Glenorchy
Tasmania 7010 Australia
Phone: 61 3 62497868 (am)
Phone: 61 3 62713000 (pm)
Fax: 61 3 62730010
www.tececo.com
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497 Main Road Glenorchy Tasmania 7010 Australia Phone: 61 3 62497868 (am) Phone: 61 3 62713000 (pm) Fax: 61 3 62730010 www.tececo.com |
Printed in cyberspace on recycled electrons
Keeping you informed about TecEco sustainability projects. Issue 62, 12th November 2006
Thank you for your support. I am changing my email address due to the huge amount of spam I get.
The simple message that if we copied nature and made rocks out of CO2, a process I have termed geomimicry, has not just conjured tremendous support, it has brought out the worst in many. We have had to cope with deliberately misleading science, court cases designed to send us broke and all sorts of vilification. What has kept me personally going is your encouragement. Thank you.
Continue to have the courage of your convictions, the tide is now turning, people are starting to understand that a holistic yet economic approach to our problems, particularly those of global warming and waste is the only way forward and that geological history can teach us what has worked in the past and will work in the future. Just when I thought interest in our technologies was starting to wane we broke another record last month with nearly 60,000 people visiting our web site!
There is enough calcium and magnesium in seawater to last indefinitely as a source of a cation to make carbonate rock. The process is simple and economic as it results in valuable by-products including fresh water. It consumes rather than produces wastes on a large scale and our magnesium Eco-Cements can glue all the rock produced together to construct our built environment. Simple, brilliant and entirely feasible.
In between the dozens of emails I get every day enquiring about TecEco technologies I also receive an annoying 150+ spams suggesting I need something to help with my sex life. I can take it no more so I am therefore phasing out my old email address.
My new email address is a--dot--john--dot--w--dot--harrison--at--tececo--dot--com. It is also on the web site under contacts in this non-standard format to foil the harvesting software used by spammers to capture e-mail addresses.
If you wish to contact me please assist by providing contact information such as a signature at the end giving your name and contact details. I do not usually respond to people who cannot tell us who they are.
Please do not add our email address to any spam list and do not quote it electronically except in the above form on your web site.
Thank you once again
John Harrison B.Sc. B.Ec. FCPA
Managing Director
TecEco Pty. Ltd.
What prompted this article was that I heard there are suggestions by some on the Australian fly ash standards committee to introduce an upper limit for MgO in fly ash based on oxide analysis.
I agree that the presence of larger cyrstals of expansive Periclase should be banned even though it is much less expansive than dead burned lime (Ramachandran V. S., Concrete Science, Heydon & Son Ltd. 1981, p 358-360). Banning MgO based on it turning up in an oxide analysis is however nonsense and for many reasons would be a disaster regardless of the way you think about it. The point is that magnesium in many forms is either harmless to concrete or highly beneficial. TecEco's particular contribution is that we have demonstrated that reactive magnesia made at low temperatures can be added to great benefit.
The whole notion of banning anything based on an oxide analysis is very unscientific. Chemical and physical properties generally belong to either discrete elements or compounds and those of compounds commonly bear little resemblance to those of the discrete component elements. The common example given for this is common salt compared to sodium metal or chlorine gas.
If magnesium compounds are sintered at high temperatures such as during the manufacture of Portland cement and slowly cooled then larger, high lattice energy periclase crystals are formed. Lattice energy is the energy required to separate completely the ions in an ionic bound solid like periclase. The higher the lattice energy the more time and energy it takes for an ionic solid to disassociate and hydration reactions occur. With a high lattice energy of 3795 Kj mol-1 crystalline periclase can take months to hydrate and when it does it causes dimensional distress if not fine grained.
If cements are cooled more quickly or not heated to the point where sintering and even melting can allow crystals to grow, then smaller crystals of periclase are the result, and in many historic cements such as Rosendale cements, the presence of magnesium in this form was not usually a problem. (see the excellent work of Prof Jan Elsen at the Katholieke Universiteit Leuven and a recent paper by Laura Powers (Powers, L. J. (2005). A New Look at an Old Cement. 27th International Conference On Cement Microscopy, Victoria, British Columbia, Canada.)
If cooling is very rapid as is the case with slag and fly ash then magnesium, if present, will remain in the glass phase. If minerals form they are high temperature species that may contain magnesium but not usually pure magnesium oxide. If the latter does form then it can only, as above, be fine grained and harmless.
How did we get to being so dogmatically wrong in the Portland cement industry? Is it because engineers tend to view materials from the top down instead of in terms of the chemistry. There is a correlation between magnesium oxide present as periclase and delayed hydration usually tested for in an autoclave. Even though magnesium can be present in many forms, the easy thing to do without having to understand the problem was to ban more than a small percentage of magnesium oxide based on oxide analysis. Within a few years of when committee C-1 on cement was first established by the newly formed ASTM in 1902 magnesia was banned based on oxide analysis with no account of the form it was in. Given the limited equipment for analysis at the time this was probably reasonable. We now have XRD and a host of other rapid analysis tools and in spite of ample historic and other evidence that magnesia is useful the dogma has not changed and many engineers still take the simplistic precaution of banning it on oxide analysis.
Possibly even as a result of my work, that magnesia in some forms in concrete is not a problem is beginning to be recognised. ACI Education Bulletin E3-01 for example now states at page 7 "some of the minor constituents may play a significant role throughout the chemical hydration process. Since the reactions that involve compound formation seldom go to completion during the clinkering operation, there are usually small amounts (less than 1% by mass) of uncombined calcium oxide (CaO referred to as free lime) present in the cement. If present in a sufficiently large amount, the expansion of free lime during hydration can cause cracking and strength loss (unsoundness) in concrete due to internal expansions. Unsoundness in concrete may also result if there are excessive amounts or certain forms of magnesium oxide (MgO) in the cement. MgO occurs in most raw materials and, when present above about 2% by mass, will crystallize as free MgO, which may also expand during the hydration of the cement. The reaction of MgO takes place very slowly, and so unsoundness may only appear after many months, or even years. An autoclave soundness test is required in ASTM C 150 to detect cements with excessive amounts of uncombined lime (CaO) or MgO. Hydrated lime [Ca(OH)2] and magnesium oxide (MgO) quenched in a glassy form will not expand."
Magnesium has been found in high percentages in many Roman concretes, and it is thought to have got there either aa contaminant in the lime that was burnt or contained in Pozzolana which is a siliceous volcanic dust containing on analysis essentially iron oxide, aluminium oxide, calcium oxide and magnesia and deriving its name from Pozzuoli, near Naples, where it was first utilized and afterwards found in great beds on the Roman Campagna. Vitruvius in his famous Ten Books on Architecture gives an account of pozzulana in book II, 6.
Mixed with lime and water magnesium in a cement makes a stronger and more enduring cement. According to the classic encyclopedia based on the Britannica of 1911 (http://www.1911encyclopedia.org/Mortar), "Cements containing magnesia are pronounced both by Vicat and Chatoney to resist the dissolving action of sea-water better than those in which no magnesia is present, and it is pretty well established by experience that cements derived from argillo-magnesian limestones furnish a durable cement for construction in the sea."
The early American experience with magnesium in cements was similar. For most of the 19th century and more than half of the 20th, natural cement from Rosendale was a prominent binder used in the construction of many buildings, monuments and structures. The Rosendale natural cement was rich in magnesium because the rock from which it was made was a dolomitic limestone. On analysis Rosendale cements contain 14-30% magnesium determined as the oxide present mainly as brucite, carbonates of magnesium and iron like sjoegrenite and biotite. The magnesium minerals have resulted in extreme durability and this has caught the attention of many modern researchers such a Laura Powers cited previously..
Rosendale cements were made in shaft kilns and the periclase that formed was generally sufficiently fine grained to hydrate rapidly enough so that dimensional distress was not an issue although sometimes problems occurred ( Heath, A. H., A Manual on Lime and Cement. Spon and Chamberlain, New York, 1893. 215 pages.) Around 1937 Rosendale cements were so considered so good than "every road built of concrete in New York State had to have one bag of Rosendale cement to every three bags of Portland cement."( http://www.willylake.com/html/story09.htm)
In 1980 P K Mehta wrote a paper suggesting that fine grained periclase could be used to control shrinkage (Mehta, P.K. Pirtz, D.,Komandant, G J "Magnesium oxide additive for producing self stress in mass concrete. Proc. Paris Congress on the Chemistry of Cements, Vol III, 1980, pp6-9.) and this has more recently been done by the Chinese in the prestigious three gorges dam.
Magnesium, usually occurs in glass and if crystalline in the form of melilite or merwinite or in the mullite phase in high temperature glasses that have been cooled such as ground granulated blast furnace slags (gbfs) and fly ash. It has rarely if at all been recorded as periclase. Some of the best fly ashes in the world have a high MgO content (on analysis) yet do not show any sign of dimensional distress due to delayed hydration. Gary Hunt of Environmental and Industrial Evaluations Ltd. has shown this for UK fly ashes. Banning MgO based on an oxide level on analysis may exclude these proven supplementary cementitious materials from use.
It is an objective for all in the cement and concrete industry to use more supplementary cementitious materials like fly ash and blast furnace slag in concrete and I have demonstrated elsewhere that reactive MgO facilitates the use of more fly ash rather than less.
There are several reasons why high fly ash concretes do not sell as well as we would all like them to. They set slowly i.e. concretes made with them show retarded strength development, in particular early strength development is slow and they do not gel up quickly allowing finishers on the job early so they can go home (this is very important!) High fly ash concretes are sticky to the screed, bull float and trowel, and thus not popular amongst finishers who sometimes even ask for more money to work with them. They tends to shrink more because of greater water demand and as a chemist I am concerned about the slow reduction in the calcium/silicon ratio of CSH that they display. All of these problems are solved by adding reactive magnesia in a mix containing fly ash as advocated by TecEco and to some extent by leaving magnesium compounds in fly ash.
The composition of a fly ash is important, particularly the calcium aluminium ratio and the amount of calcium as should the glasses crystallize the composition controls what forms. If there is some tendency to crystallinity in slag or fly ash it is rare that magnesium turns up as periclase and in most cases impossible because the composition would not allow it. There is just never enough magnesium and generally more calcium and much more silicon.
The following phase diagram from the Forschung institute (FEhS) showing isotherms gives the minerals present in the CaO-SiO2-MgO system. The figure shows the area for a periclase formation depends on the basicity (CaO/SiO2) with Al2O3-content of 10 %. I understand that increasing the Al2O3 content does not have a significant influence on whether periclase will or will not form. FEhS has never found samples of ground granulated blast furnace slag (gbfs) with periclase in them and the numbers 1 to 7 show some real gbfs with MgO up to 15 %. Note that they are still very far from the periclase area.
The diagram was constructed by the Forschung institute (FEhS) in relation to gbfs which like fly ash varies in composition but generally contains SiO2, Al2O3, Fe2O3, MgO, and CaO with at least 10% Al2O3, usually more like 20-30%. It can be seen from the diagram that much more likely in blast furnace slags are minerals containing calcium and magnesium and also silica such as merwinite and melilite. Given the similar compositions but lack of further experimental evidence available to me it would be reasonable to conclude that magensium would form in these minerals in fly ash that was not entirely glassy. We know that lower proportions of magnesium are taken up in mullite in fly ash , which together with quartz is the main mineral found. (Hulett, L. D et. al. "Chemical Species in Fly Ash from Coal-Burning Power Plants," Science, New Series, Vol 210. No. 4476 (Dec. 19, 1980, pp 1356 - 358)
Note however that even though phase diagrams are useful they do not actually show minerals present in a melt, only what could form at a temperature given the composition as a melt crystallises. If anybody has constructed or has other useful phase diagrams I would be interested.
From the above it can be concluded that the composition of a fly ash or slag is important . It is also essential that both fly ash and iron slag are cooled quickly so they remains glassy. Rapidly cooled melts form glasses that have the composition of their respective and widely varying high temperature melts and being glassy are reactive in the highly alkaline conditions found in early stage concretes.
Glasses are reactive because they are unstable. The elements in them want to reorder as compounds and the propensity is reflected in the enthalpy and free energy of formation; another measure is the ionic lattice energy (they are related). What is preventing crystals and gels forming is the kinetic barrier created by the elements themselves being trapped in a glass. In water with a silicate/aluminate network forming cations such as Na++ or Ca++ balancing hydroxyls or OH- are formed. In alkaline solutions containing an abundance of these OH- ions silica and alumina become more soluble and the glasses break down. Their surfaces are also hydroxylated. (the Si-O bond is broken and an OH added) They are therefore able to react with Ca for example in solution to form pozzolanic forms of CSH.
In such glasses MgO is not a mineral, it merely appears on analysis. Mg++ is able to go into solution as the glass is dissolved in an alkaline environment and then precipitate by association with the hydroxides present as brucite. The presence of brucite dramatically improves the durability of concrete as noted by the Romans, Vicat and more recently those examining more durable high Mg concretes of yesteryear such as those containing Rosendale cement. As the ACI point out in the above citation, Mg in a glass is harmless in relation to delayed expansion.
For those who now think they can now defeat our patents MgO in the form of a glass created by rapid cooling from high temperatures is not equivalent to low lattice energy MgO created at lower temperatures and added later. The result is similar, mechanism entirely different!!
The above article is by no means entirely correct and if anybody wishes to add anything or dispute what I have said I am keen to talk to them.
With permission from noted author George Montbiot
You have to pinch yourself. Until now the Sun has denounced environmentalists as "loonies" and "eco beards". Last week it published "photographic proof that climate change is real". In a page that could have come straight from a Greenpeace pamphlet, it laid down 10 "rules" for its readers to follow: "Use public transport when possible; use energy-saving light bulbs; turn off electric gadgets at the wall; do not use a tumble dryer ... "
Two weeks ago the Economist also recanted. In the past it has asserted that "Mr Bush was right to reject the prohibitively expensive Kyoto pact". It co-published the Copenhagen Consensus papers, which put climate change at the bottom of the list of global priorities. Now, in a special issue devoted to scaring the living daylights out of its readers, it maintains that "the slice of global output that would have to be spent to control emissions is probably ... below 1%". It calls for carbon taxes and an ambitious programme of government spending.
Almost everywhere, climate change denial now looks as stupid and as unacceptable as Holocaust denial. But I'm not celebrating yet. The danger is not that we will stop talking about climate change, or recognising that it presents an existential threat to humankind. The danger is that we will talk ourselves to kingdom come.
If the biosphere is wrecked, it will not be done by those who couldn't give a damn about it, as they now belong to a diminishing minority. It will be destroyed by nice, well-meaning, cosmopolitan people who accept the case for cutting emissions, but who won't change by one iota the way they live. I know people who profess to care deeply about global warming, but who would sooner drink Toilet Duck than get rid of their Agas, patio heaters and plasma TVs, all of which are staggeringly wasteful. A recent brochure published by the Co-operative Bank boasts that its "solar tower" in Manchester "will generate enough electricity every year to make 9 million cups of tea". On the previous page it urges its customers "to live the dream and purchase that perfect holiday home ... With low cost flights now available, jetting off to your home in the sun at the drop of a hat is far more achievable than you think."
Environmentalism has always been characterised as a middle-class concern; while this has often been unfair, there is now an undeniable nexus of class politics and morally superior consumerism. People allow themselves to believe that their impact on the planet is lower than that of the great unwashed because they shop at Waitrose rather than Asda, buy Tomme de Savoie instead of processed cheese slices and take eco-safaris in the Serengeti instead of package holidays in Torremolinos. In reality, carbon emissions are closely related to income: the richer you are, the more likely you are to be wrecking the planet, however much stripped wood and hand-thrown crockery there is in your kitchen.
It doesn't help that politicians, businesses and even climate-change campaigners seek to shield us from the brutal truth of just how much has to change. Last week Friends of the Earth published the report it had commissioned from the Tyndall Centre for Climate Change Research, which laid out the case for a 90% reduction in carbon emissions by 2050. This caused astonishment in the media. But other calculations, using the same sources, show that even this ambitious target is two decades too late. It becomes rather complicated, but please bear with me, for our future rests on these numbers.
The Tyndall Centre says that to prevent the earth from warming by more than two degrees above pre industrial levels, carbon dioxide concentrations in the atmosphere must be stabilised at 450 parts per million or less (they currently stand at 380). But this, as its sources show, is plainly insufficient. The reason is that carbon dioxide (CO2) is not the only greenhouse gas. The others - such as methane, nitrous oxide and hydrofluorocarbons - boost its impacts by around 15%. When you add the concentrations of CO2 and the other greenhouse gases together, you get a figure known as "CO2 equivalent". But the Tyndall Centre uses "CO2" and "CO2 equivalent" interchangeably, permitting an embarrassing scientific mish-mash.
"Concentrations of 450 parts per million CO2 equivalent or lower", it says, provide a "reasonable to high probability of not exceeding 2C". This is true, but the report is not calling for a limit of 450 parts of "CO2 equivalent". It is calling for a limit of 450 parts of CO2, which means at least 500 parts of CO2 equivalent. At this level there is a low to very low probability of keeping the temperature rise below two degrees. So why on earth has this reputable scientific institution muddled the figures?
You can find the answer on page 16 of the report. "As with all client-consultant relationships, boundary conditions were established within which to conduct the analysis ... Friends of the Earth, in conjunction with a consortium of NGOs and with increasing cross-party support from MPs, have been lobbying hard for the introduction of a 'climate change bill' ... [The bill] is founded essentially on a correlation of 2C with 450 parts per million of CO2."
In other words, Friends of the Earth had already set the target before it asked its researchers to find out what the target should be. I suspect that it chose the wrong number because it believed a 90% cut by 2030 would not be politically acceptable.
This echoes the refusal of Sir David King, the government's chief scientist, to call for a target of less than 550 parts per million of CO2 in the atmosphere, on the grounds that it would be "politically unrealistic". The message seems to be that the science can go to hell - we will tell people what we think they can bear.
So we all deceive ourselves and deceive each other about the change that needs to take place. The middle classes think they have gone green because they buy organic cotton pyjamas and handmade soaps with bits of leaf in them - though they still heat their conservatories and retain their holiday homes in Croatia. The people who should be confronting them with hard truths balk at the scale of the challenge. And the politicians won't jump until the rest of us do.
On Sunday the Liberal Democrats announced that they are making climate change their top political priority, and on Tuesday they voted to shift taxation from people to pollution. At first sight it looks bold, but then you discover that they have scarcely touched the problem. While total tax receipts in the United Kingdom amount to £350bn a year, they intend to shift just £8bn - or 2.3%.
So the question which now confronts everyone - politicians, campaign groups, scientists, readers of the Guardian as well as the Economist and the Sun - is this: how much reality can you take? Do you really want to stop climate chaos, or do you just want to feel better about yourself?
George Monbiot's book Heat: How to Stop the Planet Burning is published by Allen Lane next week. He has also launched a website - turnuptheheat.org - exposing false environmental claims made by corporations and celebrities. www.monbiot.com
I think I am Brave Two
Michael Quinion
Editor, World Wide Words
E-mail: wordseditor@worldwidewords.org
Web: http://www.worldwidewords.org
It’s a brave man who challenges the world-wide cement industry, which produces about two billion tonnes of the stuff every year. All of it is Portland cement, invented by a Leeds stonemason named Joseph Aspidin two centuries ago (it was called that because its finish was thought to resemble stone from quarries at Portland in Dorset). Portland cement is made by cooking a mixture of chalk or limestone with clay in a kiln at high temperatures, a process that gives off large amounts of carbon dioxide. Now John Harrison, an inventor from Tasmania, has found a way to make a cement that’s more ecologically acceptable. He replaces the calcium-based lime with its magnesium equivalent, magnesia. This can be kilned at a much lower temperature making it easier to capture any releases and so) needing less fuel; more importantly it rapidly absorbs large amounts of carbon dioxide from the air when it sets and cures (Portland cement does this, too, but much more slowly. Also, the new Eco-Cement permits large amounts of organic waste material to be incorporated. The result, Mr Harrison claims, is a cement that can act as a net carbon dioxide absorber; in other words, putting up a building using his cement would be much like planting a grove of trees.
Readers interested in pervious pavement should check out the article in the Eagle-Tribue October 22, 2006 titled "Porous asphalt could be salt of the earth for budget, environment" by Terry Date, an in house reporter. Sooner or later the councils ARRB and others in Australia will wake up.