RCC - Ready Mix concrete checks

Ready Mix Concrete:

1) Transit trucks shall comply with the relevant code, with an agitating speed between 2 and 3 RPM and mixing speeds in the range of 10-20 RPM.
2) Before unloading of any truck at the site, the
RMC supplier shall supply a certificate/batch sheet (a computerized sheet) along with moisture correction for the concrete, mentioning proportions of all the ingredients, w/c ratio, dosage of plasticizer and relevant admixtures etc. (please refer Specification for Supply of RMC).
3) The maximum water cement ratio, as specified in the approved mix design shall not be exceeded.
4) The information provided by RMC supplier shall be cross checked at site, and in all cases slump shall be taken prior to concreting. The accuracy of the measuring equipment shall be within + 2 percent of the quantity of cement and mineral admixtures being measured and within + 3 percent of the quantity of aggregate, chemical admixture and water being measured.
5) Concrete which needs to be pumped shall have workability between 120 to 150 mm or as specified when the transit mixer arrives. Any concrete shall be designed for a minimum three hours retention/open time. The workability of the concrete shall be controlled on a continuous basis during production and any corrective action necessary shall be taken. No additional water, other than the amount required to produce the specified grade of concrete as per mix design, shall be added to the truck mixer drum before discharge unless specifically requested and signed for by representative. Redosing or split dosing shall be allowed subject to the written permission of trained technicians and Engineers . In any case, the total dose should not exceed the maximum dose of admixture declared by Supplier or recommended by Admixture supplier.
6) It shall be ensured that the retardation time achieved by the use of admixtures does not exceed the time required for transit and actual placement of concrete. This shall be achieved by checking the time of dispatch of transit mixer mentioned on challan. Any Concrete is being designed with the help of water reducing agents and retarders for a stipulated retention time. So the concrete must be consumed within the same time as considered in design. Our all concrete mixes must be designed for 3 hours retention time, so concrete must be consumed with in 3 Hours from the time of batching. If the workability of concrete is higher than desired workability and segregation & bleeding is observed, we should allow some time to elapse before discharge till workability drops to the range of 120 to 150 mm. If workability is less, then redosing or split dosing shall be allowed but in any case, the total dose should not exceed the maximum dose of admixture declared by Supplier of concrete or recommended by Admixture supplier. We must avoid over dosing which may cause delay in setting of concrete

7) Temperature of concrete at the time of pumping shall be less than 40oC or as mutually agreed between engineer and Supplier of Concrete.
8) The cohesiveness and mixing of the concrete should be checked, there should be no lumps, bleeding or segregation in the concrete.
9) 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. Supplier of concrete shall be immediately informed as this variation may impact yield of concrete or desired properties of the concrete 10) Concrete carrying pipes shall not be allowed to rest on top reinforcement which is likely to bend. Leakage of slurry from concrete pipeline should be checked and rectified.
12) At high altitudes wind breakers shall be provided while concreting.