Compositions: coating or plastic – Materials or ingredients – Additive materials for inorganic cements which contain a...
Patent
1996-10-10
1998-05-19
Marcantoni, Paul
Compositions: coating or plastic
Materials or ingredients
Additive materials for inorganic cements which contain a...
106724, 106728, 106802, C09D 712
Patent
active
057530378
DESCRIPTION:
BRIEF SUMMARY
This invention relates to cementitious compositions and more particularly to cementitious compositions with predetermined fluidity characteristics.
Cementitious mixes are required to be fluid or workable for at least part of their lives. This allows them to be placed easily prior to their "set-up" (becoming rigid) and subsequently hardening (sometimes called "setting") (the formation of a hard material by a complex series of hydration reactions). The fluidity or workability of cementitious compositions such as concretes or mortars may be measured, for example, by the slump test, defined in ASTM C143.
Achieving sufficient fluidity for a sufficiently long period can prove difficult under some conditions, and it can happen that a cementitious composition loses fluidity too quickly and sets up before the composition is in place, with unfortunate consequences. The art-recognized plasticizers and superplasticizers cannot rectify this problem.
In copending patent application PCT/EP 93/01910, it has been suggested that the use of a two-component system can produce considerable improvements. In such a system, a polyalkylene oxide and a selected plasticizer or superplasticizer are added to the cementitious composition at mixing and a .beta.-naphthalene sulphonate condensate ("BNS") is added just before application. The polyalkylene oxide and (super)plasticizer give increased fluidity (allowing, for example, the composition to be pumped easily or to flow to an adequate extent around complicated formwork) and the BNS abruptly reduces the fluidity (causing a sudden loss of flow and setting up). The composition can then set conventionally, or, in special cases such as application by spraying (such as "shotcreting"), setting or hardening is augmented by known accelerators.
It has now been found that the fluidity of cementitious compositions may be varied by the use therein of certain materials. There is therefore provided, according to the present invention, a process of rapidly altering the fluidity of a fluid cementitious composition, comprising the addition thereto of an aqueous dispersion of at least one comb polymer which comprises pendant carboxylic moieties.
By "comb" polymer is meant a branched polymer which comprises a backbone polymer from which depend a number of branches. The term is well known in the art (as, for example, "Polymer Science Dictionary" by M. S. M. Alger (Elsevier, 1989)). In the comb polymer useful in the present invention, the branches pendant from the backbone (whose chemical nature is largely irrelevant) are carboxyl group-bearing moieties. These moieties may be up to 100 units long and may comprise monomer residues of, for example, (meth)acrylic acid, maleic acid or fumaric acid. It should be noted that polymerised unsaturated acids such as poly(meth)acrylic acid are not comb polymers.
A preferred backbone is a random addition copolymer in which one of the monomers from which the copolymer was prepared comprised more than one, and preferably two, polymerizable double bonds. The backbone also preferably comprises styrene. For the polymers of this invention, "styrene" includes styrene itself and substituted styrenes such as .alpha.-methyl styrene, ethyl styrene, dimethyl styrene and the mixed isomers commercially available as "vinyl toluene". It is possible to use styrenes with more than one polymerisable double bond, for example, divinyl benzene, but such monomers should comprise no more than 5% by weight of the styrene. The preferred monomer is styrene, but other styrenes may also be used in combination.
The monomer with more than one double bond may be selected from such monomers as isoprene, butadiene, chloroprene and the various diallyl monomers such as diallyl phthalate and diallyl adipate. The preferred monomer is butadiene, but, again, more than one such monomer may be used.
A preferred copolymer is a styrene-butadiene copolymer. To such a copolymer (which may have pendant and/or in-chain polymerizable double bonds) carboxyl group-containing monomers such as acrylic acid, methacrylic
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Drs Josef Franz
Oppliger Max
Valenti Salvatore
Marcantoni Paul
MBT Holding AG
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