California.

The sad ending to that mid-1970’s tale is riddled with premature cracking and pavement failures, which today’s research attributes to lack of performance-based specs, a lack of rejuvenators, improper gradation control, and inadequate mixing or heating in the batch plants of the day.

As everyone knows, our industry didn’t give up on the concept.

As early as 1980-1982, the Federal Highway Administration (FHWA) gave the green light for formal studies on the viability of RAP in pavement design. By the mid-1980s, Florida seemed to be on board, completing a handful of 100% cold-in-place recycling projects incorporating emulsified asphalt. Minnesota was right behind them with 100% RAP sections on low-volume roads. Our industry was learning how to use various percentages of RAP correctly in mix design because our industry is environmentally responsible. We find ways to incorporate recycle with long-lasting performance.

“RAP material sourced from different origins will have different characteristics with inherent performance variability. Importantly, even RAP sourced from the same location can have variable characteristics, making homogenization a critical step whenever a plant is preparing to use the material.”—Krishna Srinivasan

From reporting on the use of RAP in various layers of the pavement system, to its status within the FHWA and National Asphalt Pavement Association (NAPA) annual RAP and warm-mix asphalt (WMA) survey, AsphaltPro has kept the recycle topic in heavy rotation for nearly 20 years. When it comes to the RAP discussion, we’ve covered performance specs with various National Center for Asphalt Technology (NCAT) engineers, we’ve covered the use of rejuvenators with a number of suppliers, and we’ve covered fractionating with a number of  original equipment manufacturers (OEMs) and others in the field, but we haven’t examined “heat” as closely.

Let’s rectify that now.

Add High-RAP to Your Production

The Importance of Preheating RAP

Every asphalt producer out there understands the importance of getting temperature right in the various sections of the drying drum. Stop and consider the effect of adding ambient-temperature RAP after the combustion zone of the drum.

Carlos O. Cardenas, the Midwest area sales manager for Ammann America Inc., Orlando, spoke in terms of efficiency, safety and quality control when sharing why Ammann recommends preheating RAP before introducing it to the mixing drum.

“When RAP enters the mixing drum at ambient temperature, it can cause significant operational challenges,” Cardenas shared. “Cold RAP can lower the temperature of the virgin aggregates, requiring the plant to use more energy to heat the mix to the desired temperature. Typically, this obstacle is overcome by superheating the virgin material, which increases fuel consumption and dust. By preheating the RAP before it enters the drum, plant operators ensure a more efficient heating process, reducing energy consumption and improving the overall mix quality. Preheating RAP enables it to blend more evenly with the virgin aggregate, resulting in a homogeneous and consistent final product.”

“The secondary mixer serves only to coat the RAP and virgin dried and mixed product with virgin liquid AC.”—Mike Mauzy

Basically, by preheating the RAP, you ensure the binder from the RAP will mix uniformly with the virgin material, thus improving the strength and durability of the asphalt mixture.

Cardenas shared that matching the temperature of RAP and virgin materials is important for safety reasons, too. “Cold RAP entering the drum can lead to inconsistent heating, creating hot spots and increasing the risk of burns or fires,” he said. “This is particularly true when high moisture is present in the RAP. Proper steam removal during the RAP preheating process is crucial for both safety and operational efficiency. Preheating the material mitigates these safety concerns by ensuring the RAP reaches the correct temperature before it enters the mixing zone, reducing the chance of accidents.”

Krishna Srinivasan, CEO at Sripath® Technologies, LLC, Mahwah, New Jersey, also spoke of efficiency and variables in production as well.

“High-RAP mixes contain 30, 40, 50+% of RAP, which is a high percentage of the material in an overall batch,” Srinivasan explained. “If the RAP comes in cold, the material will act as a heat sink and lower the mix temperature to unacceptable levels. This could not only lead to poor quality mix production, but also higher heating costs required to bring the RAP up to proper mix temperatures.

“Preheating RAP can also help drive off moisture, which can also act as a heat sink and drive up energy costs if introduced into the mix chamber. Most contractors will say that on rainy or damp days, they lower the amount of RAP in their mixes, reduce throughput tonnage, or both. Therefore, in order to maintain appropriate production throughput (i.e. tons per hour) and good quality mix that does not lead to compactability issues in the field, RAP is preheated before adding to the mixing drum at a plant.”

How to Preheat RAP Through Mechanical Means

As Cardenas mentioned above, superheating virgin material is one method plant operators will use to ensure incoming RAP reaches mix temperature, but it isn’t a recommended best practice. Mike Mauzy of Reliable Asphalt Products Inc., Shelbyville, Kentucky, brings us to the next idea in our discussion by suggesting additional methods producers can implement.

“Several producers have also recognized the benefit of lengthening the dwell and mixing time for the superheated virgin and the RAP prior to injecting the virgin liquid AC,” Mauzy shared. “This has been accomplished by substantially lengthening counterflow drum mixers, or in the case of Duval Asphalt and some others, adding a secondary mixing drum to a conventional counterflow unitized drum mixer. The secondary mixer serves only to coat the RAP and virgin dried and mixed product with virgin liquid AC.” (The concept of dwell time will be covered at length in the October edition.)

The goals of preheating RAP are, obviously, to bring it up to an optimal temperature, but you’re also eliminating steam. These goals can be achieved in the secondary drum, as outlined in detail by Cardenas.

“The optimal temperature for preheating RAP is typically between 250-300°F,” he began. “It’s essential to avoid overheating, as this can cause the binder to degrade. A secondary drum or two-stage heating process works well to achieve this. The RAP is first heated gently in a secondary drum before it enters the main mixing drum, preventing direct exposure to high temperatures and ensuring that the binder is not harmed.”

From there, Cardenas detailed steam removal. “Proper steam removal during the RAP preheating process is crucial for both safety and operational efficiency. As moisture in the RAP heats, it turns into steam, which can build up dangerous pressure if not properly managed. If steam is not removed efficiently, it can cause steam pockets to form in the mixing area, leading to inconsistent heating, operational disruptions, and even potential damage to the equipment.

“Additionally, uncontrolled steam can suddenly release and create safety hazards that could cause burns or other injuries to plant personnel,” Cardenas continued. “Ensuring proper steam removal through a well-designed venting system reduces these risks, maintains consistent temperatures, and allows the plant to operate smoothly, minimizing downtime and maximizing safety.” (See sidebar on Key Mechanisms for Steam Removal.)

P&S Raps about RAP

During a presentation titled “A Practical Guide for High-RAP Mixes” for the University of Oklahoma May 20, Srinivasan shared with the audience, “Once you start running 25, 30, 35% RAP, you need to invest in more infrastructure to make that happen.”

Multiple OEMs can help with this, of course, but two in particular shared information for this article. Meeker Equipment Co., Belleville, Pennsylvania, has U.S. Patent 5,090,813, covering the dual‑drum cycle (one drum for RAP drying/pre‑heating, the other for final mixing). Ammann offers one in its Ammann HRT (High RAP Technology) plants. It’s worth talking to your plant manufacturer about the concept if you don’t already have a secondary device for preheating higher amounts of RAP in your operation.

While producers may be hesitant to invest in a second drum for preheating RAP, it’s a best practice OEMs promote for more reasons than their own pocketbooks. By bringing RAP up to temperature in a secondary device prior to introducing it to the mixing drum, the plant operator avoids the safety hazard mentioned above and increases the chances for quality blending. Cardenas explained the key to successful RAP preheating, thus blending, lies in selecting the right heating mechanism.

He broke this into two types: indirect heating and burner heating. First, with indirect heating, he explained you’re using a secondary drum to preheat RAP at a controlled temperature before it enters the main mixing drum, which helps maintain the integrity of the recycled binder. Then, low-intensity indirect burners or counterflow drums can be set to apply heat gradually, “reducing the risk of burning off the binder,” he shared. “The gradual heat ensures that the RAP is heated without causing any significant drying or aging of the binder content.”

Once you have your heating mechanism in place, Cardenas has three steps for feeding RAP into the process.

First: Preheat the RAP in the secondary drum or pre-heating unit to a controlled temperature that doesn’t compromise the quality of the binder.

Second: Use a pugmill mixer or post-mixer to blend the pre-heated RAP with the virgin aggregate to thoroughly integrate the RAP into the mix.

Third: Inject rejuvenator at this stage. Cardenas stated specifically, “The rejuvenator should be injected just before the RAP enters the mixing drum or pugmill to ensure that it interacts properly with the RAP binder and helps achieve the desired properties in the final mix.”

RAP + Recycling & Rejuvenating Agents = Roadway Sustainability

How to Preheat and Treat RAP Through Material Management

The moisture removal discussed above harkens to material management. Srinivasan spoke to this specifically.

“Plant operators should keep in mind that stringent control and management of all raw materials, including RAP, are critical in order to produce an end product consistent in specifications and quality,” Srinivasan explained. “Pre-heating RAP to temperature has been shown to provide the advantages of drying and readying the RAP to be blended with virgin materials and dosed with an effective asphalt rejuvenator, all without negatively impacting properties in the final mix. Drum mixing (either single or double) as well as forced air burners are some of the most common, and most effective, options available for pre-heating RAP. In fact, open flame options are more likely to degrade or burn off the aged bitumen in the RAP.

“When feeding RAP, best practices include using lower capacity bins that steadily discharge the fractionated and homogenized material,” Srinivasan continued. “This should be done slowly, rather than in bulk, to reduce material compaction, and continuously, to prevent build-up or caking. RAP can be treated with an asphalt rejuvenator on the conveyor that brings the material from the bin and to the drum mixer. More commonly, dosing with a recycling agent occurs either by direct injection to a pugmill or into the bitumen tank or blender delivering the required virgin binder for the mix. This setup will vary depending on each plant’s design and equipment capabilities.”

We can’t talk about reducing moisture or material handling without talking about stockpile management. During his “High-RAP Mixes” presentation, Srinivasan said, “Every mountain of RAP is different. Every source of RAP is different.” He stressed that it’s vital we treat these stockpiles accordingly.

Pennsylvania Partnerships Place High-RAP Mix

For the AsphaltPro audience, he offered some specific best practices, ranging from building to managing. “RAP piles can vary in height, with most in my experience ranging between 10-12 feet in height. The height will often be set based on operational convenience and the storage capabilities at each individual plant. While some RAP piles can certainly be larger or smaller, the height is less important than the drainage available to the material. Sloped storage surfaces are superior to flat slabs on the ground, where water can accumulate and cause moisture issues that require more time, energy and heat to preheat the RAP. Additionally, compacted or impervious surfaces with integrated water drainage techniques and material stored under cover tend to provide better regulated moisture content.

“Homogenizing RAP for storage and before use in a mix is essential. RAP material sourced from different origins will have different characteristics with inherent performance variability. Importantly, even RAP sourced from the same location can have variable characteristics, making homogenization a critical step whenever a plant is preparing to use the material. Homogenization, or the mixing and grading of RAP that has been fractionated based on particle size, can help with quality control throughout the mix design process. Plant operators will want to homogenize RAP to achieve average properties across batches to achieve a consistent mix output.

“As a best practice, RAP piles should be turned over several times before use to homogenize the material adequately. While this step can add to the required time and resources plant operators are managing, the result can be a more reliable product that plants can be confident will meet specifications. Heavy equipment can be used to turn over the material, moving RAP from top to bottom, back to front, within the pile, but the RAP should never be driven over as this can cause undesirable compaction.”

With the increasing use of RAP in balanced mix designs and surface courses throughout North America, getting production right is key to long-lasting pavement systems. The failures of the past gave us a solid base to work from when setting modern-day performance specs, designing effective rejuvenators, figuring proper gradation control, and discovering best practices for mixing and heating the materials. For more information, each of the sources mentioned herein would be happy to discuss these concepts with you.

Express Your RAP, RAS Content

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Key Mechanisms for Steam Removal

Venting Systems: A well-designed venting system allows steam to escape safely from the preheating unit or mixing drum. These systems typically include exhaust ducts, vents, and steam condensers that direct steam away from critical areas and ensure it does not build within the equipment.

Temperature Control: Maintaining consistent temperature control during RAP preheating is essential. By monitoring and adjusting the temperature gradually, plant operators can minimize the rapid formation of steam. This helps avoid excessive pressure buildup that could lead to steam pockets. Lower, controlled heating ensures moisture evaporates at a steady rate, allowing steam to escape through the venting system.

Secondary Drums for Indirect Heating: Using a secondary drum or indirect heating systems, such as those in Ammann HRT plants, helps mitigate steam buildup. These systems apply heat to the RAP in a more controlled manner, without direct exposure to flames, allowing moisture to evaporate gradually. The steam is directed out of the secondary drum before it enters the main mixing drum, ensuring that the material enters the mixing process at the correct temperature without excessive moisture.

Continuous Monitoring: Constant monitoring of moisture levels and temperature throughout the preheating process is essential for ensuring that steam removal is effective. Sensors and automated controls can trigger adjustments in the heating process, ensuring that steam is released safely and consistently.

By integrating these strategies, asphalt plants can efficiently remove steam, maintaining both the safety of the operation and the quality of the final asphalt product. Sidebar courtesy of Ammann America

Collaboration and conservation: Myrl & Roy’s new HMA plant raises the bar

In South Dakota’s construction corridor, a new hot-mix asphalt (HMA) facility has come online. The recently completed Myrl & Roy’s asphalt plant in Harrisburg is a layered story of more than aggregate, asphalt and tons per hour. It’s about visionary planning, deliberate environmental stewardship, and a team that treats the job as a legacy.

The new 500-ton-per-hour (TPH) facility from CWMF Corp., Waite Park, Minnesota, is a shining example of what’s possible when engineering, environmental planning and collaborative partnerships align.

Myrl & Roy’s is a division of the fifth-generation, family-owned L.G. Everist, Inc., Sioux Falls, South Dakota.

An Idea Set in Asphalt and Stone

From the beginning of the project, Eric Leverson, VP construction materials, L.G. Everist, and his team at Myrl & Roy’s envisioned more than just their second plant. The new facility was designed to exceed their customers’ expectations, streamline material handling, and meet future market demands. The design includes a counterflow drum of 10 feet, 6 inches by 60 feet, four 300-ton silos, dual truck scales, and a fully paved traffic circle to eliminate bottlenecks and improve safety.

“The entire plant is designed to handle maximum production if needed,” Leverson shared. “The most important part of our business is customer service. Being able to handle their needs daily is critically important to us and them. We produce multiple mixes daily so having two scales and multiple silos coupled with the capacity of the plant allows us the flexibility to switch between mixes and customers’ needs and not sacrifice service. Our focus is to move the customers in and out in an orderly fashion and not slow them down.”

Leverson noted that this new site had to fulfill the dual function of ready-mix and asphalt operations and prepare for future expansion, including recycling capabilities. The one-way truck traffic pattern minimizes cross-traffic and confusion, helping to protect drivers and plant personnel while accelerating loadout. According to Leverson, minimizing wait times and maximizing service is vital, as 75% of the mix will go to external customers.

“When we first laid out the site plan, it was very important that we understood the different activities that would be taking place on site,” Leverson explained. “We originally developed the site for the installation of a dual lane ready-mix plant, but we also wanted to have plans in place for a future asphalt plant and recycle yard.

“My main concern was to make sure we identified not only the current needs, but also the potential future needs. With the amount of incoming and outgoing materials along with accommodating employee and public activities, traffic flow was one of the important and critical things that needed to be thought through and addressed. The original plan had a high-level conceptual idea of traffic flow, but the final plan was not developed until much of the site was completed. Temporary traffic control was used while the new ready-mix plant was operational. This allowed us to monitor traffic patterns for the operating season and identify what the final plan would look like. Striping, delineation and signage was the last activity to take place.”

“In the end, we did have a successful lift off. With only being in operation for a couple of weeks, the initial planning, execution and overall operation has been successful.”—Eric Leverson

Planning with Environmental Purpose

From concept to execution, environmental stewardship was key. Leverson and his in-house engineering staff designed the site to function as a self-contained ecosystem. “We have an in-house engineering staff that put together a rough outline of the layout and what we wanted for the site,” he said. “A local civil engineer assisted in putting together the site plan.”

Every paved surface has drainage leading to a storm sewer system that channels water into two deep retention ponds that serve multiple on-site functions.

With 75% of the site paved in concrete or asphalt, according to CWMF’s Vice President Travis Mick, airborne dust is greatly reduced. “There is drain tile under the concrete paved surface of all the material storage areas, allowing moisture to optimally drain from the stockpiles,” Mick shared. “There is a massive truck staging area out of the busy area of the plant, keeping things safe and orderly. Berms and trees surround the perimeter to keep an upscale appearance and to match the beautiful, gated entrance and exit points of the site.” These elements were installed intentionally to ensure the site would be an environmentally responsible addition to the community.

“The entire site is self-contained and has its own storm sewer system,” Leverson said. “The storm sewer drains into a network of drainage ponds which ultimately end up in two large retention ponds. The site has a network of water hydrants at various locations that are used for not only dust control, site wash down, water truck fill stations, aggregate stockpile control but also ready-mix truck wash out ponds. All the stockpile areas are paved with positive drainage that allows the moisture to drain away and get captured by the storm sewer and recycled for onsite use.

“It was important to us that we understood the impact a site like this would have on the area, not only for the traveling public but also the natural habitat. This was all taken into consideration when the site was built. We feel we have addressed not only the concerns of the public but also impacted the natural environment and habitat in a positive way.”

Leverson described how the team took extra steps to address local impact. LG Everist worked with the local governments to accommodate traffic increases and upgraded a portion of the farm-to-market road servicing the site—out of pocket. Leverson said it was part of being “good stewards of the land and the community.”

Seamless Collaboration Among Experts

CWMF served as the primary equipment provider, supplying the counterflow drum, slat conveyors, silos and control systems. CWMF’s Mick noted that this project, though not the first interaction with Myrl & Roy’s, was the first large-scale partnership with the company under LG Everist ownership. He spoke highly of the contractor’s planning and attention to neighborly details.

ARC Fabricators supplied the bins and scale conveyors. From there, CWMF contracted with Motion Engineering to install the plant and piping for the tank farm, and with Meeker Equipment to handle the tank farm.

Jeff Meeker described the intricate and safety-focused AC tank system: “Our part of the project was to supply the AC tank farm, which consists of six 40,000-gallon asphalt tanks, AC piping, hot oil heater, mass flow meter, a 10,000-gallon emulsion tank and associated pumping and loading equipment.”

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Meeker elaborated on the automation technology, sharing: “All the valves on the piping system are controlled by Meeker’s Liquid Vision valve control system and tank monitoring control. Inside the control room, we provided an Allen Bradley plc control and HMI. The plc has the logic done for normal operations and also unique situations. All scenarios are taken into consideration with the Liquid Vision.”

Motion Engineering was responsible for installation aspects. Mike Petrie, operations manager at Motion, clarified: “Motion Engineering was responsible for the mechanical installation of all equipment as well as mechanical installation of all hot oil and AC piping in the tank farm.” He pointed out the Motion Engineering team handled the insulation for the entire plant and spoke proudly of his team. “Our team did an incredible job with the insulation…and it’s becoming more important to emphasize the advantages of insulating equipment.”

“It was very clear to us at the beginning that Myrl & Roy’s was going to take the lead on exactly how they wanted everything designed,” Petrie continued, but that was no challenge for a team working in concert. Trust among the team was crucial and worked in everyone’s favor.

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“There is a great relationship that exists between Motion Engineering, Myrl and Roy’s, CWMF and Meeker,” Petrie said. “We all want to get it right at the end of the day to ensure longevity of the plant.”

Getting everything right at the end of the day requires coordination. “There is an intense amount of final fitting and changes that come with a new asphalt plant build,” Petrie emphasized. “All the AC piping/valving was prefabbed but the hot oil piping was something that we helped design in the field. We had to make sure that we built the hot oil piping according to what the OEM’s specifications are.”

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Pre-Planning for Success

Mick shared that the quoting/conversation with CMWF and Myrl & Roy’s started in November of 2022. “We were awarded the job in August of 2023. This project hit production in March of 2024. The first components were delivered in the month of May. Equipment installs started with the tank farm. From there, we continued with the silos/slat.” By Labor Day, the plant was structurally in place. Final electrical work continued through the fall and winter.

When the team fired up the plant on May 28, 2025, Leverson said they targeted 2,000 tons on the first day—and exceeded it.

Leverson acknowledged the startup came with a learning curve. The team spent about three weeks identifying and resolving issues. Still, all underground electrical and mechanical systems installed prior to the winter performed as expected.

The planning, including conduit burial and early groundwork, was vital. Leverson and his in-house team oversaw months of activity long before the drum or silos went up—grading, paving, trenching, pouring footings—all choreographed for a seamless equipment installation.

Looking ahead, Leverson sees the Harrisburg plant as a blueprint for future-ready operations. “It’s about building something responsible, scalable, and respectful of the land and the community,” he said. “That’s what we set out to do, and I believe we achieved it.”

Technology in Action

Even in its earliest weeks of operation, the Harrisburg plant’s design choices are proving their worth. Leverson shared that the facility exceeded production expectations on opening day and has shown consistent reliability since.

The advanced systems supplied by CWMF, Meeker Equipment and ARC Fabricators play a pivotal role in this performance. With multiple silos and dual truck scales, the plant can handle several mix designs in a single day without disruption to customer service.

The Liquid Vision system from Meeker Equipment is already simplifying operations. The plant operator can manage tank flows and monitor levels without stepping foot outside the control room. Drivers unloading asphalt can access real-time tank data, reducing the risk of overfills and improving efficiency.

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“If a driver is in control, he can choose the tank he is delivering to,” Meeker said. “He knows the amount of liquid AC already in the tank, and it will alarm him if the tank is getting too full.

“All of the Meeker AC tanks come with a hi-level float—what we call a stainless steel basketball,” Meeker continued. “It’s a final safety measure to stop the flow of AC into a tank.”

That emphasis on automation and safety extends across the site. From automated truck spray-downs that reduce dust and eliminate the need for drivers to leave their vehicles, to traffic signage and scale lane separation, the site is focused on safety-first productivity.

Team Pride

Throughout every phase of the project—from site selection and early grading to the final wiring and commissioning—the Myrl & Roy’s team operated with precision and a strong sense of ownership. Their in-house crews coordinated infrastructure, utility trenching and poured critical foundations while managing the complexities of a multi-vendor installation.

Leverson noted how the team’s proactive attitude made the difference. Whether troubleshooting complex mechanical systems, refining traffic flow or accommodating last-minute layout adjustments, the crew never faltered. “The main objective was to build a plant that had [higher] production capabilities if we needed it, plenty of silo storage with multiple loadout scales and plenty of liquid AC storage. We have not been in operation very long, but those choices have proved themselves already.”

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He added that the Myrl & Roy’s staff took personal pride in the facility throughout the build. Employees guarded exposed conduit installations during active phases to prevent damage and monitored subcontractors to maintain site integrity. Their commitment ensured that no detail was overlooked. “All of the conduits, wiring and airlines survived the winter. They have performed as anticipated. We spent approximately three weeks in start-up mode, troubleshooting problems and eliminating issues. With the amount of electrical and mechanical parts that are involved, this was probably not unrealistic. We had plenty of trial and error, frustration and other emotions that we fought through, but in the end, we did have a successful lift off. With only being in operation for a couple of weeks, the initial planning, execution and overall operation has been successful.”

The team’s hands-on approach created an asphalt plant that blends high production with environmental responsibility, technology integration and site safety. Leverson emphasized that the people behind the work are the plant’s greatest asset.

Looking Ahead at a Sustainable Legacy

With the new plant now fully operational, Myrl & Roy’s has laid the groundwork for a long-term model of environmental stewardship. Leverson and his team continue to monitor and fine-tune systems to optimize efficiency and minimize impact.

Future goals include increasing the use of recycled materials. Leverson reflected on the larger mission: to build infrastructure responsibly, not just for business, but for the region and the environment. “Every aspect of the Harrisburg plant was built with the future in mind—not just in terms of production, but also sustainability,” he said. “We wanted this to be a benchmark facility, one that reflects who we are as a company and how we want to serve this community.”

The facility may have only recently opened its gates, but it already stands as a powerful symbol of what a responsible, forward-looking plant build can achieve.

Stansteel Hotmix Parts & Service shares best practices to inspect the dryer at the batch plant

Assessing components at the hot-mix asphalt (HMA) plant is only one step in the overall picture of plant health. This month, the plant maintenance series from Stansteel Hotmix Parts & Service, Louisville, Kentucky, focuses on the batch plant, showcasing the dryer specifically.

Solve Blue Smoke from High RAP

Safety Notes

The first step with any plant maintenance, whether a continuous drum mix facility or a batch plant, is to make sure all inspections, markings or repairs happen while using proper OSHA Lockout/Tagout procedures. Ensure you have complete power disengagement before performing any inspections or repairs. For observations that require fans, motors or other components to be operating, listen or watch for vibration and noises from a safe distance or rely on your controls system to provide feedback on specific parameters. In this situation, you will observe and document, but do not touch the operating equipment.

For this series on assessing your asphalt plant for repairs and to avoid unplanned downtime, plant owners are reminded that only fully trained personnel should be allowed to conduct work on or around the equipment. For safety’s sake, the worker(s) should be fully trained on and act in accordance with all federal, state, county and local laws and regulations, and that includes OSHA and MSHA laws. You want your workers to be familiar with and act in accordance with the equipment specifications and manuals as well as your site-specific safety rules and regulations.

Workers have to take responsibility for their own actions, inactions, consequences and results, but you can ensure the best possible outcome for their safety and your operation’s success when you take the time to train and educate each worker who has access to the equipment and material at your facility.

Always utilize OSHA Confined Space procedures.

9 Tips for Asphalt Plant Maintenance

 

Before You Power Down

While the dryer is still running, from a safe distance, observe the following:

• Are motors operating at normal temperatures? (Non-contacting infrared temperature guns work well and from a safe distance.)
• Is there excessive noise or vibration during motors’ operation?
• Do you smell any unusual odors during operation?
• Are bearings operating at normal temperatures?
• Is there excessive noise or vibration during operation of the bearings?

Start With the Big Picture

With proper lockout/tagout procedure in place, perform a visual inspection of the complete dryer system. You’re looking for noticeable issues—any areas that might be damaged or in need of immediate repair or replacement. Depending on what damage you see, you may circle it with spray paint, paint or mark with a Sharpie to indicate exactly where the problem is, or place some other type of tape or marker where the mechanic or grounds crew can find and fix the damage efficiently. You will also record the damage or problem in your company’s log, whether that’s a paper worksheet or an app on the Tablet you carry into the field.

Also look at the dryer seals. You’re looking for cracked seals or missing sections. Make a note of these for repair or replacement.

While still outside the dryer, perform a shell thickness test in multiple areas. It’s helpful to “map” your drum with not only a thickness profile down the length of the drum, dryer or rotary mixer, but also to capture a temperature profile while in operation and note operational details such as tons per hour, percentages of reclaimed material being used, fuel used, etc. This can help to identify flighting problems or poorly tuned burners in the future.

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Inspect Inside

Following OSHA standards for Confined Space entry, it’s time to look inside the dryer.

• Are there any missing flights?
• Are there any broken flights?
• Are there any bent flights?
• Are there any heat-distorted flights?
• Are there any missing flight clips?
• Are there any missing or damaged materials dams?
• Inspect the inlet spiral flights and make notes for repairs.
• Inspect shell integrity, looking for excessive wear throughout.
• Check the combustion flight zone, where excessive heat from the burner flame exists; perform shell thickness tests in this area.
• Take photos of the interior, of the flights and of the burner area and date them.

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Inspect Discharge Area

You want to give special attention to the discharge paddles and check for the following:

• Are there any missing discharge paddles?
• Are there any bent discharge paddles?
• Are there any missing connection bolts?
• Inspect the discharge paddle ring and wear bars.
• Inspect the discharge chute for visible wear.
• Inspect the discharge chute for missing or worn liners.

Inspect Drive Components with Power Off

The observations while the dryer was running gave you some information at the beginning of the inspection. Now with power off and proper lockout/tagout procedures, it’s time to get closer to the motors, reducers, sprockets and guards.

• Are all motors properly ventilated? (Is heat dissipating; fins clean?)
• Are all motors connected to drive coupling with no signs of misalignment?
• Check and maintain proper oil levels in motors/reducers.
• Double-check that oil samples have been taken and that recommended oil changes have occurred.
• Are drive or driven sprockets showing signs of wear?
• Are there any visible cracks in shafts?
• If you have drive belts, are any cracking? Are they tensioned properly?
• Are sheaves showing signs of wear?
• Is the drive chain showing signs of wear?
• If you have a cradle chain drive, is there chain shoe wear?
• If you have a cradle chain drive, inspect the drive/driven sprocket.
• If you have a cradle chain drive, inspect the circumferential sprocket.
• If you have a ring gear drive, inspect the ring and pinion gear.
• If you have a trunnion drive, inspect the trunnion and tire faces as they can provide indications of poor wear patterns before excessive damage occurs.
• Are bearings properly lubricated?
• Is there visual abnormal coloration? (blackened grease)
• Is there excessive grease or oil escaping the bearings?
• Are bearing mounting bolts tight?
• Are there any cracks in bearing housings?
• Inspect tires for misaligned wear, as well as making sure all tire rigging is intact.
• If any rigging bars are missing, note for immediate repair and replacement.
• Check and measure the gap between the tire inner diameter and the surface of the support rigging. This is most important at the 12 o’clock position. Note if the drum is cool or hot.

Inspect Trunnions

The trunnion alignment and maintenance is so important that AsphaltPro Magazine has included several articles about this topic over the years. If you see excessive wear on trunnions and tires, this could be because of improper trunnion alignment. Stansteel Hotmix Parts offers the T-Trac Alignment System that is designed to establish a properly skewed trunnion roller setting to thrust the drum/dryer/rotary mixer in the uphill direction to its desired neutral thrust operating position. This can save thousands of dollars in premature trunnion and tire wear. Make sure you inspect and note the trunnion for immediate repair and replacement, if needed. Also inspect the thrust rollers and bearings for excessive wear as well as spacing.

If you have comments on any of the dryer elements you’ve inspected, make those notes for your grounds crew or mechanic and set a date by which you’ll check back on the progress of repairs. A well-maintained and properly functioning dryer is integral to the success of your batch plant. Keeping it in good working order keeps your operation safe as well as efficient.