INITIAL AND FINAL SETTING TIME OF CONCRETE BY PENETROMETER TEST (IS-8142-1976)

Objective

Determination of initial and final setting time of concrete as per IS-8142-1976.

Apparatus

• Non absorptive metal container having minimum lateral dimension of 150 mm and minimum depth of 150 mm.
• Penetration resistance apparatus having a pressure gauge of capacity 700 to 900 N. Removable needles of 645, 323, 161, 65, 32 & 16 mm2.
• Pipette
• Tamping rod of 16 mm dia.

Sample Preparation & Storing

•选择一个代表性的混凝土fficient volume to provide enough mortar to fill the test container to a depth of at least 140 mm.
• Sieve the concrete through 4.75 mm IS sieve in order to remove all the mortar from concrete.
• Mix the mortar thoroughly and place it in the container in layers. Compact each layer of mortar using tamping rod. The final height of mortar after tamping should be less than 13 mm from the height of the container. This space is required for the collection and removal of bleeding water.
• Cover the specimen in the container, with a suitable tight fitting, water impermeable blanket for the duration of the test.

Test Procedure

1. Before testing, remove the bleeding water from the surface of the mortar by means of a pipette.
2. Attach the needle with the penetration resistance apparatus.
3. Bring the bearing surface of the needle in contact with the mortar surface.
4. Gradually and uniformly apply a vertical downward force on the apparatus until the needle penetrates to a depth of 25 mm, as indicated by scribe mark. The time taken to penetrate 25 mm depth could be about 10 secs.
5. Record the force required to produce 25 mm penetration and time of inserting, from the time water is added to the cement.
6. Repeat step 2 to step 8, with the remaining needles of different bearing area, at an hourly interval. The initial penetration test is carried out after 3 to 4 hours of adding water to the mix.
7. For the subsequent penetration avoid the area where the mixture has been disturbed. The clear distance should be two times the diameter of bearing area. Needle is inserted at least 25 mm away from the wall of container.
8. Not less than six penetration resistance determination is made. Continue the test until one penetration resistance of at least 26.97 MPa is reached. Penetration resistance is calculated in N/mm2, by dividing the force required to cause 25 mm depth of penetration of the needle by the area of bearing face of the needle.

Plotting of Graph

• Plot a graph of penetration resistance as ordinate and elapsed time a abscissa.
• Connect the various points by a smooth curve.

Finding out Initial and Final Setting Time from the Graph

• From the penetration resistance equal to3.43 MPa, draw a horizontal line. The point of intersection of this with the smooth curve is read on the x-axis which givesinitial setting time.
• Similarly a horizontal line is drawn from the penetration resistance of26.97 MPaand point it cuts the smooth curve is read on the x-axis which gives thefinal setting time.
• Time of setting shall be reported in hours and minutes to the nearest minutes.