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Outdoor Problems of the Householder: Gravel
Sand and Gravel. The term sand, as used by concrete mixers, includes all grains and small pebbles that pass through a wire screen with 1-inch mesh and are retained upon a screen having 40 meshes to the linear inch.
Gravel in general is pebbles and stone retained upon a 4-inch screen.
It is quite commonly supposed that any kind of sand or gravel will make a good concrete mixture but this is far from being the case. Sand from pits or gravel banks varies greatly in character. Hence to secure the best results, care must be exercised in selecting materials.
Coarse, hard sand, free from clay or dirt, produces the best and strongest concrete and requires much less cement than if fine, soft or dirty. To procure good sand and gravel, screen the material at the bank twice.
First use a 1-inch screen to keep out the gravel. Set the screen upright at an angle of 45°. Then screen a second time, on a 40-mesh screen, the sand which has thus been freed from gravel. Reject all the fine sand and earth which will pass through the 40-mesh screen. The result will be material, both sand and gravel, of known character. By mixing these in exact proportions, not only will the finished work be more reliable, but enough cement can be saved to more than pay for the labor of screening.
Or fine loam and clay can be removed from the sand by washing. To test the material, fill a pint preserving jar with an average sample to the depth of 4 inches. Fill the jar with clear water to within 1 inch of the top, fasten on the lid and shake vigorously. Now set the jar upright and let the contents settle. The sand will fall to the bottom, next the clay, next the loam, and the water will come to the top. If there is a layer of more than inch of clay or loam the sand must be rejected or washed.
To Wash Sand or Gravel. - Build a loose board platform 10 or 15 feet long. Have one end 12 inches higher than the other. Nail 2 by 6-inch plank across the lower end and along both sides to hold the sand. Spread out the sand on this platform in a layer 3 or 4 inches thick and wash with a 4-inch garden hose. Begin at the upper end and let the water run through the sand and over the 2 by 6 edge at the bottom.
Reinforced Concrete. - For reinforced concrete and most ordinary purposes, reject stones over 1 inch in diameter. But for heavy foundation ture means 1 part cement, 2½ times as much sand and 5 times as much stone or gravel. The whole consists of 8½ parts. In other words of a 1:2:4 mixture is cement and somewhat less than of a 1:24:5 mixture. The 1:2:4 mixture is, therefore, stronger and is to be preferred for foundations and other work carrying heavy loads. The accompanying table, prepared by the national Office of Public Roads, QUANTITIES OF MATERIALS AND THE RESULTING AMOUNT OF CONCRETE FOR A TWO-BAG BATCH Proportions by parts Materials Sizes of measuring boxes (inside measurements) Kinds of concrete mixture Cement Sand Stone or gravel Cement (bags) Sand (cubic feet) Stone or gravel (cubic feet) Concrete (cubic feet) 1:2:4....... 1 2 4 2 37 8 2 feet by 2 feet by 2 feet by 4 feet by 10 11½ inches. 11½ inches. 1:25...... 1 2 5 2 4 9 10 2 feet by 2 feet 62 feet 6 inches by 12 inches by 114 4 feet by 11 inches. inches.
Sand Stone or gravel or abutment work, include larger stones and pebbles up to 2 inches or more in diameter. For best results use a mixture of sizes of gravel from to 1 inch or more in diameter. In ordering crushed stone specify the size of the stone and screenings wanted. The crusher dust should be washed out.
Measurements of Materials.
First figure the number of cubic feet of concrete that will be required for the job. Next determine the proportions of material, i. e., the kind of concrete you will employ. Finally figure the amount of each kind of material that will be necessary. The two most usual formulæ are 1:2:4 and 1:21:5. The proportions are always measured by volume. A 1:2:4 mixture means 1 part cement, twice as much sand and 4 times as much stone or gravel. The whole mixture thus consists of 7 parts. A 1:24:5 mixgives the size of measuring boxes required for a two-bag batch of concrete. These boxes are made with straight sides of any kind of rough boards. They have no top or bottom.
A bag of Portland cement is practically one cubic foot. A barrel contains four cubic feet or bags. The sand, stone or gravel are measured loosely in the box, not packed. For a four-bag batch of concrete double the quantities given in this table.
To determine the total quantities of material required, multiply the total number of cubic feet of concrete needed for the job by the number given under the proper column as shown by the table on the next page, given by the Office of Public Roads.
This will give the amount of cement, sand and stone or gravel needed.
Example: Let us suppose that the work consists of a concrete silo requiring in all 935 cubic feet of con- Water for medium wet mixture (gallons) OUTDOOR PROBLEMS OF THE HOUSEHOLDER 283 crete, of which 750 cubic feet are to be 1:2:4 concrete, and 185 cubic feet are to be 1:21:5 concrete. Enough sand and cement are also needed to paint the silo inside and outside, amounting in all to 400 square yards of surface, with a 1:1 mixture of sheet iron bed; garden rake, water barrel, two 2-gallon water buckets; 4 by 4-inch tamper, 2 feet 6 inches in length with handles nailed to it; garden spade; and 2 screens, one ainch mesh, the other 40 meshes to the inch. These may be made by nailing QUANTITIES OF MATERIALS IN ONE CUBIC FOOT OF CONCRETE Mixture of Concrete Cement (by barrels) Sand (by cubic yards) 0.058 .048 0.0163 .0176 Stone or gravel (by cubic yards) 0.0326 .0352 1:2:4. 1:21:5. sand and cement. One cubic foot of 1:1 mortar paints about 15 square yards of surface and requires 0.1856 barrel of cement and 0.0263 cubic yard of sand. The problem thus works out as follows:
CEMENT: a section of screen 2½ by 5 feet in size to a frame made of boards 2 by 4 feet.
To make a concrete board for two men to mix a 2-bag batch, order 9 pieces by 12 inches by 10 feet For the 750 cubic feet of 1:2:4 concrete (750x0.058). For the 185 cubic feet of 1:2 : 5 concrete (185x0.048) For painting (400-15x0.1856).
SAND: