TIPS FOR MAKING GOOD CONCRETE

1.            Cement: Select the appropriate type of cement. Use fresh cement of approved quality. Store it properly to prevent deterioration.

2.            Aggregates: use well graded aggregates, free from silt, organic matter and other undesirable impurities. Store aggregates properly and don’t allow different fractions to mix together.

3.            Water: Use potable quality of water. It should be free from impurities and harmful ingredients. It should be within the tolerable limits specified by BIS.

4.            Chemical Admixtures: Use appropriate type of admixtures in correct dosages, as recommended by the manufacturer, and or confirmed by laboratory tests. Ensure that the admixtures are compatible with the cement and other ingredients. Trial mixes should be mad, if necessary. Ensure that there is no batch to batch variation in quality.

5.            Durability: Ensure that the durability requirements like minimum cement content, maximum

water cement ratio, grade of concrete, cover to reinforcement, etc as specified in IS 456:2000 are satisfied for the given Exposure Conditions.

6.            Mix Design: Use of properly designed concrete mix is essential for large jobs. BIS permits use of nominal mixes for works using concrete grades of M 20 and below.

7.            Batching: Batching materials by weight is preferable and the BIS emphasize its use. If batched on volume basis, use measurement boxes in units of 35 liters, which is the capacity of one 50 kg bag of cement. The cement should, in any case, be batched only by weight and preferably by whole bags. Allowance for water on account of bulking of sand and surface water carried by coarse aggregates is essential.

8.            Quantity of mixing water: Use the minimum quantity of mixing water, consistent with the degree of workability required to enable easy placing and compaction of concrete.

9.            Mixing: Use a mixing machine. There should be uniform distribution of the material until the mass is uniform in colour and consistency. Avoid hand mixing.

10.         Transportation: Avoid drying out, segregation, setting, loss of any ingredients, and ingress of foreign matter or water during transportation.

11.         Placing: Place concrete in its final position before setting starts: avoid segregation of materials and disturbance of the forms: lay concrete in suitable layers without any break of continuity; maximum free-fall of concrete should not exceed 1.5m.

12.         Compaction: Ensure thorough compaction, particularly around the reinforcement and embedded fixtures and into the corners of the formworks. Use internal/external form vibrators: avoid under and over vibration.

13.         Finishing: Finish after a little stiffening.

14.         Curing: Keep concrete continuously moist, preferably for a period of 7 to 14 days.

15.         Formwork: Use formwork which is rigid and closely fitted, with sufficient strength to support the wet concrete and to prevent loss of slurry. The face of the form work should be treated with form release agents.

16.         Reinforcement: Make sure that the reinforcement used is free from loose rust, oil, paint, mud, etc. The reinforcement shall be placed and maintained in position by providing proper cover blocks, spacers, supporting bars, etc. Reinforcement shall be placed and tied such that concrete placement is possible without segregation, and compaction possible by an immersion vibrator.

List of Laboratory Testing for Quality concrete