Blue Lias Flagging.
—A blue lias flagging does not make a first-rate pavement, as although it is very cheap, durable, clean, and has many other good qualities, it sometimes wears slippery and is then dangerous to pedestrians; but the Devonian limestone, which is much used in the west of England, has not apparently this defect.
Concrete Footpaths.
—These have been tried in this country, but generally without success; the concrete or cement cracks, and in addition to this the paths wear slippery and greasy, and as some time is necessary in order to allow the concrete to thoroughly set before the traffic can be allowed on them, they have not found much favour.
In the United States, however, concrete footpaths seem to be made successfully; the following detail particulars of such a foot-pavement will, I think, be of great interest and use.[107]
“Concrete footpaths should be laid upon a form of well-compacted sand, or fine gravel, or a mixture of sand, gravel and loam. The natural soil, if sufficiently porous to provide thorough sub-drainage, will answer.[108]
“It is not usual to attempt to guard entirely against the lifting effects of frost, but to provide for it by laying the concrete in squares or rectangles, each containing from 12 to 16 superficial feet, which will yield to upheaval individually, like flagging stones, without breaking and without producing extensive disturbance in the general surface.
“When a case arises, however, where it is deemed necessary to prevent any movement whatever, it can be done by underlying the pavement with a bed of broken stone, or a mixture of broken stone and gravel, or with ordinary pit gravel containing just enough of detritus and loam to bind it together. In high latitudes this bed should be 1 foot and upwards in thickness, and should be so thoroughly subdrained that it will always be free from standing water. It is formed in the usual manner of making broken stone or gravel roads already described, and finished off on top with a layer of sand or fine gravel, about 1 inch in depth, for the concrete to rest upon.
“The concrete should not be less than 3¹⁄₂, and need rarely exceed 4 to 4¹⁄₂ inches in thickness, the upper surface to the depth of ¹⁄₂ an inch should be composed of hydraulic cement and sand only. Portland cement is best for this top layer. For the rest, any natural American cement of standard quality will answer. The following proportions are recommended for this bottom layer.
| Rosendale or other American cement | 1 | measure | |
| Clean sharp sand | 2 | ¹⁄₂ | „ |
| Stone and gravel | 5 | „ |