Bulk Density and Specific Gravity

A H M 531

Bulk Density and Specific Gravity

By: Ahmed Essam Mansour

1. Calculating the bulk bulk density of coarse coarse and fine aggregate samples. samples. 2. Calculating the Apparent Specific Specific Gravity for coarse and fine aggregate samples. 3. Calculating the water absorption of coarse and and fine aggregate aggregate samples.

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B.S. 812 – 1967

A H M 531 Engineering Center 1. The BulkCivil Density when dealing with aggregates it is important to know the voids that presents between the aggregate particles, so that we decide whether to fill them with wit h finer aggregate or with cement paste. We all know that the Density we often deal with equals the mass divided by the volume, when using this law to measure the density of aggregates the volume we use is the volume of aggregate + the volume of the voids, and in this case we get a new quantity called the Bulk Density. Bulk Density = Mass of the aggregate \ Volume of aggregate particles with voids between them. This bulk density is used to convert quantities by mass to quantities by volume. Bulk density depends on several factors: Size distribution of aggregates, Shape of particles and degree of compaction. There are two methods this quantity is measured by: 1- Loose method. 2-Compaction method.

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But in our experiment we used the loose method which is described in the procedures.

2.

Specific Gravity: The specific gravity of a material is defined as: The ratio of a weight of a material of a specific volume to the weight of water of the same volume. And we can distinguish two types of specific gravity: 1- Absolute specific gravity: Where the volume of the material is taken excluding all pores. 2- Apparent specific gravity: Where the volume of the material is taken including the impermeable pores only. In our study to aggregates we will care only of the apparent specific gravity. The specific gravity for the aggregates indicates the amount of voids inside the aggregate particle itself. The apparent specific gravity is measured using the following law:

A H M 531 The Civil Engineering Center where, Wod: weight of aggregate in oven dried condition. Wssd: Weight of aggregate in Saturated Surface dry condition. Wa: Weight of aggregate in water.

3.

Water Absorption: Water absorption is determined by measuring the decrease ins mass of a saturated surface dry sample after oven drying for 24 hours. The ration of the decrease in mass to the mass of the dry sample expressed as a percentage is termed absorption.

Where, Wod: weight of aggregate in oven dried condition. Wssd: Weight of aggregate in Saturated Surface dry condition.



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1.


Bulk Density: 1- Container. 2- Glass Plate. 3- Fine and Coarse aggregate sample. 4- Water 5- Weighting Machine.

2.

Specific Gravity: 1- Container. 2- Glass Plate. 3- Shallow trays. 4- Dry soft absorbent clothes. 5- Fine and Coarse aggregate samples. 6- Weighting machine. 7- Sieves, (#9, #4 and # 200). 8- Stove

A H M 531 The Civil Engineering Center

Bulk Density: It is the same procedures for fine and coarse aggregate samples. 1. Weighing the empty container with the glass plate. (Wtools) 2. We fill the container with coarse aggregate to over flowing and then using the plate to level the surface, and the weight of the container and the plate and the coarse sample is found. (W1) 3. We empty the container from the coarse aggregate and refill it with the fine aggregate to over flowing and then level the surface using the plate, and the weight of the container and the plate and the fine sample is found. (W2) 4. We empty the container again and this time we fill it with water till the rim of it and place the plate on it, no water bubbles should



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present on the surface, and we weight the container and the plate and the water. (W3)

Specific Gravity: 1- For Coarse aggregate. 1. The coarse aggregate should be retained at sieve # 9, and then wash it to get rid of sand and dust.

2. We fill the container with water till the rim of it and place the plate on it, no water bubbles should present on the surface, and we weight the container and the plate and the water. (W3) 3. Putting the coarse aggregate sample into the water in the container, and then weighing it. (W1) 4. We weigh an empty tray. (WTC)


5. We empty the container of water, and the aggregates are thrown on the dry clothe. The surface of the aggregate is dried using the clothe piece till the coarse aggregate sample is Saturated Surface dried. Then they are placed in a tray of and weighted them. (Wssd + WTC) 6. The sample then is places in the oven of temperature of 105-110 Cº for 24 hours; so that the Oven dried condition will be reached. And we weighted them. (Wod + WTC)

2- For fine aggregate: 1. The fine aggregate should pass from sieve # 4 and retained at sieve # 200. 2. For the fine aggregate we fill the container filled with water, with the fine aggregate to its third only and then we weigh it. (W2) 3. We weigh an empty tray. (WTF) 4. We place the fine aggregate in the tray and dry them using the stove, till they are in the Saturated Surface Dried condition. And we weight them. (Wssd + WTF)



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5. Placing the aggregate in the oven under 105-110 Cº for 24 hours; so that they are in the Oven Dried condition. And we weight them. (Wod + WTF).

The Bulk density of the fine aggregate is Larger than it for the coarse aggregate. I think it is a natural conclusion as the bulk density and the Voids between aggregate mixes are inversely proportional. In concrete design our aim should be to make a high bulk density of aggregate but not the maximum; because maximum Bulk density will make min voids so that there won’t be much space for the cement paste (binding medium). The apparent specific gravity of fine aggregate is larger that it for the coarse aggregate. The higher the specific gravity is the less voids are there in the aggregate. The water absorption of the fine aggregate is higher the absorption of the coarse aggregate.




Bulk Density and Specific Gravity

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