Life cycle assessment (LCA) of concrete

Transcription

1 Life cycle assessment (LCA) of concrete The goal of the study, for example: comparison of two or more different types of concrete or concrete structural elements, assessment of the whole building or bridge, determination of the sources of the relevant impacts and possible optimization potentials, etc. The function of the product or product system, i.e. functional unit. The system boundaries. The relevant impacts. The necessary data to reach the goal of the study. 1

2 The functional unit: The function of the product or product system For a material, the functional unit can include the quantity (m 3 ), the mechanical properties (in appropriate units) and durability related properties (in years). For a building, the functional unit can include the size (m 2 ), the lifetime (years), the need for maintenance or the materials used. Cradle-to-gate Cradle-to-gate is an assessment of a partial product life cycle from resource extraction (cradle) to the factory gate (i.e., before it is transported to the consumer). The use phase and disposal phase of the product are omitted in this case. Cradle-to-gate assessments are sometimes the basis for environmental product declarations (EPD) termed business-to-business EDPs. The assessment of the environmental impact of the concrete as a building material or a specific structural element (for example, a precast bridge girder), i.e. the assessment of the production phase only. 2

3 Cradle-to-grave Cradle-to-grave is the full Life Cycle Assessment from resource extraction ('cradle') to use phase and disposal phase ('grave'). The assessment of the environmental impact of the concrete structure or structural element as a part of a building, bridge, road or some other kind of the construction work. to evaluate the environmental impact of the building, bridge, road, etc., as a whole. Cradle-to-cradle or closed loop production Cradle-to-cradle is a specific kind of cradle-to-grave assessment, where the end-of-life disposal step for the product is a recycling process. It is a method used to minimize the environmental impact of products by employing sustainable production, operation, and disposal practices From the recycling process originate new, identical products (e.g., concrete from recycled concrete aggregate). 3

4 LCA of CONCRETE QUARRY Raw material production (aggregate, cement, steel) TRANSPORT Production of concrete or concrete element Cradle - to - gate TRANSPORT Construction Operation (maintenance, repair, renovation) End-of-life (demolition, dismantling) Cradle - to - grave TRANSPORT Reuse and recovery (Recycling of steel and concrete) Disposal in landfill Quarrying Clinker production Quarrying of raw materials (limestone, clay, iron ore and gypsum stone ) Transport to the cement plant Crushing of raw materials Mixing of raw materials Milling and drying of raw materials Preheating of raw materials Burning of raw materials in a kiln Cement Production Storing of cooled cement clinker Cement clinker & gypsum grinding Transport of the cement to RMC plant Cement grinding and distribution Cement clinker cooling 4

5 Energy and material flows and emissions of a unit process. Raw materials Energy and fuels Water Other Process Products Co-products Waste Bill of quantities Emissions to air, water and soil dust, noise Bill of quantities? CO2 emissions and energy consumption for concrete and steel Portland cement Natural aggregate Reinforcement steel Inventory data, cradle-togate CO 2 emissions Energy use (kgco 2 /kg) (MJ/kg) Lower Upper Remarks Lower: river aggregate Upper: crushed Stone aggregate Lower: electric arc furnace; only scrap Upper: blast furnace; no recycled material 5

6 Cement Production Cement production is responsible for 5 7% of total world CO 2 emissions. These emissions are due to CO 2 release from the calcination process of limestone (to produce cement clinker), combustion of fossil fuels used for achieving the necessary temperature in the kiln ( C), from power generation In Europe: the average emissions per 1 kg of Portland cement type I (95% of clinker and 5% of gypsum) are: approximately 800 g of CO2, 2.4 g of NO x, 0.5 g of SO 2 and g of dust. average total energy consumption is about 4.3 MJ. 6

7 One solution to this problem is to replace a part of the cement clinker with industrial waste materials that have pozzolanic activity, such as blast furnace slag (BFS) and fly ash (FA). Two benefits are gained in this way: application of waste material in the new product, so decreasing the amount of waste to be disposed of in landfills, and lowering the CO2 emissions from clinker production. This procedure is already included in the cement production technology in many European countries, including Turkey. Life cycle impact assessment (LCIA) There are two different types of impact assessment methods. The first one is called the damage-oriented approach (also the top-down approach or endpoints ) and the second one is called the problem-oriented approach (also the bottom-up approach or midpoints ). 7

8 Concept of category indicators acidification example LCI results LCI results assigned to impact category Category indicator Impact category Characterization model Environmental relevance SOx, HCl, etc. (kg/functional unit) Acidification Acidifying emission (NOx, SOx, etc.) assigned to acidification Proton release H+aq Environmental mechanism Category endpoint Forest vegetation etc. Examples of intermediate variables (midpoints) and endpoints Impact category Climate change Stratospheric ozone depletion Acidification Eutrophication Human toxicity Ecotoxicity Choice of indicator level Examples of intermediate variables Infrared radiation, temperature, sea-level UV-B radiation Proton release, ph, basecation level, Al/Ca ratio Concentration of macronutrients (nitrogen, phosphorus) Concentration of toxic substances İn environment, human exposure Concentration or bioavailability of Toxic substances in environment Examples of category endpoints Human life expectancy, coral reefs, natural vegetation, forests, crops, buildings Human skin, ocean biodiversity, crops Biodiversity of forests, wood production, fish populations, materials Biodiversity of terrestrial and aquatic ecosystems Aspects of human health (organ functioning, human life expectancy, number of illness days) Plant and animal species populations 8

9 Examples of intermediate variables (midpoints) and endpoints Impact category Climate change Stratospheric ozone depletion Acidification Choice of indicator level Examples of Examples of category intermediate endpoints variables Infrared radiation, temperature, sealevel UV-B radiation Proton release, ph, basecation level, Al/Ca ratio Human life expectancy, coral reefs, natural vegetation, forests, crops, buildings Human skin, ocean biodiversity, crops Biodiversity of forests, wood production, fish populations, materials Impact category Choice of indicator level Examples of Examples of category intermediate variables endpoints Eutrophication Human toxicity Ecotoxicity Concentration of macronutrients (nitrogen, phosphorus) Concentration of toxic substances in environment, human exposure Concentration or bioavailability of toxic substances in environment Biodiversity of terrestrial and aquatic ecosystems Aspects of human health (organ functioning, human lifeexpectancy, number of illness days) Plant and animal species populations 9

10 Characterization model The link between the LCI results (extraction of resources, emissions and waste), and the category indicator is normally given by clear modeling algorithms (ISO, 2003). Climate change: The indicator result is estimated by calculating the product of the amount of emitted greenhouse gas per functional unit of produced material (mi) and the Global warming potential (GWP) given in CO 2 - equivalents for each gas (GWP i ) Climate change = Σ i GWP i m i Database Country Function Software Level Web site Athena Canada Database + Tool Impact Estimator Eco Calculator Specific building BEES USA Tool BEES Specific building Boustead UK Eco- Quantum Envest 2.0 Database + Tool Tool s/ BEESSoftware.cfm Netherlands Boustead General Eco- Specific Quantum building =1 UK Tool Envest Specific building GEMIS Germany Database + Tool List of some LCA databases and tools GEMIS General ce/gemis/en/ 10

11 Stratospheric ozone depletion: the characterization model of the World Meteorological Organization). Stratospheric ozone depletion potentials (ODPs) for a steady state in terms of CFC-11 equivalents: Stratospheric ozone depletion = Σ i ODPi m i The indicator result is expressed in kg of the reference substance, CFC-11* equivalent. ODPi is the steady state ozone depletion potential for substance i, while m i (kg) is the quantity of substance i emitted. *trichlorofluoromethane (CCl 3 F = CFC-11) Summary of impact categories data Impact category Climate change Stratospheric ozone depletion Description LCI results Category indicator Temperature increase in the lower atmosphere Decomposition of the stratospheric ozone layer which causes an increased UV radiation Emissions of greenhouse gases Emissions of ozon edepleting gases Increase of infrared radiative forcing (W/m2 ) Increase of stratospheric ozone breakdown Character -ization model IPCC WMO Characterization factor Global warming potential (GWP) for each emission (kg CO2-eq./kg emission) Ozone depletion potential (ODP) for each emission (kg CFC-11- eq./kg emission) Indicator result Kilograms of CO2- equivalents Kilograms of CFC-11- equivalents Category endpoint Years of life lost (YLL), coral reefs, crops, buildings Illness days, marine productivity, crops 11

12 Impact category Photo-oxidant formation Acidifica-tion Eutrophication Description LCI results Category indicator Creation of Emissions of smog as a substances local impact and (VOC, CO) tropospheric to air ozone as a regional impact Acidification Emissions of of aquatic acidifying and terrestrial substances ecosystems to air (acid rains, acid lakes ) Enrichment of aquatic and terrestrial ecosystems with nutrients Emissions of nutrients to air, water and soil Quantity of tropospheric ozone formed Maximum CML release of protons (H+) Deposition increase divided by N/P equivalents in biomass Charact erization model CML CML Characterizatio n factor Photochemical ozone creation potential (POCP) for each emission (kg ethyleneeq./ kg emission) Acidification Potential (AP) for each emission (kg SO2-eq./kg emission) Eutrophication potential (EP) for each emission (kg PO4 3 - eq./kg emission) Indicator result Kilograms of ethylene equivalents Illness days, crops Kilograms of Biodiversity, SO2 equivalents natural vegetation, wood, fish, monuments Kilograms of PO4 3 equivalents Category endpoint Biodiversity, natural vegetation, algal bloom Case study: ready-mixed concrete production in Belgrade, Serbia Example of the LCIA of ready-mixed concrete production in the capital of Serbia Belgrade. The impact assessment follows the standard protocol of LCA (ISO, 2006a). Therefore, the goal of the study is the LCIA of ready-mixed concrete production in Belgrade. This goal determines the system boundaries: production and transport of aggregate and cement, and production of concrete (the production of admixtures and water is not included as their contribution is very small) cradle-to-gate type of assessment (Fig. 3.7). The functional unit of 1 m3 of ready-mixed concrete is used in this work. 12

13 The production of ready-mixed concrete is located in Serbia, so all the LCI data for aggregate, cement and concrete production were collected from local suppliers and manufacturers Emission data for diesel production and transportation, natural gas distribution and transport that could not be collected for local conditions were taken from GEMIS database Data were taken from no earlier than 2000, so the processes analyzed in this work are based on recent technologies and normal production conditions. The problem-oriented (midpoints) methodology is chosen for the impact assessment. The total energy consumption expressed in MJ (energy use) is calculated instead of the depletion of abiotic resources. The impact categories included in this work are: climate change, eutrophication, acidification and photo-oxidant creation (POC). 13

14 Transport types and distances are estimated as typical for the construction site located in Belgrade. Cement is transported by heavy trucks from cement factory to concrete plant and assumed transport distance is equal to 150 km. River aggregate is most often used in Serbia for concrete production and is transported by medium-sized ships; assumed transport distance is equal to 100 km. Water Admixture Natural Aggregates Extraction&Screening Cement T R A S P O R T Production of concrete Transport Construction phase Service phase Demolition 14

15 The mix proportion of concrete was determined from two conditions: the target concrete strength class was C25/30 (characteristic compressive cylinder/cube strength equal to 25/30 MPa), according to TS EN 206 and the target slump 20 minutes after mixing was 6±2 cm. Concrete mix proportions and tested properties for concrete for C25/30 Components Unit Amount Cement CEM I Aggregate 0/4 mm (kg/m3) 658 (river aggregate, 4/8 mm (kg/m3) 338 Morava river) 8/16 mm (kg/m3) /31.5 mm (kg/m3) 601 Water 180 w/c a/c Properties Density (kg/m3) 2396 Slump after 20 minutes (cm) 5.5 Compressive strength at 28 days (MPa)

16 LCI data for various phases of the concrete life cycle Production of cement (kg) Energy (MJ) Coal Natural gas Production of aggrega. (kg) Production of concrete (1 m3) Transport (tkm) Heavy truck Medium-sized ship Diesel Electricity Emissions to air (g) CO NOx SOx CH CO Category indicator results per 1 m 3 of concrete Category Indicator result Energy use MJ Climate change g CO2-eq. Eutrophication g PO4 3 -eq. Acidification g SO2-eq. POC g C2H4- eq. Cement Aggregate Concrete Transport Total

17 Contribution of different life-cycle phases to category indicators 1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 Cement Aggregate Concrete Transport 17