Note: Descriptions are shown in the official language in which they were submitted.
214~738
Binder for hydraulically setting self-levelling floor screeds
The invention relates to a binder for hydrauli-
cally setting self-levelling floor screeds comprising a mixture of
calcium sulphate and slag sand.
DE-C 38 43 635 discloses the use for self-levelling floor
screeds of a binder comprising calcium sulphate alpha-
hemihydrate and flour-like slag sand in a ratio of from
90:10 to 70:30, if desired together with ayy eyates and
additives. The calcium sulphate alpha-hemihydrate here
has a favourable influence on the initial strength. Such
slurry screeds generally possess, as a result of the high
proportion of calcium sulphate, a sufficiently low
shrinkage on drying and final setting and a sufficient
surface strength, with the latter becoming poorer with
increasing slag sand contents, for which reason its
content is restricted to the prescribed range. This thus
leads to a very high usage of calcium sulphate alpha-
hemihydrate which is a product which is relatively
complicated to produce and thus expensive.
A screed based on slag sand would be, owing to
its long reaction time, extremely sensitive to drying out
and would run the risk of suffering from lack of mois-
ture. Rewatering would counteract this, but is
inconvenient and thus undesired. In addition, strength
and surface problems occur which are caused by
insufficient reaction of slag sand. Even amounts of up to
30% by weight of calcium sulphate hemihydrate, which does
give a more favourable initial ~trength, reduce only the
sensitivity to drying out, but do not eliminate this or
the surface problems resulting from early carbonation.
It is known that, in sulphate slag cement in
accordance with 2IN 4210 (1954), which has long been no
longer available and contained, apart from slag sand and
calcium sulphate, up to about 2.5% by weight of Portland
cement clinker, the problem of the insufficient surface
strength does not exist, but the Portland cement clinker
here impairs the shrinkage behaviour resultiDg in form-
ation of cracks which have been accepted in concrete but
are not tolerable in a screed.
*) the German standard
2145738
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A screed based on calcium sulphate and a Portland
cement or Portland cement clinker is low in shrinkage
and, with rising Portland cement content, tends to blow
if the screed becomes wet. Thus, a correspQn~;ng screed
is sensitive to aqueous base coats or primers as are used
nowadays in place of those which contain organic liquids
as solvent. To counter this problem, according to exactly
the abovementioned DE-C 38 43 625, slag sand is used in
place of the Portland cement or its clinker, 80 as to
make the screed water-resistant and insensitive to
blowing.
It is an object of the invention to provide a
binder which makes possible the production of hydraulically setting
self-levelling floor screeds
i which have, with a reduced proportion of
calcium sulphate, a sufficient surface strength.
This object is achieved by reactive aluminates,
calculated as CA, which can if desired be partially
replaced by calcium hydroxide, being present in addition
to calcium sulphate and slag sand, with the mixture in
the three-material diagram calcium sulphate/slag
sand/reactive aluminate being made up within a window
which extends along the calcium sulphate - slag sand axis
from 35 to 70% by weight of calcium sulphate, calculated
as CaS04, and in the direction of reactive aluminates
from about 0.5 to 5% by weight, in such a way that a
st~n~rd mortar prism comprising a mixture of three parts
by weight of quartz sand and one part by weight of a
binder at an age of 28 days, 21 days of which is storage
at 20C and 65% relative atmospheric humidity after
previous moist or water storage, has a shrinkage of less
than 0.3 mm/m, in particular less than 0.2 mm/m.
This makes it possible to produce water-resistant
self-levelling screeds which are suitable even for
industrial floors and which have a high in-i~ial strength,
sufficient ~urface strength with high final compressive
strength and a shrinkage on drying and final setting
which is 80 small that no tearing or dishing results.
The st~n~rd mortar prisms are produced in
~` 214S73~
-- 3
accordance with the European St~n~rd EN 196 Part 1 which
i8 applicable to cement, using a ratio of water to binder
of about 0.46. The measurement of the shrinkage is
carried out on the st~n~rd mortar prisms in accordance
with the directions of EN 196 at an age of 28 days with
initial moist storage for two days and subsequent water
storage for five days.
Furthermore, the formulation is advantageously
made up within the window of the three-material diagram
in such a way that swelling on water storage for 26 days,
(after prior moist storage for two days) is at most
1 mm/m, in particular 0.5 mm!m.
The reactive aluminates can be present, in
particular, in the form of C12A7 and/or C3A which have an
excess of CaO and thus, in the reaction in the fresh
mortar, on the one hand eliminate calcium hydroxide and,
on the other hand, increase the surface strength by
formation of aluminate hydration products. The Ca(OH) 2
which is eliminated serves as a buffer against early
carbonation of the fresh mortar on the screed surface.
The reactive aluminates can, however, also be
present in the form of CA or C~AF, with a part of the
reactive aluminates being able to be replaced by calcium
hydroxide.
The proportion of the reactive aluminates is
preferably below 2.5% by weight.
The reactive aluminates can, together with
reactive silicates such as C2S and C3S, be present, for
instance, in the form of aluminous or fused aluminous
cement, Portland cement clinker or Portland cement, iron
Portland cement or blast furnace slag cement or mixtures
thereof.
The individual components are milled separately
and subsequently mixed. Here, the individual components
should preferably have a Blaine specific surface area of
at least 3000 cm~/g.
Suitable forms of calcium sulphate, which posi-
tively influences virtually only theinitialstrength, are
CaSO~.xH20 in general and also mixtures of various calcium
2145738
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sulphates, i.e. it is possible to use, for example,
calcium sulphate beta-hemihydrate but also, and indeed in
particular, hard plaster having a water requirement of
~ 0.4 such as calcium sulphate alpha-hemihydrate or
anhyrite-II or anhydrite-III, if desired as a mixture,
with the use of calcium sulphate alpha-hemihydrate being
particularly preferred. The calcium sulphate can be used
in finely milled or powder $orm. Particularly for use in
travelling mixers, it i8 also possible to use moist FGD
gypsum (flue gas desulphurization gypsum) which is then
to be m;Ye~ in during the production of the fresh mortar.
The same applies to returned material from travelling
mixers which has been freed of ayy~eyate.
Suitable ayy~eyates are, for example, quartz
sands, gra~els, chippings or other quartz-cont~;n;ng
materials. Furthermore, additives such as stone flours
and fly ashes can be added.
In addition, it is possible to add activators, in
particular for the slag sand, e.g. chloride, retarders,
accelerators, stabilizers and flow improvers.
Several binder compositions and the shrinkage and
swelling values of st~n~d mortar prisms prepared
therefrom and having an age of 28 days are given below.
2145738
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Calcium Slag Reactive Calcium Other Water~ Shrinkage Swell-
aulphate sand aluminate- hydro- wt. % binder ,/m ing
alpha- wt.% cont~i ni ~g xide mm/m
hemi- ~.~po tion wt.%
hydrat- wt. %
wt. %
42.7 6.8~ 0.5 0.47 0.128 0.859
46.4 3.4* 0.25 0.47 0.133 0.288
41.7 38.6 2.9 16.9* 0.46 0.16 0.288
63 2**~ ~ 0.45 0.096 0.263
34.6 62.4 3**~ 0.46 0.032 0.175
* Portland cement cl;n~r
** 16.7% by weight of bituminou~ coal fly ash
+ O.2% by w-ight of other material
*** Al~minou~ cement
**** 2% by weight of al~m;nou~ com-nt
+ 1% by w-ight of calcium hydL~'de
