|Número de publicación||WO1991002703 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||PCT/NO1990/000131|
|Fecha de publicación||7 Mar 1991|
|Fecha de presentación||17 Ago 1990|
|Fecha de prioridad||21 Ago 1989|
|Número de publicación||PCT/1990/131, PCT/NO/1990/000131, PCT/NO/1990/00131, PCT/NO/90/000131, PCT/NO/90/00131, PCT/NO1990/000131, PCT/NO1990/00131, PCT/NO1990000131, PCT/NO199000131, PCT/NO90/000131, PCT/NO90/00131, PCT/NO90000131, PCT/NO9000131, WO 1991/002703 A1, WO 1991002703 A1, WO 1991002703A1, WO 9102703 A1, WO 9102703A1, WO-A1-1991002703, WO-A1-9102703, WO1991/002703A1, WO1991002703 A1, WO1991002703A1, WO9102703 A1, WO9102703A1|
|Inventores||Simon Philip John Dennington, Harald Justnes|
|Solicitante||Borregaard Industries Limited|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (5), Otras citas (1), Citada por (22), Clasificaciones (11), Eventos legales (3)|
|Enlaces externos: Patentscope, Espacenet|
Use of copolymers as additives for cement mortar mixtures or for coating of cured or partially cured concrete.
Cement-based mortar mixtures have been used for the preparation of construction materials for over 150 years. Such mixtures are in general satisfactory, but for certain applications they have deficiencies which it is desirable to rectify. One example is that construction elements fabricated from such cement mortar mixtures are prone to corrosive attack in seawater. There have been many attempts to reduce this corrosion by various means, among other things there has been much work involving the addition of polymers to reduce corrosion caused by the chloride in seawater in particular. Another property that it has been found desirable to improve is the cement mortar mixture's fluidity, that is to say, that it should flow smoothly out when e.g. laying floors.
The polymers most usually used as concrete additives are largely based on styrene-butadiene or vinyl acetate, although other types have been used.
It has now been found possible to produce cement mortar mixtures with greatly improved resistance to corrosion caused by seawater by adding to the cement mortar mixture a copolymer consisting of monomers chosen from among those of formula
A. CH2=C COOH
where R is hydrogen or methyl
B. CH5=^C —COOR^
where R1 is hydrogen or methyl, and R2 is C^ gal yl where the amount of one or two different A-units in the copolymer totals 5-10 weight% and the remainder consists mainly of one or more different B-units. The copolymer is advantageously used in the form of a latex, and as well as being added to cement mortar mixtures it can be applied as a coating to cured or partially cured concrete.
Monomer A can be acrylic acid or methacrylic acid, and it is possible to use both of these in the same copolymer. Monomer B comprises various esters of acrylic acid and methacrylic acid, and it is similarly possible to use several different esters in the same copolymer.
Especially suitable ester monomers B are those where R1 is hydrogen or methyl, and R2 is methyl or n-butyl.
An especially suitable acid monomer A is methacrylic acid, while especially suitable ester monomers B are butyl acrylate and methyl methacrylate.
Especially suitable copolymers are those where the amount of A monomer, especially methacrylic acid, is 6-8 weight %, and the remainder of the copolymer consists mainly of B monomers. The B monomers are preferably butyl acrylate and methyl methacrylate in the ratio 50:50-70:30, especially 65:35, on a weight basis.
In general, the higher the content of hydrophobic ester monomer, the higher the content of acid monomer in the copolymer should be. Normally it will similarly be possible to use somewhat less acrylic acid than methacrylic acid to acheive the same effect.
In addition to the monomers A and B, the copolymer used can also contain minor amounts, e.g. up to 10 weight%, of other ethylenically-unsaturated monomers, such as styrene.
The polymer latex used as an additive to cement mortar mixtures or applied to cured or partially cured concrete, has preferentially a solids content of 10-60% weight%, especially 30-60 weight%. A high water content in the latex will allow a corresponding reduction in the amount of water used to make the cement mortar mixture. The amount of polymer latex to be added to a cement mortar mixture is preferably from 2 to 25 weight%, and especially from 5 to 15 weight%, expressed as weight of polymer solids/ weight of cement powder.
The chloride ingress/corrosion which occurs in concrete in seawater is especially serious because it is followed by corrosion of the steel reinforcing bars when the chloride ions reach these. Corrosion of the reinforcing bars leads to expansion and resulting cracking of the concrete. To illustrate the improvement achieved by this invention compared to the use of other polymers, an accelerated test of chloride penetration in cured cement mortar was carried out.
The test was carried out in the following manner: A steel reinforcing bar was cast inside a cylinder of cement mortar which was partially immersed in seawater with the exposed part of the reinforcing bar above the surface of the water. This reinforcing bar was used as the anode, and a metal electrode immersed in the seawater was used as the cathode. The voltage across the electrodes was 5 volts D.C. In the following tables the results of such tests are given as the number of days before chloride penetration caused the current through the cylinder to increase sharply. Testing was carried out with two different mortars having differing water/cement ratios. The polymer latex used contained 50 weight% of polymer. The quoted additions of polymer are calculated on the basis of dry weight of polymer solids/ weight of cement powder.
Control (water/cement = 0.55) 3±1 days (1:3 mortar without polymer)
# Only one of two parallels failed + Testing discontinued after 1 year
Control (water/cement 0.40) 105±35 days (1:3 mortar without polymer)
* Still no current increase when table compiled
* Only one of two parallels failed
The polymer latexes used were as follows:
Polymer 1 = Commercial latex based on the terpolymer vinylacetate/vinyl chloride/ethylene
Polymer 2 = Commercial latex based on the copolymer vinyl acetate/"versatic" ester
Polymer 3 = Commercial latex based on styrene/butadiene rubber
Polymer 4 = 50 weight% solids content latex consisting of a copolymer of 7% methacrylic acid, 60.5% butyl acrylate and 32.5% methyl methacrylate by weight according to this invention
From the results it can be seen that Polymer 4 used in accordance with this invention resulted in considerably greater resistance to chloride penetration than the other commonly used latexes.
A polymer latex for use in accordance with this invention was prepared as follows: 2 grams of sodiummetabisulphite dissolved in 4.9 litres of water was heated towards 80 °C in a reactor. When the temperature reached 70 °C a solution of 12.5 grams of potassium persulphate (initiator) in 125 millilitres of water was added to the reactor.
A pre-emulsion was prepared from 6.4 litres of water, 350 grams of "Berol 295" (surfactant) , 840 grams of "Disponil AES 60" (surfactant) , 7569 grams of butyl acrylate, 4075 grams of methyl methacrylate and 856 grams of methacrylic acid. 10% of this pre-emulsion was thereafter added to the reactor when the aqueous solution it contained had reached a temperature of 75 °C. When this first portion had reacted, the remainder of the pre-emulsion was added over a period of 2 hours, while the temperature of the reactor was maintained at 80 ± 2 °C. Addition of a solution of 12.5 gram potassium persulphate in 900 millilitres of water was started at the same time as commencement of addition of the remainder of the pre-emulsion, and completed over 3 hours. The reactor temperature was maintained at 80 °C for a further 1 hour after the addition of the potassium persulphate solution was finished, then cooled down. 50 grams of the antifoaming agent "FOAM-MASTER ENA 224" were added at 65 °C. On final cooling to room temperature a 50 weight% solids content polymer latex was obtained, with particle size 100 - 200 nm.
This latex is used either as an additive for cement mortar mixtures or for applying as a coating to cured or partially- cured concrete to reduce the ingress of chloride. It is also suitable as an additive to improve the fluidity and workability of cement mortar-based mixtures.
The rheological properties are comprised, among other things, of workability and fluidity. Table III (below) shows the results of adding a polymer latex used according to this invention to a cement mortar compared to an unmodified cement mortar and a polymer-cement mortar containing a commercial styrene-butadiene (SBR) latex.
The polymer that was used according to this invention contained butyl acrylate (BA) and methyl methacrylate (MMA) in the specified weight ratio, with and without methacrylic acid (MAA) (expressed as the weight% of the total polymer) .
Table III Rheological properties of polymer-cement mortars with and without the addition of various latexes.
Ref.mortar 3.7 3.2 145(15)
Ref.mortar + SBR 8.0< 9.5 220(15)
Ref.mortar + latex 50/50 10.5 9.5 160 (0) 205 (6)
Ref.mortar + latex 50/50 3.7 >11.5 >225 (0)
a) Measured at 0.50 atm. instead of 1.0 atm. , and the result multiplied by 1.5
■°) The figures in brackets are the number of impacts to the flow-board necessary to achieve the given spread. The fewer the impacts, the better the flow.
It can be seen that the best result was achieved using the polymer containing BA/MMA in the ratio 50/50 and a MAA content of 7%, all expressed on a weight basis.
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|Clasificación internacional||C04B41/63, C04B41/48, C04B24/26|
|Clasificación cooperativa||C04B41/009, C04B41/63, C04B24/2641, C04B41/483|
|Clasificación europea||C04B41/00V, C04B24/26K, C04B41/48K, C04B41/63|
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