GB2510118A

GB2510118A - Electrically conductive building material containing pulverized fuel ash or fly ash derivatives

Info

Publication number: GB2510118A
Application number: GB1301204.2A
Authority: GB
Inventors: Brian Bellingham
Original assignee: ELECTRO CONDUCTIVE CONCRETE Ltd
Current assignee: ELECTRO CONDUCTIVE CONCRETE Ltd
Priority date: 2013-01-23
Filing date: 2013-01-23
Publication date: 2014-07-30
Also published as: GB201301204D0

Abstract

An electrically conductive building material comprises a binder and an aggregate, wherein the material further comprises a high carbon content particulate material or a high iron content particulate material or a mixture of these particulate materials. The high carbon particulate material contains greater than 25% carbon by weight and may be a derivative of pulverized fuel ash or fly ash, with the optional addition of calcined petroleum coke. The material shields against electromagnetic radiation and may be used to line an electromagnetically screened room 1. The electrically conductive material has a wide range of other applications including: covering the surface of an alarm system being electrically integrated into the alarm system; a leak detection mechanism comprising a vessel covered at least in part with the material; and a slug repellant pot, trough or paving slab.

Description

Electrically Conductive Building Material The present application relates to an electrically conductive building material. In particular, it relates to an electrically conductive anechoic building material.

It is known to use electrically conductive building materials as shields against electromagnetic radiation. These materials are provided to attenuate electromagnetic radiation. Attenuation is achieved by the absorption and reflection phenomena, wherein the attenuation of a material may be considered as the sum of the capacity of that material to absorb and reflect signals.

An example prior art electrically conductive building material is known from [P 0759017, which comprises a mixture of graphite and amorphous carbon, sand and a binder, and is provided to cut electromagnetic radiation.

Whilst prior art electrically conductive building materials, such as that disclosed in [P 0759017, may be effective at attenuating electromagnetic radiation, even across a broad range of frequencies, their attenuation is more greatly attributed to reflection than absorption.

The present inventors, through considerable research and testing, arrived at an electrically conductive building material capable of minimising the reflection of electromagnetic radiation whilst ensuring sufficient attenuation of electromagnetic radiation, i.e. a more anechoic material. The material, due it its unique make up, is useful, however, not only in attenuating electromagnetic radiation but also has a range of further applications.

According to the present invention, in a first aspect, there is provided an electrically conductive building material comprising a binder and an aggregate, wherein the material further comprises a high carbon content particulate material or a high iron content particulate material or a mixture of these particulate materials.

The particulate materials may be derivatives of pulverized fuel ash (PEA) or fly ash.

The high carbon particulate material may be a mixture consisting only of derivatives of pulverized fuel ash (PEA) or fly ash mixed with calcined petroleum coke (CPC). The high carbon content particulate material may, however, comprise additional materials. The proportion of either the derivatives of pulverized fuel ash (PEA) or the derivatives of fly ash in the mixture forming the high carbon content particulate material may be between 10% and 90%, more preferably between 20 and 30% of the mixture, with the remainder of the mixture comprising calcined petroleum coke (CPC).

The high iron particulate material may be derived from pulverized fuel ash (PEA) or fly ash, or from mined and processed mineral products, orfrom secondary byproducts from a range of processes, or may be a mixture of these.

A preferred characteristic of the high carbon particulate matter is that the average particle size is less than 500 jim. The particle shape is preferably either spherical or angular, but not fibrous. These characteristics enable better distribution of the carbon in the binder of the building material which is important to maximize the electroconductive and anechoic characteristics of the building material.

By high carbon content particulate material, it is meant a particulate material which comprises over 25% carbon by weight. By high iron content particulate material, it is meant a particulate material, which comprises over 25% iron by weight. It is possible that the high carbon content particulate material may comprise over 50% carbon by weight. It is also possible that the high iron content particulate material may comprise over 50% iron by weight. The iron in the high iron content particulate material may be present as Ee203.

The high carbon content particulate material may omit the calcined petroleum coke (CPC) when the pulverized fuel ash (PFA) or fly ash has a suitably high carbon content itself.

An example of such a material, may contain, in addition to carbon, Si02, A1203, Ee203, K20, CaO, MgO, Ti02, Na20, P205 and Cr203. The compounds may be provided in the following amounts by weight of the high carbon content particulate material: Si02-13 to 14%, A1203 - 7 to 9%, Fe203 -3 to 4%, K20 -<1%, CaO -1 to 2%, MgO -<1%, Ti02 -<0.5%, Na20 - <0.5%, P205-<0.3%, and Cr203-<0.02%.

A suitable high iron content particulate material, as a derivative of pulverized fuel ash (PFA) or fly ash, may contain, in addition to iron oxide, Si02, A1203, K20, CaO, MgO, Ti02, Na20, P205, BaO, Cr203, V205, Zr02, ZnO, S. SrO, Mn304. The compounds may be provided in the following amounts by weight of the high iron content particulate material: Fe203 -57 to 68%, Si02 -18 to 23%, A1203 -10 to 13%,, K20 -0.6 to 0.9%, CaO -2 to 4%, MgO -1 to 3%, Ti02 -0.4 to 0.5%, Na20 -0.1 to 0.5%, P205-<1.0%, BaO -<0.1%, Cr203-<0.1%, V205- <0.1%, Zr02 -<0.05%, ZnO -<0.1%, S -<0.2%, SrO -<0.05%, Mn304 -0.2-0.3%.

A mixture of any of the above mentioned high carbon content particulate materials with any suitable high iron content particulate material may be provided, which features a greater proportion of the high carbon content particulate material than the high iron content particulate material. The mixture may, for example, comprise 10% or more by weight of the high iron content particulate material. The mixture may alternatively, for example, comprise 5% or less by weight of the high iron content particulate material.

Alternatively, a mixture of the particulate materials may be provided, which features a greater proportion of the high iron content particulate material than the high carbon content particulate material. The mixture may comprise 70% or more by weight of the high iron content particulate material.

The building material of the present invention may be used to form building blocks, bricks, tiles, or otherwise; it may be poured or cast to form large structures or articles of complex shape or otherwise; it may be used as a flooring or wall covering; or it may be used in any other suitable form.

Although it should be appreciated that it is not to be limited as such, it is preferable that the electrically conductive building material of the present invention comprises a cementitious material. It may be a mortar, a concrete, or a mortar or concrete based composite material. Mortars are distinguished from concretes by the aggregates used to form them. Mortars are formed using aggregates having a greater overall fineness than the aggregates used for forming concretes.

A mortar or concrete may be provided in accordance with the present invention, which comprises any known cement (or mix of cements) and any known, compatible, aggregate (or aggregate mix). Mortars or concretes according to the present invention will further comprise, in addition to the cement and aggregate a particulate material having a high carbon content or a high iron content, or a mix of these particulate materials. Any of the particulate materials or combinations thereof that are discussed below may be used.

Non-limiting examples of binders for the electrically conductive building material according to one or more embodiments comprise Ordinary Portland Cement (OPC), Sulphate Resisting Cement, Portland cement blends with materials such as, but not limited to, pozzolans, pulverized fuel ash and ground granulated blast furnace slag, and various special cements.

Non-limiting examples of aggregates for the electrically conductive building material according to one or more embodiments comprise either sand or gravel or crushed rock or a combination of these elements. Any suitable known aggregates produced from waste products may also be used.

Those skilled in the art will readily appreciate that numerous electrically conductive building materials will be possible within the scope of the claimed invention, which comprise a binder, a compatible aggregate and the particulate material(s).

A suitable, exemplary, building material features OPC as the binder and a crushed rock coarse aggregate and sand fine aggregate mix. An alternative, exemplary, building material comprises OPC as the binder and sand as the aggregate.

As discussed, added to the binder and aggregate is a high carbon content particulate material, which increases conductivity, or a high iron content particulate material, which increases magnetic permeability, or a mixture of the two materials.

In contrast to prior art materials, there is preferably no graphite present in the electrically conductive building material according to the present invention. As detailed, the high carbon content particulate material is preferably a derivative of pulverized fuel ash (PFA) or fly ash or a mixture of materials derived from pulverized fuel ash or fly ash and calcined petroleum coke. However, graphite can be added to the electrically conductive building material, as could other additives beyond those required under the invention to modify various properties of the material.

The properties of the electrically conductive building material may, principally, be varied in two ways: structurally and technically. Structural variation will result in variants of the material which are useful for different building purposes. Technical variation will result in variants of the material which are useful for different technical purposes, electromagnetic shielding, energy storage, heating, etc. Structural variations will depend on the requirements of the construction and the approach adopted to deliver this and can depend, for example, on the choice of the binder and aggregate used and on the ratio of these constituents to one another and to the particulate material.

Technical variations will depend primarily on the use of either just the high carbon particulate material or the high iron particulate material or a combination in different proportions.

The particulate materials, as discussed, may be derivatives of pulverized fuel ash (PEA) or fly ash with or without calcined petroleum coke (CPC) added thereto. To form the derivatives of pulverized fuel ash (PFA) or fly ash, PFA or fly ash can be classified through different processes to produce the PFA or fly ash derived products. The high carbon content

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particulate material may, for example, be taken off by froth flotation and the high iron content particulate material may, for example, be taken off by magnetic separation.

The high carbon content particulate material taken off by froth separation consists of a mixture of carbon based particles of varying size and shape and spherical inorganic particles of varying sizes, wherein the inorganic particles are present as loose individual particles and a number of the inorganic particles fill voids present in the carbon based matrix.

Furthermore, in the high carbon content particulate material, there may be "sub surface" particles embedded within some of the specimens, which results from particles embedded in small sub surface internal voids and/or due to a relatively low level of particles genuinely fused into the matrix during production.

An exemplary high carbon content particulate material has the above structure and the following composition: Moisture Content: "45% as filter cake or <1% dried Fixed Carbon/LOl -dry basis: 70-80 Particle Size Distribution d97: 200jim Particle Size Distribution d50: 6ojim Calorific Value, DAF: 32,000-34,000kJ/kg Volatile Matter: <5% Total Sulphur: <1% Typical Chemical Analysis: 5i02 13-14% MgO <1% A1203 7-9% Ti02 <0.5% Fe203 3-4% Na20 <0.5% K20 <1% P205 <0.3% cao 1-2% cr203 <0.02% This exemplary high carbon content material has a suitably high carbon content that the material may be used without adding any further carbon rich material. With alternative materials having a lower carbon content calcined petroleum coke (CPC) may be added to increase the carbon content, as desired.

The high iron content particulate material taken off by magnetic separation consists of loose spherical, predominately hollow, particles plus agglomerated particles that can be easily broken down.

The spherical particles comprise a mixture of inorganic particles consistent, at least in part, with those present in the high carbon content particulate material, and particles that are predominately iron based. The iron rich hollow spherical particles comprise a combination of iron based hollow spheres with inorganic particles embedded in the internal voids or encapsulated within them plus spherical particles where the iron based material is coating/growing/etc around the inorganic particles.

An exemplary high iron content particulate material has the above structure and the following composition: Moisture Content: <0.5% Particle Specific Gravity: 3.4-3.6g/cm3 Particle Size Distribution d97: 200Rm Particle Size Distribution d10: l8jim Median particle size d50: 65jim Typical Chemical Analysis: Fe203 57-68% Si02 18-23%, A1203 10-13% K20 0.6-0.9%, CaO 2-4% MgO 1-3%, Ti02 0.4-0.5% Na20 0.1-0.5%, P205 <1.0% BaD <0.1%, Cr203 <0.1% V205 <0.1% Zr02 <0.05% ZnO <0.1% s,I <0.2% SrD <0.05%, Mn304 0.2-0.3% The exemplary particulate materials detailed above are available commercially from RockTron Research Ltd, UK under the respective trade names Coke and Maglron7O.

As discussed, the technical features of the material may be altered in dependence on the particulate material used or on the mix of the particulate material used.

The high carbon content particulate material increases conductivity of the building material and the high iron content particulate material increases magnetic permeability of the building material. With only the high carbon content particulate material provided or with a mix containing a high proportion of the high carbon content particulate material a highly conductive building material may be provided. With only the high iron content particulate material provided or with a mix containing a high proportion of the high iron content particulate material a building material having excellent magnetic permeability may be provided. As will be readily appreciated by those skilled in the art, these properties may be tailored to specific uses/circumstances by balancing the ratios of the particulate materials in any mix used.

The building material may be altered to allow for attenuation of electromagnetic radiation of different frequencies, wherein the higher the frequencies to be attenuated, the greater the amount of the high carbon content particulate material will be provided in the building material and the lower the frequencies to be attenuated, the greater the amount of the high iron content particulate material will be included in the building material.

However, the more of the high iron content particulate material that is included in the material, the greater the reflectivity of the material to electromagnetic radiation.

Accordingly, where it is desired to shield high frequency electromagnetic radiation (above 1 GHz) and substantially prevent reflection a material may be provided that includes only the high carbon content particulate material with none of the high iron content particulate material. Such a material is substantially anechoic.

As will be appreciated by the skilled person, depending on the frequencies of radiation, or the frequency range of radiation, that it is sought to attenuate, and the acceptable reflectivity of the material, the amounts of the high carbon and iron content particulate materials in the building material will be varied relative both to one another and to the building material as a whole.

The building material may be altered to allow for differing heat storage and release characteristics, and moreover, used with different voltages. These properties enable the material to be used as an energy store. The iron has much lower conductivity than the carbon but is useful for its heat retention and radiation. The carbon being highly conductive is useful, since it facilitates use of the building material, as a heating element, with lower voltage power supplies than would otherwise be possible. The lower the power supply voltage, the greater the amount of the high carbon content particulate material that will be included and the higher the voltage the lower the amount of the high carbon content particulate material that will be included. The greater the amount of the high iron content particulate material, the greater the amount of heat that may be retained in the building material.

As will be appreciated by the skilled person, depending on the desired thermal properties of the material (if it is to be used for heating) and on the voltage that is to be supplied to the material, the amounts of the high carbon and iron content particulate materials in the building material will be varied relative to one another and to the building material as a whole.

Where only the high carbon content particulate material is provided, it is preferably provided in an amount of between 5% to 50% by weight of the electrically conductive building material. It is more preferably provided in an amount of at least 15% by weight of the electrically conductive building material. It may be provided in an amount of 15 to 19% or 15 to 16% by weight of the electrically conductive building material.

An electrically conductive building material featuring only the high carbon content particulate material may be used, for example, as a building material for buildings that it is desired to hide from radar, wherein the material will not be reflective to electromagnetic radiation.

A further possible use clan electrically conductive building material featuring only the high carbon content particulate material is for electricity production. When such a material is wet, a small current of electricity is generated (in the order of milliamps). Such a material, may, for example, be used to form roof tiles, or otherwise. Larger blocks could be used in rivers, or other wet environments, to generate greater amounts of electricity.

Such a material could be used as a surface covering or material to be integrated into burglar alarms or fire detection equipment, or as a building material for detecting leaks or cracks in large storage vessels, dams etc. that are formed therefrom or covered thereby.

A yet further possible use of an electrically conductive building material featuring only the high carbon content particulate material is for de-icing pavements. For example, the material may be provided as a surface for pedestrian or vehicle access pavements and ramps, car park spaces, or aircraft stands, wherein current could be passed through the material to raise the temperature sufficiently to prevent ice developing on the surface.

An exemplary material, which contains only the high carbon content particulate material and is suited for use as such a heating element, consists of a binder of OPC, a coarse aggregate of crushed rock, a fine aggregate of sand, and the high carbon content particulate material.

Where only the high iron content particulate material is provided, it is preferably provided in an amount of 5% to 50% by weight of the electrically conductive building material.

An electrically conductive building material featuring only the high iron content particulate material may be used, for example, as a heating element for use with a high voltage electrical supply, or as a building material for slot antennae or for alternative military and commercial uses in the telecommunications field.

An exemplary material, which contains only the high iron content particulate material and is suited for use as such a heating element, consists of a binder of OPC, a coarse aggregate of crushed rock, a fine aggregate of sand, and the high iron content particulate material.

Where a mix of the particulate materials is provided, it is preferably provided in an amount of 5% to 50% by weight of the electrically conductive building material.

Electrically conductive building materials that comprise a mix of the particulate materials are useful as heating elements.

An exemplary material, which contains a mix of the particulate materials and is suited for use as a heating element, consists of a binder of OPC, a coarse aggregate of crushed rock and a fine aggregate of sand with the mixture of the high iron content and high carbon content particulate materials.

With a mix of the particulate materials, the conductivity and magnetic permeability of the material may be balanced, as desired, which expands the possible uses of the material beyond any prior art conductive building material.

Among the possible uses for a building material, in accordance with the present invention, which comprises a mixture of the high carbon content and high iron content particulate materials, are the following: 1) As a building material for buildings around airports, wherein by virtue of the materials ability to absorb radiation, such buildings may be built higher and safer. Here a greater proportion by weight of the high carbon content particulate material will be provided in the particulate material mix. The high iron content particulate material may comprise 10% or more of the particulate material mix. Existing buildings can be upgraded to provide some of the safety advantages of new builds using the anechoic render mix as previously described.

2) As a building material for providing shielding against low frequency magnetic interference caused by power cables, in roads, houses, etc. Here the particulate material mix would be as above in (1).

3) As a building material for providing shielding against the signals from telephone masts and pylons by using the material to make tiles, building blocks, etc. Here a greater proportion by weight of the high iron content particulate material will be provided in the particulate material mix. The high iron content particulate material will comprise over 10% of the particulate material mix.

4) As a building material for providing screening of nuclear Installations and nuclear waste before it is stored underground. Here a greater proportion by weight of the high carbon content particulate material will be provided in the particulate material mix. The high carbon content particulate material may comprise over 50% of the particulate material mix.

5) As a building material for use in energy storage or production. Here a greater proportion by weight of the high carbon content particulate material will be provided in the particulate material mix. The high iron content particulate material may comprise 5% or less of the particulate material mix.

6) As a building material for ground earthing. Here a greater proportion by weight of the high iron content particulate material will be provided in the particulate material mix.

The high iron content particulate material may comprise 70% or more of the particulate material mix.

7) As anti static flooring. Here the particulate material mix would be as above in (3).

8) As a building material in the construction of recording Studios, television studios, etc. or otherwise. Here the particulate material mix would be as above in (5).

9) As a means of controlling slugs and certain other Garden pests by making troughs, pots or other items from the material, which pots troughs or other items due to their conductive nature will stop slugs entering the pot or trough. Here the particulate material mix would be as above in (1).

With reference to Figure 1, there is shown, in plan view, an electromagnetically screened room 1 that has its floor, ceiling and walls 3 formed from and/or covered with any of the above described building materials according to the present invention. The room may form part of a larger building or may comprise a standalone structure. The room may, for example, be formed from blocks or panels formed from materials of the present invention with the floor, wall and ceiling subsequently rendered with further materials according to the present invention.

The room, as shown, is entirely closed with the exception of a doorway 4. A labyrinth passage 2 provides sole access to the doorway from outside the room. The labyrinth passage is arranged such that there is no line of sight into the room from outside the passage. The passage is joined directly to the outside of the room and seals around the doorway. The walls, floor and ceiling of the labyrinth passage (as well as the room) are formed from and/or covered with materials according to the present invention, in the same manner as the room.

The doorway is closed with a door. Since any electromagnetic radiation passing through the doorway is effectively absorbed by the surfaces of the labyrinth passage, a simple (and cheap) door, such as a conventional steel door, may be provided to close the doorway. This contrasts with prior art electromagnetically shielded rooms that require an expensive screened door to prevent the escape of electromagnetic radiation. The opposite end of the passage may be closed off with a further door as desired, again this may be a simple door.

Whilst a substantially U-shaped passage is shown it should be noted that numerous alternative passages may be provided, which prevent a direct line of sight into the room from outside the passage, and which, by virtue of their being formed from and/or covered with any of the above described building materials according to the present invention, will provide an effective barrier to electromagnetic radiation.

Claims

Claims 1. An electrically conductive building material comprising a binder and an aggregate, wherein the material further comprises a high carbon content particulate material or a high iron content particulate material ora mixture of these particulate materials.
2. The material of Claim 1, wherein the particulate materials are derivatives of pulverized fuel ash (PEA) or fly ash.
3. The material of Claim 1, wherein the high carbon particulate material is a mixture comprising derivatives of pulverized fuel ash (PFA) or fly ash and calcined petroleum coke (CPC) mixed with the derivatives of pulverized fuel ash (PEA) or fly ash.
4. The material of Claim 3, wherein the derivatives of pulverized fuel ash (PEA) or fly ash comprise 20 to 30% by weight of the mixture comprising the high carbon particulate material.
5. The material of Claim 3, wherein the derivatives of pulverized fuel ash (PEA) or fly ash comprise less than 20% by weight of the mixture comprising the high carbon particulate material.
6. The material of any of Claims 3 to 5, wherein the mixture comprising the high carbon particulate material comprises only the derivatives of pulverized fuel ash (PEA) or fly ash and the calcined petroleum coke (CPC) mixed therewith.
7. The material of any preceding claim, wherein the average particle size of the high carbon particulate material is 500 jim or less.
8. The material of any preceding claim, wherein the particles forming the particulate material are non-fibrous.
9. The material of any preceding claim, wherein the particles forming the particulate material are spherical or angular.
10. The material of any preceding claim, wherein only the high carbon content particulate material is provided and the high carbon content particulate material is provided in an amount of 5 to 50% by weight of the building material.
11. The material of any preceding claim, wherein only the high carbon content particulate material is provided and the high carbon content particulate material is provided in an amount of 15% or more by weight of the building material.
12. The material of any preceding claim, wherein only the high carbon content particulate material is provided and the high carbon content particulate material is provided in an amount of 15% to 19% by weight of the building material.
13. The material of any preceding claim, wherein only the high carbon content particulate material is provided and the high carbon content particulate material is provided in an amount of 15% to 16% by weight of the building material.
14. The material of any preceding claim, wherein a mixture of the particulate materials is provided, which features a greater proportion by weight of the high carbon content particulate material than the high iron content particulate material.
15. The material of Claim 14, wherein the mixture comprises 10% or more by weight of the high iron content particulate material.
16. The material of Claim 14, wherein the mixture comprises 5% or less by weight of the high iron content particulate material.
17. The material of any of Claims ito 13, wherein a mixture of the particulate materials is provided, which features a greater proportion by weight of the high iron content particulate material than the high carbon content particulate material.
18. The material of Claim 17, wherein the mixture comprises 70% or more by weight of the high iron content particulate material.
19. The material of Claim 2, or any of Claims ito 18 when dependent on Claim 2, wherein the high carbon content particulate material contains, in addition to carbon, Si02, A1203, Fe203, K20, CaO, MgQ, Ti02, Na20, P205 and Cr203.
20. The material of Claim 19, wherein the compounds are provided in the following amounts by weight of the high carbon content particulate material: 5i02-13 to 14%, A1203- 7 to 9%, Fe203 -3 to 4%, K20 -<1%, CaO -1 to 2%, MgO -<1%, Ti02 -<0.5%, Na20 - <0.5%, P205-<0.3%, and Cr203-cO.02%.
21. The material of any preceding claim, wherein the high iron content particulate material contains, in addition to iron oxide, Si02, A1203, K20, CaO, MgO, Ti02, Na20, P205, BaO, Cr203, V205, Zr02, ZnO, 5, SrO, Mn304.
22. The material of Claim 21, wherein the compounds are provided in the following amounts by weight of the high iron content particulate material: Fe203 -57 to 68%, 5i02 -18 to 23%, A1203 -10 to 13%,, K20 -0.6 to 0.9%, CaO -2 to 4%, MgO -1 to 3%, Ti02 -0.4 to 0.5%, Na20 -0.1 to 0.5%, P205-<1.0%, BaO -<0.1%, Cr203-<0.1%, V205-<0.1%, Zr02- <0.05%, ZnO -<0.1%, S -<0.2%, SrO -<0.05%, Mn304 -0.2-0.3%.
23. An alarm system comprising one or more surfaces covered with the material of any preceding claim, the material being electrically integrated into the alarm system.
24. A leak detection mechanism comprising a vessel, surface or container formed by or covered at least in part with the material of any preceding claim.
25. A slug repellant element comprising a body that is formed by or covered at least in part with the material of any preceding claim.
26. The slug repellant element of Claim 25, wherein the element comprises a pot, trough or paving slab.
27. A building comprising a room that is entirely closed with the exception of a doorway, and a labyrinth passage providing sole access to the doorway from outside the room, the labyrinth passage being arranged such that there is no line of sight into the room from outside the passage, wherein the walls, floor and ceiling of the room and the labyrinth passage are formed from and/or covered with the material of any preceding claim.
28. An electrically conductive building material as hereinbefore described.