Setting Time Test of Cement

 

SETTING TIME TEST FOR CEMENT

The Setting Time Test determines how long cement takes to change from a plastic state to a solid state. This is essential for construction scheduling, ensuring enough time for mixing, transporting, and placing cement before it starts to harden.

ASTM Standard Code

The ASTM C191 standard outlines the procedure for determining the setting time of hydraulic cement using the Vicat Apparatus.

Apparatus Required

• Vicat Apparatus – Consists of a vertical frame with a scale, a plunger, an initial setting needle (1 mm² cross-section), and a final setting needle.
• Vicat Mould – A cylindrical mould (inner diameter 70 mm, height 40 mm).
• Weighing Balance – Accuracy 0.01g.
• Glass Plate – A non-porous, smooth surface to hold the cement paste.
• Stopwatch – To measure time intervals accurately.
• Measuring Cylinder – To measure the required water amount.
• Trowel and Mixing Tools – For proper paste preparation.

Test Procedure

1. Sample Preparation

• Weigh 400g of cement and place it on a clean, dry surface.
• Add water equal to the standard consistency (determined using the Vicat test, usually 25-35% by weight of cement).
• Mix thoroughly for 3-5 minutes to form a uniform paste.

2. Initial Setting Time Measurement

• Fill the Vicat mould with the paste and level it.
• Place the mould on the glass plate under the Vicat apparatus.
• Lower the initial setting needle until it touches the paste's surface, then release it.
• Repeat every 10 minutes until the needle penetrates 5 mm or less from the bottom.
• Record the time from the moment water was added to the cement.

3. Final Setting Time Measurement

• Replace the initial setting needle with the final setting needle.
• Lower it gently onto the paste's surface and release it.
• The final setting time is recorded when the needle fails to make an impression on the paste.

 

Result Criteria (ASTM C191)

• Initial Setting Time: Should not be less than 45 minutes.
• Final Setting Time: Should not exceed 375 minutes (6 hours 15 minutes).

Note: Setting times may vary based on cement type and environmental conditions.

 

Limitations of the Test

• Environmental Conditions – Temperature (27±2°C) and humidity (90%) significantly affect setting time.
• Human Error – Releasing the needle improperly or inconsistent mixing can lead to inaccurate results.
• Water Content Sensitivity – A slight variation in water-to-cement ratio can impact setting time.
• Storage Conditions – Cement exposed to moisture or air can give misleading results due to premature hydration.