Specific gravity of cement: Definition and importance

The behaviour of any substance in water may be predicted by knowing its specific gravity, and we can predict whether the substance will sink or float. Every constituent of our surrounding environment has a  fixed specific gravity value. In this article, we will talk about the specific gravity of cement, its significance, and how to calculate it.

What is the specific gravity of cement and why is it important?

Specific gravity refers to the ratio of a material’s density to the density of a standard substance at the same temperature. . Another way to put it is that specific gravity is the proportion of one substance’s mass to that of another The same may be said about cement, incidentally. Cement’s specific gravity is defined as the mass-to-density ratio of cement relative to some other standard material.

However, regardless of mass or density, the volume in each condition should be the same. No particular gravity can exist if the volume changes. Simply said, the substance or standard substance will no longer be the same after the alteration.

Significance of specific gravity of cement

• Concrete design is heavily influenced by a number of important parameters, one of the most important being the density of the cement. Due to the volumetric nature of the concrete mix concept, density is the most crucial component to consider.
• It is essential to have an accurate understanding of the specific gravity of cement since it is one of the factors that determines the density of the cement.
• Due to this, it is possible for the cement to have a high level of moisture if it is subjected to a wide range of conditions and different levels of humidity.
• The water-to-cement ratio is well-known to be a crucial component of cement paste. It correlates positively with both productive capacity and relationship integrity. For example, if the cement has a high moisture content to begin with, increasing the water-cement ratio would not improve the cement paste’s workability or strength because of the increased moisture content.
• The bonding properties of the mix will suffer if the specific gravity of cement is greater than 3.19, which indicates that the cement was not ground fine enough in accordance with industry standards or that it contains too much water. Because of this, it is common to discover a great deal of debris when using old cement to make concrete.
• Particles of solid matter and pores in a substance, which may have moisture content under harsh weather, are inherent to every material. And it might mean an increase in a material’s specific gravity.
• Cement undergoes a chemical reaction after its specific gravity hits 3.19, which occurs when its pores are saturated with water. Hydration describes this action.
• When determining whether or not cement meets the requirements of the Indian Standard Specification, the specific gravity test must be performed if the cement is more than 3 months old.
• Cement with a specific gravity of 3.15 is often used to make a nominal mix. Changing this value will have an effect on the mix structure. The percentage of water to cement might rise, decreasing the workability and increasing the strength of the concrete.|

See also about: Cement Density

Using specific gravity in cement mix design

Specific gravity separates bad particles which are lighter than other particles, from good aggregates. Using specific gravity in cement mix design, we calculate the solid volume of aggregates in concrete mix. Gavel, water and cement are used for this test.

One of the most important property of cement is specific gravity as it’s related to density and viscosity. One can determine moisture content in cement if specific gravity of cement is greater than 3.19. This will affect the bonding and mix of the cement.

Why is kerosene used to determine the specific gravity of cement?

Water is the standard material for comparison. Moreover, it has to be about four degrees Celsius. The standard temperature for gases is 25 degrees Celsius, which is room temperature. However, kerosine would serve as the standard if Cement were to be employed as the sample material. It’s because when water combines with cement, it hydrates and turns into calcium oxide. But cement and kerosene won’t react in any noticeable way.

Measuring specific gravity of cement for quality control

Source: Pinterest

The specific gravity of cement may be quickly and readily calculated using the Le Chatelier Flask technique. This experiment is a simple way to find out the specific gravity of cement on the job site. The following is a list of the materials and equipment used for the specific gravity test:

1. Kerosene
2. Ordinary Portland Cement
3. 250 ml Le-Chatelier flask or 100 ml Specific Gravity Bottle/Pycnometer
4. Weighing balance

The flask that was created by Le Chatelier is constructed of thin glass and includes a bulb at the base. The bulb holds roughly 250 ml of liquid. The average diameter of this bulb is 7.8 centimetres. There are millimetre markings down the length of the handle. When measured from the peak of the bulb, zero is located at a height of 8.8 cm. Another bulb, this one measuring 3.5 cm in length and holding 17 ml, may be found at a distance of 2 cm from zero. The stem is graduated close to 24 ml from the bulb and is marked at 18 ml at 1 cm. The section beyond the 24-millilitre line is shaped like a funnel with a 5-centimetre opening.

1. The process for determining the specific gravity merely consists of four stages. The following are the four processes that need to be performed in order to run a test to determine the cement’s specific gravity:
2. The flask must not contain any liquid, which implies that it must be completely dry inside and out. Put the empty flask on the scale. Which gives W1.
3. Pour cement into the bottle until it fills about half the flask and after that weigh it using the cap on the bottle. Which gives W2.
4. Kerosene should be added to the cement until it reaches the top of the container. To eliminate the air bubbles, give it a thorough mixing. Put some cement and kerosene into the flask, and then weigh it. Which gives W3.
5. Clear out the flask. Put as much kerosene as possible into the bottle, and then weigh the flask to determine how much W4 there is.

To determine the specific gravity of cement once you have completed the steps above, apply the formula that is provided below.

Sg= (W2-W1)/((W2-W1)-(W3-W4)×0.79)

Precautions for testing

• Always remember to clean the equipment before and after using it.
• The test has to be conducted in a quiet, vibration-free environment.
• Dress appropriately for the test by donning a helmet, boots, and hand gloves.
• It’s important to be careful while putting cement into the specific gravity bottle so that it doesn’t splatter and doesn’t stick to the interior of the flask.
• The Naphtha or kerosene must be absolutely devoid of any moisture.
• Before each weighing, make sure the specific gravity bottle has been maintained in a water bath at the same temperature.
• Putting the stopper in place after the device has been filled will ensure that no air bubbles are present.
• The difference between the two measurements of cement’s specific gravity should be no more than 0.01.

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