Last week I talked to an environmental specialist from a local Public Works department here in Florida who told me about a recently awarded grant that stipulated they use a boardwalk product produced with recycled materials. This is a topic we are discussing often now, as taxpayers and grant administrators want to see money spent on products that are as environmentally friendly as possible. This makes good sense; I believe we all need to be responsible users of our natural resources.
But as I meet with landscape architects or engineers, I am reminded that most do not see reinforced, precast concrete as an environmentally friendly material. To those working outside the industry, it may not sound very environmentally friendly.
What determines if a product is environmentally friendly?
- The material’s impact to the surrounding environment (from creation to retirement of the material).
- Sustainability, or how often the material will last: The way we use our resources to develop our world in a way that allows future generations to develop theirs.
Of course I am personally biased given my company’s product, but I’d like to share a bit of factual industry information about sustainability, CO2 emissions, and the long-term impact different boardwalk materials will have on our ecosystem. Comparing with timber and composite materials, we’ll look at how environmentally friendly, and how sustainable, a precast concrete boardwalk really is.
Pressure Treated Pine (PT), such as Southern Yellow Pine
Today PT remains the most often used boardwalk material, more prevalent than composite lumber or concrete systems. “Change is hard,” as they say. Pros of using pressure treated pine have little to do with environmental benefits: PT is dirt cheap, and readily available in large quantities.
A pressure treated timber boardwalk system used in a commercial setting will generally be expected to survive anywhere from 5-12 years. The only reason this material can be stretched to those limits is due to the chemical treatment process the Southern Yellow Pine goes through.
- Chromated Copper Arsenate (CCA), a mixture of chromium, copper and arsenic, was originally used in the 1930’s and continued as the standard for nearly a century. However, CCA treated pine for timber boardwalks leaches harmful chemicals, principally arsenic, into the surrounding soils over time. Even more dangerous is burning of the CCA treated pine once it has worn out its service life as a boardwalk product, and the common answer to disposing of treated pine is a landfill. This was eventually banned by environmentally conscious agencies as testing showed the chemicals were harmful to the environment. This no longer flies so well with groups like Sierra Club and Rainforest Relief. As a result, you’d be hard pressed to find a CCA treated timber boardwalk these days.
- Alkaline Copper Quaternary (ACQ), a water-based preservative, has replaced CCA treatment in recent years. Compared to CCA, ACQ wood treatment is more environmentally friendly, but there are still issues with outside preservative chemicals eventually leaching out of the wood and into the surrounding soils.
The larger issue with pressure treated pine, however, is the lifespan of the product, requiring the removal and replacement of boardwalk component over such a short period of time. “Time for a redecking,” we hear often in Florida. This could happen after just 3-5 years of normal wear and tear.
What happens to the treated pine that is removed? While it cannot be burnt to let off harmful chemicals, it will eventually find its way to a landfill. Burning in approved incinerators is an option, but this process is seen as more expensive than it’s worth. As such, this is rarely undertaken, more than likely the wood will end up in a landfill. Then the cycle continues: harvesting Southern Yellow Pine tree species, treating with a chemical, installing boardwalks, annual maintenance to maintain a safe walking surface, removing and redecking the boardwalk after 3-5 years, then the leftover wood heads to the landfill. This process repeats itself 5-10 times over the course of 50 years.
Bottom line with PT: an unsustainable solution as a commercial boardwalk product.
Composite Lumber – Recycled Plastic Decking, such as Trex
Roughly 10 years ago a company called Trex burst onto the scene with a recycled plastic decking product. They’ve had a lot of success with homeowners looking for a lower maintenance boardwalk system, one with color options and design support for residential hardscape.
Soon cities and counties looked to Trex to solve their ongoing maintenance issues with pressure treated wood: rotting, splitting, termite damage, nails popping up, etc. But the Trex product was never originally intended for commercial, public use. The plastic composite products will invariably break down after prolonged UV exposure, wet-dry cycles, and the beating from thousands of walkers, runners and cyclists.
Plastic is an oil-based product; the wood-plastic composite boardwalk planks break down as they experience UV exposure and prolonged time in the sun. As the plastic components of these materials break down, the boards lose their design strength, become slippery, sag, or warp. These maintenance issues are improved from what they were with pressure treated boardwalk systems, but they still remain. These considerations all lead to a shorter product lifespan of the product itself.
What is that expected lifespan? Most designers and owners would expect 7-25 years before the entire composite boardwalk will need to be replaced. Some product warranties will claim 30 or 40 years expected lifetime. However, the fine print reveals these warranties to cover limited structural liabilities: mold, decay, and splitting of the boards. Nothing more. Ongoing maintenance efforts to replace popping screws, replace failing individual boards, and provide a solution to the slipperiness of the walking surface remain.
Now, I can’t argue with the intentions of the manufacturers-- who doesn’t like the sound of turning 100 leftover milk jugs into a few boardwalk planks? But the sustainability argument gets boiled down into something very simple: a short lifespan demands more replacement structures. Plastic composite products aren’t biodegradable, and as the boardwalk is replaced, old boardwalk components go the landfill. The process for a commercial boardwalk repeats itself 2-7 times over a 50 year period.
End result: composite materials are not a sustainable commercial boardwalk solution.
Reinforced, Precast Concrete, such as PermaTrak
Through the 90’s and early 2000’s, precast concrete was generally not seen as a “green” or “environmentally friendly” material. But “the times, they are a-changin’!” Precast concrete boardwalk systems are considered environmentally friendly for these simple reasons.
- The materials that go into precast concrete production (sand, coarse and fine stone) occur naturally and are abundant throughout North America.
- These materials are found locally, nearby the precast plant where they will go into production process. This significantly reduces the fossil fuel usage from transportation efforts to import materials found thousands of miles away.
- Sand and stone are organic – they do not require heavy processing (less energy use) and aren’t reliant on chemical treatment to prepare them for use.
- Precast concrete materials are much less disruptive to the environment where the boardwalk is installed – less dust, noise, and pollution on the project site.
- Concrete boardwalks are easy to crush and reuse as recycled aggregate for other precast concrete production efforts.
- Precast concrete is inert; it will not emit any gases or toxic compounds during its service life.
- The Army Corps of Engineers has documented that reinforced, precast concrete carries a design life of 50-75 years.
The biggest consideration I have come across when discussing "environmental friendliness" of a product with consultants is how this relates to sustainability.
A truly sustainable boardwalk solution would offer: maintenance free performance, a 50 year service life, and the ability to be recycled or reused in other capacities.
Last photo by: photologue_np