Group No.: 3 Group Leader: Name: Mago, Monique O. Date Performed: September 10, 2015Course, Year & Section: BSCE-4C Date Submitted: September 17, 2015

LABORATORY TESTSPECIFIC GRAVITY OF FINE AGGREGATES

OBJECTIVE

This test method covers the determination of specific gravity and absorption of fine aggregate. The specific gravity may be expressed as bulk specific gravity or apparent specific gravity. The bulk specific gravity and absorption are based on aggregate after 24 hour soaking in water.

REFERENCE

ASTM C 128-79 Specific gravity and absorption of fine aggregateJIS A 11110-79 Method of test for specific gravity and absorption of fine aggregate

MAIN PRINCIPLES

Although the concept of determination of specific gravity and absorption of fine aggregates is essentially similar to that of the coarse aggregate, there are some differences that should be stated. One is fine aggregate can hold water not only in the permeable pores of a particle but also in spaces beween particles. This somehow complicated the determination of the satrurated surface-dry (SSD) condition of fine aggregate. However, laboratory experiments led to the development of the cone test procedure by which the attainment of SSD condition can be determined.

REQUIRED EQUIPMENT

Chapman flask (500 ml) sand cone test apparatus balance (0.05 g sensitivity) spoon

TEST PROCEDURE

A. Preparation

1. Soak the test sample in water for 24±4 hours.2. Decant excess water with care to avoid loss of fines.

3. Expose the sample to a gently moving current of warm air. Stir frequently to secure homogeneous drying.4. Perform the cone test to determine if the sample has attaine dthe saturated surface-dry (SSD) condition.

B. Cone Test Procedure

1. Hold the cone firmly on a smooth non-absorbent surface.2. Plaec the fine aggregate loosely into the cone by filling it to overflowing.3. Lightly tamp the fine aggregate with 25 drops of the tamper. Distribute the drops all over the entire ares.4. Remove the loose sand from the base and lift the mold vertically.5. If the fine aggregate slumps slightly, it indicates that the sample has reacged the saturated surface-dry (SSD) condition.

C. Test Procedure1. Weigh the Chapman flask (Wf).2. Pour water into the flask to about 50% capacity.3. Weigh approximately 500 g of saturated surface-dry aggregate (Ws).4. Pour the sample into the flask. Add water to about 90% of the flask’s capacity.5. Roll, invert and agitate the flask to eliminate all air bubbles.6. Bring the water level in the flask to its calibrated capacity.7. Immerse the flask in a water bath at a temperature of 20 degrees Centigrade for 3 hours.8. Weigh the flask with the sample and water (Wt).

D. Determination of Water Absorption1. After obtaining the necessary data for determining the specific gravity, pour out the sample into a pan.2. Dry to constant weight at a temperature of 100±5 degrees Centigrade for 24 hours.3. Weigh the oven-dried sample (Wd).

CALCULATION

Specific gravity

SG=W s

500−W t+W f+W s

where SG is the specific gravity of aggregate at SSD conditionWs is the weight of sample in air at SSD condition (g)Wf is the weight of the flask (g)Wt is the weight of the flask with sample and water (g)

Water Absorption

Absorption=W s−W d

W d

×100

where Ws is the weight of sample in air at SSD condition (g)Wd is the oven-dried weight of aggregate (g)

DATA SHEET

Weight of SSD aggregate in air, Ws

525 gWeight of Chapman flask, Wf

415 gWeight of flask with sample and water, Wt

1225 gWeight of oven-dried aggregate, Wd

Specific gravity of coarse aggregate, SG2.442

Absorption, %

SAMPLE CALCULATION

Specific gravity

SG=W s

500−W t+W f+W s

SG= 525g500−1225g+415 g+525g

SG=2.442

Water Absorption

Absorption=W a−W d

W d

DISCUSSION

Bulk specific gravity is the characteristics generally used for calculation of the volume occupied by the aggregate in various mixtures containing aggregate including Portland cement concrete, bituminous concrete and other mixtures that are proportioned or analyzed on an absolute volume basis. Bulk specific gravity is also used in the computation of voids in aggregate in AASHTO T 19 and the determination of moisture in aggregate by displacement in water in AASHTO T 142. Bulk specific gravity determined on the saturated surface-dry basis is used if the aggregate is wet, that is, if its absorption has been satisfied.Conversely, the bulk specific gravity determined on the oven-dry basis is used for computations when the aggregate is dry or assumed to be dry.

Absorption values are used to calculate the change in the weight of an aggregate due to water absorbed in the pore spaces within the constituent particles, compared to the dry condition, when it is deemed that the aggregate has been in contact with water long enough to satisfy most of the absorption potential. The laboratory standard for absorption is that obtained after submerging dry aggregate for approximately 15 h in water. Aggregates mined from below the water table may have a higher absorption when used, if not allowed to dry. Conversely, some aggregates when used may contain an amount of absorbed moisture less than the 15 h soaked condition: For an aggregate that has been in contact with water and that has free moisture on the particle surfaces, the percentage of free moisture can be determined by deducting the absorption from the total moisture content determined by NDR T 255 by drying.

OBSERVATION

If the aggregate slumps on the first Cone Test, it is assumed that the aggregate has already dried beyond the SSD condition (Figure 10). The aggregate can be restored by thoroughly mixing in a small amount of water and allowing the aggregate to stand in a covered container for 30 minutes. The drying process can then be resumed (AASHTO, 2000c)

This agitation procedure should be repeated several times in order to ensure that any entrapped air is eliminated. This process usually takes 15 to 20 minutes total. Agitation does not have to be constant (AASHTO, 2000a[2]).

ANALYSIS

Specific gravities can vary widely depending upon aggregate type. Some lightweight shales (not

used in HMA production) can have specific gravities near 1.050, while other aggregate can have

specific gravities above 3.000. Typically, aggregate used in HMA production will have a bulk specific

gravity between about 2.400 and 3.000 with 2.700 being fairly typical of limestone. Bulk SSD specific

gravities can be on the order of 0.050 to 0.100 higher than bulk oven dry specific gravities, while

apparent specific gravities can be 0.050 to 0.100 higher still.

For a particular aggregate type or source, fine aggregate specific gravities can be slightly higher

than coarse aggregate specific gravities because as the aggregate particles get smaller, the fraction

of pores exposed to the aggregate surface (and thus excluded from the specific gravity calculation

because they are water-permeable) increases.

Aggregate absorption can also vary widely depending upon aggregate type. Some lightweight shales

(not used in HMA production) can have absorptions approaching 30 percent, while other aggregate

types can have near zero absorption. Typically, aggregate used in HMA production will have an

absorption between just above zero and 5 percent. Absorptions above about 5 percent tend to make

HMA mixtures uneconomical because extra asphalt binder is required to account for the high

aggregate absorption.

If absorption is incorrectly accounted for, the resulting HMA could be overly dry and have low

durability (absorption calculated lower than it actually is) or over-asphalted and susceptible to

distortion and rutting (absorption calculated higher than it actually is).

Certainly, the accuracy of all measurements is important. However, of specific concern is the mass of the SSD sample. The determination of SSD conditions can be difficult. If the sample is actually still wet on the surface then the mass of the SSD sample will be higher than it ought to be, which will cause a lower calculated bulk specific gravity. Conversely, if the sample is beyond SSD and some of the pore water has evaporated (which is more likely), the mass of the SSD sample will be lower than it ought to be, which will cause a higher calculated bulk specific gravity. Either type of error will have a cascading effect on volumetric parameters in other tests that require specific gravity as an input and Superpave mix design

CONCLUSION