A Treatise On The Principles And Practice Of Harbour Engineering

104 HARBOUR ENGINEERING. conditions of fineness. One hundred grammes (4 ozs. approx.) shall be con- tinuously sifted for a period of fifteen minutes with the following results : — “ The residue on a sieve 76 by 76 = 5776 meshes per square inch is not to exceed 3 per cent. “ The residue on a sieve 180 by 180 = 32,400 meshes per square inch is not to exceed 18 per cent. “ The sieves are to be prepared from standard wire, the size of the wire for the 5776 mesh being '0044 inch, and for the 32,400 mesh, '002 inch. The wire cloth shall be woven (not twilled), the cloth being carefully mounted on the frames without distortion. ‘ 'The spécifie gravity of the cement, when fresh burnt and ground, shall not be less than 3'15 or 3’10 when it can be proved to the satisfaction of the engineer (or of the purchaser) that the cement has been ground for four weeks.” The cement shall be delivered in packages marked with the manu- facturer’s name.1 Chemical Composition.—“The cement shall comply with the following conditions as to its chemical composition. There shall be no excess of lime; that is to say, the proportion of lime shall not be greater than is necessary to saturate the silica and alumina present.2 The percentage of insoluble residue shall not exceed 1-5 per cent.; that of magnesia shall not exceed 3 per cent. ; and that of sulphuric anhydride shall not exceed 2'75 per cent. “ The quantity of water used in gauging shall be appropriate to the quality of the cement, and shall be so proportioned that when the cement is gauged it shall form a smooth, easily worked paste, that will leave the trowel cleanly in a compact mass. Fresh water shall be used for gauging, and the temperature thereof and that of the test-room, at the time the said operations are performed, shall be from 58 to 64 degrees Fahrenheit. The cement gauged as above shall be filled, without mechanical ramming, into moulds of the form shown in fig. 88, each mould resting upon an iron plate until the cement has set. When the cement has set sufficiently to enable the mould to be removed without injury to the briquette such removal is to be effected. The briquette shall be kept in a damp atmosphère for twenty-four hours after gauging, when it shall be placed in fresh water Fig. 88. —Standard Briquette. and allowed to remain there until required for breaking, the water in 1 Any purchaser wishing to have the cement delivered in sealed bags, or in bags of any certain size, should so specify at the time of ordering. 2 The proportion of lime to silica and alumina shall not be greater than the ratio (calculated in chemical équivalents) represented by o^rrrr = 2'85. The molecular weight of lime = 56 ; silica=60 ; alumina = 102.