Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-04-24
2004-03-16
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106SDIG001, C264SDIG004
Reexamination Certificate
active
06706111
ABSTRACT:
FIELD OF THE INVENTION
Applicant's invention relates to a method of pretreating any component of a cementitious composition, particularly ash, that exhibits a high or highly varying adsorption characteristic, or both. The treatment method transforms the chemical adsorption characteristic of the component to a low constant value for use in processes that utilize the component. An important aspect of the present invention is that the method shifts the process of controlling the adsorption effects of the components from the end user to the component marketer.
The present invention relates to a method of treating a component or components of a cementitious composition that contains an appropriate surface morphology, such as that exhibited by unburned carbon or zeolite materials in fly ash, or both, for which the component exhibits the ability to adsorb chemicals from an aqueous solution.
The approach of the method is to satiate the adsorptive potential associated with the surface morphology by adding effective, trace amounts of a treatment agent or agents to the component(s) prior to addition of the component to the composition slurry. Thus, satiation of the adsorption potential occurs only after the treated component is placed in an aqueous solution. It is believed the addition to the aqueous solution (the composition slurry) enables mass transport of the intentionally added effective, trace amount of agent(s) to the adsorption sites.
BACKGROUND OF THE INVENTION
Traditionally, the air entrainment quality of a cementitious composition has been controlled by the end user of the composition. Because of high or high variable adsorption characteristics, or both, the end user has the tedious task of adding the proper quantities of the various components of the cementitious composition. It is often by trial and error that a proper mix is achieved. There is a tremendous need for a way to control the consistency of the adsorption characteristics of mix components at the component supplier. There are numerous components of cementitious compositions which have varying adsorption potentials requiring control. These include ash, sand, cement aggregates, crushed stone, gravels, mortars, cements, clay, lime, lime sand, limestone, and various siliceous and aluminous materials.
While the discussion below focuses on fly ash as a component with high or highly variable adsorptive characteristics, it should be understood that any of the above identified components (and their equivalents) may be pretreated as discussed. The principles set forth are applicable to all of these components.
Ash is a byproduct of the combustion process. The major producer of ash in the United States is coal fired power plants, which generate on the order of 1×10
8
tons of fly and bottom ash annually.
A significant portion of the ash is pozzolanic in nature, which means that in the presence of moisture the ash will react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties. This pozzolanic nature of ash enables ash to be substituted for Portland cement in concrete in amounts up to 50%. While there are other uses for ash, the use of ash in concrete represents the single largest application that beneficially utilizes ash in a product. Unfortunately, however, the majority of ash that is generated at coal fired power plants is never utilized.
Federal clean air standards imposed upon coal burning power plants caused the power plants to reduce the combustion temperature in the boilers in order to reduce NO
x
emissions. The reduced combustion temperature causes a substantial increase in the amount of unburned carbon present in the ash. As a result of the thermal cycle, the unburned carbon in the ash exhibits some of the characteristics of a low-grade activated carbon, in particular, the ability to adsorb a wide range of chemicals. Traditionally ash with a high amount of unburned carbon is referred to as an ash with a high loss on ignition (LOI) content. LOI occurs when the ash is heated in the presence of air to temperatures that completely combust the unburned carbon to gaseous CO
2
Ash with high LOI has traditionally been considered to be ash with high adsorption potential.
The adsorption potential of a high LOI ash is detrimental to the use of the ash as a Portland substitute in concrete due to the ash's tendency to adsorb important cementitious chemical admixtures from the concrete during the mixing process rendering the admixtures unavailable to effect their intended purpose. Virtually all large scale commercial concrete applications require the use of cementitious admixtures for purposes such as entraining air for freeze-thaw protection, reducing water content for higher strength, and retarding or accelerating the initial set of the concrete.
However, it has been found that LOI is not a good indicator of ash adsorption potential. The specific amount of unburned carbon in the ash is a function of the specific combustion condition of the boiler when the coal is burned. Changing demands for electrical power result in changing combustion conditions which in turn results in varying amounts of unburned carbon in the ash. The variability associated with the amount of unburned carbon in the ash increases with increasing LOI. Thus, different loads of ash that are delivered to the concrete manufacturer will differ in LOI content and the amount of difference increases as the average LOI content increases. In addition, the changing combustion conditions influence the surface morphology of the unburned carbon, which directly influences the specific adsorption potential of the unburned carbon. Therefore, two different ash samples with the same LOI can exhibit radically different adsorption potentials. Furthermore, some combustion conditions can produce a surface morphology on the mineral phase of the ash that is capable of adsorption in a manner analogous to activated carbon. This zeolitic type of adsorption cannot be predicted based on the LOI of the ash.
The continuously varying adsorption potential of the ash (and all of the components to the cementitious composition) means that the admixture dosage necessary to compensate for the adsorption effect does not remain constant. The concrete industry, as a whole, is a low technology industry with low profit margins, and as such employs a trial and error method of determining the necessary compensatory admixture dosage. The combination of increased variability of the component adsorption potential with increasing LOI, low correlation between LOI and true adsorption potential of the component, and the trial and error method of determining the compensatory admixture dosage has resulted in enough off specification concrete to cause state regulatory bodies to lower the maximum ash LOI that is permitted to be used in concrete manufactured under their respective jurisdictions.
The concrete industry has responded to this problem by trying to develop admixtures that are both effective for their intended purpose and are not adsorbed by carbon. U.S. Pat. Nos. 4,453,978; 4,828,619; 5,110,362; and 5,654,352, teach and illustrate approaches to resolving this current problem. The methods have not been successful.
For example, the fundamental problem with developing admixtures that do not adsorb into the surface of carbon in ash is the wide range of surface morphologies that are produced on the carbon and mineral phases that are present in the ash by the differing combustion environments associated with the coal fired power plants.
U.S. Pat. No. 5,286,292 issued to Tsukada et al. introduced a new approach of satiating the adsorption potential of the ash before the ash is used. Their approach is to expose the ash to halogen gas (preferably fluorine or chlorine) which readily adsorbs onto the surface of the unburned carbon. Their preferred embodiment includes placing the ash into an enclosed vessel followed by the introduction of the fluorine and/or chlorine gas for a time period from 10 to 60 minutes. After this time, the prepared ash is us
Jackson Walker L.L.P.
Mainland Laboratory, Ltd.
Marcantoni Paul
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