HMA Evaluation at Different Aggregate Gradations
HMA Evaluation at Different Aggregate Gradations
HMA Evaluation at Different Aggregate Gradations
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Abstract: The properties of coarse and fine aggregates used in hot-mix asphalt (HMA) mixtures
significantly affect the performance of the highway pavements in which they are used. The selection of
aggregate gradation for use in HMA pavement is important to pavement performance. This study was
conducted to evaluate the effectiveness of aggregate gradation on HMA according to JKR
specification/1988 and JKR specification/rev. 2005. The laboratory tests carried out to determine the
properties of aggregates included sieve analysis, the Los Angeles Abrasion Test, Aggregate Impact
Value and Aggregate Crushing Value. A Resilient Modulus Test and Static Creep Test were also
carried out to determine the performance of HMA by using Materials Testing Apparatus. In general,
the aggregate gradation of Mixture 2, which follows JKR specification/rev. 2005, is better than the
aggregate gradation of Mixture 1, which follows JKR specification/1988.
Key words: hot-mix asphalt, aggregates, creep, Marshall Stability and Flow.
INTRODUCTION
Hot-mix asphalt (HMA) is defined as a complex mixture composed of bituminous binders and mineral
aggregate. The bitumen, black or dark brown in colour, acts as an adhesive, gluing the aggregate into a dense
mass and waterproofing the aggregate particles. The mineral aggregate, when bound together, acts as a stone
framework to give strength and toughness to the composite system. HMA performance is affected by the
individual properties of both aggregate and bitumen and the interaction between them (Reubush, 1999).
HMA contains a significant amount of mineral aggregate, approximately 95% by weight and 85% by
volume (Liu and You, 2011). The American Society for Testing and Materials (ASTM) defines aggregate as a
granular material of mineral composition such as sand, gravel, shell, slag, or crushed stone, with a cementing
medium to form mortar or concrete, or alone as in base course or railroad ballast. Aggregates for HMA are
usually classified by size as coarse aggregates, fine aggregates, or mineral fillers. ASTM also defines coarse
aggregates as particles retained on a No. 4 (4.75 mm) sieve, fine aggregate as that passing through a No. 4 sieve
(4.75 mm) and mineral filler as material with at least 70 per cent passing through a No. 200 (75 µm) sieve
(ASTM, 2003).
Aggregate gradation is the most important property of HMA, as well as stiffness, stability, durability,
workability, fatigue resistance and resistance to moisture damage. Aggregate grading is the distribution of
particle size expressed as a percentage of the total weight. Grading is determined by passing the aggregate
through a series of sieves stacked with progressively smaller holes from top to bottom, and weighing the
material retained on each sieve. The gradation of an aggregate is normally expressed as the percentage passing
through various sieve sizes (Robert et al., 1996).
The large increase in the number of vehicles and the volume of heavy traffic on the roads has consequently
increased the tire pressure and axle loads imposed on the pavement structure. Hence, there is a need to enhance
asphalt pavement mixtures that may prone to rutting and cracking to withstand the increase in loading, mitigate
the adverse effects on pavement performance and reduce the occurrence of premature rutting. Therefore, the
selection of aggregate gradation for use in HMA pavement is important to pavement performance (White et al.,
2006). The proper gradation of aggregates is strongly affected by the mix properties such as air voids, stability
and resistance to permanent deformation.
This study was conducted to evaluate the effectiveness of aggregate gradation on HMA according to
Malaysian Public Works Department specification; namely JKR specification (ACW14, 1988) and JKR
specification (ACW14, 2005). This study also aims to vary aggregate gradation in the HMA mixtures to
determine the effects on HMA criteria such as stability, density and strength. The laboratory tests carried out to
determine the properties of the aggregates included sieve analysis, the Los Angeles Abrasion Test (LAAT),
Aggregate Impact Value (AIV) and Aggregate Crushing Value (ACV). A Resilient Modulus Test and Static
Creep Test were also carried out to determine the performance of HMA by using Materials Testing Apparatus
Corresponding Author: Sustainable Urban Transport Research Centre Dept. of Civil and Structural Engineering Faculty
of Engineering and Built Environment Universiti Kebangsaan Malaysia 43600 Bangi, Selangor
Malaysia
E-mail: izzi@eng.ukm.my
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Aust. J. Basic & Appl. Sci., 6(7): 9-14, 2012
(MATTA). Samples were prepared by means of the Marshall Design method, in accordance with Malaysian
Public Work Department Specifications.
2. Experimental Design:
2.1 Bitumen:
Penetration grade 80/100 bitumen was used in this study, supplied from one source in order to ensure the
consistency of the original bitumen properties. Basically, this pen-grade bitumen has been used extensively for
bituminous pavement in Malaysia.
2.2 Aggregates:
In this study, two commonly used aggregates were prepared; namely fine and coarse aggregates. All testing
was conducted based on the “JKR Standard Specification for Road Works”. A sieve analysis was made of each
range, and then a quantity of aggregate of the selected blend was prepared into several sizes by the sieve
method. Other aggregate properties measured included the Los Angeles Abrasion Test (LAAT), Aggregate
Impact Value (AIV) and Aggregate Crushing Value (ACV). Details of the results are discussed in the following
section.
The gradation of an aggregate is normally expressed as the total percentage passing through various sieve
sizes. Tables 2 and 3 show the gradation of the aggregates for both mixtures. From the result, Mixture 1, mixed
according to JKR/1988, has 55% fine aggregate and 38% coarse aggregate of the total weight, while Mixture 2,
mixed according to the JKR/rev. 2005 specification, has 44% coarse aggregate and 55% fine aggregate. In
addition, Mixture 1 has a higher percentage of mineral filler than Mixture 2.
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Aust. J. Basic & Appl. Sci., 6(7): 9-14, 2012
Weight of aggregate
5000 5000
before test, A (gm.)
Weight of aggregate
3933 3927
after test, B (gm.)
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Aust. J. Basic & Appl. Sci., 6(7): 9-14, 2012
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Aust. J. Basic & Appl. Sci., 6(7): 9-14, 2012
Fig. 1: Selection of optimum asphalt binder contents for Mixture 1 and Mixture 2
Conclusions:
Based on the analysis presented, the following conclusions can be made:
The indirect tensile strength of Mixture 1 is higher than Mixture 2. This indicates that Mixture 1 has higher
values of resilient modulus at failure indirect tensile strength under a static load. This would further imply that
Mixture 1 appears to be capable of withstanding larger tensile strains prior to cracking (internal resistance).
The Marshall Stability value of Mixture 2 is higher than Mixture 1. The reasons behind these results are that
the asphalt and dust content is higher in Mixture 1 than Mixture 2.
For the static creep test, the results indicate that the value of permanent strain of Mixture 1 is higher than
Mixture 2. This could be attributed to the higher mineral filler content, the percentage of particle sizes of the
aggregate and the low mechanical interaction between the asphalt and the aggregate.
In general, the aggregate gradation of Mixture 2, which follows JKR specification/rev. 2005, is better than
the aggregate gradation of Mixture 1, which follows JKR specification/1988. This could be due to the mineral
filler and particle size of the aggregate. In addition, the higher asphalt content of Mixture 1 provides a higher
resilient modulus and lower values of the Marshall Stability and creep modulus. Another reason could be that
there is too much asphalt cement in the mixture, causing a loss of internal friction between the aggregate
particles and the asphalt cement. This may lead to high permanent deformation.
REFERENCES
American Society for Testing and Materials, 2003. Annual Book of ASTM Standards. Volume 04.03, Road
and Paving Materials; Vehicle-Pavement Systems. ASTM International, West Conshohocken, Pennsylvania.
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Aust. J. Basic & Appl. Sci., 6(7): 9-14, 2012
Liu, Y., and Z. You. 2011. Discrete-Element Modeling: Impacts of Aggregate Sphericity, Orientation, and
Angularity on Creep Stiffness of Idealized Asphalt Mixtures. J. Eng. Mech., 137(4): 294-303.
Public Works Department Malaysia, 1988. Specification for Road Works. Kuala Lumpur.
Public Works Department Malaysia. Rev., 2005. Specification for Road Works. Kuala Lumpur.
Reubush, S.D., 1999. Effects of Storage on the Linear Viscoelastic Response of Polymer-Modified Asphalt
at Intermediate to High Temperature. MSc Dissertation, the Virginia Polytechnic Institute and State University.
Roberts, F.L., P.S. Kandhal, E.R. Brown, D.Y. Lee, and T.W. Kennedy, 1996. Hot-Mix Asphalt Materials,
Mixture Design and Construction, 2nd Edition. NAPA Education Foundation, Lanham, Maryland.
White, T.D., J.E. Haddock and E. Rismantojo, 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used
in Pavements. NCHRP Report 557. Transportation Research Board, Washington D.C.
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