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Allied Gyan. In this article I have explained about test for setting time of concrete with admixture.
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setting time for concrete with admixture easily. So please continue to the end
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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).
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: 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
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Penetrometer |
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Digital Lcd Concrete Penetrometer |
Penetration of
Concrete:-
- Prepare the concrete mix both with and without admixture except in the case of air-entraining admixture.
- The air-entraining admixtures are used as the reference or control concrete mixture.
- The admixture shall be used in accordance with the recommendation of the manufactures.
- 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.
- The concrete mix shall be proportioned to have the cement content specified for the work and to meet the stipulated workability and strength requirements.
- In case of air entrained concrete. The air content specified for the work shall be used.
- 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.
- 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:-
- Note the time of mixing water with cement with admixture (t1).
- After mixing it is sieved through 4.75 mm.
- Fill the passing material in the mould (15×15×15) cm³ in two layer up to 2/3rd of volume.
- Finish the top surface with the trowel.
- The reading may be taken at 1 hour’s interval.
- Gradually and uniformly apply a vertical force downward on the apparatus until the needle.
- 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.
- 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:-