Styrene in the Polymer Concrete Industry
Styrene monomer, or its derivative vinyl toluene, is incorporated into almost all thermosetting resins, such as those used in most polymer concrete, as a reactive diluent. The styrene monomer in the resin improves the viscosity, lowers the reaction temperature, and leads to better curing all together. Without those improvements, polymer concrete production would be nearly impossible. However, styrene carries with it some significant issues and concerns, and for that reason, P3 Polymers only uses resins that don't contain styrene monomer or any Volatile Organic Compounds (VOCs) like it.
The Health Impacts of Styrene
Styrene is a VOC, and as such it evaporates into the surrounding environment quickly, and it can have several detrimental impacts to people's health. According to the OSHA website, "Health effects of styrene include irritation of the skin, eyes, and the upper respiratory tract. Acute exposure may also result in gastrointestinal effects. Chronic exposure affects the central nervous system showing symptoms such as depression, headache, fatigue, weakness, and may cause minor effects on kidney function." Additionally, styrene is one of the most anticipated carcinogens warned about by the NIH.
The employees at the polymer concrete production facilities are likely to suffer the most direct impact, as most of the styrene is reacted away during the curing process. However, some styrene remains unreacted in the polymer concrete for up to several weeks. The Virginia Department of Transportation conducted a study on cured-in-place pipes, which use the same types of resin as polymer concrete, and found that styrene continued to be leached into the environment and air for up to 88 days after cure. This is especially concerning for the workers that will be down in the confined space of a manhole during installation.
The Environmental Impacts of Styrene
Styrene is not only dangerous for humans, but it is also toxic for many animals, especially aquatic life. This can put wildlife near polymer concrete production facilities at risk, but it can also impact the ecosystem of the area the structure is installed. As mentioned earlier, some styrene can continue to leach out of these structures well after they leave the plant are put in place.
The Structural Impacts of Styrene
Not only is styrene dangerous for the people and environment around it, it is also detrimental to the structural integrity of the polymer concrete structure. The thermosetting resins used in most polymer concrete applications contain anywhere from 35%-45% styrene by weight. Throughout the curing process, this styrene is either reacted or evaporated out of the mix. That serves to increase shrinkage of the material during cure. Shrinkage on its own can be compensated for, and doesn't pose much of a problem. The issue comes when reinforcement is added to the structures. Steel reinforcement provides a nucleation point for cracks to develop during the curing and shrinking. These cracks start small, but grow during transport and can lead to critical failures in the structure. Some polymer concrete manufactures get around this issue by only using FRP reinforcement instead of steel. FRP bar is made with similar resins, and doesn't provide the same nucleation point. However, FRP is inferior to steel rebar for a number of reasons including the lower elastic modulus. Other manufactures continue to use steel rebar, but compensate for the cracking by making their walls much thicker. This doesn't truly solve the problem, but it does make the structure much more expensive. We have chosen to use a styrene free resin to reduce the shrinkage from 10% as it is in most resins to virtually zero. That allows us to use steel rebar with no concerns about cracking.