CVNG 3009: Highway Engineering
Experiment #1: Aggregate Grading
Name: Liam Smith
UWI ID: 816010566
Date: 07/10/19
Course Code: CVNG 3009
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Table of Contents
Abstract ................................................................................................................................................... 1
Introduction ............................................................................................................................................ 2
Aim .......................................................................................................................................................... 4
Objectives ............................................................................................................................................... 4
Apparatus & Materials ............................................................................................................................ 4
Procedure................................................................................................................................................ 5
Results ..................................................................................................................................................... 6
Sample Calculations .............................................................................................................................. 12
Discussion.............................................................................................................................................. 14
Limitations ............................................................................................................................................ 15
Sources of Error .................................................................................................................................... 15
Precautions ........................................................................................................................................... 16
Conclusion ............................................................................................................................................. 16
References ............................................................................................................................................ 17
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Abstract
This lab report addresses and discusses the fundamentals of HMA mix design for a road
pavement. This involves the blending of different aggregates being tested and analysed for the mix
design. The gradation of each aggregate is included and a grain size analysis for the aggregate samples
tested. A trial and error procedure was employed to achieve an optimum mix design to produce a
blend of aggregates of specified grading. The mix design proportions were determined to be:
•
1/2” Limestone – 20%
•
3/8” Limestone – 25%
•
Limestone Dust – 30%
•
Sharp Sand – 25%
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Introduction
The materials used in the design of Hot Mix Asphalt (HMA) consists of a combination of two or
more aggregates mixed at an appropriate ratio to obtain necessary the gradation requirements. This
combination is determined by executing a gradation test, producing the particle size distribution
which can be used in production of the asphalt concrete mixture. This is known as the job-mix formula
which consists of two parts:
1. The Combined Gradation of the aggregates to be used to produce a satisfactory mix meeting
all specification requirements.
2. The Asphalt Content which is necessary to produce a satisfactory mix meeting all the
specification requirements.
The gradation of the aggregates used in the final mixture can affect its volumetric properties such
as stability and workability. Stability being the maximum load that can be sustained and workability
being the ease of forming the mix. The particle distribution will affect the density of the mix and as a
result, the volume of voids in the mineral aggregate. An excessive volume of voids is undesirable in
the mixture neither is too dense of a mix as some void volume is needed to facilitate the application
of binder.
Figure 1. Showing a close-up of HMA and volumetric properties.
(https://www.pavementinteractive.org)
Hence, a mathematical trial and error method is applied to obtain acceptable design mix
percentages for each aggregate. These percentages must fall within the range of the two limit curves
in the Percent Passing vs. log (Sieve Size) graph. The maximum density is not usually applied in the
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field. However, it provides a good reference point for sieve analysis. The Fuller and Thompson
equation defines this maximum density such that a graphical plot can be generated. Given by the
equation:
𝑑 𝑛
𝑃 = ( ) ∗ 100
𝐷
Where; P = Percent passing a sieve size
D = maximum aggregate size
d = aggregate size being considered
n = parameter which adjusts curve for fineness or coarseness (for maximum particle density
n = 0.45 according to Fuller and Thompson)
The gradation type for a mixture will be found when comparing the percent passing curve and 0.45
power curve for a given maximum aggregate size regardless of density, uniformity openness or gap
grading. Generally, a dense gradation is used for HMA mixtures, which is very compact and varies near
to the 0.45 power curve which is the straight-line graph amongst the gap, dense, open and uniform
curves shown below.
Gap
0.45 Power curve
Uniform
Dense
Open
Figure 2. Showing the curves representing various gradation characteristics
(https://www.pavementinteractive.org)
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Aim
The aim of this lab is to educate students on the importance of gradation testing via first-hand
laboratory execution. Also, by allowing them to select their own design mix chosen by mathematical
trial and error procedure.
Objectives
•
To perform a sieve analysis on four different aggregates.
•
To determine the gradation requirements for bituminous concrete
•
To determine the mix blend for a dense mix asphalt via trial and error procedure.
Apparatus & Materials
•
Electronic Balance.
•
Aggregates: 1/2” limestone, 3/8” limestone, limestone dust & sharp sand.
•
Tap water.
•
Sieves: ¾”, ½”, 3/8”, No. 4, No. 8, No.30, No.50, No.100, No. 200 & Pan.
•
Mechanical sieve shaker.
•
Oven.
•
Bronze brush.
•
Hand brush.
•
Spatula.
•
Large pans required for drying and handling sample.
•
Bowls for weighing.
•
Heat resistant gloves.
•
Fan.
•
Scoop.
•
Ear plugs.
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Procedure
1. A portion of the aggregates was taken from the bin and weighed to approximately 1000g on
the electric balance using a scoop and a metal bowl.
2. The aggregates were then rinsed under the tap through a No. 200 sieve to remove clay and
silt form the aggregate and was transferred to the large pan for heating in the oven.
3. Samples were checked every so often and the spatula was used to stir the aggregate in the
pan.
4. When the aggregates were sufficiently dried, the pan was removed from the oven and placed
to cool in front of a fan
5. Once the samples were cooled, the sieves were placed in order of decreasing size from top to
bottom.
6. The aggregates were poured into the stack and manually shaken.
7. The stack was covered and placed in the mechanical sieve shaker which was turned on for
approximately 3 minutes.
8. The sieve stack was then taken apart and the amount of aggregates left on each size was
weighed and the cumulative weight retained was recorded.
9. The cumulative weight, percentage retained and the percentage passing on each sieve size
was recorded and tabulated.
10. A graph was plotted for the percent passing against sieve size.
11. In order to get a final mix design, a mathematical trial and error procedure was utilized
(Microsoft Excel) such that an optimum mix would fall within the target values.
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Results
Sample Description
1/2" Limestone
Quantity (g)
1000
Standard
(mm)
Alternate
Cumm. Weight
Retained (g)
Cumm. Percentage
Retained (%)
Percent
Passing (%)
25
1"
0
0
100
19
3/4"
0
0
100
12.5
1/2"
599
59.9
40.1
9.5
3/8"
932
93.2
6.8
4.75
4
995
99.5
0.5
2.36
8
995
99.5
0.5
0.6
30
995
99.5
0.5
0.3
50
995
99.5
0.5
0.15
100
995
99.5
0.5
0.075
200
995
99.5
Table 1. Showing Sieve Analysis Data for 1/2” Limestone.
0.5
Gradation of 1/2" Limestone
120
Percent Passing (%)
100
80
60
40
20
0
0.01
0.1
1
10
100
Sieve Size (mm)
Graph 1. Showing the Gradation of 1/2" Limestone.
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Sample Description
3/8" Limestone
Quantity (g)
1000
Standard
(mm)
Alternate
Cumm. Weight
Retained (g)
Cumm. Percentage
Retained (%)
Percent
Passing (%)
25
1"
0
0
100
19
3/4"
0
0
100
12.5
1/2"
0
0
100
9.5
3/8"
81
8.1
91.9
4.75
4
916
91.6
8.4
2.36
8
986
98.6
1.4
0.6
30
986
98.6
1.4
0.3
50
986
98.6
1.4
0.15
100
986
98.6
1.4
0.075
200
988
98.8
Table 2. Showing Sieve Analysis Data for 3/8” Limestone.
1.2
Gradation of 3/8" Limestone
120
Percent Passing (%)
100
80
60
40
20
0
0.01
0.1
1
10
100
Sieve Size (mm)
Graph 2. Showing the Gradation of 3/8” Limestone.
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Sample Description
Limestone Dust
Quantity (g)
1000
Standard
(mm)
Alternate
Cumm. Weight
Retained (g)
Cumm. Percentage
Retained (%)
Percent
Passing (%)
25
1"
0
0
100
19
3/4"
0
0
100
12.5
1/2"
0
0
100
9.5
3/8"
0
0
100
4.75
4
43
4.3
95.7
2.36
8
299
29.9
70.1
0.6
30
582
58.2
41.8
0.3
50
668
66.8
33.2
0.15
100
738
73.8
26.2
0.075
200
813
81.3
Table 3. Showing Sieve Analysis Data for Limestone Dust.
18.7
Gradation of Limestone Dust
120
Percent Passing (%)
100
80
60
40
20
0
0.01
0.1
1
10
100
Sieve Size (mm)
Graph 3. Showing the Gradation of Limestone Dust.
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Sample Description
Sharp Sand
Quantity (g)
1000
Standard
(mm)
Alternate
Cumm. Weight
Retained (g)
Cumm. Percentage
Retained (%)
Percent
Passing (%)
25
1"
0
0
100
19
3/4"
0
0
100
12.5
1/2"
3
0.3
99.7
9.5
3/8"
3
0.3
99.7
4.75
4
43
4.3
95.7
2.36
8
204
20.4
79.6
0.6
30
471
47.1
52.9
0.3
50
633
63.3
36.7
0.15
100
861
86.1
13.9
200
963
96.3
Table 4. Showing Sieve Analysis Data for Sharp Sand.
3.7
0.075
Gradation of Sharp Sand
120
Percent Passing (%)
100
80
60
40
20
0
0.01
0.1
1
Sieve Size (mm)
10
100
Graph 4. Showing the Gradation of Sharp Sand.
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Blending Data Sheet
1"
3/4"
1/2"
3/8"
No. 4
No. 8
No.
30
No.
50
Size (mm)
25.000
19.000
12.500
9.500
4.750
2.360
0.600
0.300
0.150
0.075
1/2" Limestone
100
100
40.1
6.8
0.5
0.5
0.5
0.5
0.5
0.5
3/8" Limestone
100
100
100
91.9
8.4
1.4
1.4
1.4
1.4
1.2
Limestone Dust
100
100
100
100
95.7
70.1
41.8
33.2
26.2
18.7
Sharp Sand
100
100
99.7
99.7
95.7
79.6
52.9
36.7
13.9
3.3
Specs. (lower limit)
100
100
80
70
50
35
18
13
8
4
Mix Design
100
100
87.9
79.3
54.8
41.4
26.2
19.6
11.8
6.8
Specs. (upper limit)
100
100
100
90
70
50
29
23
16
Table 5. Showing the Percentages of all Aggregates in the Mix Design and their Properties.
10
Sieve
Aggregate Size
Final Mix Design Proportions (%)
1/2" Limestone
20%
3/8" Limestone
25%
Limestone Dust
30%
Sharp Sand
25%
No.
100
No.
200
Total (sum)
100%
Table 6. Showing the Proportions Required for the Mix design.
Aggregate
Original weight (g)
Total Cumulative Weight (g)
Percentage Loss (%)
1/2" Limestone
1000
995
0.5
3/8" Limestone
1000
988
1.2
Limestone dust
1000
963
3.7
Sharp sand
1000
813
18.7
Table 7. Showing the Percentage of Particles Lost after Washing.
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Combined Gradation of Aggregates (Mix Design)
120
100
Percent Passing (%)
80
60
40
20
0
0.010
0.100
1.000
10.000
100.000
Sieve Size (mm)
Specs. (lower limit)
Specs. (upper limit)
Mix Design
Graph 5. Showing the Combined Gradation of Aggregates.
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Sample Calculations
Sample calculations for 1/2" Limestone aggregate:
•
Calculating Percent Mass Lost for validation;
Total cumulative weight = 995g
Total percent mass lost =
1000−995
x
1000
100
= 0.5%
•
Calculating Percent Mass Retained;
Using No. 100 Sieve Size,
Cumulative weight retained = 995 g
So, Cumulative Percent Retained =
Cumulative Weight Retained
x
Original Weight of Sample
100
995
= 1000 x 100
= 99.5%
•
Calculating Percent Passing;
Percent Passing = 100% - Cumulative Percent Retained
= 100% - 99.5%
= 0.5%
•
Calculating Mix Design Proportions;
Using No. 100 Sieve Size,
Percent passing sieve size No. 100 from each sample of aggregate:
▪
1/2“ Limestone – 0.5%
▪
3/8“ Limestone – 1.4%
▪
Limestone Dust – 26.2%
▪
Sharp Sand – 13.9%
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Mix Design Proportions after trial and error:
•
•
1/2“ Limestone – 20%
•
3/8“ Limestone – 25%
•
Limestone Dust – 30%
•
Sharp Sand – 25%
Calculating total percentage passing through the No. 100 sieve using the mix design
proportions.
Total % Passing = (0.5 x 0.20) + (1.4 x 0.25) + (26.4 x 0.30) + (13.9 x 0.25)
= 11.85%
This percent is acceptable as it falls within the acceptable range for the No. 100 Sieve (8% to
16%) ensuring that specifications are met. Mix designs were found for each sieve and it was
ensured that they fell within their respective ranges. These calculations were executed for all
aggregates and the respective data.
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Discussion
In the execution of this test, an acceptable aggregate grading for an HMA mix design has been
selected via trial and error. In so doing gradation tests were utilized as mentioned prior, to meet the
design and production requirements as well as the specifications throughout this process. This test
also serves to minimize the number of voids within the aggregate mix.
In dense-graded mixtures HMA, aggregate accounts for most of the volume in the mix and
reflects on the performance of the pavement after use. For the sake of this experiment, 1/2"
Limestone, 3/8” Limestone, Limestone Dust and Sharp Sand were the aggregates utilized for the mix
design. Which were analyzed and results were recorded and can be further classified based on their
sample distribution as either coarse or fine graded depending on passage of sieves.
Upon observation of the gradation graphs/particle distribution of each aggregate (Percent
Passing vs. Sieve Size), it can be said that 1/2" and 3/8” Limestone were uniformly graded. Whereas,
Limestone Dust was observed to be densely graded and Sharp Sand was said to be open/well graded.
These grading deductions were made in relation to the graphs in figure 2 in the Introduction above.
The particle distribution of the aggregates based on results obtained also shows that:
•
1/2" Limestone consisted of 99.5% coarse aggregate whilst 0.5% of the sample’s mass was
lost during the experiment.
•
3/8” Limestone consisted of 91.6% coarse aggregate and 7% fines whilst 1.4% of the sample’s
mass was lost during the experiment.
•
Limestone Dust consisted of 4.3% coarse aggregate and 77% fines whilst 18.7% of the sample’s
mass was lost during the experiment.
•
Sharp Sand consisted of 4.3% coarse aggregate and 92% fines whilst 3.7% of the sample’s mass
was lost during the experiment.
In the AASHTO T27 code it states that the allowable percent of aggregate lost should not
exceed 0.3% of the sample’s mass. Thus, with reference to the samples used for testing, all failed. This
failure is due to high levels of impurities (silt and clay) in the aggregates as well as weighing
inaccuracies as the electric balance is of low precision from its digital readings and possible loss during
shaking and transferring fractions between the various containers and surfaces.
Failure cannot be an option when it comes to creating ideal road surfaces. The creation of a
mix design that contains the optimum combination of aggregate (coarse and fines) is facilitated by the
trial and error method, mentioned often in this report. This procedure was executed in Microsoft
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Excel, where after all values were inputted it was just a matter of altering the aggregate proportions
and distributing them amongst the gradations or sieve sizes passing. The design mix was plotted
between the upper and lower limits as given in the lab manual and the proportions were varied until
the design mix graph fell within the two limits.
An opinion made in deciding when the process should be ended at the most evenly distributed
location. The final design mix conformed to the specifications of Type E Wearing Course, falling within
the limits as shown in Graph 5, making it acceptable for use in the final design of HMA for the surface
course. The mix design obtained for the experiment was:
1/2” Limestone – 20%, 3/8” Limestone – 25%, Limestone Dust – 30%, Sharp Sand – 25%
Limitations
•
The levels of impurities (silt and clay) in the aggregates which all exceeded AASHTO T27 limit
of 0.3% lost to the procedures of the experiment.
•
Sieve analysis assumes that all particles are completely round or spherical so that they will
pass through the sieve openings.
•
Dissolving, erosion, swelling or reactions can occur during the washing process hence resulting
in changes in individual aggregate sizing and overall mass of sample.
•
The determination of material passing through the no. 200 sieve cannot be accurately made.
Sources of Error
•
Precision error in electric balance when measuring aggregates.
•
Loss of aggregates to the environment when transferring aggregates from different containers
and surfaces.
•
Samples experienced some form of change due to being washed then dried bringing up the
possibility of swelling, dissolving, erosion or reactions when in contact with water.
•
Long term shaking of aggregates in the mechanical sieve shaker can cause degradation of
aggregates resulting in loss or gain in fractions of the sieve.
•
Possibility of aggregates blocking sieve openings preventing some aggregates from passing
through.
•
Aggregates can get lodged in the brushes when brushing sieves.
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Precautions
•
The aggregates were dried thoroughly before conducting the sieve analysis.
•
The aggregates were washed until the water flowing out of the No. 200 sieve appeared clear
indicating that the sample was washed until clear of silt and clay.
•
A brush was used to ensure that the sieves were completely free of aggregates when
transferring and weighing.
•
Mittens were worn by the person handling the metal pans in the oven to avoid damages to
person.
•
Students wore earplugs when loud machinery was in operation.
•
One sieve larger and smaller than the specified sieve sizes were added to the stack for
precautionary measures.
Conclusion
The mix design chosen in compliance with the design requirements and limit range was determined
to be:
•
•
•
•
1/2” Limestone – 20%
3/8” Limestone – 25%
Limestone Dust – 30%
Sharp Sand – 25%
These proportions were considered the most ideal based on personal opinion/preference.
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References
•
University of the West Indies, Highway & Transport Laboratory Manual - "Experiment 1Aggregate Grading “Accessed October 1st, 2019.
•
AASHTO T 27-06, “Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates,”
American Association of State Highway and Transportation Officials, Accessed October 7th,
2019.
•
Pavement interactive. “Gradation Test” Accessed October 3rd , 2019.
https://www.pavementinteractive.org/reference-desk/testing/aggregate-tests/gradationtest/
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