The following suggestions can help reduce waste and other environmental impacts associated with concrete for common applications such as cast-in-place, precast, stucco, and concrete masonry units:

• For previously developed sites, consider designing to reuse portions of existing structures, such as slabs or walls in suitable condition.
• Concrete slabs and structures slated for demolition can be ground and recycled as aggregate or fill material for new projects, or recycled at the Buena Vista and Dimeo Lane landfills.
• Incorporate the maximum amount of fly ash, blast furnace slag, silica fume, and/or rice husk slag appropriate to the project, which can reduce cement use by 15-100%.
• When using fly ash, ask the supplier for a declaration that it does not contain radioactive heavy metal waste, such as from medical waste incineration. (Such contamination is rare.)
• Consider precast systems to minimize waste of forming material and the impact of wash water on soils.
• Decide whether other materials can be incorporated or substituted for concrete:
  • Consider insulating concrete formwork (ICF) to reduce waste, enhance thermal performance and, in some cases, accelerate project completion.
  • Consider cellular, foamed, autoclaved aerated (AAC) and other lightweight concretes that incorporate air, low-density aggregate, and/or fibrous materials, adding insulation value while reducing weight and concrete required.
  • Earthen and rapidly renewable structural materials, such as rammed earth, cob (clay with straw), straw bale construction with clay plasters or earthen floors, can perform comparably to concrete and can reduce the need for insulation and finish materials in both residential and commercial projects.
    See http://www.ecocomposite.org/building/commercial.htm
  • Consider salvaged or locally quarried stone, and other durable salvaged materials.
• Consider leaving concrete exposed, using it as a finish material.
• When sealants are required, utilize a low or zero VOC product.
• For color, consider relatively benign concrete stains, which are often less expensive than embedded colorants or acid stains. For example, the common plant fertilizer iron sulphate (also called ferrous sulphate), can create tones ranging from yellow to rusted umber. Leftover ferrous sulfate is a useful soil amendment.
  (See www.cathy-moore.com/house/stain.html) However, embedded color is the most durable finish option, reducing long-term waste or maintenance.
• Stamping can add a variety of textures to concrete finishes.
• Inlayed materials such as pebbles can add additional color and texture.
• Use non-toxic form-release agents.
• Minimize waste by carefully planning concrete requirements.
• Suppliers can use excess ready-mix returned from job sites in cast products for non-structural applications, such as retaining walls, steps, medians and security barriers, parking curbs, and fences.

Strong, inexpensive, and durable, concrete is the most widely used structural building material in the United States. Due to the vast scale of concrete demand, the impacts of its manufacture, use, and demolition are widespread, including habitat disturbance from extraction of cement components, sand, and rock; energy use in extraction, production, and shipping of cement; and toxic air and water emissions from cement manufacturing. Cement dust contains free silicon dioxide crystals (the cause of silicosis), the trace element chromate (a cause of stomach cancer and skin allergies) and its lime content may burn the skin. Mixing concrete requires a great deal of water and generates alkaline waste water; sites should be carefully managed to prevent run-off, which can contaminate nearby waterways and vegetation.

Concrete is a mixture of aggregate (usually sand and crushed stone), paste (most commonly Portland cement), and water. To control transit cost, local sand and stone are commonly used, limiting embodied energy somewhat. However, incorporating recycled aggregate (such as ground concrete from demolition) is an excellent way to reduce local environmental impacts, including solid waste, transit emissions, and habitat disturbance. Coordination with code officials is necessary for structural applications.

Cement manufacture is energy intensive. Approximately one ton of carbon dioxide is released per ton of cement produced, totaling 7-8% of anthropogenic (man-made) CO2 emissions. Concrete is only about 9-13% cement, but cement accounts for 92% of its embodied energy. Substituting other pozzolans (i.e., substances that act like cement when they react with alkaline materials) for Portland cement significantly reduces energy use and carbon dioxide emissions. Sources of pozzolans include industrial byproducts such as fly ash, silica fume, rice husk ash, and furnace slag, along with volcanic tuff. Fly ash (the residue from coal combustion) is a popular and widely available cement substitute because it generally decreases porosity, increases durability, and improves plasticity, workability, and compressive strength, though at the cost of increased curing time. Fly ash often makes up 10-15% of standard mixes, but it can substitute for 35-60% of cement in many applications, and certain types of fly ash (Class C) can completely replace cement for some projects. Fly ash is also used for fill, soil stabilization, and waste remediation.

Trapping air in the finished product and the use of a wide variety of low-density aggregates are methods of reducing concrete use. Onsite or local methods of air entrainment include the addition of chemical foaming agents, such as with Neopor blocks; heat and steam, such as with autoclaved aerated blocks (AAC); and mechanical systems, such as with AirCrete concrete foam for non-toxic non-structural insulating fill. Trapped air displaces concrete, enhances insulation value, reduces weight and material costs, and retains the durability and fire-resistance of standard concrete. Voids reduce strength of the concrete, but some foamed concrete products can be used for certain structural applications. Low-density aggregates generally have minute voids that provide similar insulation and weight-reduction benefits; examples include pumice and expanded vermiculite, perlite, and shale, along with polystyrene beads and mineral fiber.

For do-it-yourself projects, the above criteria can help you select concrete products from local retailers. For larger projects, these suggestions can help green your specifications. Work with your contractors and designers to incorporate recycled aggregate and fly ash or other cement substitutes into the mix for your project. Many green concrete products and practices suggested here are becoming relatively common. Several local contractors and materials suppliers provide these products and services.
The following resources provide additional information about the products on the market:

RECYCLED AGGREGATE

CIWMB Recycled Content Product providers list

Debris Recyclers Database

Santa Cruz County Buena Vista Landfill
Accepts clean and sorted concrete, asphalt, brick, base rock, and porcelain for recycling at a reduced fee.

City of Santa Cruz Resource Recovery Facility: (831) 420-5545

USGS Report - "Recycled Aggregates - Profitable Resource Conservation"

LIGHTWEIGHT AGGREGATE

Your local supplier is very likely to offer lightweight pumice. For more information:

Green Home Building.com
examples and direction to technical information on lightweight concrete using pumice

Glass Mountain Pumice
Pumice supplier, with office in Sacramento

HIGH FLY-ASH CONCRETE

Fly ash is inexpensive and imparts useful properties to many standard mixes. Any custom mix supplier should have little trouble incorporating additional fly ash to meet the specifications for your project. If your supplier or contractor is unfamiliar with fly ash, ISG Resources offers technical instructions and materials.

Fly Ash Resource Center

Silica Fume Association

FOAMED CONCRETE

Autoclaved Aerated Concrete Products Association

GENERAL INFORMATION

GreenSpec
A fee-based service searchable by the standard UniFormat. It is probably the most comprehensive single source of green building product information.

Oikos
A free website with information about a wide range of greener construction products

Center for Resourceful Building Technology
A free website with information about a wide range of greener construction products

EPA Environmentally Preferable Purchasing

California Integrated Waste Management Board

David Hertz (1995) "A Material for a Finite Planet"

Concrete Network
Though it does not emphasize sustainability, the Concrete Network site is an excellent semi-technical resource.

Program Contact: Green Building

Ecology Action Phone: 831.426.5925 Fax: 831.425.1404