Cement Quiz: Chemical Compositions!

Explanation
As cement is a calcareous material.

Explanation
Calcium sulphate is commonly known as gypsum, which is used as a retarder in various industries. As a retarder, it slows down the setting time of materials such as cement, allowing for better workability and longer working time. Gypsum is often added to cement or concrete mixes to control the setting time and prevent rapid hardening. Therefore, the correct answer for this question is "Retarder".

Explanation
The given statement is false. The heat of hydration of OPC (Ordinary Portland Cement) at 7 days is not 90 to 100 cal/gm. The heat of hydration refers to the heat released during the chemical reaction between cement and water, which leads to the hardening of concrete. The specific value for the heat of hydration can vary depending on factors such as the type of cement, water-cement ratio, and curing conditions.

Explanation
Mass specific gravity is 1.5 and true specific gravity is 3.15

Explanation
The specific gravity of cement is indeed determined using a Le Chatelier flask. This device is specifically designed to measure the specific gravity of materials, including cement. It works by measuring the displacement of a liquid when a sample of the material is placed in the flask. By comparing the weight of the displaced liquid to the weight of an equal volume of water, the specific gravity of the cement can be calculated. Therefore, the statement that the specific gravity of cement is determined using a Le Chatelier flask is true.

Explanation
The statement is true because during the fineness test in sieve, the content should not exceed 5% for rapid hardening cement. This means that the cement particles should be finely ground and have a maximum particle size of 45 microns. If the content exceeds 5%, it indicates that the cement is not finely ground and may have a coarse texture, which can affect its performance and strength. Therefore, to ensure the quality and effectiveness of rapid hardening cement, it is important to meet the fineness requirement during the sieve test.

Explanation
The ratio of compressive strength of a cylinder to a cube is given as 0.92. This means that the compressive strength of a cylinder is 0.92 times the compressive strength of a cube. In other words, the cube has a higher compressive strength compared to the cylinder. This ratio is important in engineering and construction as it helps determine the strength and stability of different structures.

Explanation
The correct answer is 3.5 hours. The initial setting time of high alumina cement refers to the time it takes for the cement to start hardening after it is mixed with water. In this case, it takes approximately 3.5 hours for the high alumina cement to reach its initial setting point, at which it becomes solid and can no longer be easily manipulated.

Explanation
The statement is suggesting that the total loss on ignition should not exceed 4%. This means that the amount of weight lost when a substance is heated to high temperatures should not be more than 4% of the original weight. This is important because a higher loss on ignition could indicate the presence of impurities or contaminants in the substance. Therefore, the statement is true, as it is necessary to ensure that the total loss on ignition does not exceed 4% for quality control purposes.