Methods of using cement dispersants for producing concrete

Details Methods of using cement dispersants for producing concrete Methods of using cement dispersants for producing concrete

2000-07-13

2001-05-08

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S287000, C526S318400, C526S320000, C526S328500, C526S332000, C106S725000, C106S809000, C524S005000

Reexamination Certificate

active

06228962

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to methods of using cement dispersants to produce better concrete. At work sites where cement compositions are used, it is important to be able to provide high fluidity to cement compositions, to reduce the drop in the provided fluidity with time (“the slump loss”) and to obtain a sufficient early strength during the initial period of hardening such that the frames can be removed quickly and the work efficiency can be thereby improved. This invention relates to cement dispersants which can respond to such requirements, as well as methods of using such cement dispersants to produce concrete with improved quality.
Examples of prior art cement dispersant for providing fluidity to cement compositions include salts of high condensates of naphthalene sulfonic acid formaldehyde and melamine sulfonic acid formaldehyde, as well as water-soluble vinyl copolymers. Cement compositions prepared by using salts of high condensates of naphthalene sulfonic acid formaldehyde or melamine sulfonic acid formaldehyde, however, have the problem of a high slump loss. Those prepared by using water-soluble vinyl copolymers of the conventionally proposed kind (such as disclosed in Japanese Patent Publications Tokko 58-38380, 59-18338 and 5-11057 and U.S. Pat. Nos. 4,962,173, 5,087,648, 5,290,869 and 5,362,829) have smaller slump losses but there are problems wherein their setting times become longer and hence a sufficient early strength cannot be obtained during the early period of hardening. This problem is particularly significant with high-strength cement compositions with a limited water-to-cement ratio.
SUMMARY OF THE INVENTION
The problem to be overcome by the present invention is that prior art cement dispersants could produce only cement compositions with a large slump loss or incapable of providing a sufficiently large early strength, this problem being particularly significant with high-strength cement compositions with a limited water-to-cement ratio.
The present invention was accomplished as a result of investigations by the present inventors and is based on their discovery that the aforementioned problems can be responded to if two specified kinds of water-soluble vinyl copolymers are mixed at a specified ratio.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to methods of using cement dispersants comprised of Component (a) and Component (b) to be described below at weight ratio ((a)/(b)) of 99/1-70/30, wherein Component (a) is a water-soluble vinyl copolymer with number average molecular weight 3500-50000, having as its constituent units Unit A shown below by Formula (1) by 55-80 molar %, Unit B shown below by Formula (2) by 2-25 molar %, Unit C shown below by Formula (3) by 3-20 molar % and Unit D shown below by Formula (4) by 1-15 molar % (the total being 100 molar %) and wherein Component (b) is another water-soluble vinyl copolymer with number average molecular weight 1500-25000, having as its constituent units Unit A shown below by Formula (1) by 45-80 molar %, Unit B shown below by Formula (2) by 2-15 molar %, Unit C shown below by Formula (3) by 4-20 molar % and Unit E shown below by Formula (5) by 10-40 molar % (the total being 100 molar %), Formulas (1)-(5) being as follows:
where R
1
, R
2
and R
3
are each either H or CH
3
, R
4
is an alkyl group with 1-3 carbon atoms, M
1
and M
2
are each an alkali metal, an alkali earth metal, ammonium or an organic amine, m is an integer 51-105, and n is an integer 5-25.
In summary, a cement dispersant according to this invention is characterized as containing both aforementioned Components (a) and (b). Component (a) is a water-soluble vinyl polymer having Units A, B, C and D as its constituent units at a specified ratio, and Component (b) is another water-soluble vinyl polymer having Units A, B, C and E as its constituent units at another specified ratio. Both in Components (a) and (b), each Unit A, B, C, D or E is formed by copolymerizing its corresponding vinyl monomers.
Examples of vinyl monomers which form Unit A shown by Formula (1) include (1) alkali metal salts, alkali earth metal salts and organic amine salts of methacrylic acid, and (2) alkali metal salts, alkali earth metal salts and organic amine salts of acrylic acid. Of these, alkali metal salts such as sodium and potassium salts of methacrylic acid are preferred.
Examples of vinyl monomers which form Unit B shown by Formula (2) include alkali metal salts, alkali earth metal salts and organic amine salts of methallyl sulfonic acid. Of these, alkali metal salts such as sodium and potassium salts of methallyl sulfonic acid are preferred.
Examples of vinyl monomers which form Unit C shown by Formula (3) include methyl acrylate and methyl methacrylate.
Examples of vinyl monomers which form Unit D shown by Formula (4) include alkoxy polyethoxy ethyl (meth)acrylates with 1-3 carbon atoms and the repetition number of oxyethylene units 51-105, such as methoxy polyethoxy ethyl (meth)acrylates, ethoxy polyethoxy ethyl (meth)acrylates, and n-propoxy polyethoxy ethyl (meth)acrylates. Of these, methoxy polyethoxy ethyl methacrylates with the repetition number of oxyethylene units 55-95 are preferred.
Examples of vinyl monomers which form Unit E shown by Formula (5) include methoxy polyethoxy ethyl methacrylates with the repetition number of oxyethylene units 5-25. Of these, those with the repetition number of oxyethylene units 7-23 are preferred.
The water-soluble vinyl copolymers of Component (a) are obtained by radical copolymerization of vinyl monomers forming Units A-D at a specified copolymerization ratio in the presence of a radical initiator. The radical copolymerization is carried out by aqueous solution polymerization using water or a mixed solvent with water and a water-soluble organic solvent. Explained more in detail, each of the vinyl monomers are initially dissolved in water to prepare an aqueous solution containing these vinyl monomers by 10-45 weight % as their total. Next, a radical initiator is added to this aqueous solution within a nitrogen gas atmosphere to carry out a radical copolymerization reaction at 50-70° C. for 5-8 hours and to thereby obtain water-soluble vinyl copolymer. Any radical initiator which generates radicals by decomposing at the reaction temperature of copolymerization may be used for the copolymerization reaction of either of the vinyl monomers, but the use of a water-soluble radical initiator is preferred. Examples of such water-soluble radical initiator include persulfates such as potassium persulfate and ammonium persulfate, hydrogen peroxide, and 2,2-azobis (2-amidinopropane) dihydrochloride. They may be combined with a reducing agent such as a sulfite and L-ascorbic acid or amines to be used as a redox initiator.
The water-soluble vinyl copolymers of Component (a) thus obtained contain Unit A by 55-80 molar % (or preferably 55-75 molar %), Unit B by 2-25 molar % (or preferably 4-20 molar %), Unit C by 3-20 molar % (or preferably 5-15 molar %), and Unit D by 1-15 molar % (or preferably 2-12 molar %), the total being 100 molar %. Their number average molecular weight (hereinafter always pullulan converted by GPC method) is 3500-50000, and preferably 5000-40000.
The water-soluble vinyl copolymers of Component (b) can be obtained similarly as described above for those of Component (a). The water-soluble vinyl copolymers of Component (b), by contrast, contain Unit A by 45-80 molar % (or preferably 50-75 molar %), Unit B by 2-15 molar % (or preferably 3-13 molar %), Unit C by 4-20 molar % (or preferably 5-15 molar %), and Unit E by 10-40 molar % (or preferably 12-35 molar %), the total being 100 molar %. Their number average molecular weight is 1500-25000, and preferably 2500-20000.
Cement dispersants of this invention are characterized not only as comprising water-soluble vinyl copolymers of aforementioned Components (a) and (b) but also as containing Components (a) and (b) at a weight ratio ((a)/(b)) of 99/1-70/30, or preferably 97/3-75/25. If this weight ratio is greater than 99/

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