I. Site Mixed Concrete:
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| site mixer |
1) Weights of aggregates shall be adjusted in the first 5 batches to get required slump, without changing the
water cement ratio given in the
mix design.
2) Corrections shall be done in the mix proportions (aggregates, sand volume correction) to get cohesive homogeneous mix of desired workability.
3) Batching shall be done by sandwiching the cement between fine and coarse aggregate. Preferable sequence is coarse aggregate, cement and then sand.
4) Minimum mixing time of 11⁄2 minutes shall be adhered to, for every batch of concrete. Hence maximum output of mixer shall not exceed @30 bags per hour, if one bag mixer is used.
5) Unloading of concrete mix shall be done on MS tray / concrete platform.
6) Slump reading shall be recorded after every 25 bags and slump variation shall not exceed 25mm from the designed workability.
7) Presence of qualified supervisor at the weigh batcher / concrete mixer, at place of concreting and at shuttering shall be required.
8) First batch of concrete shall be prepared by addition of 10% extra cement to allow for loss in the drum.
9) Exact quantity of water as per moisture correction applicable shall be added using water dispenser / calibrated cans. Buckets shall not be used.
10) Concreting works shall be arranged so as to have minimum cold joints.
11) While pouring concrete, segregation of concrete shall not be observed.
12) Cubes shall be taken during every concreting. Number of samples and testing shall be in accordance with IS 456 -2000. Each cube shall have proper identification mark as regards grade, date of casting, location etc. Cube sampling shall spread over entire period of concreting.
13) While cubes are being taken for testing, corresponding slump shall also be recorded, in cube testing register. Cubes shall be cast in the presence of Engineer.
14) During every day’s concrete unit weight of concrete as specified in IS: 1199 shall be checked and compared with theoretical density of concrete (sum of weight of all ingredients). If any significant deviation is observed, it indicates corrective measures are required in Concrete Mix Design.
15) In case of pre stressed concrete more no. of cubes shall be casted for estimation of desired strength on the day of stressing.
16) At high altitudes wind breakers shall be provided while concreting.
mix design.
2) Corrections shall be done in the mix proportions (aggregates, sand volume correction) to get cohesive homogeneous mix of desired workability.
3) Batching shall be done by sandwiching the cement between fine and coarse aggregate. Preferable sequence is coarse aggregate, cement and then sand.
4) Minimum mixing time of 11⁄2 minutes shall be adhered to, for every batch of concrete. Hence maximum output of mixer shall not exceed @30 bags per hour, if one bag mixer is used.
5) Unloading of concrete mix shall be done on MS tray / concrete platform.
6) Slump reading shall be recorded after every 25 bags and slump variation shall not exceed 25mm from the designed workability.
7) Presence of qualified supervisor at the weigh batcher / concrete mixer, at place of concreting and at shuttering shall be required.
8) First batch of concrete shall be prepared by addition of 10% extra cement to allow for loss in the drum.
9) Exact quantity of water as per moisture correction applicable shall be added using water dispenser / calibrated cans. Buckets shall not be used.
10) Concreting works shall be arranged so as to have minimum cold joints.
11) While pouring concrete, segregation of concrete shall not be observed.
12) Cubes shall be taken during every concreting. Number of samples and testing shall be in accordance with IS 456 -2000. Each cube shall have proper identification mark as regards grade, date of casting, location etc. Cube sampling shall spread over entire period of concreting.
13) While cubes are being taken for testing, corresponding slump shall also be recorded, in cube testing register. Cubes shall be cast in the presence of Engineer.
14) During every day’s concrete unit weight of concrete as specified in IS: 1199 shall be checked and compared with theoretical density of concrete (sum of weight of all ingredients). If any significant deviation is observed, it indicates corrective measures are required in Concrete Mix Design.
15) In case of pre stressed concrete more no. of cubes shall be casted for estimation of desired strength on the day of stressing.
16) At high altitudes wind breakers shall be provided while concreting.
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