GB2301543A

GB2301543A - Method of separating aggregate and cement fines contained in concrete slurry

Info

Publication number: GB2301543A
Application number: GB9619852A
Authority: GB
Inventors: Geoff Shaw; William James Hodgson
Original assignee: TARMAC QUARRY PRODUCTS Ltd
Current assignee: TARMAC QUARRY PRODUCTS Ltd
Priority date: 1996-09-24
Filing date: 1996-09-24
Publication date: 1996-12-11
Anticipated expiration: 2016-09-24
Also published as: GB2301543B; GB9619852D0

Abstract

A method of separating aggregate and cement fines contained in a concrete slurry and /or fresh wet concrete comprises the steps of conveying the concrete into a washing tank (13) in which the concrete is flushed with a flushing liquid without being agitated by the washing tank (13), to wash at least some of the cement fines from the aggregate, permitting the flushing residue and the aggregate to flow from the washing tank (13) to a separating means (19) which has sized openings so that flushing residue containing cement fines can pass therethrough whilst the aggregate is retained, further flushing the aggregate to wash further fines from the aggregate, and permitting the aggregate to flow from the separating means (19) to a collection point.

Description

Title: Method of Separating Aggregate and Cement Fines Contained in a Concrete Slurry or in Fresh Wet Concrete.

Description of Invention This invention relates to a method of separating aggregate and cement fines contained in a concrete slurry or in fresh wet concrete.

When a concrete mixer truck returns from delivering a load of concrete, any excess fresh wet concrete is emptied out and the mixer drum is washed out and a mixture of cement, aggregate (which may include sand) and water is discharged in the form of a concrete slurry. The cement may be in the form of fines bound to the aggregate and other cement fines in the slurry.

It is desirable to separate the aggregate and cement fines in the fresh wet concrete and in the slurry so that at least the aggregate can be recycled.

Concrete recycling apparatus are known. One such prior art apparatus comprises a rotatable drum or the like in which the slurry is flushed and the flushing residue which contains the cement fines passes through a mesh or the like in the drum which retains the aggregate. Another prior art apparatus comprises a rotatable auger or the like which moves the concrete mixture in one direction against a counterflow of flushing liquid which carries the cement fines to one end of the auger whilst the aggregate is carried to an opposite end of the auger.

Both such prior art apparatus thus rely entirely on moving parts in contact with the slurry which can present mechanical problems, and furthermore, in the case of a rotatable drum after separation, and in the case of an auger during separation, it is necessary to convey the aggregate against gravity to a collection point.

Such apparatus also tend to be closed in which can make subsequent cleaning difficult.

According to one aspect of the invention we provide a method of separating aggregate and cement fines contained in a concrete slurry or in fresh wet concrete comprising the steps of conveying the concrete into a washing tank in which the concrete is flushed with a flushing liquid without being agitated by the washing tank, to wash at least some of the cement fines from the aggregate, permitting the flushing residue and the aggregate to flow from the washing tank to a separating means which has sized openings so that flushing residue containing the cement fines can pass therethrough whilst the aggregate is retained, further flushing the aggregate to wash further fines from the aggregate, permitting the aggregate to flow from the separating means to a collection point.

The method may include permitting the flushing residue containing cement fines which passes through the separating means to flow into a settling tank where the cement fines may settle out of the flushing liquid.

Thus utilising the two stage separation method of the invention, many of the problems with prior art apparatus can be overcome.

The method essentially includes a static washing step in which cement fines are washed from the aggregate in which no moving parts are required to agitate the slurry, followed by a separation step in which some further washing occurs.

There is no need to convey the aggregate against gravity during separation as with an auger type arrangement, as both the flushing residue and the aggregate flow at all stages of the method.

With known rotating drum type arrangements, after separation in the drum, it is necessary to remove the aggregate from the drum, typically by some conveying means such as scoops or the like to prepare the drum for receiving a further batch of concrete slurry.

Preferably, where the method is utilised to separate aggregate and cement fines contained in fresh wet concrete leftovers and/or slurry being a washing residue from a mixer truck, the mixer truck may discharge concrete and/or the slurry directly into the washing tank which may thus be substantially open topped, although in another application, the concrete and/or slurry may otherwise be conveyed to the washing tank.

The flushing liquid is preferably sprayed onto the fresh wet concrete and/or slurry in the washing tank. It will be appreciated that the flushing liquid may disturb the contents of the washing tank and thus agitate the concrete/slurry, but the washing tank itself need have no means for agitating the contents of the tank as it is washed.

If desired, the washing tank may enable at least some of the flushing residue to flow from the washing tank ahead of the aggregate to the separating means so that the separating means is not subjected to all of the slurry flowing thereto at once. The at least some of the flushing residue may thus pass through the sized openings of the separating means ahead of the aggregate and remaining flushing residue flowing to the separating means.

The washing tank may comprise a first part to which the fresh concrete and/or slurry is conveyed, and a second part into which the flushing residue and the aggregate may flow, the second part being adapted to permit the flushing residue and aggregate to fall to the separating means positioned generally below.

The separating means may comprise a mesh screen or other apertured member in which case the method may comprise sieving the aggregate and flushing residue in the separating means Preferably the separating means includes means to vibrate the aggregate so that the method includes vibrating the aggregate at the separating means.

The method may include utilising at least some of the flushing liquid from the settling tank for washing in the washing tank or separating means, and/or for mixing with cement and aggregate for making a further concrete mixture.

According to a second aspect of the invention we provide an apparatus for performing the method of the first aspect of the invention comprising a washing tank to which a concrete slurry and/or fresh wet concrete is conveyed, means to flush the slurry and/or concrete in the washing tank with a flushing liquid to wash at least some of the cement fines from the aggregate, the washing tank comprising means to permit the flushing residue and aggregate to flow to a separating means which has sized openings so that flushing residue containing cement fines can pass therethrough whilst the aggregate is retained, and means further to flush the aggregate to wash further fines from the aggregate.

The apparatus may further comprise a settling tank into which the flushing residue containing cement fines flows from the separating means.

The invention will now be described with reference to and with the aid of the accompanying drawing which is a purely illustrative drawing of an apparatus in accordance with and for performing the method of the invention.

Referring to the drawing there is shown an apparatus 10 for separating aggregate from cement fines in a concrete slurry such as from a mixer truck 11 in concrete leftovers after a load has been delivered and/or washing residue when a drum 12 of the truck 11 has been washed out after delivering a load.

The apparatus comprises a washing tank 13 positioned conveniently so that the leftovers of fresh wet concrete and/or slurry can be discharged directly into the tank 13 utilising the delivery chute 14 of the mixer truck 11. In this embodiment, the washing tank 13 comprises two parts, namely a first part 15 which is separated from a second part 16 by a gate device 17. The first part 15 receives the concrete and/or slurry (with the gate device 17 set at a predetermined aperture size) and there are water spray heads 18a by means of which water for flushing the slurry and/or wet concrete can be sprayed into the tank 13 in the first part 15 of the tank 13. In this example, the spray heads 18a are in the form of spray bars which extend along and are able to deliver water over substantially the entire width of the tank 13 The tank 13 is static in that there are no moving parts for agitating the slurry during washing although of course the action of spraying water into the tank 13 and discharging the contents of the tank 13 will cause some agitation of the contents of the tank 13. Further the tank 13 is substantially open topped which facilitates subsequent cleaning e.g. by operating the spray heads 18a in the absence of any slurry. The sides of the tank 13 ( first 15 and/or second 16 parts) may be inclined towards one another from top to bottom further to facilitate cleaning.

As water is sprayed into the first part 15 of the tank 13, the gate device 17 permits the contents of the first part 15 of the tank 13 to flow therefrom into the second part 16 of the tank 13 which has an elongate opening in its underside (not seen) through which the contents of the tank 13 fall to a separating means 19 below. The opening extends along the separating means 19 so as to spread the washed concrete and slurry over the separating means 19. Preferably, by having the gate device 17 initially open a small amount, at least some if not the majority of the flushing residue can be arranged to flow to the separating means 18 ahead of the majority of the aggregate although of course some aggregate may escape.

The separating means 19 comprises a mesh screen 20 having openings therein of a predetermined size to permit the flushing residue containing cement fines to pass therethrough but to prevent the aggregate passing therethrough. A typical mesh size may be 2mm or 5mm. It will be appreciated though that particularly where the aggregate contains sand, some fine grains of sand may be permitted to pass through the mesh screen 20 whereas other less fine grains of sand will not.

The mesh screen 20 is preferably inclined to the horizontal at an angle of preferably about 300 and so the aggregate which is not able to pass through the mesh screen 20 will tend to flow over the screen 20 to a collection point 21. To assist this the separating means 19 or at least the mesh screen 20 may be vibrated.

The aggregate may thus be recycled. If desired, the separating means 19 or at least the mesh screen 20 may be arranged to be tipped in the direction indicated by arrow A in the drawing when all of substantial all the flushing residue has passed through the mesh screen 20 to a position where any aggregate lodged in the mesh of the screen 20 can be discharged therefrom.

In the separating means 19, the flushing residue and aggregate are subjected to further washing by means of further spray heads 18b which assists the flow of the aggregate over the mesh screen 20 and from the mesh screen 20 to the collection point 21.

The flushing residue which passes through the mesh screen 20 flows is permitted to flow into a settling tank 22 where the cement fines may be permitted to separate out of the water. At least a portion of the separated out water may be recycled and fed to the spray heads 18a over the washing tank 13 or to the spray heads 18b over the separating means 19, and/or may be fed to a water weighing tank for subsequent mixing with cement and aggregate in the right proportions to make a fresh concrete mix. This may be achieved by pumping the water from a top region of the settling tank 22 direct to the spray heads 18a and or 18b or water weighing tank or indirectly via a further separating tank/filter as desired.

If desired at least a proportion of the separated cement fines may be recycled too. This may be achieved by pumping the concentrated fines-rich slurry from the bottom of the settling tank 22 for treatment prior to mixing in a fresh concrete batch. In any event, the settling tank 22 may be emptied of concentrated fines-rich slurry by pumping, e.g. to a sump.

Various modifications may be made without departing from the scope of the invention. For example the washing tank 13 need not be constructed as described in two parts and the aperture size afforded by the gate 17 may be adjustable or fixed as desired.

Although the separating means 20 described is inclined to the horizontal at 30 , other angles may be used as appropriate. Also, other arrangements are possible which permit the aggregate to flow from the separating means 19 to the collection point 21 which do not have an inclined screen 20 such as a separating means with a generally horizontal mesh screen 20 or the like which intermittently is tipped to a tipped condition.

If desired instead of a mesh screen, any other screen or other member having sized apertures may be provided in the separating means 10.

The washed aggregate and flushing residue need not flow to the separating means 19 by falling as in the example described, but may otherwise be permitted to flow thereto.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A method of separating aggregate and cement fines contained in a concrete slurry or in fresh wet concrete comprising the steps of conveying the concrete into a washing tank in which the concrete is flushed with a flushing liquid without being agitated by the washing tank, to wash at least some of the cement fines from the aggregate, permitting the flushing residue and the aggregate to flow from the washing tank to a separating means which has sized openings so that flushing residue containing cement fines can pass therethrough whilst the aggregate is retained and further flushing the aggregate to wash further fines from the aggregate, permitting the aggregate to flow from the separating means to a collection point.

2. A method according to claim 1 which includes permitting the flushing residue containing cement fines which passes through the separating member to flow into a settling tank where the cement fines may settle out of the flushing liquid.

3. A method according to claim 1 or claim 2 wherein the method includes discharging the slurry and/or fresh wet concrete directly into the washing tank

4. A method according to any one of claims 1 to 3 wherein the flushing liquid is sprayed onto the slurry and/or fresh wet concrete in the washing tank.

5. A method according to any one of claims 1 to 4 wherein the method includes permitting at least some of the flushing residue to flow from the washing tank ahead of the aggregate to the separating means.

6. A method according to any one of the preceding claims which comprises the step of sieving the aggregate and flushing residue in the separating means

7. A method according to any one of the preceding claims wherein the method includes vibrating the aggregate at the separating means.

8. A method according to any one of the preceding claims which includes utilising at least some of the flushing liquid from the settling tank for washing the slurry in the washing tank or washing the aggregate in the separating means, and/or for mixing with cement and aggregate for making a further concrete mixture.

9. A method of separating aggregate and cement fines from a concrete slurry substantially as hereinbefore described with reference to the accompanying drawing.

10. An apparatus for performing the method of any one of the preceding claims comprising a washing tank to which a concrete slurry and/or fresh wet concrete is conveyed, means to flush the slurry and/or concrete in the washing tank with a flushing liquid to wash at least some of the cement fines from the aggregate, the washing tank comprising means to permit the flushing residue and aggregate to flow to a separating means which has sized openings so that flushing residue containing cement fines can pass therethrough whilst the aggregate is retained, and means further to flush the aggregate to wash further fines from the aggregate.

11. An apparatus according to claim 10 wherein a settling tank is provided into which the flushing residue containing cement fines flows from the separating means.

12. An apparatus according to claim 10 or claim 11 wherein means are provided in the washing tank to enable at least some of the flushing residue to flow from the washing tank ahead of the aggregate to the separating means.

13. An apparatus according to claim 12 wherein the washing tank comprises a first part which receives the slurry and to which the slurry is conveyed, and a second part into which the flushing residue and the aggregate may flow, the second part being adapted to permit the flushing residue and aggregate to fall to the separating means positioned generally below.

14. An apparatus according to any one of claims 10 to 13 wherein the separating means comprises an apertured member.

15. An apparatus according to any one on claims 10 to 14 wherein the separating means includes means to vibrate the aggregate.

16. An apparatus for separating aggregate and concrete fines contained in a concrete slurry substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

17. Any novel feature or novel combination of features hereinbefore described and/or as shown in the accompanying drawing.