Test title: MIX DESIGN ANALYSIS
Introduction: Hot Hot mix mix asph asphal altt (HMA (HMA)) is one one type type of prem premix ix wide widely ly us use e in constr construct uctio ion n worl worldwi dwide. de. It is consid considere ered d by many many engin engineer eers s 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 from engi engine neer er and and rese resear arch cher er over over the the worl world d beca becaus use e of its 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: Passing retained 25mm – 9.3mm 9.5mm – 4.75mm 4.75mm – 1.18mm 1.18mm – 75um Total
Weight (kg): 0.23 0.31 0.37 0.23 0.06 1.20
2. 6.5% Bitumen
Procedures:
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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.
Result: Height of the sample (cm)
7.45 3
Diameter of the sample (cm) Flow(mm) Stability (unit)
10.0 6.87 135
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.
From the graph, the correlation ratio is obtain is : By interpolation method, 71.4 – 68.7 0.83 – X
= 7 1.4 – 68.3 0.83-0.86
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2. 7 = -103.33 0.83-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.
Conclusion:
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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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