Concrete is all around us and is an inexpensive, long-lasting, multipurpose building material. As an undergraduate student in civil engineering, I found concrete fascinating. It cures by absorbing water (hydration) not by drying like many people think. This magic rock-like stuff gets stronger with age--especially with continued exposure to water. I was present for the ceremony in 1998 at UW-Madison for the 100th year in a long-running experiment load-testing concrete cylinders that had been mixed by undergraduate students in 1898! Each year, the cylinders stored in a room with 100% humidity continued to grow in strength whereas those left in dry conditions had long since plateaued. What could be wrong with concrete?
Concrete is made from water, cement, and aggregate (sand & gravel). While water and aggregate are relatively easy to come by and inexpensive, cement is not. Cement is 85% lime and silica by mass plus gypsum and trace amounts of aluminum and iron. Cement is typically made from calcium carbonate that must be mined, transported, and crushed before being loaded into a kiln. These kilns are 12 feet in diameter and as long as a football field and heat the calcium carbonate to 2700 degrees F producing lime and lots of carbon dioxide. The foreign elements, including toxic heavy metals such as mercury and cadmium, evaporate off and the remaining marble-sized material called "clinker" is then ground-up into a very fine powder we know as Portland cement mix. The high temperature kilns require significant amounts of fossil fuels to bring up to operating temperature so these kilns are run continuously. There are about 100 cement plants in North America. The cement is transported all over North America by rail and truck for use in our highways, bridges, buildings, and of course, concrete burial vaults.
The environmental impact of concrete adds up quickly. To manufacture and distribute cement and then mix and transport concrete is very expensive in terms of carbon life cycle analysis. The concrete industry estimates that a little less than 1 ton of CO2 is released into the atmosphere for each ton of concrete we produce--and this includes a 30% improvement in CO2 production from concrete since then 1960s! On a global scale, concrete production accounts for 5% to 10% of the total world carbon footprint. In 2010 the United States alone produced an estimated 63.5 million tons of concrete. In that same year, the funeral industry buried 1.6 million tons of concrete burial vaults. Surprisingly, the funeral industry accounts for 2.5% of domestic concrete production.
A single concrete burial vault weights 1800 lbs. and ranges upward to 3000 lbs. For a 1 ton burial vault we produce about 1 ton of CO2 to manufacture and transport the vault to a cemetery. This is the same amount of CO2 that a four-person family produces in about 9 days. It takes a tree about 40 years to sequester 1 ton of CO2.
With the exception of only two or three states, Massachusetts being one, most states do not require concrete or steel burial vaults. However, most municipal and church maintained cemeteries do require burial vaults. Burial vaults do have a practical purpose and every vault manufacture's web site is quick to explain the safety and aesthetic value of vaults in preventing grave collapse. A cemetery operator would also tell you it is far easier to locate neighboring graves with a thin rod when identifying where to dig a new grave if the adjacent graves are vaulted. Aside from the Green Burial Council's position to forego the vault altogether, could there be a green alternative to the concrete burial vault?
There are some ideas among green-thinking funeral directors and cemetery operators. One simple idea is to use a vault lid to cover the casket. If the grave is dug several inches wider than the casket on all sides with a casket-sized channel at the bottom of the grave, the soil could support a simple slab--just a vault lid--and get the benefit of preventing grave collapse with less concrete. We can do better.
There's no shortage of research on greener concrete. Carbon tax laws in countries like Australia have implemented a tax of $25 per ton of CO2 produced. While such laws and regulations are prompting the building industry to improve concrete production methods by adding fly ash, bottom ash, or slag. One Italian company has developed a concrete that is supposed to fight air pollution. The mix includes titanium dioxide that absorbs ultraviolet light and purportedly breaks down pollutants in the air that collide with the concrete. The Jubilee Church in Rome is made from this type of concrete. In any case, all of these attempts to make green concrete are minimal at best in reducing carbon emissions. We can do better.
There's a new vault company on the scene--since 2009, that is. Massachusetts-based, Duke Burial Vaults, markets a plastic burial vault that is five times stronger than concrete, ten times lighter than concrete, and costs less. Before we get too far, yes, plastic (even recycled plastic) comes with some cost in environmental impact and carbon life cycle analysis. However, at 140 lbs shipping weight and as much as $1500 savings over concrete burial vaults, Duke has a value-proposition worth a good look. The vaults are made from polyethylene inner and outer shells with polyethylene structural foam molded in between. Lighter. Stronger. Cheaper. But is it Greener? Polyethylene ranges in CO2 output of 1-3 lbs. per 1 lb. of product produced. Even at 3 lbs. CO2, that 140 lb vault might be responsible for 500 lbs. CO2 even after freight distribution. The National Institutes of Health final report on the safety assessment on polyethylene tells us this stuff is pretty safe. Which is good news because polyethylene is widely used in cosmetics, food packaging, prosthetics, and various implant devices in medicine.
So what is the Green verdict? If one can forego a burial vault altogether, that is the greenest option. But if a vault is required, a Duke burial vault is at least 4 times less harmful in terms of carbon life cycle analysis, and has almost zero impact in terms of environmental pollution. And if you are a funeral directory or cemetery operator, the best news might be that this green alternative can save money and add a few dollars to your bottom line.
Concrete Burial Vault Facts
- Concrete Burial vaults range from 1800 lbs to 2400 lbs.
- 1 ton of concrete produces ~1 ton of CO2
- The concrete industry accounts for 5% to 10% of the world's carbon footprint
- The average household of 4 people in America produces 40 tons of CO2 per year
- It takes a tree about 40 years to absorb 1 ton of CO2.
- The US Congress has proposed carbon tax $25/ton of CO2-e (this already exists in Australia)
- Every year, we bury 1,636,000 tons of reinforced concrete burial vaults in America's cemeteries
- The total concrete in made in the US in 2010 is a combined total of 63.5 million tonnes