Fibre reinforced plastics (FRP) have demonstrated suitability for construction projects due to their strength and durability, while weighing very little. The attributes of FRPs were examined as well as, their applicability in hot, desert temperatures for road barriers and other road safety units.
Background – Composite Materials
Strength and stiffness are the main mechanical properties fibres add to composite materials. The fibres must have uniform diameter, similar strength between each fibre, and very large length-to-diameter ratio. Crystals within the fibre that are aligned with fibre length create high tensile strength. Fibres need to have air space and fibre packing needs to be random within the composite.
Figure 1 Microscopic view of suitable fibre spacing
Advantages of FRP reinforced concrete
The most important trait for durability is the bonding capability of the fibres and the resin system. In an FRP bar when the axial load imposed by grip mechanism moves unilaterally as in fig.2, the stress distribution is normal. The elasticity of a reinforcing bar determines the potential strength. DEAr(Achillides 1998 cited by Tepfers et al. 2000: 337) High elastic modulus values (E) of about E = 115 GPa is much better than low values, because when E = 45 GPa high splitting stresses develop.
Figure 2 Grip mechanisms on rebar’s axial load
Attributes of concrete reinforced with FRP dowels were compared to those of steel I-beams showed that FRP reinforced concrete needed only 50% of the energy it takes to produce a steel I-beam. The amount of water pollution was about 50% less for the FRP reinforced concrete. (Stuble and Godfrey 2004)
Figure 3 Concrete reinforced with FRP dowels (l.) steel I-beam (r.)
Short-glass-fibre reinforced thermoplastics, carbon and other organic fibres (ceramic, Kevlar, silicon carbide, boron, etc.) are typically used. Different composite types are sandwiched together A composite formed with three layers, each with a fibre at different orientation, is an example of a design that takes advantage of the individual traits. Figure 4 shows a laminate produced with 90°/0°/90 oriented composite. (Dutta 1998:4 & 5)
Figure 4 Creation of a 90°/0°/90° sandwiched 3-fibre composite
Proto-types are made in order to meet specific attributes. A CRREL-5 laminate W-beam prototype was designed to handle maximum strength by combining glass fibre reinforced polymers laminated to a W-beam. Figure 5 shows the configuration of the layers. (Dutta1998)
The beams were coated with Ultra-violet protective gel and then painted. Fifteen guard rails were measured from 6 to 6.1 meters long and 12.7 mm thick were fabricated. A vinyl ester and iso-polyesters (in different thicknesses) were sandwiched together between glass micro-layers. Isophthalic polyester and a silver metallic gel-coat was used to create the 1.46 gm/cm³ resin. (Dutta1998)
The layers consist of the following materials.
C1 – One layer of a C-glass mat
E1 – One layer of bidirectional stitched E-glass
S4 – Four layers of S-2 (unidirectional) 0º and 90º alternate
E9 – Nine layers of bidirectional stitched E-glass
Figure 5 CRREL-5 laminate W-beam
Beams are shaped, produced, and painted in modular form for easy transport and easy assembling on site. (See fig. 6)
Figure 6 FRP painted guard rails
An FRP beam design must pass a standard deflection test before manufacture for use as guard rails along a road. The cyclic shape of the graph shows the deflection caused by the load and then, the bounce back to normal size. (See fig. 7) The cyclic shape of the graph shows the deflection caused by the load and then the bounce back to normal size (Dutta 1998: 12). The test method measures the transverse shear strength via double shear fixture in order to test FRP composite textured bars and smooth round rods. The test is important because when either FRP bars or rods are used as dowels to reinforce concrete pavements the loading is usually in the transverse shear direction (Dutta 1998: 12).
Figure 7 Graph of loading and deflection test data
FRP dowels are used to reinforce highway pavement. One design is like a mesh made of dowels that are put in place on site and then the highway construction is finished by encasing the dowels in the road cover material. (See fig. 8 top) FRP pavement panels and thermoplastic FRP offset block for guardrails have been used with success. (CFC-@VU) FRP modules can be filled with 300 litres of water and then used as permanent or temporary safety on concrete and steel barriers.(See fig. 8)
Figure 8 ABSORB 350® Crash Cushion (CSP 2013)
Suitability for use in Kuwait
Published research indicates that Kuwait has ideal conditions for use of FRP’s for road safety (a) low relative humidity and (b) high temperatures. The most damaging atmosphere is one with high humidity and extremely low temperatures. (Myers and Ekelnel 2003: 1571) Research needs to be done in desert conditions for accurate testing.