Tar Sand-Substitute for Asphalt


Tar Sands (also referred to as oil sands) are a combination of clay, sand, water, and bitumen, a heavy black viscous oil. Tar sands can be mined and processed to extract the oil-rich bitumen, which is then refined into oil. The bitumen in tar sands cannot be pumped from the ground in its natural state; instead tar sand deposits are mined, usually using strip mining or open pit techniques, or the oil is extracted by underground heating with additional upgrading.

Tar sands are mined and processed to generate oil similar to oil pumped from conventional oil wells, but extracting oil from tar sands is more complex than conventional oil recovery. Oil sands recovery processes include extraction and separation systems to separate the bitumen from the clay, sand, and water that make up the tar sands. Bitumen also requires additional upgrading before it can be refined. Because it is so viscous (thick), it also requires dilution with lighter hydrocarbons to make it transportable by pipelines.

Photo:
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Tar Sand ;Source: Suncor Energy inc.


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Tar Sand Mining Photo: Source: Suncor Energy,inc

Tar Sand Resources:


Much of the world's oil (more than 2 trillion barrels) is in the form of tar sands, although it is not all recoverable. While tar sands are found in many places worldwide, the largest deposits in the world are found in Canada (Alberta) and Venezuela, and much of the rest is found in various countries in the Middle East. In the United States, tar sands resources are primarily concentrated in Eastern Utah , mostly on public lands. The in-place tar sands oil resources in Utah are estimated at 12 to 19 million barrels.


Estimates of Utah Tar Sands And Locations




Known (MMB)
Additional Projected (MMB)
Sunnyside
4,400
1,700
Tar Sand Triangle
2,500
420
PR Spring
2,140
2,230
Asphalt Ridge
830
310
Circle Cliffs
590
1,140
Other
1,410
1,530
Total:
11,870
7,330

MMB: Million Barrels
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Source: BLM



Advantages of Tar Sands
  • Large reserves available, and in countries such as Canada which are close to the countries that are major users of oil, for eg., USA.
Disadvantages of Tar Sands
  • Production cannot be ramped up as quickly as conventional oil production, owing to the operational processes used in deriving oil from the sands.
  • Extracting oil from tar sands entails high production costs and low net useful energy yields.
  • Production of oil from tar sands has high negative environmental impacts

Research Objective:
Use Tarsand instead of Asphalt in Asphalt concrete.
Questions to Answer:
How to we subsitute instead of asphalt?
Replacing the asphalt content in the HMA with Tarsand and making samples for mechanical testing.
What type of tests do I run?
Tests the samples in Bending beam Rheometer for stiffness calculation of the mixture at low temperatures and comparing those values with the HMA samples.


Hamburg wheel Tracking Device is used for testing rutting and moisture suscpetibility


Moisture susceptibility is a primary cause of distress in HMA pavements. HMA should not degrade substantially from moisture penetration into the mix. HMA mixtures may be considered susceptible to moisture if the internal asphalt binder-to-aggregate bond weakens in the presence of water. This weakening, if severe enough, can result in stripping .

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Failure due to stripping



Hamburg Wheel Tracking Device
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Figure3: Hamburg Wheel Tracking Device Source: Google

It Measures the rutting and moisture susceptibility of an asphalt paving mixture by rolling a steel wheel across the surface of an asphalt concrete slab that is immersed in hot water (generally held at 50°C.) Susceptibilities to rutting and moisture are based on pass/fail criteria.

The Hamburg Wheel-Tracking Device measures the combined effects of rutting and moisture damage by rolling a steel wheel across the surface of an asphalt concrete slab that is immersed in hot water. The device was developed in the 1970's by Esso A.G. of Hamburg, Germany, based on a similar British device that had a rubber tire. The machine was originally called the Esso Wheel-Tracking Device. The City of Hamburg finalized the test method and developed a pass/fail criterion to guarantee that mixtures that pass the test have a very low susceptibility to rutting.(1) This device costs $60,000 and is shown in figures 1 and 2.

The device was originally used by the City of Hamburg to measure rutting susceptibility. The test was performed for 9,540 wheel passes at either 40 or 50°C. Water was used to obtain the required test temperature instead of an environmental air chamber. The City of Hamburg later increased the number of wheel passes to 19,200 and found that some mixtures began to deteriorate from moisture damage. Greater than 10,000 wheel passes was generally needed to show the effects of moisture damage.

The machine tests slabs that typically have a length of 320 mm, a width of 260 mm, and a thickness of either 40, 80, or 120 mm. Thicknesses up to 150 mm can be tested. The thickness of the slab is specified to be a minimum of three times the nominal maximum aggregate size.(A) The mass of a slab having a thickness of 80 mm is approximately 15 kg. Pavement cores having a minimum diameter of 250 mm can also be tested.

The required air-void level for laboratory-prepared specimens is not given by the City of Hamburg procedure. The Federal Highway Administration at the Turner-Fairbank Highway Research Center is using 7 ±1 percent air voids for dense-graded hot-mix asphalts, and 5.5 ±0.5 percent for stone matrix asphalts. The Colorado Department of Transportation (CDOT) also uses 7 ±1 percent air voids for dense-graded hot-mix asphalts.(2)

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Figure 4: Rut depth vs. number of wheel passes

Specimens are secured in reusable steel containers using plaster of Paris. Each specimen is placed into a container so that its surface is level with the top edge of the container. This allows the full range of the rut depth measurement system to be utilized. Containers are manufactured in heights of 40, 80, and 120 mm. Steel spacers can be placed under cores and pavement slabs if needed. The container with the specimen is then placed into the wheel-tracking device. The container rests on steel; this provides a rigid, load-bearing base for the specimen.

The temperature of the water bath can be set from 25 to 70°C. The most commonly used test temperature in Hamburg is 50°C, although 40°C has been used when testing certain base mixtures. A water temperature of 50°C is reached within 45 min. Specimens are conditioned at the test temperature for a minimum of 30 min. Heat is provided by heated coils in the water. The temperature of the water is then maintained by these heating coils and by introducing cold water from a faucet.(B)

The device tests two slabs simultaneously using two reciprocating solid steel wheels. The wheels have a diameter of 203.5 mm and a width of 47.0 mm. The load is fixed at 685 N and the average contact stress given by the manufacturer is 0.73 MPa. This assumes an average contact area of 970 m2, which is based on the 47.0-mm wheel width and an average contact length of 20.6 mm in the direction of travel. However, the contact area increases with rut depth, and thus the contact stress is variable. The manufacturer states that a contact stress of 0.73 MPa approximates the stress produced by one rear tire of a double-axle truck. The average speed of each wheel is approximately 1.1 km/h; each wheel travels approximately 230 mm before reversing direction, and the device operates at approximately 53 ±2 wheel passes/min.

The number of wheel passes being used in the United States is 20,000, although up to 100,000 wheel passes can be applied. CDOT recommends maximum allowable rut depths of 4 mm at 10,000 wheel passes and 10 mm at 20,000 wheel passes, based on correlations between the test results and moisture damage in dense-graded hot-mix asphalt pavements.(3) The City of Hamburg uses a maximum allowable rut depth of 4 mm at 19,200 wheel passes. The rut depth in each slab is measured automatically and continuously by a linear variable differential transformer that has an accuracy of 0.01 mm. A printout of the data can be obtained at every 20, 50,100, or 200 wheel passes. Approximately 6.5 h are needed to apply 20,000 wheel passes; however, the device will automatically stop if the rut depth in one of the slabs exceeds 30 mm. The total time to perform a test from start to finish, including specimen fabrication, is 3 days.

The post-compaction consolidation, creep slope, stripping inflection point, and stripping slope, shown in figure 3, can also be analyzed.(4) The post-compaction consolidation is the deformation (mm) at 1,000 wheel passes. It is called post-compaction consolidation because it is assumed that the wheel is densifying the mixture within the first 1,000 wheel passes.

The creep slope is used to measure rutting susceptibility. It measures the accumulation of permanent deformation primarily due to mechanisms other than moisture damage. It is the inverse of the rate of deformation (wheel passes per 1-mm rut depth) in the linear region of the plot between the post-compaction consolidation and the stripping inflection point. Creep slopes have been used to evaluate rutting susceptibility instead of rut depths because the number of wheel passes at which moisture damage starts to affect performance varies widely from mixture to mixture. Furthermore, the rut depths often exceed the maximum measurable rut depth of 25 to 30 mm, even if there is no moisture damage.

The stripping inflection point and the stripping slope are used to measure moisture damage. The stripping inflection point is the number of wheel passes at the intersection of the creep slope and the stripping slope. This is the number of wheel passes at which moisture damage starts to dominate performance. CDOT reports that an inflection point below 10,000 wheel passes indicates moisture susceptibility.(3) The stripping slope measures the accumulation of permanent deformation primarily due to moisture damage. It is the inverse of the rate of deformation (wheel passes per 1-mm rut depth) after the stripping inflection point.

Inverse slopes are used for both the creep slope and the stripping slope so that these slopes can be reported in terms of wheel passes along with the number of wheel passes at the stripping inflection point. Higher creep slopes, stripping inflection points, and stripping slopes indicate less damage.(4)

The shape of the curve in figure 4 is the same as typical permanent deformation curves provided by creep and repeated load tests. The curves from these tests are also broken down into three regions. The final region, called the tertiary region, is where the specimen is rapidly failing. Based on the examination of many slabs and pavement cores, the tertiary regions of the curves produced by the Hamburg Wheel-Tracking Device appear to be primarily related to moisture damage, rather than to other mechanisms that cause permanent deformation, such as viscous flow. Mixtures that are susceptible to moisture damage also tend to start losing fine aggregates around the stripping inflection point, and coarse aggregate particles may become dislodged. However, there is no method for separating the deformation due to viscous flow from the deformation due to moisture damage, because dry specimens cannot be tested. There is also no method for determining the amount of deformation and the amount of fine particles generated if any of the aggregate particles are crushed by the steel wheel.(C)

Additional disadvantages are that the data cannot be used in mechanistic pavement analyses and cannot be used to determine the modulus of the mixture or layer coefficients used by American Association of State Highway and Transportation Officials thickness design procedures. This is due to the complex and unknown state of stress in the slab.

FOOTNOTES

A. The effect of thickness on the test results has not been determined.

B. There may be some variability in the data resulting from the use of tap water effectiveness of some antistripping additives. Distilled water is specified in most test methods used to determine the moisture susceptibility of asphalt mixtures in order to reduce the between-laboratory testing variability.

C. Correlating the test data to field performance is difficult since the test combines two distress modes and the steel wheel can crush some aggregates.

Equipment Linear Kneading Compactor

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Figure1: Linear Kneading Compactor with plates inside the mold

Used to compact asphalt paving mixtures into slabs needed for various mixture testing devices. The mixture is placed in a mold and loaded through a series of vertically aligned steel plates that compress the asphalt mixture into a flat slab of predetermined thickness and density.

The Linear Kneading Compactor produces slabs that are used for testing asphalt mixtures for various properties. A mixture is placed in a steel mold in the compactor and a series of vertically aligned steel plates are positioned on top of it. A steel roller then transmits a rolling action force through the steel plates, one plate at a time. The mixture is kneaded and compressed into a flat slab of predetermined thickness and density. The trade name for this compactor is HasDek SLAB-PAC. It is manufactured by R/H Specialty & Machine, Terre Haute, Indiana. This compactor costs $66,000 and is shown in figure 1.

The Linear Kneading Compactor is called "linear" because of the lateral motion involved. The mold, mixture, and steel plates move back and forth on a sliding table under the roller. It is called "kneading" because only a fraction of the mixture is compacted at any given time. This kneading action allows the mixture to be compacted without excessively fracturing the aggregate.


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Figure2: Rollers inside the compactor

The density of the mixture at the required air-void level and the dimensions of the slab are used to calculate the mass of mixture needed. Once the mixture is placed in the mold, 5 to 15 min are required to achieve the desired density. Two different mold sizes are available-a 260- by 320-mm mold that provides slabs used by the Hamburg Wheel-Tracking Device, and a 180- by 500-mm mold that provides slabs used by the French Pavement Rutting Tester. Other mold sizes can be easily accommodated. The slabs produced by this compactor can also be cored or sawed into beams. Beam specimens needed for the Georgia Loaded-Wheel Tester are provided by cutting the slab for the Hamburg Wheel-Tracking Device in half.

SPECIMEN PREPARATION:

1.HMA or other designed mix , and the mould components are first heated in the oven to the desired temperature.

2.When the desired temperature is reached , the mix is placed in the compactor and then compacted to the mould size.

3.After compaction, the specimen is transferred into mould at is left till it cools to warm temperature.

4.Once it reaches the warm temperature, specimen is removed from mould and its weight, weight in water (at 25C) and weight in Surface saturated Dry condition are taken for measurement of air voids.

5.The specimen is now ready for testing.


Procedure:

1. Power on the Hamburg wheel tracking device.

2. Fill the bath with water and wait till the temperature of the bath reaches 50C.

3. Place the specimen with mould in the device.

4. The device will start automatically once the consistent temperature is attained in the mould and bath.

5. The wheel passes continue for 6 hours and rut depth is measured.


Screenshot:
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Specimen Reports:

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Figure showing the passed specimen


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Figure showing the passed specimen

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Figure showing the passed specimen


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Figure showing the failed specimen

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Figure showing the failed specimen

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Failed Specimen

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Other Equipment that can be used to measure rutting:

The more popular laboratory wheel tracking devices in the U.S. are generally recognized, in order of decreasing popularity, as the Asphalt Pavement Analyzer (APA),and French Rutting Tester (FRT). These devices are all capable of proof testing HMA mixtures (i.e., providing a pass-fail test based on rutting potential) and can be reasonably well correlated to field rut performance. However, none should be relied on to predict field rut depths for specific projects based on laboratory wheel tracking rut depth relationships developed on other projects with different geographical locations and traffic. Additionally, due to the complex stress state of the samples, these tests cannot be used for mechanistic pavement design input.


Sources:

  1. Wikipedia

  2. http://ostseis.anl.gov/guide/tarsands/index.cfm

  3. Tracking Test, Determination of the Track Depth of High-Stability Binding Layers. Construction Bureau, Civil Engineering Office, Department of City Traffic, Hamburg, Germany, 1991.

  4. Aschenbrener, T. "Evaluation of the Hamburg Wheel-Tracking Device to Predict Moisture Damage in Hot-Mix Asphalt." Transportation Research Record 1492, Transportation Research Board, Washington, DC, 1995, pp. 193-201

  5. Hines, M. "The Hamburg Wheel-Tracking Device." Proceedings of the Twenty-Eighth Paving and Transportation Conference. Civil Engineering Department, The University of New Mexico, Albuquerque, NM, 1991.

  6. Aschenbrener, T., R. Terrel, and R. Zamora. Comparison of the Hamburg Wheel-Tracking Device and the Environmental Conditioning System to Pavements of Known Stripping Performance (CDOT-DTD-R-94-1) Colorado Department of Transportation, Denver, CO, January 1994.

  7. http://www.fhwa.dot.gov/pavement