Effects of Different Fillers on the Mechanical Properties of Hot Mix Asphalt
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Date
2015-11
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AAU
Abstract
Asphalt concrete road construction is a crucial part of the Growth and Transformation Plan (GTP) of
Ethiopia for building a high performance transportation networks for its economic development. Currently
many asphalt concrete road construction activities are taking place, especially on trunk and main access
roads.
In this study the effect of different types of mineral fillers and their proportion at a given filler percentage
by total weight of the mixture in hot mix asphalt concrete performance are investigated and alternative filler
proportions are proposed for the construction of asphalt concrete pavement for Gambella –Itang –Jikawo
road and it will serve as a guide to use alternative fillers for construction of asphalt concrete pavement in
Ethiopia.
Investigation was made to adjust the Job Mix Formula using different filler proportion under the project
specification. The mineral fillers, with given percentages by total weight of the mixture, used in this
study were crushed stone, Pagag Sand, Cement and Marble dust passing 0.075mm sieve. After determining
the optimum bitumen content with Marshall Stability test a number of trial mixes have been performed
using the Marshal Mix design procedure to arrive at asphalt concrete mixtures that fulfill the Marshal
criteria. The effects of each mineral filler type on Marshal Properties of the asphalt mixtures at a
given optimum asphalt content 5% were evaluated and possible basis for such difference in properties
was discussed.
Results of this study indicate that the addition of cement and marble dust to asphalt concrete as filler has
produced relatively the same comparable Marshall properties. However, the Marshall Stability property
obtained from replacement of these fillers was not good as compared with Pagag sand (natural sand).
It can be concluded that Pagag sand replacement up to 50% in the mixture shows acceptable air voids,
Marshall Stability and flow values and maximum VMA values. However, from the VFA values we can
understand that the replacement of Pagag sand by more than 10% shows a decrease in values below the
specification limit as the result of air voids increases when the Pagag sand in the mixes increases that
indicate the mixture needs more than 5% asphalt content which is not economical.
The use of cement 50% from the total proportion of design filler content (8.06%) in the mixture satisfies all
the Marshall Properties. However, increasing the more than 50% replacement in the mixture test result
shows it fulfills the Marshall properties under the project specification except the stability requirement. It is
also observed that the Marshall Stability values obtained from cement filler is not uniform when we
increase the replacement proportion. This may be due to creation of stabilization that leads to shrinkage
cracking or asphalt stiffening effect. Since the cement filler Marshall Stability property obtained is not
uniform, it would be difficult to give an explanation on this property based on this laboratory investigation
only.
The results of this research work may be used as basis for further detail investigation on the effects of
mineral fillers especially cement and marble dust on Marshall Stability and Flow properties of hot mix
asphalt.
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Keywords
Fillers, Hot Mix Asphalt, Jikawo Road Project