Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-10-09
2003-11-11
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S707000, C106S709000, C106S714000, C106S716000, C106SDIG001
Reexamination Certificate
active
06645290
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of settable compositions for general purpose concrete construction containing Class-F fly ash, Class-C fly ash or slag, and cement kiln dust (CKD) as a substantial replacement for Portland cement conventionally used in such compositions.
BACKGROUND OF THE INVENTION
This invention is concerned with the utilization of four industrial by-products; namely, Class-F fly ash, Class-C fly ash, blast furnace slag, and cement kiln dust (CKD) in general purpose concrete-making composition. When finely divided or pulverized coal is combusted at high temperatures, for example, in boilers for the steam generation of electricity, the ash consisting of the incombustible residue plus a small amount of residual combustible matter, is made up of two fractions, a bottom ash recovered from the furnace or boiler in the form of a slag-like material and a fly ash which remains suspended in the flue gases from the combustion until separated therefrom by known separation techniques, such as electrostatic precipitation. This fly ash is an extremely finely divided material generally in the form of spherical bead-like particles, with at least 70% by weight passing a 200 mesh sieve and has a generally glassy state, resulting from fusion or sintering during combustion. As recognized in the American Society of Testing Materials (ASTM) specification designations C618-00 entitled “Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete” and D5370-96 entitled “Standard Specification for Pozzolanic Blended Materials in Construction Application,” fly ash is subdivided into two distinct classifications; namely, Class-F and Class-C. The definitions of these two classes are as follows:
“Class-F—Fly ash normally produced from burning anthracite or bituminous coal that meets the applicable requirements for this class as given herein. This class fly ash has Pozzolanic properties.
Class-C—Fly ash normally produced from lignite or subbituminous coal that meets the applicable requirements for this class as given herein. This class of fly ash, in addition to having pozzolanic properties, also has some cementitious properties. Some Class-C fly ashes may contain lime contents higher than 10%.”
The latter reference to “pozzolanic properties” refers to the capability of certain mixtures that are not in themselves cementitious, but are capable of undergoing a cementitious reaction when mixed with calcium hydroxide in the presence of water. Class-C fly ash possesses direct cementitious properties as well as pozzolanic properties. ASTM C618-00 is also applicable to natural pozzolanic materials that are separately classified as Class N but are not pertinent here.
As the above quotation indicates, the type of coal to be combusted generally determines which class fly ash results, and the type of coal in turn is often dependent on its geographic origin. Thus, Class-C fly ash frequently results from coals mined in the Midwest; whereas Class-F fly ash often comes from coals mined in the Appalachian region. The ASTM specification imposes certain chemical and physical requirements upon the respective fly ash classifications which are set forth in U.S. Pat. No. 5,520,730 which is incorporated herein by reference.
CKD, on the other hand, is a by-product of the production of Portland cement clinkers by the high temperature furmacing of appropriate raw materials, typically mixtures of limestone and clay or a low grade limestone already containing a sufficient quantity of argillaceous materials often with added quantities of lime to adjust the final composition. The resultant clinkers are pulverized by grinding with gypsum to a high degree of fineness and these particles upon admixture with sand gravel and sufficient water undergo a cementitious reaction and produce the solid product generally referred to as concrete, which exhibits high compressive strength and is thus highly useful in construction of a great variety of building or supporting structures. Generally, rotary furnaces are used for producing Portland cement clinkers and a certain quantity of finely divided dust is produced as a by-product that is carried off in the flue gases from such furnaces. The dust content can range from about 5% of the clinkers output in so-called wet process plants up to as high as 15% in dry process plants. The suspended dust is removed by various separating techniques and remains as a by-product of the cement making operation. Part of the CKD can be returned to the furnace as recycled raw material, but it is not readily reincorporated into clinker formation and, in addition, tends to excessively elevate the alkalinity of the ultimate Portland cement.
Blast furnace slag is a by-product from the production of iron in a blast furnace; silicon, calcium, aluminum, magnesium and oxygen are the major elemental components of the slag. Blast furnace slags include air-cooled slag resulting from solidification of molten blast furnace slag under atmospheric conditions; granulated blast furnace slag, a glassy granular material formed when molten blast furnace slag is rapidly chilled as by immersion in water; and pelletized blast furnace slag produced by passing molten slag over a vibrating feed plate where it is expanded and cooled by water sprays, whence it passes onto a rotating drum from which it is dispatched into the air where it rapidly solidifies to spherical pellets. In general the glass content of the slag determines the cementitious character, rapidly cooled slags have a higher glass content and are cementitious; slowly cooled slags are non-glassy and crystalline and thus do not have significant cementitious properties.
The quantities of these by-product materials that are produced annually are enormous and are likely only to increase in the future. As petroleum oil as the fuel for the generation of electricity is reduced because of conservation efforts and unfavorable economics, and as political considerations increasingly preclude the construction of new nuclear power electrical generating facilities, or even the operation of already completed units of this type, greater reliance will necessarily fall on coal as the fuel for generating electricity. As of 1979, the amount of CKD was estimated as accumulating at a rate of 4-12 million tons per year in the United States alone, whereas the amount of Class-F fly ash that is available is estimated to be about five times what can be readily utilized. The estimated yearly total production of coal ash in the U.S. is about 66.8 million tons, while the yearly total coal ash sales in the U.S. is about 14.5 million tons. Further, in Canada, the recovery of copper, nickel, lead and zinc from their ores produces over twelve million tons of slag per year, which usually accumulated near the smelters without significant use. Obviously, there is an urgent growing need to find effective ways of employing these unavoidable industrial by-products since otherwise they will collect at a staggering rate and create crucial concerns over their adverse environmental effect.
Various proposals have already been made for utilizing both fly ash and CKD. According to Lea (1971),
The Chemistry of Cement and Concrete
, Chemical Publishing Company, Inc., page 421 et seq., fly ash, i.e., Class-F type, from boilers was first reported to be potentially useful as a partial replacement for Portland cement in concrete construction about 50 years ago, and its utilization for that purpose has since become increasingly widespread. It is generally accepted that the proportion of Portland cement replaced by the usual fly ash should not exceed about 20% to avoid significant reduction in the compressive strength of the resultant concrete, although some more cautious jurisdictions may impose lower limits, e.g., the 15% maximum authorized by the Virginia Department of Highways and Transportation (VDHT). As described in Lea on page 437, the substitution of fly ash tends to retard the early rate of hardening of the concrete so that the concrete show
Blank Rome LLP
Marcantoni Paul
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