354 STATE BOARD OF AGRICULTURE. 



grains will be obtained by observing that the practice whicli has been 

 recognized as best, specifies that not more than twenty per cent shall 

 pass a sieve having fifty meshes per linear inch and not more than six 

 per cent shall pass a sieve having one hnndred meshes to the linear 

 inch. 



When aggregate is graded as specified, the concrete mixture for tile 

 should consist of not less than one sack of Portland cement to three 

 cubic feet of sand meeting the requirements already stated. Methods of 

 measuring the materials should be such as to insure separate and uni- 

 form proportions of each ingredient at all times. 



The Bureau of Standards has recently published, in its Technologic 

 Papers No. 44, the results of a year's investigations on the durability of 

 cement drain tile in alkali soils. In a summary of these investigations 

 the Bureau states that the published results of the year's labors are by 

 no means to be taken as conclusive but that, so far, its observations have 

 pointed to the necessity for employing only the best materials and good 

 workmanship in manufacturing drain tile and preferably adhering to 

 mixtures no leaner than one sack of cement to three cubic feet of sand. 

 In the Bureau experiments it was disclosed that drain tile properly 

 manufactured of such mixtures is "apparently unaffected structurally 

 when exposed for one year in operating drains in very concentrated 

 alkali soils." This should point to an ultimate conclusion that the 

 durability of concrete tile rests entirely upon the process of manufac- 

 ture, which means an observance of requirements previously outlined. 



A good method of examining finished concrete to determine whether 

 the proportioning has been properly done is the following: Take several 

 small broken pieces of the finished product, smooth some of the broken 

 surfaces on a grindstone and examine these finished surfaces with a 

 small lens or reading-glass. Many voids or air-spaces indicate too little 

 fine material or poor packing, while too little coarse material will be 

 indicated by a great deal of mortar between the larger particles. The 

 proportion of cement used in concrete tile is greater than for other kinds 

 of concrete work. This excess of cement is used to insure filling all the 

 void spaces and coating all the sand particles with cement, the particles 

 of which are ground very fine. 



Mixing: Too much emphasis cannot be placed on the necessity for 

 thoroughly mixing the materials. For this purpose a batch mixer is 

 advisable because, if properly used, it may be expected to give the great- 

 est uniformity of results, provided mixing be continued for at least 

 one minute after all materials, including the water, are in the mixer. 

 Enough water should be used to produce a consistency that will allow 

 immediate removal of the outer casing from the tile, yet wet enough 

 so that when the outer casings are removed web-like markings, or water- 

 marks, will appear on the outside tile surface, indicating a sufficient 

 amount of water. Interior surfaces of the tile should show trowel 

 marks caused by moisture coming to the surface under the troweling 

 action of the revolving packer head, or core, in case such is used. It 

 is recommended that an automatic measuring device be used to measure 

 the amount of water for each batch of concrete and, after the desired 

 consistency -has-been determined, tliis amount should be used in each 

 batch until working conditions demand a change, 



