highly modified binder and reducing the thickness of the asphalt pavement.
use of high polymer-modified binder for asphalt pavement (HDI) to reduce the thickness of the coating layer while maintaining or exceeding the performance of more powerful layers of asphalt with conventional coatings even under extremely heavy traffic.These results came National Center asphalt Technology (NCAT) after testing.
fourth cycle of research (2009-2012), conducted in the NCAT test track in Opelika, Alabama, United States, shows that the experimental section of the landfill with asphalt laid on the basis of HDI rut depth an average of less than 1/3,than in the control segment tracks (the thickness of the control segment is 18% more than in the pilot).The segment with the asphalt-based VMPS and a control segment were provided with a coating, made by one process technology Superave [1].
The test results were published at the conference on the range (28-29 February 2012) Hotel Auburn University and Dixon Conference Center, Auburn, Alabama.
Research Opportunities landfill
NCAT test track was built in 2000.Its length - 2,7 km, the track shape - ellipse.Purpose of the route - the accelerated test at intervals of 60 m, which track wear throughout the life of the simulated within 2 years.Test sites allow engineers and researchers to measure, record and analyze the reaction of the coating for heavy loads with the aim of developing more efficient and effective coatings.
Land available for research sponsors such as the Federal Highway Administration (FHWA), State Department of Transportation and private companies to test compounds for road surfaces on each cycle.Construction, operation and exploration at the site funded by the joint efforts of agencies and private companies, each of which performs its own research program.
subject of a recent series of studies began structural and surface characteristics of the coating.Preparation for the study include reconstruction or vosstanovlenie17 sections of the route (of a total of 46).One portion was N7, which has been laid asphalt based HDI technology developed sponsor section by Kraton Performance Polymers.
duration of one study cycle - three years.During this time, possible to build or rebuild sites, to simulate a period of two years, the flow of freight transport, analyze data and prepare reports.Currently at the site planned for the fifth series of studies in which will be removed unused sections (Spring 2012) and the construction of new (late summer 2012).Start on range of motion is scheduled to perform in August 2012.
Extreme load ordeal
motion simulation is performed using the following program: applied to sections of the landfill 10 million cycles for the estimated 8.2 tons of equivalent axle load (ESAL) for 2 years.Trucks carry out movement in two shifts.This is an 8-axle 70-ton trucks with trailers that perform continuous movement every day from 5.00 to 23.00.Each of the five passes truck 1,100 km per day.
To facilitate testing at the site found various accessories: thermistors installed at different depths of asphalt pavement and connected with an automatic weather station at the site.These data help to evaluate the operating conditions of each of the sites.Reaction of the coating on the load is measured with strain gauges and pressure sensors installed at certain depths.Wireless network installed across the road, provides high-speed data to the main server.
NCAT weekly checks using inertial profiler dual scanning laser meter gauge: roughness is measured each wheel path, makrotekstura right wheel path track each wheel on each test interval.And taken other measures: non-destructive, density and profile cuts.Every week falling weight impact tests and deflectometer, as well as mapping the surface cracking.Once a month friction tests (using a full-size recorder friction).Testing the integrity and permeability are held once a quarter.Sampling for the determination of each seal coating layer is also conducted on a quarterly basis.
To simplify a correlation between measurements of parameters in the laboratory and field personnel NCAT selects a large portion of the mixture in the factory during the construction of each test site and subsequently used for the manufacture of a mixture of samples for laboratory testing.For example, a mixture of the base layer is tested for fatigue loading (samples-sticks) and antiphase load.The mixture for the top layer is being tested to determine the dynamic modulus, fluidity test analyzer asphalt pavement and wheel-rolling unit to calculate the resistance to permanent deformation.Mixes for the top layer are also experiencing overlay checked for creeping deformation and stretching, energy ratio.All this allows the potential of the mixture to cracking.
Research structural parameters
the fourth test cycle NCAT includes advanced research sites (sponsors continued research started earlier), the research areas of the new coated mixtures structural studies.Reconstruction and rehabilitation of 17 sites have been completed in August 2009, the contractor appointed through a competitive tender.Among these six areas they were intended for structural tests, sponsored by departments of transportation in six states.Among them are the portion of the company Kraton.The coatings are made in the areas of technology for hot mix asphalt Superpave.The thickness of the layer for structural testing ranged from 175 mm to 140 mm (portion of Kraton), in separate sections of 225 mm (of which more than 150 mm - of the base material and high density rigid substrate).The whole bitumen used for reconstruction of the coating contained 0.5% protivozadirochnoy additive.Coating
portion of Kraton (N7) is made using HDI, thickness - 140 mm.The binder comprises 7.5% modified styrene-butadiene stirenovogo (SBS) polymer.The control portion has a thickness of 175 mm, the top two layers are made with 3% SBS-polymer.
Federal administration by road confirms the benefits of polymer modification
binders modified with polymers, such as three-way copolymer SBS, are becoming more widely used in the manufacture HS (data of the Federal Administration for roads).The technical report for September 2010. [2] The Administration notes that the modified binder more elastic and has a high stiffness characteristics (viscosity) at low and high temperatures, which are better suited to the specifications of high-quality binders for asphalt grade Superpave [3].These specifications are tied to environmental and traffic conditions of a specific object.The polymer modified binders are generally classified and are used in those cases where the index of PG (grade low temperature + grade at high temperature) is greater than 90 (eg., PG 70-22).
Further, the report shows the advantages of using polymers, "Being more expensive pure binders for asphalt mixtures, polymer modified binders in hot mixes offer a clear increase in performance - less rutting, reduced fatigue cracking, reduced cracking under the influence of temperature - especiallyunder heavy loads and difficult climatic conditions.Depending on the cost and performance characteristics that are specific to a particular area (ie, geographical conditions), the cost of mixtures based on polymer modified binders during the life cycle can be significantly lower than the cost of mixtures with unmodified binders. "
The report also says that the experience of operation of such coatings is positive, and that, since it changes for the better, in accordance with the development of technology.
overcoming restrictions imposed polymers and laying thin asphalt pavements
company Kraton Performance Polymers has developed a technology DGVC to increase the strength of the coating and its resistance to rutting, potholes and cracks while reducing the thickness of the coating.
to conduct field trials of this product the company has issued NCAT contract for the construction of the coating layer thickness of 140 mm in the area N7 for the research cycle 2009-2012.
content polymer-modified SBS (7.5%) used in the composition of the binder is 1.5-2 times the normal amount of polymer used to modify the binder.
If the amount of polymer in the binder above this level, the viscosity of the binder is increased so that the mixture becomes very difficult to produce and extremely difficult to lay on the subject.Company developed Kraton D0243 SBS-polymer, which may be mixed with a bituminous binder in amount of 7.5% or higher, without increasing the viscosity of the binder.
development of a new polymer is a continuation of work begun in 2004 by researchers in collaboration with experts of road engineering laboratory Delft University of Technology (Netherlands), the largest and oldest state technical university.The main aim of the researchers predict the following: to find out whether it is possible to increase the service life of the pavement base layers using the SBS-modified and / or reduce the thickness of the asphalt pavement.
Method of research - testing of samples of asphalt fatigue and stiffness by bending four points, complicated mechanical tensile test and compression.Evaluate different types of polymer (SBS) and different concentrations.Fatigue tests showed that a significant change in the properties of the asphalt mixture needs more SBS-polymer.Accordingly, the object of the last stage of testing began with binders SBS content of 6% and 7.5%.
Complicated mechanical testing asphalt mixtures showed improved performance of mixtures of modified SBS compared to unmodified compounds.The results also showed some differences in the spread of destruction (accumulated irreversible deformation) coating based on modified and unmodified binders.Even a thin layer of coating (150 mm) of the SBS-modified asphalt damage recorded in the volume is 4 times less than the 250 mm layer of the unmodified asphalt.Unmodified, more powerful, the coating showed 4.5 times more irreversible deformation than thin coating of the modified asphalt.
Construction segment N7, compared with the control plots
Coating segment N7 test site was constructed of three layers of hot mix (Table 1).Nominal base layer (55 mm) and middle layer (55 mm) were fabricated from a mixture of particles with a diameter of 19 mm granite.The topsheet (30 mm) made of a mixture of granite (9.5 mm).All three layers of the mixture on the basis of modified binder with a content of 7.5% SBS.The formulation mixture, seal, and other parameters are similar to the control area (the only difference is in the binder and the layer thickness).
Covering test area S9 has a total thickness of 175 mm, and consists of three layers - the base of 75 mm, a middle layer of 70 mm and a top layer of 30 mm (Table 2).Upper and middle layers are made from the mixture using a binder, 3% SBS modified.On the test and control sites mixture prepared by the method SUPERPAVE [1], using the same material, but in the area N7 cover 18% thinner than on the control section S9, used binder - HiMA instead of PG 76-22 (used in the control area).Both sites are built on the hard canvas.
Result: less depth gauge
Transportation tests at the site was completed in September 2011, when the load was carried 10 million. Cycles equivalent to the calculated axial load.NCAT staff held expert studies and examined the data collected.At a conference in February 2012, in addition to other data were presented information about the average strain on the road rolling wheel (rutting):
- Deformation control section S9 with a coating thickness of 175 mm was 7.1 mm.On the site N7 (HiMA) with a coating thickness of 144 mm rut depth was 2.2 mm.
- Map of cracking on the site N7 revealed no fracture of the coating.Analyses carried out on the basis NCAT actual load data and calculations based on the measurements, as well as the fatigue endurance limit of the samples as a cube, it has shown that the fatigue strength of the coating at the site N7 improved considerably.Furthermore, coating characteristics can be better than the control plot, including positions with the propagation of fatigue cracks from the bottom up.
repair the damaged area with a mixture based on HiMA
potential to reduce the thickness of an asphalt coating, while ensuring high performance - one of the advantages of binder HiMA, and it was found on a nearby area test site.
plot N8, which is sponsored by the Oklahoma State Department of Transportation, was damaged during the research cycle 2009-2012.It was not the first injury, recorded at the site.
At the end of the research cycle 2006-2009.the section was observed extensive fatigue cracking.In the construction site contractor N8 laid coating thickness of 250 mm by 1.2 m fabric of poor quality, which is different from the hard canvas in the control plot.
Even during the construction phase of Oklahoma Department of Transportation demanded NCAT used as a canvas defined soil type, soil characteristics similar in Oklahoma, known for its low bearing capacity.The coating is destroyed and the damaged area was renovated: was cut to 125 mm top layer, in place of which was placed a mixture of similar composition.Recycled layer also collapsed, this time in just 8 months research cycle 2009-2012.This 6 pilot sites and 4 private sponsored landfill sites cracking was identified.
After repeated destruction of land administration NCAT noted the good performance of operating the nearby area N7, and proposed to use for the repair of the N8 mixture based binder HiMA, which would enable it to analyze the behavior of the damaged area.Representatives
Oklahoma State Department of Transportation agreed to apply the mixture to the area N7, however, for the base layer, a mixture of particles with a diameter of 9.5 mm (composition similar to the composition of the mixture for the top layer, but with a thickness of 55 mm).During the reconstruction of 145 mm was cut off the damaged coating around the damaged 105 mm base layer was left.Then it was laid 145 mm new mixture on the basis of HiMA.
When the surface is new trucks again drove through the repaired section segment N8, and devices NCAT again began recording data in the experimental section.
in September 2011, when the traffic load over 4 cycles, was recorded deformation depth plot N8 at 2.7 mm.In a direct comparison can be seen that after the initial track and significant repair cracks formed after 4 million. Cycles equivalent axial load, while after application of cementitious repair HiMA no cracks, after the track is minimal 5.7 million. Cycles equivalent axial load.Oklahoma Department of Transportation will continue sponsoring this area during the cycle of 2012-2014.to monitor the performance of the coating.
Conclusion
shown that the use of high molecular weight polymer modified binder in the asphalt mixture reduces the thickness of the coating, even under extreme loads.
