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					                                                                                               CONCRETE TECHNOLOGY


          Fibre reinforced concrete in the USA                                                                       SPECIAL
                                                                                                                             PRI
                                                                                                                       CPI 05/ NT
                                                                                                                              06
Premix Glass-Fiber Reinforced
Concrete – Production Processes and
Product Applications
Premix glass fiber reinforced concrete products                       mixing processes and the methods of manufac-
are formed by mixing pre-chopped glass fibers                         ture of Premix glass fiber reinforced concrete pro-
and a sand/cement concrete (no large aggregate)                       ducts. The composite will be referred to in the
and processing the resulting fiber reinforced com-                    shortened term Premix.
posite. This paper discusses the commonly used

                  John Jones,                 Two-speed mixers are also preferred for         to medium volume operations. Larger
    Nippon Electric Glass America Inc., USA   manufacturing Premix. The 2-speed high          volume operations usually use mixing
                                              shear mixer provides much better quality        systems like the one shown in Figure 1,
The two most common processes in the          mixes than conventional concrete mixers,        where varying degrees of automation can
USA for the manufacture of products in        whose action requires the presence of           be used. The lowest capital cost usually
Premix are casting (usually incorporating     aggregate to achieve optimum mix quali-         involves manually feeding pre-weighed
vibration) and spraying. Irrespective of      ty. Conventional mortar and concrete            dry materials with volumetric metering of
which process is used, manufacture starts     mixers can be used but are less efficient       liquids. For full automation the dry materi-
with mixing of the individual ingredients.    than high shear mixers, in that mix pre-        als are fed from silos or hoppers via screw
Like GFRC the basic Premix matrix com-        paration takes longer. Also these mixers        augers. They are automatically batched in
prises sand/cement slurry. There is no        present problems with fibers collecting on      a weigh-hopper and then discharged into
large aggregate in the mix. Figures 1 and     the mixer blades than do high shear             the mixer. The glass fibers are usually fed
2 show typical batch mixing systems for       mixers. Figure 2 shows the simplest type        from continuous roving and chopped to
Premix. The most popular mixing principle     of mixer in which all materials are hand-       the desired length directly into the mixer.
for Premix is one that achieves a shearing    fed and the mixer is also controlled manu-      The glass fiber chopper (Figure 3) is con-
action in the mix.                            ally. This type of mixer is popular for small   trolled either by a timer or loss-in-weight




   1                                                                                            2

Automated batch mixing plant for Premix that uses 2-speed high shear mixer                    Manual High Shear Mixer

www.cpi-worldwide.com                                                                                           CPI – Concrete Plant International – # 5 – October 2006   1
    CONCRETE TECHNOLOGY


                                                                    Table 1: Typical mix formulation for Premix casting

                                                                             Ingredient          Weight [kg]                 Comment

                                                                     cement                      45

                                                                     Silica sand                 30-45         Higher content reduces workability

                                                                     water                       13            w/c ratio= 0.34 with water from polymer

                                                                     Polyplex Polymer            5             Emulsion, approx. 50% water

                                                                     Superplasticiser            150-290 ml Exact amount to suit application
        3
                                                                     AR Glass Fiber chopped 3-4,5              Typical lengths between 12 mm and 25 mm
    Multi-roving Chopper Feeder                                      strands, NEG PH901X,                      or blends of different lengths
                                                                     or H530X

    scale, which are pre-set to give the desi-                      in fiber balling, poor fiber distribution,
    red fiber content. The choice between par-                      and poor quality Premix. The maximum
    tial and full automation depends on scale                       recommended mixing time for the fibers is
    of operation and local labor costs.                             two minutes. The systems referred to
    The order of adding materials is the same                       above require less than 30 seconds to
    for manual systems or automated systems.                        achieve uniform fiber distribution. After
    All liquids are first dispensed followed by                     preparation of the composite, the mix is
    sand, cement and any other dry materials.                       ready to be placed in the mold. This is usu-
    The mixer is run at its high speed (usually                     ally achieved by either casting or spray-
    around 1,000 rpm) to provide a good                             ing.
    quality, uniform slurry. The mixer is slowed
                                                                                                                     5
    to its slow speed of less than 200 rpm for                      Casting
    addition of the glass fibers; mixing the
    glass fibers at the higher speed would                          In this process the mix is poured into the
    damage the fibers. The glass fibers are                         mold. As it is being poured it is usually
    always added last and mixed for the mini-                       vibrated, either by vibrating the material
    mum time required to achieve uniform                            directly with a vibrating screed or trowel,
    dispersion of the chopped strands. It is                        or by vibrating the mold. Vibration achieves
    important to ensure that minimum time is                        two objectives; firstly it causes the Premix
    spent mixing the fibers because they can                        to flow and thereby fill the mold and
    be damaged by excessive mixing. The                             secondly it expels air from the composite
    glass fibers used in Premix are bundles of
    filaments and these bundles can be
    broken down, or filamentized, by excessi-                                                                        6
    ve mixing. Filamentization usually results
                                                                                                                   Spray-Premix process


                               John Jones was a member of the                                                      and compacts it, which is necessary for
                               original market development group                                                   good quality Premix. A major necessity in
                               in Pilkington Brothers Ltd. in the                                                  vibration casting is to avoid excessive
                               UK that developed Alkali Resistant                                                  fiber orientation, which will cause non-uni-
                               (AR) glass fibers and the related
                               Glass Fiber Reinforced Concrete                                                     form strengths in the composite. This can
                               (GFRC or GRC) technology in the                                                     be achieved by avoiding excessively long
       early 1970’s. Since then he has been in involved in deve-                                                   flows of the Premix by charging the mold
       loping and manufacturing of a wide variety of GFRC pro-                                                     at more than one location. However, flow
       ducts. He is currently the manager for the AR Glass Fiber
       Division in Nippon Electric Glass America Inc. in USA and                                                   or knit-lines must be avoided. These can
       is responsible for the sales and marketing throughout                                                       be caused where two material flows meet
       USA, Canada, Mexico, and Central and South America.                                                         but do not merge, thereby causing a weak
       Nippon Electric Glass is a leading manufacturer of AR                                                       plane in the product. Stiff or dry mixes can
       glass fibers and is headquartered in Japan.                   4
                                          JJones@negamerica.com                                                    be prone to this problem, so it advisable
                                                                    Peristaltic Pump                               to use high flowability mixes in the casting

2   CPI – Concrete Plant International – # 5 – October 2006                                                                                         www.cpi-worldwide.com
                                                                                                  CONCRETE TECHNOLOGY


Table 2: Typical mix formulation for Spray-Premix                                                ling eliminate entrapped air and provide
                                                                                                 high composite density. As with Cast-
                 Ingredient   Weight [kg]                    Comment                             Premix other mix ingredients may be used
                                                                                                 for specific features.
   cement                     45
                                                                                                 Comparison of Cast Premix
   sand                       35              Spraying needs good workability, hence             and Spray Premix
                                              lower sand content
                                                                                                 Spray-Premix is particularly suitable for
   Water                      15                                                                 products with a high degree of shape or
                                                                                                 ornamentation, and where a high degree
   Polyplex Polymer           7                                                                  of finish is required. Spraying allows pro-
                                                                                                 ducts to be produced with a uniform thick-
   Superplasticiser           150-290 ml                                                         ness (typically 20 mm) in an open mold,
                                                                                                 irrespective of shape or profile. Casting
   Pump aid                   15 g            Optional                                           such products requires more expensive
                                                                                                 matched molds. Spray-Premix is also very
   AR Glass Fiber chopped 2.5 - 4             Typical lengths are 12 mm to 36 mm,                suitable where an architectural finish is
   strands, NEG PH901X                        or blends of different lengths                     required. This can easily be achieved by
   or H530X                                                                                      first spraying or applying a face-coat of
                                                                                                 the desired finish on to the mold surface
                                                                                                 before the Spray-Premix is deposited.
process. Other mix ingredients that are           tube as they rotate. Figure 4 shows a typi-    Casting, or vibration, can disturb the finish
used for specific processing characteri-          cal peristaltic pump. The pump forces the      and affect its quality. Vibration casting
stics and product performance include             Premix along a material delivery hose to       can be advantageous in high volume pro-
pozzolans, fast-set cements, lightweight          a spray nozzle. The composite is ato-          duction where the higher capital costs of
fillers, and slag cement.                         mized in the nozzle by air jets. The result-   matched molds can be profitably ab-
                                                  ing atomized spray is deposited onto the       sorbed. It is also very suitable for the high
Spray-Premix                                      mold surface (Figures 5 and 6). The com-       volume manufacture of products that are
                                                  posite is usually sprayed down in layers.      essentially flat with a simple surface tex-
In this process the mix is discharged from        Compaction rolling is done between lay-        ture.
the mixer into the hopper of a peristaltic-       ers to expel air and compact the compo-
pump. A peristaltic pump operates by              site. Vibration is not usually needed in       Product Applications of Premix
squeezing the mix through a rubber                spray-Premix because the material does         Glass Fiber reinforced
pump-tube by means of a rotating carou-           not need to flow to fill the mold and the      Concrete
sel of steel rollers that compress the pump       force of the spray and the compaction rol-
                                                                                                 Cast premix panels for modular buildings

                                                                                                 Figure 7 shows a simulated split-block pat-
                                                                                                 tern on exterior wall panels for a con-
                                                                                                 venience store. An automated plant simi-
                                                                                                 lar to that shown in Figure 4 is used for
                                                                                                 producing the Premix. The mix is vibration
                                                                                                 cast into molds that are moved past the
                                                                                                 mixer on a carousel conveyor. A fast set
                                                                                                 cement mix is used that allows de-mold
                                                                                                 after about 1 hour. Standard panels, 2.4
                                                                                                 m x 1.2 and 3 m x 1.2 m are produced. A
                                                                                                 variety of patterns are available including,
                                                                                                 brick, stone, and textured stucco. The
                                                                                                 panels are painted to provide the re-
                                                                                                 quired color. The panels are installed by
                                                                                                 fastening through the face to a stud-frame
                                                                                                 support.

                                                                                                 Insulated panels
   7
                                                                                                 Figure 8 shows insulated panels used in a
Premix panels with a simulated split-block pattern used for convenience store wall panels        developmental energy-efficient house.

www.cpi-worldwide.com                                                                                               CPI – Concrete Plant International – # 5 – October 2006   3
    CONCRETE TECHNOLOGY


                                                                  cooling systems. The heat and humidity
                                                                  patterns throughout the house are con-
                                                                  tinuously monitored by a computer to pro-
                                                                  vide the data to demonstrate the energy
                                                                  efficiency of the design. The house is lived
                                                                  in by a family.

                                                                  Cast-Premix roof tiles

                                                                  Figure 9 shows an example of Premix roof
                                                                  tiles manufactured using Cast-Premix. The
                                                              8   Premix is prepared in a semi-automated
                                                                  batch plant as shown in Figure 1. The
    The insulated panels in an energy-efficient                   Premix is cast into a mold where up to 12
    house                                                         tiles are cast at one time. The molds are
                                                                  then stacked and the tiles are de-molded
                                                                  the following day. The tiles are nominally
                                                                  6 mm thick and various sizes up to 360 x
                                                                  540 mm. The tiles meet ASTM C1186-02
                                                                  freeze thaw test. Initial testing has shown
                                                                  them to resist damage from hail stones but
                                                                  there is no standard test to reference at
                                                                  this time. The Premix tiles are competitive
                                                                  with flame retardant cedar wood shakes
                                                                  and other premium residential roofing pro-
                                                                  ducts. A full range of slate colors are avail-
                                                                  able.

                                                              9   Dome Panels and Terra-Cotta Replicas

    Cast-Premix roof tiles                                        Figures 10 and 11 show dome panels
                                                                  manufactured using Spray-Premix. These
                                                                  panels were manufactured using the mold
                                                                  shown in Figure 6. Figure 12 illustrates a        Acknowledgements
    These panels were produced using the                          replica of simulated terra-cotta piece
    Spray-Premix process. The panels have                         made in Spray-Premix.                             Figures 1-5 courtesy of Powersprays
    sandwich construction with 12 mm outer-                                                                             Co. Ltd.
    skins of Premix and a 250 mm poly-                                                                              Figures 6 and 12 courtesy of GFRC
    styrene core. The house was designed by                                                                             Inc.
    Zero-Net Inc. and is part of an Alliant                                                                         Figure 7 courtesy of Innovative
    Energy Co. program to research energy                                                                               Concrete Products Inc.
    efficient house design. The house contains                                                                      Figure 8 courtesy of Zero Net Inc
    all state-of-the-art energy efficient applian-                                                                  Figure 9 courtesy of Slate Select Co.
    ces, windows, doors, and heating and                                                                                Inc




                                                                                                                   12
      10                                                          11
                                                                                                                   Replica of simulated terra-cotta piece
    Dome panels made by Spray-Premix                              Finished dome                                    made in Spray-Premix

4   CPI – Concrete Plant International – # 5 – October 2006                                                                                        www.cpi-worldwide.com

				
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