Concrete Roads
and Their Construction

174 CONCRETE ROADS Fig. 123.—Method of constructing submerged concrete kerb in Surrey. sidered necessary, this conclusion being substantiated by the total absence of cracks, damage, or movement so far as obser- vations can. detect. This retaining kerb performs its functions successfully and is one to be recommended in rural areas where building developments are slow. For use upon, main roads and others in districts where, in anticipation of housing schemes, foot- paths are essential in the completed road, an elaboration of this kerb was adopted, and is designed not only to retain the road crust but also to keep traffic within the boundaries of the carriage- way and form an edge to the footpath. It is shown in Fig. 124. The trench in this case is dug 9 in. wide and generally to a depth of fourteen inches below the intended path level, and a layer of concrete 9 in. wide and 5 in. thick composed of five parts ballast to pass a 1-in. mesh sieve, two parts broken clinker and ashes, one part clean sharp sand, and one part Portland cement, is laid in the trench. The shutters, which are again 9 in. by 2 in., planed on one face, and coated with oil or soft soap, are secured in position on this bed of concrete to show 5 in. between faces. The reinforcement is fixed in the line of neutral axis on a vertical plane in order to resist as far as possible reversals of normal stress which undoubtedly occur, and although not in conformity with theory, it was contemplated that in this position it would oppose the necessary tensile resistance to any bending and unbalanced stresses brought to bear upon, it in any direction and avoid the cost of two lines of reinforcement. It consists of a strip of “ Exmet ” expanded metal f-in. diamond mesh 9 in. wide, cut in lengths of about 16 ft. for convenient handling. To ensure continuity of the reinforcement an overlap of about 2 in. is arranged at each join, but to provide for expan- sion of the concrete, joints are made at every 15 to 18 ft. by intro- ducing a layer of tarred felt into the cross section of the kerb. This is slit and passed over the reinforcement. Five to one con- crete is then poured in to such a height as will bring the kerb