Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2000-12-11
2001-08-21
Green, Anthony (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
06277191
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 oxyalkylene shrinkage reducing admixtures (“SRAs”) and/or water soluble salts such as calcium nitrite and/or calcium nitrate.
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 agents or 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 polyhydroxy compound containing an oxyalkylene group.
When an oxyalkylene SRA is used with a water soluble salt (such as calcium nitrite), however, 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 agents, such as tall oil and vinsol resin. Accordingly, a novel air entraining admixture or system is needed.
SUMMARY OF THE INVENTION
In surmounting the difficulties of the prior art, the inventors have discovered that polyoxyalkylene copolymers provide stable and controllable entrained air, in concrete and mortar, with oxyalkylene shrinkage reducing admixtures (SRAs) and particularly for such SRAs used in combination with water soluble salts, such as alkali or alkaline earth metal salts, preferably calcium salts such as calcium nitrite, calcium nitrate, or a mixture thereof.
An exemplary method of the invention, for improving air entrainment in a hydraulic cementitious composition having an oxyalkylene SRA, comprises introducing to the oxyalkylene SRA a polyoxyalkylene copolymer. Preferably, the copolymer is a nonionic block copolymer, preferably having a predominantly di-block structure, and having a molecular weight of at least 1000. Further exemplary methods include introducing into a hydraulic cementitious composition an oxyalkylene SRA, a water soluble salt, (preferably a calcium salt, e.g., calcium nitrite), and a polyoxyalkylene di-block copolymer. These can be added separately or combined as one or two components.
Exemplary admixtures of the invention comprise a mixture of an oxyalkylene SRA, optionally a water soluble salt (e.g., calcium nitrite), and a polyoxyalkylene copolymer. In further exemplary embodiments, an additional and conventional AEA, such as tall oil, vinsol resin, can be used to improve air entrainment further. The present invention further relates to cement compositions comprising an oxyalkylene SRA, a water soluble salt (e.g., calcium nitrite), and a polyoxyalkylene copolymer.
In especially preferred methods and admixtures, an oxyalkylene SRA comprising di-propylene-t-butyl ether is added to the cementitious composition with a polyoxyalkylene copolymer which comprises a block-like structure comprised substantially of polyethylene oxide and another block-like structure comprised substantially of a higher polyalkylene (such as oxypropylene and/or oxybutylene) groups, the copolymer having a molecular weight of at least 1000, preferably at least 2000, and more preferably at least 4000. Further features and advantages of the invention are described 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, 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) 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.
The present invention allows for air entrainment in concrete containing oxyalkylene SRAs in conjunction with water soluble salts (especially calcium salts, and particularly calcium nitrite). It has been unexpectedly found that small doses of relatively higher molecular weight (e.g., at least 1,000) polyoxyalkylene copolymers (non-ionic, primarily di-block) provide stable, controllable, and desirable degrees of entrained air in concrete containing the above durability enhancing admixtures.
Exemplary polyoxyalkylene copolymers suitable for use in the invention preferably have substantially block, more preferably predominantly di-block, structures. A preferred polyoxyalkylene copolymer, having approximately 4000 molecular weight (50% by weight polyethylene, 50% by weight polypropylene, di-block polymer) was obtained from Arco Chemical under the tradename POLYOL R2633, and tested as described Her below.
Other exemplary polyoxyalkylene copolymers suitable for use in the present invention have the following general formula:
R
1
—[OA
1
]
m
—[OA
2
]
n
—OR
2
;
or
R
1
—[OA
2
]
n
—[OA
1
]
m
—OR
2
wherein R
1
and R
2
comprise a hydrogen, an alkyl group (e.g., C
1
-C
7
), a cyclo alkyl group (e.g., C
5
-C
6
), or an aryl group; OA
1
is a generally hydrophilic oxyalkylene group wherein O represents oxygen and A
1
comprises primarily ethylene groups; and OA
2
is a generally hydrophobic oxyalkylene group wherein O represents oxygen, and A
2
comprises primarily propylene groups (including isopropylene), butyl groups (including t-butyl), or a mixture thereof; m is an integer of 5-200; and n is an integer of 5-200. Preferably, the sum of m and n is in the range of 10 to 400. More preferably, m and n are each an integer of about 30-60. R
1
and R
2
are preferably a hydrogen or methyl group. The polyoxyalkylene copolymer may have a molecular weight of about 100-10,000 (EO/PO block form), and preferably at least 1,000; more preferably, at least 2,000; and most preferably at least 4,000 mol. weight. The foregoing statement that A
1
comprises primarily ethylene groups is an acknowledgment that “OA
1
” may not be purely ethylene oxide, but may include a small portion (less than 50% and preferably less than 20%) larger alkylenes such as propylene or butylene. In other words, the ethylene oxide group should predominate in OA
1
because this is believed to confer hydrophilicity to the copoly
Budiansky Noah D.
Chun Byong-Wa
Williams Brent S.
Baker William L.
Green Anthony
Leon Craig K.
W. R. Grace & Co.,-Conn.
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