Hollow-Concrete Block Construction.

Progress, Volume II, Issue 4, 1 February 1907, Page 137

Hollow-Concrete Block Construction.

By Spencer B Newberry

THIRD PAPER. The accompanying table of tests of various mixtures, made by the writer, shows the good results that can be obtained with low proportions of cement,

had, almost without cost, in unlimited quantities, concrete blocks made from such a mixture would be far cheaper than lumber, and ought easily to replace all other building materials. All that is needed to bring this about is practical demonstration, and the requisite skill and ingenuity on the part of architects and builders It is conceivable that a type of construction for small dwellings, using a 4-inch or 5-inch hollow block, might easily be developed, and these could be turned out, two at a time on 8-mch or 10-inch machines, provided with suitable cores and partition The possibilities of development in this direction seem almost limitless The terms " porosity " and " permeabihtv " are often used and by many supposed to be ct the same meaning. The porosity of concrete is however the proportion of voids, or empty spaces, which it contains, while the permeability is the rate of speed with -which water, under a certain pressure, will pass through it All concietes and mortars are more or less porous, and all are somewhat permeable by water under heavy pressure. Tt is well known that, with the same proportion of cement mixtures of fine sand are more porous than those of coarse sand The latter are however much more permeable than the former Feret has shown that the porosity is the total amount of voids contained in the mass, while the permeability depends on the size of the individual openings The least porous concrete may, therefore, be the most permeable and vice versa If, however, both fine and coarse grams are present in proper proportion, the mass will show the least porosity and at the same time be the least permeable The con-

even objectionable, owing to their tendency to " sweat " from the deposition of moisture on the inside surface. For health and dryness it is necessary that a gradual circulation of air through the walls should take place, and that any moisture condensing on the inside shall be absorbed and carried aw ay. Sufficient impermeability for practical purposes, to avoid all danger of dampness penetrating from the outside, may be secured by use of Sufficiently large proportion of cement, Addition of hydrate lime, Suitable sand and gravel or screenings, containing both fine and coarse material. With poorer mixtures, which would otheiwise be too absorbent for use in the walls of dwellings, any desired water-proof qualities may be secured by the addition of a very small percentage of waterproof compound, as already explained

Colour, etc. The experience of the writer has been that the natural stone colour, obtained by the use of ordinary sand and gravel or screenings, is more popular with purchasers of blocks than any tint which may be given by addition of pigments to the mixture. Limestone screenings give a lighter colour than most kinds of sands, but the colour is chiefly determined by the cement used, and the tint obtained with white sand is very little lighter than that with sand of ordinary grey shade. The addition of hydrate lime makes the blocks decidedly lighter in colour and the same result is obtained, in still greater degree, by making the mixture ar wet as

workers might grasp its full significance. For instance here are the district totals for five consecutive quarters —

Sep 30, Dec 31, Mar. 31, June 3o, Sep 30 1905 1905 1906 1906 1906 Tons Tons Tons Tons Tons Belfast 213,530 194,510 171 130 166 790 132,540' 3arro\v j tvorkmg- ~ 56 ° 3>24 ° 3 00 ° 4'olo4 ' 010 4'o4(>4 ' 04(> ton ° ) :i\de 486,970 503,335 537,836 527,930 515,241 riartle- j pool 65 570 76 630 84 620 80,815 56,460 vVhitb} ) Fees 84,220 88 051 95,245 92,859 74,843 r>ne 253,915 253 894 265,547 285 216 232,613 kVear 169 835 174,109 187 766 179,864 190,389

Proportions by Weight. Tensile , height Water Materials Strength Per Cii. Ft. Absorp- fnr qg _ m 22 Days Pounds. tion Block 334 | 130 0 7.72 ' old Cement 150 i Hyd. Lime 0 [ Sand 600) Cement 125] Hyd. Lime . . . ..25 / Sand 600 j 3GO 136 i 5.75 . s£d Cement 100) Hyd. Lime 50 Sand 600 ) 278 139 5 5 23 5d Cement 100) Hyd. Lime 25 Sand GOOJ 197 130 0 5 75 4W Cement ... .... .... 50 | Hyd. Lime 50 - Sand 600 ) I I I IS2 132 6 703 ', 33 il