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Effect of Bitumen and RAP Content on Resilient Modulus of AsphaltConcrete

H. ZiariDepartment of Civil Engineering, Iran science and Technology University, Tehran, Iran

M. M. KhabiriDepartment of Civil Engineering, Vali-Asr University, Rafsanjan, Iran

ABSTRACT: Economic and environmental considerations have prompted the recycling of steel,aluminum, plastic, and many other materials. One of these recyclable materials is hot mix asphalt(HMA).This paper presents research findings from the Investigation of Recycled AsphaltPavement (RAP) Mixtures project.

The RAP material was characterized in a number of ways. Asphalt content was determined byextraction method. RAP aggregate grading was determined before and after the asphalt binderwas removed by solvent extraction. The properties of the RAP aggregate were also evaluated bydetermining the specific gravity.

Samples were compacted in the laboratory using a Marshall compactor. The samplescontained from 0 to 40 percent RAP from a highway of Tehran. RAP material was blended withvirgin aggregate such that all samples tested had approximately the same grading.

Samples were tested for resilient modulus. The resilient modulus test provides a measure ofthe elastic properties of the mixture.

KEY WORDS: Recycled Asphalt Pavement, resilient modulus, bitumen content, marshall mixdesign

1 INTRODUCTION

Economic and environmental considerations have prompted the recycling of steel, aluminum,plastic, and many other materials. One of these recyclable materials is hot mix asphalt (HMA).This paper presents research findings from the Investigation of Recycled Asphalt Pavement(RAP) Mixtures project (Ziari , Khabiri 2005).

Resilient modulus tests were conducted on all samples to evaluate mixture temperaturesusceptibility and for use as a reference to earlier testing. Though it was once believed that stifferpavements had greater resistance to permanent deformation, it has been concluded that resilientmodulus at low temperatures is somewhat related to cracking, as stiffer mixes (higher MR) at lowtemperatures tend to crack earlier than more flexible mixtures (lower MR). (Michel , Bruce,2002).

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Resilient modulus testing was conducted in accordance with ASTM D 4123-82, StandardTest Method for Indirect Tension Test for Resilient Modulus of Bituminous Mixtures.. Upontest completion, the resilient modulus was calculated using Equation 1. (MS-2, 1977).

tU

PM

R

.

)27.0(

+=

(1)

Where:MR= resilient modulus, PaP = applied load, N

U = horizontal change in length, mmt = sample thickness, mmv = Poissons Ratio

Poissons Ratio for a 150-mm sample was calculated using Equation 2.

27.009.4

=

V

U

(2)

Where:

U = horizontal change in length, mm

V = vertical change in length, mm

Two samples from each mixture were tested in accordance with ASTM D 4123. The averageresilient modulus at 1 Hz and the coefficient of variation for each mixture are shown in Table 1.

There were two primary objectives to this sequence of resilient modulus testing:

1. Examine the effect of bitumen content2. Examine the effect of the addition of RAP

Table 1 Resilient modulus results, 1.0 Hz (MPa)

RAP Content %Bitumen

Content% 0 10 20 30 40

4 5202 5236 6342 6742 7348

5 4386 4782 5486 5730 6398

6 3567 4237 4793 4861 5730

7 2755 3649 3681 3846 4210

2 EFFECT OF BITUMEN CONTENT ON RESILENT MODULUS

In general, the data at 25 C do not clearly show how resilient modulus is affected by asphaltgrade and RAP content. Figure 1 shows the relationship observed between resilient modulus and

bitumen content for the different percent RAP mixtures. The resilient modulus rapidly decreaseswith increasing temperature. This is due to the softening of the asphalt binder as the temperature

is increased. (Ziari , Khabiri 2005)

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3 EFFECT OF RAP CONTENT ON RESILENT MODULUS

The addition of RAP to the mixture also had a pronounced effect on the resilient modulus. Theaddition of RAP will result in a stiffer mixture. Again, this relationship is clear at the higher testtemperatures, but not at the lowest temperature. Figure 2 illustrates the increase in resilientmodulus with the addition of RAP.

Figure 1: Effect of Bitumen Content on Resilient Modulus for Mixtures, 1.0 Hz

Figure 2: Effect of RAP Content on Resilient Modulus for Mixtures, 1.0 Hz

4 CONCLUSIONS

1. Addition of RAP to a mixture increased the resilient modulus. At 25 C, adding 40 percentRAP to control mixture resulted in a 74 percent increase in stiffness.

2. The source of the RAP affected the resilient modulus results. (Kandhal, Aao, 1997)

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REFERENCES

Ziari, H. and Khabiri, M.M., 2005.Laboratory Study of Effectiveness Addition of Hydrated Limeto Hot Asphalt Reclining.Proceedings of the International Symposium on PavementRecycling, SO Paulo SP Brazil

Michael S., Bruce A. C., and Andrew D., 2002.Investigation of Recycled Martial AsphaltPavement (RAP) Mixtures.Minnesota Department of Transportation, USA.

Mix Design Methods, 1997.Manual Series 2. Asphalt Institute, Lexington, KY, 1977.Kandhal, P. S., Rao, S. S., Watson, D. E., and Young, B., 1997. Performance of Recycled Hot-

Mix Asphalt in Georgia.Transportation Research Record, USA.