Glassfiber reinforced concrete

GLASSFIBER REINFORCED CONCRETE PROPERTIES

Modern times require introduction and use of new construction materials and procedures. One way to create a new material is to reinforce an existing one. For instance, the cost-effectiveness and strength properties of reinforced concrete are better than those of plain concrete. One of the most advanced types of concrete reinforcement is fiber reinforcement, which produces a new material called fiber reinforced concrete. Classes of fiber reinforced concrete differ by the type of fiber strings used. The most common sorts of fibers for concrete reinforcement are:

• steel fiber,
• alkali-resistant glass fiber,
• conventional glass fiber, and
• synthetic fiber.

Glass fiber reinforcement had proved to be the most economically and technologically feasible solution.

DEFINITION

Glassfiber reinforced concrete (GRC) is a variety of fiber reinforced concrete and is manufactured from fine grained concrete (concrete matrix) and reinforcing glass fiber strings that are uniformly distributed across the concrete volume of the product or its specific parts. The collaboration of concrete and fibers is ensured by bonding along their surfaces, providing a huge fiber-and-concrete contact area (which may range from 10,000 to 50,000 sq.m depending on the end-product application). This results in brand-new properties of the GRC material.


Large-scale production and use of glassfiber reinforced concrete panels is important for construction cost reduction, labor saving, and enhancing the functional reliability and durability of structural units.

Dispersed reinforcement does not only increase the strength properties of concrete, but essentially improves the structures’ performance characteristics, such as resistance to dynamic impacts, temperature, humidity, attrition, and other loads, which makes the manufacture and use of GRC structures particularly effective.

Depending on their application, glassfiber reinforced concretes can be divided into structural, waterproofing, architectural, and special GRC. According to their application, glassfiber reinforced concretes can have a variety of specific properties attainable by different combinations of short-fibered and long-fibered components of glass reinforcement and by the choice of the manufacturing technique.

GRC has exceptionally good processing properties, can be molded into virtually any shapes, has a high bending strength, impact resistance, elasticity, crack resistance, and waterproofing capacity, and can have a decorative surface finish when necessary.

Glassfiber reinforced concrete presents architects with such means of implementation of their designs which is unrivaled by any other material in terns of moldability, capability to replicate a surface geometry, and lightness. Glassfiber reinforced concrete is lightweight, easy to handle, cheap to install and transport, fire resistant, has a low water permeability level, and reduces loads on a building’s bearing structure leading to significant savings in superstructure and foundations, which is especially useful for reproduction and renovation.

CLASSIFICATION

GRC structures can have the following types of reinforcement:

Fiber reinforcement, when a structure is only reinforced with glassfiber strings uniformly distributed across the concrete of a component or its part;

Combined reinforcement, when a product is reinforced with both steel rods or wires and glassfiber strings uniformly distributed across the volume (or section) of a component.

APPLICATION

GRC is used in thin-walled members and structures of buildings and installations where dead load reduction, better cracking resistance, ensuring the waterproofness and durability of concrete (especially in corrosive environments), improved impact ductility and abrasion resistance, radio transparency, and enhancing the architectural plasticity and environmental safety are the critical issues.

GRC panels can be used as customized structural members in special purpose buildings, as modular units in serial construction, or as cladding panels in refurbishment work.

Two solutions are possible in any particular case:

• integrally stiffened single-layer panels;
• permanent formwork with subsequent casting.

Specially tailored metal, wood, plastic, or polyurethane molds provide embossed surface finishes ranging from simple designs to free forms, heraldic symbols, or decorative dressing. Using a white or gray cement base with some additions of inorganic dyes, sand, and other aggregates, a wide range of colors and finishes can be created.

 

      

      

       

The thinness of the finishing coat (not thicker than 5 or 6 mm) minimizes the material costs. A thin finishing layer imitating natural stone, slate, or stoneware tiles is made on a bonding cement panel that forms part of the bearing frame structure.

The architectural flexibility of glassfiber reinforced concrete provides a way to avoid the monotony of painted steelwork or plastic and the ponderosity and limited moldability of traditional concrete.

Apart from cladding panels, an important advantage in building reproduction and renovation is the possibility to replicate historic features. GRC is also indispensable for making window surrounds, door portals, cornices, sunscreens, and other products.

Glassfiber reinforced concrete is superior for different types of roofing. It can imitate traditional roofing materials such as slate or clay tiles but unlike these materials it is neither brittle nor heavy. On sloping roofs, GRC can reproduce both the appearance and the surface finish of natural slate. It can be fixed with usual slating nails without having to drill nail holes, because GRC is tough and cracking resistant.

GRC is playing a major role in designing urban leisure facilities in terms of aesthetics of building projects and architectural moldings and features. It can be used to arrange picturesque decorative pools, fountains, seatings, planters, balustrades, kiosks, etc. GRC architectural features have a more attractive appearance, because GRC can reproduce any shape, geometry, and surface finish to provide improved compatibility with the surrounding landscape. GRC plaster is exceptionally strong and resistant to cracking and flaking.

Glassfiber reinforced concrete is highly resistant to chemicals, including urban pollutants and salt solutions. It also has good acoustic properties and is stain, rot, corrosion and fire proof. Molded into various complex configurations, GRC products can be used in civil engineering to build highways, water ducts, storage reservoirs, wells, and tunnels.

Glassfiber reinforced concrete can also be used to manufacture large-bore pipes and can be reinforced by either chopped fibers or alkali-resistant glassfiber nettings.

The small thickness of pipe walls and the absence of union joints make it possible to decrease the trench size and the filling volume. Such pipelines can be laid under high traffic load roads, because GRC is long-lasting and has exceptional strength performance when alkali-resistant glassfiber is used as the reinforcing component.

In bridge construction, glassfiber reinforced concrete is ideal for manufacture of parapet parts and noise barriers, which can be quite long and still remain lightweight. In addition, GRC ensures a better protection for steel reinforcement and has a higher resistance to ingress of chlorides than conventional concrete of the same thickness.

Due to the light weight of products and the thinness of walls, GRC can be used for manufacture of ducts and water conduits to replace short and heavy-weight cast concrete components. A threefold reduction of product weight facilitates the erection of drainage and irrigation systems on uneven terrains. Besides, the cost of construction of underground water and cable ducts is reduced due to the smaller number of supports required.

GRC components of cable, drainage and irrigation channels can also be used as permanent formwork. In this case, GRC panels are fitted before concrete is placed and their function is to form a smooth-faced interior profile of the channel and thus eliminate the necessity of using a complicated temporary formwork.

Technological advantages over plain and armored concrete

Many of the technological and economical advantages of GRC are unrivaled by traditional materials. Therefore, its main distinctive features are:

Improved cracking resistance, impact ductility, abrasion resistance, freeze-thaw durability, and weathering stability;
The possibility to use more efficient structural solutions than in case of conventional reinforcement, e.g. the possibility to use thin-walled panels and structures without any reinforcing rods, mesh reinforcement, distribution bars, or crosswise reinforcement;
The possibility to minimize or entirely avoid steel rods, which is particularly important when cost is critical;
Labor and energy saving in reinforcement installation; a greater degree of mechanization and automation in manufacture of fiber-concrete products such as prefabricated thin sectional insulation, thin slabs, ribbed roof slabs, jointless and solid panel floors of industrial and communal buildings, permanent formwork structures, etc.

Note 1. GRC components without steel armoring may be used in structures that are mainly exposed to:

Dynamic pressures, abrasion, bursting, and atmospheric action;
Compression loads with eccentricity of normal force, such as in space frame components;
Bending loads, provided that brittle failure is excluded.

Note 2. Structural GRC panels must have combined reinforcement.

PROPERTIES OF TOP-QUALITY GRC

¹
Property
Value range
1
Dry density
1700-2250 kg/m3
2
Charpy impact strength
1.1-2.5 kg·mm/mm2
3
Compressive strength
490-840 kg/cm2
4
Modulus of rupture
210-320 kg/cm2
5
Elastic modulus
(1.0-2.5)·104 MPa

6

Axial tension strength:
- elastic limit
- ultimate strength


28-70 kg/cm2
70-112 kg/cm2

7
Strain to failure
(600-1200)·10-5 or 0.6-1.2%

8

Shear strength:
- interlaminar shear strength
- in-plane shear strength


35-54 kg/cm2
70-102 kg/cm2

9
Thermal expansion coefficient
(8-12)·10-6 ?Ñ-1
10 Thermal conductivity
0.52-0.75 W/cm2·?Ñ
11
Water resistance as per GOST 12730
W6-W20
12
Coefficient of permeability
10-8-10-10 cm/sec
13
Freeze-thaw durability as per GOST 100600 F150-F300
14
Fire endurance
Better than that of concrete
15
Combustibility
Noncombustible (no flame propagation)

16

Acoustic absorption at 15 mm thickness

125 Hz
250 Hz
500 Hz
1000 Hz
2000 Hz

27 dB
30 dB
35 dB
39 dB
40 dB

Note.

The following formula can be used to convert kg/cm2 to MPa:

Note.

The process flow diagrams, the preliminary work list, and the quality control and safety measures (depending on the manufacturing technique and materials used) are specified in the Departmental Building Regulations (VSN) named Fiber-Concrete Structures Engineering and General Provisions for Manufacturing Procedures, VSN 56-97, Moscow 1997.

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