GAIL (India) Limited

183.13 DurabilityThe durability of concrete, depending on the exposure condition, is to be taken into account whiledesigning the mix. For given aggregates, the cement content should be sufficient to make sufficientlylow water/cement ratio and Appendix A of IS: 456 shall be taken as guideline for durabilityconsiderations.3.14 Trial MixesAfter approval of the mix design by the Engineer, the Contractor shall make in presence of theEngineer the trial mixes for each grade of concrete as well as for required workability.Before starting the trial mixes, necessary preparatory works like determination of sieve analysis of theaggregates, densities of different ingredients, moisture contents in the aggregates, shall be completedaccording to the relevant BIS Codes.Each trial mix shall be handled and compacted by the method which the Contractor proposes to use forthat mix in the works and the mixes shall not show tendency of inadequate compaction by the methodproposed.The compacting factor and the slump of each trial mix shall be determined immediately after mixingand the values shall not exceed the maximum value obtained in the mix design.Five (5) 150 mm test cubes shall be made from each trial mix. These shall be cured and tested inaccordance with relevant BIS codes. In order to have the specified characteristic strength in the field,the concrete mix as designed in the design mix shall have higher average compressive strengthdepending on the degree of quality of control at site.Before commencement of the concreting works of particular grade of concrete, the Contractor mustcomplete the work of trial mixes and subsequent testing of the test cubes obtained there from and thedesire of the approved mix for that particular grade of concrete.The entire cost of all the trial mixes including all the preparatory works for trial mixes, preparation oftest cubes and their testing shall be borne by the Contractor.3.15 Nominal Mix ConcreteNominal mix concrete may be used for all concrete of grade M-10 and below. If design mix concretecannot be used for any reason for grade M-15 and M-20, nominal mix concrete may be used with thepermission of the Engineer. Nominal mix concrete shall be in accordance with Table-3 of clause 8.3 ofI S 456. The stipulations of clauses 8.3.1 and 8.3.2 of IS: 456 shall also be taken into consideration..3.16 Volumetric Mix ConcreteWhere concrete is specified in volumetric proportions such as 1:4:8, 1:3:6, 1:2:4, 1:1.5:3, 1:1:2 etc., inthe Bill of Quantities, coarse & fine aggregates shall be measured by volume & cement by weight. Thewater cement ratio shall be within 0.45 & 0.70 depending upon the workability.3.17 Batching of Concrete3.17.1 CementCement shall always be batched by weight. A separate weighing device shall be provided for weighingcement. Where the weight of cement is determined by accepting the weight per bag, a number of bagsshall be weighed separately to determine the average net weight of cement per bag and the same shallbe checked regularly.