The Effects of Moisture on Aged Asphalt with High RAP Concentrations
Barbara Reid, Sean Tarbox (Masters Candidate CiE), Dr. Jo Daniel (advisor)
Background:
Dynamic Modulus of Unaged Specimens
Dynamic Modulus Master Curve for Moisture Conditioned
HMA Specimens
18000
18000
14000
14000
12000
16000
21.1°C
37.8 °C
8000
10000
21.1°C
40%8 Days
12000
|E*| (MPa)
4000
2000
2000
0.01
0.1
1
10
100
1000
0
0.00001
10000
0.0001
0.001
0.01
Reduced Frequency (Hz)
0.1
1
10
100
1000
40%8 Days
12000
54.4 °C
Fitted
0.001
40%Unaged
6000
Fitted
Virgin 8 Days
14000
Virgin 8 Days
14000
37.8 °C
8000
4000
0
0.0001
40%Unaged
4.4 °C
54.4 °C
6000
Virgin Unaged
10000
|E*| (MPa)
10000
|E*| (MPa)
4.4 °C
Asphalt is heated and weighed before molding.
16000
Virgin Unaged
12000
|E*| (MPa)
18000
16000
16000
10000
8000
10000
8000
6000
6000
4000
4000
2000
2000
Reduced Frequency (Hz)
0
0.0001
0.001
0.01
0.1
1
10
100
1000
0
0.0001
10000
0.001
0.01
Reduced Frequency (Hz)
0.1
1
10
100
1000
10000
Reduced Frequency (Hz)
40H44
00H37
18000
18000
16000
16000
12000
4.4 °C
21.1°C
37.8 °C
8000
16000
37.8 °C
8000
54.4 °C
6000
14000
4000
12000
4000
Specimens are molded to the correct dimensions in
the gyratory compactor.
|E*| (MPa)
2000
2000
0
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
0
0.00001 0.0001
Reduced Frequency (Hz)
0.001
0.01
0.1
1
10
100
1000
10000
Reduced Frequency (Hz)
40%Unaged Moisture
16000
40%Unaged
14000
Virgin 8 Days Moisture
8000
8000
6000
4000
4000
2000
2000
0.01
0.1
1
10
Reduced Frequency (Hz)
100
1000
40%8 Days
10000
6000
0.001
40%8 Days Moisture
12000
Virgin 8 Days
10000
0
0.0001
40H45
00H38
Virgin Unaged Moisture
Virgin Unaged
Fitted
Fitted
18000
21.1°C
54.4 °C
6000
18000
4.4 °C
10000
|E*| (MPa)
10000
|E*| (MPa)
|E*| (MPa)
12000
Dynamic Modulus Master Curve for 40% RAP HMA
Dynamic Modulus Master Curve for Virgin HMA
14000
14000
0
0.0001
10000
0.001
0.01
0.1
1
10
Reduced Frequency (Hz)
100
1000
10000
18000
18000
16000
16000
14000
14000
12000
12000
4.4 °C
21.1°C
37.8 °C
8000
4.4 °C
|E*| (MPa)
10000
10000
21.1°C
Dynamic Modulus Master Curve for 0 and 40% RAP
37.8 °C
8000
54.4 °C
54.4 °C
Fitted
6000
Molded specimens numbered and allowed to cool
Fitted
4000
6000
4000
18000
2000
2000
0
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
0
0.00001
Reduced Frequency (Hz)
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
16000
Reduced Frequency (Hz)
14000
|E*| (MPa)
12000
Dynamic Modulus for Aged Specimens
Virgin Unaged Moisture
Virgin Unaged
Virgin 8 Days Moisture
Virgin 8 Days
40%Unaged Moisture
40%Unaged
40%8 Days Moisture
40%8 Days
10000
8000
6000
00H32
40H31
18000
18000
16000
16000
14000
14000
|E*| (MPa)
12000
NHDOT Type E 12.5 mm Superpave surface course mixture with PG
grade 64-28 base binder. The design was for less than 3 million ESAL’s.
One mix contained 0% RAP while the other contained 40% RAP. A total
asphalt content of 5.7% was used for all mixtures and gradations were
also constant.
21.1°C
10000
37.8 °C
54.4 °C
8000
4000
2000
12000
4.4 °C
|E*| (MPa)
Cored specimens are numbered, dried and measured
Materials:
4.4 °C
21.1°C
10000
54.4 °C
Fitted
Fitted
6000
6000
4000
4000
2000
2000
0
0.00001 0.0001
0.001
0.01
0.1
1
10
100
1000
10000
Reduced Frequency (Hz)
0
0.001
0.01
0.1
1
10
100
1000
10000
0
0
0
0
Reduced Frequency (Hz)
0
1
10
100
1000
10000
Reduced Frequency (Hz)
Conclusions:
Methods:
00H33
40H39
18000
18000
16000
16000
14000
14000
12000
4.4 °C
21.1°C
10000
37.8 °C
54.4 °C
8000
|E*| (MPa)
|E*| (MPa)
12000
4.4 °C
21.1°C
10000
37.8 °C
8000
54.4 °C
Fitted
Fitted
6000
6000
4000
4000
2000
2000
0
0.00001 0.0001
0
0.001
0.01
0.1
1
10
100
1000
10000
0
0
0
0
Reduced Frequency (Hz)
0
1
10
100
1000
10000
Reduced Frequency (Hz)
Nuts are placed for LVDT attachment
18000
18000
16000
16000
14000
14000
12000
4.4 °C
21.1°C
10000
37.8 °C
54.4 °C
8000
|E*| (MPa)
|E*| (MPa)
12000
4.4 °C
21.1°C
10000
37.8 °C
54.4 °C
8000
Fitted
Fitted
6000
6000
4000
4000
2000
2000
0
0.00001 0.0001
0.001
0.01
0.1
1
Reduced Frequency (Hz)
As expected, the 40% RAP HMA was stiffer than the virgin mix in both the unaged and aged
conditions. The increase in stiffness due to aging appears to be smaller for 40% RAP mixtures.
This again is consistent with expectations since some of the binder in the 40% RAP has
already undergone aging. Moisture conditioning seemed to have little effect on the performance
of either of the unaged samples, however there was a notable effect on the aged samples. The
aged virgin material showed softening as a result of moisture conditioning, which is the
expected outcome of moisture infiltration. The moisture conditioned aged 40% RAP samples
indicate an increased stiffening of the material. This result could be anomalous due to the
small sample size and warrants further investigation.
40H41
00H34
Dynamic modulus is measured at four temperatures
and six frequencies for each sample
0
0.0001
37.8 °C
8000
They are vacuum saturated to 70-80 %, frozen at
-18oC for 16 hours then placed in a 60oC water bath
Six 100 mm diameter by 150 mm high cylindrical specimens of virgin
HMA and six specimens with the same dimensions of HMA with 40%
RAP were created from Pike Industries NH mix. Three samples of each
specimen type were immediately moisture conditioned by vacuum
saturating them to between 70-80%, wrapping them in plastic and
placing them in a -18oC freezer for 16 hours. They were then placed in
a 60oC water bath for 24 hours. (AASHTO T-283-03) The remaining six
specimens were aged for 8 days in an 85oC oven, then moisture
conditioned using the previously described procedure. After
conditioning, all samples were tested for dynamic modulus, which is a
measure of stiffness. Dynamic modulus is determined by applying a
stress, or load, to the sample and measuring the resulting strain,
(AASHTO TP62-03). This was done at six different frequencies
(0.1,0.5,1.0,5.0, 10, 25 Hz) and four different temperatures (4.4oC,
21.1oC, 37.8oC, 54.4oC). Dynamic modulus results for the moisture
conditioned specimens were compared to previously obtained results
from unconditioned aged and unaged specimens.
Dynamic Modulus Master Curve for Unconditioned Specimens
18000
Purpose:
To compare the effects of moisture on aged HMA with 0% RAP with
aged HMA with a 40% RAP content.
Average Dynamic Modulus Master Curves
40H43
00H35
|E*| (MPa)
Hot mix asphalt (HMA) is a mixture of aggregate and asphalt binder. The
asphalt is a petroleum based substance and, since the oil embargo of the
1970’s, efforts have been underway to use recycled road materials when
formulating mixes for new roadways. Currently, most roads in the state of
New Hampshire are paved with asphalt cements that contain 10 to 15%
reclaimed asphalt pavement, or RAP. According to the NHDOT, in 2010
162,135 tons of RAP were diverted from landfills and put to use in area
roadways. This resulted in a cost savings of 3.8 million dollars. NH is also
one of the few states that currently allows RAP contents higher than 15%
in all layers of new pavement.
RAP is created when old road pavement is removed, milled and
sorted into fine and coarse grain components. These materials are
combined in specific ratios with virgin aggregate and a new asphalt
binder to produce new asphalt concrete.
The addition of this recycled material conserves petroleum
resources and reduces disposal of hazardous material. However,
inclusion of RAP can change the properties and performance of the new
pavement, so it is important to determine the best ratio of RAP to virgin
material in order to obtain maximum performance and life expectancy for
a given set of conditions.
Two important factors that determine an asphalt pavement’s life
expectancy are its viscoelasticity and its ability to resist moisture. Once a
pavement has aged it becomes stiffer and this can lead to increased
cracking of the roadway. When RAP is added to a new mix, the asphalt
binder adhered to the RAP aggregate has already aged, resulting in a
product that has an increased stiffness from the outset. Moisture also has
an effect on pavement life and properties. When water enters the asphalt
it reduces the cohesion within the binder and the adhesion between the
binder and the aggregate. This softens the pavement and can cause
stripping of asphalt binder from the aggregate material. This can lead to
the development of potholes, cracking or raveling.
The intent of this study is to look at the combined effects of aging
and moisture on asphalt concretes composed of all virgin material and
those with high RAP contents to determine if there is a difference in
material properties that could result in changes to pavement performance.
Results:
10
100
1000
10000
0
0.00001 0.0001
0.001
0.01
0.1
1
Reduced Frequency (Hz)
10
100
1000
10000
Acknowledgements:
Special thanks to Dr. Jo Daniel for her guidance and expertise, Sean Tarbox for his collaboration and invaluable
assistance, and Dr Daniel’s other graduate students: Mike Elwardany, Marcelo Medeiros, Kelly Barry, and Justin
Lowe for their sharing their knowledge and ideas. Thank you also to the National Science Foundation and the
Leitzel Center at University of New Hampshire for making this opportunity possible.