oklahoma dot changes in superpave specifications to address permeability
TRANSCRIPT
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Oklahoma DOT Changes in Superpave
Specifications to Address
Permeability
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HOW DO WE DEFINE PERMEABILITY?
Inter-connected air voids which allow air, water, and moisture vapor to infiltrate a pavement structure from the surface and / or base.
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WHY IS PERMEABILITYA PROBLEM?
Stripping – Asphalt binder is separated from the aggregate by the continued presence of water and moisture vapor.
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TEST PROCEDURE OVERVIEW
OHD L-44
MEASUREMENT OF WATER PERMEABILITY OF COMPACTED
PAVING MIXTURES
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Mold specimen to 7% air voids, 75mm height. Saturate specimen, apply thin film of Vaseline to sides
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Place specimen on permeameter and position sealing tube, which is covered by a rubber membrane
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Place upper cap assembly on specimen and clamp down. Inflate membrane to 14 psi.
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Ensure that water is flowing through the specimen at a constant rate and begin timing when water level reaches 65mm.
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Measure either:1) Time for water level to drop to zero2) Water level after 30 minutes
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The coefficient of permeability, k, is determined using the corrected water temperature.
The initial specification was a maximum of 125 x 10-5 cm/s
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IF WE HAD A PERMEABILITY TEST AND SPECIFICATION, WHY WERE THE PAVEMENTS STILL
PERMEABLE?
Could we change the permeability test to better identify problem mixes?
Could we change the Superpave specification in some way to make them inherently less permeable?
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1st Step – Check the Permeability Test Equation
k = a L
A tln( h1
h2) C
where: k = coefficient of permeability, cm/sa = inside x-sectional area of cylinder, cm2
L = avg. thickness of the test specimen, cmA = x-sectional area of test specimen, cm2
t = elapsed time between h1 and h2, sh1 = initial head across test specimen, cmh2 = final head across test specimen, cmC = temp. correction for viscosity of water
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1st Step – Check the Permeability Test Equation
• The 65 cm tall tube of water could totally drain through the specimen in 5-1/2 minutes and still meet k = 125 x 10-5 cm/s
• Dropping 45 cm in 30 minutes results in
k = 12.5 x 10-5 cm/s
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A review of existing mix designs at that time demonstrated the relationship
between nominal maximum aggregate size and permeability
MIX
NMS 1” 3/4” 1/2” 3/8”
MEETS
12.5 x 10-567.6% 77.9% 80.9% 100%
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INITIAL IN-HOUSE RESEARCH HIGHLIGHTED THE FOLLOWING:• Confirmed that permeability increases as
mix coarsens
• Confirmed that permeability increases as the density at Nini gyrations decreases
• The method used to determine 93% density for permeability testing is critical (CoreLok vs. Air Wt, Imm. Wt, SSD Wt)
• The difference between the methods increases as the mix gets coarser
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CONTINUED RESEARCH
Based on the data from the initial research, a test matrix with 1” NMS mixes at evenly spaced combined gradations was proposed. The mixes ranged from very coarse to very fine. Each mix was molded in increments from 91% to 98% density
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0
10
20
30
40
50
60
70
80
90
100P
erc
en
t P
as
sin
g
Grid LinesMaximum DensityTrial 1Trial 2Trial 3Trial 4Trial 5Trial 6
Sieves Raised to 0.45 Power
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The difference between the methods of determining density increases with mix
coarseness and lower density
91 92 93 94 95 96 97 98
% Density
0
0.5
1
1.5
2
2.5
3
3.5Mix # 1
Mix # 2
Mix # 3
Mix # 4
Mix # 5
Mix # 6
OHD L-14 minus CoreLok Density
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Absorption also increases with coarser mixes and lower density
91 92 93 94 95 96 97 98
Densit y - % of G m m
0
0. 5
1
1. 5
2
2. 5
3
% Absorption
M i x # 1
M i x # 2
M i x # 3
M i x # 4
M i x # 5
M i x # 6
% Absorption vs. Density
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There is a clear relationship between permeability and absorption
0 0.5 1 1.5 2 2.5 3 3.5
Absorption
1
10
100
1000
Pe
rm
ea
bility
Permeability vs. Absorption
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The three coarsest mixes stood out very clearly. Attaining 94% roadway density is critical.
91 92 93 94 95 96 97 98
Density - % of Gmm
0
100
200
300
400
500
600
700
800
900
Perm
eabili
ty -
cm
/s x
10-5
Mix # 1
Mix # 2
Mix # 3
Mix # 4
Mix # 5
Mix # 6
Permeability vs. Density
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RESULTING CHANGES TO ODOT’S PERMEABILITY TEST & SPECIFICATION
Specify OHD L-14 as the method by which to obtain the density of the permeability specimens
Lower the maximum permeability from 125 x 10-5 cm/s to 12.5 x 10-5 cm/s
Add minimum AC contents for each Superpave mix
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RESULTING CHANGES TO ODOT’S SUPERPAVE SPECIFICATION
Specify a minimum density of 85.5% @ Nini gyrations
Fine up Superpave gradation to make the allowable broad band more similar to to our previous A, B, C, and D blends
Remove 1-1/2” NMS mixes from the specification
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New specifications were enacted in June 2004.
All ODOT Field Divisions are reporting a marked decrease in permeability issues.
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The new specifications alone cannot guarantee that the roadway will not be permeable. There is one more important factor:
ROADWAY DENSITY
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DATA FROM OUR FIRST FIELD INVESTIGATION OF A
PERMEABLE PAVEMENT:
(AT LONGITUDINAL JOINT)
LIFT % DENSITY
6” LEFT 6” RIGHT
S4 82.6 86.1
S3 83.3 87.2
S2 (2nd Lift) 88.8 93.4
S2 Base 90.6 90.2
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DATA FROM OUR NEXT FIELD INVESTIGATION OF A
PERMEABLE PAVEMENT:
(AT LONGITUDINAL JOINT)
LIFT % DENSITY
6” LEFT 6” RIGHT
S4 91.2 89.3
S3 (2nd Lift) 84.1 91.3
S3 Base 83.3 91.1
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ODOT intends to adopt a longitudinal joint specification similar to TxDOT’s in the next few months.
Based on their experience, we believe that permeability issues will be largely resolved.
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THANK YOU!
QUESTIONS?