WASTE CEMENT AND CONCRETE MANAGEMENT AS COST- EFFECTIVE AND ENVIRONMENT FRIENDLY: PRINCIPLES AND PERSPECTIVES

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1 CD WASTE CEMENT AND CONCRETE MANAGEMENT AS COST- EFFECTIVE AND ENVIRONMENT FRIENDLY: PRINCIPLES AND PERSPECTIVES I.M. Kelayeh 1, A.A. Mounesan 2, K. Siamardi 3, M.M. Khodavirdi Zanjani 3 1 Member of Management Association, Assistant of Technology & Development, Civil 2 Civil Engineer, Sharif University of Technology, General Manager of Atisaz Company 3 Civil Engineer, Concrete Research Center, Atisaz Company ABSTRACT The use of recycled aggregates in concrete opens a whole new range of possibilities in the reuse of materials in the building industry. The utilization of recycled aggregates is a good solution to the problem of an excess of waste material, provided that the desired final product quality is reached. The studies on the use of recycled aggregates have been going on for 50 years. In fact, none of the results showed that recycled aggregates are unsuitable for structural use. Using the recycled aggregate is a cost-affective and environmental friendly solution which is required general waste concrete management knowledge. This paper is focusing on waste cement and concrete management for optimizing the construction costs. The ways for reducing the green house gases (GHG) at cement and batch plants are suggested. A comparison among Iran industrial utilized cement volume and other countries was performed. Finally, it can be concluded that application of recycling concrete could reduce the costs by reducing truck traffic, providing the Non- Renewable Resource, Better Trucking Utilization (Reduced Costs), Allow down to 10% Deleterious Materials in Iran. Keywords: waste concrete management, utilized cement volume, cement plants, concrete recycling, GHG reduction. 1. INTRODUCTION The amount of construction and demolition waste (CDW) has increased considerably over the last few years. The recycling and the reuse of this material is necessary, considering the impact that the use of natural resources and non use of CDW is causing. This would not happen if the use of recycled material were possible. The largest CDW obtained is concrete [1, 2], and it is the most used construction material nowadays. The studies with respect to the applicability of recycled concrete aggregates (RCA) are extended around the world. Furthermore, Industrial waste is causing more and more environmental pollution. Dirty water and poisonous gases are released from factories and workplaces in ever increasing quantities. This has led to a new appraisal of a company s obligation to society. A company is now seen as having as much responsibility for avoiding

2 1116 / Waste Cement and Concrete Management. environmental pollution outside the factory as for maintaining cleanliness inside. Companies must establish standards for disposing of their waste in a way that will not pollute the environment. The application of waste materials in cement and concrete industry can improve the ecology cycle and prevent environmental pollution. So, waste cement and aggregate for generating new types of waste concrete is needed to total management. 2. COMPARING IRAN UTILIZED CEMENT AND CONCRETE STATUS WITH OTHER COUNTRIES Unfortunately, new concrete technology is applied rarely except special or national construction projects in Iran. Existing structures are almost heavy and low strength and advanced concrete knowledge haven t utilized in design and construction of structures that causes in vulnerable structures subjected to ground shaking. Relation between research centers of universities and construction industry could be optimum alternative for implementation of new concrete technology in real scales. Used cement is just 10.8 % in Iran Industry. Used cement in ready mixed concrete part is 8.64% of total used cement in Iran % of used cement is subjected to construction of concrete segments while Japan used cement is 86.4% which for ready mix concrete and concrete segments is 73.2 and 13.2% respectively. United states used cement volume is 66.7% too and according this, 55.7% and 11% of cement is related to ready mix concrete and concrete segments part respectively. Turkey and Russia used cement volume in industry is 74.4 and 71.3% respectively. 62 and 52 % of used cement in mentioned countries is assigned to ready mix concrete and 12.4 and 19.3% is assigned to concrete segment respectively [3]. Comparison of industrial used cement volumes among countries is shown in figure 1. Industrial used cement volume(%) Iran United state Turky Russia Japan ready mixed concrete concrete segments Figure 1. Comparison of industrial used cement volumes among countries On the other hand, utilized cement infrastructure is still incorrect in Iran. Significant part of utilized cement generate by hand. Failed structures in past

3 3 rd International Conference on Concrete & Development / 1117 strong earthquakes have proved that existing structures is vulnerable especially in Tehran metropolitan. Past Tehran earthquakes have occurred each 150 years. Forcing the ready mixed concrete plants for issuing quality justification is effective solution as more than 75% of ready mixed concrete plants have received standard certificate. In addition, light weight structures construction for improving the seismic performance of structures is important while 20% of light weight building materials utilized in country and remained materials is exported to out of country. Application of light weight concrete in buildings is required the three administration of managers, investors and illuminates cooperation. 3. MANAGEMENT PRNCIPLES IMPORTANCE 3.1. Improves Understanding about Cement and Concrete Industry From the knowledge of principles managers get indication on how to manage the waste concrete industry. The principles enable managers to decide what should be done to accomplish given tasks and to handle situations which may arise in waste concrete management. These principles make managers more efficient Direction for Training of Managers Principles of management provide understanding of management process what managers would do to accomplish what. Thus, these are helpful in identifying the areas of management in which existing & future managers should be trained Role of Management Management principles makes the role of managers sensitive. Therefore these principles act as ready reference to the managers to check whether their decisions are appropriate. Besides these principles define managerial activities in practical terms. They tell what a manager is expected to do in specific situation Guide to Research in Management The body of management principles indicate lines along which research should be undertaken to make management practical and more effective. The principles guide managers in decision making and action. The researchers can examine whether the guidelines are useful or not. Anything which makes management research more exact & pointed will help improve management practice. 4. CEMENT PRODUCTION RELEASE GHG PROCESS Cement production generates GHG from two main sources: calcination and fuel combustion. Calcination is the chemical process in which calcium carbonate (CaCO3) is heated to high temperatures, converting it to lime or calcium oxide (CaO), and releasing carbon dioxide (CO2). So it is not surprising that the main type of GHG from cement production is carbon dioxide (CO2). The amount of CO2 released due to the calcination process alone usually varies from 50 to 60 percent the total amount of CO2 released during cement production. The remaining 40 to 50 percent is mainly due to fuel combustion. The contribution of each of these sources (calcination and fuel combustion) depends on energy efficiency. The

4 1118 / Waste Cement and Concrete Management. percent of CO2 released from fuel combustion in efficient cement plants tends to be lower since less fuel will be needed to produce the same amount of cement. Figure 2 shows the cement plant. Figure 2. Cement plant 4.1. Ways to Reduce Cement Ghg at Cement and Batch Plants Blending SCM at cement plants Blending cement with Supplementary Cementitious Materials (SCMs) reduces GHG emissions. Common SCMs in use include slag, fly ash, silica fume, and calcined clay. Using two or more SCMs together with portland cement is referred to as a ternary cement mix. Proper use of ternary mixes comprised of fly ash and slag produce not only less but also better quality concrete. The addition of SCM at cement plants has the potential to significantly impact GHG savings Environmentally friendly fuel for cement kilns Use of environmentally friendly fuels would reduce GHG emission by using less carbon intense fuels. Although coal is one of the most efficient and cost effective fuels for heating a kiln, it is also one of the most intense in terms of the CO2 emissions. Therefore, it is important to use alternative fuels instead, such as recycled materials. For example, In 2005, fuel combustion from coal constituted about 73 percent of all emissions from fuel combustion by cement plants in California. This number has decreased since 1990 when coal was responsible for about 85 percent of all fuel combustion emissions Using of interground limestone The limestone addition strategy consists of replacing cement with interground limestone. Since interground limestone is added at the end of the cement production line, the cement-related greenhouse gas (GHG) emissions will be reduced proportionally to the amount of limestone added. The GHG savings arise from avoiding GHG emissions associated with cement production during fuel combustion and calcination in the kiln.

5 3 rd International Conference on Concrete & Development / 1119 The maximum GHG savings generated by this strategy is 5 percent, which is the maximum limestone allowance per American Society of Testing Material (ASTM C 150), a major nationwide cement specification. Since the effect of limestone addition to cement had not been studied in detail, Caltrans sponsored a comprehensive study, use of raw limestone in portland cement, designed to evaluate the three primary indicators of concrete performance: strength, drying shrinkage, and permeability[4]. It was found that limestone improved strength and permeability (at early ages). Since 2007 Caltrans has been accepting 2.5 percent limestone addition. After concluding the limestone study, Caltrans will accept the full 5 percent but implement a performance-based specification to control shrinkage. Although 5 percent of limestone is allowed per ASTM C 150, it is estimated that the statewide limestone addition may not exceed 3.5 percent based on manufacturing limitations. According to reports from the portland cement association (PCA), the estimated average nationwide is only 2.5 percent [5] Production efficiency improvements Significant GHG emission reduction for California is not expected of this particular strategy. One of the reasons being that the cement industry in California is already among the most energy efficient in the world. It has been reported that one of the most recent cement plants built in California has a GHG intensity of only 0.02 below that of the 2005 California average GHG intensity factor of 0.86 ton of CO2 per ton of cementitious material. All cement plants in California except one have precalcinators. These pre-heaters significantly improve energy efficiency by heating limestone prior to its placement in the cement kiln. Another process-related piece of equipment that significantly improves energy efficiency is the dry kiln compared to wet kiln usage: All cement plants in California have dry kilns. Using one kiln instead of multiple is also recommended to further improve energy efficiency. Only one cement plant in California uses multiple kilns. According to the California Cement Industry (2008), the energy efficiency of California cement plants is 15 percent better than the average U.S. value since Another reason for a small GHG emission reduction is the fact that production efficiency improvement only affects 40 percent of the GHG emission from cement production. The other 60 percent of GHG emissions comes from calcination, which is a natural chemical process inherited from the cement production process in which limestone (CaCO3) is converted to calcium oxide (CaO) by releasing carbon dioxide (CO2) in the presence of heat, as follows: CaCO 3 + heat CaO + CO2 Since fuel combustion is responsible for only 40 percent of the GHG emissions, a reduction in energy consumption of 4.5 percent accomplished by California Portland, only reduced GHG emissions by 1.8 percent. California Portland was

6 1120 / Waste Cement and Concrete Management. named the 2007 Energy Star Partner of the Year for such energy reduction. This saved the company about $850,000 in operating costs Optimizing cement content at batch plants Optimizing cement content can be prescribed as a strategy to reduce GHG. In some cases, a higher amount of cement is used because of the desired early concrete strength. For instance, a homeowner or general contractor may need concrete with a compressive strength of only 14 MPa. This 14 MPa concrete only needs about 135 Kg of cement to gain this strength at 28 days. That strength requirement can be met if the homeowner or contractor allows more time for concrete to gain strength. Another option for homeowners and general contractors would be the use of admixtures to accelerate the strength gain of the concrete mix. While there is a cost to these admixtures, they can be used to reduce GHG through the reduction of cement. To optimize the amount of cement, concrete mixes can also reduce the amount of water used since this results in a stronger concrete. Reducing the amount of water would also involve some additional cost for plasticizer or water-reducing admixtures. This cost may be compensated for by cost savings of optimized cement content. Example: when a mix for a concrete driveway replaces 25 percent of the cement with fly ash, and uses half the normal amount of cement, as much as 5.7 tones of CO2 can be saved per driveway, assuming each ton of cement emits 0.9 tons of CO2. This is equivalent to the CO2 emissions from about one passenger car for the entire year, as the average passenger car emits about 5.2 tones of CO2, based on data from the Environmental Protection Agency (EPA). To calculate this emission, it was assumed that each car travels 19,300 Kilometer per year, gets about 8,631 Km per cubic meter and each cubic meter of fuel emits 2,235 tones of CO2 per cubic meter. To achieve this savings, it may be necessary to keep cars off of the driveway longer. If it is necessary to get strength faster so vehicles can access the driveway, these GHG savings can still be obtained by adding an accelerator to the mix at a concrete cost increase of about 10 percent Reducing concrete waste This strategy seeks to significantly reduce the concrete waste occurring at batch plants. It is estimated that approximately 5-8 percent of the concrete that is made in California every year is returned to the batch plants as waste. Concrete waste (or concrete returned to batch plants) is generated for the following two main reasons: 1) a load of concrete is not completely used, or 2) a load of concrete is rejected by an inspector due to the mix not meeting some specified characteristic. The worst case for a return in terms of GHG is when the plastic concrete is separated back to sand, gravel, and water, and the cement was then truly a waste product. Concrete is almost always left over at the end of a job. The main reason is because it is more cost-effective to overestimate rather than be short of the material needed. Here are a few ways to reduce waste, and consequently GHG: 1. Better estimating of total concrete requirements. 2. Use of volumetric trucks to handle the exact needs of the last quantities of the day.

7 3 rd International Conference on Concrete & Development / Design locations to receive the returned or left over concrete. One of the ways to re-use the concrete would be to make concrete blocks for later sale. Another is to use that last truck to make sidewalks that may have been planned for a later placement. 5. APPLICATION OF RECYCLING CONCRETE AS WASTE AGGREGATE IN CONCRETE 5.1. Aggregates are Required for Construction Projects Aggregates are composed of rock fragments that may be used in their natural state or after mechanical processing such as crushing, washing, and sizing. Natural aggregates consist of both sand and gravel, and crushed stone. Recycled aggregates consist mainly of crushed concrete and crushed asphalt pavement. Construction aggregates make up more than 80 percent of the total aggregates market, and are used mainly for road base, riprap, cement concrete, and asphalt. Aggregates provide bulk, strength, and wear resistance in these applications. Construction aggregates increased from 36 percent of all raw materials used in the United States in 1900 to 70 percent in 1958, a compound annual growth rate of 1.15 percent. From 1958 to 1998, Americans have maintained their use of construction aggregates at percent of their total raw material demand [6] Concrete Recycling Aging U.S. infrastructure, decreasing availability of landfill space, and environmental concerns work together to increase concrete recycling. There are two approaches to recycling concrete. One alternative is to haul the concrete debris to a permanent recycling facility, usually close by to minimize transportation costs, for crushing and screening. The other approach is to do the crushing and screening at the demolition site where the aggregate is reused as soon as it is processed. Recycling at the demolition site reduces heavy materials hauling, thereby reducing transportation costs, energy use, and wear and tear on roads and equipment. Figure 3 shows the schematic flow of concrete recycling. Figure 4 shows the stages of concrete recycling [7]. Figure 3. Schematic flow of concrete recycling

8 1122 / Waste Cement and Concrete Management. Figure 4. Concrete to be Recycled, Concrete Crushing, Processed Concrete 5.3. Recycling-Small Market Share, But Large Tonnage Construction Materials Recycling Association, Lisle, Illinois, states that about 100 million t of concrete is recycled annually into usable aggregates. Aggregates produced from recycled concrete supply roughly 5 percent of the total aggregates market (more than 2 billion t per year), the rest being supplied by aggregates from natural sources such as crushed stone, sand, and gravel. Preliminary data indicate that in 1998, 3,400 U.S. quarries produced about 1.5 billion tones of crushed stone, of which about 1.2 billion tones was used in construction applications. About 5,300 sand and gravel operations produced more than 1.0 billion t of construction aggregates in application of recycling concrete could reduce the costs by reducing truck traffic, providing the Non-Renewable Resource, Better Trucking Utilization (Reduced Costs), Allow down to 10% Deleterious Materials in Iran Concrete Recycling Product The bulk of the aggregates recycled from concrete an estimated 68 percent is used as road base. The remainder is used for new concrete mixes (6 percent), asphalt hot mixes (9 percent), high-value riprap (3 percent), low-value products like general fill (7 percent), and other (7 percent) [8]. The low usage rate of recycled aggregates from concrete (15 percent) in high-value new concrete and asphalt hot mixes, compared to the higher usage rates in lower valued products, is related to quality issues, both real and perceived. State agencies have been slow to accept recycled aggregates from concrete for high-quality uses such as road surfacing. Specifications, based on considerable research and favorable in-service experience, have allowed its use mostly as road base material. Some States are

9 3 rd International Conference on Concrete & Development / 1123 experimenting with the conversion of existing worn-out concrete roads to rubblein-place. The old concrete surface is broken up and compacted, and asphalt pavement is placed over the enhanced base, composed of the original base and the new layer of compacted rubble. 6. LIFE CYCLE ENERGY AND CO2 OF HIGH QUALITY RECYCLED AGGREGATE BY HRM There is a developed technology for producing high quality aggregate from demolished concrete using a "heating and rubbing method" (HRM) [9]. Using this technology, aggregate can be recycled as raw, material for ready mixed concrete, while fine powder (HRM powder) from cement paste can be recycled as raw material for cement, cement admixture, or soil stabilizer. The HRM uses a considerable amount of energy to heat and rub concrete. Life cycle CO2 and energy of the recycled aggregate are calculated to evaluate this technology. The recycled aggregate is produced from demolished concrete and the HRM powder is used for a soil stabilizer in case 1-1. The HRM powder is used as part of cement raw materials in case 1-2. The production of crashed stone, which is the most popular aggregate, is calculated in case 2. The result of life cycle CO2 is shown in figure 5. In case 1-1 and 1-2, the life cycle CO2 is a negative value because the deduction of CO2 emission during cement manufacturing by the powder is much larger than the emission during recycled aggregate production. In case 2, the CO2 emission from crashed stone production is very small but still positive. This method is proved to be very effective to reduce CO2. As for the life cycle energy, its use of recycled aggregate is greater than that of crashed stone as ordinary aggregate because the deduction of energy consumption during cement manufacturing by the powder is relatively small [9]. Figure 5. Life cycle CO2 of high-quality recycled aggregate by HRM

10 1124 / Waste Cement and Concrete Management. 7. CONCLUSION Concrete recycling has proven to be profitable, but its use has limitations. Transportation costs need to be kept low, which forces the market to be urbanoriented. The market for recycled aggregates may be restricted by user specifications and prejudices. Finally, the availability of feedstock into recycling plants is fixed by the amount of demolition taking place, which generally places the activity within older, larger cities. Depending on the size of the recycling facility, entry into the aggregates recycling business requires a capital investment. Processing costs for the aggregates recycler again depending on the size of the operation. The larger operations distribute costs over more units of output. The average production capacity for a fixed site recycling operation should be determined. Prices for the various aggregate products made from recycled concrete should be evaluated from region to region. Recyclers often have the opportunity to charge a fee for accepting concrete debris, especially where landfill space is running short and charges for depositing materials into landfills are high. In such cases, the added revenue can compensate for a lower market price for the recycled aggregate product. As natural aggregate producers dominate the market, they tend to set the terms that recyclers can obtain. The future for recycled aggregates will be driven by reduced landfill availability, greater product acceptance, continuing government recycling mandates, and the continuing decay of a large stock of existing infrastructure, as well as by the demands of a healthy economy. On the other hand, the industrial utilized cement infrastructure could be improved by observing the ways to reduce cement GHG at cement and batch plants, optimizing cement content at batch plants, reducing concrete waste, application of recycling concrete as waste aggregate in concrete in Iran. REFERENCES 1. Symonds (1999) European Commission. Construction and demolition waste management practices, and their economics impacts. Report to DGXI, European Commission. 2. Hendriks ChF, Pietersen HS, Fraay AFA (2000) Recycling of building and demolition waste. An Integrated approach, Proceedings of the International Symposium on Sustainable Construction: Use of Recycled Concrete Aggregate, London, UK, pp Mining and development Information service web site: 4. ASTM C 150. Standard Specification for Portland Cement, American Society for Testing and Materials. 5. California Department of Transportation (2009), News, Sacramento, CA, USA. 6. Wilburn, D.R., and Goonan, T.G., 1998, Aggregates from natural and recycled sources: U.S. Geological Survey Circular 1176, 36 p. 7. Kelly, T.D., 1998, The substitution of crushed cement concrete for

11 3 rd International Conference on Concrete & Development / 1125 construction aggregates: U.S. Geological Survey Circular 1177, 15 p. 8. Deal, T.A., 1997, What it costs to recycle concrete: C&D Debris Recycling, September/October, p Shima, H., Matsuhashi, Yoshida, Yoshida, Y. and Tateyashiki, H. (2003a). "Life Cycle Analysis of High Quality Recycled Aggregate Produced by Heating and Rubbing Method." IEEJ Trans. EIS, 123-C (10),