Background: 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.

Purpose:

To compare the effects of moisture on aged HMA with 0% RAP with

aged HMA with a 40% RAP content.

Materials:

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.

Methods:

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.



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.

The Effects of Moisture on Aged Asphalt with High RAP ConcentrationsBarbara Reid, Sean Tarbox (Masters Candidate CiE), Dr. Jo Daniel (advisor)

Dynamic Modulus of Unaged Specimens

Dynamic Modulus for Aged Specimens

Average Dynamic Modulus Master Curves

Asphalt is heated and weighed before molding.

00H35

0

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

) 4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

00H37

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

) 4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

00H38

0

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

) 4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

40H43

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*

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Pa) 4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

40H44

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*

| (M

Pa) 4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

40H45

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*

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Pa) 4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

00H32

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

00H33

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

00H34

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

40H31

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0 0 0 0 0 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

40H39

0

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0 0 0 0 0 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

40H41

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0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

4.4 °C

21.1 °C

37.8 °C

54.4 °C

Fitted

Dynamic Modulus Master Curve for Moisture Conditioned HMA Specimens

0

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

Virgin Unaged

40% Unaged

Virgin 8 Days

40% 8 Days

Dynamic Modulus Master Curve for Virgin HMA

0

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000Reduced Frequency (Hz)

|E*|

(MPa

)

Virgin Unaged Moisture

Virgin Unaged

Virgin 8 Days Moisture

Virgin 8 Days

Dynamic Modulus Master Curve for 40% RAP HMA

0

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000Reduced Frequency (Hz)

|E*|

(MPa

)

40% Unaged Moisture

40% Unaged

40% 8 Days Moisture

40% 8 Days

Dynamic Modulus Master Curve for Unconditioned Specimens

0

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

Virgin Unaged

Virgin 8 Days

40% Unaged

40% 8 Days

Dynamic Modulus Master Curve for 0 and 40% RAP

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0.0001 0.001 0.01 0.1 1 10 100 1000 10000

Reduced Frequency (Hz)

|E*|

(MPa

)

Virgin Unaged MoistureVirgin UnagedVirgin 8 Days MoistureVirgin 8 Days40% Unaged Moisture40% Unaged40% 8 Days Moisture40% 8 Days

Specimens are molded to the correct dimensions in

the gyratory compactor.

Molded specimens numbered and allowed to cool

Cored specimens are numbered, dried and measured

They are vacuum saturated to 70-80 %, frozen at-18oC for 16 hours then placed in a 60oC water bath

Nuts are placed for LVDT attachment

Dynamic modulus is measured at four temperatures

and six frequencies for each sample

Results:

Conclusions: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.