Masonry cement composition and method of making

Details Masonry cement composition and method of making Masonry cement composition and method of making

2001-06-13

2003-04-29

Marcantoni, Paul (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S706000, C106S707000, C106S708000, C106S709000, C106S710000, C106S737000, C106S810000, C106SDIG001, C264SDIG004

Reexamination Certificate

active

06554894

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a masonry cement composition and a method of making the cement, and more particularly, to a masonry cement composition which contains a blend of fly ash, portland cement, a retarding agent, and an air entrainment agent. The cement composition may be used to produce a mortar which exhibits good compressive strength and does not exhibit efflorescence.
Masonry cement compositions are widely used in the masonry industry and typically comprise a blend of portland cement clinker and limestone (calcium carbonate), which contains entrained air for workability of the mix and produces a product that is light and fluffy. However, a disadvantage of the addition of calcidic products such as limestone is that they can produce a mortar which exhibits efflorescense. Efflorescence generally consists of the formation of hard accretions resembling unsightly white spots or streaks on the surface of the mortar which are deposited on the concrete by the evaporation of water.
To help eliminate the problem of efflorescence, masonry cements have been developed which contain portland cement, an air entraining agent, and a filler such as limestone which provides plasticity to the cement. These components are typically interground in a ball mill to sufficient fineness to afford the desired plasticity, color and compressive strength. However, the addition of limestone has been found to reduce the compressive strength of the cement. It is important that masonry cement be able to form a mortar which adequately meets the strength and other recognized specifications such as set rate set forth by the American Society for Testing and Materials (ASTM) (ASTM C 91-98 for Masonry Cement and ASTM C 270-97 for Mortar for Unit Masonry).
In commonly assigned U.S. Pat. Nos. 5,714,003 and 5,997,632, the disclosures of which are hereby incorporated by reference, there is disclosed a blended hydraulic cement which meets the Standard Performance Specifications for Blended Hydraulic Cement in ASTM C 1157 M-95. However, while such blended hydraulic cements can be used as the base for a masonry cement, they lack the degree of air entrainment for use as a masonry cement.
Accordingly, there is still a need in the art for providing an improved masonry cement which does not contain interground limestone, and which produces a mortar having good compressive strength and an acceptable rate of set.
SUMMARY OF THE INVENTION
The present invention meets that need by providing a masonry cement composition which utilizes fly ash, Portland cement, and an air entraining agent to product a masonry cement which exhibits excellent workability, water retention, and compressive strength. The cement conforms to ASTM C-91 standard specifications for masonry cements. The resulting mortar preferably has an air content of at least 8%, and more preferably, up to 17%.
According to one aspect of the present invention, a masonry cement is provided comprising about 0.1 to 10% Portland cement, about 0.1 to 5% by weight potassium carbonate, from about 0.1 to 30% by weight of a retarding agent, from about 0.1 to 5% by weight of an air entraining agent, and the balance comprising fly ash.
The retarding agent is preferably selected from the group consisting of gypsum, borax, boric acid, citric acid, high alumina clays, and mixtures thereof.
The fly ash used in the masonry cement preferably has a lime (calcium oxide) content of at least 21% by weight, and more preferably, about 25% by weight. The fly ash used is preferably a subbituminous fly ash and preferably comprises about 80 to 95% by weight of the masonry cement composition.
In one embodiment of the invention, the air entraining agent comprises from about 0.1 to 5% by weight of a foaming agent. Where the air entraining agent comprises a foaming agent, the cement composition preferably further includes from about 01.% to about 5% by weight of a foam stabilizer. In an alternative embodiment of the invention, the air entraining agent comprises about 0.1 to 5% by weight of a resin.
The cement preferably further includes from about 0.01 to 3 by weight of a chelating agent. The cement may also include from about 0.1 to 10% by weight of a coloring agent.
The masonry cement composition also preferably includes a water repelling agent selected from the group consisting of stearates and ethylene vinyl acetate.
The masonry cement of the present invention may be mixed with sand and water in a conventional manner to produce a workable mortar suitable for all types of masonry applications. It should be noted that the cement of the present invention requires the addition of less water than prior art masonry cements. The masonry cement may be provided in a variety of colors and may have color added at a job site. In use, the mortar produced from the masonry cement sets and hardens comparably to Portland cement based masonry cements. However, the masonry cement composition of the present invention provides easier workability, greater flexibility in times to tool masonry joints, and is lighter in mass. As a result, less effort is required by the mason to lay masonry units.
The resulting mortar preferably has a compressive strength of at least 800 psi after 7 days, and more preferably, at least 1400 psi.
Accordingly, it is a feature of the present invention to provide a masonry cement composition which does not contain lime products, which provides good compressive strength, and which produces an acceptable rate of set. Other features and advantages of the invention will be apparent from the following detailed description and the appended claims.


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