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Keeping you informed about the TecEco cement project. Issue 36, 18th July 2004
H. F. W. (Hal) Taylor was for many years a professor of Inorganic Chemistry at the university of Aberdeen. Amongst his many contributions to cement science was the outstanding text "Cement Chemistry" published by Thomas Telford.
Hugh Taylor was a almost a god in the cement industry. His words of wisdom quoted below burn in my mind every time I meet some lesser mortal who wants to be silly about what it is we are doing. From time to time I wonder why it is we meet such opposition. I think it is may be because most people in the industry rely on dogma for guidance rather than true leadership as exhibited by Hugh Taylor. Science is science and religion is religion - there should be no confusion between the two.
Consider the wonders of the engineering world such as the Great Eastern, Bell Lighthouse or Brooklyn Bridge - they all broke new ground. So why is it engineers still stick to the prescription standards? What's so wrong with innovation? It is because engineers today are frightened of the consequences of error. People died building many of the engineering wonders of the world - a result that would no longer be acceptable.
Have we gone too far however? I think so as prescription standards enshrine outdated understanding with an undeserving status that stands in the way of the innovation Hugh Taylor speaks about as being so important.
I had the honor of talking to Hal by telephone and he sent me many references and papers. I recall only encouragement.
Extracts from a short paper presented by the late H.F.W. Taylor at the Conference on Advances in Cementitous Materials, 1990, Gaithersburg, MD. USA
"There is one group of problems, though, that must concern us all, and that is those of the environment. As I see it, we are entering a period in which these problems are becoming increasingly dominant. I would like to spend a few minutes of your time considering some of the ways in which I believe they may affect cement and cement research during the new few decades.
We depend on the resources of the earth in many ways. At the most basic level, it provides us with living space, air, food, shelter, and clothing. At a more sophisticated level, it gives us raw materials, energy, and places in which to deposit our waste products. Over the ages, we have exploited these resources as if they were infinite. It is now clear that they are far from infinite. In the last few decades, the rate of exploitation has increased sharply, and we are now confronted by very serious and interrelated problems of overpopulation, depletion of resources, and pollution. Together these are degrading the natural environment to an extent that threatens our future well being, and even our very existence. It certainly threatens the existence of countless other species for which we may feel responsible and on which our own survival in varying ways and degrees depends.
As I see it, we can solve these problems, but only if we summon up the will to live in something much closer than at present to an equilibrium with the natural environment. This will imply radical changes in what we consider important, in economic assumptions about the desirability of growth, and in styles of life. These changes will affect many and perhaps most of our activities, including those involving cement and concrete. I believe that we shall see major changes in how we make cement, what kinds of cement we make, how much we make, and what we use it for. These, in turn, must influence the directions taken by cement research.
One aspect of the problem is global warming. There is some disagreement as to how rapidly this is happening, but I think there is no longer any serious doubt as to the nature of the effect, the role of atmospheric carbon dioxide in promoting it, or the probably disastrous consequences if it is allowed to continue unchecked. As a personal point of view, the sooner we do a great deal about it the better. Cement production is by no means the largest source of carbon dioxide, but it is a significant one, both because it uses fossil fuels and from the de carbonation of limestone. I believe that, during the next few decades, we shall see increasing restrictions on the use of fossil fuels, and, more generally, on any processes that increase the concentration of carbon dioxide in the atmosphere.
A good deal could be done on the basis of existing technology. Modern, pre heater plants are much more fuel efficient than old, wet process plants, and if all plants were as efficient as the best, the quantity of fuel used would be much reduced. Still further improvements in fuel efficiency are no doubt possible. It may also be possible to make more use of raw materials that do not require de carbonation, especially waste materials. In the longer term, though, I suspect that more radical changes will be necessary. One possibility lies in processes in which cement production is combined with that of other materials or electrical power, and I will come back to this later. Another is the production of cement by some means in which the energy is not supplied by burning fossil fuel. Either of these options would entail major changes in technology and perhaps also in the type of cement that is produced.
Concrete is a material produced in very large amounts, and the use of waste materials is therefore particularly relevant. It reduces environmental damage in several ways. Substitution of waste materials for new raw materials conserves dwindling resources and avoids the environmental damage caused by quarrying or otherwise obtaining them. It also avoids the damage otherwise caused by disposing of the wastes. It may, but does not necessarily, decrease overall energy consumption. The partial replacement of clinker or Portland cement by slag, fly ash, or silica fume illustrates all of these points. Partial replacement by natural materials that require little or no processing, such as pozzolans or ground limestone, at least saves energy and decreases carbon dioxide emission. From the standpoint of the production and properties of concrete, the substitutions have some advantages but often some disadvantages, such as slower hardening.
I think an increasingly important objective will be to use composite cements more and more widely and to decrease the proportions of clinker that they contain, and that an important aim of future research must be to find ways of achieving this. I would expect to see a resurgence of interest in cements containing very high proportions of waste or unprocessed materials, such as super sulfated cements, and in new types of cements designed to utilize specific types of waste materials.
The technology of industries producing waste materials changes, partly because
they, too, are affected by environmental considerations. It is likely that some
familiar wastes will disappear and that new ones will take their place. Possible
examples of new ones include gasifier slags and residues from flue gas desulfurization.
We know rather little about them, and more research in this area is needed so
that the necessary knowledge will be available when it is needed. The same applies
to agricultural wastes, such as rice husk ash.
Until now, different industries have been operated without any special regard for each other. If we use slag or fly ash in a composite cement or concrete, it is essentially on a take it or leave it basis. I believe that the overriding environmental considerations will ultimately force a change in this situation, and that ways will be found to integrate the operation of different industries so as to minimize overall consumption of raw materials and energy and overall production of wastes and pollution in general. Various combined processes have been used from time to time - cement and aluminum, cement and sulfuric acid are two examples. I suspect that these have not always been particularly energy efficient or particularly non-polluting, but new and better processes of this type may be developed. The possibility of combined power generation and cement production, based on primary flue gas desulfurization, is an exciting possibility in this respect.
I will mention a few other aspects very briefly. First, we can save energy through better thermal insulation of buildings, and I see an increasing future for such materials as aerated concretes. Second, we can decrease the amount of cement that is needed in a concrete by using water reducers or superplasticizers and by incorporation of silica fume; I see this as another important area for continued development. Third, I find it sad, not to use a stronger word, that we are having to demolish buildings only 20 years old because they were so badly designed or so badly constructed that they are beyond hope of repair or alteration. I think the problems here are not mainly technological; I could point to at least one reinforced concrete railway viaduct in Scotland that was built nearly a century ago and is still in good condition, and it we could do it then we can do it now. However, they are partly technological, and I see durability in all its aspects as another field which will continue to increase in importance. There could be a big future for low volume, high price uses of cement. I think it is difficult to predict how environmental or other factors will affect the cost of cement-based materials relative to, for example, metals or plastics, but it is at least possible that cement-based materials will become increasingly attractive. This conference has included some interesting papers on DSP and MDF cements, and such cements may just represent the beginning of a growing technology.
In summary, as I see it, (1) the dominant problems affecting all human societies in the next few decades will be environmental ones. (2) These problems cannot be solved through the use of technologies having a high impact on the environment, which in the long run will only worsen the situation. We will always have to make some changes to the natural environment to satisfy our basic needs, such as food and shelter, but we will have to accept our dependence on it and to look always for ways of minimizing them. (3) This implies major changes in many and perhaps most human activities, including the production and use of cements. (4) The situation will provide many new challenges to those of us working in cement or concrete research."
Reprinted with permission of The American Ceramic Society,
www.ceramics.org. Copyright 1991. All rights reserved.
Paul Brown of the Guardian Recently reported on the comments of Sir David King, the UK government's chief scientific adviser on his return from Russia.
The article quoted Sir David as saying "there is more carbon dioxide in the atmosphere than for 55m years, enough to melt all the ice on the planet and submerge cities like London, New York and New Orleans".
Critical in climate records is the quantity of ice at the poles and in glaciers. A recent 3 km ice core record from Antarctica shows that at the peak of the ice age 12,000 years ago, the sea was 150 metres below where it is now.
Sir David was reported to have said that "You might think it is not wise, since we are currently melting ice so fast, to have built our big cities on the edge of the sea where it is now obvious they cannot remain. "On current trends, cities like London, New York and New Orleans will be among the first to go. Ice melting is a relatively slow process but is speeding up. When the Greenland ice cap goes, the sea level will rise six to seven metres, when Antarctica melts it will be another 110 metres"
The same 3 km ice core showed that during ice ages the carbon dioxide in the atmosphere was around 200 parts per million (ppm), and during warm periods reached around 270 ppm, before sinking back down again for another ice age. That pattern had been repeated many times in that period but had now been broken because of the intervention of man.
Carbon dioxide in the atmosphere had reached 360 ppm in the 1990s and now was up to 379 ppm and increasing at the rate of 3 ppm a year - reaching a level not seen for 55m years when there was no ice on the planet because the atmosphere was too warm.
Dr King was reported as describing how the ice caps like those on Mount Kilimanjaro, Tanzania, had been continuous for hundreds of thousands of years and survived through successive warm periods but were now expected to disappear in 30 to 40 years.
According to the article Dr King said that the realisation of the scale of the crisis was what prompted him to say in January that climate change was a bigger threat than global terrorism. "We are moving from a warm period into the first hot period that man has ever experienced since he walked on the planet.....the heat wave of last summer in which 25,000 Europeans died had killed more people than terrorism, yet had not been given anything like the same level of attention.....I am sure that climate change is the biggest problem that civilisation has had to face in 5,000 years."
Source: The Guardian Wednesday July 14th 2004 at http://education.guardian.co.uk/higher/sciences/story/0,12243,1260879,00.html
I have just come back from the 7th Australasian Masonry conference in Newcastle, Australia held between the 13-16th July 2004, with very mixed feelings about the directions of the industry. I attended as a scientist, however suspect the comments that follow are more from the economist within me.
Engineering papers abounded, however I could sense that the real need for discussion was about the direction of the industry itself as delegates from all over the world reported the problem of declining interest in brick and block laying as a profession and product development towards various solutions not requiring mortar as the most noticeable consequence.
In my opinion the industry should redefine itself as the unitised walling industry and competing associations and groups should amalgamate or at least co-operate with this direction in mind. Offsite manufacture and placement products including concrete masonry units, clay products and various size walling components should be included. The latter because the distinction between panels and what are large blocks is blurred. The common element would be offsite manufacture and onsite placement of walling componentry.
The industry also seriously needs to consider what the requirements of various stakeholders including its customers are. One very big stakeholder is government. Governments have the responsibility of sustainability however as yet there is little interest in the industry as to the contribution it could make. Customers also want more sustainable products, particularly if they could be offered without increase in price.
Sustainability can be achieved more easily within the new broadly defined industry as above than in any other sub-sector of the building industry.
This is because products manufactured by the the industry are made offsite and thus more easily optimised for embodied energies, waste content, net emissions, durability and other sustainable properties.
What a marketing opportunity! Not only are the market demanding more sustainable products, governments may soon as well. Kyoto is a reality globally and carbon credits may soon become available for genuine emissions reduction or abatement. Provided the technology paradigm is correct the inclusion of wastes for their physical properties rather than chemical composition should result in better economics. Properties such as light weight, tensile strength or insulating value add value.
We are already seeing many tenders coming out asking how the contractors could make works quoted on more sustainable and offering tangible economic benefits for sustainability.
Sustainability is not a threat, it is a marketing opportunity to be taken. The industry need to come to understand this.
It is essential to keep the research relevant. If you are not sure what you are doing or the relevance of the tests you wish to apply please contact John Harrison as unfortunately at least one research program that is underway has badly come of the rails with irrelevant tests using the wrong standards and incredibly bad science.
There is enormous potential for materials in the built environment to utilise wastes and sequester carbon. Many wastes will impart improved properties such as lighter weight, tensile strength and insulative "R" factor resulting in lower lifetime energies. Other properties possible but not common with cementitious composites included greater durability, thermal capacity and tensile strength.
Bad science will not help at this stage so please, before you commence a research project, listen to us and take notice of what we have to say. It will save everybody a lot of time and money.
If to prove or disprove carbonation is your aim, then start by understanding that the thermodynamics suggest slow rates that need kinetic optimisation rather than the reverse. For carbonation to occur there must be adequate exposure to the atmosphere as this is the rate controlling condition.
A lack of consistency has in the past been the main problem with lime mortars and the use of Eco-Cement mortars may well solve this problem. As the process of carbonation is mainly through solution, (there should be some discussion as to what this means), then moisture is required to provide a reaction medium. On the other hand gas transport is much much faster at moving atoms around. It follows that alternating wet dry conditions in a permeable dry mix with appropriate particle size grading are optimal. For appropriate grading of block formulations see a block making manual such as the one provided with Columbia, Hess or Besser machines. For appropriate grading of sand in mortars the standards are not of much assistance. According to experts such as in the UK Prof Norman Bright and Brian Morton and in Australia Bill Jordan it is very important that lime mortars contain the correct proportions of fine and coarse sand to retain permeability. The same applies for mortars made using Eco-Cement, otherwise they will not carbonate. Historically, references back through the centuries suggest that the sand mix should be 60% coarse sharp sand, 40% fine sand for mortar and render mixes. With Eco-Cements a 1(cement): 2(magnesia): 9 (sand) mix is suitable. See http://www.ihbc.org.uk/context_archive/53/Limemortar_dir/Limemortar_s.htm.
Results from mortars made in accordance with cements standards are just not applicable to mortars made for masonry and even less applicable to concrete blocks. To test Eco-Cements masonry standards need to be consulted and masonry practice understood. Unfortunately the standards most applicable for mortars are those covering lime formulations however there are few in existence around the world. Standards are at least available for the testing of bricks, blocks and pavers however manufacture is more of an art guarded by the various block making businesses. As mentioned above, some guidance is fortunately available in the manuals available from Besser, Hess, Columbia and others.
If finding out more about Tec-Cements is your aim then please try and understand the role and potential mechanisms of reactive magnesia before embarking on such an endeavour. For this you will need to consult the company. Given the relative lack of reactivity and coarseness of currently commercially available magnesia, a pozzolan is essential. Do not work to slump as magnesia imparts a shear thinning property resulting in Bingham plastic behavior.
A date of the 18th November has now been set for this all important conference which will be the first that takes a multidisciplinary approach to the role of innovation and materials for a sustainable built environment.
For details go to the AASMIC web site at www.aasmic.org. We understand that a conference brochure should be published in a few days.