GB368800A - Improvements in and relating to the construction of macadam roads - Google Patents

Abstract

A method of making rolled macadam roads consists in binding the road metal by a pulverulent material containing an hydraulic cement together with a bituminous substance such as asphalt, tar, or pitch. The powdered material preferably consists of a mixture of lime, tar, and cement, the tar content not exceeding 15 per cent of the mixture. According to one method, the road metal is first laid and the binding agent then applied and raked in. The road surface is then rolled, watered and rolled again. Another method consists in applying the road metal over a layer of the powdered binding medium, loosely rolling the road surface, wetting, and again rolling. In a further method, the binding agent is mixed with sand and water and applied to the road foundation, the road metal being subsequently laid thereon and rolled. The hydraulic binding medium may be gypsum, stucco, alabaster, plaster, or a mixture of gypsum with lime and cement, and is admixed with the bituminous substance in such quantities that the mixture may be prepared in a grinding mill, pug mill, colloid mill or similar apparatus. The Specification as open to inspection under Sect. 91 (3) (a) describes also a method in which the bituminous substance is added to the hydraulic binding medium in the form of a solution, or, alternatively, is poured on to the road ballast after the latter has been rolled in with the hydraulic binding agent. The impregnation of the binding agent is aided by the use of mineral salts or watery emulsions of tar or bitumen, Trinidad asphalt, or bituminous substances registered under the names of "Mexphalt" or "Spramex" dissolved in chlorinated or other hydrocarbons or tar. Old roads may be treated by applying a pulverulent hydraulic binding agent over a layer of coarse ballast. This is rolled and watered, the penetration of the water being facilitated by mixing it with alcohol, acetone, or the like. Emulsions of bitumen, or tar containing 10-20 per cent bitumen, may be used as impregnating agents. In order to retard the drying action, small quantities of glycerin, sulphite liquor, or the like, are added to the water. The rolled road metal may be hardened by impregnation with water soluble salts of the borates, phosphates, fluor-silicates, alums, or earth alkali metal chlorides. The bitumination of gypsum may be carried out by impregnating cold gypsum with tar or bitumen dissolved in organic hydrocarbons by treating it in friction mills, disintegrators, colloid mills or similar apparatus. Alternatively tar or bitumen is admixed with pulverulent gypsum in the condition in which it is discharged from the gypsum boiler, the mixture being treated in the friction mill or the like. A further method consists in adding the tar or bitumen directly in the gypsum boiler. It is stated that the bituminated gypsum is capable of absorbing 10 per cent, or more, of road tar while still remaining in a pulverulent condition. This subject-matter does not appear in the Specification as accepted.