Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-02-07
2002-09-17
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S707000, C106S713000, C106S714000, C106S715000, C106S763000, C106SDIG001
Reexamination Certificate
active
06451104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a blended cementitious composition that includes high levels of mineral additions yielding superior cement-based products such as concrete mixtures and mortar.
2. Description of Related Art
The use of concrete as a construction material has been known for thousands of years. The general properties and advantages of concrete over other construction materials are well known and concrete is presently the most widely used construction material in the world.
Through the centuries, the methods and formulations for making concrete mixtures have changed and many variables have been introduced as the technology has advanced. In general, the materials currently employed in making a concrete mixture are hydraulic cement with sand, gravel or crushed rock and water. The mixture is thoroughly intermixed, placed into the desired formwork and allowed to set. After setting and adequate hardening of the mixture the formwork is removed and the strength development continues to occur over time. The concrete mix proportions vary substantially depending upon a host of considerations. Thus, the proportions of hydraulic cement with sand, crushed rock and water are varied to suit the desired parameters. It is also known that certain types of admixtures can be added to concrete to improve the strength, durability and other properties and to reduce the cost.
It has been known, for example, to add to a concrete mixture certain admixtures known as water-reducers or plasticizers and pozzolans to achieve specific objectives in the resulting concrete product. Water-reducers are chemical admixtures which, when used in small amounts, are able to reduce the water content of a concrete mixture. Water reducing admixtures are well known and widely used throughout the industry. The reduction of water while maintaining a workable consistency or slump is desirable because of the increase in strength and impermeability of the resulting concrete. Normal water-reducing agents are commonly used in the industry and are required by ASTM C 494 to reduce the water content in a concrete mixture by at least 5 percent. The typical water reduction is between 6 percent and 7 percent. A negative side effect of large amounts of normal water-reducing agents, however, is the retardation of the setting time and early strength in the concrete. High-range water-reducing admixtures, also called superplasticizers, can be used in much larger quantities than normal plasticizers. These materials are able to reduce the mixing water by up to 25 percent for a given consistency in a fresh concrete mixture. ASTM C 494 requires a superplasticizer to provide at least a 12 percent reduction of water in the concrete mixture while maintaining the same slump. However, superplasticizers are very expensive.
Pozzolanic and cementitious additions to concrete are known as mineral admixtures. A pozzolan is defined as a siliceous material that reacts with calcium hydroxide in the presence of water at ordinary temperatures to develop cementitious properties. Pozzolans and cementitious materials such as ground, granulated blast-furnace slag can be used either as a concrete admixture or as a cement addition to form a blended portland cement.
U.S. Pat. No. 5,346,548, issued on Sep. 13, 1994 to Mehta, relates to highly durable cement products containing siliceous ashes. The patent discloses the use of a variety of types of materials, including fly ash, slag and a highly pozzolanic rice hull ash, with cementitious materials in the formation of blended cement compositions suitable for the construction of concrete structures.
The prior art, in addition to the foregoing patent, has recognized the desirability of using waste materials in the cementitious composition to enhance the properties of the concrete mixture, to reduce the cost of the mixture, and to dispose of waste materials in an ecological and cost-effective manner.
However, all such prior art methods for producing blended cement compositions known to the inventor tend to employ relatively low percentages of mineral admixtures in formulating blended cement compositions. For example, in the case of fly ash, the percentage has typically been from 5 weight percent to 20 weight percent fly ash in ASTM Type IP and Type IP(M) blended Portland cements. Notwithstanding the beneficial properties achieved in formulating such blended cement compositions, there is a continuing demand for blended cement compositions that have improved properties, both in the construction process as well as in the resultant concrete. It is recognized that in view of the massive quantities of this construction material that are employed throughout the world, it would be desirable to improve upon the properties of this construction material in regard to the workability of the fresh concrete mixture and durability of the resulting hardened concrete in the structure. Because of the extensive use of this construction material in accordance with societal demands throughout the world, there has been considerable interest in reducing the material costs associated with the use of concrete.
Therefore, it has long been known that it would be desirable to provide a method for producing a blended cement composition which permits the achievement of properties in the resultant concrete mixture which are more suited to the objectives desired to be attained; which facilitates the preparation and use of the blended cement composition in virtually all operative environments; which simultaneously with the improved operative properties is less expensive; which avoids the need for using very expensive chemical admixtures which may be intended to produce the same results, but at a great cost and with some disadvantages and side effects; which can be employed to produce a concrete or the like which has improved durability over prior art structures; and which otherwise is entirely effective in achieving its operational objectives.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved blended cement composition containing mineral additions that can be added directly to a concrete mixture, or separately as a component of the cementitious materials in the concrete mixture, which has advantages not heretofore achieved in the art.
According to one embodiment of the present invention, a method for producing a blended cementitious composition is provided. The method includes the step of intermixing at least about 5 weight percent rice hull ash, at least about 30 weight percent of a mineral addition selected from fly ash and blast furnace slag, and a hydraulic cement such as portland cement.
According to another embodiment of the present invention, a blended cement composition is provided. The blended cement composition includes at least about 30 weight percent of a hydraulic cement, from about 5 weight percent to about 20 weight percent rice hull ash and at least about 40 weight percent of a mineral additive selected from the group consisting of fly ash, granulated blast-furnace slag and mixtures thereof.
According to yet another embodiment of the present invention, a concrete mixture is provided. The concrete mixture includes a blended cement composition having at least about 30 weight percent hydraulic cement, at least about 5 weight percent rice hull ash and at least about 30 weight percent of a mineral additive selected from the group consisting of fly ash, blast furnace slag and mixtures thereof. The concrete mixture also includes aggregate and water. The rice hull ash, in combination with high amounts of the mineral additive, advantageously enables the formation of a concrete mixture having good flow properties, as measured by the concrete slump, at low levels of mixing water, without the use of a superplasticizing chemical admixture. These mixtures have good workability, high 28-day strength and low 28-day permeability.
REFERENCES:
patent: 4105459 (1978-08-01), Mehta
patent: 4668541 (1987-05-01), Fagerlund
patent: 482
Marcantoni Paul
Marsh & Fischmann & Breyfogle LLP
RHA Technology, Inc.
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