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Keeping you informed about the TecEco Cement and Tec-Kiln projects. Issue 47, 2005
"Cement is one of the world's great polluters, but environmentally conscious businessman John Harrison reckons he can clean up with a remixed version of an old classic."
Article: Adam Carey
Photos: Simon Schluter
Many countries in the world like Japan and Singapore that are signatories to the Kyoto protocol are trading nations and not having natural resources are best able to meet their Kyoto commitments through carbon trading.
My company TecEco Pty. Ltd. are uniquely able to assist in this regard with two leading technologies that can be used stand alone, in conjunction with each other or as part of a major combined process to sequester carbon in power stations, geologically and the built environment.
These technologies if adopted by member nations would provide carbon credits helping them meet their Kyoto obligations. As they result in real outputs such as silica, iron ore or materials for the built environment they can also potentially deliver economic benefits as well.
Of the two technologies Eco-Cements are the best known. Eco-Cements are a new type of cement which incorporates reactive magnesia (casutic calcined magnesia) and wastes that is more environmentally sustainable. Eco-Cement used to make permeable concretes absorbs CO2 from the atmosphere to set and harden and can also be recycled back to Eco-Cement. Wastes such as fly and bottom ash, slags etc. can also be included for their physical property as well as chemical composition without problems such as delayed reactions. TecEco hope to make reactive magnesia used in Eco-Cements utilising non fossil fuel energy in a new kiln that combines heating and grinding and captures CO2, and given this production scenario Eco-Cement concretes have the capacity to become a huge carbon sink.
As stated by Fred Pearce in the article on Eco-Cements that was published in the New Scientist magazine (Pearce 2002) “There is a way to make our city streets as green as the Amazon Forest. Almost every aspect of the built environment from bridges to factories to tower blocks, and from roads to sea walls, could be turned into structures that soak up carbon dioxide – the main greenhouse gas behind global warming. All we need to do it change the way we make cement.”
Making the built environment not only a repository for recyclable resources (referred to as waste) but a huge carbon sink is an alternative that is politically viable as it potentially results in economic benefits.
Eco-Cements are made by blending reactive magnesium oxide with conventional hydraulic cements like Portland cement. They are environmentally friendly because in permeable concretes the magnesium oxide will first hydrate using mix water and then carbonate forming significant amounts of strength giving minerals in a low alkali matrix. Many different wastes can be used as aggregates and fillers without reaction problems. The reactive magnesium oxide used in Eco-Cements is currently made from magnesite (a carbonate compound of magnesium) found in abundance. With further development it is hoped to use magnesite formed in a mineral sequestration process using magnesium silicates to sequester carbon from power stations in a total process for saving the planet.
When added to concrete magnesia hydrates to magnesium hydroxide but only in permeable materials like bricks, blocks, pavers and pervious pavements will it absorb CO2 and carbonate. The greater proportion of the elongated minerals that form is water and carbon dioxide and they bond aggregates such as sand and gravel and wastes such as saw dust, slags, bottom ash etc. Eco-Cement can include more waste than other hydraulic cements like Portland cement because it is much less alkaline reducing the incidence of delayed reactions that would reduce the strength of the concrete. Portland cement concretes on the other hand can’t include large amounts of waste because the alkaline lime that forms causes delayed and disruptive reactions.
To reverse the environmentally damaging impact of molecular flows from techno-processes such as too much CO2 in the air or wastes like heavy metals in the global commons, it is essential to use non fossil fuel energy and TecEco plan to do so to power their Tec-Kiln.
The TecEco Tec-Kiln is unfortunately somewhat secret due to patent matters. It is however the final device required to enable the companies grand plan to sequester massive amounts of CO2 using magnesium compounds. Using TecEco Tec-Kiln technology it is possible to run a sequestration cycle based on the magnesium thermodynamic cycle whereby MgO scrubs CO2 out of the air and becomes a carbonate and then what is not used in the built environment as bricks, blocks pavers etc. is re-calcined back to MgO in a closed system so no CO2 is returned to the atmosphere. With global warming problem can be beaten with 20 cycles of the Tec-Kiln starting with less than a billion tonnes of magnesium silicate.
By burning fossil fuels we are producing more CO2 than the planet can handle and so the CO2 level in the atmosphere is rising. Apart from reducing or even stopping this environmentally damaging process, to reduce the global warming predicted, not only must we reduce emissions - it is essential that we sequester carbon on a massive scale. We must change global carbon flows as in the diagram below
There are two main ways this can be done - mineral sequestration and geological sequestration and TecEco technology uniquely links the two.
Magnesium compounds are seriously being considered for mineral sequestration by a number of research groups including the Dutch TNO and US MIT, NETYL, DOE etc.
Using either forsterite or one of the serpentine minerals CO2 can be captured from emitters such as coal fired power stations. The by product which is magnesite can then be calcined using TecEco Tec-Kiln technology ready for another cycle of absorbtion by MgO. This cycle can be repeated indefinitley. CO2 is produced in volume for geological sequestration and MgO can either be used directly to sequester CO2 in another cycle or for mineral sequestration in the built environment using TecEco Eco-Cements.
Sustainable cities are a real possibility.
Kyoto member countries have more hope of persuading the US and Australia to join Kyoto if those countries are waiting for a technical solution by developing exemplars of the solution offered by TecEco. Given the options of energy rationing, massive sequestration or some combination of both, sequestration on a massive scale is most easily politically implemented.
TecEco Pty Ltd is a licensing company and will negotiate with countries the best solution to meeting their Kyoto commitments and providing stimulation to their economies meeting the challenge of a more sustainable future.
Pearce, F. (2002). "Green Foundations." New Scientist 175(2351): 39-40.
I am becoming very interested in reactive MgO added at low addition rates in what I call a tec cement.
I think by adding reactive MgO we can chemically get over a lot of placement and early life problems in concretes as amongst many other effects it increases the water tolerance of concrete and water is commonly added by finishers because they know only too well it is the best plasticiser!
We have now poured some very large slabs up to 80 cubic metres or more and have noticed that the strength development is quite different - very strong for two of three days even with added fly ash and then a straight line for a long time. Shrinkage is also definitely a lot less. At 8% around 250 - 300 microstrains which is very low. At 10% even less. After around 10% there is strength reduction.
Magnesium as a hydroxide or carbonate appears to have a very strong affinity for water. In solution Mg++ complexes with water more readily than Ca++ forming complexes of the general form [Mg(H2O)N]2+. Mg++ can also hydroxylate forming H3O+ and Mg+OH and hydrated forms of Mg+OH.
According to Skalmowski 1#,, in the first stage of magnesium oxide hydration Brucite is not formed; instead metastable magnesium hydroxide [Mg(OH)2.nH20] is formed and only after some time does it recrystallizes to Brucite which is stable.
Investigations done in Japan proved that the structure of metastable magnesium hydroxide is crystalline. It differs from Brucite in that it holds monomolecular layers of water between neighbouring Mg(OH)2 packets. Intra packet water is removed during re-crystallisation and Brucite is formed as hexagonal lamellae. Increasing the temperature increases the rate of transformation. According to Skalmowski the properties of metastable Mg(OH)2 are different from Brucite. It is four times more soluble in water, but still less soluble than Portlandite.
Tec-Cements can be significantly stronger and we suspect that one reason for this is that hydrate complexes form what amounts to a metastable perhaps even microcrystalline "gel" holding water for slow release right through the matrix of the concrete resulting in more complete hydration of PC. In ordinary PC concrete up to 15 - 20% may remain unhydrated. The hydration of more of this fraction would add to efficiency of PC as a binder and result in greater strength. There are also other reasons for strength including densification and more affective pozzolanic reactions due to retentionof alkali.
We know from pharamcuetical chemistry that magnesium hydroxide "gels" can be produced by carefully controlling conditions under which precipitation of the hydroxide is accomplished by adding an alkali - In the case of an MgO - PC mix this alkali would of course be the Ca(OH)2 coming out of hydration reaction of calcium silicates.
Are any of our readers able to shed any light on metastable Mg(OH)2.nH2O and in particular the value of n. I have done a lot of calculations lately to prove that more water can be added in the presence of reactive MgO. As this happens on site concrete is more foolproof with added MgO. I could finalise these calculation and then maybe do some more volumetric calculation if I knew the value of n.
I really cannot find much on the subject of brucite hydrates and do not have the equipment in my primative lab to find out. Besides I have not as yet thought of an experimental procedure to do so. It is however my obervation that Tec-Cement concretes do seem to internally absorb a lot of water and the MgO is thus a useful adjunct to the tricalcium aluminate gypsum reaction forming etrringite which also consumes considerable water and without which concrete would be an almost unsettable mush.
1Skalmowski, W, Chemistry of Building Materials, Warszawa, Budownictwo I Architectura
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Please contact John Harrison at TecEco