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Concrete

By HHI Staff

When it comes to demand for building materials, concrete takes the top spot as the most widely used construction product in the world. A durable and versatile material, concrete has long been a staple in residential home construction.

 

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Concrete use in homebuilding is most often associated with construction of foundations and floors. But it’s becoming increasingly popular for constructing walls, roofs, patios, walkways and interior surfaces.

 

While top rated in function, the aesthetic appeal of concrete’s dull, gray surface has traditionally been pretty limiting. Recent innovations in concrete application and design have turned around its value as an exposed surface. With a little thought and planning, concrete can create a striking architectural accent.

Design techniques which add value to concrete surfaces include:

  • Using aggregate to provide color and texture
  • Mixing or applying colorants to concrete before or after it’s poured
  • Stamping concrete with metal forms which impress brick, field stone, slate or wood plank patterns.

While these approaches require skill and are best left to an experienced contractor, they offer a variety of creative design options for the homebuilder.

From a health perspective, concrete is generally well tolerated. But like many building materials, concrete has the potential to trigger health issues for those with chemical sensitivities.

What’s in Concrete?

Concrete is a mixture of four basic ingredients:

  • Cement
  • Aggregate
  • Water
  • Admixtures
Cement

Many people mistakenly use the terms concrete and cement interchangeably. Cement is an ingredient in concrete and acts as a glue that concrete mixture together. 

Of the many varieties and brands of cement, Portland cement is by far the most common. Portland cement is available in five different types, each mixed for specific strengths and applications. Type I Portland cement, a general purpose construction cement, is the most widely used of the five types.

 

Type I Portland cement contains mostly calcium oxide, with lesser amounts of silica, alumina, and iron oxide. A small amount of gypsum may also be added. The other types of Portland cement contain similar ingredients in different proportions.

Portland cement is produced by heating the ingredients in a kiln to a temperature of about 2,700°F. The materials melt to form clinkers which are ground into a powder.

Cement kilns are fueled by coal, natural gas, electricity—and hazardous waste. Motor oil, solvents, printing inks and scrap tires are examples of waste products which can be burned in cement kilns. 

In theory, the high kiln temperature causes the hazardous waste to break down into less-toxic by-products. Promoters of this process say this is a good way to dispose of hazardous waste and, at the same time, produce a marketable product—cement.

Detractors point out that incinerators don’t always burn toxics completely; can produce air pollution; are difficult to monitor and sometimes create dangerous by-products like dioxin.

Actually, cement kilns operate at much higher temperatures than municipal solid-waste incinerators so, in theory, they should burn more cleanly, and produce fewer emissions. However, cement kilns are relatively unregulated and toxic residues can end up in cement dust, or be released into the atmosphere through a kiln’s smokestack.

Approximately half of the cement kilns in the U.S. burn some hazardous waste. If you’re concerned about the source of your cement, check with your local supplier or the product’s manufacturer.

While it’s possible that some fuels used in the production process could contaminate cement, it’s unlikely such contamination would seriously affect the air quality in a house containing concrete. This is especially true if the concrete isn’t directly exposed to the living space—as in concrete footings or in a concrete slab covered with ceramic tile.

Aggregate
The aggregate in concrete typically consists of sand and gravel or crushed stone. The strongest concrete has various sizes of aggregate packed together in the cement/water mixture. The aggregate must be clean or the cement will not adhere. Sand, gravel, limestone, granite and old concrete are common ingredients in aggregate.

In the southeastern U.S., seashells are often used for aggregate, and in some parts of the country, slag from blast furnaces is used, as well as fly ash, cinders, and volcanic material. Smashed bricks can also be used. Vermiculite and expanded polystyrene are occasionally used for aggregate in lightweight or insulating concrete.

Like some natural stone, aggregate has the potential to release small amounts of radon. Problems with radon occur when aggregate is sourced from a contaminated site such as a uranium mine or hazardous waste facility. Radon issues in concrete are uncommon and generally occur in clusters where one particular supplier is using aggregate material from a contaminated source.  Most concrete suppliers today use aggregate made from clean sand, gravel or crushed stone.

Water

The water used in making concrete must be clean and relatively uncontaminated. If not, there can be an adverse chemical reaction with the cement, resulting in weak concrete. Water stored in gasoline or oil cans should never be used. Nearly any water suitable for drinking can be used to make concrete, whether from a municipal water supply or a private well.

Admixtures

Admixtures are chemicals that are added to the basic concrete mix to give it different properties. Accelerators and retarders affect the speed at which the concrete cures. Fungicides, germicides, and insecticides are occasionally used.

Other admixtures include: air-entraining agents, gas forming agents, pozzolans, expansion inhibitors, dampproofing agents, permeability reducing agents, workability agents, and colorants. Though commonly used for commercial construction, concrete admixtures are not necessary for most residential applications.

Air-entrained Concrete

As a rule, admixtures add to the cost of concrete and are used only if a contractor specifically requests them. An exception is air-entrained concrete. Air-entrained concrete is used for outdoor spaces, such as sidewalks and patios, which are likely to be exposed to freezing temperatures.

Air-entrained concrete has literally millions of microscopic air bubbles in it—up to 10% of the volume of the concrete. These bubbles help absorb some of the pressure concrete is subjected to in freezing weather and reduce the likelihood of surface deterioration.

Air-entraining agents are sometimes added to the powdered cement at the factory. They can be identified by the addition of the letter A to the cement’s type number (e.g. Type IA). Air-entraining agents can also be added at the concrete plant as the concrete is being mixed. Alkyl benzene sulphonates and methyl-ester-derived cocamid diethanolamine are sometimes used as air-entraining admixtures.

Other agents include: wood, resin, fats and oils, wetting agents, soaps, sodium sulfate, hydrogen peroxide, and aluminum powder. When used outdoors, air-entrained concrete is unlikely to cause a problem for chemically sensitive people.

Water Reducing Agents

Water reducing agents are another type of concrete admixture. The more water used in making concrete, the more it will shrink when it hardens, and the weaker it will be. Water-reducing agents improve the workability with minimal shrinkage or loss of strength.

Water reducing agents can contain harsh chemicals—such as sulfonated melamine-formaldehyde or sulfonated naphthalene formaldehyde condensate. However, the ratio of water reducing agents in concrete is very small, typically ranging from 0.03-0.15% of a water-reducing agent per cubic yard of concrete.

Most people would not be affected by concrete treated with water-reducing agents and it’s unlikely that chemically-sensitive people would be impacted by the additive. To be safe, those with chemically-sensitivities should avoid using exposed concrete in interior living spaces. Covering concrete with ceramic tile or an insulated wall should eliminate potential health problems related to chemical additives.

Colorants

Colorants are also considered admixtures. Certain colorants, including aniline-based colors and common lampblack or dyes, are known to cause intolerance in chemically-sensitive people and should be avoided for those with health issues. These same colorants generally produce lower quality color and can be subject to fading -- additional factors which limit their value.

White cement is often recommended when using colorants to obtain a brighter color. Some colorants are made to be dusted on and worked into the surface of concrete before it cures. They tend to yield brighter colors than those mixed all the way through concrete.

It’s important to note that some colorants contain chromium or other heavy-metal compounds that can be toxic if inhaled in their powder form. Avoid these chemicals by checking ingredients and Material Safety Data Sheets for individual colorant products.

The healthiest colorants are high-quality, mineral pigments. These materials are basically ground rocks, usually forms of iron oxide. Iron-oxide pigments come in a variety of colors—variations of yellow, red, black, etc.—that are colorfast and long-lasting.

 

(This article is from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing.)
 
(Note: The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)

 

Excerpted from:
The Healthy House, 4th edition
John Bower, Author
Copyright © The Healthy House Institute

 

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Concrete:  Created on April 2nd, 2010.  Last Modified on February 28th, 2011

 

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