Cement additive, and concrete composition and structure both...

Details Cement additive, and concrete composition and structure both... Cement additive, and concrete composition and structure both...

2001-08-15

2003-10-07

Marcantoni, Paul (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S725000, C106S727000, C106S728000

Reexamination Certificate

active

06630020

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a cement additive.
BACKGROUND ART
Generally, the surface of cement, mortar and concrete exposed to the air has the problem of gradual discoloration with time by the action of sunray, dust in the air, microorganisms etc. Accordingly, a method of reducing a water-cement ratio or using a water-permeable concrete form, or applying a water repellant onto the surface of concrete has been known as the method of suppressing discoloration.
One serious drawback of cement, mortar and concrete is that there easily occurs cracking on drying, which is attributable to high shrinkage of cement on drying. Accordingly, various reducing agents for reducing the shrinkage of cement compositions on drying have been proposed, and for example an adduct of alcohol with alkylene oxide (hereinafter abbreviated to AO) and an adduct of alkyl phenol with AO are known (e.g., U.S. Pat. No. 4,547,223 and JP-B 62-10947).
The conventional methods known to suppress discoloration of the surface of concrete are problematic in that special attention should be paid to the compounding method, the type of concrete form, and application of the water repellant.
Further, the conventional admixtures for reducing the shrinkage of cement, when added to concrete compositions, have the problem that the air content is easily influenced by the mixed concrete temperature, and if the air content is attempted to be regulated by an air-entraining admixture, a slight difference in the amount of the air-entraining admixture leads to a change in the air content in concrete, thus causing the problem that concrete containing a predetermined air content is hardly obtained.
DISCLOSURE OF INVENTION
The present inventors extensively studied a cement additive for preventing discoloration of the surface of concrete and a cement additive for easily regulating the air content in concrete, and as a result they arrived at the present invention.
That is, the present invention relates to [I] a cement additive composition for preventing discoloration of the surface of concrete, which comprises a cement additive (a) and a water-reducing admixture (b), wherein (a) comprises a mixture of compounds represented by the general formula (1):
R
1
O(AO)n
1
H  (1)
(wherein R
1
is a C
1-6
alkyl group, A is an ethylene group and/or a propylene group, and n
1
is a number of 1 or more), and all the compounds wherein n
1
is 2 to 6 are present in (a), the total content thereof (i.e. the content of the compounds wherein n
1
=2 to 6) is 40% by mass or more, the average of n
1
is 1.5 to 10, the molecular weight distribution Mw/Mn is 1.05 or more, the Z average molecular weight Mz is 200 or more, and the ratio of (a):(b) by mass is (5 to 99.5):(95 to 0.5).
Further, the present invention relates to [II] a cement additive composition, which comprises a combination of (c) a compound or a mixture of two or more compounds represented by the general formula (2):
R
2
O(AO)n
2
H  (2)
(wherein R
2
is hydrogen or a C
1-6
alkyl group, A is an ethylene group and/or a propylene group, and n
2
is a number of 1 to 10 on average) and (d) a compound or a mixture of two or more compounds represented by the general formula (3):
R
3
O(C
3
H
6
O)n
3
H  (3)
(wherein R
3
is a C
1-4
alkyl group, and n
3
is a number on average of at least n
2
+1 or of more than 10 to 100), the ratio of (c):(d) by mass being 100:(0.01 to 1).
Further, the present invention relates to [III] a concrete composition comprising a cement, any one of the above compositions in an amount of 0.5 to 10% based on the mass of the cement, water and an aggregate.
Further, the present invention relates to [IV] a concrete structure produced by hardening the concrete composition described above.
DETAILED DESCRIPTION OF THE INVENTION
In the general formulae (1) and (2), the alkyl group R
1
and R
2
include a C
1-6
straight-chain or branched alkyl group such as methyl, ethyl, n- and i-propyl, n-, i- and t-butyl, n-, i- and t-pentyl, and n- and i-hexyl. The alkyl group is preferably a C
1-4
alkyl group, more preferably methyl and a straight-chain or branched butyl group.
In the general formula (1) and (2), A is an ethylene group and/or a propylene group, and AO is an oxyethylene group and/or an oxypropylene group, which are formed usually by adding ethylene oxide (hereinafter abbreviated to EO) and/or propylene oxide (hereinafter abbreviated to PO). If EO and PO are added in combination, they may be added in an arbitrary ratio (e.g., a molar ratio of from 1:99 to 99:1) in either a block or random form. When EO and PO are added in combination, block addition is preferable.
The additive (a) comprises a mixture of compounds represented by the general formula (1), in which the total content of the compounds wherein n
1
is 2 to 6 is 40% or more, preferably 50% or more. In the general formula (1), n
1
is a number of 1 or more, preferably a number of 1 to 10. The average of n
1
is 1.5 to 10, preferably 2 to 7. In the foregoing and following description, % refers to % by mass unless otherwise specified.
The molecular weight distribution (Mw/Mn) of (a) [Mw and Mn refer respectively to weight-average and number-average molecular weights determined by gel permeation chromatography (GPC)] is 1.05 or more, preferably from 1.07 to 2. The Mz of (a) (determined by GPC) is 200 or more, preferably 250 to 1000. If (a) is outside of this range, it is not possible to achieve an excellent effect of preventing discoloration of the surface of concrete.
Insofar as the water-reducing admixture (b) used in the present invention is an admixture used generally for concrete, its composition is no limited. The water-reducing admixture (b) includes e.g. materials ordinarily used as air-entraining and water-reducing admixtures, high-range water-reducing admixtures, air-entraining and high-range water-reducing admixtures and superplasticizer [described in e.g. “Developed Techniques of Concrete Admixtures” published by C. M. C. Ltd. (1995)], and examples of such materials include lignin sulfonates (i.e. salts of alkali metals such as sodium and salts of alkaline earth metals such as calcium; this also applies to salts of the following compounds), naphthalin sulfonate formalin condensate salts (degree of condensation: 5 to 20), melamine sulfonate formalin condensate salts (degree of condensation: 5 to 20), polycarbonates [e.g. poly(meth)acrylate having a Mn of 5000 to 60,000, wherein (meth)acrylate means-acrylate and/or methacrylate, and this also applies throughout the description of the specification], aminosulfonate formalin condensate salts (degree of condensation: 2 to 20), and polycarboxylates [e.g. (meth)acrylic acid-(meth)acrylic acid polyoxyalkylene ester copolymer having a Mn of 10,000 to 600,000] containing polyether group (e.g. polyoxyalkylene group having a polymerization degree of 10 to 200, containing 2 and/or 3 carbon atoms in the alkylene group thereof), and these may also be used in combination. Preferable among these water-reducing admixtures are lignin sulfonates, naphthalin sulfonate formalin condensate salts, polycarboxylates and polyether group-containing polycarboxylates, more preferably lignin sulfonates and polyether group-containing polycarboxylates.
In the cement additive composition of the present invention [I], the ratio by mass of additive (a):water-reducing admixture (b) is (5 to 99.5):(95 to 0.5), preferably (20 to 99):(80 to 1). Here, the mass of (b) refers to the net weight of the water-reducing admixture as nonvolatile matter, that is, the mass from which a diluent such as water was removed. If (a) is less than 5%, the effect of preventing discoloration of the surface of concrete is not satisfactory, while if it exceeds 99.5%, the predetermined workability (particularly consistency) as concrete cannot be achieved.
Before preparation of the concrete composition, (a) and (b) may be previously mixed, or during preparation of the concrete co

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