Portland cement is shipped in paper bags, cloth sacks, and wooden barrels (sometimes in bulk). For the average user the cloth sack is the best container, as it is easier to handle; and while the manufacturers charge more for this kind of package, they allow a rebate for the return of the sacks in good condition. A sack of Portland cement weighs 94 pounds and a barrel contains the equivalent of four sacks.
STORING.
As cement readily absorbs moisture from the atmosphere, it should be stored in a dry place; if exposed to dampness it soon becomes lumpy, or even a solid mass, and in this condition it is useless and should be thrown away. The lumps caused by pressure in piling the sacks are not injurious. They can be pulverized easily, thus distinguishing them from those due to dampness.
Cement never should be stored on the ground. Build a raised platform for it and keep it away from the sides of the shelter. As it is heavy, care should be taken not to overload the supporting floor.
FINE AGGREGATE (SAND).
All grains, small pebbles, or particles of broken stone are considered as sand if they will pass through a wire screen with one-fourth inch meshes. The particles or grains should be hard and well graded and should vary in size, as a stronger concrete is thus obtained than when the size of the grains is nearly uniform. If a large proportion of the sand is very fine an extra quantity of cement should be used and if exceptionally fine it is advisable to use 25 per cent more cement.
The sand should be clean; that is, free from vegetable matter, loam, or any considerable amount of clay. If the hands are soiled when a small quantity of sand is rubbed between them the following test should be made: Put 4 inches of sand into a pint preserving jar, fill with clear water to within an inch of the top, fasten the lid, and shake the jar vigorously until the whole is thoroughly mixed. Set the jar aside and allow the contents to settle. The sand will settle to the bottom with the clay and loam on top of it. If more than three-eighths of an inch of clay or loam shows, the sand should be rejected or washed. The difference in fineness and color shows clearly the line of division between the clay or loam and the sand.
Fig. 1.—Sand and gravel washing trough.