176 PRACTICAL DRAINAGE 



Work done at the U. S. Bureau of Standards (i, 14) 

 shows how Portland cement concrete mortar, if porous, 

 can be disintegrated by the mechanical force exerted by 

 the crystallization of salts in its pore spaces. Mixtures 

 leaner than one part cement to three parts of aggregate 

 were found to be unsuitable for use in localities having a 

 soil high in alkali. 



Headden (6) found that in the presence of solutions of 

 sodium sulphate and sodium carbonate a chemical de- 

 composition of the cement takes place with a removal 

 of silicic acid and lime which destroys the cohesiveness of 

 the concrete. 



Steik (12) found that, of the great number of solutions 

 tested, the 5 per cent sodium sulphate had the greatest 

 disintegrating action. Solutions containing chlorides, sul- 

 phates, and carbonates all had some effect. Mortars were 

 found to disintegrate faster than neat cement, which is 

 similar to the findings of Sims and Dieckman (n). The 

 latter author found that density and age are very important 

 factors in helping cement to resist alkali. Steik believes 

 that the ultimate cause of the disintegration of cement 

 by alkalies is due to the formation of compounds in the 

 cement, which subsequently are removed by solution. 



These experiments all show the necessity for care in 

 the use of cement tile to drain alkali land, but if the cement 

 is properly made it is fairly satisfactory. 



Preliminary Survey. Before actual trenching is be- 

 gun it is important to make a preliminary survey to de- 

 termine the nature of the subsoil and the slope of the land 

 to be drained. A great many test holes made with an 

 auger will reveal the location of pervious and impervious 

 strata. This information is necessary in deciding the 

 depth, location, and direction of the drains. A system 



