Patent Application
20050235875
The present invention relates to aggregate suitable for use in lightweight concrete, and to lightweight concrete including the aggregate.
The preparation of low density concrete by the incorporation of lightweight aggregates such as vermiculite, cork, slag, asbestos, bagasses and the like in a hydraulic binder such as a cement/sand/water mixture is well known. Low density concrete having much improved properties may be prepared by the incorporation of lightweight aggregate, in particular, foam particles such as polystyrene, into the binder.
However, cementitious materials do not readily bond with these lightweight aggregates, which are generally highly hydrophobic. The hydrophobic character and low density of polystyrene beads produces a tendency to float to the surface of the concrete as it sets. To overcome this problem, various bonding agents have been used to facilitate the incorporation of polystyrene foam particles into lightweight aggregates. These agents include bituminous products, coal tars and mixtures of pitch with epoxy resins or phenolic resins. The use of such bonding agents has proved problematic because coating of the polystyrene particles results in a tacky surface causing the particles to coalesce into a mass which is difficult to disperse in the cementitious matrix. Further, the coatings generally retain a strong bituminous odour which remains unacceptably detectable in the end product. More importantly, the bonding strength between the foam particles and the other components in the cured cement has not been ideal, resulting in an inferior product.
Applicant's earlier patent AU670754 (see also corresponding U.S. Pat. No. 5,472,498) the contents of which are incorporated herein by reference) provided a major advance in the art. By treating polystyrene foam particles with a bonding agent consisting of an emulsion comprising a discontinuous bituminous phase, and a continuous aqueous phase and having ferric oxide suspended in the aqueous phase. The use of this emulsion avoided the problems of surface tackiness and aggregation, provided a lightweight aggregate which was uniformly dispersible in concrete, and strongly bonded therewith providing a lightweight concrete of substantially improved strength. The ferric metal ions kept the lightweight aggregate in suspension in the wet concrete, preventing the aggregate particles from floating to the top, and also led to a strong bond between the aggregate and the concrete in the cured mixture providing a lightweight concrete of improved strength.
Prior to application to the lightweight particles, it was usual for the emulsion described in AU670754 to be diluted with water in compliance with specified concentrations. Failure to adhere to the specified concentration range would lead to a deterioration in the performance of the final product. The previous coating agent typically required addition of around 1 part of the emulsion to 2 parts water prior to application. Attempts by users to extend the emulsion by adding more water, contrary to product specifications, could result in an inferior concrete product.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
Further, the previous bonding agent did not always store well for extended periods of time in conditions of extreme temperature, exhibiting a tendency to settle. Extreme temperature fluctuations can cause stratification of the mixture.
Previous mixtures have also sometimes required the addition of a thickening agent to increase viscosity. These thickening agents are typically cellulose based and are thus vulnerable to bacterial attack.
It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or to provide a commercial alternative.
According to a first aspect, the invention provides a thermally stable composition for use in the manufacture of a lightweight aggregate including:
a continuous bituminous phase;
a discontinuous aqueous phase
an anionic oxide suspended in the discontinuous aqueous phase, and
at least one emulsifying agent.
Preferably, the anionic oxide is a naturally occurring metal oxide, for example red oxide, such as Cupric Oxide (CuO). It is highly preferred to use metal oxides having a needle like crystal structure. However, other naturally occurring oxides, for instance yellow oxide, may be used.
The discontinuous aqueous phase is preferably distilled, or deionized, water.
Grade 170 Bitumeni is preferred as the continuous bituminous phase, although other crude oil or hydrocarbons or mixtures thereof may be used.
The emulsifying agent is preferably a clay emulsifier, such as the sodium bentonites, hydrous aluminium silicose clays and montmorillonite families. A highly preferred emulsifier is Volclay® premium gel, which is a 200 mesh bentonite. Other gels having a similar structure, i.e. with an oleophilic tail and an oleophobic head have also been found suitable for use in the present invention.
Preferably, the composition further includes one or more of a thickener, an inhibitor, and a perfume. The selection of concentrated fragrance used does not appear to be critical. In the present invention, the preferred fragrance is “Eternal”. Similarly, the biocidal concentrate used does not appear to be critical, but sodium ortho-phenylphenol (“opp”) is preferred.
According to a second aspect, the invention provides lightweight aggregate particles coated with a composition according to the first aspect.
Although the coating composition can be applied to a wide range of light weight aggregate materials, it is preferred to apply the composition to polymer foam (including recycled polymer foam) particles, and it is especially desirable to select polystyrene foam particles as the lightweight aggregate to be coated.
According to a third aspect, the invention provides a building material formed from a lightweight aggregate according to the second aspect in combination with a cementitious material.
According to a fourth aspect, the present invention provides a method of forming a composition according to the first aspect, including the steps of:
optionally blending one or more of an air entrainment agent, a fragrance and a biocide with water and shearing to form a soap;
adding an emulsifier;
dispersing naturally occurring anionic oxide particles in the aqueous phase; and
dispersing the aqueous phase in a bituminous phase.
The present invention will now be described by way of example only with reference to the embodiments shown in the accompanying drawings and/or examples.
The preferred bonding agent of the present invention has the following composition (all values are wt %):
Compatible chemicals performing a similar function may be substituted for any of those exemplified in the above formulation, and the relative quantities adjusted accordingly in a manner which will be apparent to a skilled formulator based on the teachings hereof.
The binder formulations of the present invention are best formed by an “in line” emulsification procedure according to the following steps:
1. Micro-aire 940, an air entrainment agent; “Eternal”, the desired fragrance; and sodium ortho-phenylphenol, an antibacterial agent (“opp”) are added to distilled water to form a soap. This soap is circulated for 25 minutes while the temperature is raised to 35° C.
2. Volclay® premium gel is then added to the soap at a slow rate, approximately 10 kg per minute.
3. Red oxide is then dispersed in the mixture at a rate of around 10 kg per minute
4. The mixture is sheared in a high shear mill while Grade170 Bitumen at 195° C. is added at around 1500 kg per hour.
In the above method, the exact sequence of addition in the manufacture of the composition is critical for obtaining the water-in-oil emulsion structure and for providing the coating composition with its useful properties. However, those skilled in the art of emulsification will appreciate that the conditions will vary with equipment employed and formulation used and that other methods for producing the water-in-oil emulsion with a dispersed aqueous phase containing the oxide in suspension may be suitable.
The preferred physical structure of the natural anionic oxides preferred in the present invention may be classified as either “needle-like” or “spherical”. “Needle-like” oxides hold more water, so when they are formed into a paste, this tends to be drier, and thus more viscous than that formed from the corresponding “spherical oxide”. Needle-like oxides are highly preferred. However, the oxides may be either “needle-like” or “spherical”.
The droplets in the emulsion of the present invention have been found to be around 25 microns in diameter, which is considerably larger than the 5 micron diameter droplets found in typical emulsions, and contain the oxide as a suspension within the droplets.
The emulsion has been tested for prolonged exposure to freezing. No noticeable deterioration of the structure or qualities of the composition was observed.
The coating composition (1 part by weight) is mixed with water (8 parts by weight). The formulation can then be used to coat polystyrene balls in a manner similar to that described in AU670754. The coated balls are free flowing when dry and have a pink appearance.
The coated polystyrene balls form an aggregate which is mixed with cement, sand and water. Other types of conventional aggregate can be added if required.
The concrete produced using the present invention can be worked in the same way as normal concrete. The exact quantities used will depend upon the required properties of the concrete and the nature of the other materials used.
The concrete produced is compatible with the lightweight concrete described in AU670754 in terms of physical performance. The weight and other physical properties of the concrete produced in accordance with the present invention is similar to that described in AU670754. However, surprisingly, a compressive strength of around 30 MPa may be obtained using aggregate coated with bonding formulations of the present invention, which is unexpectedly 20% higher than that obtainable from the concrete of AU670754. Those skilled in the art will appreciate that lightweight concrete is designed for low load bearing applications.
Concrete weights as low as 250 kg/m3 can be obtained, but to achieve the maximum strength, 1200-1800 kg/m3 are used, which is about 50-75% the weight of conventional concrete. Concrete density may be controlled by varying the amount of polystyrene in the mixture.
The concrete also has the desirable insulation properties of the lightweight concrete in AU670754, namely a thermal insulation coefficient of 0.065 w/m degree C., and R up to 1.9. The sound insulation properties are also as for the concrete in AU670754, with an STC rating of 40-55.
Although the invention has been described with reference to a specific example, it will be appreciated by those skilled in the art that the compositions and methods of manufacture may be varied without departing from the inventive concept herein disclosed and that the invention may be embodied in many other forms.
| Number | Date | Country | Kind |
|---|---|---|---|
| PR 0992 | Oct 2000 | AU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU01/01351 | 10/22/2001 | WO | 4/18/2005 |
