GB2499603A

GB2499603A - Cleaning apparatus used in concreting operations

Info

Publication number: GB2499603A
Application number: GB1202956.7A
Authority: GB
Inventors: Richard Henry Coulton
Original assignee: Siltbuster Ltd
Current assignee: Siltbuster Ltd
Priority date: 2012-02-21
Filing date: 2012-02-21
Publication date: 2013-08-28
Anticipated expiration: 2032-02-21
Also published as: GB2499603B; GB201202956D0; WO2013124639A1

Abstract

A unit for cleaning apparatus used in concreting operations comprises: an open-topped receiving hopper 4 for receiving apparatus to be cleaned; a pump for providing a flow of liquid onto apparatus in the hopper for washing the apparatus and creating washout; a tank for receiving the washout, separating solids from the washwater and adjusting the pH of the washwater; and a further tank for receiving pH adjusted washwater from the first-mentioned tank and for separating solids from the washwater. In another aspect, a first tank 18 receives the washout from the hopper and separates aggregate from the washwater; a second tank 20 receives washwater from the first tank; a pH reducer (32, 34, Fig. 4) associated with the second tank reduces the pH of the washwater therein, the pH reducer being connected to a source 15 of a pH reducing agent, such as carbon dioxide; a third tank 22 receives pH adjusted washwater from the second tank and separates solids from the pH adjusted washwater; and a fourth tank 24 receives and stores cleaned and pH adjusted washwater from the third tank. A method of cleaning apparatus used in concreting operations is also claimed.

Description

- 1 -

Concrete washout unit and method

This invention relates generally to a unit for, and a method of, cleaning apparatus used in concreting 5 operations.

In the construction industry, concrete is emptied from trucks via a discharge chute mounted on the truck. Concrete may also be poured by a tower crane using an attachment known as a concrete "skip". After the concrete has been 10 emptied, the discharge chute or skip must be washed out. The waste so generated, referred to herein as "washout", comprises waste concrete solids and a volume of high pH, alkaline water hereinafter referred to as washwater even when only some of the solids have been removed. Sometimes 15 the pH of the washwater can be as high as pH 13.

Traditionally, the washout (containing the waste concrete and the alkaline water either released from the concrete itself or from washing concreting equipment) is dumped into a plastic-lined skip at the construction site. 20 When the skip is full, it is transported to a tip to be disposed of. Transporting the skip to a tip causes problems. Firstly, the washwater is highly alkaline and is often spilt over the road on the way to the tip. Secondly, it is illegal to tip liquid waste into landfill. Hence, 25 once the skip arrives at the tip, the washwater cannot be disposed of simply.

Some of these problems are addressed by the washout collecting unit described in W02010/082038. This unit is a

- 2 -

portable unit which includes apparatus for separating the solids out of the washout, and further apparatus for treating the washwater with carbon dioxide to neutralise it. The treated washwater can then be easily disposed of.

5 The collecting unit of W02010/082038 has the disadvantage that it is only suitable for collecting washout from truck discharge chutes. It also provides no means for recycling the treated water, so it must regularly be emptied.

10 Another kind of unit is shown in FR 2 942 417. In this unit, there is a recycling capability but the unit suffers from various disadvantages including that, perhaps in order to allow the unit to be of manageable size, there is only a limited facility for treating the washout; that 15 in turn limits the amount of recycling of water that is effective.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved unit for, 20 and a method of, cleaning apparatus used in concreting operations.

Summary of the invention

25 According to the invention there is provided a unit for cleaning apparatus used in concreting operations, the unit comprising: an open-topped receiving hopper for receiving apparatus to be cleaned; a pump for providing a

- 3 -

flow of liquid onto apparatus received in the open-topped hopper for washing the apparatus and creating washout; a first tank for receiving the washout from the hopper and separating aggregate from the washwater; a second tank for 5 receiving washwater from the first tank and adjusting the pH of the washwater; a pH reducer associated with the second tank for reducing the pH of the washwater in the tank, the pH reducer being able to be connected to a source of an agent for reducing the pH and being arranged to 10 supply the pH reducing agent to the washwater in the second tank; a third tank for receiving pH adjusted washwater from the second tank and for separating solids from the pH adjusted washwater; and a fourth tank for receiving and storing cleaned and pH adjusted washwater from the third 15 tank.

By providing three treatment tanks in addition to an open-topped hopper and a fourth storage tank, it becomes possible to effect a good treatment of the washwater resulting from the cleaning of the concreting apparatus, so 20 that the washwater can be recycled many times. At the same time, it is possible to arrange all the tanks within a single unit which, in a preferred embodiment of the invention, is portable.

The flow of liquid onto apparatus received in the 25 open-topped hopper preferably comprises cleaned and pH adjusted washwater from the fourth tank. With such an arrangement the unit is able to operate continuously.

The unit preferably comprises a perforated screen

- 4 -

associated with the first hopper for filtering coarse aggregate out of the washout. The perforated screen preferably divides the hopper into a receiving portion for receiving apparatus to be cleaned and a tank portion for 5 receiving washout passing through the screen. The perforated screen can provide an initial coarse filtering stage. The screen is preferably disposed in an approximately vertical plane or at least a plane steeply inclined to the horizontal. Whilst the receiving portion 10 of the hopper is preferably open across at least the majority of its top, the tank portion of the hopper may be closed.

The tank portion of the hopper preferably comprises a sump for collecting washout that has passed through the 15 perforated screen. A pump may be provided for pumping washout from the hopper, for example from the sump of the hopper, to the first tank. The pump preferably is arranged to pump washout into a top region of the first tank. A water level sensor may be provided in the sump for 20 detecting a high water level in the sump and turning on the pump in response to the detection. Another water level sensor may be provided in the sump for detecting a low water level in the sump and turning off the pump in response to the detection. In that way the transfer of 25 washout from the hopper into a treatment tank can be automated.

The first tank is preferably arranged to accommodate a removable liner for collecting solids. Solids settling out

- 5 -

in the first tank may be retained within the removable liner whilst the washwater passes into the second tank. The pump for pumping washout from the hopper to the first tank may be arranged to pump the washout into the top of 5 the removable liner.

The removable liner may be a flexible or rigid container. The container may for example be a flexible bag, which may be made of a fabric material; the bag may for example be an intermediate flexible bulk container. 10 Once full of solids, the container, if removable, can be lifted out and replaced with an empty container.

The pH reducer preferably comprises a system for introducing carbon dioxide into the washwater. Another possibility is for the pH reducer to comprise a system for 15 introducing acid into the washwater. The system preferably includes a store for one or more cylinders of carbon dioxide. The carbon dioxide is preferably arranged to be introduced into the bottom of the second tank. The carbon dioxide may be introduced through a sparger arrangement; 20 another possibility is for the carbon dioxide to be introduced through a diffuser placed within the tank. One or more mixers are preferably mounted in the second tank for mixing the pH reducing agent with the washwater. In a case where a sparger arrangement is provided a mixer may be 25 provided above the sparger arrangement for disbursing the carbon dioxide.

- 6 -

The third tank preferably includes a multiplicity of inclined plates for separating solids from the pH adjusted washwater.

The unit preferably further comprises a platform for 5 supporting at least one person during cleaning of the apparatus. The platform is preferably located above the first, second, third and fourth tanks. The platform is preferably also located abovepH reducing agent store, if one is provided.

10 Washwater may be arranged to overflow from the first tank into the second tank. In that case there is no need to provide a pump to transfer washwater from the first tank to the second tank and the transfer can be automatic.

pH adjusted washwater may be arranged to overflow from 15 the second tank into the third tank. In that case there is no need to provide a pump to transfer washwater from the second tank to the third tank and the transfer can be automatic.

Preferably the pH adjusted washwater is arranged to 20 flow between the inclined plates in the third tank. In that way fine solids can be separated out, the solids sliding down the surfaces of the plates.

Arrangement of the tanks in an especially preferred embodiment of the invention is specially selected to 25 provide, in a small space, a high efficiency of treatment. In a preferred embodiment of the invention, the first and second tanks are adjacent to one another. In a preferred embodiment, the third tank is adjacent to the first and

- 7 -

second tanks. More particularly, in the preferred embodiment, the first and second tanks are disposed on one side of the unit and the third tank is disposed on the other side of the unit. In such an arrangement the first, 5 second and third tanks may together occupy a generally cuboidal space with the combined lengths of the first and second tanks approximately the same as the length of the third tank. Extra length for the third tank is desirable to accommodate a sufficient number of inclined plates to 10 achieve effective separation of the fine solids.

In the especially preferred arrangement of tanks referred to above, the fourth tank may be disposed in any of a variety of locations. For example, it may be disposed below the three treatment tanks but in a preferred 15 arrangement it is located immediately forward of the three treatment tanks. Preferably an equipment space is provided below the three treatment tanks for pumps and/or other equipment. The fourth tank may extend over the full height of the unit from its bottom to the platform. 20 The platform may be immediately above the three treatment tanks. It may also be immediately above the fourth tank. It is then easy to provide access to the top of any tank through a door/lid in the platform.

The receiving hopper preferably comprises a body and 25 at least one side panel. More commonly, the receiving hopper comprises side panels on three sides of the body, the fourth being an interior side. The fourth side may be adjacent to one or more of the tanks; in an embodiment of

- 8 -

the invention described below, the fourth side is adjacent to the fourth tank. At least one side panel is preferably hingedly connected to the body. The side panel preferably extends downwardly to a position adjacent to the bottom of 5 the unit. The side panel may then be able to be hinged to a position allowing contents of the hopper to be removed. Alternatively, the side panel may be able to be completely removed to give clear access to the hopper for cleaning purposes.

10 The hopper may be provided with a non-stick coating to prevent solids adhering to it. A suitable mould release agent may be applied to the coating before use of the hopper. Another possibility is for the hopper to be fitted with a liner of plastics material from which solid 15 materials can readily be removed. If desired, an inflatable bag may be provided beneath the flexible liner to facilitate release of the solids. The inflatable bag may be inflated immediately prior to emptying using gas from carbon dioxide cylinders provided for adjusting the pH of 20 the washwater.

The unit is preferably portable. The unit may be configured to be transported using a hook-lift system. The unit may include lifting eyes and/or ISO corner fittings of the kind provided on a freight container.

25 In the invention defined above reference is made to first, second and third treatment tanks and to a fourth storage tank. It should be understood that it is within the scope of this aspect of the invention for there also to

- 9 -

be one or more further tanks. Such further tanks may provide for different treatments and/or may provide additional capacity for storage or treatment already carried out in one of the other tanks. It should also be 5 appreciated that it is within the scope of the broadest aspect of the invention for there to be fewer tanks than are defined above. According to that broadest aspect of the invention there is provided a unit for cleaning apparatus used in concreting operations, the unit 10 comprising: an open-topped receiving hopper for receiving apparatus to be cleaned; a pump for providing a flow of liquid onto apparatus received in the open-topped hopper for washing the apparatus and creating washout; a tank for receiving the washout from the hopper, separating solids 15 from the washwater and adjusting the pH of the washwater; a pH reducer associated with the tank for reducing the pH of the washwater in the tank, the pH reducer being able to be connected to a source of an agent for reducing the pH and being arranged to supply the pH reducing agent to the 20 washwater in the tank; and a further tank for receiving pH adjusted washwater from the first-mentioned tank and for separating solids from the pH adjusted washwater.

The unit according to the broadest aspect of the invention may also be provided with any of the other 25 features mentioned above in respect of the invention.

According to the invention, there is also provided a method of cleaning apparatus used in concreting operations, comprising the steps of:

- 10 -

(a) providing a unit as defined above,

(b) providing apparatus to be cleaned;

(c) providing a flow of liquid onto the apparatus;

(d) collecting the liquid used in step (c)in the 5 hopper of the unit; and

(e) removing solids from, and reducing the pH of, the liquid collected in step (d);

wherein the flow of liquid provided in step (c) comprises liquid produced as a result of carrying out 10 step (e) .

It will be appreciated that the apparatus of the invention and the method of the invention as described herein are closely related and that therefore essential or preferred features of one may, unless indicated otherwise 15 or clearly inappropriate, be incorporated into the other. Thus, features described above in respect of the apparatus of the invention may be incorporated into the method of the invention and vice versa.

By way of example an embodiment of the invention will 20 now be described with reference to the accompanying schematic drawings, of which:

Fig. 1 is an isometric view from one side and the front of a unit;

Fig. 2 is an isometric view from an opposite side and 25 the rear of the washout unit of Fig. 1;

Fig. 3 is a plan view of a rear portion of the unit with a platform and tank lids removed; and

- 11 -

Fig. 4 is a diagrammatic view of various treatment stages in the unit.

Referring first to Figs. 1 and 2, a washout unit 1 embodying the invention is shown. The washout unit has a 5 front section 2 and a rear section 3. The front section 2 has a low-level hopper having a front open-topped receiving portion 4. When the washout unit is in use, the skip or mixer chute being washed is placed on or held over the open-topped receiving portion 4 so that the washout and 10 waste concrete is collected in the hopper. The bottom 5 of the receiving portion 4 is curved where it meets side walls 6 and 7 of the receiving portion.

The front end wall 8 of the hopper is in the form of a moveable panel which is hingedly connected to the body of 15 the hopper at its top. The panel 8 is able to swing outwards or be lifted offto allow the waste concrete to be removed from the hopper, which can be tipped if desired. The panel 8 is fitted with a flexible rubber seal and a closing mechanism so that, when it is shut, washout is 20 retained in the hopper.

The open-topped receiving portion 4 may be fitted with splash screens (not shown in the drawings) that are hingedly connected to the top of the main body of the hopper. When a skip or chute is being washed these screens 25 may be moved to the upright position to prevent washout splashing out of the hopper. At other times the screens can be folded down to facilitate removal of waste concrete from any of the front three sides of the hopper.

- 12 -

The hopper is fitted with a perforated screen 9 which retains coarse aggregate in the front receiving portion of the hopper, but allows the washwater and finer aggregate and cement particles to flow through into a rear portion 10 5 of the hopper, which may be referred to as a sump portion of the hopper. The screen is in this example made of metal although it may alternatively be of a resilient plastics material and can be removed for cleaning.

The rear portion or sump portion 10 of the hopper is 10 disposed in the bottom of the front of the rear section 3

of the washout unit 1. The rear section 3 is closed at the top and has a raised access platform 12 on which an operator can stand while washing a skip or chute. The platform 12 has a post and hand rail 13 around most of its 15 perimeter to prevent the operator falling off the platform. The rail 13 can be collapsed to reduce the overall height of the unit, making it easier to transport. The platform 12 also includes a connector to which a hose pipe may be attached (not shown). An operator can gain access to the 20 platform via a ladder 14 mounted on the rear section 3 of the washout unit. The ladder 14 is mounted to the unit so that it can be swung out to an angle of 70° when in use, or folded away during transport of the unit.

Cylinders 15 of carbon dioxide are mounted on the 25 outside of the rear section of the unit 1 next to the ladder 14 and underneath the platform. In a particular example of the invention, each cylinder contains 34kg of carbon dioxide.

- 13 -

The space underneath the platform 12 contains a series of tanks in which treatment of the washout takes place, as described below.

Referring now also to Figs. 3 and 4, the space 5 underneath the rear section 3 of the unit contains in its interior: the sump portion 10 of the hopper at the bottom front extending partway across the width of the unit; an equipment storage space 16 behind the sump portion 10 and extending about halfway across the width of the unit; a 10 first treatment tank 18 extending across about one half of the width of the unit and disposed below a front portion of the platform 12; a second treatment tank 20 extending across about one half of the width of the unit behind the tank 18 and disposed below a rear portion of the platform 15 12; a third treatment tank 22 extending across about one half of the width of the unit below both front and rear portions of the platform 12 and being disposed alongside the tanks 18 and 20; and a storage tank 24 extending from the side of the unit to the sump portion 10 and immediately 20 in front of the treatment tanks 18 and 22.

Referring now also to Fig. 4, the first treatment tank 18 is a settlement tank. A pump (not shown) is provided in the sump portion 10 of the hopper and high level and low level detectors, for example conductivity probes, are 25 provided in the sump portion 10 to control operation of the pump; when the level in the sump portion 10 rises to the level detected by the high level detector, the pump is operated and pumps the washout from the sump portion 10

- 14 -

through an inlet 26 (Fig. 4)into the settlement tank 18 which contains an open topped liner 28. Solids in the washout are retained in the liner 28, whilst washwater flows over the top of the liner and out of the top of the 5 tank 18, into a passageway 30 which leads to the bottom of the second treatment tank 20. In the tank 20, the pH of the washwater is reduced by bubbling carbon dioxide into the tank via a sparging arrangement 32. A paddle mixer 34 serves to agitate the washwater in the tanks and break up 10 the bubbles of carbon dioxide rising from the sparging arrangement 32.

The introduction of carbon dioxide and the operation of the mixer 34 are controlled by a control unit which may be contained in the equipment storage space 16 or on a 15 control panel mounted on the side of the unit. The control unit is typically arranged to activate the introduction of carbon dioxide and the mixer 34 when the pump in the sump portion is activated. The activation may then be continued for a predetermined period of time after the pump is 20 switched off, or may be continued until the pH in the tank 20 reduces to below a predetermined level, measured by a sensor in the tank. When the pH of the washwater in the tank is reduced, calcium carbonate is created and precipitates out. Washwater in the tank 20 overflows, 25 together with the precipitate from the top of the tank 20 and enters an intake portion 36 of the tank 22. The washwater and precipitate passes from the intake portion 36 into a bottom region of the tank 22, below a stack of

- 15 -

inclined parallel plates 38, and passes up through the spaces between the plates. The fine solids settle out as the washwater passes between the plates and slide down the plates into bottom of the tank 22. Treated washwater 5 emerging from the top of the stack of plates 38 flows out of the top of the tank 22 into the storage tank 24. The presence of inclined plates in the tank 22 makes it desirable for this tank to be longer than the tanks 18 or 20 and this is achieved by devoting one side of the space 10 under the platform 12 to the tank 22, whilst providing the tanks 18 and 20 on the other side. The volume of the tank 22 relative to the tanks 18 and 20 can be selected by choosing whether the vertical longitudinal plane between the tanks is midway across the unit or spaced to one side 15 or the other of the midway position.

As will be understood, the hose pipe connection on the platform 12 is connected to a pump in the equipment storage space 16 which, when activated by an operation, pumps washwater from the storage tank 24, that washwater being 20 directed onto the apparatus being cleaned and then falling into the hopper receiving portion 4. In the case of a skip, this operation will usually be carried out by an operator standing on the platform 12 with the skip resting in the hopper; in the case of a truck chute, the operation 25 may be carried out at least partly by an operator standing on the ground with the chute held above the hopper, for example still attached to the truck. In either case the operator can control the flow of washwater by adjusting a

- 16 -

valve adjacent to the free end of the hose. As washout falls into the hopper receiving portion 4, the level in the sump portion 10 rises and, when the level reaches that at which the high level detector is set, the submersible pump 5 in the sump portion 10 is activated. As will now be understood, that actuation causes washout to be pumped into the first settlement tank 18, causing washwater in the top of the first settlement tank to overflow into the bottom of the second pH adjustment tank 20 causing washwater in the 10 top of the second pH adjustment tank 20 to overflow into the bottom of the third settlement tank 22, and causing washwater in the top of the third settlement tank 22 to overflow into the storage tank 24.

During operation of the unit, concrete solids that 15 have passed through the screen 9 collect in the bag 28 in the tank 18. The tank 18 has a removable lid in the platform 12, allowing the bag 28 to be lifted out through the top of the tank 18, by a crane, forklift truck or other lifting equipment and replaced by an empty bag. Typically, 20 the bag is of 0.5 to lm3 capacity.

Some fine concrete solids and calcium carbonate settle in the bottom of the tank 22 and can, for example, be periodically removed from the tank by draining the tank, removing the stack of plates 38 and sluicing out solids, 25 using a pressure washer, via a drain valve (not shown) in the bottom of the tank 22. The tank 22 has a removable lid in the platform 12, allowing the stack of plates to be lifted out through the top of the tank.

- 17 -

The tank 20 is similarly provided with a removable lid in the platform 12, to allow access from above into that tank for maintenance.

It will be understood from the description above that 5 the unit described with reference to the drawings is able to operate continuously if required. Furthermore, apart from control of the pump for supplying washwater to the hose and control of the valve on the end of the hose for controlling flow from the hose, both of which are under the 10 control of the operator, the unit is able to operate automatically; appropriate monitoring and alarm systems may be provided for alerting an operator to any faults or the like. Electrical power is supplied to the unit via a female socket (not shown).

15 In the embodiment described above, the pH reducing agent that is employed is carbon dioxide. It should be understood, however, that it is within the scope of the invention to use other pH reducing agents, for example acids, if desired. Such acid may be stored in drums in the 20 same region as the cylinders of carbon dioxide are stored in the illustrated embodiment. In that case, of course, there may be no precipitation of calcium carbonate

Where in the foregoing description, integers or elements are mentioned which have known, obvious or 25 foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as

- 18 -

to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the 5 scope of the independent claims.

- 19 -

Claims

Claims:

1. A unit for cleaning apparatus used in concreting operations, the unit comprising: an open-topped receiving 5 hopper for receiving apparatus to be cleaned; a pump for providing a flow of liquid onto apparatus received in the open-topped hopper for washing the apparatus and creating washout; a first tank for receiving the washout from the hopper and separating aggregate from the washwater; a 10 second tank for receiving washwater from the first tank and adjusting the pH of the washwater; a pH reducer associated with the second tank for reducing the pH of the washwater in the tank, the pH reducer being able to be connected to a source of an agent for reducing the pH and being arranged 15 to supply the pH reducing agent to the washwater in the second tank; a third tank for receiving pH adjusted washwater from the second tank and for separating solids from the pH adjusted washwater; and a fourth tank for receiving and storing cleaned and pH adjusted washwater 20 from the third tank.

2. A unit according to claim 1, wherein the flow of liquid onto apparatus received in the open-topped hopper comprises cleaned and pH adjusted washwater from the fourth tank.

25 3. A unit according to claim 1 or 2, wherein the unit comprises a perforated screen associated with the first hopper for filtering coarse aggregate out of the washout.

- 20 -

4. A unit according to claim 3, wherein the perforated screen divides the hopper into a receiving portion for receiving apparatus to be cleaned and a tank portion for receiving washout passing through the screen.

5 5. A unit according to claim 3 or 4, wherein the tank portion of the hopper comprises a sump for collecting washout that has passed through the perforated screen. 6. A unit according to any preceding claim, including a pump for pumping washout from the hopper to the first tank. 10 7. A unit according to any preceding claim, in which the first tank is arranged to accommodate a removable liner for collecting solids.

8. A unit according to any preceding claim, wherein the pH reducer comprises a system for introducing carbon dioxide

15 or acid into the washwater.

9. A unit according to any preceding claim, in which the third tank includes a multiplicity of inclined plates for separating solids from the pH adjusted washwater.

10. A unit according to any preceding claim, wherein the 20 unit further comprises a platform for supporting at least one person during cleaning of the apparatus.

11. A unit according to claim 10, wherein the platform is located above the first, second, third and fourth tanks.

12. A unit according to any preceding claim, wherein

25 washwater is arranged to overflow from the first tank into the second tank.

- 21 -

13. A unit according to any preceding claim, wherein pH adjusted washwater is arranged to overflow from the second tank into the third tank.

14. A unit according to any preceding claim, wherein the 5 pH adjusted washwater is arranged to flow upwardly between the inclined plates in the third tank.

15. A unit according to any preceding claim, wherein the first and second tanks are adjacent to one another.

16. A unit according to any preceding claim, wherein the 10 third tank is adjacent to the first and second tanks.

17. A unit according to any preceding claim, wherein the first and second tanks are disposed on one side of the unit and the third tank is disposed on the other side of the unit.

15 18. A unit according to any preceding claim, wherein the fourth tank is disposed forward of the first, second and third tanks.

19. A unit according to any preceding claim, wherein the receiving hopper comprises a body and at least one side

20 panel, and wherein the at least one side panel is hingedly connected to the body.

20. A unit according to any preceding claim, wherein the unit is portable.

21. A unit according to claim 20, wherein the unit is 25 configured to be transported using a hook-lift system.

22. A unit according to claim 20 or 21, wherein the unit includes lifting eyes.

- 22 -

23. A unit for cleaning apparatus used in concreting operations, the unit comprising: an open-topped receiving hopper for receiving apparatus to be cleaned; a pump for providing a flow of liquid onto apparatus received in the

5 open-topped hopper for washing the apparatus and creating washout; a tank for receiving the washout from the hopper, separating solids from the washwater and adjusting the pH of the washwater; a pH reducer associated with the tank for reducing the pH of the washwater in the tank, the pH 10 reducer being able to be connected to a source of an agent for reducing the pH and being arranged to supply the pH reducing agent to the washwater in the tank; and a further tank for receiving pH adjusted washwater from the first-mentioned tank and for separating solids from the pH 15 adjusted washwater.

24. A unit for cleaning apparatus used in concreting operations, the unit being substantially as herein described with reference to the accompanying drawings.

25. A method of cleaning apparatus used in concreting 20 operations, comprising the steps of:

(a) providing a unit according to any preceding claim,

(b) providing apparatus to be cleaned;

(c) providing a flow of liquid onto the apparatus; 25 (d) collecting the liquid used in step (c)in the hopper of the unit; and

(e) removing solids from, and reducing the pH of, the liquid collected in step (d);

- 23 -

wherein the flow of liquid provided in step (c) comprises liquid produced as a result of carrying out step (e) .