Building Better Bioretention
BUILDING BETTER BIORETENTION
Aaron Fisher | June 8, 2024
If you are looking at addressing stormwater, one of the more common solutions in an urban or space-constrained environment is micro-bioretention. It involves a depression that allows stormwater to collect and filter through a bed of sand, soil, and organic matter—simple and effective. Another common feature of these and many other stormwater BMPs (best management practices) is that they often incorporate concrete walls. The challenge is that water will eventually cause these concrete walls to fail.
The problem with these walls is not the concrete, but rather the steel rebar inside of them. Roman aqueducts have lasted for millennia; and it’s not because they knew how to make better concrete. Rather, they avoided reinforcing with steel, which when it comes into contact with water rusts. As the rust forms it causes the concrete to crack and ultimately fail. Why then would we choose to put a time bomb inside of our concrete for stormwater?
Simple put most engineers haven’t really thought about it, and even if they had there hadn’t been an affordable alternative. That is, until fiberglass rebar came into codes and started costing less than steel rebar. As a composite material fiberglass rebar does not corrode, and as such is a great choice in a situation where the reinforced concrete would regularly be subject to water and ultimately corrosion. With this in mind many engineers and contractors are rapidly making the switch to save money and make the stormwater infrastructure more resilient and longer lasting. Much the same way as DOTs and bridge engineers have made the switch.
Furthermore, stormwater is often aligned/part of the push for more sustainable construction. One of the key metrics in sustainability is the embodied carbon of the material– how much CO2 is needed to manufacture the material (cradle-to-gate). In this metric fiberglass rebar emits 80%-90% less CO2 on a cradle-to-gate LCA basis. This only gets better the further you extend into the construction and use phase of the product.
The knowledge of building better micro-bioretention facilities can be applied to other green infrastructure and stormwater solutions. Any reinforced concrete can be built better and last when you choose fiberglass rebar.
Ready to make the jump?
