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Keeping you informed about the TecEco cement and kiln projects. Issue 41, 15th December 2004
TecEco Wish all our Supporters and Friends a Merry Christmas
We have had a great year with news we are proceeding to grant of patents in the US, Canada, New Zealand, Singapore, South Africa and many other places. There have been technical successes both with Eco-Cements and Tec-Cements. The first building using our technology is now to lock up stage (See Tececo Newsletter 40). I have new hope as the world moves into a post Kyoto era that people will seriously take up the challenge of materially changing the world.
To solve the worlds problems, more pressing now that it is obvious the icecaps are melting, it will take reductions in the consumption of fossil fuels as well as sequestration on a massive scale. Of these two options the most politically acceptable and achievable is the latter as TecEco have demonstrated that using carbon on a large scale in the built environment can be an economic process, certainly better than a forced process such as carbon rationing. Mother nature, the most frugal and efficient economist of all, used carbon in previous epochs of global warming to make oil, coal and carbonate sediments like limestone. Mimicking nature is the only way out of the mess we have created.
There are many projects going on around the world and another building is going up in Melbourne Australia right now. We have kept the structures relatively low key because we are very conscious of the need to proceed with caution.
As Nick Vlasopoulos from Imperial College London reminded me "the concept of striving for sustainable development is not so much a ‘destination’ at the end of a road but like life, more a ‘manner of traveling" . We are traveling, the ride is exciting, frustrating and also fulfilling. To all those funding agencies, management agencies, research institutions and individuals who have helped us along that undefined road - thank you.
On a more somber note I have to say that it has been disappointing that one or two research projects are not performing as they should because they are stacked with conservatives from the cement industry who seem determined to make sure we fail. I hope those concerned realise the stupidity of what they are doing, come to grips with the advantages of using the technology, understand that we are not a threat and get on with it.
We are stunned no government has put money behind our process to date given its potential for solving global problems and hope that in the coming year that we will be less frustrated by the lack of finance to get on with it.
 CICA (2002) Industry as a partner for sustainable development.
A new wholly owned subsidiary company, Tec-Cement Pty. Ltd. has been formed to market TecEco cements. It has been decided that the parent company will not trade because of exposure to legal risks and the very high value of the patents it owns. All future research and commercial dealings with third parties will be through the new company. If you are dealing with us - you are now dealing with Tec-Cement Pty. Ltd.
New from TecEco are Tec-Cement formulations for high performance pre-mix concretes which offer approximately 25% - 30% greater strength gain compared to control formulations, less dimensional change, no bleed water and greater durability.
This article answers the basic questions as to why this is so, how Tec-Cements will change pre mix concretes for the better and what the long term implications for cost are likely to be.
Hydraulic cements like Portland cement gain strength by hydration which is simply described as the incorporation of water to form solids. Stoichiometrically Portland cements require around 23 -25% water yet we add approximately 45 to 50% at cement batching plants to fluidise the mix sufficiently for placement.
If it were not for the enormous consumption of water by tri calcium aluminate as it hydrates forming ettringite in the presence of gypsum concrete would remain as a weak mush and probably never set. 26 moles of water are consumed per mole of tri calcium aluminate to from a mole of ettringite. When the ettringite later reacts with remaining tri calcium aluminate to form monsulfoalumiante hydrate a further 4 moles of water are consumed.
Consider the molar volume changes for the first part of this reaction:
C3A+3CSbarH2 + 26H ==>
89.1 + 3 X 74.2 + 26 X 18.01 ==> 715 (molar volumes)
89.1 + 222.6 + 470.6 ==> 715 – (molar volumes)
Tricalcium aluminate + gypsum + water ==> ettringite.
782.3 ==> 715 (8.6% reduction in molar volumes)
There is significant consumption of excess water forming solid ettringite, yet water still bleeds from freshly poured concretes even with plasticisers added.
Unfortunately the same water required for placement and hydration also reduces ultimate strength. All civil engineers know Duff Abrams law which dictates that for a wide range of water binder ratios strength is proportional to the water binder ratio. Unfortunately the absorption of water during the formation of ettringite is not enough. For high performance concrete the trick is to either use less water requiring expensive super plasticisers or to internally use as much of the 50% excess water necessary for fluidization as possible. Plasticisers have associated downsides and do not contribute to the mineralogy. A better alternative offered by TecEco is to internally consume the excess water.
Reactive magnesia added to a Portland cement concrete mix in low proportions of 5 - 10% will internally consume excess water during the early plastic stage reducing even more the water binder ratio resulting ultimately in a lower voids paste ratio and greater density and strength. Consider the molar volume changes that go on during the hydration of magnesia when it hydrates to form brucite.
MgO + H2O ==> Mg(OH)2
13.98 + 18.01 ==> 24.63 (molar volumes)
31.99 ==> 24.63 (23% reduction in molar volumes)
Even more significant conversion of liquids to solids!
Water reduction may be the key to strength gain with hydraulically setting cements, but what about silicification reactions? Are they improved in Tec-Cements?
For either the pozzolanic reaction, surface hydrolysis followed by re-bonding or geopolymeric type reactions highly alkaline conditions are required. What probably happens in Tec-Cements is that alkalis from the surface of cement grains and produced as part of the hydration reactions of alite and belite are concentrated and perhaps even supersaturated during the early plastic stage by the internal removal of water. Once all the lime has reacted the pH falls.
As a result of the high early pH conditions in Tec-Cements more efficient and complete silicification reactions such as the pozzolanic reaction shown below take place
1.1CH + S + H ==> C1.1SH2.1
Surface hydrolysis followed by re-bonding of fly ash and other fine particles containing silica, or silica and alumina also occurs. There is more work to do pending funding but could it be that the best features of geo polymeric and hydraulic cements can be combined?
In the above also lies the clue as to how a shrink free concrete could be formulated. Most shrinkage in concrete is through loss of water – The magnesia in TecEco Tec-Cements consumes water internally resulting in less shrinkage from this cause. If magnesia and Portland cement are blended in the correct proportions expansion and shrinkage are more closely matched resulting in less dimensional change and development of internal stresses and cracking. Early work has also indicated a higher tensile strength for Tec-Cements further reducing cracking.
Tec-cements were however devised for durability not the extra strength imparted. The Achilles tendon of Portland cement concretes is the lime that forms as it sets. Unfortunately calcium hydroxide is too mobile and reactive and has a kinetic propensity to combine with salts and carbon dioxide out of the air. The addition of pozzolans such as fly ash substantially reduce this problem because they react with lime in the pozzolanic reaction depicted above thereby removing it.
Cement chemists have however issued insufficient warning as to problems that will no doubt emerge from using fly ash without considering the pH regime required for the stability of concrete. The stability of calcium silicate hydrates (CSH) is related to the equilibrium they maintain with surrounding alkali. Remove the lime and they are destabilized, loose calcium and eventually become brittle.
The presence of lime is a problem, removal using the pozzolanic reaction creates another. Concretes as we know them today seldom last more than 50 -100 years whether fly ash is added or not.
Tec-cement concretes are much more thermodynamically and kinetically stable. TecEco replace the lime consumed in the pozzolanic reaction with brucite, a far less soluble and reactive alkali. Contrary to the opinion of many experts, magnesium does not readily participate in silicification reactions at room temperature, bonded to water it is too stable. Portlandite (lime or calcium hydroxide) does however react and is consumed in the pozzolanic reaction. As a consequence and given the addition of a pozzolan, long term pH is controlled by a much more stable brucite – CSH system not CSH alone. The equilibrium pH is somewhere between the equilibrium pH of CSH (11.2) and that of brucite (10.48). The resulting lower long term pH regime results in lower internal reactivity, less soluble heavy metals that may be included in incorporated wastes and a more stable mineral assemblage. Note however that black iron oxides that form the protective coating on steel in concrete are still stable. Tec-cements are as a consequence of this and the fact they are denser and can be made substantially crack free, much more durable.
A concrete with around 25 – 30% less binder for the same strength is less expensive to make. The manufacture of reactive magnesia is a low temperature process that is therefore more efficient. Even more exciting is the fact that such manufacture is readily driven by solar or waste energy. As energy and money are the same given economies of scale, and for all of the reasons given above, concretes should not only get better and use more marginally pozzolanic wastes, but they should become less expensive!
There are problems associated with the use of natural untreated cellulose fibres to make fibre cement composites.
Alkalis dissolve lignin and low molecular weight organics that bind the micro-fibres of cellulose together and so untreated cellulosic material including fibres cannot be used in Portland cement without modification because of slow degredation causing loss of tensile and ductile strength.
It is therefore necessary to either:
Developed countries like Australia have achieved high performance cellulose fibre reinforced cement products by using strong alkalis as well as complex technologies including Hatchek machines and autoclaving. Factories using these processes are however environmentally costly to run and the excess alkali disposed of into waterways results in the formation of salts giving rise to salinity.
An alternative to using alkalis to remove the lignin and low molecular weight organics that would be more environmentally friendly and potentially simplify the whole process would be to use low alkali cements. So far solutions have included the use of ground granulated blast furnace slags (GBFS) with Portland cement (PC) or alternatively lime and gypsum which result in lower medium and long term pore water alkalinity compared to commercial Portland cement concretes.
TecEco cements have an even lower long term pH and also stick much better to cellulose through polar bonding and are therefore potentially a better solution. The long term pH of Tec-Cement composits is controlled by brucite in equilbrium with CSH and is less than 11.2 (compared to Portland cement or limeat over 12.4). Eco-Cements set by carbonation and the pH is therefore controlled by the carbonates of magnesium and CSH ans is lower..
A further alternative is to coat the wood fibers with something resistant to alkali. Most coating solutions are proprietary and involve organic polymers.
TecEco have other strategies as well such as using other materials in the mix to take up low molecular weight acids coming out of the wood.
TecEco are keen to initiate research to demonstrate whether it is possible to utilise cellulose fibres to make tec and Eco-Cement composites without the expensive and environmentally damaging use of strong alkalis that are causing so many problems such as salinity.
The Association for the Advancement of Sustainable Materials in Construction in conjunction with RMIT University and the Center for Design held its inaugural conference on Innovation || Materials || Sustainability on the 18th and 19th November, 2004 at the Marriott Hotel, corner of Exhibition and Lonsdale Streets, Melbourne, Australia.
The conference focused on the supply chain and demonstrated a significant demand pull particularly amongst architects and specifiers.
The conference was chaired by Andrew Walker-Morison, Manager Ecospecifier, Center for Design at RMIT and speakers included: