Automated scraper strainers paired with macerators eliminate high volumes of large, suspended solids from slurries for a “set it and forget it” approach. All photos courtesy of Acme Engineering

Automated scraper strainers paired with macerators eliminate high volumes of large, suspended solids from slurries

In the asphalt industry, industrial strainers are used to separate unwanted suspended solids from liquids and slurries for efficient transloading, in which asphalt is heated to a liquid form and transferred from tank cars to trucks or from trucks to tank cars at rail facilities. However, conventional strainer methods can be improved upon to keep debris or solids of substantial size or quantity out of the liquid.

A novel blend of industrial wastewater technologies now allows for the efficient removal of solids without the need for extensive manual labor and so on. Specifically, the design involves the combination of a macerator, which breaks down large solids into smaller fragments, and an automated scraper strainer flexible enough to filter out larger debris along with tiny particles. This innovative solution is even designed to accommodate high solids loading without clogging.

The combination of these two established technologies is already being applied to some of the toughest straining applications including asphalt transloading, wastewater debris, power plant boiler water slag and meat processing waste streams. Our interest here is asphalt transloading.

“Although the macerator cuts up the biggest solids, the strainer must still be able to separate both relatively large pieces and tiny particles while handling high solids loading without becoming obstructed.”—Robert Presser

Overcoming Traditional Limitations

Duplex strainers are often used in continuous flow processes that cannot be shut down for cleaning purposes. Duplex basket strainers employ two distinct chambers that function independently. When one chamber needs cleaning, the flow is diverted to the alternate chamber, enabling the removal and cleaning of the first basket.

Cleaning is a laborious process that involves equalizing pressure between the baskets, diverting flow to the off-line chamber, opening the cover, manually removing the clogged basket, and cleaning it before refitting the basket, ensuring the seal and tightening the fasteners.

An automated scraper strainer like that from Acme Engineering is designed to continually remove both large and small suspended solids from liquids and slurries.

If an operator fails to adequately clean the basket strainers for any reason, both strainers can become clogged at the same time. This compromises the filtration process, resulting in quality issues or unexpected downtime until the problem is resolved. For many processors, this can occur simply due to having insufficient personnel to keep basket strainers clean along with their other duties.

“As an alternative, a combination of established complimentary technologies such as a macerator and an automated scraper strainer can essentially ‘knock out’ even the toughest problems related to large solids and high solids loading in an automated way,” said Robert Presser, vice president of Acme Engineering Prod. Inc., a North American manufacturer of industrial self-cleaning strainers. The company is an ISO 9001:2015 certified manufacturer of environmental controls and systems with integrated mechanical, electrical and electronic capabilities.

In this configuration, a macerator would be installed upstream to reduce large solids down to a manageable size. The capabilities of the automated strainer are crucial to the process as well, according to Presser.

“Although the macerator cuts up the biggest solids, the strainer must still be able to separate both relatively large pieces and tiny particles while handling high solids loading without becoming obstructed,” Presser explained.

Adapting strainers for the specialized filtration of uncommon liquids and slurries requires not only expertise but also collaboration with the processor as well as some design iterations.

In the case of Acme, the OEM’s automated scraper strainer is designed to continually remove both very large and very small, suspended solids from liquids and slurries. Cleaning is accomplished by a spring-loaded blade and brush system, managed by a fully automatic control system.

Four scraper brushes rotate at 8 revolutions per minute (RPM), resulting in a cleaning rate of 32 strokes per minute. The scraper brushes get into wedge-wire slots and dislodge resistant particulates and solids. This approach enables the scraper strainers to resist clogging and fouling when faced with large solids and high solids concentration.

Blowdown typically occurs only at the end of the intermittent scraping cycle when a valve is opened for a few seconds to remove solids from the collector area. Liquid loss is well below 1% of total flow.

If additional pressure is required to clean the screen, Acme Engineering can add an inexpensive trash pump to the blowdown line to assist in removing the solids from the strainer sump.

How to Perform Pressure Aging of New Mix in the Lab

“Since the solids are small, a little trash pump can pressurize the blowdown line to evacuate solids from the strainer. The combination provides quick ROI because operators no longer have to monitor and clean out heavily loaded basket strainers, resulting in substantially less labor and downtime,” Presser said.

Alternatively, the sump can be replaced by a cylinder bracketed by two gate valves that open and close as needed to remove the solids waste.

“When you are ready to empty the cylinder, you close the top gate valve momentarily and open the bottom one by depressing a button to dump the accumulated solids into a receptacle like a dump truck or a conveyor bucket so there is no manual handling required,” Presser said.

According to Presser, Acme has worked with operators and managers at rail facility intermodal terminals to implement a wide range of specialized straining systems for difficult applications with exceptionally large solids or very high solids loading.

How to Perform Degassing of New Asphalt Samples in the Lab

In one example, the OEM installed equipment to strain asphalt slurries at intermodal terminals providing rail-to-truck and truck-to-rail transloading services. One application involved using multiple cylinders with gate valves to appropriately strain liquid asphalt to the correct specification for rail-to-truck loading.

According to Presser, adapting strainers for the specialized filtration of uncommon liquids and slurries requires expertise and collaboration with the processor and some design iterations.

“For unusual applications, it may take a few attempts to get it right. You may have to adjust the timing and frequency of cleaning as well as adjust the screen slot size. There are quite a few variables involved,” Presser concluded.

For more info, visit Acme Engineering Prod. Inc. at acmeprod.com.

Editor’s Note: For 2024, AsphaltPro Magazine allows experts in the industry to share how to expand your operations to the next phase of business. Are you ready to start making your own hot-mix asphalt? Let’s turn to some professionals who have equipment, services, software and tenure to help you expand to mix design, production, hauling and more. This month’s installment looks at the best practices you can employ with the storage silo to offer customers quick, quality asphalt mix for their paving projects.

If you’re in the hot-mix asphalt (HMA) industry, you know one of the game-changing inventions of last century was the storage silo. During his “Asphalt Plant Efficiency” presentation during a World of Asphalt People, Plants and Paving session in Nashville in March 2024, Greg Renegar, the vice president of customer success for Astec Industries, Chattanooga, discussed the benefits of planning ahead with your storage silos in mind.

If your “why” is to provide mix for both customer and in-house crews, you’ll want to plan ahead for overnight storage of appropriate mixes as you build your new plant. During his presentation to the World of Asphalt audience in March, Astec’s Greg Renegar reminded attendees the plant that can start loading out customers first thing in the morning will be the plant everyone flocks to.

As he explained, even if you have older components you’ve been unable to update the past few years, you can operate efficiently if you maintain those parts, tighten up your environmental footprint, and follow best practices, such as optimizing the use of storage silos.

Notice that’s “optimizing” the use of storage silos. Not every mix design is ideal for the suggestions to come, and we’ll talk about those.

“If you are using very low absorption aggregates, it may lead to a high film thickness and the mix is more prone to drain down.”—Steve Jackson

Solve Asphalt Plant Odor Issues

Store It for Fast Startup

Renegar’s presentation included a side-by-side comparison of operations you might be able to share with your production team to showcase what’s optimal and what’s not.

Amazing Producer ABC

Using old technology

• Starts loading out of prefilled silos at 6 a.m.
• Starts up the plant at 8:30 a.m.
• Runs two to three mixes on various jobs, with enough trucks for the day
• Runs all day with changeovers but no mid-streams
• Fills the silos at the end of the day for tomorrow’s early customers

Expand into Production: Plant Ticketing Software Basics

Struggling Producer XYZ

Using new technology

• Starts making mix at 6 a.m.
• Runs two to three mixes on various jobs, short of trucks
• Mid-streams at 8:30 for 45 minutes
• Runs another 300 tons and finishes for the day!
• Cleans out
• Gets a call at 10:15 a.m. for a 150-ton parking lot job
• Fires back up at 11 a.m., runs 147 tons, then mid-streams while paving foreman figures the last bit needed

One of the two producers in our examples is using new technology for its efficiency and sustainability but isn’t using best planning strategies. Renegar shared plants that start and stop more than three times per shift use up to 20-35% more fuel than they do when they run steadily. These percentages are published in the National Asphalt Pavement Association (NAPA) publication QIP-132.

You can probably monitor the effect of starting and stopping on your own fuel use. By using the storage silo to take up the slack and prevent starts and stops, you keep a steady, even production. Renegar stated Astec’s most successful customers are the ones who use long-term storage capabilities to become more profitable.

Think about it.

Because 95% of breakdowns occur at startup, you have a leg up on the day even if unplanned downtime hits you at first light. You also have a leg up on your competition on the other side of the county if your plant already has mix in the silo while Producer XYZ is still getting fired up.

Renegar explained it this way: “Storage in multiple silos plus planning allows FOB customers to get in and out quickly in the morning. Serving the FOB customers better than your competition will result in more business.”

Expand Into Production: Navigate the Permit Process

Design Your Storage

This isn’t rocket science. But it does require forethought. Renegar cautioned producers on some reasons you might not want to store mix overnight. For example, lack of planning from your customers could result in wasted mix. There’s no point in producing a hundred tons of state mix at 300 degrees if your top five customers will show up wanting a less-pricy mix produced at 340 degrees.

If you don’t have proper heating systems in place, you run the risk of losing mix temperature. There are companies making electric heating elements that can be placed in silo cone packages to take the fear out of overnight storage. These entities might not make the silo itself, but are experts in the manufacture of electric heating components and provide these to OEMs like CWMF Corp., Waite Park, Minnesota, who then assemble the complete silo.

Even with the concern of temperature under control, you want to consider the mix design you’ll store. Renegar listed the “fear of storing polymer” as one of the reasons producers shy away from filling up the silo overnight or over a weekend. Folks in the field echo his concern when it comes to open-graded mixes due to a phenomenon known as drain down. This is when gravity pulls the liquid asphalt cement (AC) away from the aggregate and down toward the silo cone.

Steve Jackson, the vice president of plant operations and sustainability for NB West Contracting, Pacific, Missouri, spoke of this phenomenon in stone matrix asphalt (SMA) mixes. “The worst mix that I have seen for drain down is SMA,” Jackson shared. “That is why some agencies are reluctant to remove the cellulose fibers even when you add ground tire rubber or reduce the mix temperature.”

He gave an example. “I remember an SMA project where we filled a silo, and that was all the mix that we made for the night. The first sample, from the bottom of the silo, had high AC and 1.5% air voids. The second sample, toward the top of the silo, had low AC and 7% air voids. We made the mix extra hot because it was going to spend a long time in the silo.” The expensive lesson he shared was having to mill out that tonnage and replace it.

How to Become Your Own Hot-Mix Supplier

“SMA, open-graded friction course and other gap-graded mixes are the worst for this phenomenon,” Jackson continued. “They also usually have specified minimum asphalt contents. If you are using very low absorption aggregates, it may lead to a high film thickness and the mix is more prone to drain down. When Joe Schroer (NB West’s construction materials engineer) worked at MoDOT, he evaluated some of those mixes, and started calculating the volume effective binder, and approved some of the SMA mixes with less than the minimum spec requirement AC content of 6.0%.”

In other words, there’s hope for “fixing” the gap-graded mix so it can be stored overnight for quick loadout in the morning, if you’re willing to work with it.

Malcolm Swanson, industry consultant and president of e5Engineers LLC, Chickamauga, Georgia, shared his thoughts. “Coarse graded mixes, SMAs, any mix with little surface area will tend to drain down. That is a major reason for adding fiber to a mix. Fiber adds surface area without changing gradation. The added surface gives the AC a place to hang on.”

“If the state allows the contractor to design their own non-gap-graded mixes, then the mix has the absolute minimum asphalt content, so they are less likely to drain down,” Jackson said. “If there are mixes that specify a minimum asphalt content, then I would be careful. Take a look at the aggregate absorption as well. We typically use aggregates with 1% or lower water absorptions in our high type mixes, these are mixes that we try to drop the mix temperature as low as possible to prevent drain down.”

For producers looking to optimize the use of the storage silos, it’s possible to adjust the mix design and temperature to ensure you have exactly what your customers are looking for first thing in the morning. It might take a little forethought and planning, but the producer who plans ahead is the producer who can optimize all the components for a tight environmental footprint, an efficient operation and a plant that all the customers flock to.

Good business leaders understand that higher quality generally equates to lower overall risk to the company—lower risk for defective products, associated lawsuits, and the resulting loss of reputation and sales. Let’s look at building a risk-based quality management system (QMS) in your testing lab to meet or exceed a variety of accrediting agency standards, such as the American Association of State Highway and Transportation Officials (AASHTO), ASTM International (ASTM) and International Organization for Standardization/International Electrotechnical Commission (ISO/IEC).

QMS is Required

Construction materials testing (CMT) labs that provide testing services on publicly funded projects are required to have an approved QMS to meet the quality requirements of AASHTO R18, ASTM D3666, ASTM C1077, ASTM D3740, ASTM C1093 or ASTM E329. This requirement is typically contract or specification driven and will depend on the scope of work for the project. While most CMT labs pursue these standards as a framework for developing their QMS, many go above and beyond.

Many labs follow a more robust outline to deploy their QMS to showcase their lab competence and uphold higher standards. Many quality experts consider the ISO/IEC 17025 standard “General Requirements for the Competence of Testing and Calibration Laboratories” one of the most reliable standards for developing a QMS.

Deploying a risk-based QMS that conforms with AASHTO, ASTM, and ISO/IEC quality standards is a rigorous task.

When a QMS is developed to meet regulatory requirements or exceed minimum expectations, lab managers often need help to define the scope and extent of policies, procedures, processes, etc. Their challenge is exacerbated by the industry’s continuing evolution and lessening room for error. QMS is always a work in progress.

RMAEC Offers Certification for Process Control/Owners’ Acceptance Testing

Consider Risk

Risks, and their associated tolerance, are critical components for any lab operation, but they’re hard to identify. Some are harder to quantify. When risks creep into a QMS, they weaken the system, making it unreliable and prone to manipulation. At the very least, a risk assessment should include risk probability, severity and existing mitigation techniques.

The current version of the ISO/IEC 17025 standard, released in 2017, applies risk-based thinking to developing a QMS. It doesn’t provide any prescriptive solutions to manage risks. Instead, the standard requires the lab to perform a risk assessment and develop a management plan based on the risk’s influence on performance.

The standard gives sufficient discretion to lab managers to assess and manage the risks as they see appropriate. We’ll examine two sections of the ISO/IEC 17025 standard from the risk assessment and management perspective as it applies to CMT labs to demonstrate the risk-based approach to developing a QMS framework. The risk severity and probability for any given section in the ISO/IEC 17025 document will likely differ for different labs; Therefore, consider how the risk assessment and management plan discussed in this article could meet your organization’s needs.

Section 4.1: Impartiality. Risks from perceived bias have always been around, but with the current ISO/IEC 17025 standard, they need to be addressed by assessing and suitably managing them. These risks can range from innocuous to detrimental to any lab’s operation. For example, a personal relationship between a lab staff member and a customer can cause any reasonable person to question the impartiality of the lab finding. If management considers an issue like this harmful to its business, it is in the lab’s interest to establish policy guardrails to curb such problems. To manage the risk described above, the lab can have a policy that says if the customer and a lab member have a personal relationship, that lab member shall work on the customer’s project under the direct supervision of another lab personnel.

Section 8.7: Corrective action. Nonconformities are inevitable in any lab testing operation. But not all nonconformities rise to the level of requiring a risk-based corrective action. Some are isolated incidents that require a one-time corrective action. If the issues start recurring and become severe, there may be a good case for planning to manage that risk. However, it’s challenging for labs to assess the reason(s) for nonconformities and implement timely and effective corrective action. Let’s look at an example. A lab technician repeatedly failing to follow correct sampling procedures certainly could rise to the level of risk assessment. Managing this risk may include, among other things, retraining the technician to perform their task per the relevant standard methods.

Bluegrass Testing Laboratory Focuses on Asphalt Mix Designs, Binder and Aggregate Testing

PDCA

The lab should always consider the severity and probability of risks when planning the scope and extent of how to manage them. When planning risk management steps, a good formula is to use the PDCA rule: plan, do, check and act. To elaborate, plan what you will do when there is a risk, do what you planned, check if you accomplished what you wanted, and act on the gap between the plan and accomplishment. The other big part of resolving any issue is to keep all parties in the loop if needed. This will go a long way toward resolving problems and gaining stakeholder credibility.

A QMS is like a musical ensemble, if you will. In a musical ensemble, a group of well-rehearsed musicians plays a piece together in accord. It rarely happens that a change made somewhere or a lack of harmony among musical notes goes unnoticed in the final production. Like a musical ensemble, all it takes is one element of the QMS not to meet its quality objective, potentially reducing its overall effectiveness. Therefore, the lab staff should ensure that all aspects of the QMS are performing optimally. Deploying a risk-based QMS that conforms with AASHTO, ASTM, and ISO/IEC quality standards is a rigorous task. It is common to feel that the QMS is a burdensome requirement for companies to comply with. However, not having a functioning, structured, risk-based QMS could lead to failure for any lab. A reputation for inconsistent or unreliable results does the very opposite of driving sales, especially in the built environment.

Jayanth Kumar Rayapeddi Kumar, PE, ENV SP, currently serves as the quality control engineer for Jas. W. Glover Ltd. in Hawaii, and on the ASTM D04 committee on Road and Paving Materials and the ASTM E36 committee on Accreditation and Certification. Reach him at jayanthk@gloverltd.com.

Dave Savage is the director of accreditation for CMEC Inc. and serves on ASTM Executive Committees E36, Accreditation and Certification, and D04, Road and Paving Materials. Reach him at davesavage@cmec.org.

Paul Matera currently leads the Inspection Body program for the ANSI National Accreditation Board (ANAB). Before joining the ANAB staff as a senior accreditation manager, he provided assessment services to different accreditation bodies and industry groups. Reach him at pmatera@anab.org.

The U.S. Army Corps of Engineers Research Lab developed in 1976 an empirical metric for rating a pavement’s condition taking all types and severities of distresses into consideration. The international standard ASTM D6433-20 (and ASTM D-5340-20 for airports) uses the resulting pavement condition index (PCI) to determine the current condition of a pavement network, but the calculations of the PCI value can be time consuming and difficult to perform.

To do all the PCI calculations based on ASTM D6433-20 and with the functional pavement condition data within the sample unit that a user defines, Dynatest A/S, headquartered in Denmark, has launched its automated PCI calculation function as a licensed module within the Dynatest pavement analysis program, Dynatest Explorer (DE). Here’s how it works:

Because the PCI calculation tool is a module of DE, the user first takes readings of the pavement in question with the Dynatest Multi Functional Vehicle (MFV) equipped with the Road Surface Profiler (RSP) system and Laser Crack Measuring System (LCMS®), which collect pavement data.

Dynatest Data Collection (DDC) software stores and controls the data from the MFV’s survey. The data is displayed while testing or stored for export into the DE program.

The DE program analyzes the data, evaluating the functional pavement condition. DE then gives the user access to all the data, images and distresses acquired during the survey, allowing for visualization, verification, calculation and reviewing of results, which now include the PCI values.

The system can display the PCI values on a table or a graph, export them to Excel, or show them on a map exported to Google Earth.

For more information, contact Dynatest through Oline Westerdahl at owl@dynatest.com.

Editor’s Note: In the August Hawaii Asphalt Paving Industry (HAPI) newsletter, Jon Young shared a summary of the Airfield Paving Clinic Workshop (APCW) held July 11 and 12 at the Daniel K. Inouye Airport Conference Center. The goal of the workshop was to discuss changes to the Federal Aviation Administration (FAA) Advisory Circular (AC) 150/5370-10H, which is more commonly referred to as the P-401 spec. The article is reprinted with permission and goes over the changes, which were issued Dec. 21, 2018, and discussed at the workshop.

Changes to the P-401 spec have placed more emphasis on two items: quality control (QC) and tack coat.

QC is an essential component of a project. The updated spec makes the QC program, which formerly was an incidental cost, a separate pay item. The QC program includes all required sampling and testing by the contractor, and now also requires the contractor to facilitate a quality control/quality assurance (QC/QA) workshop.

Required participants in the QC/QA workshop are the engineer, resident project representative (RPR), contractor, subcontractors, testing laboratories and owner’s representative. The workshop must be held prior to start of construction.

The other change stresses the importance of tack coat by making it a separate pay item. Tack coat is the “glue” that is applied between two layers of asphalt. Adequate bonding between lifts of asphalt pavement is critical for the completed pavement structure to behave as a single unit and provide adequate strength.

Table 1. Guidance for PG selection includes grade bumping

Other changes to the P-401 spec include the following items.

1. Compaction of the mat will now be measured as a percent of Total Maximum Density (TMD) versus what it used to be, which was a percent of lab bulk density. This makes it consistent with the highway industry.
2. The spec now offers improved minimum thickness guidance. The recommended minimum construction lift thickness for Gradation 1, 2 and 3 is 3 inches, 2 inches and 1 ½ inches, respectively. Gradation 3 is intended for leveling courses. If the contractor wishes to use Gradation 3 in other locations, the contractor will need to get FAA approval to do so.
3. Gradation plans have been adjusted to match the military airfield specifications.
4. For rut testing/evaluation, there is a new loaded wheel test requirement for mix design. The default uses an Asphalt Pavement Analyzer (APA) with 250 psi hose pressure at 64 degrees centigrade in accordance with AASHTO T340. The rutting must be less than 10 millimeters at 4,000 passes. An alternative method also uses the APA, but at 100 psi hose pressure at 64 degrees centigrade in accordance with AASHTO T340, the rutting must be less than 5 millimeters at 8,000 passes. Another alternative method uses the Hamburg Device in accordance with AASHTO T324 and the rutting must be less than 10 millimeters at 20,000 passes.
5. Updated guidance on PG selection; there is an additional grade bump (See Table). The base grade is based on climate only; there is no bumping for traffic. When bumping a grade, add a PG Plus test if the upper temperature limit is 92 or greater (if there’s a modified binder). Use Asphalt Institute’s binder spec database for reference.

A handful of the most important slides from additional presentations are available if you click here.

APCW Teaches the Specs

Guy Ischinotsubo, engineering program manager for HDOT—Airport Division, addressed about 65 attendees at the APCW event. Photos courtesy Lynn Young, HAPI

The workshop attracted about 65 people from the Hawaii Department of Transportation—Airports Division, design consultants, construction managers, inspectors and paving contractors. The workshop covered many aspects of asphalt pavements, including significant changes to the P-401 spec that were made in the recently released AC 150/5370-10H.

Day 1 topics included an overview of the workshop, aggregates, asphalt binder, hot-mix asphalt mix design and contractor quality control program. The class exercise was a contractor mix design submittal review.

Guy Ischinotsubo, engineering program manager for HDOT—Airport Division, addressed about 65 attendees at the APCW event. Photos courtesy Lynn Young, HAPI

Day 2 topics included owner acceptance testing and percent within limits; prime coat, milling, and patching; tack coat; paving operations; compaction operations; and longitudinal joints. The class exercise was a pay factor analysis.

Attendees received professional development hours certificates at the end of the workshop.

Some highway agencies still rely on the British Pendulum (BP) test to qualify aggregates for asphalt pavement surface friction. Other agencies specify friction aggregate based on geology and/or mineralogy. Both approaches have allowed agencies to maintain an acceptable level of pavement friction long-term performance. However, the BP polishing and testing procedure evaluates a single size coarse aggregate and requires careful manual adjustment of the pendulum height to obtain the correct length of surface contact. Recent advances in laboratory polishing and friction testing now provide a better assessment of friction that considers the entire gradation in an asphalt mixture rather than a single aggregate source.

The dynamic friction tester (DFT) gives a better assessment of the friction of a pavement surface. The DFT procedure, standardized in ASTM E1911, provides a more consistent measurement (no manual adjustment of the device before testing) and records friction over a range of speeds. The National Center for Asphalt Technology (NCAT) developed the Three Wheel Polishing Device (TWPD) in 2006 to complement the DFT for measuring friction on asphalt mixes.

British Pendulum (BP) test

The Maryland State Highway Administration modified the TWPD concept to use a large ring of a single aggregate on an epoxy substrate. After polishing with the TWPD, the ring of aggregate can be tested with the DFT to assess the aggregate’s terminal friction value. Under Maryland’s lead, a task group of American Association of State Highway Transportation Officials (AASHTO) agency representatives and NCAT researchers are developing a new standard test procedure using the TWPD and DFT. This standard will provide equipment requirements and testing procedures to rapidly evaluate an aggregate source or asphalt surface mix for long-term friction performance.

In addition to the TWPD and DFT, the equipment includes an aggregate specimen preparation device consisting of a rigid mold for the single aggregate procedure. The mix specimen preparation procedure will permit any slab compaction procedure that produces the required size with a smooth surface compacted to a uniform target density. The testing procedure for aggregate polishing and asphalt mix polishing are slightly different but involve the same TWPD. Both procedures use the DFT for measuring friction.

NCAT developed the Three Wheel Polishing Device (TWPD) in 2006 to complement the DFT for measuring friction on asphalt mixes.

This new friction testing protocol allows an agency or aggregate supplier to determine the long term (terminal) friction properties of any aggregate or asphalt mix in about one week for a cost of less than $5,000. A few agencies have used this system to assess the friction performance of aggregate blends for surface mixes at a substantially lower cost and much shorter time period compared to full-scale field test sections with no risk to the traveling public. <endmark>

For more information or a quote from the testing lab, contact NCAT at (334) 844-7328.

Michael Heitzman is the assistant director, senior research engineer for NCAT. His specializations include pavement friction, non-destructive pavement evaluation, thin lift surfaces, rehabilitation and more. This article is reprinted from the Spring NCAT Newsletter with permission.