Experiment No: 05
DETERMINATION OF DENSITY, RELATIVE DENSITY (SPECIFIC GRAVITY), AND ABSORPTION OF FINE 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 fine aggregate particles
(not including the volume of voids between the particles), the relative density
(specific gravity), and the absorption of the fine 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 fine
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 C128—Specific
Gravity and Absorption of Fine 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.
Apparent density and apparent relative density (apparent
specific gravity) apply to the solid material making up the constituent
particles not include the pore space within the particles that is accessible to
water. This number is not widely used in building aggregate technology.
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.
Pycnometer:
Pycnometer or another suitable container into which the fine aggregate test sample can be readily introduced. The volume of the container filled to mark shall be at least 50 % greater than the space required to accommodate the test sample. A volumetric flask of capacity with a pycnometer top is satisfactory for a 500-g test sample of most fine aggregates.
Mold and Tamper for Surface Moisture Test:
The metal mold shall be in the form of a frustum
of a cone with dimensions as follows: 40 ± 3-mm inside diameter at the top, 90 ± 3-mm inside diameter at the bottom, and 75 ± 3 mm in height, with the metal
having a minimum thickness of 0.8 mm. The metal tamper shall have a mass of 340 ± 15 g and a flat circular tamping face 25 ± 3 mm in diameter
Oven:
Capable of
maintaining a uniform temperature of 110 ± 5 °C (230 ± 9 °F).
Figure: Mold, tamper,
and Pycnometer
Sampling
Thoroughly
mix the aggregate sample and reduce it to the approximate quantity needed.
Obtain approximately 1 kg of the fine aggregate sample.
Test Sample
Preparation
1.
Dry the test sample to a consistent
mass at a temperature of 110 ± 5 °C, then allow it to cool in room temperature Cover
test sample with water, either by immersion or by the addition of at least 6 %
moisture to the fine aggregate, and permit to stand for 24 ± 4 h.
2. Decant excess water with care to avoid loss of
fines, spread the sample on a flat, nonabsorbent surface exposed to a gently
moving current of warm air, and stir frequently to cause homogeneous drying. If
desired, mechanical aids such as tumbling or stirring may be used to help
achieve the saturated surface–dry condition. Continue this operation until the
test specimen approaches a free-flowing condition.
3. Test for Surface
Moisture:
3.1
Hold the mold firmly on a smooth nonabsorbent
surface with the large diameter down. Place a portion of the partially dried
fine aggregate loosely in the mold by filling it to overflowing and heaping
additional material above the top of the mold by holding it with the cupped
fingers of the hand holding the mold.
3.2
Lightly tamp the fine aggregate into the mold
with 25 light drops of the tamper. Start each drop approximately 5 mm above the
top surface of the fine aggregate. Permit the tamper to fall freely under
gravitational attraction on each drop. Adjust the starting height to the new
surface elevation after each drop and distribute the drops over the surface.
3.3
Remove loose sand from the base and lift the
mold vertically. If surface moisture is still present, the fine aggregate will
retain the molded shape. Slight slumping of the molded fine aggregate indicates
that it has reached a surface-dry condition.
3.4
When fine aggregate consists mostly of
angular-shaped particles or contains a large amount of fines, it does not
collapse in the cone test when it reaches the surface-dry state.
Conduct a test by releasing a small amount of the fine aggregate from the cone
test onto a surface measuring between 100 and 150 mm in height. Observe if the
fines become airborne. The presence of airborne fines indicates the existence
of this issue. The saturated surface-dry state for these materials is defined
as the stage at which one side of the fine aggregate experiences a minor slump
when the mold is removed.
3.5
Conduct a provisional cone test by
filling the cone mold according to the instructions provided above, but using
only 10 drops of the tamper. Add more fine aggregate and use 10 drops of the
tamper again. Proceed with adding material twice more by applying 3 and 2 drops
of the tamper, respectively. To level off the material, align it with the top
of the mold, eliminate any loose material from the base, and elevate the mold
vertically.
Procedure:
Gravimetric (Pycnometer)
Procedure:
1.
Partially fill the pycnometer with
water. Introduce into the pycnometer 500 ±10 g of saturated surface-dry fine
aggregate sample and fill with additional water to about 90 % of capacity.
Agitate the pycnometer manually or mechanically.
2.
For Manually, roll, invert, or
agitate the pycnometer or use a combination of these actions to eliminate
visible air bubbles. For Mechanically, agitate the pycnometer by external
vibration in a manner that will not degrade the sample.
3.
After eliminating all air bubbles,
adjust the temperature of the pycnometer and its contents to 23.0 ± 2.0 °C, and
bring the water level in the pycnometer to its calibrated capacity.
4.
Determine the total mass of the
pycnometer, specimen, and water.
5.
Remove the fine aggregate from the
pycnometer and dry in the oven to constant mass at a temperature of 110 ± 5 °C.
6.
After removing from oven cool the
sample in air at room temperature for 1 ± 1⁄2 h, and determine the mass.
7.
Determine the mass of the pycnometer
filled to its calibrated capacity with water at 23.0 ± 2.0 °C.
Calculations
A = mass of oven dry specimen, g
B = mass of pycnometer filled with
water, to calibration mark, g
C = mass of pycnometer filled with
specimen and water to calibration mark, g
S = mass of saturated surface-dry specimen (used in the
gravimetric procedure for density and relative density (specific gravity), or
for absorption with both procedures), g
Relative Density
(Specific Gravity):
Relative Density
(Specific Gravity) (OD)
Relative Density
(Specific Gravity) (OD)= A/(B+S-C)
Relative Density
(Specific Gravity) (SSD)
Relative density (specific gravity) (SSD) = S/(B+S-C)
Apparent Relative Density (Apparent Specific Gravity)
Apparent Relative Density (Apparent
Specific Gravity) = A/(B+A-C)
Density:
Density (OD)
Density (OD) kg/m3, = 997.5 A/ (B + S –
C)
Density (SSD)
Density (SSD) kg/m3 = 997.5 S / (B+S –
C)
Apparent Density
Apparent Density = 997.5 A / (B+A – C)
Absorption
Absorption % = [(S- A)/A] X 100
Reports
·
Report density results
·
Report absorption result
Lab Assignment Questions:
Fundamental Questions:
1. What
is specific gravity?
2. Explain
the significance of specific gravity in fine aggregates.
3. What
is water absorption, and why is it important to measure in fine aggregates?
4. How
does the specific gravity of fine aggregates affect the design of concrete
mixes?
5. What
are the types of specific gravity, and which one is commonly used in this
experiment?
6. Bulk
specific gravity, apparent specific gravity, and effective specific gravity.
Procedure-Related Questions:
7. Can
you describe the procedure for determining the specific gravity of fine
aggregates?
8. Why
is it important to remove all air bubbles when soaking the fine aggregate
sample in water?
9. What
is the role of the pycnometer in this experiment?
10. How
do you ensure that the aggregates are in a saturated surface-dry (SSD)
condition before performing the test?
11. How
do you calculate the specific gravity using the mass measurements obtained in
the experiment?
12. Why
is the sample dried to a constant weight before determining absorption?
Interpretation and Application:
13. What
is the typical range of specific gravity values for fine aggregates?
14. How
do variations in the specific gravity of fine aggregates affect concrete
properties?
15. How
does the absorption capacity of fine aggregates influence the water-cement
ratio in a concrete mix?
16. What
could be the reasons for obtaining an unusually high or low specific gravity in
your experiment?
17. How
would the presence of organic impurities in fine aggregates affect the specific
gravity and absorption test results?
18. What
corrections, if any, should be made to concrete mix designs based on the
specific gravity and absorption values of fine aggregates?
Safety and Standards:
19. What
are the safety precautions to be followed while performing the specific gravity
and absorption tests?
20. Which
ASTM or IS code is followed for determining the specific gravity and absorption
of fine aggregates?
21. What
are the limitations of the specific gravity and absorption test methods?
References
ASTM C128:
Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption
of Fine Aggregate.