EVALUATION OF ECOLOGICAL CONCRETE USING MULTI-CRITERIA ECOLOGICAL INDEX AND PERFORMANCE INDEX APPROACH

K e y w o r d s : Carbon emission; Ecological concrete; Ecological index; Environmental impact; Multi-criteria assessment; Performance index. 1/2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 97 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 1/2019 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 9 0 0 9 W . K u b i s s a , R . J a s k u l s k i , J . C h e n , P . L . N G , W . G o d l e w s k a , P . R e i t e r m a n concrete, instead it can improve various properties such as resistance to chemical attack and lower heat generation during hardening [13, 14, 18]. The use of recycled additives including fly ashes and other waste materials in pre-cast and ready-mix concrete is becoming increasingly common. Attempts are made to evaluate and appraise the implemented solutions and proposed environmentally friendly concretes. Rating systems for assessing the environmental performance of construction projects have been introduced. There are many formal sustainability rating systems for buildings in worldwide use today, with LEED (Leadership in Energy and Environmental Design) in the USA and BREEAM (Building Research Establishment Environmental Assessment Method) in the UK probably being the most wellknown and widely adopted [19, 20]. However, in the majority of real cases, the concrete is usually assessed very roughly. Under various sustainability rating systems, users are encouraged to use cement blended with additives, or an additive in the form of waste in the concrete mix, and/or recycled coarse aggregate, in order to obtain scores or points to improve the overall positive assessment of the construction projects. A number of researchers have proposed analytical methods for assessing the environmental performance of concrete based on one or more criteria [20, 21, 22, 23]. Some of the methods are quite simple to apply and are focused on determining the total carbon dioxide emission during the production of concrete components. Since carbon dioxide is a major greenhouse gas generated by artificial sources, the environmental friendliness of concrete is commonly represented by the CO2 emission [12]. Another method is to determine the impact of a building on the environment throughout its lifetime [24]. This approach is more complicated because it requires detailed data on: i) Global warming (CO2 emission); ii) Ozone depletion; iii) Acidification of soil and water; iv) Eutrophication; v) Photochemical ozone creation; and vi) Depletion of abiotic resources and fossil fuels (energy consumption) [24]. Information on how waste management is handled at the end of life of the building should also be known. The lack of such data results in the necessity of adopting less precise assumptions and reduces the reliability of the calculations and analyzes. Many different life-cycle analysis (LCA) calculation options are used and new methodologies and solutions are still being proposed recently [25, 26, 27, 28]. Most assessment methods only take into account the environmental impact, but not the engineering performance of the concrete being evaluated. The proposed method is supposed to be much simpler to apply than LCA analyzes, but at the same time it can take into account both the impact on the environment and engineering performance based on two equivalent criteria encompassed in the Ecological Index (EI) and Performance Index (PI), as explained below. The eco-friendliness of the concrete can be expressed in terms of the EI, whereas the engineering performance can be expressed in terms of the PI, where both EI and PI are calculated on the basis of selected concrete properties that are important for the given application and exposure class. This will allow to assess more comprehensively the impact of concrete on the environment and to connect it with the engineering performance of concrete. Concrete with better mechanical properties and functional parameters is usually a more durable material, and thus requires fewer repair or maintenance actions during the life cycle of the structure. This means reducing the amount of energy and materials consumption throughout the service life, which is directly related to the lowering of CO2 emission. On the other hand, the use of low-quality waste materials and decreasing the amount of binder could potentially cause, apart from a positive environmental impact, a lowering of concrete quality or performance possibly to an unacceptable level. The proposed method will allow finding the right compromise between “traditional” high-quality concrete with comparatively large amount of CEM I cement, crushed natural aggregates, additives and appropriate dose of admixtures, and “doctrinally ecological” concrete whose quality might be at the low side or even below the acceptable level. In the initial postulation of the method and for preliminary assessment of concrete, it is possible to use the data collected by the authors. Having cumulated more accurate data corresponding to the materials used, it is possible to refine the calculation by making use of the addition data to further enhance the accuracy of the concrete assessment. 2. DATA AND METHOD OF CALCULATION 2.1. Assumptions and values adopted for calculations A method based on multi-criteria, three-stage assessment of the impact of a concrete mix on the environment and the engineering performance of the resulting concrete has been proposed. The proposed method is principally intended to enable the rational 98 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 1/2019 EVALUATION OF ECOLOGICAL CONCRETE USING MULTI-CRITERIA ECOLOGICAL INDEX AND PERFORMANCE INDEX APPROACH and balanced design of concrete mix as the optimised environmentally-friendly solution to meet the specific application requirements. Basically, the impact on the environment is represented by way of the Ecological Index (EI), and the engineering performance is represented by way of the Performance Index (PI). During the assessment process, the calculated EI would be compared to the calculated PI. In the first stage, the CO2 emission and the amount of non-renewable raw materials used was determined for valuation of EI. To calculate CO2 emissions, “the individual integration method” described in [29, 30] was used. This method allows the inclusion of emissions during the production and transport of concrete components and the production of a concrete mix. Taking cement manufacturing as an example, detailed data values depend on many factors and may vary among individual cement manufacturers [31]. A similar situation occurs for other concrete ingredients and their transport. This necessitates reasonable assumptions of certain values in the calculations. The values of emission factor reported in the literature and the data for use in the calculations are summarized in Table 1. The assumed values are based on experience and latest literature data. It is noted that the exact data values from industrial production are difficult to obtain, because the exact values are dependent on a number of production parameters such as the machinery and equipment configurations, types of fuel used, manufacturing processes, and supply-chain to the production facilities. These parameters would vary from factory to factory, and would not be systematically disseminated by individual factories to third parties. Besides, there would be batch-to-batch variations of the raw materials characteristics and production parameters. Nevertheless, the purpose of the research is to develop the evaluation methodology and demonstrate its applications. When applying the proposed method, if more accurate data are available, such data can be used for evaluation of the concrete. For the calculations carried out with the proposed method, data on the compositions and properties of concretes presented in previous publications were used [11, 34, 35, 36]. The concrete mix proportions are presented in Table 2 (the unit of the concrete mix proportions is in kg/m3). C I V I L E N G I N E E R I N G e 1/2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 99 Table 1. CO2 emission factors of concrete ingredient materials Concrete ingredient material Emission factor (kg CO2/kg) Source Accepted value (kg CO2/kg) Raw materials factor (kg/kg) Ordinary Portland cement (OPC) / CEM I 0.820 0.944 0.730 1.000 [32] [29] [22] [33] 0.850 0.80 Silica fume 0.020 [22] 0.020 0.00 Metakaolin 0.175 [33] 0.175 1.54 Ground granulated blast-furnace slag 0.1430 0.0265 [32] [29] 0.100 0.00 Fly ash 0.0270 0.0196 0.0080 [32] [29] [22] 0.008 0.00 Coarse aggregates 0.0459 0.0075 0.0050 [32] [29] [22] 0.008 1.00 Fine aggregates 0.0139 0.0026 0.0050 [32] [29] [22] 0.005 0.50