Test title:

MIX DESIGN ANALYSIS

Introduction:Hot mix asphalt (HMA) is one type of premix widely use in

construction worldwide. It is considered by many engineers as

premier paving product which available at any where with any cost

and most popular with its high skid resistance, high comfort ability

and low maintenance require. In short, HMA gain a lot of attention

from engineer and researcher over the world because of its

affordable material cost and high performance.

Asphalt mix design method involved the concept that mixtures

must be stable in mix and durable in any condition. It is a complex

issue with a lot of variables involved. However two methods of mix

design have become popular worldwide. They are the Marshall Mix

Design and the Hveem Mix Design method. In Malaysia the Marshall

Mix Design has become the norm in the road industry.

Then, Marshall testing device applied a compression load on the

circumference of a cylindrical sample through semi-circuit heads.

The temperature of testing is 60°C and testing speed is rapid with

the best being continue to failure, the maximum load is recorded as

well as the deformation undergo by the sample in reaching max

load. The value knows as Marshall Stability and Marshall Flow.

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Objective:1. To prepare a standard specimens of asphalt mix.

2. To identity factors which influence the asphalt mix design.

3. To determine the stability and flow of specimen using the

Marshall machine.

Apparatus:

1. Marshall Compaction Pedestal

2. Marshall Machine

3. Oven

4. Weights.

Specimen:

1. Aggregate, graded according to the ASTM or BS standard:

Sieve size: Weight (kg):

Passing retained 0.23

25mm – 9.3mm 0.31

9.5mm – 4.75mm 0.37

4.75mm – 1.18mm 0.23

1.18mm – 75um 0.06

Total 1.20

2. 6.5% Bitumen

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Procedures:1. The aggregate which graded according to the ASTM or BS

standard and a sufficient amount is prepared and weighted

(about 1200g) for the sample preparation that may give a

height of 63.5mm when compacted in the mould.

2. The required quantity of asphalt is weighted and heated to a

temperature of about 160ºC - 185ºC.

3. The aggregate in the oven is heated to a temperature not

higher than 28ºC above the binder temperature.

4. The binder is poured in and mixing carried out until all the

aggregate are coated. The mixing temperature shall be within

the limit set for the binder temperature. The thoroughly

cleaned mould is heated on a hot plate.

5. A piece of filter paper is fitted in the bottom of the mould and

the whole mix poured in three layers. The mix is then

vigorously toweled 15 times round the perimeter and 10 in the

centre leaving a slightly rounded surface.

6. The mould is placed on the Marshall Compaction pedestal and

gives 75 blows.

7. The specimen is removed carefully from the mould,

transferred to a smooth flat surface and allowed to cool to

room temperature about 40 minutes.

8. The specimen is measured and weighted in air and water (for

volume determination).

9. Finally, the prepared specimen is place into Marshall Machine

to determine the flow and stability.

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Result:

Height of the sample (cm) 7.45

Diameter of the sample (cm) 10.0

Flow(mm) 6.87

Stability (unit) 135

Calculation:Volume of the Specimen, V= п r²h

V = п × (10.0/2) ² × 7.45

= 585 cm³

In process to produce good pavement, have to duplicate the field

condition with some correlation establish during the laboratory as:

Since the flow measure from the test is 68.7mm, it is in range of

68.3mm to 71.4mm.

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From the graph, the correlation ratio is obtain is :

By interpolation method,

71.4 – 68.7 = 7 1.4 – 68.3 0.83 – X 0.83-0.86

2. 7 = -103.330.83-X

X = 0.856

The correlation ratio times stability = 0.856 × 135 = 115.56

Discussion:1. Marshall Stability value is a measurement of the load which the

sample totally failed or yield. It indicates the resistance of mix to

deformation that higher stability means mixtures are stiffer. Since

this load applied to the sample is only around 115.56kg, it

considered that this 6.5% bitumen hot mixed asphalt is not that

strong.

2. Whereas the Marshall Flow value is the total deformation of

samples from its original shape which the measurement is in

millimeter. This deformation will decrease in vertical diameter of

the sample. Since the flow is 6.87cm which within the volume

range of the sample, this result obtain is assume acceptable. The

high flow value is considered too plastic and have tendency to

destroy easily under traffic load.

3. If the mixes with very low flow values and abnormal high

Marshall Stability, it is considered too brittle and rigid pavement.

Whereas, the low stability and high flow value is considered that

the mixture tend to rut and deform under a load. As the result

obtain have a low stability and moderate flow, it may conclude

this sample in the second category stated.

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Conclusion:

1. The factor influence the asphalt mix design is the compaction

temperature, the moisture content of the mixture,

proportional of aggregate size and bitumen percentage, the

workmanship of asphalt mixing and the compaction method.

2. The stability and flow of specimen is 115.56 and 6.87cm.

References:

British Standard Methods of four determination of California

Bearing Ratio (CBR). BS1377: Part 4: 1990.

Kenneth N. Derucher and George P. Korfiatis, Materials for Civil

and Highway Engineers, Prentice Hall, Khandal et. al Hot Mix

Asphalt Materials, Mixtures, Design and construction NAPA

Foundation Maryland 199.

B.L. Gupta, and Amil Gupta, 2003, Highway And Bridge

Engineering, Third Edition, Standard Publishers Distributors.

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