Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-05-02
2002-10-08
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S728000, C106S823000, C524S005000
Reexamination Certificate
active
06461425
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to cementitious dry cast mixtures, such as those for which vibration is used to consolidate and compact the dry cast mixture in a mold or extruder. Specifically, the invention is directed to the use of derivatized polycarboxylate additives that function at least in part as dispersants in cementitious dry cast mixtures to allow for reduced water usage, consolidation and compaction of the dry cast mixture, providing for increased compressive strength and reduced cycle time of dry cast formation. The invention is further directed to the use of derivatized polycarboxylate polymer dispersants in combination with surface active agents/air entraining agents to provide increased swipe and early compressive strength.
BACKGROUND OF THE INVENTION
A cementitious dry cast mixture refers to pastes, mortars, and concrete compositions comprising a hydraulic cement binder having consistencies ranging from stiff to extremely dry as defined in ACI 211.3R, Table 2.3.1. Pastes are defined as mixtures composed of a hydraulic cement binder, either alone or in combination with pozzolans such as fly ash, silica fume, or blast furnace slag, and water. Mortars are defined as pastes that additionally include fine aggregate. Concretes additionally include coarse aggregate. These compositions may additionally include other admixtures such as set retarders, set accelerators, defoaming agents, air-entraining or air detraining agents, corrosion inhibitors, water reducing agents, pigments, and any other admixture that does not adversely affect the advantageous results obtained by the admixtures of the present invention.
Cementitious dry cast mixtures are used to form many articles, for example, concrete pipe, roof tile, masonry units, paver units, extruded plank, and any other preformed cementitious articles, in a mold or from an extrusion die. Each of these applications has basic desired characteristics that are critical in terms of producing quality finished units.
In masonry block applications, production speed, sufficient green strength, and the ability to resist slumping, sagging or deforming when stripped from the mold is critical since stripping occurs immediately after casting. The same is true for concrete pipe or roof tile with the additional desired property of improved surface appearance with reduced surface imperfections and reduced roller and/or die wear on equipment producing extruded pieces.
It is desired to reduce the cycle time of the manufacture of each article. The reduction of cycle time reduces the cost of manufacture for each article and increases the number of articles that can be produced in a given time. Cycle time is defined as the time to complete one full cycle from the beginning of feed to the end, or next beginning of feed. The beginning of feed is when the dry cast mixture is fed from a collection hopper into the process. It is also desired to improve the compaction and consolidation of the cementitious dry cast mixture without altering the consistency of the mixture.
Green strength refers to the stability of the article in retaining its shape once the article is removed from the mold or extruder. Green strength is dependent on the consistency of the cementitious dry cast mixture, the amount of fines in the cementitious dry cast mixture, and the moldability of the cementitious dry cast mixture.
Currently, the water to cement (W/C) ratio used in present dry cast mixtures is from about 0.25 to about 0.60. It is desired to minimize the amount of water needed in a cementitious dry cast mixture to achieve consolidation and no sag or deformation in an article produced from the cementitious dry cast mixture.
Another property of cementitious dry cast mixtures for certain dry cast industries is swipe. Swipe is defined as surface effect on a cast article when the mold is removed. Swipe is measured by visually evaluating the surface of the finished article. Swipe is ranked from no swipe to heavy swipe. It is desired to achieve a selected amount of swipe for a finished article.
A further limitation in the present art is the compressive strength of articles produced from cementitious dry cast mixtures. Early compressive strength is defined as the compressive strength achieved within 24 hours with or without steam cure. Compressive strength is determined by ASTM C-1176-2.
Another limiting factor in the improvement of dry cast mixtures is the type and amount of dispersant used. Conventional dispersant chemistries such as naphthalene sulfonates, melamine sulfonates, and lignosulfonates have a lower limit to their effective dosage; below which they are not effective. At levels above the effective dosage of these dispersants, the dry cast mixture becomes critically sensitive to very slight changes in water or moisture content. This makes the use of these dispersants impractical.
The art lacks a cementitious dry cast mixture containing a dispersant that has a low effective dosage, that is not critically sensitive to changes in water or moisture content, that functions in mixtures having a slump of less than about one (1) inch, that permits mixture consolidation and compaction in response to vibration energy, that has increased green strength and compressive strength, and that provides for reduced cycle time in the manufacture of articles from dry cast mixtures. The art also lacks a cementitious dry cast mixture containing a combination of a derivatized polycarboxylate dispersant with a surface active agent/air entraining agent to provide for increased swipe and increased early compressive strength.
It is an object of the invention to provide a combination of a derivatized polycarboxylate dispersant with a surface active agent/air entraining agent to increase the swipe and early compressive strength of a cementitious dry cast mixture.
It is another object of the invention to lower the effective dose of dispersant required to consolidate a cementitious dry cast mixture into the range of from about 0.005 to about 0.12% by weight of cement.
It is another object of the invention to provide a cementitious dry cast mixture article that has increased green strength and increased compressive strength.
SUMMARY OF THE INVENTION
The present invention is directed to cementitious dry cast mixtures for forming cementitious articles. In particular, the invention is directed to a cementitious dry cast mixture comprising cement, water, coarse aggregate, fine aggregate, and including a dispersant, wherein said dispersant is a derivatized polycarboxylate dispersant, or combination of polycarboxylate dispersants, which is a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer.
The present invention is also directed to a method for making a dry cast cementitious article comprising providing a mixture of hydraulic cement, water, coarse aggregate, fine aggregate, and including a dispersant, wherein said dispersant is a derivatized polycarboxylate dispersant which is a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer; and forming the article from the mixture.
The present invention is also directed to cementitious dry cast mixtures for forming cementitious articles. In particular, the invention is directed to a cementitious dry cast mixture comprising cement, water, coarse aggregate, fine aggregate, surface active agent/air entraining agent, and including a dispersant, wherein said dispersant is a derivatized
Brown Heath
Bury Jeffrey R.
Huang Lan
Lu Runhai
Osborne Jesse
Marcantoni Paul
MBT Holding AG
Renner Kenner Greive Bobak Taylor & Weber
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