A Treatise On The Principles And Practice Of Harbour Engineering

STONE: NATURAL AND ARTIFICIAL. IOQ site. Where this is impossible, the higher part of it must be racked or stepped downwards to mect the lower, in steps about 5 feet high by 2 feet broad, and vertical joints must be avoided unless necessitated by particular requirements. The scum arising from the concrete is to be allowed to drain away, and any that settles on the surface of a layer is to be carefully removed. After a layer has set, for which purpose two days must be allowed, an additional layer may be deposited, but not before the surface of the former layer has been well picked, washed with cleau water, and brushed. The surfaces of all brickwork, masonry, or concrete, on or against which concrete is to be laid, must be thoroughly cleaned and wetted immediately be- fore the concrete is applied. All wooden moulding boards are to have their surfaces paid over with oil, or a suitable composition, to prevent the concrete from adhering to them. The exposed surfaces of all concrete work must present a fair and smooth appearance where such is desired, and any superficial irregularities must be made good with mortar composed of 1 part Portland cement to 2 parts of clean, sharp sand. Where a facing of higher quality concrete is to be worked on to a lower quality backing, the division between the two portions is to be formed by a movable hånd shutter. The two qualifies (as 8 to 1 and 6 to 1) are to be deposited simultaneously and the shutter gradually raised, so that there may be thorough incorporation and the absence of any break or joint. Inspection.— Finally, it may be observed that owing to the dependence of sound concrete upon perfect manipulation, both in mixing and in depositing, too much stress cannot be laid upon the desirability of appointing a trust- worthy and competent man to personally supervise all concreting operations. In the case of work done by contract, it is a most essential step; in this way alone can the character of the workmanship be guaranteed, and without that, the best materials may prove practically worthiess. As a matter of interesting comparison, the conditions laid down in a modern Japanese spécification are appcnded. Concrete in Blocks at Osaka Harbour Works, Japan.1 The proportions of the concrete were as follows :— Portland cement, . 25 Ibs. to 1 cubic foot of sand. Sand, . . • 2I by volume. Gravel, ... Since each block contained 120 cubic feet, the corresponding ingrédients were :— Cement, . . . ■ 1500 Ibs. Sand, .... 60 cubic feet. Gravel .... 90 cubic feet. 1 Shima on Osaka Harbour Works, Trans. Am. Soc. C.E., vol. liv.; Int. Eng. Conf., 1904.