This page is designed as a first introduction to Enviro-Cement, for lay people or students to year 10 or 12.
Enviro-Cement is a new type of cement which incorporates reactive magnesia and wastes that is more environmentally sustainable. Wastes can be included for their physical property as well as chemical composition without problems such as delayed reactions.
Enviro-Cements are a spin off from John Harrison's work on Tec-Cements.
How do Enviro-Cements Work?
Enviro-Cement is made by blending a small amount of reactive magnesia with conventional hydraulic cements like Portland cement. A pozzolan is also generally added. Lime produced as a result of the hydration of Portland cement is consumed by what is known as the pozzolanic reaction with silica and alumina and replaced by brucite which is magnesium hydroxide and a much more stable and less soluble alkali. The result is that rheology and durability are significantly improved and shrinkage reduced.
Enviro-Cements are relatively low alkali and therefore can be used as a repository for a large range of waste materials some of which can contribute properties to the resulting composites. The reduction in micro and macro cracking due to greater dimensional stability also results in greater durability.
The pH of TecEco cements is lower
The pH controlled by brucite, the predominant mineral, is in the range of the minimum solubility of most heavy metals, brucite can form a number of nano composites holding various electronically balanced minerals in its layered structure by polar bonding and the calcium silicate hydrates present take up lead.
Magnesia also "sets" many clayey and other soils making it useful for contaminated sites.
The reactive magnesium oxide used in Enviro-Cements is currently made from magnesite (a carbonate compound of magnesium) found in abundance. In the future TecEco hope to make Enviro-Cement using magnesite produced by power stations as a result of their carbon storing or sequestration activities.
Steps involved in making Enviro-Cements
1. Magnesite (a compound of magnesium) is heated in a kiln to around 600 to 750 degrees C.
The lower firing temperature of the Tec-Kiln makes it easier to use free energy such as wind or solar or even waste energy and TecEco plan to make a kiln that does not use fossil fuels and in which the CO2 gases produced from the magnesium carbonate as it decomposes is captured and contained for further use or safe disposal.
2. TecEco also want to grind in the hot area of this kiln for increased efficiency.
3. The heating process produces reactive magnesia.
4. The reactive magnesia (powder) is added to a pre-determined, but variable amount of hydraulic cement such as Portland cement, and if desired, supplementary cementitious materials like fly ash.
5. The resulting blended powder is Enviro-Cement.
6. When mixed with water and aggregates such as sand, gravel and wastes, Enviro-Cement concretes are ready for pouring into concrete or pressing into blocks.
7. Enviro-Cement can also be mixed with contaminated soils, wastes etc. and will generally immobilise them.
 Reactive magnesia (rMgO) is more reactive than caustic calcined magnesia, caustic magnesia or CCM. It is pyroprocessed below about 750 deg C as the temperature of firing has a greater influence on reactivity than grind size as excess energy goes into developing crystal structure. Magnesia calcined above this temperature will cause long term dimensional distress and should not be used in hydraulic compositions. Technical information about reactive magnesia is available in the technical area of our web site.