Setting Time of Concrete with Admixtures, IS: 8142 - 1976

SETTING TIME OF CONCRETE WITH ADMIXTURE, IS: 8142 - 1976

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What are Admixtures ?

Admixtures are natural or manufactured chemicals other than water, aggregates, or cement which are added to the concrete or mortar before or during mixing to control setting, early hardening, workability and to provide qualities to concrete.

Admixtures are classified according to function. There are five distinct classes of chemical admixtures: air-entraining, water reducing, retarding, accelerating and plasticizers (superplasticizer).

What is the Setting Time of Concrete with Admixture ?

Setting time for concrete with admixture:- The initial setting time and final setting time are the time the time interval required for mortar sieved from the concrete admixture to reach the prescribed penetration resistance after the initial contact with the cement and water.

IS Code of Test for Setting Time of Concrete with Admixture :-

• IS: 8142 - 1976

APPARATUS REQUIRED FOR TEST:-

• Concrete penetrometer; (needle size, area, 645, 323, 161, 65, 32 & 16 mm²) size 4.75 mm
• Mould; size 150 mm×150 mm
• IS sieve

Penetrometer

Digital Lcd Concrete Penetrometer

Penetration of Concrete:-

1. Prepare the concrete mix both with and without admixture except in the case of air-entraining admixture.
2. The air-entraining admixtures are used as the reference or control concrete mixture.
3. The admixture shall be used in accordance with the recommendation of the manufactures.
4. When an admixture is to be tested specifically for air-entraining admixtures it shall be used in control concrete, such as a quantity that it produces air content in the range of 3.5 to 7 percent.
5. The concrete mix shall be proportioned to have the cement content specified for the work and to meet the stipulated workability and strength requirements.
6. In case of air entrained concrete. The air content specified for the work shall be used.
7. If the maximum size of coarse aggregate is greater than 20 mm. The concrete mix shall be wet- screened over 20 mm IS sieve before test.
8. The concrete mix may be designed according to any accepted method of mix design to meet the following requirement.

(a). The cement content of the mix shall be (304 to 307)kg/m³.

(b). The concrete mix shall have a slump of 40 mm to 60 mm or a compaction factor of 0.85 to 0.90 facilate compaction by hand rodding.

PROCEDURE OF THE TEST:- 

1. Note the time of mixing water with cement with admixture (t₁).
2. After mixing it is sieved through 4.75 mm.
3. Fill the passing material in the mould (15×15×15) cm³ in two layer up to 2/3^rd of volume.
4. Finish the top surface with the trowel.
5. The reading may be taken at 1 hour’s interval.
6. Gradually and uniformly apply a vertical force downward on the apparatus until the needle.
7. Penetrate the mortar to a depth of 25 mm as indicated by the scribe mark. Penetrate to the 25 mm depth shall be approximately 10 second.
8. Now when the penetration needle achieves the strength of 35 kg/ cm² time is noted (t₂).

Repeat the process for final setting time when the needle achieved the strength of 275 kg/ cm² time is noted (t₃)_.

RESULT:-

Initial setting time of concrete with admixture = t₂- t₁

Final setting time of concrete with admixture  = t₃- t₁