S&F Ref: 889991 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Boral Resources (Vic.) Pty Limited, of Applicant: an Australian company, ACN 004 620 731, of 1 Glenferrie Road, Malvern, Victoria, 3144, Australia Actual Inventor(s): Leo Boesten, Matthew Flynn, Peter Head, Mario Tabone Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Method of producing recycled aggregate from concrete Associated Provisional Application Details: [33] Country: [31] Appl'n No(s): [32] Application Date: AU 2008903570 11 Jul 2008 AU 2008905568 29 Oct2008 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(1905568_1) METHOD OF PRODUCING RECYCLED AGGREGATE FROM CONCRETE Technical Field The present invention relates to a method of producing recycled aggregate from 5 concrete, and particularly producing such aggregate from crushed concrete. Background of the Invention It is known to use crushed concrete as a supplementary (recycled) aggregate in the production of premix concrete. Crushed concrete for use as aggregate is produced by 1o crushing hardened concrete from building demolition sites and the like into a particulate form. Foreign building waste, such as plastic, reinforcing steel, timber and the like is generally removed from the crushed concrete, often ineffectively, such that the crushed concrete supplied for use as recycled aggregate often still contains such foreign building waste. IS Premix concrete has a reasonably small tolerance for variability in grading. A disadvantage of crushed concrete aggregate produced using known techniques is that it has a variable grading. Accordingly, the aggregate is limited to applications where a wide grading tolerance is permissible, with low design strengths and a generally broad specification. 20 A further disadvantage of crushed concrete aggregate is that it can contain remnant foreign building waste, as noted above. Such foreign materials can block and damage concrete pumps and present a safety risk. Yet another disadvantage of known crushed concrete aggregate is that it typically contains a significant percentage of relatively fine particles, which cause premix concrete 25 to harden prematurely, particularly when exposed to high ambient temperatures. The predominance of fine particles also disadvantageously increases the water demand of the concrete mix and results in excessive shrinkage of the concrete, thereby causing cracking. Prior to batching premix concrete, aggregate is typically stored in large storage bins with a tapered lower portion terminating in a gate. The fine particles in known 30 crushed concrete aggregate disadvantageously compacts in the tapered portion of the bins, which can block the gate and prevent or hinder the flow of aggregate from the bin and can cause a safety risk and slow or stop production of premix concrete.
-2 As a result of the above disadvantages, the use of crushed concrete has met with limited commercial success as a concrete aggregate. Object of the Invention 5 It is the object of the present invention to substantially overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative. Summary of the Invention In a first aspect, the present invention provides a method of producing recycled 1o aggregate, said method comprising the steps of: providing crushed concrete; feeding said crushed concrete onto a first sieve having a first predetermined aperture size; allowing particles of said crushed concrete having a size smaller than the first is predetermined aperture size to pass through said first sieve, said particles constituting an intermediate product; feeding said intermediate product onto a second sieve having a second predetermined aperture size less than that of said first sieve; allowing particles of said intermediate product having a size smaller than said 20 second predetermined aperture size to pass through said second sieve, retaining particles of said intermediate product having a size larger than the second predetermined aperture size on the second sieve, the retained particles remaining in a coalesced concrete form and constituting a recycled aggregate; and collecting said recycled aggregate for use in producing a pre-mix concrete 25 without further mechanical breakdown of said recycled aggregate. The first predetermined aperture size is typically between 10mm and 30mm and more preferably approximately 20mm. The second predetermined aperture size is typically between 3mm and 7mm and more preferably approximately 5mm. 30 The method preferably includes the step of removing foreign building waste from said crushed concrete prior to passing said crushed concrete onto said first sieve. The foreign building waste typically includes steel that is removed using a magnet. A -3 plurality of magnets is preferably used. A magnet is additionally, or alternatively applied to the intermediate product and/or said recycled aggregate to remove residual steel. The foreign building waste may additionally or alternatively include plastic. The removal of plastics is preferably performed manually. 5 The first sieve is preferably vibrated to facilitate passage of particles of the crushed concrete of a size less than the first predetermined size through the first sieve. The second sieve is preferably vibrated to facilitate passage of particles of the intermediate product of a size less than the second predetermined size through the second sieve. 10 Particles of the crushed concrete of a size less than the first predetermined size are preferably fed through the first sieve under gravity. Particles of the intermediate product of a size less than the second predetermined size are preferably fed through the second sieve under gravity. The method will typically be carried out on crushed concrete that has been is provided in bulk following previous crushing of hardened concrete. Alternatively, crushing of the concrete may be carried out as part of the recycled aggregate production process. In a second aspect, the present invention provides recycled aggregate produced in accordance with the method as defined in the first aspect above. 20 In a third aspect, the present invention provides a method of producing pre-mix concrete, said method comprising the steps of: producing recycled aggregate according to the method defined above; and mixing said recycled aggregate with sand, cement and water. Optionally, the method may further comprise the step of mixing said recycled 25 aggregate with virgin aggregate. Brief Description of the Drawings A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings, in which: 30 Fig I is flowchart of a method of producing recycled aggregate from concrete; and Fig 2 is a schematic view of apparatus for performing the method of Fig 1.
-4 Detailed Description of the Preferred Embodiment Referring to Figs I and 2, a method of producing aggregate from hardened concrete involves providing a supply of hardened concrete, which is usually recycled concrete, and crushing the hardened concrete using a plurality of cone crushers. Magnets s are then passed through the crushed concrete to remove foreign building waste in the form of reinforcing steel and steel plumbing components. Other foreign building waste, such as plastic materials, including electrical conduits and plastic plumbing components, are removed manually. The crushed concrete will generally be commercially provided in this form for subsequent processing, however, it is envisaged that the above processes io may be incorporated as part of a single processing line. After foreign building waste has been removed, the crushed concrete is fed, by conveyor 10, onto a first sieve 12 having a first predetermined aperture size of approximately 20mm. The first sieve 12 is vibrated and particles of the crushed concrete smaller than 20mm fall therethrough under gravity. These particles constitute an 15 intermediate product. The intermediate product is subsequently fed, by conveyor 14, onto a second sieve 16 having a smaller, second predetermined aperture size of approximately 5mm. The second sieve 16 is vibrated and particles of the intermediate product smaller than 5mm fall therethrough under gravity. A magnet may be applied to the particles accumulated on the second sieve to remove residual steel. The remaining particles 20 accumulated on the second sieve remain in the form of particles of crushed concrete, being a coalesced mass of concrete constituent materials constituting a recycled aggregate. The recycled aggregate is collected for use in producing a pre-mix concrete without any further mechanical breakdown. The fine particles passing the second sieve 16 can be collected for disposal or use 25 in other applications, such as forming up of house slabs. There is some potential for these fine particles to be rescreened to produce a "manufactured" sand, which could substitute diminishing sand stocks in the manufacture of concrete. The course particles collected on the first sieve 16 are separated for use in other general purpose aggregates. When a sample of concrete was subjected to the method described above, 30 crushed concrete recycled aggregate collected from the second sieve 16 displayed the following grading: -5 AS Sieve Size (mm) Coarse Fraction Fine Fraction 26.0 100 19.0 97 13.2 80 9.5 56 100 6.7 35 97 4.75 16 93 2.36 9 76 1.18 8 60 0.600 7 45 0.425 6 38 0.300 6 28 0.150 4 16 0.075 3 11 The crushed concrete recycled aggregate collected on the second sieve 16 also displayed the following properties: AS1141.21 Aggregate Crushing Value Aggregate Crushing Value 22.4% Size of Fraction Tested -13.2mm to +9.50mm AS1141.22 Wet/dry strength Dry strength (kN) 131 Wet strength (kN) 88 Wet/dry strength variation (%) 33 Size of Fraction Tested -13.22mm to +9.50mm Breakdown No AS1141.23 Los Angeles value Los Angeles Value (%)27 Grading B AS1141.24 Aggregate soundness Weighted percentage loss, coarse (%) 9.8 Weighted percentage loss, fine (%) 4.8 Total Weighted percentage loss (%) 9.18 AS1141.25.1 Degradation factor (source rock) Degradation Factor 9 Description of deleterious material No material removed Was wash water clear? No -6 AS1141.6.1 Particle density and water absorption of coarse aggregate (t/m3) Apparent particle density (t/m3) 2.82 Particle density on a dry basis (t/m3) 2.36 Particle density on a saturated surface-dry basis (t/m3) 2.52 Water absorption (%) 6.8 The crushed concrete recycled aggregate is suitable for use as aggregate in producing pre-mix concrete without further mechanical breakdown by further mechanical processing such as crushing, grinding or washing. The only further processing of the 5 recycled aggregate is, optionally, removal of residual foreign building waste such as plastic, metal or timber. However, such foreign building waste would typically be removed prior to feeding the crushed concrete into the first sieve as discussed above. Pre-mixed concrete may be produced using the recycled aggregate produced using the method described above, replacing the normal virgin aggregate either in part or to in full. The recycled aggregate will typically comprise between 20% to 100% of the total aggregate in the concrete pre-mix, depending upon the customer's replacement requirements and the design characteristics of the mix. A normal 25 MpA concrete pre mix for general coating use mixes 9 parts by mass of recycled aggregate, 10 parts by mass of sand, 2.5 parts by mass of cement and 2 parts by mass of water. is Crushed concrete recycled aggregate created using the method described above has a good grading consistency, and is suited for use in premix concrete. The recycled aggregate also has a relatively low proportion of fines and, accordingly, concrete mixes using the aggregate can be used at any time of year, without being unduly susceptible to premature hardening. The relatively low percentage of fine particles in the aggregate also 20 reduces water demand in concrete mixes utilising the aggregate. This reduction in water demand also results in a reduction in cement content, whilst maintaining the desired water: cement ratio. The lower proportion of fines also reduces the likelihood of fines compacting in the lower portions of aggregate storage bins. Due to the higher quality of the crushed concrete aggregate produced using the above described method, a higher ratio 25 of recycled to virgin aggregate can be used in concrete mixes. This results in a significant -7 cost saving, as virgin aggregate is substantially more expensive than recycled aggregate. The use of this recycled aggregate will significantly improve the life of scarce virgin aggregates. Whilst the invention has been described with reference to a specific embodiment, 5 it will be appreciated that it may also be embodied in various other forms. For example: e Foreign building waste, such as reinforcing metal, plumbing and electrical conduits, can be identified by visual inspection and removed manually; and/or * Sieves with different aperture sizings can be used to achieve different aggregate having various gradings.