Before the widespread use of Portland cement, magnesium oxide-based cements were among the world’s most popular cement products. By the late 19th century, the use of Portland cement had spread around the world. Although Portland cement has now essentially cornered the market, it has some inherent drawbacks when compared to the magnesium oxide-based cements used by our ancestors. Portland cement manufacturers are currently allocating enormous R&D funding to overcoming deficiencies that impact the environment, human health, and the strength, durability, and usability of Portland cement. Billions of dollars are being spent in an effort to make Portland cement do what magnesium phosphate — and magnesium oxychloride-based cements do naturally.
No one ever purposely set out to make a problematic cement; quite the opposite. When Joseph Aspdin invented his water-activated Portland cement in his Leeds, England, kitchen in 1824, it seemed to be a viable and exciting advance in addressing the needs of the Industrial Revolution, which was hungry for construction materials. His
new product was convenient to use and the raw materials to make it were in abundant supply.
Portland cement is created by heating raw materials to 2,700 degrees Fahrenheit to create clinkers. It is common knowledge that the worldwide production of Portland cement, which is increasing at a rate of 5 percent annually, currently creates as much as 12 percent of the greenhouse gas emissions responsible for global warming.
Some of the most harmful effects of concrete made with Portland cement come when it is "enhanced" with plastics. The concrete never cures, or does so extremely slowly, which may enhance the strength of the concrete but not the health of a building’s occupants. Furthermore, concrete treated with these plastics outgasses and is toxic, particularly when it is mixed with mold. The high temperatures used in the production of Portland cement make it extremely thirsty for water (hydrophilic), causing a number of problems including the promotion of mold growth.
In many buildings today, 50 to 90 percent by weight of a solid concrete envelope is involved in holding up its own "dead weight."ln the future, the
Other recycled materials such as crushed brick are highly absorbent and may have been exposed to atmospheric pollutants prior to being used in concrete. Aggregate that is free of toxins and acquired odors should be specified as follows:
fly ash (unless it is possible to verify that it contains no heavy metals or toxic substances), cinder, and volcanic material (other than pumice). The contractor shall verify the aggregate content with the concrete supplier prior to pouring.
• Only clean, natural mineral aggregates are acceptable. The following are unacceptable aggregates: crushed brick, crushed sandstone, crushed concrete slag,
Many different types of admixtures may be added to the concrete mix to modify various
use of ultra-high-strength magnesium oxide cements could reduce the use of structural cement materials significantly, thereby increasing the percentage of more insulative, nonstructural infill elements and creating far more energy-efficient envelopes.
Magnesium cements have consistently proven to be superior to Portland cement in strength, versatility, and environmental integrity. Yet until recently magnesium cements had virtually fallen into disuse over the past 175 years. A brief history of magnesium cements will explain why these ancient building materials are of such great historic importance and, more importantly, why they may now hold the key to the future of worldwide sustainable building practices. This cement alternative (often called ceramic cement) provides unique advantages over Portland cement.
Blends of magnesium oxide were used in ancient times in Germany, France, Mexico and Latin America, Switzerland, India, China, and New Zealand, among other countries. The Great Wall of China and many of the stupas in India, still standing today, were made with magnesium-based cements. Ancient European artisans used a timber frame with magnesium oxide infill in constructing homes. No gaps are visible in the 8oo-year-old walls that remain in use.
Magnesium deposits exist in abundance in every corner of the Earth and cover roughly 8 percent of its surface. Depending on where they are mined, magnesium oxide cements require only 20 to 40 percent of the energy used to produce Portland cement.
Magnesium-based cements have exceptional health-promoting properties for the occupants of homes in which they are used as a building material. For example, research at Argonne National Laboratories has documented that occupants of homes made with traditional cow dung and magnesium oxide located right next to the Chernobyl nuclear power plant had less radiation sickness from the nuclear accident than any other group. Occupants of modern stud frame and concrete homes, even miles away, succumbed at higher rates to radiation sickness.
These natural cements bind exceptionally well to all things cellulose (such as plant fibers
properties. For example, air entrainment admixtures disperse air bubbles throughout the concrete to improve resistance to freezing and thawing. Water reducing admixtures decrease the amount of water required. Retarders and accelerators modify the setting time of concrete. Super plasticizers allow for lower water to cement ratios. They frequently contain sul — fonated melamine, formaldehyde condensates, sulfonated naphthalene, and other potentially harmful ingredients.
Water reducing agents and air entrainment
admixtures are frequently added to concrete mixtures even when not specifically requested. The exact ingredients of an admixture are usually proprietary. Although admixtures generally make up a very small portion of the concrete and do not pose a significant problem to any but the most sensitive individuals, they can be completely eliminated if concrete work is scheduled for warm weather and if the concrete supplier is aware of this requirement. Even with admixtures, concrete must never be poured on frozen soil or when there is a risk
and wood chips) and are often referred to as living cements. Although the cost of magnesium oxide cement is currently considerably higher than that of Portland cement, a wide variety of indigenous rock, plant and wood fibers, and other cellulose granules can be added to it as aggregate, extending the basic cement material by up to 95 percent and thereby reducing its cost. This is in sharp contrast to Portland cement, which repels cellulose.
Magnesium-based cements commonly achieve compressive strengths of 9,000 to 45,000 pounds per square inch and tension strength of over 800 pounds per square inch, many times stronger than conventional concrete. Combined with clays and cellulose, magnesium oxide forms cements that "breathe" water vapors, a significant plus. The clay in magnesium oxide balances and enhances the movement of moisture. The material never rots because it always expels moisture.
Magnesium-based cements are completely nonconductive of electricity, as well as heat and cold, and have been used for flooring for radar stations and hospital operating rooms.
Until the early 1930s almost ail terrazzo floors were made with magnesium phosphate or magnesium oxychloride. These materials were used extensively throughout the United States until Portland cement offered what appeared at the time to be a less costly, more user-friendly alternative. The successful manufacture, marketing, and proliferation of Portland cement occurred at a time when energy was cheap and public awareness of environmental health concerns was virtually nonexistent.
Recently magnesium-based products have become available from several sources:
Argonne National Laboratory (anl. gov) and others have now licensed firms to market magnesium-based cements underthe nameCeramicrete. These companies have patents on their products. US Gypsum, the original American maker of Portland cement, is also introducing magnesium oxide as a nontoxic accelerant and additive. Aquacast is one magnesium oxide product being marketed by US Gypsum.
Grancrete, a spray-on structural cement, has been developed by scientists at Argonne National Laboratory and Casa Grande LLC as one of
 |
 |
• No admixtures shall be used in the concrete. It is the contractor’s responsibility to comply with the necessary climatic parameters so that required strengths and finishes are obtained without additives. Verify with the supplier that all concrete is free of admixtures, including air entrain
