Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to fibre r~inforced cement
compositions, of the type which utilize short, chopped
fi~res for reinforcement purposesr and which are to be used
as general construction materials.
Short-length-fibre reinforced compositions of
cement based materials of various strengths are known.
Examples include asbestos-cement sheets, glass fibre
reinforced cement board, and short steel wire reinforced
concreteO One method of making them is the simple mixing
of short reinforcing fibres, for example asbestos or chopped
glass s-trands, with the matrix material in liquid formt for
example a slurry of portland cement, and subsequently
allowing -the mixture to harden. The strength of such
composites is generally relatively low, because insufficient
shor~ length fibres ~usually below 1% by volume) can be added
without increasing the viscosity of the matrix materiaI when in
its liquid form to such an extent that it becomes unhandleable.
As the viscosity increases, it becomes increasingly difficult
to coat the fibres properly. Further dilution of the cement
slurry with watex will reduce the viscosity, but at the same
time impairs the strength of the final, hardened material.
The slurry can be concentrated after mixing in the fibres,
e.g. by removing excess water under vacuum, by centrifuging
or by pressing, but thi~ adds an expensive processing step.
In another method, a continuous fibre to be used
for reinforcement is chopped ln a cut-ter and sprayed in a
sieparate stream simultaneously with the cementitious slurry,
to form the liquid composite ready for hardening. This
process rPquires comp1Px equipmene, and does not ensure
-- 1 --
~3~
uniform distribution of the fibres within the cementitious
matrix~
In another method, the fibre cement slurry (for
ex~lple asbes~os cement slurry with a very low solids
content) is poured onto a conveyor belt, and the thin sheet
of wet asbestos cement composite is picked up and wound on-to
a drum. A flat sheet of the material is produced by cutting
the material on the drum and placing it flat, with or
withou-t subsequent pressing, to remove moisture from the
lQ asbestos cemen~ composite. This process requires heavy
and complex machinery, and is no-t suitable for small-scale
operations~
These methods of the prior art all suffer from the
co~mon disadvantage, that in order to incorporate therein
a sufficient amount of short length fibres to provide good
strength characteristics (5-6% by volume of the composite),
high water content mixes have to be preparedO This is
necessary in order to provide a liquid cementitious slurry
of sufficiently low viscosity to be workable r to permit
ZO.shaping, casting, etc~ Howeverl the use of large amounts
of water in preparing cementitious composites leads to undes--
irable properties in the final~ hardened compos.ite, notably
lower strength. This is at least partly due to poor
bonding between the fibres and the matrix, and increased
porosity of the cured, hardened composite, which also has
the- effect of lowering the strength ~thereof~
The present invention provides methods ~y which
chopped fihre reinforced cementitiou5 composite5 may be
prepared which incorporate larger amounts of chopped fibres
-- 2 -
~3~
so as to increase the strength of the resulting composites,
which methods also use smaller amounts of water so as to produce
final hardened composites of improved propertles, whilst using
simple process steps and apparatus. The invention also provides
novel fibre reinforced cementitious composites.
According to one aspect of the present invention, there
is provided a fibre reinforced composite having improved
post-cracking strength, said composite comprising:
a matrix of inorganic cementitious material having
chopped fibres embedded therein, said chopped fibres comprising
first chopped fibres of a brittle, highly stiff nature
consisting essentially of mineral fibres;
and second chopped fibres of a tough, flexible nature
and selected Erom the group consisting of polypropylene fibres,
polyethylene fibres, polyamide fibres, polyimide fibres and
polyester fibres;
the average length of said first chopped fibres and
said second chopped fibres being not greater than about 2.0
inches.
Preferred mineral fibres are glass fibres and asbestos
fibres. It has been found that the use of mixtures of chopped
fibres as described above, one of the fibres being a shor-t high
stiffness, brittle fibre and the other being a low stiffness,
tough fibre, enables cementitious composites of improved
strengths to be prepared whilst using smaller volumes of water
in their preparation. Such composites have high ultimate
strength and high post-cracking strength. By the term
~'post-cracking strength" there is meant the strength
-- 3 --
~3
by which the fibre cement composite is held together, even
after serious cracking has occurred in the composite. In the
composites according to the present invention, after reachlng
their ultimate tensile st~el~gth and cracking or breaking, -the
composites exhibit a substantial residual stress resistance,
and the broken pieces remain held together by the tough
flexible second chopped fibres~ In this way, a catastrophic
failure of the fibre cement composite may be avoided~
One of the reasons why so much water has previously
had to be used in preparing chopped glass fibre reinforced
cement compositions is that the glass fibre absorbs large
quantities of water. Sufficient water must, therefore, be
added to saturate the glass fibres, and then to make a slurry
of sufficiently low viscosity to be handleableO This use of
large amounts of water leads to substantial reductions in
strength of the final, cured composite, as previously
discussed. In the present invention, however, a large
proportion of the glass fibres can be replaced with a
hydrophobic or at least less water absorbent fibre such as
chopped polypropylene. ~y this meansl less water i5 used in
preparing the composite, and a laxger amount of fibres can
be incorporatedl leading to a stronger finishedS cured
compositeO In addition, as noted above, there is obtained
the extra advantage of improved post~cracking strength,
when using combination of fibres according to the present
invention.
The reinforcing of cement compositions with fibres
results from several different effects and interactions,
depending upon the na~ure of pxoperties of ~he cement~ and
- 4 -
of the chosen fibres. In all cases, a bond is formed
between the cementitious material and the fibres. IE this
bond at the fibre-cement interface is not very strong
initlally, a tough composite may be Eormed, but the
composite may become brittle on aging and under natural
weather conditions. This happens, for example, in the case
of cementitious composites reinforced with asbestos fibres,
due to the type of manufacturing processe~ commonly used
(involving dewatering and pressing), and the chemical
affinity between cement and asbestos fibres. In the case of
glass fibre cement composites, the bond de~elGps over some-
what longer periods to time, due to continou~ fusion of the
glass fibre and the cement, but brittleness sets up with
natural weatheringO Composites of cement reinforced with
glass fibres alone, according to the prior art, have been
reported to become undesirably brit~le af~er 3-5 years
weathering in a natural environment. When such composites
fail, the failure may be catastrophic, as discussed above,
hecause of their lack of post-cracking strength. The brittle
nature of asbestos fibres and glass fibres themselves tends
to contribute to the problem of brittleness developing during
natural weathering. On the other hand, r~in~orcement of
cement composites solely with low stiffness, tough non-brittle
fibres results in composites of very low ultimate strength,
since such fibres weaken the cement matrix and al~o have lower
stiffness and ultimate strength than the glass fibres.
The use of mixture~ of the two types of fibres~ e.g.
mixtures of chopped glass fibres and chopped polypropylene
fibres, leads to fibre reinforced composites of much improved~
~3t7~
over-all, all-round strength properties r and processes for
their manufacture.
The term "cement" as used herein refers to inorganic
cements such as portland cements, phosphate cements, high
alumina cements, high gypsum cements or gypsum-~ree cements,
or combinations thereof, where these cements are distinguished
by their ability to cure in the presence of, or immersed in,
water. The term also embraces such cements which have added
thereto inorganic and organ~c compounds for improvement of
10 their 5~tting, strength gain, chemical resistance, permeability
and other properties, as known in the art.
Preferably according to the present invention, the
first and second fibres are present in the composite in total
in an amount of from about 0.5 to about 10 parts by weight,
per 100 parts by weight of inorganic components o~ said matrix.
Also/ it is preferred to use a weight ratio of first chopped
fibre to second chopped fibre of from about 5:1 to about lo~.
It is also preferred that the fibres he randomly oriented in
all directions, within the cementitiows matrix.
The most preferred fibres for use in the present
invention are chopped glass fibres as the first fibres, ar.d
chopped polypropylene fibres as the second fibres. The vas~
majority of su~h fibres should have a length not greater than
20 0 inches and most preferably the fibre length o~ both
fibre component~ should be about Q.5 inches~
~ccording to another aspect of the present invention,
the chopped glass ~i~res used in reinforcing the cementitious
composites are precoated with a hydrophobic composition, prior
to being incorporated in the inorganic cementitiolls matrix.
! 6 ~
~3~
Typical compounds which may be ~lsed for procoating for this
purpose are polyvinyl ace-tates, polyacrylics, (i.e. polymers
and copolymers o~ acrylic acid, acrylic acid ester or
acrylonitrite) polyvinyl chlorides, styrene-butadiene resins,
silicone resins, polyethylene, nylon, polystyrene and
paraffinic hydrocarbo~ waxes. Preferred precoating compounds
for use in the present invention are polyvinyl acetate,
polyacrylics and silicones~ The use of such hydrophobic,
water-repellent coatings has the effect of drastically
xeducing the amount of water which the chopped glass fibres
will absorb. This allows mixes containing high amounts of
absorbent fibres such as glass to be made with lower water
contents in the mixes, to produce a mix of workable viscosity,
and a final composite of improved strengthu
In addition to the provision of water resistance
to the glass fibres, such coatings also provide the glass
fibres with protection against alkali attack. Ordinary
glass is liable to attack by alkalis commonly contained in
cement. Special alkali resistant glasses are available but
are comparatively expensive. By using the coatings described
above, ordinary glass fibres can be given a degree of
protection against alkali attack and hence used in the
present invention with ordinary alkali content cements.
According to a further aspect of the present
invention, the cementitious composite may include various
plasti~izing additives, such as sulfona~ed naphthalene,
melamine-formaldehyde condensates~ sulfonated melamine~
formaldehyde condensates, modified ligno sul~onates and
polymeric additives such as acrylate based latexes and solid
-- 7 ~
water dispersible polymeric additives which can be re-
em~llsified to form a latex-like material in the cement slurry.
These plasticizing additives have the furlction of dispersing
the solids, including the cement, fibres and any aggregates
that may be used in the liquid mixture at relatively low
water/cement ratios, and provide sufficient workability for
direct casting or spraying of such composites. This improved
solids dispersion ensures the formation of more fluid mixtures
even at high solids contents, and improves the evenness and
random orientation of the fibres.
One preferred embodiment of the present invention
is light weight fibre reinEorced cementitious composites, in
which a mixture of first chopped fibres of a brittle, highly
stiff nature and second chopped fibres of a tough Elexible
nature as previously defined are used as the reinforcement.
Such light weight composites have densities in the range
from about 30 to about 130 pounds per cubic foot. Normal
fibre cement co~posites previously available on the market
have densities in the 130 - 160 pounds per cubic foot range.
There is a definite demand in the marketplace fcr strong,
tough, non-combustible light weight materials such as these
light weight reinforced composites, for example in light
weight partition walls, or light weight modular houses. Low
density fLbre cement composites have not previvusly been
availa~le~ mainly due to a lack of a suitable method for
their fabrication~ Attempts have previously been made to
prepare light weight cements by incorporation of light weight
aggregates into the cements, such as perlite, vermiculite or
fly ashO Due to their high porosity, however, these
3'7~
aggregates absorb large amounts of water, usually three to
five times their dry weight, even when they are treated with
water repellent materials. Consequently, the amount of water
required for mixing is very large, and the amount of fibres
which can be incorpora-ted in any such fibre-cement composite
is limited due to the bulk occupied by the aggregatPs. The
large amounts of water required for mixing these small volume
of fibres and the poor bond between the matrix and fibres
results in poor propexties of the light weight fibre cements.
It has also been previously proposed to make light
~eight cements by i~parting a uniform cellular structure into
the cement. This has been attempted using high speed mixing
during which air entrainment is effected by vigorous mixing
of water with a foaming agent. The second method employed in
producing cellular cements is by using gas forming chemicals
suoh as aluminum powder or hydrogen peroxide and calcium
hypochlorite. The cement foam produced by this method
however is not s~able in its newly formed state. Thus, the
foam changes its volume while the gas forming reaction takes
place, which in production of precast products is a disadvantage,
since the products which are mainly blocks or slabs have to
be cut to required dimensions. All these light weight cement
composites previously prepared have low strength and low
fracture toughness, but with incorporation of fibres
according to the present invention, th~s strength and fracture
toughness can be significantly pro~ed.
In one process according to the present invention~
firstly a stable, uniform air cell s~ructure foam is
pxepared by vigorous mixing of 40 to 80 parts of water and
~3~
0.20 to 0.~5 parts per 100 parts of cement by weight, of a
suitable air entraining agentO I~ is preferred to use air
entraining agents which produce a s~able, uniform foam by
using standard mortar or concrete mixlng equipment. Suitable
such air entraining agents are hydrolyzed protein and keratin
compounds, sodi~n isopropyl naphthalene sulfonate, petrolewn
naphthalene sulfate, sodium secondary alkyl sulate, saponin,
sodium alkyl aryl sulfate and highly stabilized saponified
rosin and resin compounds. The amount of air entraining
agent and the mixing procedure controls the amount of foam
produced and consequently the final density of the fibre
cement compositeO The reinforcing fibres, as previcusly
described, are then incorporated into the foam in amounts
varying from about 0.1 parts to 10 parts by weight per 130
parts by weight of cement. Alternatively, the fibres can
under some circumstances be added to the foam along with or
prior to the addition of the cement and aggregates.
It is preferred ~o use a combination of chopped
glass and chopped polypropylene fibres to obtain both
~0 strength improvement and post-cracking strength~ After the
fibre air cell foam is prepared, the cement ingredients in
the amount of 100 parts by weight, such as portlan~ cements
(including any of the types I - V), regulated set port7and
cements, gypsum cements, pozzolapic cements, magnesium
oxysulfate, magnesium oxychloride, zinc oxysulfate~ zinc
oxychlorid~, magnesium oxyphosphate, ~ZiDC oxyphosphate, methyl
silicates such as calcium sil.ica~e and alumina silicates are
then added. It is preferred to use portland cements and
regulated set portland cements as the cementitious binder.
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I
7~
Other aggregates, for example sand such as common
or silica sand, or light weight aggregat~s such as perlite,
~ermiculite, fly ash, pumice, expanded clay, or polystyrene
or carb3n beads can also be added if desired, further to
control the density of the light weight fibre cement
composite, and consequently its compressive stren~th. Sand-
can be added in amounts varying from 0 - 250 par-ts, per 100
parts of cement. The light weight aggregates can be added
in amounts varying from 0 - 50 parts by weight, per 100
parts of cement. It is preferred to use sand for
densities above 30 pounds per cubic foot composites, and
perlite for densities below 30 pounas per cubic foot
composites.
Further improvements in the strength of light weight
cement composites in accordance with the present invention
can be achieved by adding polymeric modifiers to the cement
formulation. Such modifiers are suitably added in amounts
from about 6.5 to about 27 parts by weight of dry polymeric
solids, per 100 parts by weight of cement. Commonly~ the
polymeric modi~iers are added in liquid, latex form.
Suitable such modifiers include acrylate polymers and
copolymers such as acrylonicrile polymers and copolymers,
acrylic-methacrylic acid copolymers, acrylic-styrene
copolymers, polyvinyl acetatet polyvinyl acetate modified
with versatic acid, vinyl propionate polymers, vinyl
ch1oride copolymers, polyvinyl chlorlde, vinyl propionate -
vinyl chloride ~opolymer, vinyl chloride - vinylidene
chloride copolymer and butadiene- styrene copolymer latexes.
It is preferred to use acrylate copolymers a~ modifiers for
'7~
the light weight fibre cement composites, since such
composites have good long term durability and superior
mechanical and chemical properties.
.. , ., .. ., , _ . _ . ...
The.strength.of light ~eight Ei~re'cement composites
according to the invention can be'further i~.proved by addiny
plasticizing addit.ives' such as sulfo.nated naphthalene,
melam.ine-formaldehyde condensates, sulfonated melamine~
formaldehyde condensates and modified lignosulfonates', as
previously described~ It is preferred to use these
plasticizing additives in amounts varying from about'O.l to
about 6 par~s by weight, per lQ~ parts by weight of cement.
It is preferred to add both the polymeric modifiers and the
.plasticizers into the stable air cell foam~
A typical composition of a ligh.t weight fibre
cement mix according to the present invention is as follows:
Portland cemen~, Type III100.0 parts
Water 40.0 parts
Plast.icizing additive1.5 parts
Glass fibres, 0.5 inches long 5.0 parts
Polypropylene, chopped monofilament '
fibre, O ~ 5 inches long 2.0 parts
Air entraining agent0.37 parts
The invention is further illustrated in the
following specific examples:
In all of the following specific examples, portland
cement type III was obtained from St. Lawxence Cement Company,
Toronto; silica sand was prepared and supplied by Cana~ian
Foundaries htd., Toronto plast.icizer Melment L-10~ a
sulfonated melamin~-formaldehyde condensate, was supplied by
;
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~i3~7~
Sternson Ltd., Brantford, Ontario. The ~R glass fibres were
those available from Fiberglas Canada Ltd., Guelph, Ontario,
and are alkaline-resistant glass fibres, designa-ted AR
chopped strand 385 CD, 0.5 inches long. The E glass fibres
were also obtained Erom Eiberglas Canada I,td., Guelph,
Ontario, and are tnose designated E glass chopped strand
01-956 899-00, 0.5 inches longO The polypropylene
monofilament fibre, 0.5 inches long and 0.006 inches in
diameter, was supplied by Whiting Co., Burlington, Vermont,
U.S.A.
EXA~LE 1
Two types of fibre cement composites were prepared
to illustrate the advantages of the present invention. The
composite referred to hereinafter as A is a control and
contains glass fibre as so~e reinforcement. The composite
referred to hereinafter as B is reinforced with the
combination of glass and polypropylene fibres, in accordance
with the present invention. The mixes had the following
cornpositions:
20 A. Portland cement, type III 100 parts
Sillca sand, mesh 40 50 parts
Superplasticizer Melment L-105 parts
Chopped AR glass fibres, 0.5 inches long 5 parts
Water 30 parts
B~ Portland cement, type III 100 parts
Silica sand, mesh 40 50 parts
Superplasticizer~ Melment L-lQ5 parts
Chopped AR glass fi~res, Q.5 inches long 5 parts
Chopped polypropylene monofilament fi~re~ 2 parts
.
~ater 30 parts
7Z~
Both compositions were hand mixed and a layer about
29 1/4 inch.es thick was cast. After one week curing at 1~0
relative humidity, the~strip~ 1 inches ~ide and 7 inche~
long were tested in tension using the Universal Instron
Testiny Machine. The average ultimate'strengths of composites
A and B were 640 psi and 700 psi respectivelyD Whils~
the ultimate strengths of both composites are'comparable,
the fracture modes differ. Composite A does' not exhibit any
residual strength after the ultimate tensile strength i5
10 reached, the stress in the composite is zero, and the
composite is broken into two separate pieces. Composite B,
after reaching its ultimate tensile strength, exhibits a
residual stress of 250 psi and the two broXen pieces are
held together by the polypropylene fibres.
The example demonstra-tes the advantaye of using a
combination of high and low stiffness fibres as rein-forcement
for cement, since such a combination prevents a catastrophic
failure of the fibre cement composite.
EXAMPLE 2
Two types of light weight fibre cement composites
were prepared tv illustrate the advantages of the present
,invention. The compvsite referrea to hereinafter as C
is a control and contains glass fibre as sole reinforcement.
I'he composite referred to hereinafter as D i5 reinforced
with the combination of glass and polypropylene fibres, in
accordance with the present invention. The mixes have the
following compositions:
~ t7~
C. Portland cementr. type III . lOO.parts
~ater 60 parts
Celluchem air entraining agent 0.37 parts
Chopped AR glass fibres, 0.5 inches long 5 pa~ts
-
D. Portland cement~. type III lQ~ parts
Water 60 parts
Celluchem air entraining agent 0.37 parts
Chopped AR glass fibres, 0~5 inches long 2.5 parts
Chopped polypropylene monofilament fibres 1 part
~ .. . . . . . . . . ....... . . . .
Celluchem air entraining agent~ which is a
mixture of an air entraining and a non-air entraining agent
in an inert base was supplied by Bowaine Ltd., Boxmoor,
Hemel Hempstead, England.
In preparation of both composites, the air cell
foam was formed first by mixing water and the air entraining
agent for 3 minutes, using a Hobart food mixer~ The fibres
were added into the air cell foam and mixed for 1 minute
and then the cement was added and mixed for an additional
2 minutesO
Specimens measuring 2 inches by 2 inches by 2 inches
were cast from bo-th mixes and air cured for 7 days. The
average compresive strength of both composites was 580 psi's;
however their behavior after reaching the ultimate
compresive strength was different~ Sample D, containing the
combination of glass~and polypropy1ene fibres~ exhibited
more ductile fractuIe behavior and also when gross cracking
occurred, the composite was still held together, whereas
the sample C was broken to individual pieces. The densi~y
of the sample5 ranged fronl 33 pounds per cubic foot to
,:
37 pounds per cubic foot.
EXAMPLE 3
.
Two types of fibre cement composites were
prepared. The composite referred to hereinafter as E was
rein~`orced with treated chopped glass fibre and chopped
polypropylene fibre. The composite referxed to
hereinafter as F contained non-treated glass fibre in
combination with chopped po~yprop~lene fibre. The mixes
had the following compositions:
E. Portland cement, type III 100 parts
Silica sand, mesh 40 50 parts
Latex E--330 30 parts
Chopped E glass fibres, 0~5 inches longl treated 3 parts
Chopped polypropylene, monofilament fibre 0.5 parts
Water 17 parts
Anti-foaminy agent AF-60 0.1 parts
F. Portland cement~ type III100 parts
Silica sand, mesh 40 50 parts
Latex E-330 30 parts
Chopped E glass fibres, 0.5 inches long~
non-treated 9 parts
Chopped polypropylenej mono~ilament fibre 0.5 parts
Water 27 parts
Anti-foaming agent AF-60 ~0.1 parts
Lat~x E-330, which is an acrylate copolymer latex,
was supplied by Rohm and ~aas Corpora~ion ~imited, Toronto;
the anti-foaming agent AF-60, which is a silicone base~
material, was supplied by Canadian General Electric, Toronto.
Ordinary tap water was used in preparing the mixes~
. :
16 -
'725~
The glass fibres of mix E were txeated by soaking
them for several minutes in a water~repellent compound
comprising a soluti.on of a paraffinic hydrocarbon wax and a
silicone in a suitable solvent, and hot ai.r dried.
Both mixes were hand mixed b~ first mixing the
solids, i.e. the cement and sand into the liquids, i.e. water,
latex and anti-foaming agent, and then the chopped
polypropylene and glass fibres were addedO Flat sheets,
1/4 inch thick, were cast and air cured for one week. Samples
7 inches long and 1 inch wide were cut and tested in
tension using the Instron. The specimens of composite E
exhibited an average ul~imate tensile strength of 1150 psi;
the specimens of composite F exhibited an average ultimate
tensile strenth of 8~0 psi.
..... ~ .. . . . . .
The lower strength of composite F was primarily due
to the higher water content in the composite (27 parts as
opposed to 17 parts of water in composite E), which was
required to obtain similar workabilities of both mixes.
The higher water xequirement in composite F is
consistent with the higher water abscrption of non-treated
fibres. It was found that the treated fibres absorbed,
on average, 42% water relative to their dry weight, whereas
:: : :
the non-treated fibres absorbed an average of 142~ by weight
..of water.
EXAMPLE 4
. _ :
The composite prepared in this exàmple is a typical
: example o~ polymer-modified~cement, but reinforced with a
:: :
combination of chopped polypropylene and gIass fi~res in
accordance with the invention The mlx had the following
- composition: :
~ 17
99
Portland cement, type III100 parts
Silica sand, mesh 40 50 parts
Latex E-330 30 parts
Chopped AR glass fibre, 0 5 inches 10n~ 4 parts
Chopped polypropylene monofilament fibre,
0.5 inches long 0~7 parts
Anti-foaming agent AF-60 0.1 parts
The composition was hand mixed by first mixing
the solids, i.e. the cement and sand into the liquids~ i.e.-
the water, latex and anti-foaming agent, and then the
chopped polypropylene and glass fibres were added.
A flat sheet, 1/4 inch thick, was cast and air cured for
1 week. The samples, 7 inches long and 1 inch wide were
... ... . ... . . . . . . . .
cut and tested in bending using the Instron. The average
modulus of rupture was 3950 psi.
E~AMPLE 5
In this example, the plasticizing effect which is
desirable in the absence of a latex modifier in the cement,
is shown. The following mix was prepared:
Portland cement, type III100 parts
Silica sand, mesh 40 50 parts
Plasticizer Melment L-10 5 parts
Chopped AR ~lass fibre, 1.0 inches long 5 parts
Chopped polypropylene, monofilament fibreJ
0.5 inches ~ong 0.6 parts
Water 33 parts
The presence of the plasticizer Melment L 10 not
only makes the cement slurry castable at given amounts of
water, but also allo~s mixing in o the required amount of
-~18 -
fibres necessary for obtaining a composite of sufficient
strength.
An attempt was made to prepare a composite having
~he same water content as that of the mix given ahove in
this example, without adding the plasticizing agent Melment
L-10. The viscosity of the prepared cement slurry was so
high that it did not allow mixing in of any significant
amount of chopped fibres.
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