The mixers are usually charged by means of wheelbarrows, although other means are sometimes used. Fig. 140 shows the type of wheelbarrow generally used for this work. The capacity varies from 2 cubic feet to 4 cubic-feet, the latter size being generally used, as with good runways, a man can handle four cubic feet of stone or sand in a well-constructed wheelbarrow.

Fig. 138. Detail of Hoisting Tower, with Automatic Dumping Bucket.

Fig. 138. Detail of Hoisting Tower, with Automatic Dumping Bucket.

In ordinary massive concrete construction, as foundations, piers, etc., where it is not necessary to hoist the concrete after it is mixed, the mixer is usually elevated so that the concrete can be discharged directly into wheelbarrows, carts, cars, or a chute from which the wheelbarrows or carts are filled. It is much better to discharge the concrete into a receiving chute than to discharge it directly into the conveyor. The chute can be emptied while the mixer is being charged and rotated; while, if the concrete is discharged directly into wheelbarrows or carts, there must be sufficient wheelbarrows or carts waiting to receive the discharge, or the man charging the mixer will be idle while the mixer is being discharged. A greater objection is that if the man in charge of the mixer finds that the charging men or conveying men are waiting, he is very apt to discharge the concrete before it is thoroughly mixed, in an effort to keep all the men busy. A platform is built at the elevation of the top of the hopper, through which the materials are fed to the mixer, Fig. 141. This is a rather expensive operation for mixing concrete, and should always be avoided when possible.

Fig. 139. Ransome Concrete Hoist Bucket.

Fig. 139. "Ransome" Concrete Hoist-Bucket.

Fig. 140. Sterling Contractor's Wheelbarrow.

Fig. 140. "Sterling" Contractor's Wheelbarrow.

Fig. 142 shows a charging elevator devised by the McKelvey Machinery Company. The bucket is raised and lowered by the same engine by which the concrete is mixed, and operated by the same man. The capacity of the charging bucket is the same as that of the mixer.

In Fig. 143 is shown an automatic loading bucket which has been devised by the Koehring Machine Company for charging the mixers made by them. The bucket is operated by a friction clutch, and is provided with an automatic stop. In using either make of these charging buckets, it is necessary to use wheelbarrows to charge the buckets, unless the materials are close to the mixer.

Fig. 141. Concrete Mixer Erected.

Fig. 141. Concrete Mixer Erected.