GAIL (India) Limited

173.11 Water/Cement RatioWhere a particular water/cement ratio is stipulated in the design or drawing along with thecharacteristic grade of concrete, the design of mix shall be carried out by adjusting the other variablefactors to obtain characteristic strength of concrete with stipulated water/cement ratio.In the structures where the impermeability and shrinkage of concrete have an important bearing on thedurability and serviceability of the structures, such as water retaining structures, basements,underground premises, tunnels, pump houses, exposed structures near sea side or deserts, pre-stressedstructure, thin precast members etc., the water/cement ratio shall be kept low and preferably notexceeding 0.45.The water cement ratio as achieved in the mix design or as specified in the drawings shall be adhered tostrictly and shall not be varied without the permission of the Engineer.3.12 WorkabilityThe workability of fresh concrete shall be such that the concrete is just suitable for the conditions ofhandling and placing so that after compaction, it becomes completely consistent and homogeneouslysurrounds all the reinforcement and completely fills the formwork.The workability of fresh concrete at the place of batching/mixing shall be measured by compactingfactor test and at the place of disposition by means of slump test. During the finalization of trial mixes,the relationship between compacting factor and slump test shall be established for each grade ofconcrete as well as for various levels for workability.Normally, in the condition of low water cement ratio as well as for medium/high workability, theworkability shall be achieved by increasing the cement content.In cases where the cement content is to be limited to reduce the heat of hydration, and the water /cement ratio is also to be kept low to reduce the permeability or due to other requirements the desiredworkability may be achieved with the use of limited doses of plasticizer or air entraining agent. In suchcases, the method of mixing and dosage of the plasticiser / air entraining agent shall be according to themanufacturer's specification and with the approval of the Engineer.Consistency and workability of concrete shall be checked by measuring the slump of a truncated coneof concrete straight from the mixer under normal working conditions. The conical mould shall be ofmetal, 300 mm high and 100 mm and 200 mm in diameter at top and base respectively.Moulds shall be prepared by the Contractor. The slump range of concrete shall be as per the tabulationgiven below, as well as standards.Slump tests shall be performed as per IS:1881 at intervals established by the Engineer at theContractor's cost in such a way as to check that the degree of consistency established by the Engineerfor work in progress is maintained. The table below gives the general slump range to be followed forvarious types of construction unless otherwise shown on drawings or instructed by the Engineer.Various types of construction ....Slump (in mm)... Max. Min.Reinforced foundation walls and footings 80 35Plain footings, caissons and structure walls 75 20Compressor foundations and for heavy mass constructions 50 20Pumps and other misc. equipment foundations 75 35Columns, slabs, beams and reinforced walls 100 50