Disclosure of the Invention Accordingly the invention resides in a method of forming a soil conditioning agent comprising washing an unset concrete composition by adding water thereto to form a slurry which is unable to set where the resultant slurry comprises the soil conditioning agent.

According to a preferred feature of the invention the aggregate is separated from the resultant slurry.

According to a preferred feature of the invention the resultant slurry is allowed to settle to settle, the liquid is separated from the settled solids wherein the said decanted liquid and the settled solids comprise the soil conditioning agent.

According to a further preferred feature the large aggregate is separated from the slurry before the slurry is allowed to settle.

According to a preferred feature of the invention the liquid is separated from the settled solids shortly after the slurry is initially allowed to settle. According to a preferred embodiment the separated liquid is permitted to settle to allow for at least some of the finely suspended solids to settle and the settled finely suspended solids are separated from the liquid. According to a further preferred feature the large aggregate is separated from the slurry before the slurry is allowed to settle.

Accordingly, in another aspect of the invention the soil conditioning agent resides in a slurry of watered down concrete which is unable to set. According to a preferred feature the aggregate has been removed from the slurry Accordingly, in another aspect of the invention the soil conditioning agent resides in the settled solids which are obtained from unset concrete according to the method as described above.

Accordingly, in another aspect the invention resides in the separated liquid which is obtained from unset concrete according to the method as described above.

Accordingly, in another aspect the invention resides in the settled finely suspended solids which is obtained from unset concrete according to the method as described above.

Accordingly, in another aspect the invention resides in a method of treating soil by applying a solid and/or liquid soil conditioning agent which has been formed according to the method described above.

Description of Specific Embodiments The invention will be more fully understood in the light of the following description of several specific embodiments.

The embodiments relate to the formation of a soil conditioning agent from an unset concrete composition.

It has been found that in concrete batching plants, in which concrete is formed to be delivered to a site by vehicles, it is not an uncommon circumstance for those delivery vehicles to return to the batching plant with some residual concrete remaining in the vehicle. In the past, it has been usual practice to merely wash the residual concrete from the vehicle and deposit the resultant slurry into a waste sump, allow the water to drain from the slurry and then break up the resultant

solid material resident in the sump in order that the resultant solid material can be used as road base. According to alternative proposals the waste concrete is washed from the vehicle, the aggregate and sand is separated from the slurry for use in making fresh concrete or as road base and the resultant liquid is used for the production of fresh concrete.

According to the first embodiment, the residual concrete in the vehicles is washed from the vehicle and delivered into a roller screen whereby most of the aggregate material is separated from the slurry passing from the vehicle. The separated aggregate is collecte for reuse either in fresh concrete or elsewhere. The resultant screened slurry is then allowed to pass from the screen and is collecte in a sump where the solids in the slurry are allowed to settle. After a period of time which is sufficient to allow for the adequate settlement of the solids, the water is decanted or drained from the sump to leave the settled solids. The settled solids are then extracted from the sump and are further dewatered. This dewatering may comprise forming the settled solids into a heap and allowing for the natural drainage of the water from the heaped material.

It has been found that the resultant material can serve as a soil conditioning agent which can be utilise to adjust the pH of acidic soils. In addition, it has been found that the resultant material carries a significant quantity of trace elements which serve to further enhance the quality of the soil to which it is applied.

According to one example of the invention, the method of the embodiment was applied to waste concrete which had been manufactured at a batching plant in Capel, Western Australia and which was formed from an aggregate formed from a basalt rock which was derived from the Gelorup quarry. In addition the concrete contained sand which had been obtained locally. The application of the method was found to produce a soil conditioning agent having a pH of 12 and having the following constituents:

Phosphate 55 mg/Kg Potassium 266 mg/Kg Calcium 7080 mg/Kg Magnesium 250 mg/Kg Zinc < 0.1 mg/Kg Copper 0.2 mg/Kg Iron 110 mg/Kg Manganese 3.6 mg/Kg It is believed that use of the soil conditioning agent derived from the example referred to above, acidic soils (which may be either naturally occurring or which have been acidified as a result of the repetitive application of fertilisers to the soil) can be improved significantly.

It is anticipated that the soil conditioning agent according to the first embodiment can be applied directly to the soil. Alternatively, the solid soil conditioning agent can be mixed with a fertiliser prior to the application to the soil. Alternatively, the solid soil conditioning agent can be incorporated into a fertiliser to be applied jointly with the fertiliser to the soil.

According to a second embodiment of the invention the liquid suspension which in the case of the first embodiment is decanted or drained from the sump subsequent to settling can be used as a soil conditioning agent in the light of it's alkalinity and the presence of it's dissolved contents. It is anticipated that the

separated liquid can be sprayed directly onto the soil to reduce the soil's acidity and otherwise improve the soil.

According to a third embodiment of the invention the separated liquid of the second embodiment comprises liquid suspension of fine particulate material. In the case of the third embodiment the liq1uid suspension is allowed to settle to permit a substantial portion of the fine particulate material to settle. The liquid is then separated from the settled fine particulate material and both the liquid and the settled fine particulate material is used separately as a soil conditioning agent.

According to an example of the third embodiment the decanted or drained liquid which was separated in the example of the first embodiment described above produced a separated liquid suspension which if allowed to fully settle resulted in a liquid portion and a sediment portion which both had a pH of 12. The liquid portion had the following constituents; Total Phosphorous 41 microg/litre Potassium 35.1 mg/Itr Calcium 206.8 mg/ltr Magnesium 0.2 mg/Itr Zinc 0.2 mg/Itr Copper <0.1 mg/ltr Iron 1. 6 mg/ltr Manganese <0.1 mg/Itr

while the sediment portion had the following constituents: Phosphate 251 mg/Kg Potassium 748 mg/Kg Calcium 54337 mg/Kg Magnesium 4396 mg/Kg Zinc 46.5 mg/Kg Copper 31.1 mg/Kg Iron 9166 mg/Kg Manganese 127.8 mg/Kg Therefore the decanted liquid suspension provides a valable means of conditioning soil in that it can be used to improve the pH of acidic soils as well as a source of certain trace elements. In addition the sediment can be used as a soil conditioning agent.

According to a fourth, fifth and sixth embodiment of the invention, the aggregate is not separated from the slurry prior to settling in case of the first second and third embodiments respectively.

According to a seventh embodiment of the invention the waste concrete is washed from the vehicle and if desired the resultant slurry is further diluted to produce a concrete slurry which is unable to set to form a solid and the resultant the slurry is used as a soil conditioning agent. In use of the concrete slurry as a soil conditioning agent it may be necessary to provide a means of agitating the

slurry to keep the solid constituents in suspension, at least during the application phase.

According to a eighth embodiment which is a variation of the seventh embodiment the aggregate is separated from the concrete slurry before the slurry is used as a soil conditioning agent. In use of the concrete slurry as a soil conditioning agent it may be necessary to provide a means of agitating the slurry to keep the solid constituents in suspension, at least during the application phase.

Throughout the specification, unless the context requires otherwise, the word "comprise"or variations such as"comprises"or"comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

It should be appreciated that the scope of the present invention need not be limited to the particular scope of the embodiment described above.