By Jake Ables, director of concrete promotion, Silvi Materials
When choosing a pavement surface for large-scale industrial facilities, there are several different factors that developers may want to consider. Chief among those factors, in the context of our current construction economy, is sustainability.
Current trends in the Mid-Atlantic warehouse markets, for example are pushing developers, contractors and suppliers towards sustainable construction practices. We have seen evidence of this with the implementation of environmental product declarations (EPDs) that disclose the global warming potential (GWP) of building materials on various construction projects. The purpose of these documents is to quantify the environmental impacts of building materials. As the push for sustainability increases, it behooves developers to look for sustainable value when and where they can find it.
Life Cycle Thinking
As the push for sustainability intensifies over the coming years, property developers’ will see their priorities adjust to compensate for changing market conditions. While costs will always be at the forefront of concerns for developers, sustainability is becoming an ever-higher priority.
So what does that mean for developers? We believe it means a shifting mindset toward sustainable value over costs. Concrete paving provides the life cycle value that developers are seeking in three distinct ways.
First, examining the differences between cradle-to-grave verses cradle-to-gate phase analysis (more on that to follow) will allow us to see how concrete pavements are mischaracterized and overlooked from a sustainability standpoint.
Second, concrete pavements allow for a process called carbonization to take place. Carbonization is the process of carbon dioxide being absorbed by concrete pavements through a natural chemical reaction. Once the carbon dioxide is absorbed into the pavement, the gas is sequestered there as opposed to being otherwise dispersed into the atmosphere, further contributing to climate change.
This makes paving with concrete a proactive approach to addressing climate change and sustainability.
Lastly, concrete has a high albedo factor and is three times more reflective than asphalt. This means that concrete will reflect far more sunlight than it absorbs, which results in a cooler pavement surface, thus decreasing urban heat island effect of the surrounding area. The highly reflective nature of concrete pavements means that site lighting will also travel further across the surface, resulting in higher site visibility and reducing the risk of accidents caused by poor visibility.
Cradle to Gate v. Cradle to Grave
“Cradle-to-gate” refers to the process of examining the environmental impacts of a substance from the production of the raw materials — in our case cement, stone and sand — to installation. The issue with cradle-to gate-analysis is that it only tells half of the story for concrete pavement, neglecting the use phase, which could be 30 years or more.
A much more accurate measurement of the environmental impact of concrete paving is “cradle-to-grave”. This term refers to the measuring of everything cradle-to-gate does but includes the use phase. This is where concrete closes the gap and surpasses asphalt as the more sustainable material.
Maintenance and preservation during the use phase is the primary differentiator. The useful life of a concrete pavement is essentially limitless if properly constructed and minimally maintained. The reduction in maintenance requirements lowers the overall carbon footprint of a project.
Taken a step further to the end-of-life stage of the project, concrete pavement is 100 percent recyclable and can be crushed to a finely graded aggregate and reused as construction aggregates, extending the overall life of the original concrete product. It should be noted that the end-of-life phase of a concrete pavement could conservatively be estimated as taking place 40 to 50 years after the initial materials production phase, when the individual raw materials were first produced at the source. At the end-of-life stage of a project, assuming the pavement is in acceptable condition, the concrete pavement should be left in place and a new structure erected on the site of the original building.
Carbonization
Carbonization is the process of carbon dioxide (CO2) being attracted to the calcium hydroxide (CaOH2) in cement. The result is that free CO2 in the atmosphere is permanently absorbed by the concrete pavement. In a market where sustainability is increasingly valuable — and mandated — this is an incredible inherent benefit of a building material.
The Massachusetts Institute of Technology’s Concrete Sustainability Hub conducted a study that evaluated the CO2 absorption potential of concrete pavements. The organization’s models determined that 8.6 million tons of CO2 could be absorbed in the United States by utilizing concrete pavements. Because of the expansive concrete pavement area on industrial warehouse projects, the carbonization process provides tremendous environmental value in CO2 reduction.
Albedo, Urban Heat Island Effect
Albedo is the fraction of light that a surface reflects. The higher a surfaces albedo rating, the more light it reflects, and the cooler that surface becomes. Concrete has an albedo rating of .4, meaning 40 percent of the light hitting the surface is reflected. Asphalt has an albedo rating of .1, meaning that 90 percent of the light striking the surface is absorbed.
A study conducted by the American Concrete Pavement Association compared asphalt pavements to concrete pavements over two sections of Phoenix’s freeway system.
The study found that even with the cooling impact of the traffic, the asphalt rubber surface remained hotter than the concrete pavement throughout the course of the entire day. The asphalt was found to range from 2 to 6 degrees Fahrenheit hotter than the adjacent concrete pavement travel lanes throughout the day.
A temperate difference of 2 to 6 degrees might not seem like much when taken in the context of one geographic location, but if you extrapolate the findings to cover the entire U.S. interstate highway system, the differences become stark. A uniform increase or decrease within these temperate ranges will have a significant impact on global warming potential.
Additionally, the albedo value of concrete paving allows for more visible and safer sites. Site lighting will travel further across the pavements surface and allow for noticeably brighter sites. Higher visibility results in less slips, trips and falls on sites, which will reduce property owners’ liability related to these issues.
For all of these reasons, concrete pavement is an economically durable solution to a brighter and sustainable future.