What Is Specific Gravity Cement | Why We Calculate Specific Gravity Cement | Specific Gravity Test on Cement

What Is Specific Gravity Cement?

Specific gravity is generally defined as the ratio between the mass of a given volume of material and mass of an equal volume of water. One of the methods of determining the specific gravity of cement is by the use of a liquid such as water-free kerosene, which does not react with cement.

A specific gravity bottle may be employed, or a standard Le Chatelier specific gravity flask may be used. In addition to hydraulic cement, the Le Chatelier specific gravity flask can also be used to obtain the specific gravity of dust, sand, and other fine materials.

This specific gravity of cement is a need for mixture-proportioning calculations. This specific gravity of portland cement (without voids between particles) is about 3.15 and can be determined according to ASTM C188.

This density of the bulk cement (including voids between particles) varies considerably, depending on how it is handled and stored. For example, vibration during transportation of bulk cement consolidates the cement and increases its bulk density. Thus, cement quantifies are specified and measured by weight rather than volume.

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Why We Calculate Specific Gravity?

The specific gravity of any substance to know the behavior of the material in water, and we can see the material will sink or floats in the water. All of the materials at our environment have a fixed specific gravity.

The usual range is 1-100. If the specific gravity isn’t less than 1, then it sinks in water. If the specific gravity isn’t greater than 1, it floats at the water. So if this specific gravity of any substance is known to us, we can use the materials in a suitable place of any work.

The specific gravity defines that the substance is how much heavier than water or reference substance of the same volume. This specific gravity of cement ranging from 3.1 to 3.16 g/cc. By this statement, we may ensure that cement 3.1-3.16 times heavier than this water of this same volume, and it sinks in water.

Because the specific gravity isn’t less than 1, every material consists of so many little pores, which can contain voids in it, and the material becomes useless when any void present in the material.

When a cement covered by extreme moisture content because of bad weather conditions, then a specific gravity of cement can go up to 3.19. If this specific gravity value reaches 3.19, then these pores at cement are filled with moisture.

The cement undergoes a chemical reaction when it reacts with this atmospheric moisture. The process is terminated as hydration. Moisture is very harmful to cement. Cement becomes useless once it is hydrated with water.

This presence of excessive moisture is the reason for finding a lot of lumps at old cement is due to content it.

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Specific Gravity Test on Cement

Apparatus for Specific Gravity Test on Cement

#1. Weighing Balance-

A weighing balance is a device to measure weight or mass. These are also known as mass scales, mass balance, weight scales, weight balance, or balance scale.

Weighing balance

#2. Le Chatelier Specific Gravity Flask with a Ground Glass Stopper-

The Le Chatelier flask shown in as below fig. is made of thin glass having a bulb at this bottom. The capacity of this bulb is nearly 250 ml. The bulb is 78 mm in mean diameter. The stem is graduated milliliters; the small oval bulb in the neck holds 17 ml, below this bulb, are graduations from 0-1ml; above the bulb, the neck is graduate from 18-24 ml. This portion above the 24 ml mark is in the form of a funnel having a top diameter as 50 mm. Thus the total capacity of the stem of a bulb is 24 ml. A glass stopper or nipple is fitted in the stem to cover the flask.

Le Chaterlier”s flask

#3. Specific Gravity Bottle-

Specific gravity bottles determine liquid densities by measuring the difference between an empty and filled bottle and dividing by an equal volume of water to find the specific gravity of the substance. These bottles are also known as a density bottle or relative-density bottles.

Specific gravity bottle

#4. Constant Temperature Water Bath-

The water bath is laboratory equipment made from a container filled with heated water. It is used to incubate samples at the water at a constant temperature over a long period of time.

Constant temperature water bath.

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Procedure Specific Gravity Test on Cement

Step 1: With a Specific Gravity Bottle  

• Weigh the specific gravity bottle dry. Let the mass of the empty bottle be W1.
• Fill the bottle with distilled water and weigh. Let the mass be W2.
• Wipe dry the specific gravity bottle and fill it with kerosene and weigh. Let this mass be W3.
• Pour some of the kerosene out and introduce a weighed quantity of cement, W5 (about 50 g) into the bottle. Roll the bottle gently in an inclined position until no further air bubbles rise to the surface. Fill the bottle to the top with kerosene and weigh it. Let this mass be W4.
• From these data, calculate the specific gravity of the cement, S.

The specific gravity of kerosene, S = (W3 – W1) / (W2 – W1)

The volume of bottle = W2 – W1

The volume of cement = W5 /S 

The volume of kerosene after the cement has been added = (W2 – W1) – W5 / S

Wherefrom mass of kerosene after the cement has been added = [ (W2 – W1) – W5 / S ] s

Therefore, [ ( W2 – W1) – W5 / S ] s + W5 + W1 = W4

Substituting the value of s sand on simplification,

• • • W5 / S = (W5 + W3 – W4) X {(W2 – W1) / (W3 – W1)}

Therefore, specific gravity of cement,

• • • S = [ W5 ( W3 – W1)] / [ (W5 + W3 – W4) x (W2 – W1)]

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Observations and Calculations 

Step 2: With Le Chatelier flask

• Dry the flask carefully and fill with kerosene or Naphtha to a point on the stem between zero and 1 ml.
• Dry the inside of the flask above the level of the liquid.
• Immerse the flask in a constant temperature water bath maintained at room temperature for a sufficient period before taking any reading so as to avoid variation greater than 0.2°C in the temperature of the liquid in the flask.
• Record the level of the liquid in the flask as initial reading, V1.
• Place a weighed quantity of cement, W1 (about 60 g) into the flask so that the level of kerosene rises to about say 22 ml mark. Care is taken to avoid splashing and to see that cement does not adhere to the sides of the flask above the liquid.
• After putting all the cement into a flask, insert the nipple and roll the flask gently in an inclined position to free the cement from the air until no further air bubble rises to the surface of the liquid.
• Keep the flask back in a constant temperature water bath and note down the new liquid level as final reading, V2.

Calculate the specific gravity, S.

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Observations and Calculations 

Precautions

The kerosene or Naphtha used should be free from water. The specific gravity bottle and the Le Chatelier flask should be held in a constant temperature water bath sufficiently long to ensure the same temperature before each weighing is made.

Duplicate determination of specific gravity should agree within 0.01. While introducing cement, care should be taken to avoid splashing and cement should not adhere to the inside of the flask above the liquid

Discussion

In case a specific gravity bottle shown in as per above fig.  is used, it is necessary to determine the specific gravity of kerosene or other liquid used and all the measurements are made entirely by mass.

If Le Chatelier flask is used, some of the measurements are made by volume and it is not necessary to know the specific gravity of kerosene.

The relative density of kerosene is 0.8. The specific gravity of ordinary Portland cement is in the range of 2.15.

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