How Green is Building with ICF’s and Concrete?

A CELBLOX wall assembly is made up of five materials: molded expanded polystyrene, polypropylene, steel rebar and small steel connector pins (that hold CELBLOX together) and concrete.

Given the fact that CELBLOX forms become part of the structure in which they are used, the materials used to manufacture them are not discarded until the structure is destroyed. Neither do they deteriorate over time. So the appropriate place to look for the environmental impact of the materials used in CELBLOX is at the beginning of the lifecycle of a material from the extraction of the raw materials contained in it through the manufacturing and delivery processes.

Molded, expanded polystyrene – EPS manufacturing is friendlier to the environment than is the manufacture of cardboard. EPS requires none of the chemicals required to make the kraft for cardboard facing nor does it require the amount of energy needed to make kraft. 2”x6” wood studs are made from trees, EPS is not. In fact, a typical ICF built home may save 50 trees. The gas used to expand EPS resin (pentane) is non-carcinogenic and has no fluorocarbons in it. EPS is 100% recyclable although discarded EPS normally goes to a landfill because it is so light that transporting it to recycling facilities is not economical. In the case of ICF’s, the EPS remains on the concrete wall and is never sent to a landfill. What little waste there is on a job site (smaller segments of ICF’s that are cut from larger forms on site are typically used somewhere in a wall section elsewhere) can be recycled in a number of ways including being incinerated and used to create energy. EPS will not degrade over time.

Polypropylene: Polypropylene is easily recyclable many times over into other products like paint cans, flower pots, pallets and even composite lumber. In the manufacture of polypropylene significantly less CO2 equivalents by weight are produced than in the manufacture of PET or PVC. The polypropylene production process generates low water and air emissions and because the use of the raw materials used to produce polypropylene is so efficient, the manufacturing process minimizes solid waste. The polypropylene used in CELBLOX ICF’s does not deteriorate over time and will not end up in a landfill unless the building it is contained in is destroyed and even then, it is recyclable.

Steel Rebar and Connecting Pins: The manufacture of steel is energy intensive. It begins with the extraction of iron ore which is then reduced to “pig iron.” ½ of the energy used to manufacture steel is used during this process. Much of the energy used is electricity and natural gas which both are insignificant to the creation of greenhouse gases although depending on the source of electricity generation such as coal, CO2 emissions could be created upstream. In addition, roughly 20% of the raw material used to manufacture steel is scrap. Again, the steel used in rebar and the connector pins never degrade and as long as the building is in existence is never reintroduced into the environment. If it is at some point, it also is recyclable.

Concrete: Cement is the key ingredient in concrete and is roughly 12% of the average residential grade ready mix concrete. It is the binding agent that holds the sand and other aggregates in concrete together. Concrete is produced by mixing cement with fine aggregate like sand and fly ash, coarse aggregate like gravel or crushed stone, water and small amounts of chemicals called admixtures. When water is added to the cement, it forms concrete. A typical concrete mix is 6% air, 10% cement, 25% sand, 41% crushed stone and 18% water.

Indirect fuel usage for mining and transporting raw materials and making cement has the greatest impact on the environment through the emission of CO2. Cement is processed in kilns at very high temperatures. The fuel used to heat these kilns is typically coal (61%) which emits CO2, nitrous oxide and sulfur. A sizeable amount of the energy used to heat these kilns is electricity (25%), but much of that electricity is generated from coal as well. Natural gas makes up 8.2% of the fuel used to make cement and waste fuels from other sources that are incinerated make up about 5%.

A study comparing the energy used in the production of concrete and other building materials for raw material extraction, transportation and manufacturing concluded that the energy required to produce one metric ton of reinforced concrete was 2.2 million BTU’s per ton compared to 25.8 million BTU’s per ton for steel and 1.7 million BTU’s per ton for wood. The same study compared the CO2 emissions of building materials for residential construction and concluded that concrete accounted for 324 pounds of CO2, metals accounted for 6,614 pounds of CO2 and wood accounted for 280 pounds of CO2.*

Carbonation is basically the on-going absorption of CO2 by concrete over time. Although there are significant emissions of CO2 in the manufacture of cement, given the long life of concrete walls, the carbonation of CO2 by concrete should be considered when considering the environmental impact of the material. When it is considered as part of the evaluation, an amount equal to 60% of all of the CO2 emitted by the use of fuels in the production of cement will be consumed back into concrete and will not increase the amount of greenhouse gas in the atmosphere by this amount. A normal indoor concrete structure carbonates almost completely in about 100 years.

*Concrete and Sustainable Development, ACI Materials Journal, September/October 1997, Vesa Pentatala