ENVIRONMENTAL ASPECTS

The world needs an environmentally friendly construction material because of the desire to reduce CO2 emissions, save nonrenewable energy resources, provide aesthetically pleasing and healthy surroundings and at the same time minimize waste

Envıronmental Aspects Of : Problems And Solutıons

The world needs an environmentally friendly construction material because of the desire to reduce CO₂ emissions, save nonrenewable energy resources, provide aesthetically pleasing and healthy surroundings and at the same time minimize waste. Fortunately we have just such a material - , and most of the essential research has been done to enable  to fill this role.

Research is being done in a large number of countries and the results are undeniably positive but what seems to be lacking is the dissemination of this knowledge to a broader audience. After reviewing the state of our industry, a strategy for gaining a wide acceptance of  as an environmentally friendly material will be presented. This should provide the climate for national and international organizations to join with us in securing a more environmentally friendly world. keywords: cement, , environment, fly ash, global warming, greenhouse gas, pollution, silica fume, slag

The author: Theodore W. Bremner is an Honorary Research Professor at the University of New Brunswick, Department of Civil Engineering, P.O. Box 4400, Fredericton, N.B., Canada, E3B 5A3. Tel: (506) 453-5105; Fax: (506) 453-3568; [email protected] . He is a fellow of the American Institution and of the Canadian Society for Civil Engineering. His research interests include durability of  structural lightweight , and the properties of fresh and hardened . Invited Paper for the Plenary Session of the 1st All-Russian Conference on  and Reinforced , 9-14 September 2001.

INTRODUCTION

Around the world political pressure is forcing various industrial sectors to become more environmentally friendly, and in most cases significant change can only be accomplished with difficulty. The problem, environmentalists tell us, is that we have focussed closely on each individual part and perfected the part without considering how our industrial sector interacts with society and the biosphere (1). The only solution is for us to spend less time in such reductionist pursuits and more on a holistic examination of how we can make our industry more responsive to the needs of all who inhabit the earth. Individually we can do our part to end poverty, make sure all people get their fair share of global resources, and maintain a sustainable ecosystem even without being politically active. But collectively we can be a catalyst that strengthens the political will to enhance our environment.

Globalization has come to the cement and  industry and is perhaps more characteristic of our industry than of others. In many ways it seems that American industrial and business practice has spread to countries around the world with management and financing coming from Europe. In the last three decades Canada has gone from having 80% of its cement industry being owned by Canadians to only 20% being owned by us now with the majority of the companies based in Paris and Brussels. A similar trend is developing in the United States. These multinational companies favour vertical integration of the raw materials supply, cement plants, shipping facilities, ready-mix plants and precast factories. Globalization of production has been driven by innovation in production, communication, and control processes which allow for smaller production units (2). As with all global companies they have benefited greatly from a reduction in trade barriers and the easy transfer of materials and wealth between nations.

Globalization brings cost efficient methods of production to regions with minimum labour and environmental costs. According to the World Trade Organization (WTO) a world without barriers should make everyone, including poor countries at the bottom better off, but the thousands of protesters at the WTO meeting in Seattle in 1999 believe otherwise (3).

Rather than see globalization as a problem, we must have the political will to control it and recognize it as an effective force for change. Because our industry is vertically integrated and owned by a relatively few international companies, they can effect change in a short time period. Before advocating change it is essential to identify the relative importance of the environmental problems caused by our  industry and consider carefully how change can be effected.

ENVIRONMENTAL PROBLEMS WITH 

The environmental problems with  will be discussed next in order of decreasing importance according to my perception of the problems they create.

CO₂ emissions

The most serious problem with our industry is that it is a major CO₂ emitter causing global warming. With every ton of cement produced, almost a ton of CO₂ is emitted (4). About 0.5 tons comes from the decomposition of the limestone and the balance is generated by the power plant supplying the electricity to turn the kiln and ball mills to grind the cement plus the fuel burned to fire the kiln. All other generation such as operating ready mix trucks adds only a minor amount to the CO₂ emissions. In terms of conventional  mixtures (i.e. not using fly ash, slag or silica fume), about 480 kg of CO2 is emitted per cubic metre of  or 20 kg of CO₂ per 100 kg of produced. All of this amounts to about 7% of the total CO₂ generated worldwide (5). Enhanced efficiency is not likely to change this but replacement of some of the cement by a supplementary cementing material not associated with CO₂ emission can substantially reduce these emissions. This will be discussed later.

Nitrous oxide emissions

Nitrous oxide emissions come from burning gasoline, coal or other fossil fuels. Ozone is formed when nitrogen oxides and volatile organic compounds mix in sunlight. The volatile organic compounds come from sources ranging from industrial solvents to volatile resins in trees. Ozone near the ground can cause a number of health problems such as asthma attack, sore throat, coughing and other health difficulties. In addition, nitrous oxide, carbon dioxide and methane are the most important greenhouse gases (6).

The NOx emissions from Canadian cement kilns range from 1.5 to 9.5 kg/tonne of clinker produced with a proposed limit of 2.3 kg of NOx per tonne (4). Using 2.3 kg of NOx per tonne, the world release of NOx by the 1625 million tons of cement produced in the year 2000 would be 3.7 million tons of NOx. This is a fifth of the NOx released in all of continental Asia in a year (7). Reduction in nitrous oxides is normally achieved by reducing the burning temperature or by injecting ammonia compounds into the high temperature exhaust stream (4). This seems like a good idea but when these actions are taken to reduce the NOx in coal fired electric power generating stations, it adversely affects the quality of the fly ash produced. The fly ash then needs to be treated to remove the unburnt coal and ammonia gas before it can be used in  mixtures and several plants doing this are in operation. Several research programs are currently underway to find out how best to beneficiate fly ash to correct this problem.

Particulate air emissions

Particulate emissions from the exhaust gas range from 0.3 to 1.0 kg/tonne and much of this kiln dust is collected in fabric filter baghouses and then reintroduced into the kiln feed. It is normally very rich in sodium and potassium which have vaporization temperatures of only 883°C and 774°C respectively. In the past, before there was a  effort to capture the particulate emission, the sodium and potassium plume from cement plant chimneys settled over the countryside where it helped to combat acid rain. Now it is mainly carried out in the clinker stream where it creates problems with alkali aggregate reaction.

The Canadian Council of Ministers of the Environment (CCME) has prepared a guideline for emission limits for hazardous and non-hazardous wastes in cement kilns. This further reduces the particulate matter limits imposed by the Provincial Governments when waste fuels are burnt in the kiln (8).

Visual pollution

Visual pollution resulting from quarries used to gain raw material for cement production or for obtaining sand and gravel can be sculptured to meet the natural topography and when abandoned can be planted with vegetation that can make them blend in with the natural surroundings. Unfortunately most quarries have a very long life and any attempt to sculpture the topography for a visual effect is counter-productive to the efficiency of the quarrying process. The most effective end use might be for educational or recreation purposes with special attention being paid to public safety.

Traffic congestion

Traffic congestion in the delivery of the cement and of ready-mix  is being mitigated by using large energy-efficient delivery vehicles. With appropriate attention to noise suppression and dust control at ready-mix plants there is a tendency to tolerate the placing of the ready-mix plant close to where  is needed thereby reducing traffic congestion.

Noise pollution

Noise pollution is not normally a public as the cement plant is usually placed at a distance from habitation. The ready-mix plant, if it wishes to be located near to its customers must be greatly  about noise pollution. At the construction site the use of superplasticizers to produce high slump  that requires a minimum of vibration has greatly reduced the problem of on-site noise.

Adverse health effects

Currently the health of employees is being adversely affected by the increased chromium content of the cement. The increased chromium content in the cement is mostly derived from the burning of waste products. The only solution seems to be to prevent contact of fresh with human flesh and most containers of cement carry such a warning.

Water pollution

On average each ready mix truck returns about one half cubic metre of cement per day. After this is discharged there is still about 300 kg of solids (cement, sand and stone) that is washed out with about 1000 litres of water. In the past the returned and the solids were dumped in a pit at the job site or at the plant. Considering that this represents 2 to 4% of the total produced, it is now considered too valuable to waste and can be recycled or reclaimed as sand and gravel. To reclaim the sand and gravel a “reclaimer” is used. It involves adding water to the returned and then agitating it followed by wet screening to obtain the sand and gravel.

Also, the cement-water slurry from the reclaimer, the wash out water, water to clean the outside of the truck, plus any stormwater in the past usually was directed into somewhat inefficient settling basins and then into a local water course. Now in the U.S. failure to treat this waste water properly results in a fine of $50,000 per day per violator, a prison sentence of up to 3 years, or both. In Canada and the U.S. the “process water” from settling ponds or from a reclaimer can be used as mix-water for subsequent  mixtures.

Recent developments have enabled the retained and any  clinging to the inside of the truck drum plus any wash out water to be stabilized overnight or over the weekend by the addition of a hydration stabilizing admixture. This stabilized  with an accelerating admixture is used to make up part of the proportions for the next load. In this way there is essentially no water pollution (9, 10).

ENVIRONMENTAL BENEFITS OF 

Became the most widely used construction material in the world for a very good reason - it benefits mankind more effectively than any other building material. In decreasing order of importance, according to my perception, the environmental benefits of will be discussed next.

Low maintenance

Low maintenance is the hallmark of when it is made properly. Some of the first  made in 1847 with Joseph Aspdin’s cement was still in good condition in 1983. The  was made with a low water to cement ratio and was well compacted. The  from a study of a piece of  taken from a boundary wall built by Joseph’s son is that it “is possible to make of several hundred years’ durability” (11). In the 1930s lack of freezing and thawing resistance presented a problem which was solved with an air entraining agent being added to the  mixture. In the 1970s change in cement manufacturing resulted in an increased alkali content which brought on deterioration from alkali-aggregate reaction. This problem has been overcome by developing reliable tests to identify and reject unsuitable aggregates and to limit the alkali content of the cement to manageable levels. In spite of these temporary setbacks  is the material of choice to resist severe exposure conditions.

Low energy consumption

The raw material to make both the cement and is generally evenly distributed around the world so that transportation is not normally a significant consideration. Also the technology to make cement and  is in many ways similar to the technology used by the mining industry and the advances in this industry have been adopted by the cement and  industry. In comparison with steel, aluminum, glass and plastics, the energy spent to create a  facility is often an order of magnitude less than that needed to create a comparable amount of a competing material. This is because a cement kiln is a very energy efficient device and the energy to make is mainly spent in making the cement. As a result of the increase in energy cost over the past three decades,  finds itself in a very favourable position on a first cost basis.

Desirable engineering properties

Perhaps the most important property of  is its ability to be cast in the shape of a containment vessel and to be relatively impermeable. This enables to be especially effective for domestic water supply and for disposal of domestic liquid wastes. This apparently was the first use made of  by the Romans some two thousand years ago and some of the facilities still serve a useful function today. These properties enable  to be used to effectively contain hazardous wastes. Hazardous waste also can be incorporated into a  mixture so that the objectionable material is immobilized within the mass of the  Wood and clay masonry are the main competitors of  in the building industry. The fact that  can be cast monolithically into visually attractive forms and can be effectively reinforced with steel reinforcement makes it the material of choice for many designers. The fact that strength, stiffness, and durability are variables in the hands of the designer means that can be made only as good as it needs to be. Unfortunately, as we all know, unskilful or uncaring designers can create structural and visual disasters. Of course when this happens any savings are nullified when a structure has to be repaired or replaced prematurely. The special engineering properties of make it ideal for all types of streets and highways. The surface reflects light, improving night time driving, and does not washboard, rut or pothole. With a proper surface, the risk of hydroplaning is eliminated. A recently released study of fuel costs for trucks running on either an asphalt or test circuit revealed that a 11% fuel consumption savings can be achieved on a road as compared to an asphalt one (12). This is based on a fully loaded tractor semi-trailer at a test speed of 100 km/hr. For 75 and 60 km/hr the saving in fuel was 8% and 6% respectively. It seems that asphalt pavement deflects more under the truck tire than does the  pavement. This National Research Council of Canada Study concluded that less fuel is used because the rigid  highway surface has less rolling resistance than does the more flexible asphalt surface. Also there is more than just a monetary savings in fuel cost; a significant reduction in greenhouse gas emissions and smog is also realized.

Sink for liquid combustible hazardous waste

Hazardous combustible liquid waste, not always disposed of in a safe way in the past, finds a ready use in fuelling kilns to make cement clinker and low density aggregates. These wastes are solvents, sewage sludge, used oil and in fact almost any combustible liquid or sludge that can be pumped and has fuel value. However asbestos contaminated waste and radioactive and pesticide based wastes are not normally used. Currently about half of the plants in North America have a permit to burn waste and of these two-thirds derive at least half of their required fuel value from waste material. This waste material rather than being a fuel cost to the kiln operator is a source of revenue in that they are paid by the waste producer to take it away and dispose of it in an environmentally benign way.

Sink for silica rich industrial wastes

Blast furnace slag and various other solid wastes from the metals refining industry can be disposed of as aggregate for . The most effective way of using blast furnace slag is to pelletize it to produce a low density aggregate with a particle density of 1.4 which makes it competitive with most other low density manufactured aggregates. Alternatively the blast furnace slag can be ground into a powder and used as slag cement to replace some or all of the Portland cement. Fly ash from coal fired electric generating plants can be pelletized and then fired in a travelling grate to produce a low density aggregate. Also the fly ash can be used as a pozzolan to partially replace Portland cement. With the use of slag, fly ash and silica fume as a pozzolan, the CO2 emission associated with the production of can be reduced by a half or more. Considerable success has been reported by Pavlenko in the production of cementless  using the byproducts of the metallurgical industry. There is normally little or no CO2 or NOx release associated with these products (13).

Thermal mass saves heating and cooling cost

Heat transfer through a material with a low thermal diffusivity like is slow and the amount of heat stored in it is relatively high. Consequently such a material responds slowly to outside temperature change (14). In most places there is a large daily outside air thermal fluctuation and buildings made with tend to smooth out the low temperature that occurs at about 6 a.m. and the high temperature that occurs about 2 p.m. Also, the thermal mass effect causes the peak demand for maximum heating to be delayed from about 6 a.m. to late afternoon. People, equipment and appliances can also effectively reduce the peak heat load as can solar gain from south-facing windows. All of this can be translated into a reduction in heating plant size of about 5% or more in Canadian cities.

The heat loss or gain for very light wall construction with low thermal mass tends to follow closely the exterior temperature profiles and has the potential for excessive interior temperature swings depending on the size and location of windows. High thermal mass material used for wall construction with the insulation placed on the exposed side can play an important role in providing comfortable living conditions while saving energy in the process. In Canada in the winter a house built of heavy construction can accommodate about 50% more window area on the south side than a house of light construction without overheating and, as a result, its purchased energy for heating would be reduced by 10 to 20% (15).

Green aggregates

Low density aggregates made from expanding shale, clay, slate or blast furnace slag can be used effectively to make an environmentally-friendly material - lightweight . Lightweight is about 28% lighter than ordinary , and, in a design where the dead load is equal to the live load, a saving of 14% in the energy intensive steel reinforcement can be achieved. For long span bridges, the live load is a minor part of the total load and there a reduction in density is translated into reductions in not only mass but also in section size. This is especially true where prestressing can induce load balancing effects that compensate for the reduced modulus of lightweight as compared to normal weight  Energy savings result from the increased thermal resistance of lightweight  which is normally six times that of normal weight . Also because the low density aggregates tend to have a stiffness that matches the stiffness of the cement paste matrix the stress concentrations within the are reduced resulting in fewer microcracks as compared to normal density aggregates where the stiffness is three to six times that of the cement paste matrix. The uniform stress distribution on the micro-level in lightweight  leads to enhanced durability in severe environments and to greater impermeability of the  as compared to normal weight .

The energy input from the manufacture of the lightweight aggregates traditionally has been coal; however in recent years a major part of the fuel requirement has come from the burning of combustible liquid waste products that otherwise would have to be disposed of in an incinerator. In this way the energy input to make lightweight is only marginally higher than normal weightand this is quite insignificant when compared to the energy savings that results from the reduced dead load and increased thermal and durability characteristics of lightweight as compared to normal weight . The product is currently widely used and its properties well established, thanks in part to the excellent work done at NIIZ Keramzite in Samara, Russia over the past four decades.

Waste can be recycled

Waste generation need not be a problem with the  industry as the aggregates can be reclaimed from remaining after placing is completed. This normally only represents about 2% of the total freshand the ludge remaining after the aggregates are reclaimed can be combined with the water from truck washing. This cement paste sludge can be de-watered, dried,and then used to replace some of the fine aggregate; however it can find its best use as a soil conditioner or as roadbed material, uses that do not incur energy costs. Hydration stabilizing admixtures are now available to enable all returned  at the end of the day, plus all water used to wash down the inside of the drum to be saved inside the drum overnight and then used to make up part of the  proportions for the first load when work starts again the next day. In this way the fresh  is fully recycled.

Recycling of  demolition waste is common in Japan and Europe where the cost of disposing of construction waste is high. It entails  and sieving to recover the aggregates. In preparing  using recycled aggregate, it is necessary to increase the unit quantity of water for attaining the desired workability because the hardened cement paste adhering to the aggregates absorbs the mixing water (16). Alternatively, the debris after can be used as roadbed materials eliminating the need to use somewhat more expensive recycling procedures.

Discarded automobiles as steel for reinforced Abandoned automobiles that can be a blight on the landscape are collected and after stripping them of the copper wiring, they are processed by an electric arc furnace into steel that can be rolled into steel reinforcement for . This generates much less pollution than using steel from the blast and open hearth furnace that is used for manufacturing the original steel for automobiles.

WHAT IS TO BE DONE

With the exception of CO₂ and nitrous oxide emissions, all the perceived environmental problems with are or can be effectively addressed using our current technology. Our industry needs to focus on these two greenhouse gases. The Intergovernmental Panel on Climate Change (IPCC) meeting in Geneva earlier this year warned that the average temperature is expected to rise between 1.4 and 5.8 C° over the next 100 years. Five years ago the panel predicted a maximum of 3.5°C rise over the same period. The average global temperature has risen only 0.6°C over the past 100 years (17). Greenhouse gases are cited as the cause of these changes. The IPCC is considered the definitive scientific standard that serves to influence government policy around the world and they predict more people will be harmed than will benefit from climate change. Instead of warmer climates more extreme weather - heat waves, floods, drought and windstorms are in the offing.

Industries that cannot reduce their emissions need to pay a carbon tax or they can purchase carbon credits from another company that can more easily reduce its emissions (18). A consortium in the U.S. has been formed to serve the developing market in emissions trading (19). In this way companies that reduce carbon emissions can sell excess capacity in the form of “credits” to heavy polluters, although ultimately all industry must take responsibility for its own emissions. In the industry the easiest and most effective way to reduce green house gases is to increase the use of such silica rich by-products as fly ash, slag and silica fume thereby reducing the amount of cement used per cubic metre of . generates about 7% of the total CO2 generated world wide. About 1625 million tons of cement was produced in 2000. If a ton of cement produces a ton of CO2, and if only 18.5% of the cement can be replaced with slag or fly ash, then the CO2 reduction would be 300 million tons per year world wide. Over the past decade the average annual increase in CO2 emissions is 1.3 percent or nearly 300 million tons a year world wide. Our industry alone could easily reduce global warming and at the same time enhance the properties of the produced. Not only can our industry greatly reduce global warming but we can roll it back, as 18.5% cement reduction pales in comparison to what should be used for optimum  properties.

In 1985 the Canadian Centre for Mineral and Energy Technology now called the International Centre for Sustainable Development of Cement and  has shown that a 65% replacement by weight of cement with fly ash combined with a generous amount of superplasticizer provides excellent mechanical properties, low permeability, superior durability and low temperature rise during curing. This system has been successfully used in high rise office buildings, sidewalks, streets and marine facilities.

The above mixture will normally provide a slump of 180 to 220 mm and the autogenous temperature rise is normally sufficiently low that mass  with 65% fly ash will experience only a modest temperature rise. The early strength (i.e. at 1 day) is relatively low and as a result the  must be prevented from premature drying by moist curing for an adequate length of time.

Laboratory and field investigations involving over two dozen different fly ashes and cements from Canada and the USA have shown excellent durability of the high-volume fly ash  system. Prisms of dimensions 305 x 305 x 915 mm have been exposed at Treat Island, Maine, U.S.A. on a mid-tide wharf. After ten years of exposure and over 1,000 cycles of freezing and thawing, the high-volume fly ash prisms with a water to cementious ratio of 0.31 are in excellent condition but those with a water to cementious ratio of 0.35 show some surface scaling Based on the CANMET work it is apparent that our industry can make a substantial step towards meeting the 1997 Kyoto Protocol and at the same time enhance the properties of the  without a significant inconvenience in the production of the product or the diminishing of our natural resources. The problem now is one of disseminating this knowledge to a broader audience.

Implementation

Silica-rich supplementary materials such as fly ash, slag, silica fume, calcined diatomaceous earth, rice husk ash, and heat treated shale are all suitable candidates to replace Portland cement and at the same time enhance the properties of the. There are two ways to incorporate one or more of these silica-rich materials into the  mixture. The older method is to simply add the cement and the supplementary cementing material to the mixer separately. This requires that ready-mix firms have additional storage facilities for the supplementary cementing materials. Frequently in North America the supplementary cementing material is supplied by the cement company usually through a subsidiary company. This subsidiary company will contract with an electric power plant or a steel mill to take their by-product at a price that is normally much less than the price of cement. Alternatively a private company might contract with the by-product producer to take their output and sell it to the ready-mix producer. The other method is to use blended cement in which the silica rich material is added at some stage in the manufacture of the cement. Usually it involves intergrinding it with the cement clinker. It is important at this stage to point out that all of this has been done in many places for several decades and is well accepted by the industry generally even though on a world wide basis little supplementary cementing material is currently being used. In Canada in the last year fly ash interground with the cement clinker is available from one international company and slag interground with the cement clinker is available from another international company. Both sell the product (blended cement) under the same company name as they sell their various types of cement.

The price of the supplementary cementing materials depends on the method of production - whether added at the mixer or added as a blended cement. Restraint of trade legislation will hopefully prevent the multinational supplier of blended cement from pricing the blended cement and normal Portland cement at such a level as to prevent the establishment of an independent supplier of supplementary cementing materials. In any event not only is the price of producing being reduced regardless of how the supplementary cementing material is handled, but the quality of the end product is enhanced. The profitability of this is apparently now being realized by most of the multinational cement companies in Canada and by pricing it fairly they can demonstrate their commitment to reducing greenhouse gases.

SELLING THE IDEA

The large companies and industries that are on the wrong side of environmental and social issues know how costly it can be and are now thinking of a “triple bottom line” that includes not only profitability but also social and environmental factors as well (22). In controversial matters, good sense and regulatory compliance are not always enough. You need to be open and honest with the public about the risks. Social problems that reflect badly on our industry will not go away. Likewise if we can easily improve our performance in a big way by the use of supplementary cementing materials, and in various other small ways, we should do so. The public will recognize that corporate attention in the cement industry is now focussed on being a sustainable business that has not only a financial but also a social and environmental dimension as well, and that we can truly refer to as being "green".

Fly ash and ground granulated slag has been used extensively in Europe since after World War II and fly ash is well known to anyone familiar with Federal projects in the U.S. So why, at this time, is only a small amount of the available fly ash and slag being used by our industry when the benefits are so great? The answer perhaps is provided by Alan Miller in this excerpt from his book, "Environmental Problem Solving" (23):

Traditionally, the elites responsible for managing environmentalproblems have retained control of the problem-solving process, occasionally seeking technical and other information from their expert advisors, while excluding the broader public from meaningful involvement. Although such technical organizations as the AmericanC Institute and the International Federation for Structural  (fib) serve our technical needs well, it seems we need a better window to the public and I believe that the United Nations can provide the appropriate forum for announcing what good things  can do for our environment.

The United Nations Environment Program (UNEP) can provide an international forum to promote the idea of “green”and what our industry can do for the environment. In 1997, UNEP publishedTechnicalReportNo. 38 on the “Steel Industryand the Environment”- Technicaland Management Issues”, which described what the steel industrycando to reduce its negative impact on the environment (24). I suggest we ask UNEP to turn their attention to and to do a similar report. In this way the ideas from all countries could be consolidated in one document in a form that the international business community might recognize. This would give the supporters of the Global Economy anopportunityto prove their commitment to the environment - in particular the multinational companies who control so much of our  industry. I ask that you join with me in asking the United Nations to prepare a document on the  Industryand the Environment - Technicaland Management Issues”.

REFERENCES

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5. Malhotra, V.M., “Making  “Greener” withFly Ash”, in International, Vol. 21, No. 5, May 1999, pp. 61-66.
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