Concrete Roads
and Their Construction

112 CONCRETE ROADS The track was laid on steel sleepers and bolted together in 20-ft. sections, so that each section could be easily and economically handled by two men. The material was deposited along the road, behind the mixer, in such quantities that as concreting progressed and the mixer moved backwards there was always just sufficient material on hand, with no waste or shortage. Each train load carried cement, sand and stone in the desired proportion, so that there was no delay in concreting due to in- sufficiency of one of the materials. The sub grade consisted of the natural soil, mostly sand. It was rolled flat with a 10-ton rollerand thoroughly wetted down to prevent absorption of moisture from the concrete. Side forms for the concrete pavement were 6-in. iron channels, which were accurately lined up and staked in place by instrument, for some distance ahead of concreting. Materials were mixed by half cu. yd. mechanical mixers, steam-driven. Water was pumped from the nearest available supply. The amount of water used in mixing was accurately gauged by a meter fixed to the machine and was varied to suit different aggre- gates, but was kept constant for any particular aggregate. This correct proportioning of water is very essential in road work and is a point often overlooked. It ensures a uniform mixture and is an important point in preventing cracks. The materials were mixed in the drum of the mixer for a specified time, and the concrete was then dumped out into a bucket which travelled along a 20-ft. boom, to be deposited where required. Construction of Road.—The cross section of the road was a parabola, 6 in. thick at the sides and in. at the crown, laid in one course. As the concrete was deposited it was levelled off by a template, handled by two men, and resting on the sido channel forms. Following up were the cement finishers, who worked from a wooden bridge spanning the pavement. They floated up the surface with wooden trowels, just sufficiently to bring the moisture to the top. No attempt was made to render the surface smooth, as a slight roughness gives a better foothold, and too much trowelling will bring the fine particles to the top, which would be liable to cause dust. All pavement, was laid in 35-ft. sections. Between each section