Setting Time of Concrete

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.

Penetration Resistance Apparatus

SAMPLE PREPARATION & STORING

• Select a representative sample of concrete o f sufficient volume to provide enough mortar mo rtar to fill the test container to a depth of at least 140 mm. • Sieve the concrete through 4.75 4.7 5 mm IS sieve in order to remove all the mortar from concrete. concrete. • Mix the mortar thoroughly and place it in the container in la yers. Compact each layer of mortar using tamping rod. The final height of mortar after tamping should b e 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 th e duration of the test.

TEST PROCEDURE

1. Before testing, remove the bleeding wate r 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 a rea. Needle is inserted at least 25 mm away from the wall of container. 8. Not less than six penetration resistance determination is made. Con tinue 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

Setting time plot • 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 to 3.43 MPa, draw a horizontal line. The point of intersection of this with the smooth curve is read on the x-axis which gives initial setting time . • Similarly a horizontal line is drawn from the penetration resistance of 26.97 MPa and point it cuts the smooth curve is read on the x-axis which gives the final setting time . • Time of setting shall be reported in hours and minutes to the nearest minutes.