Specific gravity for coarse, fine and sand aggregates

Aggregate with its different sizes and sand are very important materials in building operations especially in concrete mixture, because using these materials in the mixture gives cohesion to the cement grains, and they play no part in chemical reactions that cause the concrete to set. Specific gravity is one of the various tests engineers do on aggregate in order to determine the most suitable aggregate and sand that fit with concrete mixture and the use of this mixture. Water absorption test is also an important test to do on aggregate because it helps the engineers to determine the exact water content in the mixture.

Fine aggregate mixed with sand

Objectives

The aim of this article is to:

1. Determine the specific gravity expressed as bulk specific gravity, bulk (saturated-surface-dry) specific gravity, as well as apparent specific gravity for three different samples of fine and coarse aggregates.
2. Determine the percentage of water absorption for the three samples of fine and coarse aggregate after 24 hours of soaking in water.

Theory

Specific Gravity: is the ratio of the unit weight or density of solid mass, to unit weight or density of water at a specified temperature and it's a dimensionless term.

Apparent Specific Gravity: is the ratio of the unit weight or density of solid mass in air of the impermeable portion of aggregate, to the unit weight or density of water at a specified temperature.

Bulk Specific Gravity: is the ration of the unit weight or density of solid mass in air excluding the voids between particles and including the permeable and impermeable voids to the unit weight or density of water at a specified temperature

Bulk Specific Gravity (SSD): is the ration of the unit weight or density of solid mass including the weight of water in the voids after submersion for 24 hours and excluding voids between particles, to the unit weight or density of water at a specified temperature

Absorption ratio: is the change in the weight that happens to the dry aggregate (dry at 110 °C in the oven) when water is added and fills the pores of the material, but not including water at the outside surface.


Part A (Specific Gravity and Absorption for coarse Aggregates)
Where:

            A= Dry weight
            B= Weight in SSD in air
            C= Weight of sample soaked in water


Part B (Specific Gravity and Absorption for Fine Aggregates)
Testing the specific gravity and absorption ratio of fine aggregates consists of determining the weight of the sample in three conditions:

➧ Dry weight, which is obtained after drying the sample in the oven.
➧ Saturated- surface dry weight, which is obtained after soaking the sample and then drying the surfaces only.
➧ Submerged weight, which is obtained after subtracting the weight of pycnometer filled with water from the weight of the pycnometer filled with water containing the sample.

The following formulas are used to determine the specific gravity and absorption ratio of fine aggregates:
Where:

            A= Weight in (SSD) condition
            B= Weight of pycnometer filled with water
            C= Weight of pycnometer containing the sample and filled with water
            D= Dry weight

Part C (Specific Gravity and Absorption for sand)
Dry weight which is obtained after drying the sample in the oven.









Where:

            A= Weight in (SSD) condition
            B= Weight of pycnometer filled with water
            C= Weight of pycnometer containing the sample and filled with water
            D= Dry weight

Tools and Instruments

1. Container suitable for immersion of the sample and the water network cart.
2. Conical Mold and Tamper
3. Pycnometer Top and Glass Jar
4. Drying oven: has temperature of 100 ºC.
5. Balance of a capacity of 5kg and at least its sensitivity of 5g.
6. Sample Containers
7. Small heater
8. Piece of cloth
9. Water tank
10. Basket of fine openings
11. Wire suspending the basket

Procedure

1. The samples of coarse aggregate, fine aggregate and sand were put in pots separately, and each pot had inside it small amount of water.
2. The coarse aggregates were dried by using towels until they reached the saturated surface dry (SSD) condition.
3. The fine aggregates and sand were dried by using electronic oven until they reached (SSD) condition.
4. The weights of the SSD coarse aggregates, fine aggregates and sand were measured by using balance.
5. A flask was filled with(500 ml) of water in order to measure the weight of the submerged fine aggregate and sand by subtracting (weight of flask + weight of (500ml) water) from (the flask weight + 500ml of water weight + involved sample weight).
6. The weight of the submerged coarse aggregate was measured by using balance.
7. The samples were put inside pots inside a big electronic oven for 2 days.
8. The weights of the dry samples were measured by using a balance.

Data and Calculations

Part A: Coarse Aggregate
Table-1 shows the data collected to determine specific gravity and absorption rate for coarse aggregates.

Calculation:
Bulk specific gravity (oven-dry) = 2.43