CONCRETE LINING FOE IRRIGATION CANALS. 53 
In experiments with oil-mixed Portland cement concrete/ the con- 
crete was damp-proofed by the incorporation of semiasphaltic oil. 
In hand mixing, the sand, cement, and water were first mixed to a 
mushy consistency, the oil added and mixed until no trace of it was 
visible on the mortar surface, and then the broken stone or gravel 
was mixed in. In machine mixing the sand, cement, and water were 
first mixed to a mortar followed by alternate batches of stone and 
oil which were added and mixed. The proportion of oil used was 
based on a comparison of its weight to the weight of the cement used 
in the concrete. The results of tests show that oil-mixed mortar; 
containing 5 to 10 per cent of oil, is dampproof as well as water- 
proof, and indicate that its use may prove desirable in the construc- 
tion of irrigation canal linings exposed to the action of alkali (fig. 1). 
Good practice in concrete fining construction where alkali must be 
reckoned with necessitates the following precautions : 
(1) Do not use sand, gravel, or water containing alkali. 
(2) Keep soil waters charged with alkali from coming into contact 
with the concrete by the use of suitable drainage. 
(3) Give careful attention to the proper proportioning of materials 
and use more cement than is needed to fill the voids. 
(4) Protect the surface by a thin plaster coat of dense mortar of 
granular sand. 
(5) Both the concrete and the mortar used for the lining may be 
dampproof ed by the addition of 5 to 10 per cent of semiasphaltic oil 
when mixing the materials. 
THE EXPANSION AND CONTRACTION OF CONCRETE. 
FIELD TESTS AT LOGAN. UTAH. 
During the summer of 1913 field experiments were conducted by 
Prof. B. P. Fleming, of the State University of Iowa, working under 
the direction of this office, at Logan, Utah, for the purpose of deter- 
mining the coefficient of expansion of concrete slabs. An effort was 
made to secure conditions as nearly as possible like those found for 
canal linings. It will be noted, however, that the slabs were not 
tested to find the effect produced by being wet on one side. 
The variations in length were measured with two micrometer 
microscopes focused upon lines in the highly polished tops of two 
steel pins projecting above the surface of the slab, one at each end. 
This device permitted making direct readings from the micrometer 
scale, giving measurements to 0.0008 of a millimeter. The ther- 
mometers used were graduated to 0.10° C. and could be estimated 
easily to 0.025°. All measurements of the slab length were direct, 
and no part of the apparatus was in contact with the slab. The 
idea of maintaining the latter condition was to prevent in every 
possible way influences which might affect the expansion of the slab. 
i U. S. Dept. Agr., Office Pub. Roads Bill. 46 (1912). 
