Step 1: Understanding the Question:
The question asks to identify the specific laboratory instrument or apparatus used in civil engineering and materials science to determine the initial setting time of cement paste.
Step 2: Detailed Explanation:
Vicat Apparatus: This is the standard instrument used to find the consistency, initial setting time, and final setting time of cement.
It consists of a frame with a movable rod of a certain weight, to which different attachments like a plunger (for consistency), a needle (for initial setting), and a needle with an annular collar (for final setting) can be fixed.
Initial Setting Time Procedure: For initial setting time, a needle of 1 mm square or circular cross-section is used.
The initial setting time is defined as the duration from the moment water is added to the cement until the needle fails to penetrate the test block to a depth of 5 mm to 7 mm from the bottom of the Vicat mold.
Comparison with other options:
Autoclave: This is used to test the soundness of cement, specifically looking for expansion caused by delayed hydration of magnesia.
Sieve: Sieving is used to determine the fineness of cement, which affects the rate of hydration and gain of strength.
Lechatelier Apparatus: This is used to measure the soundness of cement due to free lime only.
Step 3: Final Answer:
The Vicat apparatus is the correct tool for determining the initial setting time of cement.