Experiment No: 04
Determination
of Density, Relative Density (Specific Gravity), and Absorption of Coarse
Aggregate
Introduction
The specific gravity of an aggregate
is defined as the ratio of the mass of solid in a particular volume of sample
to the mass of an equivalent volume of water at the same temperature. Since the
aggregate often contains voids, there are numerous sorts of specific gravities.
The absolute specific gravity refers
to the volume of solid material excluding the voids, and hence, is defined as
the ratio of the mass of solid to the mass of an equal void free volume of
water at a particular temperature.
If the volume of aggregate includes
the voids, the resultant specific gravity is termed the apparent specific
gravity. As the aggregate often contains both impermeable and capillary voids,
(voids between particles) the apparent specific gravity refers to volume
including impermeable voids alone. It is consequently, the ratio of the mass of
the aggregate dried in an oven at 100 to 110°C for 24 hours to the mass of the
water occupying a volume equivalent to that of solids including impermeable
voids or pores.
This specific gravity is necessary
for the calculations of the production of concrete or of the quantity of
aggregate required for a specific volume of concrete. The specific gravity of
an aggregate delivers significant information about its quality and qualities.
It is noticed that greater the specific c gravity of an aggregate harder and
stronger it will be. If the specific gravity is above or below that generally
attributed to a specific type of aggregate, it may suggest that the shape and
grading of the aggregate has modified.
Scope
This test method involves the
determination of the average density of a quantity of coarse aggregate
particles (not including the volume of voids between the particles), the
relative density (specific gravity), and the absorption of the coarse
aggregate. Depending on the process employed, the density (kg/m3(lb/ft3)) is
given as oven-dry (OD), saturated-surface-dry (SSD), or as apparent density.
Likewise, relative density (specific gravity), a dimensionless quantity, is
stated as OD, SSD, or as apparent relative density (apparent specific gravity).
The OD density and OD relative density are obtained after drying the aggregate.
The SSD density, SSD relative density, and absorption are measured after
soaking the aggregate in water for a defined period.
Purpose
To determine the specific gravity and
absorption of coarse aggregate. The specific gravity may be expressed as bulk
specific gravity, bulk specific gravity SSD (saturated-surface dry), or
apparent specific gravity.
ASTM Designation
ASTM C127—Specific Gravity and Absorption of
Coarse Aggregate.
Terminology
Absorption
The increase in mass of aggregate
owing to water penetration into the pores of the particles within a prescribed
duration of time, but not including water adherence to the exterior surface of
the particles, expressed as a percentage of the dry mass.
Oven-dry (OD)
The condition in which the aggregates have been dried by heating
in an oven at 110 ± 5 °C for required time to reach a constant mass.
Saturated-Surface-Dry
(SSD)
The situation in which the permeable
pores of aggregate particle are filled with water to the extent attained by
immersing in water for the required period of time, but without free water on
the surface of the particles.
Density
The mass
per unit volume of a material, expressed as kilograms per cubic meter (pounds
per cubic foot).
Density (Od)
The mass of oven dry aggregate per unit volume of aggregate
particles, including the volume of permeable and impermeable pores within the
particles, but not including the voids between the particles.
Density (SSD)
The mass of
saturated-surface-dry aggregate per unit volume of the aggregate particles,
including the volume of impermeable pores and permeable, water-filled pores
within the particles, but not including the voids between the particles.
Apparent density
The mass per
unit volume of the impermeable portion of the aggregate particles.
Relative density (specific gravity)
The ratio
of the density of a material to the density of distilled water at a stated
temperature; the values are dimensionless.
Relative density
(specific gravity) (OD)
The ratio of the density (OD) of the aggregate
to the density of distilled water at a stated temperature.
Relative density
(specific gravity) (SSD)
The ratio of the
density (SSD) of the aggregate to the density of distilled water at a stated
temperature.
Apparent relative
density (apparent specific gravity)
The ratio of the apparent density of aggregate
to the density of distilled water at a stated temperature.
Significance and Use
Relative density (specific gravity)
Used for calculating aggregate volume in mixtures like Portland cement concrete
and bituminous concrete. Also used in computation of voids in aggregate. Relative
density (specific gravity) (SSD) is used when aggregate is wet, satisfying
absorption. relative density (specific gravity) (OD) is used for computations
when the aggregate is dry or assumed to be dry. Absorption values are used to
calculate the mass change of an aggregate due to water absorbed in its pore
spaces compared to the dry condition. The standard for absorption is obtained
after submerging dry aggregate for a specified time. Aggregates mined below the
water table typically have a higher moisture content than the absorption
determined by this test method if used without opportunity to dry prior to use.
Conversely, some aggregates that have not been continuously maintained in a
moist condition until used may have less absorbed moisture than the
24-hour-soaked condition. The percentage of free moisture in an aggregate that
has been in contact with water is determined by deducting absorption from total
moisture content.
Apparatus
Balance:
Balance accurate to
0.05% of the sample weight or 0.5 g, whichever is greater
Sample Container:
Wire basket 3.35 mm (No.
6) or finer mesh (Figure below)
Water tank:
where the sample container is placed while suspended below the
balance
Sieve:
75-mm (No. 4) sieve or
other sizes as needed
Oven:
Capable of
maintaining a uniform temperature of 110 ± 5 °C (230 ± 9 °F).
Figure: Wire Basket
Sampling
Thoroughly
mix the aggregate sample and reduce it to the approximate quantity needed. Reject all materials
passing 4.74 mm sieve by dry sieving and thoroughly washing to remove
dust or other coatings from the surface.
The minimum
mass of test sample to be used is given as follows:
|
Nominal
Maximum Size, mm (in.) |
Minimum Mass of Test
Sample, kg (lb) |
|
12.5 (1⁄2) or less |
2 (4.4) |
|
19.0 (3⁄4) |
3 (6.6) |
|
25.0 (1) |
4 (8.8) |
|
37.5 (1 1⁄2) |
5 (11) |
|
50 (2) |
8 (18) |
|
63 (21⁄2) |
12 (26) |
|
75 (3) |
18 (40) |
|
90 (31⁄2) |
25 (55) |
|
100 (4) |
40 (88) |
|
125 (5) |
75 (165) |
Procedure
1.
Dry the test sample to a consistent
mass at a temperature of 110 ± 5 °C, then allow it to cool in room temperature
air for 1 to 3 hours.
2.
Therefore, submerge the aggregate in
water at ambient temperature for a duration of 24 hours.
3.
Remove the test sample from the
water and thereafter roll it in a wide absorbent cloth until all observable
water films have been eliminated. Individually clean the bigger particles. Take
care to prevent the evaporation of water from the pores of the aggregate during
the process of surface-drying.
4.
Determine the mass of the test
sample in the saturated surface-dry condition.
5.
Place the specimen in the wire
basket and calculate its weight while it is submerged in water at a temperature
of 23 ± 2.0 °C and note the mass. Take
care to eliminate all entrapped air before weighing it by shaking the container
while it is immersed.
6.
Dry the test sample in the oven to
constant mass at a temperature of 110 ± 5 °C, cool in air at room temperature 1
to 3 h, or until the aggregate has cooled to a temperature that is easy to
handle and determine the mass
Calculations
A = mass of oven-dry test sample in air, g,
B = mass of saturated-surface-dry test sample in air, g, and
C = apparent mass of saturated test sample in water, g.
Relative Density (Specific Gravity):
Relative Density
(Specific Gravity) (OD)
Relative Density
(Specific Gravity) (OD)= A/(B-C)
Relative Density
(Specific Gravity) (SSD)
Relative density (specific gravity) (SSD) = B/(B-C)
Apparent Relative Density (Apparent Specific Gravity)
Apparent Relative Density (Apparent
Specific Gravity) = A/(A-C)
Density:
Density (OD)
Density (OD) kg/m3, =
997.5 A/ (B – C)
Density (SSD)
Density (SSD) kg/m3 =
997.5 B / (B – C)
Apparent Density
Apparent Density = 997.5
A / (A – C)
Absorption
Absorption, %5 = [(B- A)/A] X
100
Reports
·
Report density results
·
Report absorption result
Lab assignment Questions
Basic Conceptual Questions:
1. What
is specific gravity, and why is it important in civil engineering?
2. Can
you explain the difference between apparent, bulk, and effective specific
gravity?
3. Why
do we determine the specific gravity of coarse aggregates?
4. What
is water absorption in aggregates, and how is it measured?
5. How
does the specific gravity of coarse aggregates affect concrete mix design?
6. What
are the typical values of specific gravity for different types of coarse
aggregates?
Test Procedure Questions:
7. Describe
the procedure for determining the specific gravity of coarse aggregates.
8. Why
is the aggregate sample soaked for 24 hours before testing for water
absorption?
9. What
is the significance of drying the aggregate sample to a constant weight?
10. What
are the possible errors that can occur during the determination of specific
gravity and absorption?
11. Why
is it necessary to fill the aggregate sample with water to eliminate air voids
during testing?
12. Can
you explain the role of the wire basket in this test procedure?
Application Questions:
13. How
does the water absorption value of coarse aggregates affect the durability of
concrete?
14. What
effect does high specific gravity have on the compressive strength of concrete?
15. How
can variations in specific gravity and absorption impact the batching of
concrete?
References
ASTM C127: Standard Test
Method for Density, Relative Density (Specific Gravity), and Absorption of
Coarse Aggregate.