Tags
Aggregates Equipment
Asphalt Equipment

Asphalt segretation busters – protect your reputation

For every ton of asphalt paved, your reputation is on the line. Asphalt producers and paving contractors take pride in delivering a durable road that lasts for 15 or 20 years or longer.

Sending segregated mix to the jobsite or laying a mat with patches of segregation can ruin a company’s reputation, not to mention significantly affect the bottom line. No matter where segregation occurs – in the aggregate stockpile, at the plant, on its way to the jobsite or behind the screed – it must be addressed. If not, the paved road suffers distresses such as raveling, rutting and cracking, which leads to costly rehabilitation ahead of schedule.


Manufacturers have been working with asphalt producers and contractors to develop equipment to help mitigate segregation occurrences. And there are several tactics that both producers and contractors can implement to reduce segregated mix. 
 
Mixing it up
Prior to making the mix, the way producers handle aggregate has a profound impact on segregation. Building aggregate stockpiles in layers with radial stackers vs. large conical shaped stockpiles reduces aggregate segregation, especially when it comes to larger size stone. Loader operators can also help the process by blending the material from the fine and coarse areas of a segregated stockpile.


At the plant, operators should keep cold-feed bins as full as possible to avoid larger aggregate from separating from the fine material. “To promote proper aggregate gradation, many producers are now using more cold-feed bins to store different stone sizes,” says Joe Musil, senior engineering fellow with Terex Roadbuilding.


Today’s asphalt producers incorporate more additives in the mix, and they must pay attention to additive sizing and introduce these items at the right point in the mixing process. Recycled asphalt product (RAP) and shingles, baghouse fines and warm mix asphalt all have their proper timing for introduction into the drum, and the mixer must have the flexibility to accommodate all the different additives.


“The drum is the ultimate commingler of the material, and that is why Terex asphalt plants have mixing zones that retain material between two and four minutes, much longer than the 45 to 60 seconds experienced with pugmills,” says Musil. “Long mixing zones help to avoid asphalt ‘balling’ of fines and deliver more uniform temperatures throughout the mix when introducing RAP and shingles into the design.”


When loading transport vehicles from the silo, using the three-dump method – loading two batches at each truck end and the final batch in the middle – will avoid large particle run-off to the truck’s sides and ends. Also, according to Terex Asphalt Paver Application Specialist, Bill Rieken, the type of truck used to transport asphalt makes a significant difference in reducing particle and thermal segregation.


Rieken says that end-dump trucks are the least preferred vehicle, especially with mainline and highway paving. “A dump truck is basically a box, where more of the asphalt comes into contact with the metal, which cools the asphalt at the ends,” he says. “The mix will segregate as the particles roll to the truck’s sides and ends during transport to the jobsite.”


Live-bottom trucks offer more protection against material and thermal segregation during transport. There is less surface area for the asphalt to come in contact with, so less cooling takes place, and the bed is shaped like a “V” to reduce particle segregation. 

Smooth and consistent
No matter if it’s warm mix or hot mix asphalt, paving contractors have equipment options to mitigate segregation occurrences at the site and, in some regions, this additional equipment is a requirement to meet government specifications. “Some specifications are so strict for mainline paving, that they cannot be met with a traditional slat paver alone,” comments Rieken.


Material transfer vehicles (MTVs) and devices (MTDs) are arguably the contractor’s best allies in the battle against segregation. However, there are key design differences, so contractors must carefully review the equipment options to ensure they are getting the right machine for the job.


Early MTV designs offered large storage capacities and some reblending capabilities. “The intent of those first designs was to allow crews to pave continuously to eliminate truck-end segregation,” explains Rieken. 


A newer generation of MTVs builds on the continuous paving benefits of previous designs, offers improved reblending capabilities and lowers ground contact pressures.


New innovations of variable-pitch, counter-rotating auger sets, like those found on the Terex CR662RM RoadMix MTV/paver, thoroughly reblend 100 percent of the mix to virtually eliminate thermal and material segregation. Low machine centre of gravity lowers the conveyor’s discharge point to lessen the chance of drop segregation. Also, track drives reduce fully loaded ground contact pressure to less than 20 psi, eliminating many of the issues associated with wheeled MTVs.


Low psi MTVs usher in the ability to be used on base lifts for reducing material segregation. Fear of subbase rutting with high psi wheeled machines has led many government specifications to limit MTV usage to the top paving lifts. “This is counterintuitive and counterproductive,” says Rieken. “Base mixes are made with larger stone sizes that are more prone to segregate, so we should be using MTVs on the base lifts. We have customers using the CR662RM RoadMix to pave base lifts, but it cannot be used as an MTV by spec.”


Similar to MTVs, MTDs establish continuous paving and can be used in conjunction with either dump truck or windrow paving. Unlike MTVs, these machines attach to and are guided by the paver, eliminating the need for an additional operator. Some, like the Terex MS-4 Mat Smoothness Machine, have shock-absorbing push rollers to eliminate truck “bumping” and screed settling. Several designs will also reblend material and have a low discharge height to eliminate drop segregation.


For contractors working with mixes prone to particle segregation – such as Stone Matrix Asphalt (SMA) – who don’t want to use a transfer vehicle or device, Terex Remix Anti-Segregation System pavers offer an alternative. Replacing the traditional slat conveyor with two sets of two counter-rotating augers, these pavers offer the same aggressive reblending capabilities as the new generation MTVs with the added benefit of doing so at the last stage of paving. This combats material as well as thermal segregation.

Segregation busting advances
Without adding specialized equipment to the paving train, a properly sized hopper insert goes a long way in reducing segregated mix. Inserts channel asphalt directly into the paver’s conveyor system – whether traditional slat or Remix counter rotating augers – to create a live bottom action that reduces particle segregation. Offering extra surge capacity to aid in continuous paving, the hopper insert design promotes a natural reblending of material and prevents larger, cooler material from building up in the hopper’s wings.


Rieken cautions contractors not to think that bigger is better. “Insert size,” he says, “must be matched to the paver hopper, or material will pool off to the sides, which will flow into the conveyor as the asphalt level drops. This results in random patch segregation.”


At the screed, consistency is paramount in reducing longitudinal segregation. Operators must monitor that the ratio pots or flow gates are set to deliver enough, but not too much, material to the spread augers so that they run continuously. If the augers are allowed to spin too slowly, larger aggregate drops off at the outboard bearing support, which results in longitudinal segregation. 


A major topic of concern today is centreline segregation, which results in top-down cracking. This occurs under the auger chain drive, and manufacturers counteract this problem by including variations of reversing augers to force material under the housing. Creating material confinement through lead crown adjustments and housing baffles mitigates this form of segregation.


On mainline pavers like the Terex CR600 Series, manufacturers are replacing the centre gearbox altogether by relying on outboard drive motors for the spread augers. “If you eliminate the centre drive housing, you eliminate centreline segregation,” says Rieken. With outboard drive, the auger sections back up to each other, leaving no separation in the centre. This eliminates the need for a centre gearbox drive and reversing augers.  

Back to basics
Before adding equipment to the paving train and before searching out paver options, paving success ultimately comes down to training the operators. Crews must be thoroughly educated in correct paving techniques and how to properly use each piece of equipment.


Crews should know the capabilities and limitations of the paving equipment. No amount of equipment will end segregation unless it’s operated in the correct manner.


Manufacturers work with contractors at the jobsite to help crews get the most out of their equipment. Additionally, contractors can attend equipment training schools at the factory like those offered through Terex Roadbuilding University.

Five keys to help prevent material and thermal segregation
Beyond equipment selection and following proper paving techniques, Rieken leaves the operators he trains with five keys to help prevent material and thermal segregation.


“Keep material confined; avoid dropping it; prevent mix dribbling; pave in a smooth, uniform and uninterrupted fashion; and don’t spill asphalt in front of the paver,” he says.
 

Company Info

Related News

Tags
Aggregates Equipment

Sandvik’s New Prisec 3 CI531 & CI532 HSI Crushers

Sandvik Construction has announce the launch of the all new CI531 primary and CI532 secondary, Prisec 3 Horizontal Shaft Impact (HSI) crushers. These new generation crushers provides customers with a low capital cost solution, optimum performance and good cubical shape, while ensuring the lowest operating cost per ton for a wide range of materials and applications.

The latest additions to the CI500 Prisec Horizontal Shaft Impactor (HSI) range of crushers, the Prisec3 primary CI531, and the secondary CI532, have been developed to deliver exceptional rates of productivity and efficiency. As with the rest of the Prisec range these new HSI crushers possess the ability to be configured into either a primary or secondary crusher operating mode and with this unique, exclusive to Sandvik, patented design, providing customers with unparalleled adaptability. Additionally single stage crushing is also a possibility with the ability to recirculate material to the primary versions of the crushers.

Read More

Tags
Aggregates Equipment

Superior’s Aggre-Dry Dewatering Washer Saves Valuable Material From Waste Pond

Superior Industries, Inc., a major U.S. manufacturer and global supplier of material handling systems and their related components, says its washing fines recovery system was granted patent protection from the United States Patent and Trademark Office.

This exclusive technology, manufactured into the company’s Aggre-Dry Dewatering Washer, reroutes minus 25mm material fines from an onboard dewatering screen back to the integrated sand screw. Traditionally, the company says, these fines are lost to waste ponds, but the recovery system processes this material to the saleable stockpile. Depending on production rates, the extra material can add tens of thousands of dollars to sand producer’s bottom line.

Read More

Tags
Aggregates Equipment

Density separator makes sand classification easy

Density separator at Guytec Industries’ sand plant in Alberta.
Density separator at Guytec Industries’ sand plant in Alberta.

The methodology for classifying sand has been around for decades but separation technology from CFS Inc. is proving especially valuable for sand plants whose raw materials are often contaminated with clays, coal and other light ends.

The density separator from CFS, based in Michigan, is designed to classify sand into a variety of end products. The Groundworx Co, a Canadian aggregates equipment dealer, recently became the Western Canadian dealer for CFS and sold its first density separator to Guytec Industries Ltd. out of Pine Lake, Alberta.

Read More

Tags
Asphalt Equipment

Caterpillar Adds AP1000F and AP1055F Pavers

Performance improvements and technology with a customer-friendly interface are key benefits of the new F-Series Pavers from Cat Paving Products. Several features help improve fuel economy while maintaining high performance levels. Engine performance is aided by the 167 kw (225 hp) Cat C7.1 ACERT engine, which meets European Stage IV and U.S. EPA Tier 4 Final emissions regulations without sacrificing power. On some F-Series models, a Cat C7.1 engine is also available that meets emissions equivalent to U.S. EPA Tier 3 and E.U. Stage IIIA. It provides power of 186 kW (249 hp).

Eco-mode is standard on F-Series pavers. When used with automatic engine speed control, Eco-mode efficiently manages engine RPMs to optimize fuel economy, reduce sound levels and keep the paver running smoothly. The control automatically adjusts RPMs when the engine reaches a high load threshold or needs additional cooling.

Read More

Join our mailing list

Latest headlines
delivered to you weekly

Heavy Equipment Guide
Tags
Aggregates Equipment

New Kleemann Cone Crushers Offer Fuel-Efficient Operation

The new Mobicone MCO 9i EVO/MCO 9i S EVO mobile cone crushers from Kleemann offer aggregate producers high-productivity secondary or tertiary crushing in a fuel-efficient, Tier 4 Final emissions-compliant machine.

The S-version of the MCO 9i EVO provides a discharge conveyor-mounted final classifying screen with oversized aggregate return conveyor. This permits a closed material cycle and production of final particle sizes without a stand-alone screen. The oversize can be optionally discharged via the swivel-mounted return conveyor at the side.

Read More

Tags
Asphalt Equipment

BOMAG Makes Additional Investment in Its New Facility

BOMAG Americas, Inc. has announced plans for product manufacturing transitions to its new North American headquarters in Ridgeway, S.C. 

In August, 2015, BOMAG will begin transitioning its Cedarapids asphalt paving and CMI reclamation/stabilization equipment production from the current Oklahoma City, Okla. facility.

Read More

Tags
Asphalt Equipment

New DuraPatcher ECO Released

Cimline Pavement Maintenance Group has redesigned their successful DuraPatcher trailer-mounted spray injection pothole patcher. The new DuraPatcher ECO combines environmental, safety and cost-saving features while maintaining the performance of the leading pothole patcher. The Strategic Highway Research Program (SHRP) cites spray injection as the most cost-effective and fastest pothole repair method.

The new machine receives a fully compliant Tier IV diesel engine/blower package that is enclosed for security and safety. With 18% better fuel economy, the new engine powers the machine’s blower that is the basis for the spray injection process. A high volume, low-pressure air stream is used to transport the aggregate / emulsion mix with sufficient force to compact the material and provide a permanent patch. The DuraPatcher system utilizes virtually no moving parts in the delivery system. The new low profile design provides better visibility.

Read More

Tags
Asphalt Equipment

Astec V-Pack Stack Temperature Control System Receives Patent

ASTEC, Inc., has been awarded patent number 8,863,404 for its V-Pack Stack Temperature Control System. The V-Pack Stack Temperature Control System extends the range of mixes that can be produced without requiring that the flights be adjusted. The system’s “V-flights,” unique drum flights with a deep V-shape, and its use of variable frequency drives (VFDs), which provide control of the drum rotational speed, are keys to the control system managing an asphalt plant’s exhaust gas temperature and increasing overall efficiency.

The Stack Temperature Control System automatically controls exhaust gas temperature across a range of mix types and operating conditions by making drum speed changes. The system keeps baghouse temperature relatively stable as mix temperature changes and even as mix types change from hot mix to warm mix, from virgin to high RAP, and from dense graded to open graded mixes. These kinds of production changes would cause baghouse temperature changes of over 100° F (38° C) without the V-Pack Stack Temperature Control System.

Read More

Tags
Aggregates Equipment

Sandvik Launches the New QA441 Doublescreen

Sandvik Construction has announced the launch of the new QA441 Doublescreen.This latest addition to the Premium range has been upgraded to encompass the many product refinements of the larger QA451 triple deck version in order to improve operation, efficiency and ease of maintenance.

New features on the QA441 include a color-coded push button control system with sequential start-up for ease of operation as well as an updated feeder hopper and feeder drive system for increased throughput. To speed-up screen media changes, the QA441 includes hydraulic screen separation, new wrap around walkways, a newly designed access ladder, optimized screen drives and hydraulic raise / lower facility on the main conveyor. The standard radio remote control and upgraded electrical system will also further enhance operator safety and control.

Read More