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|Keeping you informed about the Eco-Cement project||Issue 21||30 June 2002|
A patent, the news of our technology introduced to the world and the promise of an exciting 2003.
Welcome to a number of new shareholders - Dr Vivian Mawson, John White from Delta Hydraulics, Geoff Rosan from Bartercard and Ken (the pen) Farrell.
Both Vivian and Ken have skill with the pen; may the pen be mightier than the sword!!
At the moment we are trying hard to raise funds so we can pay the patent fees to secure as many countries as possible, so this influx of new blood could not have come at a better time. We have raised about $ 70,000 so our short term future is secure, but this is still only half the budget for immediate patent expenses.
I am also considering an option on the offie next door for TecEco. Whether we proceed will depend on funding.
Thank you all of you for your support – I will do my utmost to live up to you confidence in TecEco.
I am a lousy mathematician (but least good enough to notice my own errors!) I have corrected the numbers on sequestration for TecEco technology presented in the previous newsletter. The corrected newsletter was loaded onto our web site on the 10th June 2002. There was not a huge change.
I have written this article because a number of people have asked me how and why TecEco technology has improved hydraulic cements.
To answer this question I will first describe what the TecEco Technology is then describe what Portland cements, slag cements and Geopolymers are, what strengths and weaknesses they have, and how the TecEco technology interacts with them.
Tececo have applied for international patents for a new cement system whereby reactive magnesia is blended with other hydraulic cements such as Portland cement.
The combination can be in virtually any proportion and at the high Portland cement end of the scale the hydration of reactive magnesia results in the formation of brucite which replaces Portlandite consumed in most TecEco formulations by a pozzolan such as fly ash. Because Brucite is alkaline it maintains the stability of CSH minerals but being much less soluble, when formed throughout a cement matrix it densifies and proofs against the corrosion of steel reinforcing and breakdown of concrete by slat attack. TecEco technology is therefore also suitable as a means of immobilising toxic and hazardous wastes.
With high proportions of recyclable industrial materials such as fly ash and reactive magnesia, particularly in permeable materials the magnesia not only hydrates, but carbonates, completing the thermodynamic cycle by reabsorbing the carbon dioxide produced during calcining and becoming magnesite and hydromagnesite again. Because magnesite is quite strong and often fibrous and acicular it is an excellent binder and will also hold a high proportion of wastes. If the mix includes pozzolans, they in time also bond, mainly as a result of surface hydrolysis at high pH's. (The hydrolysis of alumina and silica both increase markedly over pH 9) further adding to strength in the long term. As for ancient Roman cements, the addition of a small quantity of reactive aluminous materials promotes this process.
TecEco refer to these new low cost cements as Eco-Cements. They are recyclable as it is part of a low energy thermodynamic loop, they can contain high proportions of waste and set by absorbing carbon dioxide. At worst they are carbon dioxide neutral and at best a carbon net sink as TecEco plan to use sustainable energy and capture CO2 at source during calcining. If waste carbon based fibres are also included even greater sequestration potential is achieved.
Eco-cement is the first building material of high thermal capacity with a low embodied energy containing a large proportion of recyclable industrial materials (Bricks for example can include over 90%). Because of the immense footprint of the built environment (over 405 of all materials flows) it has enormous potential for sequestration.
TecEco have proved that reactive magnesia can be blended with other hydraulic cements, and that previously reported dimensional distress was because the magnesia present was insufficiently reactive, having been through the high temperature process of Portland clinker production.
Geopolymers are stable silicon and aluminium tetrahedral chains in which all the oxygen atoms are shared and in which the excess negative charge on the oxygen atoms is balanced by the presence of alkali ions such as K+, Na+ and Ca++(1). They are an important new materials science and many of the principles of silicification inherent in them are utilized in Eco-Cements as they strengthen in the longer term.
Both Eco-Cements and geopolymers can be made in existing cement factories with existing capital equipment. Again like Eco-Cements the process for geopolymers does not require high temperatures (750 degrees Centigrade compared to 500 – 700 degrees Centigrade for Eco-Cements.) This means that less fuel is required for production, with a consequent reduction in emissions including carbon dioxide, sulfur dioxide, nitrogen oxides and particulate emissions. Geopolymers claim an 80% plus reduction in emissions, mainly from reductions in fuel usage.
Unfortunately however geopolymers tend to be difficult to make and require an uncommon knowledge and skill. Those that make them are quite secretive about their techniques and possibly the biggest problem is that there are many patents covering their use and so large companies, other than Lone Star with Pyrament cement, have not backed them for development as the returns are considered risky due to possible patent infringements.
Portland and many related cements are made by grinding a clinker made at high temperatures from suitable mixtures of mineral materials containing calcium, silicon, aluminium and iron.
A major problem is that these processes consume considerable energy and carbon dioxide emissions are produced that are not reabsorbed in any quantity. The thermodynamics are not closed loops and the resulting cements are therefore not recyclable in the true sense of the word.
Cements of this type always generally contain lime at some stage. It may initially be present in a slag or clinker and is produced as calcium silicates hydrate as shown in cement nomenclature hereunder.:
2 C3S + 7H -> C3S2H4 + 3CH (DHor = -114 kJ.mol-1)
2 C2S + 5H -> C3S2H4 + CH (DHor = -43 kJ.mol-1)
Note that the proportion are indicative of Portland cement and that C3S2H4 tends to be non-stoichimetric.
Free lime (called Portlandite by cement chemists) is the Achilles tendon of concrete. It is alkaline and maintains an equilibrium with the Ca++ in the silicate hydrates present but is also moderately soluble and hence mobile and when it reacts with an anion such as SO4-- or Cl-or leaches out altogether the equilibrium breaks down. This process is like a chain reaction because as the Ca/Si ratio of the CSH minerals falls below certain levels they tend to break down, more lime is produced and so on. Other affects including expansion from the formation of salts such as gypsum also occur. The tendency of Portland type cements to break down in aggressive salt environments means they are not as suitable for long term storage of hazardous or toxic wastes as eco-modified Portland type cements or geopolymers.
There are other weakneses of Portland type cements. Thermodynamically they are not stable and given the longer term want to form other minerals such as hydrogarnet. Fortunately there are kinetic barriers and this process does not occur very readily.
Another weakness of all hydraulic cements is a tendency to be permeable and this is related to porosity. The porosity of concretes made with Portland cement is often reduced by adding a finely ground pozzolan such as flyash and in particular microsilica.
At high pH values silica and alumina are moderately soluble and strength giving reactions occur whereby silica and minerals containing silica and alumina first hydrolyse and then tend to bind together losing water as depicted in the diagram below.
In TecEco Eco-Cement formulations many wastes containing silica and alumina can be added in high proportion. The Portland cement minerals and reactive magnesia hydrate first followed by the formation of elongated carbonate crystals which as they grow bind together high proportions of wastes containing silica and alumina, many of which are reactive. As the pH is maintained at a relatively high levels silicification reactions similar to the reaction depicted occur further adding to strength. In this sense the TecEco Eco-Cement technology provides as suitable medium for beneficial and desirable long term silicification and possibly geopolymeric reactions to occur.
In TecEco modified Portland type cements reactive magnesia and flyash or another suitable pozzolan are added. As may be expected the free lime is consumed by the pozzolan producing more CSH minerals adding further to strength. Besides possibly reducing porosity the reactive magnesia as it hydrates to brucite, which is alkaline but much less soluble, maintains an alkaline environment. Chemical and physical barriers are introduced preventing change and the Ca/Si ratio in CSH minerals is maintained (2). TecEco eco-modified Portland type cements are also denser, less permeable and more durable and thus suitable for long term toxic and hazardous waste immobilization.
As less energy goes into making reactive magnesia than Portland type cements TecEco modified Portland cements are also more sustainable, how much so depending on the amount substituted and the degree of carbonation that occurs. Formulations with high levels of substitution are referred to as Eco-Cements because of their substantially improved sustainability.
Eco-cements utilise many industrial wastes and a brief description of useful industrial wastes that are added to cement and concrete follows together with an explanation as to how TecEco technology reduces the associated problems
Fly ash is an undesirable potential health hazard when left in landfills or if breathed in while working with it. When the material is used in concretes the question arises as to what potential there is for emissions of volatile organic compounds, or release of other chemicals such as heavy metals that may be harmful to health? Blast furnace slags are less environmentally damaging but still unsightly.
According to the EPA in America, flyash may have a slightly higher radon content that the cement it replaces, but its emanation fraction is much lower than most materials due to its glassy structure. Consequently the use of flyash as a partial cement replacement is likely to reduce the radon gas contribution of the final concrete product.
Ground granulated blast furnace slag (GGBFS), is produced by grinding a pelletized or granulated iron blast furnace slag to cement fineness. Blast furnaces, which produce iron from iron ore in the presence of limestone or dolomite fluxes, produce a molten slag. It is this slag that is tapped off the furnace separately from the iron, quenched with water through a granulation or pelletizing process and ground into a fine powder.
GGBFS and fly ash can be used to replace a portion of the cement in a concrete mix. The advantages of cements blended in this manner are improved workability and pump ability of plastic (unhardened) concrete. In hardened concrete, the use of slag cement can increase 28 day strength, whereas the use of fly ash reduces short term strengths. Both result in greater longer term strength and reduce permeability and heat of hydration, increase sulphate resistance and tend to control the alkali silica reaction. The use of blended cement during hot weather is especially useful because setting times are increased. In cold weather however, slag replacement rates are usually lowered due to its effect on set time.
Fly ash and to a lesser extent slags are used in large quantities to lower the heat associated with cement hydration that is a problem in thick pours like dams, bridges and skyscrapers. Good quality fly ash and slags are beneficial, making concrete behave in a more plastic manner during pouring. Both also reduce bleeding and segregation. In hardened concrete, fly ash increases ultimate strength, decreases permeability, increases resistance to sulfate attack, and alkali-silica reactivity, reduces drying shrinkage, lowers heat of hydration and reduces creep.
The main problem with all industrial wastes like fly ash and slag is that they vary enormously and from some sources may contain heavy metals, toxic volatile organic compounds or radon gas. How TecEco technology solves this problem is that in eco-modified Portland cements for example, an insoluble matrix of brucite is formed throughout the cement microstructure structure making the whole more dense and less permeable, preventing exit by the undesirable heavy metals, organic compounds etc. that may be associated with the fly ash or slag.
Albert Einstein once told researchers at Cal Tech, “Never forget this in the midst of your diagrams and equations. Concern for man himself and his fate must always form the chief interest of all technical endeavors.”
Technology standing on its own is not inherently good. It still matters whether it is operating from the right value system and whether it is properly available to all people.
William Jefferson Clinton
I have read with interest about the debate on forestry as a carbon sink. The consensus seems to be that mature forests are not net carbon sinks – in our time scales at least. Given geological time scales they are however very important for sequestration.
Rich natural growth such as found in forests must be encouraged. The point is that forests are part of a much bigger ecosystem – nature as a whole - and it is this system that ultimately puts carbon away forever. The whole concept of an ecosystem involves linkages and the linkages from forests stretch far and wide. They cannot, as most people assume be considered as a closed system.
There are other benefits to having trees and other plant life that are vital to eco-systems The formation of oxygen through photosynthesis is just a little vital as is the creation of new soil, the sequestering, filtering and release of water, food and homes for animals, etc, etc. Trees provide an amazing and irreplaceable array of functions and beauty.
Consider an uninhabited forest. Is the carbon cycle in such a closed system neutral? Trees die and decompose, while other trees are growing, and eventually the forest reaches a steady state where the two are almost equal.
The composition time for a tree is equal to the amount of time that the tree has lived. This is significant given the existence of trees that live upwards of a thousand years. Trees can take several times longer to decompose that to compose say upwards of two or three thousand years. Our problem is short term release of carbon which is flooding the atmosphere with more carbon than it can handle. We need to reduce and eliminate the short term release of carbon to deal with the green house effect or sequester massive amounts or better still – do both. When a tree decomposes on the forest floor, it is consumed by decomposing bacteria, insects and saprophytic organisms. So the energy and Carbon is consumed and recycled back into nutrients for the forest and through linkages to the whole ecosystem.
Given geological time some carbon is permanently sequestered, as in bogs or coals. Debate rages in relation to the formation of coals of various kinds but that they are formed from the remains of plant matter is not disputed and plant matter in the quantities required grows in forests.
It was not until the Carboniferous some 300 million years ago that land plants developed sufficiently to form the forests which produced the major coal deposits of the Northern Hemisphere. In Queensland and New South Wales Australia, coal formation occurred much later in the Permian Period some 250 million years ago. In Victoria, the coals are much younger; being deposited 15 to 50 million years ago during the Tertiary Period.
It is considered by most that in these waterlogged environments, plants and tree debris accumulated. As the layer of debris increased in thickness, the floors of these vast swamps subsided slowly and fungi and bacteria decomposed the plant material. The first stage in the "coalification" process is characterised by extensive biochemical reactions. Proteins, starches and cellulose undergo more rapid decomposition than woody material (lignin) and the waxy parts of plants (the leaf cuticles and the spore and pollen walls). Thus the remains of many types of vegetation, including tree stumps, leaves, spores, seedpods, and resin are found in Victoria's brown coal. Some of the material is similar to existing vegetation but, in general, most of the plants have not grown in Victoria for millions of years.
To varying degrees, and depending upon climatic conditions, plant constituents are decomposed under aerobic conditions to carbon dioxide, water and ammonia. This process is called "humification" and partial completion results in the formation of peat. The second stage of coalification occurs when the peat becomes covered with layers of sediment which exclude air, introducing anaerobic conditions. In this second stage the combined effects of time, temperature and pressure convert the peat firstly into brown coal (lignite) and then into sub-bituminous coal, bituminous coal and finally to anthracite. These three latter coals are usually called black coals.
Forests are also important for bio-diversity and preventing soil erosion and play an important role influencing weather patterns. Cutting them down leads to climate change. CO2 is not the only potentially harmful by product of burning trees. There are other particulates that have harmful often carcinogenic effects as well.
In summary, forests must be considered as part of the overall eco-system and their importance in geological time as opposed to our times scales realised.
TecEco’s new PHP based site is about ˝ written at the moment.
We have let our site-stats account expire, as I am writing TecEco’s own PHP-based program to do the same thing.
No changes have been made to TecEco’s site as the current focus is getting the PHP system working well.
 Geopolymers could be described as proto zeolites. i.e zeolites that have not fully attained their structure. The ratio Al2O3:Ca,Sr,Ba,Na2,K2,O in zeolites is equal to one (1) and the ratio O:Al +Si = two (2). In recent literature the strength of early Roman and some other cements has been attributed to the presence of zeolitic phases as well as the formation of CSH and more polymeric CSH phases.
 According to Fred Glasser in Portland fly ash blends there is an observable drop in the Ca/Si ratio in the calcium silicate hydrates present when reactive fly ashes are added. A minimal loss of calcium does nto appear to introduce weaknesses. A maximal loss results in breakdown of concrete. See Chapter 1 in Spence, R. D Chemistry and Microstructure of solidified Waste forms.