Technological University of the PhilippinesAyala Boulevard, Ermita, Manila

College of EngineeringDepartment of Civil Engineering

CE 49L 4AConstruction Materials and Testing, Lab.

Experiment No. 3

SPECIFIC GRAVITY OF COARSE AGGREGATES

Fesalbon, Mayson R.10-205-041

Date of Submission: August 21, 2013

Engr. Reynaldo O. BaardeInstructor

EXPERIMENT NO.2

SPECIFIC GRAVITY OF COARSE AGGREGATES

I.OBJECTIVE

To determine the specific gravity of aggregates

II.MAIN PRINCIPLE

Specific gravity is the ratio of the mass (weight in air) of a unit volume of a material to the mass of the same volume of water. In this test, the specific gravity of coarse aggregate is evaluated using the principle of buoyancy. Specific gravity is a quick indicator of the sustainability of an aggregate. Low specific gravity frequently indicates porous, weak and absorptive material, while high specific gravity often indicates high quality. The data contained from this test can be used in designing and controlling the weight of concrete.

At the end of the test, the percentage of water absorption of the coarse aggregates will be evaluated. The term absorption is defined as the capacity of the coarse aggregate to absorb water into its permeable pores. Absorption values are used to adjust the proportioning of materials in a concrete mix.

III. APPARATUS NEEDED

1. Specific gravity test apparatus for coarse aggregate2. Sieve (10mm opening)3. Sample pan4. Oven

IV. PREPARATION

1. Sieve the sample using a 10-mm sieve2. Take 5kg of aggregate from the sample retained in the 10-mm sieve.3. Soak the aggregate in water for a period of 24 4 hours.4. Remove the aggregate from water and roll it in a large absorbent cloth until visible films of water are removed. This is the saturated surface-dry (SSD) condition.

V. TEST PROCEDURE

1. Take the weight in air of the saturated surface-dry aggregate (Wa).2. Assemble the specific gravity test apparatus. Fill the container with water to its capacity.3. Determine the weight of the wire basket while submerged (Wb).4. Take the weight of the aggregate in water (Ww). Shake the aggregate while it is being placed into the wire basket. Shake the wire basket before weighing.

VI.CALCULATIONS

Where:SG = specific gravity of aggregate at SSD conditionWa= weight of SSD aggregate in air (kg)Ww = weight of aggregate in water (kg)Wb = weight of wire basket in water (kg)

VII.DETERMINATION OF WATER ABSORPTION OF COARSE AGGREGATE

Remove the coarse aggregate from the wire basket and oven dry it at 100 5oC for 24 hours. The percentage absorption is computed as follows.

Where:Wd = oven-dried weight of aggregate

VIII.DATA AND RESULTS

Weight of SSD aggregate in air, Wa (kg)5.0278

Weight of aggregate in water, Ww (kg)3.8720

Weight of Wire Basket in water, Wb (kg)0.7815

Weight of oven-dried aggregate, Wd (kg)4.9078

Specific Gravity of aggregate at SSD condition, SG2.60

Percentage of Absorption of Coarse Aggregate (%)2.45

IX.SAMPLE COMPUTATIONS

X.DISCUSSION AND OBSERVATION

A. Discussion

Another property of an aggregate is specific gravity which is defined as a ration of unit weight of an aggregate to the unit weight of another substance which is commonly water. In this experiment, the specific gravity of coarse aggregates will be determined using the principle of buoyancy.

Buoyancy. Archimedes principle of buoyancy states that a body immersed in a fluid is acted upon by an upward force equal to the weight of the displaced fluid. This principle is used in the determination of the specific gravity of the aggregate by using the derived formula shown earlier. Consider an aggregate submerged in water. Water will exert a buoyant force to the aggregate which will constitute an apparent loss of weight of the aggregate.

Saturated Surface-Dry (SSD). This condition of the aggregate is attained where an aggregate is dry in its surface but its porous spaces are filled with water to ensure that the no air is trapped at each particle of the aggregate and therefore only the weight of the dry aggregate and water in the aggregate is considered.

Water absorption (water content). Water absorption or simply the water content determines how much of the weight of the dry aggregates is composed of water during the test or the weight of water that sips into the tiny pores of the aggregates.

B. Observations

During the experiment, the following was observed:

1. Aggregates use for the test is coarse aggregates with varying sizes and colors of about 10-20mm and black to gray respectively.2. Water color turns to light brown when the aggregate was soaked.3. There is a little increase of the weight of the dry weight of aggregates and weight of the aggregates at SSD condition.4. There is an apparent loss of weight of the aggregates when weighed in water.

XI.CONCLUSION

The specific gravity of a coarse aggregate can be determined using the principle of buoyancy. In this laboratory test, it can be expressed in a formula shown below.

Where:SG = specific gravity of aggregate at SSD conditionWa= weight of SSD aggregate in air (kg)Ww = weight of aggregate in water (kg)Wb = weight of wire basket in water (kg)The percent absorption or water content of an aggregate is the ratio of the weight for water for every weight of dry aggregates. It can be expressed in a formula shown below

Where:Wa= weight of SSD aggregate in air (kg)Wd = oven-dried weight of aggregate