AU2010224346A1

AU2010224346A1 - Concrete composition

Info

Publication number: AU2010224346A1
Application number: AU2010224346A
Authority: AU
Inventors: Howard Titus
Original assignee: GROCON Pty Ltd
Current assignee: GROCON Pty Ltd
Priority date: 2009-10-01
Filing date: 2010-09-20
Publication date: 2011-04-21

Description

P/00/0 11 Regulaion 32 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Concrete composition The following statement is a full description of this invention, including the best method of performing it known to us: 2 Concrete Composition Field of the invention This invention relates generally to concrete compositions and is directed in particular to a concrete composition that is environmentally more attractive in its mode of production 5 than traditional concrete. Background of the invention Traditional concrete is primarily a mix of Portland cement and aggregate, together with water and a variety of chemical additives according to the desired properties and applications of the end product. A variation from this basic mix has partially substituted 10 the cement with suitable pozzolanic materials, most commonly flyash. In recent years, the cement industry has come to be viewed with some disfavour because the standard process for producing Portland cement is a major generator worldwide of atmospheric carbon dioxide: the desire to reduce the man-made production of greenhouse gases has given rise to standards for designating concrete as 15 "green" or environmentally friendly if it achieves prescribed levels of cement substitution and use of recycled aggregates. Favoured cement substitutes are materials that themselves have long presented a disposal problem such as flyash (a by-product of coal combustion), steelmill slag and silica fume. In Australia, the current requirements for 3-star green concrete are 30-60% cement 20 substitution, depending on the application category (post-tensioned, precast or in situ) and at least 20% of the aggregate to comprise recycled aggregate. Recycled aggregate generally comprises demolition waste, primarily broken up concrete, crushed and milled to meet necessary particle size profiles. The re-use of demolition waste in this way is not without its issues, particularly in relation to the 25 management of undesirable content, and so it is considered in some quarters that the proportion of recycled aggregate should be relatively minor.

3 It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could be reasonably expected to have ascertained, understood, regarded it as relevant or combined it in anyway at the priority date. 5 It is an object of the invention to provide a concrete composition that overall is environmentally beneficial in its production relative to traditional concrete. Summary of the invention The essential concept of the invention is to employ both cement substitution and a substantial proportion of reclaimed aggregate in the preparation of a concrete 10 composition. The invention provides a concrete composition consisting primarily of cement, one or more pozzolanic cement substitutes comprising at least 20% by weight of the total of the cement and cement substitutes, and aggregate that is at least 50% by weight of the total aggregate either (1) reclaimed aggregate, or (2) a mix of recycled and reclaimed 15 aggregate, the balance of the concrete composition including water and 5% or less total by weight chemical additives. By "reclaimed aggregate" is meant herein aggregate obtained by processing concrete waste before it has substantially cured (and is therefore still fluidic or at least soft or plastic) to substantially separate out and thereby recover the aggregate constituent for 20 re-use. Such waste may be, for example, by-product of concrete mix preparation, handling, transport or pumping, and/or may be such waste produced at construction sites. The term "aggregate" as employed herein includes fine aggregate (i.e. less than 4.75 mm) such as sand, and thus reclaimed aggregate may and typically will include fine 25 aggregate (less than 4.75 mm) such as sand. The invention also embraces each of cured concrete made from a concrete composition according to the invention, the preparation of the concrete composition by admixing 4 constituents to produce the composition, and the handling and delivery to a construction site of a concrete composition according to the invention. As used herein, except where the context requires otherwise the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not 5 intended to exclude other additives, components, integers or steps. Embodiments of the invention It is preferred that the mix of recycled and reclaimed aggregate is primarily reclaimed aggregate. Preferably, the aggregate includes said mix of recycled and reclaimed aggregate, and 10 said mix is at least 65% by weight of the total of the recycled and reclaimed aggregate, more preferably in the range 80-85%. That is, the proportion of recycled aggregate is preferably no more than about 35%. In some applications, a proportion of recycled aggregate may be desirable or acceptable. In others 100% of the mix reclaimed aggregate may be satisfactory. 15 Preferably, the reclaimed aggregate, or the mix of recycled and reclaimed aggregate, is 75% or more by weight of the aggregate in the concrete composition, for some applications in the range 90-100%. For some applications the proportion may be 100%. In certain cases, the reclaimed aggregate may provide a proportion of the cement, e.g. 5 to 10%. 20 The reclaimed aggregate is preferably a mix of fines, i.e. less than 4.75 mm in sieve diameter, and coarser particles. The fines are preferably present to at least 5% by weight of the reclaimed aggregate, at least 20% for certain applications. Preferably, the one or more pozzolanic cement substitutes comprise 50-65% by weight of the total of cement and cement substitutes.

5 The one or more pozzolanic cement substitutes are advantageously primarily flyash and slag in a ratio in the range 0.6 to 2.0. Silica fume maybe included, and offwhite cement is another option, both typically together with flyash and slag. Any added water is preferably recycled water. 5 With reference to the balance of the concrete composition including 5% or less total by weight chemical additives, these additives are typically less than 0.5% by weight of the composition and may be of the order of 0.2 to 0.3%. The preferred composition of the invention is environmentally beneficial because it can re-employ at least three major constituents that are otherwise by-products of other 10 processes - flyash, slag and reclaimed aggregate. This is enhanced in the case of the last of these by processing concrete waste before it has substantially cured: this reduces the energy expended and wear of equipment relative to the break-up and comminution of demolition waste, especially concrete demolition waste. It is believed that the present composition is the first green concrete capable of use in 15 in-situ pouring of plasticised post-tensioned suspended slabs. The composition in its optimum embodiments has good workability in that it is capable of being pumped in a slab or wall pouring operation. Examples A number of concrete compositions were prepared and tested for a range of qualities 20 determinative of satisfactory performance. Aggregates were wholly a mix of recycled and reclaimed aggregate, i.e. no fresh aggregate. Key requirements were a characteristic compressive strength of 40MPa within 56 days, air less than 5%, a drying shrinkage at 56 days no greater than 1000 and preferably no greater than 850, and a target slump selected according to the intended application of the respective 25 composition. To allow for variations between batches, and generally to build in a margin of error, the measured mean compressive strength at 56 days should be in the range 45-50MPa, which was achieved for all compositions.

6 Table 1 sets out the respective compositions, their constituents and the measured and observed properties. Table 1 Mix no. 1 2 3 4 5 "General Portland" cement (kg) 175 180 180 150 85 Offwhite Cement (kg) - - - - 90 Water (L/m3) 175 177 181 189 165 Cement Substitutes (kg) Slag 68 70 100 155 100 Flyash 207 200 170 100 170 Silica fume - - - 15 % substitution (kg) 60% 60% 60% 64% 60% Aggregates (kg) - - - - Recycled 400 250 250 330 250 Reclaimed as defined 1260 1410 1410 1320 1410 % Reclaimed 76% 85% 85% 80% 85% Admixtures Rheo (ml/100kg) 600 400 400 - 250 ADVA Plasticiser (ml/m) - 657 584 714 571 Properties Target slump 80 120 120 40/120 50/120 Actual slump 75 120 130 40/120 45/120 Plastic density - - - 2321 2320 Cylinder density 2250 2300 2290 - Air % (max 3.5%) 3.5 2.6 2.6 2.3 2.5 56 Day mean Compressive Strength (MPa) 43 49 47 50 49 (Target 40 MPa) Drying Shrinkage at 56 days (microstrain) 1090 750 640 775 810 Workability Satisfactory Satisfactory Satisfactory Good Good 5

Claims

1. A concrete composition consisting primarily of cement, one or more pozzolanic cement substitutes comprising at least 20% by weight of the total of the cement and cement substitutes, and aggregate that is at least 50% by weight of the total aggregate 5 either (1) reclaimed aggregate, or (2) a mix of recycled and reclaimed aggregate, the balance of the concrete composition including water and 5% or less total by weight chemical additives.

2. A concrete composition according to claim 1 wherein said mix of recycled and reclaimed aggregate is primarily reclaimed aggregate. 10

3. A concrete composition according to claim 2 wherein said aggregate includes said mix of recycled and reclaimed aggregate, and said mix is at least 65% by weight of the total of the recycled and reclaimed aggregate.

4. A concrete composition according to claim 3 wherein said mix is in the range 80 85% by weight of the total of the recycled and reclaimed aggregate. 15

5. A concrete composition according to any one of claims 1 to 4 wherein the reclaimed aggregate, or the mix of recycled and reclaimed aggregate, is 75% or more by weight of the aggregate in the concrete composition.

6. A concrete composition according to any one of claims 1 to 4 wherein the reclaimed aggregate, or the mix of recycled and reclaimed aggregate, is in the range 20 90-100% by weight of the aggregate in the concrete composition.

7. A concrete composition according to any one of claims 1 to 4 wherein the reclaimed aggregate, or the mix of recycled and reclaimed aggregate, is 100% by weight of the aggregate in the concrete composition.

8. A concrete composition according to any one of claims 1 to 7 wherein the 25 reclaimed aggregate is a mix of fines, i.e. less than 4.75 mm in sieve diameter, and coarser particles. 8

9. A concrete composition according to claim 8 wherein the reclaimed aggregate is at least 5% by weight fines.

10. A concrete composition according to any one of claims 1 to 9 wherein said one or more pozzolanic cement substitutes comprise 50-65% by weight of the total of cement 5 and cement substitutes.

11. A concrete composition according to any one of claims 1 to 10 wherein said one or more pozzolanic cement substitutes are primarily flyash and slag in a weight ratio in the range 0.6 to 2.0.

12. A concrete composition according to any one of claims 1 to 11 wherein said one 10 or more pozzolanic cement substitutes include silica fume.

13. A concrete composition according to any one of claims 1 to 12 wherein chemical additives comprise less than 0.5% by weight of the composition.

14. Concrete made from a concrete composition according to any one of claims 1 to 13.

15 15. A method of preparing a concrete composition according to any one of claims 1 to 13, comprising admixing constituents to produce the composition.