WO2018085880A1

WO2018085880A1 - Aerated concrete admixture

Info

Publication number: WO2018085880A1
Application number: PCT/AU2017/000235
Authority: WO
Inventors: Due Tuan NGO; Pnyantha MENDIS; David Dirk Visser
Original assignee: Speedpanel Holdings Pty Ltd
Priority date: 2016-11-10
Filing date: 2017-11-10
Publication date: 2018-05-17
Also published as: AU2017358397A1

Abstract

The present invention is an aerated concrete admixture including a matrix of substantially evenly sized and evenly distributed gas filled voids within a geopolymer material, wherein the gas filled voids substantially maintain their position and shape, both during and after the completion of the curing process of the geopolymer. The aeration is introduced into the geopolymer by way of a foam that is gently blended into the admixture so that it is able to maintain its aeration effect on the geopolymer. A plurality of fine polymer fibres may both, or individually, be included in the geopolymer, and the fine polymer fibres are substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids.

Description

Aerated Concrete Admixture

Field of the Invention

[0001 ] This invention relates to aerated concrete admixtures, particularly to admixtures that include at least one of either a plurality of fine fibres of polymer, or a pl urality of very fine fibres of carbon that are evenly distributed within the concrete admixture to provide improved aerated concrete behavior.

Background of the Invention

[0002] There is a large variety of types of aerated concrete. Aerated concretes have a significant number of advantages. Firstly, they are often environmentally friendly to produce, decreasing harmful greenhouse gas emissions. They are typically energy saving to both produce, and in operation, particularly in building related applications, where the aerate nature of the material has comparatively high heat insulation properties.

Furthermore, typical aerated concrete has excellent acoustic properties, and thereby provide an effective sound barrier. They are also typically totally inorganic and incombustible, which makes them suitable for fire-rated applications. The material is capable of

"breathing" and can therefore allow moisture to dissipate, and reduce the likelihood of mold or mildew forming. Their aerated nature allows them to be comparatively lightweight, thereby reducing the logistical equipment required to transport and manipulate material made out of the material into position.

[0003] Aerated concretes are an ideal building material. Composite building panels may comprise a hard outer shell with a hollow interior. The interior is then filled with a suitable material to enhance strength, sound attenuation properties, and improve fire resistance. Flexure resistance is also an important consideration in the case of composite panels that are used in flooring applications.

[0004] In many geographic areas, it is also a critical consideration that the building panel is able to withstand the motion and tremor forces generated by a geological event, such as an earthquake. The primary consideration, when selecting the material from which either the homogeneous or fill for a composite panel is constructed, is whether it provides all the features required for the specific use of the panel in the particular building construction while remaining lightweight.

[0005] A common lightweight material, used for both composite and homogeneous panels is inorganic-based, such as autoclaved aerated concrete (AAC), and lightweight cellular concrete (LCC) based on Portland cement. These materials have a cellular structure with high porosity and high strength to weight ratio. However, they also have significant sustainability problems associated with their production methods in addition to

considerable CO2 emissions associated with cement production. It is estimated that the cement production contributes around 7% of the total anthropogenic emissions of C0₂. In addition, the manufacturing process for AAC involves a high temperature and pressure process which requires substantial energy input, mainly supplied by the burning of the fossil fuels. Not only is this energy consumption environmentally unfriendly, but the cost of energy is considerable, and increasing, thereby AAC production is becoming

increasingly expensive.

[0006] A general method of making AAC or LCC requires the use of aluminum powder for aeration. Aluminum dust generated in the process of making AAC creates an occupational health and safety concern for workers involved in its production. Aluminum powder is potentially explosive if exposed to certain chemicals, static electricity, high temperature and humid conditions. Furthermore, use of aluminum powder as a source of aeration in AAC or LCC is often un-controllable and results in a non-homogenous void structure within the final product which deteriorates the structural properties of the building panel.

[0007] The new generation of inorganic lightweight materials, such as vacuum insulated panels (VIP) and silica aerogels, promise excellent mechanical and insulation properties, however they are currently very expensive to produce, and not suitable for many construction projects.

[0008] Lightweight aerated geopolymers have become a popular alternative for Portland cement-based material and they can also be used as homogeneous panels, or as an in-fill material for composite panels. Geopolymer overcomes many of the limitations and problems associated with the aforementioned types of common building materials including:

• significantly less greenhouse gas emissions during their manufacture

• less energy intensive in their fabrication due to the lower curing temperature

• cheaper component materials and use of industrial by-product materials

• high strength to weight ratio

• higher heat tolerance while retaining structural integrity

• long structural life time-span

• excellent fire resistance properties

• excellent acoustic attenuation properties

• excellent thermal insulation properties

[0009] Conventional aerated geopolymers are highly sensitive to water content in the slurry mixture. Geopolymers also require a high pH for curing. To achieve an optimum balance between properties, such as workability (rheology), apparent density, strength, porosity and durability, for lightweight cellular geopolymer, an appropriate combination of precursors, activators, aeration method, foaming agents, water to solid (w/s) ratio and chemical admixtures is necessary.

[0010] In addition, conventional aerated geopolymers may not have the requisite compression force resistance strength that a building panel may be subjected to while in operation. They may also not have the requisite "pull strength", and this is a major problem.

[0011 ] Another problem is that the matrix of bubbles introduced into the geopolymer mix needs to remain intact during the entire curing process. It is a common problem associated with aerated geopolymers that they suffer from bubble migration and merging. The uniform spread of smaller bubbles are advantageous to the operational properties of the cured aerated geopolymer. Producing a narrower distribution of pore size increases the mechan ical properties of aerated geopolymer after setting. [0012] It is an object of the present invention to create a lightweight aerated geopolymer that ameliorates at least some of the aforementioned problems.

Disclosure of the Invention

[]0013] In one form, the present invention is an aerated concrete admixture including a matrix of substantially evenly sized and evenly distributed gas filled voids within a geopolymer material, wherein the gas filled voids substantially maintain their position and shape, both during and after the completion of the curing process of the geopolymer.

[0014] Preferably, the aeration is introduced into the geopolymer by way of a foam that is gently blended into the admixture so that it is able to maintain its aeration effect on the geopolymer.

[0015] Preferably, a plurality of fine polymer fibres are included in the geopolymer, and the fine polymer fibres are substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids.

[0016] Preferably, the fine polymer fibres have a diameter in the range of 50 to 100 micrometres.

[0017] Alternatively, a plurality of very fine carbon fibres are included in the geopolymer, and the very fine carbon fibres are substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids.

[0018] Preferably, the very fine carbon fibres have a diameter in the range of 5 to 10 micrometres.

[0019] In another preferred embodiment, the admixture includes a plurality of fine polymer fibres, and a separate plurality of very fine carbon fibres, and the plurality of polymer and carbon fibres. All fibres are substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids. The combination of both pluralities of fibres increases the surface area per volume which improves the composite effect of the concrete, and substantially assists in maintaining the aerated foam stability, both during the blending process, and during the curing process, resulting in improved tensile strength and flexure resistance by decreasing the

geopolymer's overall brittleness.

[0020] Preferably, the ratio of the quantity of fine polymer fibres and very fine carbon fibres are selected so as to produce the most cost effective aerated concrete with the required properties.

[0021] Preferably, a low density fine aggregate or cementitious material with high sti ffness is also included within the geopolymer, and the effect of the inclusion of the low density material enhances the strength-to-weight ratio and reduce the drying shrinkage.

[0022] Preferably, the low-density and stiff material is fly ash.

[0023] Preferably, a sufficient quantity of fly ash is included so that the slurry of aerated geopolymer concrete has better workability and higher strength-to-weight ratio.

[0024] Preferably, the particles of fly ash also enhance the aerating foam stability both during the blending process and during the curing process.

[0025] Alternatively, the low-density stiff material is very fine sand.

[0026] In another form, the invention is a method of producing an aerated geopolymer, suitable for use in a composite building panel, said geopolymer having improved tensile strength, flexure resistance, and compressive load strength when fully cured, said method including the steps of:

a) adding the geopolymer precursors with a sufficient quantity of either fly ash, or very fine sand, or both, in a high speed mixing device and

b) transferring the blended wet geopolymer mix to a secondary vessel, and c) adding a sufficient quantity of fine polymer fibres, or a sufficient quantity of very fine carbon fibres, or a mixture of both, and also adding a sufficient quantity of a premade foam made by a suitable foaming agent to the wet geopolymer to aerate the geopolymer mix, and

d) transferring the aerated geopolymer mix to a third vessel and allowing the aerated geopolymer mix to stand for a sufficient time to allow the aeration to homogenise throughout the geopolymer mix, and to allow any large bubbles to settle out of the mix, and e) transferring the aerated geopolymer mix to a launder, or pouring box, and f) dispensing a sufficient quantity of wet aerated geopolymer mix from the launder or pouring box, into at least one pre-prepared outer shell of a composite building panel.

Brief Description of the Drawings

[0027] Figure 1 is a schematic of common prior art aerated geopolymers.

[0028] Figure 2 is a schematic sectional view of a section of aerated concrete admixture in accordance with the present invention.

Detailed Description of the Preferred Embodiments

[0029] We are shown in Figure 1 a schematic diagram of a section of prior art aerated geopolymer 15. As illustrated in the diagram, the prior art aerated concrete admixture typically contains a matrix of larger bubbles 17 and smaller bubbles 19. Not shown in the diagram is that many current aerated concrete admixtures also do not have a uniform distribution of the unevenly sized bubbles. Gas bubble migration, during the pouring and curing process, substantially impacts the aerated concrete admixture's bubble size and distribution homogeneity. Aerated geopolymer may have a substantially homogeneous bubble size and distribution throughout the material as it is mixed, then lose that homogeneity due to bubble migration and merging.

[0030] The uniform spread and size distribution of bubbles is critical to the mechanical and other structural properties of the material after the curing process has completed.

Uneven bubble distributions, or cluster of bubbles, that are of a different size to the average, may act as crack/fracture initiators in the material when it is placed under either compressive or tensile load. This is unacceptable in a construction related panel where predictable mechanical and structural properties of the material are absolutely critical. It is even more critical in areas where the building construction may be subjected to significant seismic event activity.

[0031] Catastrophic structural member failure when subjected to a seismic event is a critical factor in subsequent building construction collapse with an associated significant loss of life and limb.

[0032] Now turning to Figure 2, where we are shown a schematic sectional view of a typical piece of cured aerated concrete admixture 1 that accords with the present invention. Note that the illustration shown is just a tiny typical portion of a much larger block of material. The aerated concrete admixture 1 includes a geopolymer 3 that incorporates a plurality of gas filled voids 5. The gas filled voids are substantially evenly distributed throughout the aerated concrete admixture 1. The aerated concrete admixture 1 also includes a plurality of fine filaments of polymer material 7. As shown, these are also substantially evenly distributed throughout the geopolymer sample, in the regions between the gas filled voids 5. In addition to these, in a preferred embodiment of the invention, a plurality of very fine filaments of carbon 9 are also included. The filaments of polymer and carbon, 7 and 9 respectively, combine with the geopolymer 3 to form a micro concrete through the walls between the gas filled voids 5. This creates an advantage where the material maintains its air pores during the pouring, and curing process, and mitigates the problem of gas bubble migration or merging. The presence of both, or either, the fine filaments of polymer 7 or the very fine filaments of carbon 9 also greatly enhances tensile strength and flexure resistance of the aerated concrete admixture 1 once cured, and significantly improves the performance of the cured material when subjected to the wide array of loads imposed on a structural material during a seismic event.

[0033] To further improve the properties of the aerated concrete admixture 1, the geopolymer 3 includes a significant amount of either class F or class C fly ash 11. In a preferred embodiment of the invention, the geopolymer 3 also includes a si gnificant amount of very fine sand 13. The inclusion of these materials to the geopolymer greatly enhances the compressive load resistance of the cured aerated concrete admixture 1.

[0034] The present invention has greatly improved pull-strength of fixtures and fittings that incorporate the aerated concrete admixture 1 , when compared to typical aerated concrete materials. Also, building panels that incorporate the aerated concrete admixture 1 have the advantage that the aerated concrete admixture 1 incorporated remains

dimensionally stable during the curing process, and then after curing has completed, the building panel has significantly increased flexure load resistance, and can also withstand greater vibration loads from exposure to geological events, such as earthquakes and tremors.

[0035] While the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention.

[0036] It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.

[0037] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.

Claims

1. An aerated concrete admixture including a matrix of substantially evenly sized and evenly distributed gas filled voids within a geopolymer material, wherein the gas filled voids substantially maintain their position and shape, both during and after the completion of the curing process of the geopolymer, and wherein the aeration is introduced into the geopolymer by way of a foam that is blended into the admixture so that it is able to maintain stable porous structure within geopolymer.

2. The concrete aerated admixture as defined in Claim 1 wherein a plurality of fine polymer fibres are included in the geopolymer, and the fine polymer fibres are substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids.

3. The concrete aerated admixture as defined in Claim 2 wherein the fine polymer fibres have a diameter in the range of 50 to 100 micrometres.

4. The concrete aerated admixture as defined in Claim 1 a plurality of very fine carbon fibres are included in the geopolymer, and the very fine carbon fibres are substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids.

5. The concrete aerated admixture as defined in Claim 4 wherein the very fine carbon fibres have a diameter in the range of 5 to 10 micrometres.

6. The concrete aerated admixture as defined in either claims 3 or 5 wherein the admixture includes a plurality of fine polymer fibres, and a separate plurality of very fine carbon fibres, and the plurality of polymer and carbon fibres are each respectively substantially evenly distributed throughout the geopolymer material and interspersed between the matrix of gas filled voids, and the combination of both pluralities of fibres increases the surface area per volume which improves the composite effect of the concrete, and substantially assists in maintaining the aerated foam stability, both during the blending process, and during the curing process, resulting in improved tensile strength and flexure resistance by decreasing the geopolymer' s overall brittleness.

7. The concrete aerated admixture as defined in Claim 6 wherein the ratio of the quantity of fine polymer fibres and very fine carbon fibres is selected so as to produce the most cost effective aerated concrete with the required properties.

8. The concrete aerated admixture as defined in any previous claim wherein a low- density and stiff material is also included within the geopolymer, and the effect of the inclusion of the low-density and stiff material enhances the strength-to-weight ratio of the aerated geopolymer.

9. The concrete aerated admixture as defined in Claim 8 wherein the low-density and stiff material is fly ash.

10. The concrete aerated admixture as defined in Claim 9 wherein a sufficient quantity of fly ash is included so that the admixture has better workability and packing properties, and also enhance the aerating foam stability both during the blending process and during the curing process.

11. The concrete aerated admixture as defined in claim 8 wherein the low-density and stiff material is very fine sand.

12. A method of producing an aerated geopolymer, suitable for use in a composite building panel, said geopolymer having improved tensile strength, flexure resistance, and compressive load strength when fully cured, said method including the steps of:

a) adding the geopolymer precursors with a sufficient quantity of either fly ash, or very fine sand, or both, in a high speed mixing device and wet geopolymer to a first vessel, ready for mixing, and

b) transferring the blended wet geopolymer mix to a secondary vessel, and c) adding a sufficient quantity of fine polymer fibres, or a sufficient quantity of very fine carbon fibres, or a mixture of both, and also adding a sufficient quantity of a foam made of a suitable foaming agent to the wet geopolymer to aerate the geopolymer mix, and d) transferring the aerated geopolymer mix to a third vessel and allowing the aerated geopolymer mix to stand for a sufficient time to allow the aeration to homogenise throughout the geopolymer mix, and to allow any large bubbles to settle out of the mix, and e) transferring the aerated geopolymer mix to a launder, or pouring box, and f) dispensing a sufficient quantity of wet aerated geopolymer mix from the launder or pouring box, into at least one pre-prepared outer shell of a composite building panel.