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Prepacked
Shotcrete Admixture : Spray-Con WS
The Need
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Over the past 10 years, the wet shotcrete
method has become increasingly used in the repair of vertical and overhead concrete
surfaces. This is due, in part, to advances in materials such as the introduction of
silica fume (microsilica), fibers and super-plasticizers, which not only make shotcrete
easier to place, but also improve its durability. Batching all these materials in the
right proportions with sand and cement can be difficult, so many manufacturers have
developed pre-packed shotcrete repair mortars to which contractors add only water. |
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| The pre-packed materials simplify
batching and provide more consistent quality. But packaging all the dry materials
increases their cost. Gemite Products Inc. Amherst, NY developed pre-packed products
(called "concentrates"), which include all the admixtures but require
contractors to provide their own sand and cement. The material costs of concentrates mixed
with sand and cement are considerably lower when compared with complete packaged systems,
while maintaining the same quality. |
The Technology
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The
wet shotcrete admixture products, Spray-Con, are mixed on-site with locally supplied sand
and Portland cement. Spray-Con's silica fume enhanced and fiber reinforced formulations
make it easy to control air entertainment in shotcrete - an important requirement for
freeze/thaw durability and salt-scaling resistance. Its compressive strength (ASTM C109)
is between 41.4 and 45 MPa and Young's modulus is approximately 27.6 - 31 GPa. |
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| Applied to clean, sound concrete,
Spray-Con's bond strength exceeds the tensile strength of the substrate concrete. The high
bond and reinforced composition make it an ideal material for restoration of bridges,
subways, tunnels and other areas subject to vibration during application. For rock and
soil stabilization Spray-Con's admixtures and fiber reinforcement may allow its use
without mechanically placed reinforcing mesh and anchors. The low permeability of
micro-silica concrete is essential in new construction and restoration of concrete bridges
and parking decks, where resistance to chloride penetration is essential. It endures
northern climates and can be used in most applications where extreme freeze/thaw cycles
prevail. |
The Benefits
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- Applies up to 30 cm (12 inches) thick in a continuous
overhead build-up
- Minimizes down-time for application
- Allows thin to thick application
- Forms a durable, high bond surface
- Protects the substrate
- Fiber-reinforced, may eliminate the use of meshes
- Reduces labor requirements
- Low water/cement ratio
- Resists water intrusion and salt-scaling
- Resists drying shrinkage cracking
- High economy
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Status
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After its first large application in Chicago's
Grant Park garage in 1988, Spray-Con has been successfully applied to the Van Buren Street
bridge in Chicago, IL, Harrington Water-cooling tower, Amarillo, TX, the foundations of
the Manufacturer's Life Building, Ottawa, and many concrete restoration projects in
Canada, USA, Europe and Asia. |
Barriers
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Protect from freezing for 48 hours after
application. |
Points of Contact
- Dr. Ivan Razl, Gemite Products, Inc.160-3840 East Robinson
Road, Amherst, NY 14228, Phone: 800-443-6483, Fax: 888-443-6329, E-mail: <techinfo@gemite.com>, <www.gemite.com>
References
- Prepacked Shotcrete Admixture, Concrete Construction, May
1999, Vol. 44, No. 5, P4
- Spray-Con, Product Brochure of Gemite Products, Inc. 1998
- Spray-Con, Product specification of Gemite Products, Inc.
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
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