Concrete Roads
and Their Construction

154 CONCHETE HOADS portable and essentially ‘’one-man” machines. A convenient machine (Fig. 99) for this purpose is made by the Ransome Ma- chinery Co., Ltd.; it has a capacity of about 2 cu. ft. and an output of 2-21- cu. yds. per hour. The mixer is of such dimensions that a standard navvy barrow can be readily placed beneath the drum in order to receive the batch when discharged. In the“ Smith Hand mixer” (Fig. 101) made by Messrs. Stothert andPitt, Ltd., the mixed concrete is discharged on to a board placed ready to receive it, or into wheelbarrows. In the latter case it is advisable to remove the wheels, placing the machine on timbers sufficiently high to allow wheelbarrows to pass underneath and receive the charge. When desired, the mixer can be placed so as to discharge its contents into a trench, and being portable can readily be moved along as the work progresses, discharging each batch exactly where required. Two men are required to drive this mixer, which has a capacity of 3-3| cu. ft. of unmixed material, and an hourly output of 2{—3| cu. yds. of concrete. Power-driven mixers have replaced, the hand-driven machines for all except the smallest jobs, as they not only mix a larger quantity of concrete at a time [with greater certainty, but they can be arranged to discharge it precisely at that part of the road where it is required. Power-driven concrete mixers are of two chief types, (a) continuous and (&) batch mixers. Con- tinuous mixers are seldom satisfactory for road-making, as the conditions are not usually favourable ; batch mixers should, therefore, be used in most, if not all, cases. In a batch mixer, definite measurer! quantities of all the. ingredients are placed in a hopper or skip provided for the purpose, and this quantity of material—termed the batch—is introduced into the mixer, in which is added a definite and proper quantity of water'. When the process of thoroughly incorporating the ingredients is com- plete the mixed material is then completely discharged from the mixer, which is ready to receive the next measured batcli which has, meanwhile, been prepared in the hopper or skip previously mentioned. Mixers which are especially adapted for road-making have been developed to a very satisfactory and economical point. The introduction of the material into the mixing drum usually requires its elevation to a considerable height ; therefore, most of the satisfactory road mixers are equipped with some type of power- operated elevator. They are also equipped with means for