. A practical treatise on natural and artificial concrete; its varieties and constructive adaptations . rmany, wasadopted at a general conference of engineers, architects,cement-makers, and others interested in the subject; it isrepresented by Fig. 6. Its use is regulated by the followingconditions, which may be regarded as the specificationcontrolling its employment for testing, but these instruc-tions differ from the English system of testing, inasmuch asthe cement is incorporated with certain proportions of fact, it is a mortar test, and one of a very satisfactory andpractical chara
. A practical treatise on natural and artificial concrete; its varieties and constructive adaptations . rmany, wasadopted at a general conference of engineers, architects,cement-makers, and others interested in the subject; it isrepresented by Fig. 6. Its use is regulated by the followingconditions, which may be regarded as the specificationcontrolling its employment for testing, but these instruc-tions differ from the English system of testing, inasmuch asthe cement is incorporated with certain proportions of fact, it is a mortar test, and one of a very satisfactory andpractical character. MATRICES. 59 The tests are to be made with briquettes of 5 squarecentimetre section. The cement to be examined must, whenmixed with three parts of clean sharp sand (proportionsbeing weighed), be competent to stand a maximum tensilestrain of 8 kilos, per square centimetre. The briquettes areallowed to remain in the air for twenty-four hours, and thenput in water, where they remain for twenty-seven days, sothat the briquette is in reality twenty-eight days old whensubmitted to the test. Fig. Gekman Testing Machine. The required fineness of the cement in powder is equiva-lent to a gauge of 900 meshes to the square centimetre,and should pass through a sieve of that fineness, leaving aresiduum of not more than 25 per cent. The preliminary treatment of the sand is performed bysifting it in a natural state through a 60-mesh to the squarecentimetre sieve. The coarser particles being thus excluded,the remainder is again passed through a sieve of 120 meshes,by which operation it is freed from the finest particles. Quick-setting cement under such treatment cannot be 60 A PRACTICAL TREATISE ON CONCRETE. expected to reach the prescribed strength in twenty-eightdays, nor indeed with some qualities of inferior cementwould such a breaking ever be realized. The primary object of this excellent system of testing isto encourage the manufacture of high-class heavy cements, tothe exclusio
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