Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-06-14
2002-03-19
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S724000, C106S725000, C106S727000, C106S728000, C106S808000, C106S809000, C106S810000, C106S822000, C106S823000, C524S005000
Reexamination Certificate
active
06358310
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of concrete admixtures, and more particularly to controlling air entrainment in hydraulic cementitious compositions treated with at least one admixture, such as a shrinkage reducing admixture (“SRA”), and particularly an oxylalkylene SRA.
BACKGROUND OF THE INVENTION
Air entrainment is important for increasing resistance of hydraulic cementitious compositions, such as mortar, masonry, and concrete, to frost attack and deterioration due to repeated freezing and thawing. Entrained air is desirable, therefore, for long-term durability of concrete or mortar in adverse freeze-thaw conditions.
Technically speaking, air entraining admixtures (AEAs) do not generate air in the concrete, but merely stabilize the air either (1) infolded and mechanically enveloped during mixing, (2) dissolved in the mix water, (3) originally present in the intergranular spaces in the dry cement and aggregate; or (4) in the pores of the aggregate. While it is true that the entrained air is within the total mass of concrete, it is only entrained in the paste portion of the mix.
Entrained air is fundamentally different than “entrapped” air. Most of the air that is in concretes, in the absence of admixtures, is often referred to as “entrapped” air. Entrained air is characterized by uniformly dispersed, spherical spaces in cement paste; whereas entrapped air is characterized by irregularly shaped voids which are not generally uniformly sized but generally larger than “entrained” air voids. See e.g.,
Concrete Admixtures
, Vance Dodson (Van Nostrand Reinhold, New York 1990), P. 129 et seq.
The present inventors have discovered an air entrainment problem that arises when oxyalkylene based shrinkage reducing admixtures (SRAs), in concrete and mortar, are used in conjunction with water soluble salts. Oxyalkylene SRAs are known in the art. For example, U.S. Pat. No. 5,413,634 of Shawl et al., incorporated herein by reference, discloses an alkyl ether derivative of an aliphatic polyhydroxyl compound containing an oxyalkylene group.
However, when an oxyalkylene SRA is used with a water soluble salt (such as calcium nitrite), sufficient and controllable levels of entrained air are difficult to attain. This was found to be the case even when the SRAs were used in combination with conventional air entraining admixtures, such as tall oil and vinsol resin. Accordingly, a novel air entraining admixture or system is needed.
In World Patent Application Serial No. PCT/US99/13323, Budiansky et al. disclosed polyoxyalkylene polymers, such as di-block polyethylene glycol and polypropylene glycol polymers, for entraining air in cementitious compositions. These are successful in entraining air in the presence of calcium based salts such as calcium nitrite when the diether content of the SRA is below 0.4%.
In U.S. Pat. No. 5,603,760, Berke et al disclosed the addition to the SRA of at least one ammonium salt of tall oil fatty acid.
However, in both of the preceding patents, the SRA needs to have a diether impurity of under 0.5% to be effective, and even under these conditions only the system disclosed by Budiansky et al. would appear to entrain air in the presence of calcium based salts such as calcium nitrite. Moreover, as the temperature of the concrete increases, the difficult of entraining air also increases, such that the practice of incorporating surfactants to improve high temperature air entrainment would tend to provide disadvantages at lower temperatures due to the consequent entrainment of too much air.
Furthermore, the removal from the SRAs of diether impurities requires additional distillation steps which are not desirable. Thus, there is a need to overcome the problems associated with high diether content and to obtain a finer entrained air void system using oxyalkylene SRAs.
SUMMARY OF THE INVENTION
In surmounting the difficulties of the prior art, the present invention provides an additive composition for modifying a cementitious composition, comprising: at least one admixture, such as an oxyalkylene water reducer (e.g., superplasticizer), an oxyalkylene shrinkage reducing admixture, or mixture thereof; and a triblock polyoxyalkylene copolymer surfactant. The triblock polyoxyalkylene copolymer surfactant, in particular, enhances air entrainment in cementitious compositions containing one or other admixtures that typically inhibit such air entrainment.
Thus, an exemplary additive composition of the invention comprises: (A) at least one admixture comprising a shrinkage reducing admixture, an air entraining admixture, a water reducing admixture, an inorganic salt, a corrosion inhibitor, an accelerator, a retarder, or mixture thereof; and (B) a triblock polyoxyalkylene copolymer surfactant having the formula R
1
O—(A
1
O)
x
—(A
2
O)
y
—(A
1
O)
x
—R
2
wherein R
1
and R
2
represent hydrogen, a C
1
-C
7
alkyl group, a C
5
-C
6
cycloalkyl group, or an aryl group; A
1
represents a C
2
alkyl group, A
2
represents a C
3
alkyl group; “x” represents an integer of 42 to 133; and “y” represents an integer of 21 to 68. Exemplary triblock polyoxyalkylene copolymer surfactants have an hydrophilic/lipophilic balance (HLB) of 20-30, and preferably an average molecular weight between 7,000 and 20,000 and, more preferably, between 8,000 and 15,000. The present inventors have discovered that such surfactants enhance the formation of an air void system with spacing factors and surface areas within the range needed to provide resistance to freezing and thawing damage as recommended by American Concrete Institute, Detroit, Mich., as explained in ACI 212.3R-91. The inventors also discovered that the surfactants are useful, when combined with tall oil based air entraining admixtures, for example, to produce enhanced air void systems in concrete mixtures having a water reducer, superplasticizer, corrosion inhibitor, set retarder, and/or damp-proofing additives, with or without an SRA being present in the concrete mixture. It is believed that triblock polyoxyalkylene copolymer surfactants as described herein and below will work well when blended, admixed, or interground with cementitious compositions containing fly ash, silica fume, blast furnace slag, or pozzolans.
Particularly preferred additives comprise: an oxyalkylene SRA, a water soluble salt (e.g., calcium nitrite), and the above-mentioned triblock polyoxyalkylene copolymer surfactant. The present invention also pertains to cementitious compositions containing the at least one admixture and the triblock polyoxyalkene copolymer surfactant, as well as methods for modifying such cementitious composition with these additives, which may be blended or interground with cement, or incorporated into a wet cementitious slurry as an admixture.
Further advantages and features of the invention will be described further hereinafter.
DETAILED DESCRIPTION OF THE INVENTION
The term “cement composition” as may be used herein refers to pastes, mortars, grouts such as oil well cementing grouts, and concrete compositions comprising a hydraulic cement binder. The terms “paste”, “mortar” and “concrete” are terms of art: pastes are mixtures composed of a hydraulic cement binder (usually, but not exclusively, Portland cement, Masonry cement, Mortar cement, and/or gypsum, and may also include limestone, hydrated lime, fly ash, blast furnace slag, and silica fume or other materials commonly included in such cements) and water; mortars are pastes additionally including fine aggregate, and concretes are mortars additionally including coarse aggregate. The cement compositions tested in this invention are formed by mixing required amounts of certain materials, e.g., a hydraulic cement, water, and fine or coarse aggregate, as may be applicable to make the particular cement composition being formed.
As summarized above, the present invention provides an additive composition containing at least one admixture, such as a shrinkage reducing admixture, an air entraining admixture, a water reducing admixture, an inorganic salt, a corrosion inhibitor, an
Berke Neal S.
Hicks Maria C.
Malone James J.
Baker William L.
Leon Craig K.
Marcantoni Paul
W. R. Grace & Co.,-Conn.
LandOfFree
Air entraining admixture compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Air entraining admixture compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Air entraining admixture compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2882519