Concrete Options & Concrete Recycling

Concrete is used more than any other manmade material on the planet.7  It's a very strong and long-lasting material and has a great number of uses, but it also has high embodied energy: it takes a lot of energy to produce.  
For every ton of cement manufactured, about 6.5 million BTUs of energy are consumed.3
For every ton of cement manufactured, about one ton of carbon dioxide is released.3

However, there are steps being taken to make concrete into an even better product.  Fly Ash and Slag Cement are both being used in place of Portland cement, which lowers the embodied energy, conserves virgin materials and reduces pollution.2

Fly Ash:
A by product of coal fired electric generating plants.  Millions of tons are produced in the U.S. annually.  Using it in concrete diverts it from going to the landfill.1
Replacing 1 ton of Portland cement with fly ash would save enough electricity to power the average American home for 24 days and reduce carbon dioxide emissions equal to two months use of an automobile.3,4
Can be used sparingly or in large amounts to replace Portland cement by up to 60% by mass7
Improves the strength of concrete1
The tiny glass beads in Fly ash improve flow, workability and ease of pumping1, 3
Requires up to 10% less water to mix than Portland cement, so it conserves resources, is easier to use in cold weather and is less likely to crack1, 3
Somewhat lighter than Portland cement1
Meets applicable U.S. codes1
In 2003 over 15 million tons of cement were imported into the US to make up for a shortage in US cement production. If domestic fly ash had replaced those imports, the result would have been an improvement in the US balance of trade of at least $1 billion.4
There are some concerns about freeze-thaw performance1
It comes from operations in different regions, so its mineral makeup may not be consistent1

Slag Cement (Ground granulated blast furnace slag):
A by product of steel production.  Its use in concrete diverts it from the landfill.7
Used to partially replace Portland cement by up to 80% by mass and conserves virgin resources7
Like Fly ash, replacing one ton of Portland cement reduces greenhouse gas emissions by one ton5
Improves the strength and durability of hardened concrete5
Uses 3-5% less water than Portland cement6
Like Fly ash, slag improves flow, workability and ease of pumping6
Slag requires less than 1/5 of the energy to produce than cement and produces less than 1/10 of the CO2 emissions7

Concrete recycling
Concrete is recyclable, with 45 to 80% of crushed concrete usable as aggregate in new construction.3  Concrete debris was once routinely shipped to landfills for disposal, but recycling is becoming more widely used.   This saves landfill space and using recycled concrete as aggregate reduces the need for gravel mining.7
Crushing facilities accept only uncontaminated concrete, which must be free of trash, wood, paper and other such materials.7

Concrete in Framing & Foundations
ICFs (Insulated Concrete Forms):
Foam forms that are set in position and filled with reinforced concrete and reinforcement bar to create insulated structural walls1
Great for foundations and above-grade walls11
Insulating foam provides an ideal curing environment, leading to stronger concrete11
Provide an R-value of 17-261
ICFs absorb sound, leading to a 75% quieter home8
Average energy savings of 25-50% vs wood framed home8
ICF foundations require less time to install than traditional1

SIPs (Structural Insulated Panels):
Pre-made panels made from a thick layer of foam between and attached to two layers of OSB, plywood or fiber-cement1
Used above-grade (for walls, floors and roofs)11
Provide an R-value of 15-4511
Panels can reach long distances without structural support and are suitable for large-span roofing applications11
Panels are made off-site and can create any shape11
No need to locate studs when drywalling11
Can also use agricultural fibers instead of foam1

Both ICFs and SIPs
Insulation doesn't settle like other types can11
Concrete framing is more likely to withstand hurricanes and other severe weather8
A tighter building envelope increases energy efficiency and air infiltration, but proper ventilation is needed to control indoor air quality and humidity11
Both buffer the home from extreme air temperatures11, 8
Any siding can be used11
Some providers incorporate recycled content foam11
Pre-planning reduces on-site waste11
Can look just like traditionally built homes8
Both require an experienced contractor to install9
Last longer in fire tests than wood framed homes10
Less prone to termites and moisture than wood1

For more information:
Toolbase Services - www.toolbase.org
Greenbuilder.com - www.greenbuilder.com
Green Building Solutions - www.greenbuildingsolutions.org  

Sources:
1 Toolbase Services
2Greenbuilder.com
3Headwaters Resources
4King, Bruce, P.E. Making Better Concrete
5Slag Cement Association
6American Concrete Pavement Association
7Wikipedia
8Insulated Concrete Form Association
9U.S. Dept. of Energy - EERE
10Portland Cement Association
11Carol, Deniz, Green Building Solutions