The capacity per charge of the mixer and charging and distrib uting buckets used at Buffalo, was 11 cubic feet. The crew con sisted of 16 men and a foreman, and they mixed and laid from 110 to 1:%.0 cubic yards per hour. Their best record was 1,000 cubic yards in an eight-hour day. The thickness of the concrete base laid was 6 inches.
349. Concrete Block Machines. There are two general types of hollow concrete block machines on the market—those with a vertical face and those with a horizontal face. In making blocks with the vertical-faced machine, the face of the block is in a vertical position when moulded, and is simply lifted from the machine on its base-plate. The horizontal-faced (or face-down) block is made with the face down, the face-plate forming the bottom of the mould. The cores are withdrawn horizontally, or the mould is turned over and the core is taken out vertically; the block is then ready for removal. The principal difference in the two types of machine, is that, if it is desired to put a special facing on the block, it is more convenient to do it with a horizontal-faced machine. With the vertical-faced machine, the special facing is put on by the use of a parting plate. When the part ing plate is removed, the two mixtures of concrete are bonded together by tamping the coarser material into the facing mixture.
Fig. 149 shows a Hercules machine. The foundation parts can be attached for making any length of block up to 6 feet. The illus tration shows two moulds of different lengths attached. These machines are constructed of iron and steel, except that the pallets (the plates on which the blocks arc taken from the machine) may be either wood or steel. This type of machine is the horizontal or face down machine.
Another machine of the face-down type is shown in Fig. 150. This machine, the Ideal, is sim ple in construction and opera tion; they are portable, which makes them convenient to oper ate. In making blocks with this machine, the cores are removed by means of a lever, while the block is in the position in which it was made. The mould and block are then turned over, and the face- and end-plates are re leased, and the block removed on the pallet.
In Fig. 151 are shown a group of the various forms which may be made. The figure also illustrates
the facility with which concrete may be utilized for ornamental as well as structural purposes.
Cement Brick Machines. Fig. 152 shows a machine for making cement brick. Ten bricks, 2* by 3 by S inches, arc made at one operation. By using a machine in which the bricks are made on the side, a wetter mixture of concrete can he used than if they are made on the edge. The concrete usually consists of a mixture of 1 part Portland Cement and 4 parts sand. The curing of these bricks is the same as that for concrete blocks. In making these bricks, a number of wooden pallets are required, as the brick should not be removed from the pallet until the concrete has set.
350. Sand Washing. It becomes necessary sometimes to wash dirty sand when clean sand can be secured only at a high cost, while the dirty sand can be easily obtained. If only a small quantity is to be washed, it may be done with a hose. A trough should be built about 8 feet wide and 15 feet long, the bottom having a slope of about 19 inches in its entire length. The side should be about inches high at the lower end, and increase gradually to a. height of about 36 inches at the upper end. In the lower end of the trough, should be a gate about 6 inches high, sliding in guides so that it can be easily removed. The sand is placed in the upper end of the trough, and a stream of water is played on it. The sand and water flow clown the trough, and the dirt passes over the gate with the overflow water. With a trough of the above dimensions, and a stream of water from a finch hose, three cubic yards of sand should be washed in an hour.
Concrete mixers are often used for washing sand. The sand is dumped into the mixer in the usual manner, and the water is turned on. When the mixer is filled with water so that it overflows at the discharge end, the mixer is started. By revolving the mixer, the water is able to separate the dirt from the sand, and it is carried off by the overflow of water. When the water runs clear, the washing is completed, and the sand is clumped in the usual way.
When large quantities of sand arc required to be washed, special machinery for that purpose should be employed.