WO2010141976A1

WO2010141976A1 - Concrete aggregate

Info

Publication number: WO2010141976A1
Application number: PCT/AU2010/000327
Authority: WO
Inventors: Neville Fullarton
Original assignee: Polyrox Pty Ltd
Priority date: 2009-06-12
Filing date: 2010-03-23
Publication date: 2010-12-16

Abstract

A polymeric aggregate (10) such as for use in concrete, mortar or road base, wherein the aggregate is produced from ash combined with the activator.

Description

CONCRETE AGGREGATE

The present invention relates to concrete and, more particularly, to concrete aggregate, as well as a method of manufacturing that concrete aggregate. The invention will thus be generally described in this context. However, it is to be appreciated that the invention is not limited to these uses. For example, the present invention could be used in mortars, and as an aggregate in road base.

Concrete has been used in the construction of buildings and other structures for thousands of years. Modern civilisation uses concrete on a massive scale in the construction of all manner of buildings and other structures. In part, concrete is a popular building product because it is relatively easy and cheap to produce, it is strong and can be used to manufacture a huge variety of products in any practical size and/or shape.

In simple terms, concrete can be described as an artificial stone-like material made by mixing cement, sand and aggregate, etc. with water and then allowing the mixture to harden. Cement is commonly made by burning a mixture of clay and limestone. Aggregate can take several forms and is often in the form of crushed rock and/or natural stone.

Generally speaking, naturally occurring supplies of these constituents have previously been readily available where and when needed. However, the use of concrete as a building product continues to increase in popularity. As a result, in many regions of the world the supply of naturally occurring concrete constituents is dwindling. In particular, the supply of naturally occurring stone and crushed rock for use as aggregate has become relatively scarce. For example, some parts of Asia, and Northern and Eastern Europe have little natural aggregate. Other areas such as the Sydney area have some natural aggregate. However, it is quickly becoming uneconomical to produce a usable aggregate product from the naturally occurring aggregate.

It is therefore an aim of the present invention to provide an alternative to crushed rock, naturally occurring stone and other aggregates. According to one broad aspect, the present invention provides a polymeric aggregate produced from ash combined with an activator.

The polymeric aggregate could be used as a substitute for crushed rock, natural stone and other concrete aggregates presently used in the manufacture of concrete. The polymeric aggregate could also be used in the manufacture of mortar and road base.

Most preferably, the ash used in the manufacture of the polymeric aggregate is produced from the combustion of coal. In particular, it is envisaged that the ash used in the production of the polymeric aggregate will be a waste or by-product generated by the combustion of coal, particularly at power generating stations. However, it is to be appreciated that this does not preclude the use of ash from other coal combustion sources.

Most preferably, the ash includes SiO₂, AI₂O₃, Fe₂O₃, CaO, MgO, Na₂O, K₂O, SO₃.

Preferably, the SiO₂ and AI₂O₃ constituents form at least 90% by weight of the ash used in the production of the polymeric aggregate.

Preferably, the ratio of SiO₂:AI₂O₃ in the ash is at least 2:1.

Most preferably, the activator includes alkaline hydroxide(s) mixed with water. It is to be appreciated that the ratio of ash:activator could be any practical value. Further, the ratio of alkaline hydroxide(s):water could be any practical value, with the precise amounts of each constituent being related to many factors. These factors include the temperature of the ash, water and activator, as well as the ambient manufacturing temperature and humidity. Each of these factors has an effect on the various aspects of the process used to manufacture the polymeric aggregate. In one form, the activator includes Sodium Hydroxide and Potassium Hydroxide. Preferably, water is combined with the alkaline hydroxides to achieve an activator moisture content of 8% to 12% by weight.

It is to be appreciated that any practical quality of water can be used in the polymeric aggregate manufacturing process. The quality of water generally has no appreciable effect on the polymerisation process. However, it is to be appreciated that the water quality may have an effect on the chemistry of the final polymeric aggregate. Therefore, it is preferred that the quality of water used in the manufacture of the polymeric aggregate is at least similar to the quality of water currently considered acceptable for use in making ready mixed concrete.

Filler materials can be combined with ash and activator to alter the characteristics of the polymeric aggregate. For example, filler materials can be combined with the ash and activator to alter the density and/or hardness of the polymeric aggregate.

The filler materials could include any one or more of low grade ash, sand, stone, clay, metal waste, or other suitable and compatible products. It is to be appreciated, however, that the filler materials will alter the physical characteristics of the final product. Therefore, it is to be appreciated that the amount and type of filler materials (if any) should be selected carefully to ensure that they do not produce a compromised polymeric aggregate, which is ultimately unsuitable for the desired use. The above list of possible filler materials is not an exhaustive list. Other filler materials could also be used.

In one form, air entraining admixtures can be added to the ash and activator to reduce the weight of the polymeric aggregate produced. The addition of air entraining admixtures will, however, result in a reduction of the ultimate strength of the polymeric aggregate. Thus, the amount (if any) of air entraining admixtures added to the ash and activator desirably should be selected to suit a specific polymeric aggregate application.

According to another broad aspect, the present invention relates to the process of manufacturing polymeric aggregate. The process includes mixing ash and an activator. Any other desired constituents can be also be added during the mixing phase. The mixed constituents are then pressed into a usable form and are then cured.

Water is preferably mixed with the ash and the activator. Fillers could also be mixed with the ash and the activator.

Preferably, the constituents are roll-pressed.

Preferably, the constituents are pressed to produce a product at least approximating naturally occurring aggregate. Practically speaking, the size, shape and density of the polymeric aggregate product can be selected as desired. Thus, the polymeric aggregate product can be sized and shaped into units of any practical density, to enable the polymeric aggregate to be used as a replacement for any one or combination of crushed rock, natural stone and other existing aggregate forms.

Preferably, a precise combination of polymeric aggregate constituents is mixed, to ensure the production of a polymeric aggregate of desired physical characteristics.

Preferably, the mixing of constituents occurs substantially continuously, thereby enabling the substantially continuous roll-pressing of aggregate product.

The curing stage should take place for a period of time determined by, inter alia, temperature and humidity conditions.

It is to be appreciated that the most active ingredients in the ash for formation of the polymeric aggregate are available from sources other than ash, if necessary. For example, these ingredients are available from Kaolinite and Metakaolinite. However, it has been found that the SiO₂ and AI₂O₃ available from these sources are generally difficult and expensive to extract, as well as being energy inefficient and producing waste by-products. It will be convenient to hereinafter describe preferred embodiments of the invention with reference to the accompanying drawings. The particularity of the drawings is to be understood as not limiting the broad description of the invention.

Figure 1 illustrates one embodiment of a polymer aggregate product according to the present invention.

Figure 2 illustrates another embodiment of a polymer aggregate product according to the present invention.

Figure 3 illustrates another embodiment of a polymer aggregate product according to the present invention.

Figure 4 illustrates another embodiment of a polymer aggregate product according to the present invention.

Figure 5 illustrates a variety of polymeric aggregate products of various sizes and shapes.

Figure 6 is a magnified view of the polymeric aggregate products illustrated in Figure 5.

Figure 7 illustrates other polymer aggregate shapes according to the present invention.

Figure 8 illustrates diagrammatically one process for the manufacture of the polymeric aggregate product illustrated in Figures 1 to 7.

Figure 1 illustrates one possible polymeric aggregate product according to the present invention. The polymeric aggregate product 10 is provided for the production of mortar or, more preferably, as a constituent (ie. aggregate) for the addition to concrete, road base, or any other product requiring the addition of aggregate (hereinafter these various possible uses will be generalised in terms of concrete aggregate). The polymeric aggregate product 10 is that of a generally right-prism having a hexagonal cross-sectional shape. The polymeric aggregate product 10 includes generally parallel, hexagonally shaped bases 12, 14. The bases 12, 14 are each provided with a roughened and non-planar surface finish. The reason for the roughened, non-planar surface finish is to maximise the strength of the concrete to which the aggregate product 10 is added, by ensuring that the bases 12, 14 and faces 16 of adjacent aggregate products 10 are unable to rest flush against one another in the concrete. In this way, a space is provided between the bases 12, 14 and sides 16 of adjacent randomly arranged aggregate products 10 within the concrete mixture for receiving concrete binder therebetween.

Each of the substantially identical faces 16 are separated by edge ribs 18 extending between the bases 12, 14. Also, each face 16 includes a pair of grooves 20 extending between the bases 12, 14. The ribs 18 and grooves 20 are also provided to ensure that the bases 12, 14, and faces 16 are not arranged flush against those of adjacent product 10 within the concrete, as this could potentially weaken the overall strength of the concrete. Instead, the ribs 18 and grooves 20 allow for at least some concrete binder to be received between adjacent aggregate products 10.

The aggregate product 10 is produced from fly ash combined with an activator of sodium hydroxide and potassium hydroxide combined with water.

It is anticipated that the fly ash will be sourced from power stations, which produce fly ash as a by-product of the coal combustion process.

The precise composition of fly ash used in the manufacture of the polymeric aggregate will be ultimately dependent upon the particular power station or other source from which the fly ash is obtained. Generally, sources containing approximately 90% or more of SiO₂ and AI₂O₃ and with a ratio of SiO₂ and AI₂O₃ of at least 2:1 are preferred. However, fly ash sources having compositions outside of these ranges could also be used. Furthermore, suitable processing of fly ash outside of these composition ranges to provide a more suitable fly ash product may be possible. Figure 2 illustrates a polymeric aggregate product 1 OA similar in shape and composition to that of product 10 illustrated in Figure 1. However, polymeric aggregate product 1 OA is smaller in size when compared to polymeric aggregate product 10. Also, unlike product 10 illustrated in Figure 1 , product 1 OA does not include ribs 18 or grooves 20.

Figure 3 illustrates another possible polymeric aggregate product 1 OB. The composition of polymeric aggregate product 1 OB is similar to that of polymeric aggregate product 10 in Figure 1.

Polymeric aggregate product 1 OB is of a generally right-prism having triangular bases 12, 14 provided with a roughened and non-planar finish. Product 10B has a triangular cross-sectional shape. Polymeric aggregate product 10B is of a similar composition to that of product 10. Product 10B includes grooves 20 (not clearly visible).

Figure 4 illustrates another aggregate product 10C. Product 10C is similarly shaped to product 10A in Figure 2, but of a different size.

Figures 5 and 6 illustrate a variety of possible polymeric aggregate product sizes and shapes.

Figure 7 illustrates another variety of possible (and particularly preferred) polymeric aggregate product shapes including an approximately spheroid shape 10D and an obround or 3-D oval shape 10E. Polymeric aggregate product 10D and 10E is produced from substantially the same constituents as those of polymeric aggregate product 10 illustrated in Figure 1.

A process involved in manufacturing polymeric aggregate is illustrated in Figure 8. A mixer 22 is provided for mixing polymeric aggregate constituents, including fly ash, alkaline hydroxide(s), water and, optionally, filler materials. The mixer 22 is a paddle wheel-type mixer.

Fly ash is supplied to the mixer 22 from a fly ash silo 24 by conduits 26, 28, 30 via conveyor 32 and blender hopper 34. Fly ash is fed to the silo 24 from a fly ash precipitator (not illustrated). A blower 32A is provided to assist in transference from the conveyor 32.

Kaolin filler is optionally supplied to the mixer 22 from a silo 36, via conduits 38, 28, 30, conveyor 32 and hopper 34.

Alkaline hydroxide(s) is supplied to the mixer 22 from a storage device 40 via a conduit 42. It is to be appreciated that the alkaline hydroxide should be safely stored, and highly desirably, in accordance with Australian Standard [AS3780, 1994, Liquid Class 8 Material] or equivalent.

Water is supplied to the mixer 22.

The amount of aggregate constituent supplied to the mixer 22 is controlled by the combination of a mixer weigh batcher (not illustrated) and mixture moisture sensors (also not illustrated). The weigh batcher and moisture sensors can be configured to produce an aggregate of desired physical characteristics.

The provision of mixer weigh batcher and moisture sensors ensures that a sufficient amount and combination of constituents is supplied to the mixer, thereby enabling the possibility of the mixer being substantially continuously operated.

Once the mixer 22 has adequately mixed the constituents, a conduit 38 feeds them to a roll press 46. The roll press 46 is provided to produce aggregate in any one or more of the specific aggregate product types 10, 1 OA, 1 OB, 1 OC, 10D, 10E illustrated in Figures 1 to 7. However, the aggregate could also be pressed to produce any other practical aggregate size(s) and/or shape(s). The pressed aggregate is conveyed by a conveyor 48 through a heat chamber 50 where variable heat is applied for precise times to seal and harden the material.

The cured aggregate product is then fed via the conveyor 48 to a stock pile 52 for curing.

The use of polymeric aggregate in the production of concrete, rather than the use of naturally occurring aggregate provides a large number of advantages.

The present invention is successfully able to use large amounts of waste ash produced at power stations throughout Australia and the rest of the world. Thus, the production of polymeric aggregate provides a significant benefit to industry by converting much of this waste ash to a value added product.

Furthermore, production of polymeric aggregate reduces the demand for naturally occurring aggregate, thereby reducing the demand and need for quarrying, mining activities and the like. Benefits also include less waste and less energy requirements involved in producing polymeric aggregate compared to the waste generated and energy requirements of obtaining naturally occurring aggregate.

The polymeric aggregate of the present invention can be used as a substitute for naturally occurring aggregate because of the impressive properties that geopolymers can provide. Geopolymers in general consist of silico-oxo-aluminate repeating units: M_n[-(Si-θ2-)m-AI-θ2-]n where n is the degree of polymerisation, m is the Si:AI ratio and M is an alkali or alkali earth metal(s). The Si-O-Al-O-Si-O unit is the bridging unit. Increasing the ratio of Si to Al increases the degree of cross-linking.

In addition, the polymeric aggregate of the present invention advantageously can be manufactured relatively accurately in any practical shape and size, and having a wide range of possible physical characteristics. This provides many benefits over the existing methods of crushing and grading natural mined or quarried materials.

Further, the present invention emits almost no green house gases through the entire manufacture of the product. As stated earlier, the polymeric aggregate of the present invention can advantageously also be used in, for example, mortar and road base. The road base could include the aggregate in a compacted state with little or no binder such as, for example, cement or lime.

It is to be understood that various alterations, modifications and/or additions may be introduced into the product and/or process for manufacturing the product previously described without departing from the spirit or ambit of the invention.

Claims

CLAIMS:

1. A polymeric aggregate produced from ash combined with an activator.

2. A polymeric aggregate according to claim 1 , wherein the ash includes SiO₂, AI₂O₃, Fe₂O₃, CaO, MgO, Na₂O, K₂O, SO₃.

3. A polymeric aggregate according to claim 2, wherein the SiO₂ and AI₂O₃ constituents form at least 90% by weight of the ash used in the production of the polymeric aggregate.

4. A polymeric aggregate according to claim 2 or 3, wherein the ratio of SiO₂:AI₂O₃ in the ash is at least 2:1.

5. A polymeric aggregate according to any one of the preceding claims, where the activator includes alkaline hydroxide mixed with water.

6. A polymeric aggregate according to any one of the embodiments substantially as herein described and illustrated.