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In an era of heightened sensitivity to the environmental impact of building products and the manufacturing processes behind them, not to mention health and outgassing considerations, concrete is emerging as a frontrunner among natural alternatives.  Most houses built today include a substantial percentage of "engineered wood", that is, wood beams and sheets which are made of chips and sawdust, glued with resins and pressed.  Even SIP construction uses OSB.  Problem is, this engineered wood off-gasses formaldehyde and other chemicals --throughout its lifetime-- and many people are sensitive to these chemicals.

What the Heck is Concrete?

According to Wikipedia:

"Concrete is a construction admixture that consists of cement (commonly Portland cement), aggregate (generally gravel plus sand) and water.  Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration.  The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material.  It is used to make pavements, architectural structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and footings for gates, fences and poles.

Concrete is used more than any other manmade material on the planet.  As of 2005 about six billion cubic meters of concrete are made each year, which equals one cubic meter for every person on Earth.  Concrete powers a US $35 billion industry which employs more than two million workers in the United States alone.  More than 55,000 miles of freeways and highways in America are made of this material.  The People's Republic of China currently consumes 40% of the world's cement [concrete] production.
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It was discovered in the 1970's, with advances in scanning electron microscopy, that the way concrete bonds is by growing crystalline microspires out from the cement particles.  The spires interlock with one another as more grow, and as they grow longer.  The longer concrete is kept damp, the longer and more profuse are the microspires, and so the stronger it gets.  Insulated concrete forms excel in this regard because they keep concrete damp far longer than is the case with conventional slabs or formed walls.  Basement forms would have to be left on for at least 30 days in order to achieve the strength of an ICF wall, but they are rarely left on more than seven days.

Why Concrete?

First and foremost, concrete and its primary constituent, portland cement, are produced from some of the world's most abundant resources without toxic byproducts or environmentally compromising processes.  Resource depletion is not an issue for cement and concrete.  Limestone, the key ingredient of cement, is one of the most common and abundant materials on earth.  Aggregates are also plentiful;  sand and gravel are produced commercially in every U.S. state, and crushed stone is produced in every state except Delaware.

We will not 'run out' of limestone, gypsum aggregates, sand, or any of the other ingredients in concrete for a very long time, more than centuries.  The supply of most ingredients is, for all intents and purposes, inexhaustible.  In addition, the concrete industry increasingly has utilized the waste materials from other industries, e.g. slag from mining and smelting.  In doing so, to the extent that this practice is undertaken, the industry avoids altogether the use of virgin materials extracted for its use.  So it in part eliminates from the outset both the question of sustainability and the question of extraction impacts.

Other materials have less flexibility in both how and where their raw materials are extracted.  Production of steel products relies on iron ore as its principal raw material.  And unlike limestone and aggregate quarries, iron ore extraction often involves very deep pits which are rarely restored.  Duration of an iron mine may be forever.

But while the ecological impacts associated with extraction are considerable for all materials, they are the greatest for wood.  A study sponsored by Natural Resources Canada and conducted by the Canadian wood industry's research arm, Forintek, rates the effects of resource extraction for concrete, wood, and steel.  "The ecological impacts associated with the extraction of wood as a resource are more extensive than the ecological impacts associated with other materials considered in this study, in part because forests provide many ecological and physical functions including pollution absorption, climate regulation, soil production, watershed protection, carbon recycling, wildlife habitat, and human receational activity.  As well, in the case of forest extraction, more hectares are impacted per unit of building material."

According to the Study (annotated at bottom), cutting coastal forest hurts the land 3.25 times more than mining concrete's aggregates:

Impact Index:
Concrete
Aggregates Extraction 1.00
Limestone Quarrying 1.50
Steel
Iron Ore Mining 2.25
Wood
Boreal Timber Harvesting 2.50
Coastal Timber Harvesting 3.25

Although wood is a renewable resource, the environment in which trees grow is not.  Replantings take decades to grow.  In the meantime, the forest as a habitat is lost, and takes more than centuries to reestablish.  Remember, two-thirds of the world's temperate rain forest is on the northwest coast of North America.

How Green is Concrete?

Concrete requires only one product of any energy-intensive consequence. (portland cement)  Cement contents in typical residential concretes range from 11% to 15%.  Mindful of energy consumption factors, the cement industry has reduced fossil fuel consumption by 27% in the last 20 years.  And it has taken the lead in using high fuel-value waste byproducts which would have otherwise gone to landfill, to substitute for coal and natural gas in production -- all under exceedingly tight environmental regulations.

In fact, concrete recycles across the board:

  • Cement production incorporates waste-to-energy cogeneration.
  • Cement or concrete-aggregate quarries are reclaimed for recreational-land development and stormwater management.
  • ICF Development recommends that all old site concrete be salvaged for recycling.  Crushed scrap concrete provides ballast for fill dirt, bases for new roadway pavements, and aggregate for new concrete.  Some companies we know of who recycle concrete are Pacific Topsoils and Renton Concrete.
  • We always use select grades of fly ash from coal combustion and blast-furnace slag from steel production in our concrete mixes, to the greatest percentage recommended, for special performance characteristics and recycling purposes.  This helps you with LEED points, it costs the same, and as a bonus concrete with fly-ash is actually stronger than that without!
  • Many common wastes, such as polystyrene, can be recycled as aggregate in concrete.
  • Scrap steel materials, including old concrete-reinforcing bars, are melted down and used to cast new reinforcing bars.

Cement, the binder of concrete, and concrete supplies are highly local or regional so ultimate energy or fuel requirements for handling and transportation are minimized.  Cement is usually shipped within a 50-mile radius of its production, while ready-mixed concrete and concrete products are supplied far more locally.  The adaptability of formulating cement from various native deposits of clay, limestone, and shale, and supplying other concrete components from similarly local aggregate sources is one of few such luxuries enjoyed among construction materials.  In contrast to concrete, for example, wood products are routinely shipped across the country in their journey from forest to jobsite.

Concrete has superior life-cycle advantages, both in terms of cost and service.  A properly built driveway or walkway for example, requires little or no maintenance -- no coatings or chemical treatments.  Over the service life of a pavement, residential or other, ultimate waste reduction increases by the sheer elimination of maintenance or reconstruction.

Concrete can be mixed with additives to make it completely waterproof.  When designed, placed, and cured to industry guidelines, it requires no coatings or sealants of any kind.   In fact a concrete building was made recently for the Seattle Aquarium, which is almost submerged!  This waterproof property is also very useful when building a permanent rooftop patio deck.

Concrete can be painted, but does not require paint to achieve a given color or hue.  Natural-mineral pigments and coloring agents provide a rainbow of options for driveways, patios, floors, and landscape/ hardscape schemes.  Lampblack gray with dark-beige border seem to be popular for driveways now.  Stamping and impressioning technology has advanced to the point where it is difficult to tell whether it is brick, stone, or concrete.

Concrete, as homeowners worldwide can attest and appreciate, is especially suited to residential construction.  It neither burns, rots, rusts, nor harbors insects and vermin.

Concrete construction is energy efficient.  Cast-in-place concrete foundations and walls integrate easily with foam-board insulation systems, and concrete masonry units provide highly efficient walls and assemblies when used with foam boards or inserts.  Additional thermal values are realized from the large air voids in these units.  And this is not even considering the most advanced deployment of concrete yet -- in ICF structures!

References:

Assessing the Relative Ecological Carrying Capacity Impacts of Resource Extraction, by Wayne B. Trusty & Associates Ltd. in association with Environmental Policy Research, submitted to Forintek Canada Corp. for its Sustainable Materials Project, August 1994.

Ecological Carrying Capacity Effects of Building Materials Extraction, by Dr. Robert Paehlke, Natural Resources Canada, submitted to Forintek Canada Corp. for its Sustainable Materials Project, Sept. 1993.
Insulated Concrete Forms


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