Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-09-22
2001-05-15
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S728000, C106S823000
Reexamination Certificate
active
06231665
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to admixtures for cementitious compositions and masonry units, and in particular a method for preventing visible efflorescence in cement masonry units, and cement and masonry cement compositions comprising a polyacrylic acid based polymer.
BACKGROUND OF THE INVENTION
Masonry units, sometimes referred to as concrete masonry units (CMUs), include segmental retaining wall (SRW) units, pavers, and architectural blocks, all of which are made from a “masonry concrete,” which is comprised of hydratable cement binder and a fine aggregate. As used herein and hereinafter, the term “fine aggregate” means and refers to aggregate (e.g., non-cementitious) particles wherein at least 95% of said particles have an average diameter of less than 0.375 inches (0.95 cm.). Masonry concrete lacks the coarse aggregate (typically greater than 0.5 inch diameter) that is further used in conventional concrete, such as, for example, ready-mix concrete.
More significantly, masonry concrete differs from conventional concrete because it is said to have zero “slump,” or, to phrase it more accurately, a practically immeasurable fluidity. The slump property is determined by placing wet masonry concrete into an inverted cone, and then removing the cone, and measuring the distance (if any) by which the cone-molded sample drops in height. See ASTM C143 (1988) (“Standard Test Method for Slump of Portland Cement Concrete”). Typically, the slump of masonry concrete is 0-0.75 inches, and thus masonry concrete is said to have essentially “zero slump.”
The phenomenon of efflorescence is manifested as an undesirable whitish coloration or deposit on the surface of cement masonry units such as blocks, pavers, retaining wall segments, and other structures made of low-slump, cementitious mixtures. Efflorescence is a primary problem where the masonry units are used for aesthetic applications.
Currently available chemicals used for efflorescence control include the use of stearates (e.g., zinc stearate dispersions, calcium stearate dispersions) and tall oil fatty acid (TOFA), which, the inventors believe, hinders or blocks the water-borne movement of soluble salts such as calcium hydroxide to the surface of the masonry unit, thereby blocking one of the mechanisms by which efflorescence occurs.
SUMMARY OF THE INVENTION
One of the purposes of the present invention is to reduce the visual appearance of calcium carbonate deposits on the surface of the cement or masonry units.
The present inventors have discovered that this may be done using a polymer comprising a polyacrylic acid or salt or derivative thereof, which polymer has a molecular weight of 500-49,000, more preferably 1,000-19,000, and, most preferably, 1,000-10,000.
An exemplary composition of the invention comprises a hydratable cementitious binder (preferably in the amount of 5-25% based on total dry weight of the composition), a fine aggregate portion in the amount of 75 to 95% based on total dry weight of solids in the composition. When water is incorporated to wet the composition, the composition is preferably a masonry concrete having essentially zero slump when tested by the standard cone method for measuring slump (See e.g., ASTM C143 (1988) (“Standard Test Method for Slump of Portland Cement Concrete”); the composition further comprising a polymer comprising polyacrylic acid or salt or derivative thereof and having an average molecular weight in the range of 500-49,000, and most preferably in the range of 1000-10,000. Preferably, the polymer will comprise an alkali or alkaline earth metal salt (e.g., sodium polyacrylate).
Exemplary methods of the invention for preventing efflorescence in a hydratable cementitious composition involve combining a polymer comprising a polyacrylic acid or salt or derivative thereof, the polymer having an average molecular weight range between 500-49,000, with a hydratable cementitious binder.
Still further exemplary methods are directed to preventing efflorescence particularly in masonry concrete units, and this may be done by combining the above-described polymer with cement during the manufacture (e.g., grinding) of the cement or incorporation of the polymer into a masonry concrete composition, preferably as an aqueous solution, or combination of the polymer with one or more components during formulation of the masonry concrete composition.
Further features and advantages of the invention are provided hereinafter.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The term “masonry concrete” as used herein shall mean and refer to a cementitious composition containing a Portland cement 5-25% (s/s total dry weight composition) and 75-95% (s/s total dry weight composition) of a “fine aggregate” (ASTM 136 (1996)). The term “fine aggregate”, as used herein and hereinafter, means and refers to aggregate (e.g., non-cementitious) particles wherein at least 95% of the particles have an average diameter of less than 0.375 inches (0.95 cm.). Masonry concrete lacks the coarse aggregate (typically greater than 0.5 inch diameter) that is further used in conventional concrete, such as, for example, ready-mix concrete.
The term “cement masonry unit” as may be used herein refers to a structure, such as a block, paver, retaining wall segment, or other three-dimensional structure made from a hydratable cementitious mixture, such as pipes or architectural blocks.
The term “cementitious composition” is used to refer to mixtures composed of a hydratable cement or cementitious binder (usually, but not exclusively, Portland cement, masonry cement, or mortar cement and may also include limestone, hydrated lime, fly ash, blast furnace slag, and silica fume or other materials commonly included in such cements) to which water is added to introduce hydration. Such cementitious mixtures include “mortars” which are pastes containing a cement binder and also a fine aggregate (as defined above). The cementitious mixtures used for forming masonry units have a much lower slump (i.e., lower fluidity) than ready-mix concretes. The manufacture of masonry units typically involves molding cementitious structures so that they are free-standing and susceptible to subsequent curing by self-generated or external heat treatment.
Cementitious compositions of the invention may be formed by mixing required amounts of certain materials, e.g., a hydratable cementitious binder, water, and fine aggregate (as defined above), with a polyacrylic acid or salt or derivative thereof, the polymer having an average molecular weight of 500-49,000; more preferably 1,000-19,000; and most preferably, having an average molecular weight of 1,000-10,000.
Another exemplary method of the invention comprises providing a masonry concrete, comprised of a cement binder and fine aggregate (and having less than 2% by weight of coarse aggregate, which is defined as stones having an average diameter of one-half inch), and a zero slump (e.g., slump of 0-0.75 when tested by the standard cone method), and incorporating into said concrete a polymer comprising a polyacrylic acid or salt or derivative thereof, said polymer having an average molecular weight in the range of 500-49,000. The amount of the polymer is preferably 0.01-5.0 percent based on total dry weight of cementitious binder, and more preferably this amount is 0.05-1.0 percent based on total dry weight of cementitious binder.
A low molecular weight polyacrylic acid-based polymer suitable for use in the invention is commercially available from BASF (Badische Aniline & Sodafabrik, Ludwigshafen of Germany) under the tradename SOKALAN® CP-10. This is a modified sodium acrylate polymer having an average molecular weight of about 4,000. This is a dispersing agent that has been tested previously as a dispersive admixture to make flowable concrete, but the present inventors believe that until the present invention, the use of low molecular weight polyacrylic acid polymers have not been used for preventing efflorescence in cementitious compositions generally, and particularly not been known or suggested for u
Kerkar Awdhoot V.
Kumar Vikram
Baker William L.
Green Anthony
Leon Craig K.
W. R. Grace & Co.,-Conn.
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