WATER FOR CONCRETE Water has two functions to perform in con crete work. Its presence is necessary to develop the hydraulic activity of the cement. Aside from this, the part it plays in concrete is merely that of rendering the mass plastic and insuring a thorough mixture. It does not seem to have any direct bearing on the adhesive power of cement; but it indirectly affects the strength of concrete through its action in rendering possible a more thorough compacting of ingredients, and conse quently increasing the density of the resulting mass of concrete.
In all ordinary concrete work, the general rule . may be laid down, that water should be liberally used. This greatly improves the density and strength of concrete. Except in special, cases—as, for example, in making concrete blocks or casts, where the product has almost immediately to be self-support ing—enough water must be used to make the concrete thoroughly soft and plastic, so as to quake strongly when rammed. If mixed too dry, the concrete will never harden properly, and will be light, porous, and crum bling. In some work—as, for example, in plac ing concrete around reinforcing steel members —the best results can be secured only by an ex cessively wet mixture, mushy, and soft enough to run off the shovel.
Water that is to be used for concrete should, above all things, be clean. Dirty water will have the same effect as dirty sand or dirty gravel, weakening the concrete and in some cases re tarding the setting.
Fresh cement requires more water than ce ment which is stale. In cold weather, the water may be warmed; but in such cases, there arises the danger of having bubbles of air or of water vapor scattered through the interior of the con crete, leaving small holes in the mass that weak en it.
Water should also be free from acids or strong alkalis. Cement is chemically basic, and is therefore naturally active to a greater or less extent with the various acids. If concrete is to be exposed to attack from acid-laden fluids, a reliable waterproofing process should be adopted.
The action of sea water on Portland cement concrete has exercised the minds of engineers for many years. The tendency to disintegration that has been noticed is purely the result of chemical action and the formation of soluble salts. It is checked by the use of cements rela tively low in lime, alumina, and sulphates, and by the adoption of a waterproofing process which will prevent the diffusion through the concrete of the active constituents of the sea water.
Alkalis in water may hasten the setting and hardening of concrete, but are ultimately detri mental to strength. In a certain soap factory, on one occasion, water containing lye was used in laying several hundred feet of concrete flooring. It was discovered that the lye water made a harder concrete in much less time than would have been the case with pure water. The floor wore well for two years, but then began to crum ble, and rapidly disintegrated. The daily sweep ings consisted largely of concrete, and in a short time the four-inch floor of concrete was entirely swept away in spots.