“It is mixed from time to time as required for use, and is compacted with an iron-shod rammer in a single layer to a thickness less by ¹⁄₂ an inch than that of the required pavement. As soon as this is done and before the cement has had time to set, the surface is roughened by scratching, and the top layer, composed of,
1 volume of Portland cement, and
2 to 2¹⁄₂ volumes of clean fine sand,
is spread over it to a uniform thickness of about 1¹⁄₂ inch, and then compacted by rather light blows, with an iron-shod rammer. By this means its thickness is diminished to ¹⁄₂ an inch. It is then smoothed off and polished with a mason’s trowel and covered up with hay, grass, sand, or other suitable material to protect it from the rays of the sun, and prevent its drying too rapidly.
“It should be kept damp and thus protected for at least 10 days, and longer if circumstances will permit; and even after it is opened to travel, a layer of damp sand should be kept upon it for two or three weeks, to prevent wear while tender.
“At the end of one month from the date of laying, the Portland cement mixture forming the top surface will have attained nearly one-half its ultimate strength and hardness, and may then be subjected to use by foot-passengers without injury.
“The rammers for compacting the concrete should weigh from 15 to 20 lb., those used on the surface layer from 10 to 12 lb. They are made by attaching rectangular blocks of hard wood shod with iron to wood handles about 3 feet long, and are plied in an upright position. Certain precautions are necessary in mixing and ramming the materials in order to secure the best results. Especial care should be taken to avoid the use of too much water in the manipulation. The mass of concrete, when ready for use, should appear quite incoherent, and not wet and plastic, containing water however in such quantities that a thorough ramming with repeated though not hard blows will produce a thin film of moisture upon the surface under the rammer, without causing in the mass a gelatinous or quicksand motion.”
Under the head of Concrete may be included many artificial stone pavements, such as “Bucknell’s Granite Breccia” “Ransome’s Artificial Stone,” “Eureka Concrete,” “Granolithic,” and the “Silicated Victoria Stone,” this last being worth a description. The stone is really a concrete, formed by mixing very superior Portland cement with crushed Thames gravel, furnace or iron slag, Kentish rag-stone, granite chippings, or other suitable material carefully washed. This fine concrete, after being mixed in the moulds forming the slabs, is thoroughly incorporated by being rocked or jiggled in a trembling machine; this motion, as can be easily understood, making the whole mass even and homogeneous when it sets. The cost of the slabs is about 9d. per square foot, 3 inches in thickness, and they make an excellent footpath.
Brick Footpaths.
—These are sometimes constructed of ordinary bricks laid on their sides, but soon wear, and are unsuitable for the purpose.[109] Staffordshire blue paving bricks make an excellent footpath. These are bricks made of stoneware highly vitrified; they should be about 12 inches in length by 6 inches wide, by about 2⁷⁄₈ inches in thickness, their surface being chequered with a diamond pattern so as to prevent their being slippery. They are exceedingly hard and durable if well burnt, and to ascertain this a brick should be broken across and the colour, etc., noted.
They should be laid in cement mortar upon a bed of concrete or sand. The objections to this class of pavement are as follows: