Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-02-21
2002-10-08
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S711000, C106SDIG001
Reexamination Certificate
active
06461424
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to concrete and controlled low-strength materials having improved characteristics, reduced limestone content, and electrical conductivity such that when used in construction, the material is capable of conducting electrical charges such as those resulting from a lightning strike. Further, the concrete and controlled low-strength materials comprise a high carbon content fly ash, thus providing a means for utilization of a product usually considered a by-product, or a waste product, of coal burning power generation.
2. Background Information
It is widely known that fly ash can be incorporated into concrete as a pozzolanic constituent. For example, U.S. Pat. No. 4,268,316 teaches the preparation of a masonry cement comprising from about 10 to 25 percent fly ash, in combination with portland cement and kiln dust. The fly ash utilized in this patent comprises any of those fly ashes which meet the requirements of ASTM (American Society for Testing and Materials) C 618, “Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete.” The patent goes on to postulate that fly ash may be utilized as a mineral admixture in masonry cement in place of natural pozzolans, siliceous or siliceous and aluminous materials which chemically react with calcium hydroxide to form compositions possessing cementitious properties.
It is also known that fly ash can be incorporated into controlled low-strength materials (often referred to as “CLSM”). In the publication “Controlled Low-Strength Materials”, reported by American Concrete Institute Committee 229, June 1999, there is provided a description of controlled low-strength materials along with certain ingredient mixtures used to produce CLSM. Controlled low-strength materials are broadly defined in this publication as self-compacted, cementitious materials used primarily as a backfill in place of compacted fill. Conventional CLSM mixtures usually consist of water, portland cement, fly ash, and fine or coarse aggregates. Some CLSM mixtures consist of water, portland cement and fly ash. However, CLSM is not to be considered as a type of low-strength concrete. This publication also defines CLSM as a material that results in a compressive strength of 8.3 MPa (1200 psi) or less at the conventional 28 day testing period (typically without compaction), and notes that most current CLSM applications require unconfined compressive strengths of 2.1 MPa (300 psi) or less at the conventional 28 day testing period in order to allow future excavation. This publication makes reference to certain examples of CLSM mixtures which include fly ash. U.S. Pat. Nos. 5,951,751 and 4,374,672 also disclose the use of fly ashes which meet the requirements of ASTM C 618 in controlled low-strength materials. In U.S. Pat. No. 5,951,751, one composition includes 1-15% of a lime component, 10-45% of a pozzolanic material (which may be ASTM C 618 Fly Ash), 20-95% aggregate and 10-20% water by weight; and in U.S. Pat. No. 4,374,672, one composition includes 45-80% ASTM C 618 Fly Ash, 1-6% cement and 20-50% water by weight.
It is also known that fly ash is a voluminous by-product of coal burning electrical power generation plants, presenting a possible environmental disposal issue. While those fly ash varieties which meet the requirements of the ASTM Standard Specification C 618 for classes C and F are used as additives to concrete, those fly ash materials which have an excessively high carbon content may not be so used. Accordingly, much of this type of fly ash is relegated to land fill, a less than desirable solution from an environmental viewpoint.
Air dried concrete is considered a reasonably good electrical insulator, having a resistivity on the order of 10
6
ohm-cm, with oven dried concrete having a resistivity on the order of 10
11
ohm-cm. Moist concrete, on the other hand is an electrolyte having a resistivity on the order of 10
4
ohm-cm, which leads to its classification as a semiconductor. Since the transmission of electrical charge in moist concrete occurs through the movement of dissolved ions in the electrolytic solution, higher cement content and higher water content result in lower resistivity. High water content, however, is not acceptable for structural concrete, since it also results in lowered compressive strength and density. It has been found that there is a direct relationship between the degree of hydration of the cement paste and resistivity, yielding a linear relationship between resistivity and compressive strength of cement paste and concrete. That is, resistivity increases as the compressive strength increases.
Electrically conductive concrete may be produced by placing electrically conductive fibers and/or particles in close contact with each other so that a conductive network may be formed throughout the concrete. In conductive concrete, the transmission of electrical charge occurs mainly through the conductive additives, rather than through the electrolytic solution created in moist concrete. Such additives as carbon fibers, steel fibers, steel shavings, and carbon black have been found to be effective in modifying the conductivity of concrete into which they are blended. For example, U.S. Pat. No. 3,962,142 teaches the use of calcined oil coke and acetylene black aggregates in conductive concrete having satisfactory mechanical strength, while U.S. Pat. No. 5,908,584 teaches a mixture of graphite, amorphous carbon, and sand, comprising 25 to 75% of a cementitious composite useful for conducting floors, heating elements, and ground connectors.
Electrically conductive concrete and controlled low-strength materials would be advantageous where lowered electrical resistance may be sought, such as for use in structures where it is necessary to protect electrical equipment from lightning strikes. Accordingly, a means to reduce the electrical resistance of concrete or controlled low-strength materials, or to increase the conductivity thereof, is of interest in the building industry, for example. Further, since high carbon content fly ash is readily available as a waste product, and carbon is known to be highly conductive, its use as an additive to concrete or controlled low-strength materials to lower electrical resistance has now been investigated.
SUMMARY OF THE INVENTION
The present invention provides a means to increase the conductivity of concrete by the addition of high carbon content fly ash. The addition of such amounts of high carbon content fly ash has been found to lower the electrical resistance of the product concrete without seriously adversely affecting the mechanical properties thereof. The present invention also provides a means to increase the conductivity of controlled low-strength materials, by the addition of high carbon content fly ash. The addition of such amounts of high carbon content fly ash has been found to lower the electrical resistance of the product controlled low-strength material, without seriously adversely effecting the mechanical properties thereof. Moreover, this method provides a means for the environmentally acceptable beneficial utilization of such fly ash, as well as providing a low cost construction material having properties suitable for use in such applications as would benefit from an electrically conductive concrete or controlled low-strength material, such as in grounding structures for protection against lightning strikes or random electrical discharge.
Thus, it is an advantage of the present invention to provide an inexpensive method for providing electrically conductive construction materials.
It is a further advantage to provide an economically advantageous means of beneficial utilization of a waste by-product.
It is another advantage to provide electrically conductive concrete that can be inexpensively manufactured, and to provide a dry concrete mixtu
Bischke Robert F.
Noegel John J.
Ramme Bruce W.
Setchell, Jr. Richard H.
Marcantoni Paul
Quarles & Brady LLP
Wisconsin Electric Power Company
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