Tec-Cement

This page is designed as a first introduction to Tec-Cement, for lay people or students to year 10 or 12.

Introduction

Tec-Cement is a new type of more sustainable cement which incorporates reactive magnesia[1] and wastes that is much more durable and encourages the greater use of pozzolans and is therefore more sustainable. Wastes such as fly ash and slag can potentially be included in higher proportions as Tec-Cement concretes harden more quickly in the early stages of setting and are easier to finish even when these wastes are added. Wastes such as fly ash and slag can potentially be included in higher proportions without loss in long term strength development

Inspiration

Tec-Cements are a spin off from John Harrison's work on Eco-Cements. See the simple explanation about Eco-Cements.

How do Tec-Cements Work?

Tec-Cement is made by blending a small amount of reactive magnesia[1] with conventional hydraulic cements like Portland cement. As the magnesia[1] hydrates it consumes water forming brucite hydrates which can later deliver more water for the more complete hydration of other hydraulic cement components adding to long term strength development.

We maintain that lime should not be allowed to remain in concrete as it is far too mobile and reactive. Put some in your next cup of tea if you do not believe this! In Tec-Cement concretes 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 durability is significantly improved.

Many other properties of concrete are favourably affected including the flow characteristics (rheology) and dimensional change.

Strength Characteristics

Tec-Cements are more complex to understand than Enviro and Eco-Cements but like them 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 reactive magnesium oxide used in Tec-Cements is currently made from magnesite(a carbonate compound of magnesium) found in abundance. TecEco hope to make Tec-Cement using magnesium from sea water and carbon dioxide produced by power stations.

Steps involved in making the cement

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 his kiln for increased efficiency.

3. The heating process produces reactive magnesia[1].

4. The reactive magnesia[1] (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 Tec-Cement.

6. When mixed with water and aggregates such as sand, gravel and wastes, Tec-Cement concretes are ready for pouring into concrete or pressing into blocks.

[1] Reactive magnesia is also variously known as caustic calcined magnesia, caustic magnesia or CCM. The temperature of firing has a greater influence on reactivity than grind size as excess energy goes into lattice energy.

Technical information about reactive magnesia is available in the technical area of our web site.