Environmental product declaration of ready-mix products. A practical application

Transcription

1 Environmental product declaration of ready-mix products. A practical application Abstract: this paper presents the calculation of Environmental Product Declaration, EPD, of functional units consisting in concrete waffle and flat slabs, from the environmental profile of its constituents: cement, concrete and steel, by applying the Product Category Rules that are being developed by the European Technical Committee CEN TC 104 Concrete. The implementation of module B( use), C (end of life), and D where carbonation, use of resources and thermal mass are involved, is presented. Some conclusions on the reliability of the information provided in cradle to grave DAPs at both, product and building level, are also provided. Key words: Environmental Product Declaration, concrete, functional unit, Product Category Rule. Arturo Alarcón Barrio, IECA; Pilar López Torres, PROMSA; Alejandro Josa García Tornell, UPC; Juan Eugenio Cañadas Bouzas, ANEFHOP. Introduction. The Environmental Declaration of Products has the explicit purpose of assessing and comparing product reliably from an environmental point of view and from a Life Cycle Analysis approach. This information can de considered as an input regarding the purchase decision-making, whether public or private. To this purpose, many evaluation schemes have proliferated internationally. Only in relation to the carbon footprint, 62 different initiatives in this field have been identified by the European Commission. Initiatives that do not evaluate the same parameters, use different criteria and weight the indicators in different ways. The solution proposed by the EC seems to be the Product Environmental Footprint, PEF (1). This scheme, designed to calculate, report and compare the environmental footprint of any product, evaluates 14 environmental impact categories. However, construction products have their own assessment methodology, based on the EN (2) European Standard, since The reasons why these products have a particular method are well known and can be summarized in the fact that comparison only makes sense if we know exactly the function in which they were designed for. Its environmental performance becomes full meaning in the context of the building in which they are going to be installed. EN evaluates seven impact categories plus 17 auxiliary indicators. On the other hand, the Construction Products Regulation, CPR, (3) lays down conditions for the placing or making available on the market of construction products by establishing harmonized rules on how to express the performance of construction products in relation to their essential characteristics and on the use of CE marking. This means that the free choice of a construction product for a given function or technical requirement, takes into account the Declaration of Performance (DoP) and the existence of the CE marking on it. 8291

2 In addition, CPR establishes a new Basic Work Requirement of sustainable use of the resources, BWR7: which will be included in the DoP of construction products. CPR itself establishes that the tools to do so are the Environmental Product Declarations. If the DoP must include, in a near future, information on the BWR7, this environmental information will be taken into account at the time of the purchase decision. It is, therefore, extremely important to identify the comparability criteria of the environmental information provided in the DoP when is required and when environmental impacts are included. This article presents EPDs of functional units of structural concrete and aims to highlight the difficulties mentioned regarding the comparability and interpretation of results of EPDs. Finally, proposes, at the light of the results, specific proposals to clarify, under which conditions, environmental information can be transmitted and used in a meaningful efficient and reliable way, particularly in the case of functional concrete elements. Foreword. According EN , EPD communicates verifiable, accurate, not misleading environmental information for the products and their applications, thereby supporting scientifically based, fair decision-making and stimulating the potential for market-driven continuous environmental improvement. EPDs of declared (4) and functional units are very different conceptually. It is not possible to compare declared units because the precise function of the product or scenarios for its life cycle stages at the building level are not stated or are unknown. Examples of declared units are usually basic construction materials as 1 ton of cement or 1m3 of concrete. In this article EPDs of functional units are calculated. For a complete definition of these units, the quantified, relevant functional use or performance characteristics of the construction product when integrated into a building, shall be provided. In these cases, the FU supplies the basis for the addition of material flows and environmental impacts for any stage of life cycle. This means that information of the components of a construction system can be added in a bottom-top approach. Comparability of EPDs. From our point of view, a EPD of a functional unit in a cradle to gate approach is highly reliable. In this case, the uncertainty is minimal because it is no necessary to establish hypothesis out of the production process itself. Extrapolation of EPDs to the construction and use phases can only be done in a generic way, and with limitations that need to be highlighted. For example, a concrete flat slab serving as slab in a building, is a functional unit whose environmental loads can be fully known in a cradle to gate approach. At building level the prominence moves to the building s functional equivalent, like intended use of the building, location, orientation, compactness, insulation systems etc. Only when generic scenarios defined at product level are particularized at building level in a certain and specific project, all the information necessary to perform the evaluation cradle to grave, becomes fully reliable. This is absolutely clear in cases where the functional unit considered has implications on the 9292

3 operational energy consumption in the building, for example, due to the high thermal inertia of concrete walls and slabs, or due to the type of insulation of the building. In the following sections, the scenarios and assumptions for concrete functional units according Product Category Rule developed by the CEN Technical Committee 104 Concrete will be analyzed. Concrete product category rules. The latest available version of PCR that are being developed by CEN TC 104 Concrete has been used in the calculations. These specific RCPs will be published as a European Standard and will constitute the harmonized way in which DAPs of concrete products shall be declared in the future. The scope of the Standard includes how the parameters of EN can be particularized for concrete and, therefore, driven by the concrete RCP and not by the Standard. These parameters are: boundary limits, modeling and evaluation of specific characteristics of the constituents of concrete, allocation rules in the production chain, rules for the definition of the Inventory and calculation of ACV itself etc. Modularity approach. Modular scheme of EN is the basis to develop scenarios for any construction product. The most remarkable feature of the concrete PCR is, from our point of view, the end of waste criteria, the consideration of Module D and the influence of operational energy consumption at, either, product and building level. Regarding the end of waste condition, figure 1 summarizes the different possibilities considered. These alternatives involve module C, with three subcategories directly linked to four possible destinations of concrete as a waste: reuse in recovered concrete elements, land restoration, substitution of primary material, use as aggregate in fresh concrete. The figure shows when the end of waste boundary is reached and the relations between module C and D in each case

4 Figure 1. Typical processes at the end-of-life of concrete and concrete product and their attribution to the life cycle modules C1-C4 and D. Module D can include the environmental benefits of concrete recycling (cells 3, 4, 5, 7 and 8). The benefits from the substitution of primary materials shall be included in this module. In our case disposal of concrete debris at a landfill site has been selected as reference scenario, therefore no benefits from substitution of primary materials have been accounted to module D. On the other hand, carbonation of concrete is a benefit that shall be allocated in the stage in which the process takes place. Carbonation is a natural process by which concrete absorbs carbon dioxide from the atmosphere. Atmospheric carbon dioxide reacts with particular cementitious compounds in concrete to form solid products that are either precipitated on the surface or within the matrix. In terms of EN 15804, carbonation may be considered as a negative emission, and as a consequence it should be allotted to the range of life cycle stages in the same way as other emissions. Carbonation of concrete can occur during the use stage (B1) and during the end of life stage (C3 or C4). In this article both contributions have been calculated. Concrete PCR includes a chapter of guidance requirements and guidance on calculation of carbonation impacts. The carbonation front progresses from the surface into the concrete with a speed that can be calculated by the equation d=k*sqr(t). k-factors are chosen depending on the strength class, exposure conditions, degree of carbonation and type of structural concrete according to the criteria set in the guidance chapter of the PCR. Description of Functional Units: reinforced concrete waffle slabs and flat slabs 1m 2 of waffle slabs and flat slabs has been considered as a functional unit, FU. Table 1 presents the constituents and main characteristics of these FUs. Constituents Flat slab Waffle slab Concrete HA25/B/20/IIa (m 3 ) 0,252 0,163 Corrugated steel UNE EN BS500 S (kg) Formwork system (m 2 ) 1,1 1,1 Separators (ud) 3 1,2 Demoulding agent (l) 0,05 0,05 Concrete block (ud) -- 3,495 Electro welded wire mesh ME 20X20 Ø 5-5 B 500 T 6X2,20 (m 2 ) -- 1,1 Table 1. Main constituents of functional unit expressed as per m 2 Where the environmental loads of the constituents are summarized in table 2. Impact category Unit (5) Concrete per m 3 (6) Steel per tonne (7) Cement per tonne Global warming potential [kg CO 2 eq] 2,25E ,56E02 Depletion potential of the stratospheric ozone layer [kg CFC-11eq] 8.19E-06 1,39E-07 7,27E-05 Acidification potential of land and water [kg SO 2 eq] 3,86E-01 3,52 1,83 Eutrophication potential [kg PO 3-4 eq] 8,27E-02 3,7E-01 4,44E-01 Formation potential of tropospheric ozone photochemical oxidants [kg C 2 H 4 eq] 1,41E-02 6,98E-01 1,98E

5 Abiotic depletion potential for non fossil resources [kg Sb eq] 5,51E-01 2,85E-04 1,02E-04 Abiotic depletion potential for fossil resources [MJ] 1,30E ,17E03 Table 2. Main impact categories of constituents expressed as declared unit. The concrete considered is a HA25B20IIa with the following key characteristics: Units in kg/m 3 Data Water 170 Additive 3 Gravel 1025 Sand 875 Cement CEM II 280 Water cement ratio 0.6 Table 3. Main characteristics of concrete expressed in kg/m3 as declared unit Definition of Scenarios According the PCR, the main topics to be included in the appropriate life cycle stages are the following: A1-A3 production phase, downstream transport (A4); reinforcement type and quantity (A5); method of installation on site (A5); Reference Service Life for the Unit and relevant in-use conditions (B1 to B7); finally, if the case, % of re-use of demolition concrete (C1 to C3). Regarding the in-use stage, some important considerations are established by the PCR. As a general rule, there are no environmental impacts related to the normal use of concrete or concrete products other than the potential release of substances, the carbonation process and the consequences of the thermal mass provided by concrete elements on the overall energy consumption of the building. Tables 4 and 5 present the scenarios provided by the PCR for concrete slabs (per m 2 ): Production stage Construction stage End of life Scenario A1-A3 A4 A5 C1 C2 C3 C4 Structural concrete or concrete elements for buildings (interior) Flat slab Waffle slab Flat slab and waffle slab Adapted from its constituents at impact level (see table 1) Adapted from its constituents at impact level (see table 1) With A2 With A2 With A2 Energy consumption during in site construction. 20,06 MJ/m 2 Water consumption in curing: 3l/m 2 Waste generated (kg) Wood: 0,66 Steel: 1,10 Waste concrete: 5, 45 Waste generated Wood: 0,85 Steel: 0,91 Waste concrete: 14,18 Plastic: 0,015 Package: 0,020 Demolition Table 4. LCI and LCA data by module and by functional unit. Transport to the landfill Crushed and stockpile d Landfiled Carbonation [kg CO 2 eq] Flat slab:-42,9 Waffle slab:- 27,

6 And the selected scenario for use phase according the PCR: USE STAGE Module RSL B1 B2 B3 B4 B5 B6 B7 Structural concrete or concrete elements for buildings (interior) ESL: 100 years Carbonation process Maintenance. According Article of EHE 08, article 8 part I of CTE and, DB-SE of CTE, no maintenance activities are considered Repair. According PCR, no repair activities have been considered Replaceme nt According PCR, no repair activities have been considered Refurbishment According PCR, no repair activities have been considered Energy used for operating heating and cooling systems integrated in the element Result Recarbonation [kg CO 2 eq] Flat slab:-4,16 Waffle slab:-4,16 Table 5. LCI and LCA datas by module and by functional unit. The analysis of the functional units for the seven main impact categories is the following: Flat Slab Waffle slab Impact category Unit A1-A3 Module A1-A3 Global warming potential [kg CO 2eq] 9,49E+01 6,83E+01 Depletion potential of the stratospheric ozone layer [kg CFC-11eq] 2,07E-06 1,48E-06 Acidification potential of land and water [kg SO 2eq] 1,75E-01 1,26E-01 Eutrophication potential [kg PO 3-4 eq] 2,90E-02 2,08E-02 Formation potential of tropospheric ozone photochemical oxidants [kg C 2H 4eq] 1,89E-02 1,37E-02 Abiotic depletion potential for non fossil resources [kg Sb eq] 1,39E-01 9,92E-02 Abiotic depletion potential for fossil resources [MJ] 7,02E+02 5,06E+02 Table 6. LCA results by module and by functional unit for seven impact categories. As expected more significant results for the assessment are those related to the production stage and not so to the use phase. The durability of concrete has a strong influence in the advantages of being virtually free of maintenance and, therefore, free of the corresponding environmental loads during the use stage. The extension of the study to B and C modules has always to take into account ESL upto 100 years and how to the end of waste condition is reached. - Water used for operating heating and cooling systems integrated in the element**. Regarding the LCA results, it can be highlighted that the contribution of environmental loads from cement and steel per m 2 to the functional unit is approximately 60/40% in both cases for GWP. In the case of other impact categories, the relative contribution may vary strongly depending on the order of magnitude of each basic material.gwp is the impact category which has a significant variation between the slabs due to their different content of steel and concrete. Data for carbonation allocated to B1 and C3 are also in line to the figures recently shown in the literature (8) an in the PCR itself

7 Nevertheless, it can be stressed that when elements as concrete slabs or concrete walls may have an influence in the thermal inertia of the entire building, this effect can assessed carefully at building level. The benefits from enhanced thermal mass in buildings can reduce the overal energy consumption by 16% (9) in passive systems and up to 40% in active walls and slabs (10). Conclusions. Environmental declarations of functional units are the natural step forward from the construction basic materials to assembled systems. As long as EPDs of functional units become more close to a particular project or building, the combination of the Standard , at product level, and the EN , at building level, provide the more accurate and actual results. Meanwhile, the product category rules that are being developed by product TCs across Europe represent a major breakthrough in order to modeling the environmental performance of FUs without knowing the specific project/building. The knowledge and experience in the context of CEN product TCs, allow environmental declarations of functional units developed under harmonized PCRs, to go beyond the product stage retaining the quality of the results and modeling in a proper way the use and end of life phases of LCAs. PCRs involving scenarios for functional units, like concrete slabs and other elements of structural concrete, provide a good approximation to the environmental performance in a real building. In our view, if a cradle to grave approach is required, the combination of EN and EN into a specific building is the best option to assess the environmental performance of a functional unit, especially when operational use of energy is involved even at product level. In other cases, the second best option is modeling the behavior of functional units according the scenarios predetermined in PCRs developed by product TCs as has been stated in this paper. References (01) (02) EN Sustainability of construction works; Environmental product declarations; Core rules for the product category of construction products. The standard has been developed in the CEN/C 350 sustainability of construction works. (3) Regulation (EU) nº 305/2011 Of The European Parliament and of the Council of 9 March 2011 laying down harmonized conditions for the marketing of construction products and repealing Council Directive 89/106/EEC. (4) As defined in EN (5) Source: own elaboration, data from ANEFHOP. (6) Source: Institut Bauen und Umwelt e.v. (IBU), structural steel. BAUFORUMSTHAL e.v (7) Source: own elaboration, data from OFICEMEN. Spanish Association of Cement Producers 14297

8 (8) Galán García, Andrade Perdrix, Prieto Rábade, Mora Peris, López Agüí, San Juan Barbudo, Study of the CO2 (2010). Sink Effect of Cement Based Materials. IETCC, OFICEMEN, IECA (9) Tenorio, J.A.; Vega, L.; Turmo, J.; Burón, M.; Alarcón, A.;Martín Consuegra, F.; Burón, A.; D Andrea, R.: Los requisitos del Código Técnico de la Edificación. Eficiencia energetica e incremento de la sostenibilidad. Aplicación a los edificios de hormigon. Cemento Hormigon no 937, marzo abril (10)