Zemedkun Bereket Samuel
ID No- 16503984

Fundamental study on performance ofrecycled HMA mixtures with various
RAP contentsI.

INTRODUCTION

From 1970’s, year by year, use of reclaimed asphalt
pavement (RAP) has been an indispensable part ofpavement technology due to its feasibility in terms ofenvironmental, economic, and technical benefits.
Investigation and application of RAP is achallenging task due to its nature of variability, anundocumented source of its origin, and contamination.
Most previous researchers have done research in wider
intervals i.e. 10%-25% RAP content to assess theperformance of mixtures. The variable nature of RAP
is known, the present study evaluated recycled HMA
mixtures containing RAP with 5% interval to assess
the marginal difference in mixtures performance. In
the current study, three different pavement distresses
were selected, those are moisture damage, rutting andcracking. For the study four laboratory tests wereconducted, namely, Marshall stability and flow test,
Indirect tensile strength test (IDT), wheel tracking test(WTT), and three-point bending test (3PBBT). Thetests assessed the stability, moisture susceptibility,rutting, and cracking performance of mixtures
respectively.
Past studies showed that inclusion of RAP in asphalt
mixes changes the physical, mechanical, and chemical
properties of the HMA mixes. The existing findings on
the effect of RAP in recycled HMA can be identified
into three groups, improvement, and/or decline, orsimilarity in the performance achieved compared to
the new or less RAP containing mixtures. Therefore, it
is difficult to have consent among researchers on
predicting the effect of RAP in a performance of mixes
consistently. This happened due to varies research
approaches and differences in materials source usedfor experimental work.
On the current study the following two objectives wereaddressed;- To assess the recycled HMA mixtures having
5% interval of RAP contents.
- To give recommendations for taking necessary
measures when using recycled HMA mixtures.

II. MATERIALS AND METHODS
On this section, the ingredients used for research workand mix design procedure were discussed.

A. Materials

The aggregate:-new and RAP aggregates had anominal maximum aggregate size(NMAS) of 12.5mm
and the combined gradation were done to satisfy
specification limit for wearing course of Ethiopianstandard.
Asphalt binders:- the old asphalt from RAP materials
had a penetration grade of 15(1/10mm). The newasphalt which was used as a softening agent wasstraight asphalt with penetration grade of 60/80.
B. Methods (Laboratory tests)
Marshall Mix design procedure:- generally theprocedure consists of; aggregate and asphalt selection,specimen
preparation,
volumetricparameters
calculation, stability and flow determination, andoptimum asphalt content selection. On this study, thedesign of recycled HMA mixtures was done byassuming 100% re-activation binders from RAP.
Moisture susceptibility test: - moisture damage is thedeterioration of asphalt mixtures important
performance properties, due to the presence of water
inside the mass of mixtures. On the present study oneof the moisture susceptibility tests, IDT was conducted.
The indirect tensile strength of asphalt samples can becalculated by using equation 1.
2P(1)
π ×h×dWhereas ITS is indirect tensile strength in (MPa), P ispeak load at failure in N, h is specimen thickness inmm, d= specimen diameter in mm.
The tensile strength ratio (TSR) was used as anindicator for damages caused by moisture on mixtures,by providing the retained indirect tensile strength ofspecimens after conditioning the samples. The TSR ofspecimens was calculated using equation 2:
ITSconditioned
TSR =(2)ITSunconditioned
Whereas:ITS conditioned = conditioned specimen indirect tensilestrength
ITS unconditioned = unconditioned specimen indirecttensile strength
The higher TSR value indicates mixtures which areresistant to moisture damage. In general, a value above
0.70 is the most likely acceptable limit.
ITS =Permanent deformation test:- rutting is distress whichleads to a permanent deformation in pavement
structure. WTT is used to assess the rutting
performance of HMA mixtures. As per the Japanesestandard Dynamic Stability (DS) expressed in cycle

per millimeter is used as an indicator of rutting
performance of the mixture. DS can be calculatedusing equation.
DS = 1.5 x

42 x15d 60 − d 45

(3)

Whereas, D60 and d45 are rutting depth at 60thand 45th minutes respectively in mm.
Cracking test:- cracking can happen due to theenvironmental effects and/or repeated traffic load. TheTPBBT used to evaluate the flexural properties of theasphalt mixtures in term of resistance to cracking. TheTPBB tensile have two outputs, i.e. stress (σf) andtension strain (εf) at failure. The parameters of The
TPBB test can be calculated as follows (JRA B005):
3 P ×Lσ f = × ult 22 b×h(4)6× h=×d
εfL2(5)
Whereas, Pult is a peak load; L is a span of the bending
support; h is a height or a thickness of prismaticspecimen; b is a width of prismatic specimens, and d isa deformation at the peak load.

III. Results AND DISCUSSIONS
A. Marshall stability results

The Marshall mix design results showed that allmixtures in the study satisfied the specification rangeof most of the volumetric parameters, except the slightdecrease of VMA at the 30% RAP containing mixture.
The stability which indicates the mixtures resistances
to deformation, the RAP containing mixtures
performed well compared to 0% RAP mixture. Thismay be due to the stiffness of mixtures due to agedasphalt from RAP.
B. Indirect tensile strength test resultsThe test result clearly showed that the 0% RAP
mixture and 20% RAP mixtures had insignificant
differences on the IDT values. On the other hand,adding 30% of RAP showed significant improvementof IDT value on unconditioned specimens. For theconditioned specimens, it has been seen that the IDTvalues increased up until 25% RAP inclusion and it
declined slightly at 30% RAP mixture.
The test results showed that the TSR of 0% (controlled)and 20% RAP mixtures exhibit similar tendency inresisting moisture damage. On the other hand, theaddition of 25% RAP improved the resistance tomoisture damage. Here it was seen that 5% RAP
increment i.e. from 20% to 25% increased the TSRvalue about 54%. On the other hand, increasing RAP

from 25% to 30% in mixtures declined the TSR value
by 15 %.
C. Wheel tracking test results

From the WTT it was observed that as the RAP
content increased in the mixtures the rutting depth ofdecreased.
The 20%, 25%, and 30% RAP recycled mixture
increased the DS values of mixtures by 107%, 121%,
and 248% respectively.
RAP increment by 5%, i.e. from 20% to 25% had an
insignificant change in DS values. Whereas, increasing
the RAP content from 25% to 30% improved the DS
value by 57%. The DS value of 0% RAP found lesser
compared to the RAP containing mixtures. The lower
DS value of 0% RAP was might be due to instabilityof virgin asphalt at the testing temperatures.
D. Three point bending test results

The test results showed that the bending stresses ofRAP containing mixtures were higher compared to 0%
RAP containing mixtures. On the other hand, strain
value of 0% RAP at the failure points of mixtures hasthe highest value. The highest tensile strain value
indicates the ductility of materials, which means thatthe material withstands extended external stress before
its failure strain.

IV. CONCLUSIONS
The findings of the current study are summarized asfollows; The study showed that addition of RAP in themixtures improved the stability, rutting
resistance, and moisture susceptibility.
 Alteration of 5% RAP interval has insignificant
effects on the stability and cracking of RAP
containing mixtures. On the other hand, a 5%change of RAP content considerably affects therutting resistance and moisture susceptibility ofthe mixtures.
 Based on the findings, it is important toconsider 5% RAP content variation, while
designing for rutting, moisture damage andcracking.

Reference Japan Road Association: Manual for Test Method ofPavements, 2005.
 Imad Al-Qadi, et.al. Impact of high RAP contenton
structural and performance properties of asphalt
mixtures ( Illinois Center forTransportation, Urbana,2012).
 McDaniel, R, Shah, A, Huber, GA & Copeland, A,
Effects of reclaimed asphalt pavement content andvirgin binder grade on properties of plant produced
mixtures’2012.