GAIL (India) Limited

29PoundingPonding is widely used for curing slabs and pavement. Earth bands are formed over the slabs and wateris pumped or poured into them and the same is replenished at interval to make up for the loss ofevaporation. As this type of curing is one of the best methods, 10 days of curing after final setting issufficient.By Spraying WaterCuring is done by spraying water by suitable means at approved time intervals. While spraying, it shallbe ensured that the complete area is covered. In order to avoid cracking, cold water shall not be appliedto massive members immediately after striking the form work, while the concrete is still warm.Alternative wetting and over drying shall be avoided.Curing by spraying water shall be continued as least for 18 days.b) Curing of Concrete with Absorbent Material Kept DampThe entire concrete surface is covered either with hessian, burlap, sawdust, sand, canvas orsimilar material and kept wet continuously for at least 12 days after final settings.c) Curing by Covering Concrete Surface with an Impressive SheetThis is achieved by covering the entire concrete surface with water proof paper or plasticsheets specially manufactured for this purpose. The waterproof papers are stuck together byadhesive compound and the plastic sheets can be welded at site.Such type of covering shall be kept at least for 24 days after the final setting. It is preferableto have sheet as white in appearance since the white colour will reflect hot sunrays and keepthe concrete temperature at reasonable level.d) Curing by Providing Protective Membrane by Applying curing compoundThis is achieved by applying a membrane forming compound (curing compound) over theconcrete surface. Generally, these are available in the emulsion form. The application of thecuring compound should be started immediately after stripping off the shuttering in case offormed surface and after the surface has hardened in case of unformed surface.The curing compound membrane forming emulsions dry up within 3 to 4 hours afterapplication and forms a continuous coherent adhesive membrane over the concrete surface.Such membrane serves as a physical barrier to prevent the loss of moisture from the concreteitself. Membrane forming emulsions are generally coloured black or white to improvevisibility for ensuring uniform application. Black colour shall never be used for curing in veryhot weather. In order to prevent glare, a colouring pigment may be added to whitecompounds.Black curing compounds are either Bituminous or Asphaltic emulsions and shall be used tosurfaces which are to be covered by back filling or on the floor which is to be covered withtiles and linoleum.White curing compound shall be used for the surfaces of tall structures under exposure of hotsun where other method of curing can not be properly ensured.e) Curing by Chemical CoatingFor chemical curing, sodium silicate or calcium chloride is used. The use of calcium chlorideshall be done with the approval of the Engineer. Normally, the sodium silicate mixed withwater is applied over concrete surface and, when it dries up, it forms a thin varnish like film,which fills up the pores, and surface voids and prevents evaporation of water. This also actslike curing compound but only difference is that curing compounds are available in readymixed emulsion forms while sodium silicate is to be mixed with water at site.