Concrete Construction: Methods and Costs

by Halbert Powers Gillette; Charles Shattuck Hill

"The minimum permeability is found in mortars where the proportion of medium-sized grains is small, and the coarse and fine grains are about equal to each other."

Mr. Feret also found that permeability decreased with time and that wet mixtures were less permeable than dry mixtures.

Tests made by Messrs. J. B. McIntyre and A. L. True at the Thayer School of Civil Engineering in 1902 gave the following results:

All the specimens composed of 1-1 mortar in the proportions of 30, 35, 40 and 45 per cent. of the whole mass were impermeable. Some of the specimens composed of 1-2 mortar in the proportions of 40 and 45 per cent. were also impermeable, as well as the 1-2-4 and 1-2½-4 mixtures. All other mixtures leaked at the high pressure (80 lbs. per sq. in.) and in a general way exhibited a degree of imperviousness in direct proportion to the proportion of mortar in them, with the lower pressures from 20 lbs. per sq. in. up as well as for the 80-lb. pressure.

Other tests confirm those cited. In general we may conclude that those mixtures richest in cement and mortar are the most impervious. It is doubtless practicable by exercising proper care to proportion, mix and place a concrete mixture which will be so nearly impervious that visible leakage will be small. The task, however, is one difficult to perform in actual construction work, and its accomplishment is never certain.

STAR STETTIN CEMENT.—Star Stettin cement is a Portland cement made by grinding a clinker which has been "impregnated" with substances which impart waterproofing properties to the ground product. The process is the invention of Richard Liebold, and the cement is made by the Star Stettin Portland Cement Works, Stettin, Germany. It is asserted that a 1-4 fine sand mortar made with this cement is impervious. To use it the ordinary precautions adopted in the employment of Portland cement are necessary, and in addition the following: The cement must be mixed with moist instead of dry sand before the water is added; the sand should be clean, sharp and fine of grain; the mortar must be more perfectly mixed than ordinarily, and somewhat more water should be used than is ordinarily used. Perfectly even mixing is essential to the best results.

MEDUSA WATERPROOFING COMPOUND.—This compound is a dry powder which is mixed with the cement in proportions of from 1 per cent. to 2 per cent. by weight, or from 4 lbs. to 8 lbs. per barrel of cement. The compound costs 12 cts. per lb., so that its addition increases the cost from 48 to 96 cts. per barrel of cement. Thorough mixing of the compound with the cement is of the utmost importance, otherwise none but the ordinary precautions in the use of Portland cement is necessary. Absorption tests on concrete blocks treated and untreated with the compound and nine months old have shown the absorbtion of treated blocks to be about one-fourth or one-fifth that of untreated blocks. The compound is made by the Sandusky Portland Cement Co., Sandusky, Ohio.

NOVOID WATERPROOFING COMPOUND.—This compound is a dry powder which is mixed dry with the cement in the proportion of 1 to 2 per cent. by weight or about 1 to 2 lbs. per bag of cement. The compound costs 12 cts. per pound or about from 48 to 96 cts. per barrel of cement. Directions for making waterproofing mortar are: To 100 lbs. of Portland cement add 2 to 2½ lbs. of compound and 200 lbs. of clean and sharp sand and mix the materials dry and very thoroughly. The water is then added in the proportion necessary to make a good working mortar and the mortar mixed and applied in the ordinary manner. Used as a wash 2 lbs. of compound are thoroughly mixed dry with a bag of cement. Any portion of the mixture is then mixed with water to produce a creamy grout, which is applied to a thoroughly wet surface with a brush. This compound is made by The Abbey-Dodge-Brooks Concrete Co., Newark, N. J.

IMPERMEABLE COATINGS AND WASHES.—The most common means employed for rendering concrete structures waterproof is to coat or wash the surface with some substance itself impervious to water or having the property of closing the pores of the surface skin of concrete so that water cannot penetrate.

Bituminous Coatings.—Bituminous coatings of one composition or another are among the most commonly used of impermeable coatings. The bituminous compound is used both alone and in combination with layers of a fabric of some sort to form the coating. Where bituminous coatings are used on surfaces exposed to the sun and frost attention must be given to the fact that a compound of different properties is required where the range of temperature is great than is required where this range is smaller. Asphalt, for example, should have a flow point of 212° F. and a brittle point of -15° F. when exposed directly to sun and frost as compared with say a flow point of 185° F. and a brittle point of 0° F. when covered from the direct action of sun and frost. Another point to be kept in mind particularly in using exterior coatings is that the concrete surface must be properly prepared to receive the coating or else it will peel off. The following are examples from actual practice of waterproofing with bituminous coatings.