Test: Cement, Mortar & Lime - 2 - Civil Engineering (CE) MCQ

A good quality cement will not sink to the bottom of the bucket. A handful of cement thrown into a bucket of water should not sink immediately, because if it sinks immediately it indicates that cement has formed lumped mass which means there is the presence of moisture near cement bags and some portion of hydration reaction has already started which give rise to lumped mass.

• Definition of sound cement: Sound cement refers to cement that does not contain free lime, which can cause expansion and cracking.


• Importance of sound cement: Sound cement is crucial for the durability and strength of concrete structures.


• Presence of free lime: Free lime in cement can lead to efflorescence, which is the formation of white deposits on the surface of concrete.


• Testing for soundness: Soundness of cement is tested by Le-Chatelier method or Autoclave method to ensure the absence of free lime.


• Components of cement: Cement primarily consists of compounds such as tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite.

A Portland cement with low C₃A and C₄A Fcontents is very effective against sulphate attack, such cement is called sulphate resisting cement. The use of sulphate resisting cement is recommended for concretes to be used in marine environment foundations in chemically aggressive soils.

If expansion is more than 10 mm, cement is said to be unsound.
In autoclave expansion should not be more than 0.8%

• Purpose: The device is used for determining the soundness of cement.


• Method: Le Chatelier’s device consists of a small split cylinder that can be opened or closed using a pair of external indicators.


• Procedure: To determine the soundness of cement, a test specimen is placed in the Le Chatelier’s device and then subjected to water bath or steam curing for a specific period of time.


• Observation: After the test period, the amount of expansion or contraction of the test specimen is measured using the indicators on the device.


• Interpretation: The soundness of cement is determined based on the expansion or contraction of the test specimen. Excessive expansion indicates unsoundness of cement.

The initial setting time for OPC should not be less than 30 minutes. The final salting time should not be greater than 10 hours.

• Final Setting Time: Final setting time is the time taken by cement to harden and achieve its final setting state.


• IS Specifications: The Indian Standard specifications for ordinary Portland cement specify the maximum final setting time.


• Maximum Final Setting Time: According to IS specifications, the maximum final setting time for ordinary Portland cement should be 10 hours.


• Options:
  
  
  
  • A: 30 minutes - This is incorrect as the maximum final setting time is 10 hours.
  
  
  • B: 1 hour - This is incorrect as the maximum final setting time is 10 hours.
  
  
  • C: 6 hours - This is incorrect as the maximum final setting time is 10 hours.
  
  
  • D: 10 hours - This is the correct option according to IS specifications.
  
  
  
  

• Given: p is the standard consistency of cement


• Amount of water: 0.85p (Option B)

• Standard consistency of cement (p): The amount of water required to produce a cement paste of standard consistency.


• For conducting the initial setting time test on cement, a specific amount of water is added to the cement paste to form a standardized mixture.


• The water-cement ratio for conducting the initial setting time test is usually higher than the standard consistency to ensure proper hydration and setting of cement.


• Option B (0.85p) provides a slightly higher amount of water compared to the standard consistency (p), which is suitable for conducting the initial setting time test effectively.


• Therefore, the correct amount of water used in conducting the initial setting time test on cement is 0.85p (Option B).

Super plasticizers are improved version of plasticizers and they interact with cement both physically and chemically. They are anionic in nature and impart negative charge on cement particles causing them to disperse and release the entrapped air and water. This makes the mix more workable with less amount of water.

Below figure shows the effect of super plasticizer.