CHEMICAL AND PHYSICAL PAPERS. 81 



THE EFFECT OF CLAY AND LOAM ON THE STRENGTH 

 OF PORTLAND CEMENT MORTARS. 



By W, C. HoAD, University of Kansas, Lawrence. 

 Read before the Academy, at Topelia, December 30, 1904. 



T N constrnctive engineering, the use of cement mortar, both as a 

 -*- binding material for stone and brick masonry and as a matrix for 

 concrete, is increasing every year by enormous strides. This cement 

 mortar, made of hydraulic cement, sand, and water, is very much 

 stronger, more convenient to handle and can be used in many more 

 ways than the old lime mortar, whose place it has largely taken. It 

 is also more costly. On account of both this greater cost and the 

 greatly enlarged field of usefulness of cement mortar, the quality of 

 the sand used in its manufacture is of greatly increased importance. 



Frequently, on work involving concrete or masonry construction, 

 dirty sand — that is, sand with a small admixture of clay or fine silt 

 — is the only kind practically available, and the question as to whether 

 such sand may be properly used as it is, or whether it must be washed 

 before being used, is often a very troublesome one to the inspector in 

 charge of the work, as well as to the engineer who draws up the speci- 

 fications. 



Under circumstances of this kind, there naturally arises the ques- 

 tion, How much does this dirt in the sand detract from the strength 

 of the resulting mortar? and until recently reliable data on this 

 point were almost entirely lacking. There has been, it is true, a feel- 

 ing among the users of mortar that perfectly clean sand was the best 

 for this purpose, and that any adulterant, like dust or dirt, was in- 

 jurious. Indeed, the idea has become so firmly rooted that the speci- 

 fication that "the sand used on this work shall be clean, sharp and 

 coarse" has almost hardened into a formula. But, as the thorough 

 washing of dirty sand is an expensive operation, the cost of structures 

 where this specification is enforced is obviously increased, sometimes 

 by a rather large percentage of the total cost. 



Largely owing to the greatly increased use of concrete in engineer- 

 ing structures and the correspondingly increased importance of a 

 thorough knowledge of the effect of dirt in the sand upon the strength 

 of the mortar, an investigation into the subject was undertaken last 

 winter, as a graduation thesis in the department of civil engineering 

 at the University of Kansas, by Messrs. Ben. C. Hoefer and Earle 

 Nelson. This investigation consisted for the most part of a series of 

 tests of the tensile strength of mortar made of Portland cement and 

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