FARM MANAGEMENT 55 



(1) Cement; (2) sand; (3) gravel or crushed stone; and (4) 

 water. 



Cement is therefore only one part of a concrete mixture. A 

 far greater proportion of sand and gravel than cement is required. 

 The quantity of cement to be used and the strength of the concrete 

 depend entirely on the quality and size of the sand and gravel, 

 and it is of the utmost importance that these be of the right kind. 

 With an equal amount of cement a far stronger concrete may be 

 made, if the sand and gravel are of the proper size and correctly 

 proportioned. It is sometimes thought that any kind of soil of 

 a sandy nature, mixed with a small percentage of cement, will make 

 concrete, but this idea is incorrect. As a guide in the selection of 

 the proper materials, especially sand and gravel, the following sug- 

 gestions should be observed : 



Sand. In the selection of sand the greatest care should be used, 

 and critical attention should be given to its quality, for sand con- 

 tributes from one-third to one-half of the amount of the materials 

 used in making concrete. Sand may be considered as including all 

 grains and small pebbles that will pass through a wire screen with 

 i/i-inch meshes, while gravel in general is the pebbles and stones 

 retained upon such a screen. The sand should be clean, coarse, and 

 if possible free from loam, clay, and vegetable matter. (F. B. 461.) 



Experiments demonstrate that an exceedingly fine sand requires 

 about seven times the amount of cement required by a coarser sand 

 without increasing the strength of the concrete. If the sand must be 

 washed, the simplest way is to build a loose board platform from 10 

 to 15 feet long, with one end 12 inches higher than the other. On 

 the lower end and on the sides an edge 2 inches by 6 inches should be 

 nailed to hold the sand. The sand should be spread over the platform 

 in a layer of 3 or 4 inches thick and washed with a %-inch garden 

 hose. The washing should be started at the high end and the water 

 allowed to run through the sand and over the 2-inch by 6-inch piece 

 at the bottom. A small quantity of clay or loam does not injure the 

 sand, but any amount over 10 per cent should be washed out. (F. 

 B. 461.) 



Gravel. The largest part of concrete is the gravel or crushed 

 stone. This should be clean ; that is, free from loam, clay, or vege- 

 table matter. The best results are obtained from a mixture of sizes 

 graded from the smallest, which is retained on a ^-inch screen, 

 to the larger ones that will pass a 1^-inch ring. For heavy foun- 

 dation and abutment work, larger sized pebbles and stones might 

 be used, while for reinforced concrete work pebbles larger than those 

 passing a 1-inch ring should not be used. If crushed stone and 

 screenings are used, the same care in selecting the sizes must be ex- 

 ercised as in selecting the gravel. In ordering from the crusher 

 plant, the sizes of the stone and screenings should be specified in 

 the order. The crusher dust should always be removed. 



Sometimes bank or creek gravel, which will answer the pur- 

 pose of sand and gravel combined, can be obtained, and it is fre- 

 quently used on the farm and in small jobs of concrete work just 



