FRP bar properties - Reinforced Concrete with FRP Bars: Mechanics and Design - page 51

Figure 3.15 Typical GFRP bar sample at the end of the ignition loss test.
Figure 3.16 Voids in the cured material due to lack of glass.
Inaccurate proportions between resin and reinforcement may cause
internal defects in the cured material, which would ultimately induce lower
durability and mechanical properties. An example of void due to lack of
reinforcing glass is shown in Figure 3.16.
According to ACI440-6, polyester cannot be used as the base polymer
in FRP bar manufacturing because of the high content of styrene. 1 Styrene
can be added to any polymer resin during processing, but its content cannot
exceed 10% by mass of the polymer resin.
1 Styrene has been recently described by the US National Toxicology Program as a possible
carcinogen for human health.