This invention relates to apparatus for the batch reclamation of aggregate from waste plastic concrete. A certain amount of waste plastic concrete is generated at ready mixed and precast concrete plants. There are various causes, including plastic concrete being returned by customers and breakdowns. Disposing of this waste to tip is expensive and is becoming increasingly difficult due to environmental pressures. In addition the cost of aggregates is increasing and in some parts of the U.K. they are in short supply.

There have been several proposals for recovering the ingredients of waste plastic concrete using a series of compartments with weirs between them. The concrete is mixed with water and delivered to the first compartment and water or thin slurry overspills from that to successive compart¬ ments. The coarsest material settles in the first one, the less coarse in the second one, and so on. But then the material has to be extracted from the bottom of each compartment, and there have been various ways suggested. In one example an auger carries the aggregate away, and in another it is pumped out. But these techniques have considerable drawbacks. Not only is expensive and complex machinery required, but it is vulnerable to wear and obstruction, aggregate being highly abrasive and containing lumps not always susceptible to flow through restricted

passages.

Screens have also been used for separation of compo¬ nents but these too are subject to wear and clogging, and they need careful cleaning after every use. The object of this invention is to provide simple, relatively unsophisticated apparatus for removing cement and some aggregate fines from waste plastic concrete and to return the coarse aggregate (stone) and a large proportion of the fine aggregate (sand) to stock for reuse. According to the present invention there is provided apparatus for batch reclamation of aggregate from waste plastic concrete, the apparatus comprising a base, an open-topped container hinged to the base, means for moving the container relative to the base from a substantially level, working position to a tilted, discharging position, partitions in the container extending transversely to the hinge and dividing it into at least three tanks with the upper edges of the partitions providing weirs from a first tank to a second tank and so on, and means for introducing water under pressure downwards into said first tank, wherein, in use with the container in said working position, waste plastic concrete is deposited in said first tank and subjected to water under pressure, which causes cement and fine aggregate to be washed out of the concrete and separ- ated from coarse aggregate by being carried over a first weir for collection in said second tank, the latter overspilling a second weir into a third tank with cement particles and some aggregate fines in suspension, and

wherein after such separation the contents of said first and second tanks are removed by tilting the container to said discharging position.

At least one drain outlet will conveniently b provided for discharging a slurry of cement and fines from the third tank, and this may go to a separator for further treatment. This could be a hydrocyclone or a settling tank/pit.

Means will preferably be provided for preventing the separated fine and coarse aggregate from mixing during discharge from the container, and conveniently the discharge end of the container includes an aggregate stop, to allo surplus water to escape first. The container may b equipped with a hopper for loading the waste concrete into the washing tank and .at least one load cell may be provided between the container and its mounting.

It is advantageous to introduce air with the water under pressure delivered to the first tank by means of a plurality of downwardly extending pipes, connected to a common supply line. Each pipe may comprise an inner tube and an outer tube, the outer tube being provided with one or more air inlets, and the inner tube being connected to th water supply line. In this way the water flowing through the inner tube draws in air through the inlets so that the washing action is a combination of water and air treatment. The pipes may be oscillated across the first tank to provid uniform washing, and they may be vertical or offset from th vertical.

Preferably the second tank will be provided with agitating means to keep the very fine material in suspen¬ sion.

For a better understanding of the invention one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view of aggregate reclamation apparatus,

Figure 2 is a diagrammatic plan view of the apparatus of Figure 1,

Figure 3 is a diagrammatic cross-section on the line III-III of Figure 2,

Figure 4 is a longitudinal section of a pipe forming part of the apparatus, Figure 5 shows the apparatus in its working condition; and

Figure 6 shows the apparatus in its discharging condition.

Referring to Figures 1, 2 and 3, the apparatus comprises a generally rectangular container 1 with an open top and a sloping end. It is provided with longitudinal partitions 2 and 3 which divide the container into a washing

(first) tank A , a settling (second) tank 5, and a drain

(third) tank 6. Although shown as flat-bottomed in the drawings, the bases of at least some of these tanks may be of shallow V or U-Section. The partition 2 slopes to make the top of the tank 4 wider than its base, and its upper edge is higher than that of the partition 3. These upper

edges form weirs 7 and 8. Pipes 9 (to be described in more detail later) extend downwardly into the washing tank 4 and are supplied with water under pressure from a common supply line 10. A loading hopper 11 is provided in one side wall of the container 1 at about the mid-length of the washing tank 4, and drain outlets 12 are provided in the base of the drain tank 6. A paddle 13 extending virtually the length of the container is suspended into the settling tank 5 and can be oscillated transversely between the partitions 2 and 3. At the sloping end of the container 1, the upper edge of the partition 2 leads into a wedge-like formation 14 widening to the lip of that sloping end, and this is flanked by inwardly projecting stop ledges 15 extending to the sides of the con¬ tainer. The container 1 is pivotally mounted on a support base 16 by a transverse hinge 17 a short distance below the lip of the sloping end. Hydraulic actuators 18, symmetri¬ cally arranged one on each side, are coupled between the container 1 and its support base 16. One or more load cells (not shown) are also provided between the container 1 and the support base 16 to control loading of waste concrete into the washing tank 4.

The construction of the pipes 9 is shown in more detail in Figure 4. Each pipe comprises an inner tube 19 arranged co-axially within an outer tube 20 extending down beyond the tube 19. The inner tube connects with the water supply line 10, and the outer tube has a number of air inlets 21 near its upper end. In use, water under pressure

is delivered from the line 10 into the inner tube 19. Its jet-like exit from the lower end of that tube causes air to be drawn into the air inlets 21 so that a mixture of water and air is discharged from the end of the outer tube 20 into the washing tank 4. The lower end of each pipe 9 extends below the level of weir 7, whilst the air inlets 21 are kept above the level of the weir and so above the .level of the liquid in the washing tank ^• 4. The pipes are preferably arranged to oscillate to and fro across the washing tank 4. More than one set of pipes may be used, and the pipes may be vertical or offset from the vertical.

In use waste plastic concrete with a collapsed slump is loaded into the washing tank 4 via the hopper 11. The concrete in the washing tank 4 is subjected to the action of water, combined with air, from the pipes 9. Cement, sand and fine aggregate below about 5mm particle size are washed out of the concrete in the washing tank 4 and carried over the weir 7 into the settling tank 5, the coarse aggregate being retained in the washing tank 4. Sand particles are retained in the settling tank 5 whilst cement and fines are carried over the weir 8 into the drain tank 6, the paddle 13 keeping the contents agitated to ensure that the fine particulate material remains in suspension. A slurry of cement and fines is discharged from the drain tank 6, via the drain outlets 12, to a hydrocyclone or settlement pit or tank for eventual removal off site.

After completion of the washing process and emptying of the tank 6, the container 1 is tipped up from

the Figure 5 to the Figure 6 position to discharge aggregate retained in the tanks 4 and 5. First, water will spill out and it will be allowed to run away to drain. At a certain angle, before all the water has escaped, the coarse and fine aggregate will start to slide, first towards the sloping end and then, as the angle increases, over that end towards the ledges 15. These form aggregate stops and temporarily halt the aggregates as the last of the "free" water pours away over them. But then, with the container 1 approaching the Figure 6 position, the aggregates will avalanche over the stop ledges 15 and over the lip of the sloping end.

The coarse and fine aggregates from the tanks 4 and 5 are prevented from mixing together whilst being discharged by the wedge formation 14, which directs them to the side end regions 22 and 23 of the container.

Although described with three tanks, which should be sufficient, the container could have more, for more grad¬ uated separation.