Page:Popular Science Monthly Volume 89.djvu/425

 Blowing Concrete Into Place

��Dotted Square Is Position of Mixing Box Above Concrete Mixer

��Air CyHndcr for

Main HoistingMixing Sand and

Water Box to Top of Smalt Gravel

Tank Concrete Mixer Water Mixing

Tank Box

���A Specially Constructed Steel Car Which Conveys Concrete at the Rate of Fifty Feet a Second by Utilizing Compressed Air. The Car Propels Itself with the Aid of a Gasoline Equipment

��ANEW system for conveying con- crete to the place where it is to be used employs compressed air and the concrete travels at the rate of fifty feet a second. It is especially appli- cable for lining tunnels with concrete. The mixing may be done outside the excavation and the concrete conveyed by a pipe line to the point of use. Or, to cite a recent instance on the line of the Carolina, Clinchfield & Ohio Rail- road, the mixing may be done on the spot upon a movable car.

It was desired to put the concrete lining into Sandy Ridge tunnel near Dante, Va., without shutting off the railway traffir through it. The concrete ret|uired amounted to some 50,000 or 60,000 cubic yards. A steel car was specially constructed, and pro\ided with a gasoline equipment by means of w-hich it could be made to propel itself. Half way between the ends is located the mixing compartment — open on hotli

��sides of the car. At a higher level, extending the whole length of the car, are located the stone bin, the water tank and the sand bin. The water is immediately above the mixer compart- ment. The tW'O end bins have inclined bottoms sloping towards the mixing chamber where they deliver the sand and the stone by suitable chutes. The gasoline engine is located at one end of the car beneath the sloping bottom of one of the bins. Beneath the sloping bottom of the other bin is placed the air receix'cr and the bags of cement. When the supply of compressed air runs low, a fresh supply ma\' be taken from an air main running through the tunnel. The mixing chamber contains two principal pieces of apparatus. One is the mixer itself, placed on one side of the car. The other is the charging skip. Its permanent place is on the other side of the car between the two chutes. When these chutes have delivered their

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