The present invention generally relates to concrete or
cementitious materials reinforced with a fabric, especially a weft insertion warp
knit fabric, and to a fabric for such reinforcement. Such reinforced concrete or
cementitious materials can be formed as plates or panels, undulated or not, used
in applications such as the flooring or covering of constructions intended for agriculture,
industry, such plates or panels can also be used for the domestic dwellings in both
the covering and as cementitious boards.
discloses an open grid fabric for reinforcing wall segments having high
strength, alkali resistance, and impact resistance. The fabric has warp, weft, and
tie yarns and comprises certain knits and leno weaves, including a warp knit weft
inserted fabric, and bears an alkali resistant resin coating. However, this document
does not teach that the warp and weft yarns may be monofilaments or twisted multifilaments,
or that the tie yarns may be knitted with a tight tension.
There is a need for a knitted reinforcement fabric that
can withstand the alkaline environment of concrete and has a precise construction
with evenly spaced and parallel wales.
Brief Description of the Drawings
In the following, preferred embodiments of the invention
will be exemplified with reference to the accompanying drawings.
- FIG. 1
- is a cross sectional drawing of one embodiment of the reinforced concrete;
- FIG. 2
- is a cross sectional drawing of one embodiment of the reinforcing fabric;
- FIG. 3
- is a drawing of an in-lay warp cord in weft insertion warp knitted fabric on
the front face;
- FIG. 4
- is a drawing of in-lay warp cord in weft insertion warp knitted fabric on the
- FIG. 5a
- is a drawing of the pattern chains for one embodiment of the inlay warp cord
in weft insertion warp knitted fabric shown in FIGS. 3 and 4.
- FIG. 5b
- is a drawing of the lapping movement for ore embodiment of the in-lay warp cord
in weft insertion warp knitted fabric shown in FIGS. 3 and 4.
- FIG. 6
- is a photograph of an embodiment of the weft inserted warp knit fabric according
to the present invention.
Fig. 1 shows reinforced concrete (10) containing a cementitious
material (100) and a reinforcing fabric (200). The fabric is shown embedded in the
concrete material towards the surface of the concrete, but is not limited to this
construction and may be on an outer side of the concrete or more towards the middle.
Additionally, more than the one shown layer of reinforcing fabric (200) may be used.
Concrete is made up principally of cementitious material,
fine aggregate, coarse aggregate, water, air, chemical admixtures, and fiber. The
cementitious material is the glue that holds concrete together. Typical cementitious
materials used in concrete are Portland cement, fly ash, blast furnace slag, and
silica fume. Portland cement is the dominant cementitious material used, andthe
other cementitious materials will typically be added to the Portland material to
adjust its performance and cost.
Portland cement is a mixture of many compounds, and the
four major constituents are tricalcium silicate, dicalcium silicate, tricalcium
aluminate and tetracalcium aluminoferrite. Each Portland cement contains different
amounts of these major components. The calcium silicates (representing ~75 wt.-%
of the Portland cement) react with water to form calcium hydroxide and calcium silicate
hydrate. The calcium silicate hydrates provide the principal performance benefits
of cement. The highly alkaline environment of cement is due to the hydroxides such
as calcium hydroxide and the lime (CaO) present in the cement.
Fine aggregate consists of natural or manmade sand with
a particle size distribution whose maximum size is typically 9.5 mm. Coarse aggregate
consists of natural or manufactured particles (typically rocks) with a size of approximately
1.2-152 mm (0.3-6 inches). Aggregates typically make up 6075% of the final concrete.
The water is critical for the hydration of the cement.
The water/cementitious material ratio determines many of the critical properties
The reinforcing fabric of the invention is typically used
towards the center of the cementitious material. In wall applications or backing
for tile, the fabric is typically used towards the outside of the cementitious material
on one or both outside surfaces.
Fig. 2 shows a cross sectional drawing of the reinforcing
fabric (200) made up of the weft inserted warp knit fabric (210) and the alkali
resistant coating (220). The coating completely covers the fabric yarns to protect
the yarns from the cement environment.
Figs. 3 and 4 show the weft inserted warp knit fabric (210),
which is made in a weft insertion warp knit machine with in-lay warp yarns (212),
weft inserted yarns (213), and stitching yarns (211). The stitching yarns stitch
in a specific chain stitch pattern wherein the fabric (210) is stabilized and precisely
maintained in a parallel way. The reinforcing fabric has at least one layer of a
weft inserted warp knit fabric (210) including in-lay warp yarns (212), stitching
yarns (211), and weft inserted yarns (213), wherein each stitching yarn (211) forms
a wale around a corresponding inlay warp yarn (212), and wherein the weft insertion
yarns (213) are inserted in a parallel repetitive construction in the stitches of
the stitching yarns (211).
The in-lay warp yarns (212), stitching yarns (211) and
weft yarns (213) may be formed with any man-made material that meets the necessary
physical properties, such as polyamide, polyester, rayon, para-aramid, fiberglass,
polyolefin, polyvinyl, polyvinyl alcohol (PVA), steel, carbon, meta-aramid and derivates,
polyacrylic and any other known yarn material containing artificial or natural fibers.
Also, hybrid yarns made of at least two fibers of different materials can be used.
These different fiber materials can produce hybrid yarns with different chemical
and physical properties. Hybrid yarns are able to change the physical properties
of the final product they are used in. Preferred examples of hybrid yarns include
an aramid fiber with any of a nylon fiber, a rayon fiber, and a polyester fiber.
In some embodiments, the warp and weft yarns are not sized
The inlay warp yarns (212) and/or weft yarns (213) preferably
may be any of single monofilament yarns, multiply twisted filament yarns, and substantially
twisted multifilament yarns. "Twisted filament" here means a multifilament yarn
having a twist of preferably at least Z60 or S60 (60 turns/m in the right (Z) or
left (S) direction). It also includes several multifilament yarns twisted together,
preferably by at least Z100 or S100 twist. Each individual multifilament yarn could
be untwisted or could be pre-twisted before being assembled or cabled to get together
a final additional twist of preferably at least Z100 or S100.
A concrete example useful in the present invention is a
1100 dtex f210 PVA yarn twisted Z60, then assembled at four of these yarns and twisted
again with S100 (a twisted filament yarn referred to as (1100 dtex f 210 Z60) x
4 S100). The warp and weft yarns may also be formed from staple fibers. The warp
yarns (212) and weft yarns (213) are not roving.
The in-lay warp yarns (212) and weft yarns (213) preferably
have a weight per unit length of 100 to 23,500 dtex (90 to 21,000 deniers) made
with single or multiple yarns (for example, 235 dtex (single end); or (235 dtex
x 2 x 3 plies) = 1,410 dtex or (1,100 dtex x 3 x 3 plies) = 9,900 dtex (multiple
ends)). In some fabric constructions, the in-lay warp yarns (212) are placed such
that there are 0.1-4 ends/cm (0.25-10 ends/inch) in the weft inserted warp knit
fabric (210). The number of ends is defined as the number of wales or the number
of needles (or gauge) on a warp knitted fabric or the number of warp yarns per cm
The stitching yarns (211) may be made with any single monofilament
or twisted multifilament, or may be made of staple fibers. In a preferred embodiment
the stitching yarn (211) has a weight per unit length of 22700 dtex (20-630 deniers)
and may be a single yarn or may be twisted multiply yarns.
Fig. 3 shows the front side of one embodiment of the invention
where the weft yarn (213) inserted every forth stitch of the stitching yarn (211).
Fig. 4 shows the backside of the embodiment of Fig. 3. Each individual stitch yarn
(211) forms a wale of stitches along an associated warp yarn (212). The stitching
yarns (211) join a sheet of weft yarns (213) with a sheet of warp yarns (212) when
each of the weft yarns (213) are inserted in the corresponding stitch of the stitching
yarns (211) along the warp yarn (212). This particular joining between the two sheets
of reinforcing yarns (warp and weft yarns) maintains a parallel and equal interval
between these reinforcing yarns.
The fabric (210) of the invention can be produced on a
weft insertion warp knit machine, which is wider and faster than a traditional weaving
machine makingthe process economical. For the fabric (210), the chain stitch pattern
is worked on one needle for each individual warp yarn (212) and weft yarns (213)
are inserted in a repetitive construction. Fig. 5a shows the chain pattern of the
embodiment of the present invention shown in Figures 3 and 4. Fig. 5b shows the
lapping movement for the embodiment of the present invention shown in Figs. 3 and
4. An image of the weft inserted warp knit fabric (210) is shown in Fig. 6.
The stitch used for the stitching yarn (211), as shown
in Figs. 3, 4, 5a and 5b, is a chain stitch working always on the same needle. The
chain stitch may be made with opened stitches (0.1/1.0 or 1.0/0.1) as represented
in all figures. The chain stitch may also be made with closed stitches (0.1/0.1
or 1.0/1.0) or a combination or mixture of both open and closed stitches (as example
only: 0.1/0.1/1.0/1.0). In one embodiment, the pattern for the chain stitching yarn
used for the in-lay cord warp (212) is a 0.0/1.1 movement around the same needle,
alternatively changing at each stitch, one stitch on the right side of the needle
and next stitch on the other left side of the same needle, or in opposite way, first
stitch on the left side then second stitch on the right side of the same needle
(1.1/0.0). If closed stitch and opened stitch are mixed, the in-lay movement of
in-lay bar would be adapted following the result needed, it is possible to also
mix the movement of inlay bar versus the stitching bar (as example: 0.0/1.1/1.1/1.1/0.0/0.0),
without any limitation.
In one embodiment, the stitching yarn (211) stitches with
high tension creating a secure connection between the in-lay warp (212) and weft-inserted
yarns (213). Prior art teaches that loose tension is preferred because it permits
a polymer coating to penetrate the warp yarn strands more uniformly and deeply.
It has been found that using a high or tight tension on the stitching yarn (211)
creates a fabric with a precise construction of the warp yarns (212) and weft yarns
(213) in terms of geometry, spacing, and stability, while at the same time having
an even coating on the yarns (211), (212), and (213). In a preferred embodiment
of the invention, the ratio of the length of stitching yarn (211) to the length
of in-lay warp yarn (212) is 3.1 or less, and more preferably the ratio is within
the range of 2.63.0.
The denier of the stitching yarn (211) may be approximately
the same or different than the denier of the inlay warp yarn (212).
The weft insertion warp knit machine gives the possibility
to stabilize the inlay warp yarn (212) on a flat plane with the insertion of a weft
yarn (213) in the chosen stitches of the stitching yarn (211). The weft yarn (213)
may be inserted in each stitch or in a repetitive construction (repetitive construction
including each stitch or any multiplicity of stitches), for example one weft in
each four stitches. The terminology used to describe this weft insertion is one
stitch with a weft inserted in (called "1 in") with three consecutive stitches without
a weft inserted in (called "3 out").
There is no limitation in the construction and in the repeat
of the pattern, for example: 1 in 1 out, 1 in 2 out, 1 in 3 out (Figs. 3-5b), 1
in 4 out, 1 in 5 out, etc. In a preferred embodiment, the weft inserted yarns(213)
are inserted every 4 stitches of the stitching yarn (211). In this embodiment one
can increase the size of the open scrim without losing any stability and geometry
of the scrim. To obtain an open scrim, having less weft yarns inserted per cm (inch)
is preferred over increasing the size of each individual stitch having a weft inserted
in each stitch.
For example, with one weft each four stitches, the fabric
has 6.3 stitches/cm (16 per inch) and 1.6 weft yarns/cm inserted (4 per inch), which
means that each of the stitches has a small size. On the other hand, with one weft
per stitch, the fabric will have only 1.6 stitches/cm (4 per inch) and 1.6 weft
yarns/cm inserted (4 per inch), which means that each stitch is much larger. Having
one weft insertedevery 4 stitches enables the stability and geometry of the fabric.
The fabric is desired to be open allowing the cementitious
material to pass through the fabric. More closed fabrics, such as when a weft yarn
(213) is inserted at each stitch of the stitching yarn (211), produce a fabric that
will not allow for as much penetration as a more open fabric.
It is desirable to keep the length of each stitch as small
as possible and having several stitches without weft inserted, compared to maintaining
the rafe of one weft/one stitch and increasing the length of stitch to open the
space between weft yarns. Increasing the length of the stitch may cause the fabric
to become loose and not stabilize the fabric as much. Hence, the present fabric
has a structure, which is sufficiently open to allow a good flow of the cementitious
material through the fabric, thus allowing easy processing, and at the same time
good stabilizing and reinforcing properties are achieved.
In one preferred embodiment, the weft yarns are inserted
at a rate of 0.8-16 stitches/cm (2-40 stitches/ inch). As an example, with one weft
in each four stitches (1 in 3 out), the fabric will contain 0.2-4 wefts/cm (0.5-10
wefts/inch). Another embodiment of the invention may have 0.1-4 wales/cm (0.25-10
wales/inch). As an example, with 2.36 needles/cm (6 needles/inch) and one in-lay
yarn and one stitching yarn per needle, the number of wales could be 2,36 wales/cm
(6 per inch). The space needed between wefts will determine the construction per
After the weft inserted warp knit fabric (210) is formed,
it is then coated with the alkali resistant coating (220) (See Fig. 2). Such coatings
include, but are not limited to composite plate, rubber material, styrene butadiene
rubber (SBR), and polyvinyl alcohol (PVA) coatings. The coating (220) must be resistant
to bases such as NaOH, KOH, and Ca(OH)2. The coating may be applied by
any known means such that all of the yarns of the fabric (210) are coated in the
alkali resistant material. Preferably, the weight of the coating (220) should be
within the range of 1560 g/m2, more preferably 20-50 g/m2,
even more preferably 25-40 g/m2 to protect the fabric (210) against the
alkaline of the cementitous material (100). A preferred specific example may be
a coating weight of about 30 g/m2.
The fabric (210) coated with the alkali resistant coating
(220) should pass at least one of the Austria norm test B 61 22, the FR norm tests
(Building Norm M1) and the test according to German DIN 4102. These tests are related
to concrete products, which are used in the internal portion of buildings. The geometric
shape, or stability of the fabric, needs to be held stable. Stability of the fabric
(210) is to the thickness of the fabric and stiffness is related to the Tg (glasstransition
temperature) of the alkali resistant coating.
In one embodiment, the alkali resistant chemical of the
coating (220) is Penformax® 18034 F, which is a formulated compound,
based on a blend of a soft and stiff carboxylated SBR latex, in order to modify
the Tgof the coating. The soft SBR has a styrene content of 50 wt.-%, a butadiene
content of 50 wt.-%, and a Tg of -2°C. The stiff SBR has a styrene content
of 75 wt.-%, a butadiene content of 25 wt.-%, and a Tg of +54°C. The styrene
and butadiene content of the soft and stiff SBR may be varied to obtain the desired
physical characteristics. In Performax® 18034 F the weight ratio
of soft SBR to stiff SBR is 60:40. In other SBR mixtures, the soft and stiff SBR
polymers may be present in a weight ratio of 90:10 to 10:90, more preferably 60:40
to 40:60, depending on the stiffness desired to achieve. The SBR mixture imparts
excellent alkali resistance to the fabric (210) and good adhesion to the cementitious
material (100). Optionally, melamine resin may be added to the polymer of the coating
(220) in order to modify the stiffness.
In another embodiment, PVA is used as the coating (220)
because of its compatibility with concrete (tensile strength, temperature stability,
elongation at break, and temperature stability) as well as its excellent alkali
resistance. PVA is available as, for example, as Vibatex KN® (Ciba
Geigy). PVA may also be modified with a fluororesin, such as Flovan CGN®,
other fluororesin chemicals, or other chemicals.
The fabric (210) or the yarns, (211), (212), (213) making
up the fabric may also be subjected to chemicals that improve the adhesion of the
reinforcing fabric (200) to the cementitious material (100) or to give other advantages
such as nonwicking and/or fire proofing. In certain embodiments, a blue or other
coloration may be added for identification of the fabric.