“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 2¹⁄₂ „ Stone and gravel 5 „ “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.