A Treatise On The Principles And Practice Of Harbour Engineering

I08 HARBOUR ENGINEERING. from date of gauging, the whole of the cement represented by the defective briquettes will be condemned. The whole of any individual consignment of cement must be delivered on the site of the works sufficiently in advance of its intended use to allow of the foregoing tests being completed and adjudicated upon. Contractors, or others using the cement, must provide on the site a suitable, water-tight, dry, wooden-floored store, capable of accommodating one- hundred ton lots so as to be kept distinct from each other. The cement is to be spread out over the floor to a depth not exceeding 3 feet, for a period of three weeks, immediately prior to using, and is to be turned over twice a week.1 In humid weather the cement is to be protected from an excessive absorption of moisture. The stock must never be allowed to fall below six weeks’ requirements. Cement which has failed to corne up to the requirements of the spécifica- tion must be removed forthwith, and no cement must be used until a certificate pf its efficiency has been issued. For the purpose of gauging the ingredients for concrete, strongly constructed measuring boxes are to be provided. The mixing of the concrete may be done either by haud or by a machine of approved make. For hand-mixing the following procedure is to be adopted. A wooden platform must first be laid down, and upon this a cubie yard of the aggregate will be deposited and spread out into a uniform layer 12 inches in depth. This layer is to be evenly covered by the proper proportion of cement, and the whole turned over three times dry. Then water is to be added, applied through a rose-ended sprinkler, while the concrete is again turned over three times wet. On no account is the concrete to be deposited until perfect incor- poration has been effected. The quantity of water used must be adequate to bring the concrete to a viscous condition, of the consistency of slime. There must not be any excess, however, such as would wash the cement from the aggregate.2 In windy weather suitable screens are to be provided to prevent loss of cement. In frosty weather no concrete is to be prepared without definite sanction and under appropriate conditions.3 No concrete is to be allowed to stand after being mixed, but must be used forthwith. It may not be thrown into foundations from a greater height than 6 feet, and it must be deposited in such a manner as to secure homogeneity and compactness. Concrete work shall, as far as practicable, be carried on continuously in a series of layers not exceeding 3 feet in thickness, extending over the whole of the 1 In view of modern methods of treating the cement prior to delivery, this clause is not now generally necessary. 2 This applies to concrete used in situations free from water. For deposition under water, special measures are required which cannot be covered by a general spécification. 3 Such as the use of very salt water and, possibly, of sugar. The work will also require covering. 1