210 THE farmers' handbook. 



ASH CONCRETE.* 



Portland cement concrete is an artificial compound, generally made by 

 mixing cement, stone, sand, and water together in such proportions as will 

 form a solid conglomerate. 



To make the strongest and heaviest concrete, the stone must be hard, 

 rough, and somewhat porous, affording a rough surface to which the cement 

 mortar will readily adhere- * 



Technically the stone is called the aggregate, and the mortar made from 

 the sand, cement, and water is known as the matrix. 



For many classes of work, such as small farm buildings, cottages, floors, 

 surface drains, &c., heavy concrete is not necessary, and for such purposes 

 there are other materials that provide a suitable aggregate. Amongst these 

 is the ash, generally a waste product obtainable from coke ovens, foundries, 

 gasworks, and railway loco, sheds. This is generally found to be of a 

 mixture that requires only the addition of the cement and water to make 

 good concrete. Generally speaking, however, it is found desirable to add a 

 proportion of sand, as it is always safer to have a little too much than too 

 little matrix in the mixture. All materials used in the manufacture of 

 concrete must be clean, and free from any vegetable matter. 



. Sand that is of a loamy nature, although good for mortar, is not suitable 

 for concrete; for which purpose it should be sharp and gritty. The quality 

 of the cement is assured, and may be procured with the certificate of the 

 Government tester attached. The local manufacture is equal in quality to 

 the best imported cements, and for convenience is put up in bags containing 

 about 128 lb. It would, however, be much more convenient if it were put up 

 in bags containing exactly 1 cubic foot, as all concrete is mixed by measure. 

 Until it is to be used the cement must be kept perfectly dry; as it is very 

 sensitive to even slight moisture, it should be laid on planks or boards 

 raised a few inches from the ground, so that the air can pass freely under it. 



Often it will be found that a bag of cement out of the stack will have 

 become apparently solid, from pressure only. This does not injure it in 

 the least, as it is quite easily knocked into powder again; but if the 

 hardening is due to moisture it is quite useless — not even fit to be broken 

 up and used with the aggregate. 



When water is added to cement it becomes pasty, and will remain so for 

 about twenty minutes (if not exposed to the sun); after this time it begins 

 to harden or set. To disturb it after this has taken place weakens the 

 mixture, and to do so after it has set destroys it altogether. It should not, 

 during the first five or six days after setting, be exposed to the hot sun or 

 wind, but if possible be shaded and wetted at least twice daily. If this be 

 done the concrete will be thoroughly hard all through; while if not, it will 

 become chalky, easily damaged, and appear to have insufficient cement in 

 the mixture. 



* A. Brooks. Works Overseer, Department of Agriculture. 



