A Treatise On The Principles And Practice Of Harbour Engineering

STONE: NATURAL AND ARTIFICIAL. 103 Totalling the aggregates, we have : — Gravel and stone, 60 parts Sand, . . 40 „ 100 „ Cement, . . 13 ,, 113 „ or a limiting ratio for the conerete of 8^ to 1. For general work in bulk,1 8 to 1 is a serviceable proportion ; for vertical facings, 6 to 1 ; for quay floors, 4 to 1 ; for quay steps and landings, 2 to 1.] Displacers or plums—large stones and boulders of quality at least equal to that specified for the aggregate—may be inserted in the body of the concrete- forming mass or bulk work, provided that no two stones corne within 6 indres of each other and that no part of any stone corne within 6 inches of a moulded face. The rock or stone used for the purpose must either be brought fresh from the quarry, or, if old material from paving or building works, it must be thoroughly cleaned by picking and washing so as to free from all mortar, earth, and other accretions. The plums must be Sound, hard, compact, and shapely, with no excessive elongation or attenuation and no cracks or flaws, and they must possess rough, preferably rugged, surfaces.2 The matrix shall consist of Portland cement manufactured by a firm of good standing, and conforming in all respects to the tests and conditions stated below. “ The cement shall be prepared by intimately mixing together calcareous and argillaceous materials, burning them at a clinkering temperature, and grinding the resultant clinker. No addition of any material is to be made after burning.”3 (The standard spécification permits the addition of water or calcium sulphate, in neither case exceeding 2 per cent., but only by the express permission of the purchaser.) As soon as possible after the delivery of the whole of any consigument on the works, samples for testing will be taken from ten separate bags or parcels, in different positions. Equal portions of the several samples will be mixed together, and the cement so obtained will be considered as representative of the whole consignment and tested accordingly. “ Before gauging the tests the resultant sample shall be spread out for a depth of 3 inches for twenty-four hours, in a temperature of 58 to 64 degrees Fahrenheit.”4 Grinding.—“ The cement shall be ground to comply with the following 1 10 to 1 conerete is sometimes used for hearting purposes, but the proportion is some- what extreme. 2 No limits of size need be imposed. 3 This paragraph not transcribed in full. The limits of temperature throughout are applicable to the climate of the British Isles.