Cement spraying admixture

A method for coating a substrate with a cementitious composition by spraying, comprising the addition to the initial cementitious mix one of a .beta.-naphthalene sulphonate-formaldehyde condensate and a water-soluble poly(alkylene oxide) of molecular weight from 100,000-8,000,000, the other being added at the spraying nozzle, there being additionally added at the nozzle (preferably as a single component with the other nozzle-added material) an accelerator selected from aluminium sulphate, aluminium hydroxide and aluminium hydroxysulphate. In a preferred embodiment, the material added at the nozzle also contains a superplasticiser.

This invention relates to the spraying of cementitious compositions and to 
admixtures for use therein. 
The oldest and most widely-used assessment of the workability of concrete 
or mortar is the slump test, defined in ASTM C143. A frusto-conical mound 
of concrete is moulded on a table and the mould then removed, the slump 
being the difference in height from the table between the top of the 
original mound and the level to which it falls. The bigger the slump, the 
better the workability. 
In the case of sprayed concrete, sometimes known as "shotcrete", it is 
highly desirable that a concrete be pumpable (a condition which requires 
considerable slump), but when it is sprayed on to a substrate, that it 
become stiff very quickly (a condition which allows nearly no slump). A 
system for achieving this goal is described in PCT Published Application 
WO 94/02428, wherein a two-component admixture is used, one component 
being added at the mixing stage and the second just before final use. In 
the case of spraying concrete, the second component is added at the nozzle 
from which the concrete is sprayed. In the case of sprayed concrete, an 
accelerator is also used, the accelerator being added in conventional 
fashion (at the nozzle) and being selected from conventional accelerators. 
It has now been found that a combination of the two-component admixture 
hereinabove described and a particular accelerator gives unexpectedly good 
results. There is therefore provided, according to the present invention, 
a process for coating a substrate with a cementitious composition, 
comprising the preparation of a hydraulic cementitious mix and its 
application on to the substrate by spraying through a nozzle, there being 
added to the mix one component of a two-component admixture, the other 
component being added at the nozzle, the components being a 
.beta.-naphthalene sulphonate-formaldehyde condensate ("BNS") and a 
water-soluble poly(alkylene oxide) of molecular weight (weight-average) of 
from 100,000-8,000,000 ("PAO"), there being additionally added at the 
nozzle an accelerator which is selected from the group consisting of 
aluminium sulphate, aluminium hydroxide and aluminium hydroxysulphate 
("aluminium-based compound"). 
In a further embodiment of the invention, the aluminium-based compound 
forms part of the component added at the nozzle. 
In a still further embodiment of the invention, there is provided a 
two-component admixture for a sprayable concrete mixture which is adapted 
to be applied to a substrate by a spray nozzle, one of which components is 
incorporated at the mixing stage of the concrete mixture and the other of 
which is added at the nozzle, one component comprising a 
.beta.-naphthalene sulphonate-formaldehyde condensate, and the other 
component comprising a water-soluble poly(alkylene oxide) of molecular 
weight (weight-average) of from 100,000-8,000,000, there being 
additionally present in the component which is added at the nozzle an 
aluminium compound selected from aluminium sulphate, aluminium hydroxide 
and aluminium hydroxysulphate. 
The invention also provides a two-component admixture for use with a 
sprayable cementitious composition, of the type hereinbefore described, 
one component of the admixture comprising BNS and the other component 
comprising PAO and an aluminium-based compound. 
The invention further provides a two-component admixture for use with a 
sprayable cementitious composition, of the type hereinbefore described, 
one component of the admixture comprising BNS and an aluminium-based 
compound, and the other component comprising PAO. 
For the purposes of this invention, where reference is made to a single 
material, the possibility of using two or more such materials is also 
comprehended thereby. By "cementitious composition" is meant any 
cementitious composition, such as mortar and grout. However, the major use 
of this invention is in the field of "shotcrete" (sprayable concrete). 
For the purposes of this invention, the term "two-component admixture" 
refers to an admixture whose two components interact with each other to 
achieve a result which is not given by the addition of the individual 
components alone and which is therefore functionally a single admixture. 
In this particular case, the individual components are not mixed (indeed 
must not be mixed) before addition to the cementitious composition, but 
are added separately, the second at the nozzle. 
The PAO suitable for use in this invention may be selected from any such 
suitable materials known to the art. The requirement that the material be 
water-soluble means that the material must include at least a high 
proportion of oxyethylene units. It is preferable that the material be 
pure poly(ethylene oxide). It is also preferable that the molecular weight 
lie in the range 2,000,000-5,000,000. Typical commercial products useful 
in the working of this invention may be found, for example, in the 
"POLYOX" (trade mark) range of Union Carbide Chemicals and Plastics 
Company, Inc. 
The BNS for use in this invention is a readily-available material, widely 
used as a superplasticizer in the concrete industry. It can be used as a 
powder but it is preferred to use an aqueous solution containing 
approximately 40% of active substance in the form of the sodium salt. 
There has been recent interest in accelerators comprising amorphous 
aluminium hydroxide, largely because their low alkalinity makes conditions 
in spraying sites more tolerable. Examples of accelerators based on 
amorphous aluminium hydroxide have included blends thereof with various 
water-soluble salts. However, it has been found that when the 
aluminium-based compounds hereinabove described are used in conjunction 
with poly(alkylene oxide) and BNS as hereinabove described, the results 
are especially and surprisingly good. For example, it has been found that 
the achievement of thick sprayed layers on walls and ceilings is 
relatively easy. 
In the particular circumstances of this invention, aluminium 
hydroxysulphate is often a better accelerator than aluminium hydroxide and 
is therefore preferred. It is possible to use a mixture of aluminium 
hydroxysulphate with aluminium hydroxide and/or aluminium sulphate, but it 
is preferable to use the hydroxysulphate alone. A typical 
commercially-available aluminium hydroxysulphate is "GECEDRAL" (trade 
mark) L (ex Guilini Chemie GmbH, Ludwigshafen/-Rhein, Germany). 
It is possible to add either component to the mix and the other component 
at the nozzle. The component which is added at the nozzle contains the 
aluminium-based compound. The components and the aluminium-based compound 
are preferably added in the form of aqueous solutions or dispersions. 
While it is possible for the aluminium-based compound to be added 
separately from the component at the nozzle, it has been found that better 
results are achieved when the aluminium-based compound is combined with 
the component. In this case, both are added together in a single aqueous 
additive. This has the additional benefits of reducing both the complexity 
of the equipment and the number of materials which have to be handled. 
It is preferable to add the BNS to the mix and the PAO at the nozzle. Thus, 
the material added at the nozzle is preferably an aqueous solution or 
dispersion of PAO and aluminium-based compound. 
In a further preferred embodiment of the invention, there is additionally 
added at the nozzle in combination with the aluminium-based compound a 
superplasticiser which is selected from lignosulphonates, melamine 
sulphonate-formaidehyde condensates and styrene-maleic anhydride ("SMA") 
copolymer-based superplasticisers. SMA-based superplasticisers are 
preferred, and an especially preferred type of such plasticiser is 
described in U.S. Pat. No. 5,158,916 and French Published Application 2 
671 090 the contents whereof are incorporated herein by reference. These 
are styrene-maleic anhydride-derived copolymers in free acid or salt form 
and selected from the group consisting of those having the following types 
and numbers of monomer units: 
##STR1## 
in which R is an C.sub.2-6 alkylene radical R.sub.1 is a C.sub.1-20 
alkyl-, C.sub.6-9 cycloalkyl- or phenyl group, 
x, y and z are numbers from 0.01 to 100 
m is a number from 1 to 100 and 
n is a number from 10 to 100 
with the provisos, that 
i) the ratio of x to (y+z) is from 1:10 to 10:1 inclusive, 
ii) the ratio of z:y is from 3:1 to 100:1 and 
iii) m+n=15-100 
and those having the following types and numbers of monomer units: 
##STR2## 
in which M is hydrogen or the residue of a hydrophobic polyalkylene glycol 
or polysiloxane, 
R.sub.1, m and n are as hereinabove defined, 
x, y and z are numbers from 1 to 100 
with the provisos that 
i) the ratio of x to (y+z) is from 1:10 to 10:1 inclusive, 
ii) the ratio of z:y is from 5:1 to 100:1 and 
iii) m+n=15-100. 
Although the addition of a superplasticiser at a point where less flow 
rather than more is required is not normal, it has been found that the 
performance of the invention is enhanced by this addition. When the 
aluminium-based compound and the component added at the nozzle are 
included in a single aqueous additive, the superplasticiser is also 
included in the component. It also brings the advantage that less water is 
needed and the aqueous additive may be more concentrated. The invention 
therefore also provides a process of coating a substrate as hereinabove 
described, wherein there is added at the nozzle with the aluminium-based 
compound a superplasticiser as hereinabove described. There is also 
provided a two-component admixture as hereinabove described, wherein the 
component added at the nozzle additionally comprises a superplasticiser as 
hereinabove defined. This component preferably comprises PAO. 
The mode of use of the invention is that one component is mixed into the 
concrete mix when it is made (prior to pumping) and the other component of 
the admixture is added at the nozzle. The substances injected at the 
nozzle may be injected separately, or preferably, as hereinabove 
described, they are pre-mixed and added as a single addition. 
Use of the admixture of the present invention gives a cementitious 
composition which is readily pumped, but which, when it is sprayed on a 
substrate, forms a coating with little rebound, develops strength quickly 
and has good final strength. 
The relative quantities of the substances to be used in the working of this 
invention and their relation to the quantity of concrete mix may vary over 
wide limits, depending largely on the composition of the mix, the desired 
speed with which the slump properties are to change and the desired 
initial and final slumps. Other factors such as ambient temperature may 
have an effect on the proportions needed. 
With only minor experimentation the skilled person can readily determine 
suitable proportions in any given case. As a general guideline quantities 
of 0.001 to 0.01% by weight of poly(alkylene oxide) and 0.1 to 1.5% by 
weight of the BNS (calculated as active substance), based on the weight of 
cement, will be used. The ratio of poly(alkylene oxide) to BNS is from 
1:100 to 1:30. When a superplasticiser is used, it is present to the 
extent of from 10-30%, preferably 15-25% of the aluminium-based compound 
(by weight on solids). The aluminium-based compound is present at a rate 
of from 0.1-5.0% by weight of cement. 
The invention is generally applicable to all sprayable concrete mixes, 
where a relatively rapid transformation from an initial high slump to a 
final low slump is required. It is especially valuable in the creation of 
permanent final linings, including fiber shotcrete. It is, however, also 
applicable in sprayable thixotropic plastering mortar. 
The invention is further described with reference to the following examples 
.

EXAMPLE 1 
A sprayable concrete mixture is made by thoroughly mixing the following 
components: 
Portland cement 450 Kg 
aggregate (crushed stone 1700 " max. diam. 8 mm) 
water 200 " 
BNS (40% aqueous solution) 1.1 " 
This mixture is fed to a spraying nozzle. At the nozzle, there is injected 
into the mixture an aqueous dispersion of the following weight 
constitution 
water 69.1 parts 
polyalkylene oxide.sup.1 0.025 " 
aluminium hydroxysulphate.sup.2 25.5 " 
SMA-based superplasticiser.sup.3 5.375 " 
1. "POLYOX" WSR 301 ex Union Carbide Chemicals 
2. "GECEDRAL" L ex Giulini Chemie GmbH 
3. "RHEOBUILD" 3520 ex MBT 
such that there is injected 0.02 Kg. polyalkylene oxide and 6.9 Kg. 
aluminium hydroxysulphate per cubic meter of concrete. The concrete is 
sprayed out on rock in a single pass to give a layer of thickness 30-40 
cm. This layer is subjected to testing according to the Guidelines on 
Shotcrete published by the Austrian Concrete Society, a publication well 
known to those in the industry. Set is determined by the well-known Vicat 
needles and strength by testing drilled cores with a penetrometer. The 
results are as follows: 
initial set 2 min. 
final set 2 min. 40 sec. 
strength development 
1 day 12 N/mm .sup.2 
7 days 41 N/mm.sup.2 
The 28 day compressive strength compared to unaccelerated concrete is 
reduced by 12%, a remarkable improvement over shotcrete accelerated by 
art-recognised methods, where the loss of strength ranges from 20-50%. 
EXAMPLE 2 
Example 1 is repeated, using the following injected aqueous dispersion at 
the nozzle (the materials and proportions used being otherwise the same) 
water 72.5 parts 
polyalkylene oxide.sup.1 0.4 " 
aluminium hydroxysulphate.sup.2 22.5 " 
SMA-based superplasticiser.sup.3 0.5 " 
The compressive strength shows the same excellent improvement over the 
known art. 
EXAMPLE 3 
Example 1 is repeated, using the following concrete mix: 
Portland cement 350 Kg 
fly ash 60 " 
aggregate 1690 " 
BNS 1.5 " 
sufficient water being added to give a water/cement ratio of 0.5. 
At the nozzle, the aqueous dispersion described in Example 2 is added such 
that there is injected 0.11 Kg polyalkylene oxide and 5.54 Kg aluminium 
hydroxysulphate per cubic metre. Testing results are as follows: 
initial set 1 min. 20 sec. 
final set 2 min. 00 sec. 
strength development 
6 min. 0.35 N/mm.sup.2 
1 day 18.1 N/mm.sup.2 
7 days 27.9 N/mm.sup.2 
The loss of compressive strength in comparison with unaccelerated shotcrete 
is 6%. 
EXAMPLE 4 
The following weight-based shotcrete composition is made: 
cement 425Kg/m.sup.3 
BNS (40% aqueous solution) 1.5% 
The mix has a W/C ratio of 0.48 and a slump of 22cm and a spread of 53.5cm. 
This mix is sprayed, there being added at the nozzle the aqueous dispersion 
of Example 2. This is added at a rate of 5% by weight solids on cement. 
The compressive strength is measured over time and is as follows: 
2 hours 0.9 MPa.sup.1 
4 hours 1.3 MPa.sup.2 
1 day 15.0 MPa.sup.2 
7 days 25 MPa.sup.3 
1. needle measurement 
2. Hilti measurement 
3. core measurement 
EXAMPLE 5 
A shotcrete mix is prepared as follows: 
cement 425 Kg 
aggregate (0-8mm) 1713 " 
BNS 1.5% by weight 
The W/C ratio is 0.47, the slump is 20 cm and the spread is 51 cm. 
Individual samples of the mix are dosed with 4% and 5% by weight solids on 
cement of the aqueous dispersion of Example 2 and the compressive 
strengths are measured by penetration needle. The results are shown in the 
following table: 
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strengths (MPa) measured at 
accelerator dosage 
15 m. 30 m. 1 h. 4 h. 6 h. 12 h. 
24 h. 
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4% 0.5 0.5 0.6 1.0 7.0 14.0 24.1 
5% 0.5 0.5 0.6 1.0 7.0 15.0 29.5 
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