A patterned microtexture to reduce friction and increase ...
Measuring Microtexture of Aggregates Using the Dynamic ...
Transcript of Measuring Microtexture of Aggregates Using the Dynamic ...
2020 Transportation Short Course October 13, 2020
2020 Virtual Transportation Short CourseRichard Izzo, P.E.Soils & Aggregates SectionMaterials and Tests Division
October 13th, 2020
Measuring Microtexture of Aggregates Using the Dynamic Friction Tester (DFT)
2020 Transportation Short Course October 13, 2020
Why measure the texture of aggregate?
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Improve safety & maintain skid resistance of
hot mix asphalt pavements.
Vision – Texas envisions a future with zero
traffic fatalities and serious injuries.
2020 Transportation Short Course October 13, 2020
Why measure the texture of aggregate?
3
Texas Transportation Commission set goals of cutting fatal crashes in half by 2035 and zero
fatalities by 2050.
Road to Zero
TxDOT #EndTheStreakTX Campaign
November 7th, 2000 is the last deathless day on Texas roadways.
One person has died on Texas roadways every single day since then.
Focus is on ‘Engineering: Roadway Factors.’
Wet Surface Crash Reduction Program (formerly Wet Weather Accident Reduction Program)
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Stone-Matrix Asphalt (SMA) ~ 1 Year Old
Improve skid resistance. Safety hazard, loss of skid resistance
& prone to wet surface crashes
Why measure the texture of aggregate?
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Frictional Properties of Aggregate
(<0.5mm)(0.5mm - 5cm)
Macrotexture
HighLow
Microtexture
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Frictional Properties of Aggregate
Tex-499-A, Aggregate Quality Monitoring ProgramTable 1 – Classification Criteria
Property Test Method SAC A SAC B SAC C
Acid Insoluble Residue,% Minimum Tex-612-J 55 ---- ----
5-Cycle Mg Sulfate Soundness,% Maximum
Tex-411-A 25 30 35
Surface Aggregate Classification (SAC) is determined for each aggregate source for texture.
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Dynamic Friction Test (DFT) measures a friction value on wet pavement surface (ASTM E1911).
Spinning disk with 3 rubber sliders that contact the pavement surface as disk rotates.
Dynamic Friction Tester (DFT)
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Spinning disk with 3 rubber sliders
L ¾”, W ⅝”, H ¼”
Water is applied to pavement
surface.
Disk contacts the pavement surface
at 50 mph.
Dynamic Friction Tester (DFT)
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DFT value is an average of data
collected at 37, 25, and 12 mph
(60, 40, and 20 kph).
37 1225
Dynamic Friction Tester (DFT)
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Maryland DOT Testing
Passing ½” and retained 3/8”
~ 24 hours with curing.
5-3/4”
1”
14”
Laboratory Implementation of DFT
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Maryland DOT Testing
Circular Track Polishing Machine (3-Wheel Polisher)
100,000 revolutions (~36 hours)
No water is used during polishing.
Laboratory Implementation of DFT
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Maryland DOT Specifications
DYNAMIC FRICTION VALUE (DFV)
Category DFV, minimum
HDFV I
High DFV
50
HDFV II 45
HDFV III 40
SDFV IVStandard DFV
30
SDFV V 25
LDFV VI Low DFV 20
Blended DFT values based on aggregate bin %’s and gradations from HMA mixture designs.
High DFV includes SMA, Open Graded Friction Course (PFC), & Surface Courses.
• DFV greater than 40
Standard DFV includes Surface Courses only.
• DFV greater than 25
RAP assigned a DFV of 30
Laboratory Implementation of DFT
2020 Transportation Short Course October 13, 2020
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Laboratory Implementation of DFT
TxDOT Implementation
Simulate loss of texture by polishing aggregate using the Micro-Deval testing machine.
10,500 revolutions for 1-¾ hours.
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Laboratory testing of aggregate passing 3/8” and retained on ¼” sieves (same as polish value).
Laboratory Implementation of DFT
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Polyester resin (bondo) is used to hold the ¼” aggregate in place.
~30 minutes to prepare aggregate ring, tedious process to place and align aggregate, and a minimum of 4 hours for curing before testing.
1”½” Thickness
12”
Laboratory Implementation of DFT
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Laboratory Implementation of DFT
We try to spread and lay the aggregate with the flat face up
as much as possible, so good surface area is available for
contact with DFT rubber sliders.
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DFT values of individual aggregate
sources, not blended values.
All material codes combined – Dolomite,
Gravel, Igneous, Lightweight, Limestone,
and Sandstone.
Poor correlation/trend of Soundness to
DFT Value for SAC A sources.
Soundness not a strong indicator of
friction for SAC A sources.
Laboratory DFT Test Results
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Laboratory DFT Test Results
All material codes combined – Dolomite,
Gravel, Igneous, Lightweight, Limestone,
and Sandstone.
Poor correlation/trend of Soundness to
DFT Value for SAC B sources.
Soundness not a strong indicator of
friction for SAC B sources.
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DFT value compared with acid insoluble
for SAC A and SAC B sources.
All material codes combined –
Dolomite, Gravel, Igneous, Lightweight,
Limestone, and Sandstone.
Generally, a high AI > 55 will produce a
higher DFT Value.
DFT does a good job differentiating
aggregate sources with lower AI values.
Laboratory DFT Test Results
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Laboratory DFT Test Results
DFT differentiates the aggregate sources as
well as the acid insoluble.
DFT does a good job differentiating
aggregate sources with lower AI values.
Gravel sources identified as ‘Limestone &
Gravel’ are predominately comprised of
limestone, calcium carbonate.
Gravel sources identified as ‘Gravel &
Limestone’ are predominately comprised of
siliceous gravel, silica.
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Hot Mix Asphalt (HMA) Mix Design Blended DFT Value
DFT values used to calculate a
blended value for HMA mix.
Blended DFT value will be based on
gradation and % retained on the #4
or #8 sieve.
Fine aggregates will be assigned
coarse aggregate DFT value.
DFT value of 30 assigned for RAP.
DFT blended value assigned to the mix design.
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Hot Mix Asphalt (HMA) Mix Design Blended DFT Value
2020 Transportation Short Course October 13, 2020
Skid resistance on State-maintained highways are usually made every 0.5 mile.
Skid measurements are taken while traveling 50 miles per hour with a smooth tire.
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Field Skid Information
2020 Transportation Short Course October 13, 2020
Field Skid Information
Factors/variables to consider when comparing and looking at roadway skid information.
• Traffic, Annual Average Daily Traffic (AADT).
• Service life, age of pavement at the time of skid testing.
• Roadbed, such as main lanes, frontage roads, different lanes.
• Hot mix asphalt (HMA) mixture type, coarse vs dense-graded mixtures.
• Surface Aggregate Classification (SAC) of HMA.
• Pavement condition score, roadway could be flushing at the time of skid testing.
2020 Transportation Short Course October 13, 2020
Acknowledgments
Started designing and building the prototype testing mold in September, 2016
Performed over +800 laboratory tests since October, 2016.
People involved in this effort.
• Edward Morgan, P.G. - Soils & Aggregates Section (SA) /Materials & Tests Division (MTD)
• Jeffrey Perabo, G.I.T. – SA/MTD
• Andre Smit, P.E. – Quality Assurance/MTD
• Victor Vogt, E.I.T. – SA/MTD
• Blake Lawrence, E.I.T. – SA/MTD
2020 Transportation Short Course October 13, 2020
Acknowledgments
People involved in this effort.
• Adam Sherrill – Contract Employee
• Chizitelu Modebelu – TxDOT Summer Hire
• Jackie Rambo – Contract Student Employee
• Kenley Ulveling – TxDOT Summer Hire
• Michael Ramos-Yeo – TxDOT Summer Hire
• Roy De La Rosa – Contract Employee
• SA/MTD Aggregate Laboratory Technicians