Test For Setting Time Of Concrete Mixture Based On ASTM C403-16

Sometimes, it is essential to identify the setting time of concrete mixture so that the construction sequence can be prepared accordingly. Furthermore, if it was planned to obtain concrete from far away batching plants, then it was of utmost importance to transport, pore and finish the surface before concrete gets hardened.

The penetration resistance test was used to determine the initial and final setting time of concrete mixture in project site, and to identify the effects of variables, such as water content; type and amount of cementitious material; or admixtures, upon the time of setting of concrete. The test is conducted on a sample of sieved mortar.

Initial setting time of cement is the time at which cement begins to harden and lose its plasticity. The final setting time begins when concrete loses its plasticity completely and hardens. According to ASTM C403M-16, the initial and final time of concrete can be determined when the penetration resistance equals 3.5 MPa, 27.6 MPa, respectively.

Apparatus used in Testing of Setting Time Of Concrete Mixture

• Mold - The lateral dimension shall be at least 150 mm and the height at least 150 mm.

• Tamping Rod - It is round and straight steel rod with 16 mm in diameter and approximately 600 mm in length.
• Pipet - It is used for drawing off bleed water from the surface of the test specimen.
• Thermometer - The thermometer shall be capable of measuring the temperature of the fresh mortar to 60.5⁰C.
• Stop Watch
• Penetration Needles - Penetration needles, which commonly attached to the loading apparatus, have the following bearing areas 645, 323, 161, 65, 32, and 16 mm².

• Loading Apparatus - It is used to measure the force required to cause penetration of the needles. The device shall be capable of measuring the penetration force with an accuracy of 10 N and shall have a capacity of at least 600 N.

Sample Preparations

1. Obtain a representative sample of the fresh concrete in order to obtain three specimens for the test and that concrete is passed through a 4.75-mm sieve before putting it to the molds.
2. Place the mortar in the mold in a single layer and remove air pockets in the specimen by tapping the sides of the container with the tamping rod and measure the temperature of the mortar.
3. Finally, level the top surface.

Procedure after the leveling the surface

1. Eliminate bleed water from specimen surface using pipet and based on the degree of mortar setting time, insert suitable needle size in the penetration resistance apparatus.
2. Bring the bearing surface of the needle into contact with the mortar surface.
3. Apply a vertical force gradually and uniformly downward on the apparatus until the needle penetrates the mortar and record the force needed to penetrate the needle to a depth of 25 ± 2 mm.
4. Record the time of load application, measured as elapsed time after initial contact of cement and water.

The following precautions shall be considered before the next test conducted on the sample on which first penetration test is conducted.

1. The minimum distance between needle impressions is 15 mm.
2. The maximum and minimum clear distance between any needle impression and the side of the container 25 mm and 50 mm, respectively.
3. For concrete mixtures containing accelerators, it is advisable to make the initial test after an elapsed time of 1 to 2 h and subsequent tests at 1 to 2-h intervals.
4. For concrete mixtures containing retarders, the initial test may be postponed until an elapsed time of 4 to 6 h.
5. Make at least six penetrations for each time-of-setting test, with time intervals of such duration as to provide a satisfactory curve of penetration resistance versus elapsed time.
6. Continue testing until one at least penetration resistance reading equals or exceeds 27.6 MPa

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Graphing of test results

The plot of penetration resistance versus elapsed time will provide information on the rate of setting. The graph of penetration resistance is created on y-axis versus elapsed time x-axis, using a scale such that 3.5 MPa and 1 h are each represented by a distance of at least 15 mm. Visually, determine the times of initial and final setting when the penetration resistance equals 3.5 MPa, 27.6 MPa, respectively.