Temperature Differential Damage / Temperature Segregation! ROADTEC an Astec Industries company is based in USA and manufactures 'The Shuttle uggy® MTV', Material Transfer Vehicle that eliminates a crucial Segregation Problem and allows you the advantage of Non-Stop Paving. It not only reduces your lucking costs by eliminating truck delay, but also helps making your paving operation more efficient and also dramatically improves paving quality. The key words in the production of long life hot mix asphalt is "uniformity or consistency Uniformity in gradation, asphalt content and air void".
Even as the mix is placed on the road, segregation can be visually observed. And where large aggregate is used for base and binder materials, the segregated spots can be easily identified. On the finer surface mixes, however, apparent segregation spots often cannot be visually noticed as the mix is placed and may not show up until six to twelve months later. Since the surface mix is the top lift and the one most susceptible to traffic and weather conditions, any segregation of the surface mix, just like the segregation in other layers, leads to a shortening of the pavement life and premature failure.
Mr. Steve Read, a graduate student at the University of Washington was the first to recognize this phenomenon in the summer of 1996, while conducting studies of segregation problems in paving operation for his master's thesis. In his thesis he says "When a pavement rehabilitation project is affected by this phenomenon, the expected life of the overlay can be reduced to roughly half of the 12 to 15 years that the Washington State Department of Transportation normally expects. There has been no way to be able to predict which projects will be affected by cyclic segregation and the problem has proven to be particularly insidious in that it may not manifest itself during construction but will show up in a project as long as two years after completion."
The 'Cyclic Segregation' is related to a differential in temperature of the HMA mass in the truck developed during transport from the HMA manufacturing facility to the job site and is known as 'Temperature Differential Damage'. According to Mr. Read, "This title seemed appropriate in that the mechanism that causes the problem is related to temperature differentials in the load of HMA prior to placement and the damage to the project occurs during construction; the other problems (e.g., stripping, lower compaction, raveling, etc.) are merely symptoms of damage that has already occurred to the HMA matrix during the construction process."
"The mechanism by which temperature differential damage occurs begins when a truck load of HMA is dumped into the paver. If the load is exhibiting temperature differentials, the very cool material that is along the sides of the load is extruded out towards the sides of the paver hopper. When the truck is emptied and the pile in the hopper is run down, this cool material falls inward to lay on the top of the material over the slat conveyors. When the next truck arrives and dumps in to the paver, this cool mix is subsequently conveyed back to the auger chamber and screeded out. The screed is unable to consolidate the colder mix and open, segregation appearing area (temperature differential damage) show in the mat. As this mechanism can work for each load placed, the cyclic nature of the phenomenon becomes apparent."
In this condition, are you able to achieve the desired Compaction? No, because Pavement Smoothness is affected when Non-uniform Densities occur. If the temperatures within the rolling zones are not uniform and even if the recommended rolling patters are followed, uniform density will not necessarily be achieved.
The compactability of a mix varies with the temperature of the mix and therefore, temperature variations in the mat will cause non-uniform densities in the finished pavement. If the mix, placed at the front of the paver screed and the rollers compress the material, while it is cold in certain areas, one of the two things will occur during compaction. The mix located in the cold spot will not compress the full amount, causing the paver screed to rise or fall, thus leaving a rough place in the pavement, or cracking will occur due to extreme heavy load caused by cold area supporting the entire roller. The result being a - substandard pavement that will be short-lived.
Solution: Remixing prior to placement and you will achieve longer lasting roads without premature failure in certain areas of the road, thereby resulting in more economical, longer lasting pavements!
But how do you accomplish this?
It could be accomplished by 'Windrow Pickup Device'. Yes, you can reduce the amount of differential temperature segregation, but keeping the exact amount of mix in the windrow uniformly is difficult. The excess or deficiencies in the windrow leads to mix being stored for longer or shorter times in the paver hopper, contributing to temperature segregation. Also, belly dump trailers usually dump from the centre first with the cold material on the sides being discharged last, leading to concentrations of cold material at the end of each load. Thus the mat is improved but the temperature segregation is not eliminated.
Any other Material Transfer Vehicle is basically a transfer machine allowing more storage in the paver but doing little remixing! In contrast, these machines will improve your mat, but demonstrate the same amount of temperature segregation.
The Right Solution is "Roadtec Shuttle Buggy"® 'Roadtec Shuttle Buggy®' has the triple pitch augers in the bottom of the hoper. It will store approx. 25 metric tons or 30 short tons. When the augers are used without changing the pitch, no remixing occurs since all of the mix is fed in from the inlet end of the auger. This results in all of the material being conveyed from the outside of the hopper with the centre emptying last.
By changing changed pitch of the auger, new material can enter the flights as the flights spread out or the pitch changes. Since pitch changes twice on each side of the hopper(transversely to the direction of the paver) material is remixed or re-blended, with the cold or coarse material being re-blended with the hot r finer material from the quarter points and the centre of the machine.
It is as recent as 3 years ago, when this phenomenon was first recognized by a contractor in Arkansas while laying thin lifts of asphalt in February. He observed that while using the Roadtec Shuttle Buggy, his smoothness increased significantly and his pay for density went from 80 % to 100 %. He observed that the machine remixes for temperature and, according to him "it is more important than remixing for segregation". Thus the realization of the significance of temperature segregation!
Roadtec Shuttle Buggy® Thus the exact solution to produce a long lasting smooth pavement with consistent densities and thus consistent air voids is by remixing the material directly prior to placement.
Other Products and Service: Roadtec, the US based manufacturer is also providing a complete line of cold planning and recycling equipment, material transfer vehicles and asphalt paving machines of highest standards, emphasizing simplicity, productivity, versatility and accessibility. With their extensive global network of dealers and direct sales managers, including in India, Roadtec is ubiquitous. Roadtec cold planers, with its revolutionary recycling technology reduces road relaying costs in a big way by producing a recyclable asphalt product by milling old pavement during the road reconstruction process and to prepare surface for repaving. With aggregates and other road materials becoming scarcer and costlier, this technology provides a cost effective technology for smooth roads. The firm offers cold planers in sizes from utility to full-lane, with a range consisting of RX-400, RX-500, RX-700 and the mammoth RX-900. The 950 hp RX- 00 is a cold planer available with three or four track assemblies. This versatile machine allows contractors to cut up to 14" (355mm) deep with widths of 7' 2" (2.18m), 8' 2" (2.5m), 10' (3m), or 12' 6"(3.81m). The RX-900 offers contractors more versatility and productivity. A 42" (1.07 m) wide front load-out conveyor, with 60° swing to either side, provides ample loading capacity. These beasts provide the optimum balance between horsepower, production and maneuverability. Track models can be equipped with a bi-directional feature to achieve down cutting in the reverse direction of travel. Roadtec pavers are the most reliable and maintenance-free pavers in the industry. They are simply-designed and well-balanced for maximum traction effort and can be equipped with a variety of screeds and controls. Roadtec is the first U.S. paver manufacturer to make electric screed heat standard equipment on all models. This insures that the screed plates are heated evenly from front to back and from end to end, eliminating the "hot" spots found with diesel or propane burners.
Again, Roadtec's new and innovative gravity-fed Stealth® paver was designed to work in conjunction with the SB-2500 Shuttle Buggy® material transfer vehicle and the MTV-1000C material transfer vehicle. The Stealth® Pavers are low-maintenance machines that do not require conveyors or hopper wings. The design significantly reduces customers' maintenance cost and purchase price. The Shuttle Buggy is a mobile, self-propelled surge bin with an anti segregation auger design that remixes material to produce a consistent to Today, Roadtec is perfectly positioned to help Indian road builders meet highest standards and smoothness apart from improving efficiency of paving operations by significantly cutting costs savings in asphalt trucking costs. In India, it is high time that Engineers, Decision makers, Legislators and Governments of Local Municipalities, Townships, Urban Centers, Metropolis and that of the nation itself, take good notice of this cost effective advanced technology and start providing the country with immaculate Roads that are at par with advanced nations.
For details: Mr. Subhash Niyogi,
Director, Sales & Marketing (India)
No:500, 17th Cross,, Ideal Home Society Township,
Rajarajeswary Nagar, Bangalore 560 098.
Tel: +91-80-28604527, Fax: +91-80-28604528
Mob: +91-9900521746
E-mail: subhashchniyogi@rediffmail.com ,
niyogi.subhash1960@gmail.com
Web: www.roadtec.com
