https://doi.org/10.14311/APP.2022.33.0610 Acta Polytechnica CTU Proceedings 33:610–616, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague EFFECT OF USING BIOMASS FLY ASH ON THE CONCRETE SUSTAINABILITY Elisabete Rodrigues Teixeiraa, ∗, Aires Camõesb, Fernando G. Brancoc a University of Minho, ISISE, Department of Civil Engineering, Guimarães, Portugal b CTAC, Department of Civil Engineering, School of Engineering, University of Minho, Campus de Azur’em, 4800-058 Guimarães, Portugal c University of Coimbra, ISISE, Department of Civil Engineering, Coimbra, Portugal ∗ corresponding author: b8416@civil.uminho.pt Abstract. Biomass fly ash has been studied has a partial cement material, since this material has a positive effect on concrete properties. Even though, some mixes with BFA presents a positive benefit, they need to be economically competitive and present a good environmental performance. So, the analyse and comparison of concrete that uses BFA as raw material substitution in terms of environmental impacts related to the production of conventional concrete. One of the best approaches to develop this type of study is to use the life cycle assessment (LCA) method. This method quantifies both the input flows, such as energy, water and materials, as well as the output flows, such as CO2 emission, solid wastes and liquid wastes. Based both on the abovementioned context and methodological approach, a quantification and comparison of potential environmental impacts resulting from the production of 1 m3 of concrete was made, using different types of binder and quantities of cement substitution. Keywords: Life cycle analysis, sustainability, wastes. 1. Introduction Biomass fly ash (BFA) has an effect on concrete prop- erties, presenting similar results to concrete with tra- ditional pozzolanic materials such as coal fly ash [1]. Moreover, the analysis of the potential environmental impacts related to the production of a concrete that uses BFA as raw material substitution is mandatory. This analysis needs to be compared with the produc- tion of plain cement concrete. One of the best ap- proaches to develop this type of study is using the life cycle assessment (LCA) method [2]. This method en- ables the quantification of the potential environmen- tal impacts of products or services. It quantifies both the input flows, such as energy, water and materials, as well as the output flows, such as CO2 emission, solid wastes and liquid wastes [3]. LCA allows esti- mating the potential impact on humans and nature and enables identifying areas with improvement po- tential [3]. Based both on the abovementioned con- text and methodological approach, a quantification and comparison of potential environmental impacts resulting from the production of 1 m3 of concrete was made, using different types of binder: i) Portland ce- ment; ii) Portland cement and CFA or/and BFA, iii) Portland cement and CFA and HL; and iv) Portland cement, CFA, BFA and HL. This work was presented for the defence of the first author PhD degree and it is presented in [4]. 2. Methods and Methodology 2.1. Goal and Scope The main goal of this study was to evaluate the en- vironmental performances of various concrete formu- lations using biomass fly ash as a cement replace- ment material (Table 1) [4]. The method used in this study followed the phases of an LCA. The use of LCA is done according to the ISO 14040 standard, which provides a consensual framework, terminology and methodological phases [3]. The implementation of this method is based on four major phases: i) goal and scope definition; ii) inventory analysis; iii) impact assessment; and iv) interpretation [3]. The goal and scope express the purpose, objectives, product sys- tem, boundaries and functional unit. In the inventory analysis, the data necessary to analyse the life cycle of the product is collected. In the impact assessment, the life cycle inventory (LCI) flows are classified, char- acterized and normalized, using one of many possible Life Cycle Impact Assessment (LCIA) methodologies to estimate the potential environmental impacts. The last phase, interpretation, is very important to : i) identify, quantify and evaluate the information that results from the last two phases; ii) communicate the information in a correct way; and iii) recommend im- provements within the analysed system [3, 4]. The comparative analysis and the aggregation of indicators were developed using the multicriteria decision support Methodology for the Relative Sustainability Assessment of Building Technologies (MARS-SC) [5]. The MARS-SC methodology is 610 https://doi.org/10.14311/APP.2022.33.0610 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 33/2022 Biomass Fly Ash on the Concrete Sustainability Concrete Mix %wt w/b Cement BFA CFA HL REF 100.0 0.0 0.0 0.0 0.50 CFA20 80.0 0.0 20.0 0.0 0.50 BFA20 80.0 20.0 0.0 0.0 0.50 CFA40 60.0 0.0 40.0 0.0 0.50 BFA40 60.0 40.0 0.0 0.0 0.50 CFA50 50.0 0.0 50.0 0.0 0.50 CFA50b 50.0 0.0 50.0 0.0 0.35 BFA50 50.0 50.0 0.0 0.0 0.5 CFA60 40.0 0.0 60.0 0.0 0.5 BFA60 40.0 60.0 0.0 0.0 0.5 CFA49.5HL0.5 50.0 0.0 49.5 0.5 0.35 CFA49.5BFA0.5 50.0 0.5 49.5 0.0 0.35 CFA48.8BFA1.3 50.0 1.3 48.8 0.0 0.35 CFA45BFA5 50.0 5.0 45.0 0.0 0.35 CFA48.8BFA0.6HL0.6 50.0 0.6 48.8 0.6 0.35 Table 1. Binder fraction and water/binder ratio used in the concrete formulations [4]. based on three groups of sustainability categories: environmental, functional and economic [6]. Since this research aimed at assessing the environmental performance of different concrete formulations, only the environmental category of MARS-SC was con- sidered. The MARS-SC methodology is processed in five steps: i) definition of the sustainability indi- cators; ii) quantification of the indicators (including the life cycle inventory); iii) normalization of the indicators; iv) aggregation of the indicators; and v) sustainable score calculation and global assessment [5]. 2.2. System Boundaries and Functional Unit The boundaries of this work mark the embodied en- vironmental impacts (cradle-to-gate) of the different concrete compositions as well as the environmental impacts that result from the transportation of the materials to the concrete plant and their mixing. The choice of limiting the study to the cradle-to-gate stage is justified by the fact that, in the studied compositions, the use and disposal of concrete will result in similar environmental impacts [4]. The declared functional unit is dependent on the goal of life cycle analysis and therefore constitutes 1 m3 of concrete. 2.3. Inventory Analysis To quantify the sustainability indicators, it is neces- sary to first develop the inventory analysis [6]. The inventory is used to quantify the inputs (e.g. energy, materials and chemical) and outputs (e.g. emissions and wastes) of the product system [7].) Table 2 shows the inventory of the materials and transportation considered for each concrete formula- tion [4]. This inventory took into consideration the specific context of the Portuguese concrete industry. The life cycle analysis software SimaPro 7.3.3 was used to facilitate the quantification of the impact cat- egories. In this study, the specific consumption of raw materials, energy and fuels and the emissions released to air, water and soil during the cement production of an important Portuguese cement plant, located in the south of Portugal, was considered. The data used are described in the public Environmental Declara- tion [8] of this cement plant. For this research, it was considered that this plant supplied the cement used for the preparation of the different concrete formula- tions. It was necessary to quantify the impact cat- egories, since the environmental declaration did not cover all impact categories necessary for this study, being limited to those mandatorily declared accord- ing to Portuguese environmental legislation [4]. Using the inventory listed in the environmental declaration, the SimaPro software was used to assess the potential environmental impacts of the used Portland cement. Regarding each type of fly ashes, it was necessary to make the allocation of flows of the power plant according to the place of production. Allocation is necessary in the case of joint coproduction, where the processes cannot be sub-divided, as is the case in fly ashes production [9]. Allocation shall respect the main purpose of the processes studied, appropri- ately allocating all relevant products and functions. Since the main purpose of a thermal power plant is to produce electricity and since the difference in rev- enue between the electricity and the fly ashes is high, it is not possible to use an allocation process based on physical proprieties (e.g. mass and volume). There- fore, the allocation process used in this research was based on economic values [4]. Due to the environmental report [10] from a major Portuguese coal power plant (located in the centre 611 E. R. Teixeira, A. Camões, F. G. Branco Acta Polytechnica CTU Proceedings Formulations PC* Gravel Sand Water SP* CFA BFA HL Material Input (kg) REF 350.0 969.2 738.1 200.0 0.0 0.0 0.0 0.0 CFA20 280.0 982.1 756.7 149.5 0.0 70.0 0.0 0.0 BFA20 280.0 985.3 759.1 149.4 0.0 0.0 70.0 0.0 CFA40 210.0 973.0 749.6 149.7 0.0 140.0 0.0 0.0 BFA40 210.0 979.3 754.5 149.5 0.0 0.0 140.0 0.0 CFA50 175.0 968.4 745.1 149.8 0.0 175.0 0.0 0.0 CFA50b 175.0 1044.3 804.5 88.4 8.8 175.0 0.0 0.0 BFA50 175.0 976.3 752.2 149.6 0.0 0.0 175.0 0.0 CFA60 140.0 963.8 742.5 149.9 0.0 210.0 0.0 0.0 BFA60 140.0 973.3 749.9 149.7 0.0 0.0 210.0 0.0 CFA49.5HL0.5 175.0 1049.0 768.6 91.5 5.3 173.5 0.0 1.9 CFA49.5BFA0.5 175.0 1049.0 795.2 91.5 11.4 173.5 1.9 0.0 CFA48.8BFA1.3 175.0 1050.1 842.8 35.5 11.4 170.6 4.4 0.0 CFA45BFA5 175.0 1049.5 838.9 42.4 3.9 160.0 17.8 0.0 CFA48.8BFA0.6HL0.6 175.0 1067.2 832.9 36.9 2.5 170.6 2.2 2.2 Transportation (tkm) REF 14.5 357.6 272.4 − − − − − CFA20 11.6 362.4 279.2 − − 12.4 − − BFA20 11.6 363.6 280.1 − − − 10.2 − CFA40 8.7 359.0 276.6 − − 24.8 − − BFA40 8.7 361.4 278.4 − − − 20.3 − CFA50 7.3 357.3 274.9 − − 31.0 − − CFA50b 7.3 385.3 296.9 − 2.9 31.0 − − BFA50 7.3 360.3 277.6 − − − 25.4 − CFA60 5.8 355.6 274.0 − − 37.2 − − BFA60 5.8 359.1 276.7 − − − 30.5 CFA49.5HL0.5 7.3 387.1 283.6 − 1.7 30.7 − 0.2 CFA49.5BFA0.5 7.3 387.1 293.4 − 3.8 30.7 0.3 − CFA48.8BFA1.3 7.3 387.5 311.0 − 3.8 30.2 0.6 − CFA45BFA5 7.3 387.3 309.6 − 1.3 28.3 2.6 − CFA49.5BFA0.6HL0.6 7.3 393.8 307.3 − 0.8 30.2 0.3 0.3 PC - Portland Cement; SP - Superplasticizer Table 2. Binder Inventory results of the material and transportation inputs for each concrete (per m3 of produced concrete) [4]. of the country), it is possible to known how many tons of coal are consumed to produce 1 kWh of elec- tricity as well as the quantity of CFA produced dur- ing coal combustion. In Portugal, the commercial value of CFA is about 18e/ton and the value of the electricity is 0.16e/kWh. Therefore, the economic allocation coefficient of 0.17 % is applied to the im- pacts of the extraction, transportation and combus- tion of the coal from that power plant. As with the cement plant, this environmental report only covered the impact categories that are mandatory according to Portuguese environmental legislation. As a re- sult, all the flows (inputs and outputs) declared in this report were introduced in the SimaPro software, taking into consideration the quantified economic al- location coefficient of 0.17 %. Regarding BFA, it is important to highlight that in Portugal this kind of fly ash is considered a waste product and therefore they do not provide an economic value. Because of this fact and according to the allocation rules pre- sented in ISO 14040, no flows from the thermal power plant are allocated in the production of BFA. With respect to the life-cycle inventory of the other used materials (gravel, sand, water and superplasticizer), generic data was used. Since the development of spe- cific environmental information for products is very time and cost consuming, initial LCA studies, whose main goal was to compare different design scenar- ios, are normally based on generic (average) data [4,6]. For this reason and due to the lack of public available specific data for the abovementioned mate- rials, this information was gathered from one of the most internationally accredited generic environmen- tal databases of the Ecoinvent report V2.2 [11]. The nearest context to the Portuguese one was considered for this study. Since the energy consumed during the manufacturing process is the parameter that most in- fluences the life-cycle environmental impact [12] and 612 vol. 33/2022 Biomass Fly Ash on the Concrete Sustainability since the Portuguese energy mix is different from the European average [13], a contextualization of the en- ergy used in each process was developed. This means that all used processes from the Ecoinvent database were edited, and all energy input flows were changed to consider the Portuguese energy mix. In the inven- tory of the transportation processes, the study con- sidered the distances between the Portuguese places of raw material extraction or raw materials storage fa- cilities and the concrete mixing plant in question [4]. The distance between the raw materials production facilities and concrete production was considered for this study. The kilometres considered as the trans- portation distance of cement (Secil Group), sand and gravel (MIBAL - Minas de Barqueiros, S.A.), coal fly ashes (Pegop-energia Eléctrica Sa), biomass fly ash (Altri), superplasticizer (BASF) and hydrated lime (Lusical-companhia Lusitana De Cal Sa) to the con- crete industry considered in this study were 41.5, 369, 177, 145, 329 and 117 km, respectively. The inventory related to the production of concrete was quantified taking into account the Environmental Product Declaration (EPD) of a specific Portuguese concrete plant [14], where the different concrete formulations are supposedly produced. From this EPD, only the flows related to the concrete mixing phase were considered. 2.4. Impact Assessment The life cycle inventory data was converted into potential environmental impact, using the lifecycle impact assessment (LCIA) methods. In MARS-SC, the definition of the sustainability indicators de- pends, above all, on the type of analysed product or building element and on the aims of the study. In this method, the environmental performance as- sessment is based on the following six environmental impact categories: i) Global warming; ii) Ozone depletion; iii) Acidification of soil and water; iv) Eutrophication; v) Photochemical ozone creation; and vi) Depletion of abiotic resources-fossil fuels. Compared with the list of impact categories found in the EN15804:2012 [15] standard, MARS SC does not consider the Depletion of abiotic resources-elements as an impact category. 2.5. Normalization, Aggregation and Global Assessment To avoid the scale effects in the aggregation of pa- rameters of the different indicators and in order to minimize the possibility that some of the parameters are of the type. higher is better and lower is bad, it was necessary to normalize the indicators [15]. The normalization was done using the Diaz-Balteiro [16]. After normalization, is important to calculate the ag- gregation of each environmental indicator in terms of a global indicator, describing the overall environmen- tal performance (NDA). The global indicator NDA results from the weighting average of each normal- ized. The sum of all weights must be equal to 1. For aggregation purposes, this study considers the weights (Table 3) set in a study developed by the US Environmental Protection Agency’s Science Advisory Board (SAB) [17]. In each sustainable profile, the global performance of a respective concrete with fly ash was monitored and compared with that of the reference concrete. Indicator Weight (%) GWP 38 ODP 12 AP 12 EP 12 POCP 14 ADP_FF 12 Table 3. Weight for each environmental indicator [17]. 3. Results and Discussion Table 4 summarizes the values obtained in the quan- tification of the environmental impact categories, re- lated with the production of the different concrete mixes. Analysing the results, when it used just ce- ment as binder, concrete presents the highest values of CO2 emission. The high emission of CO2 is a re- sult of the chemical reactions (calcination) that occur during clinker production [4,18]. The incorporation of the BFA blended with CFA allows a reduction in all environmental impacts, moreover the environmental impacts decrease with increasing of cement substitution. At this stage, it is necessary to highlight the effect of the allocation step on the obtained results. In Portugal, BFA are consid- ered a waste product without economic value [18] and therefore there are no flows from the biomass power plant allocated to its production [4]. The same does not happen with CFA, as they have a market value and consequently a percentage of the power plant’s flows is allocated to their production [19]. Concrete mixes 0.5%wt and 1.3%wt of BFA decreased the envi- ronmental impact related with the CO2 emissions but an increase on the values of the others environmental indicators was observed [4]. This is a not result of the incorporation of BFA, since this result is not noted in the mixes with 5, 20, 40 and 60%wt, but it is due to the fact of these two mixes presented a higher super- plasticizer content. It was concluded in other studies that superplasticizer had high influence on e.g. ODP and ADP_FF impact categories, but did not have a significant influence on GWP that most influences the overall environmental impact concrete with ashes, which confirm the results achieved in this study [4]. The normalization of the values obtained for each en- vironmental impact category was obtained and the 613 E. R. Teixeira, A. Camões, F. G. Branco Acta Polytechnica CTU Proceedings Formulations GWP100 ODP AP EP POCP ADP_FF kg (×102) kg (×10−5) kg kg (×10−1) kg (×10−2) kg (×103) REF 4.02 2.67 1.00 2.53 4.00 2.71 CFA20 3.44 2.55 0.91 2.32 3.64 2.56 BFA20 3.44 2.55 0.91 2.27 3.64 2.53 CFA40 2.83 2.38 0.80 2.08 3.23 2.36 BFA40 2.83 2.38 0.80 1.98 3.22 2.30 CFA50 2.53 2.30 0.75 1.96 3.02 2.26 CFA50b 2.88 2.69 0.90 2.41 3.97 3.10 BFA50 2.53 2.29 0.75 1.83 3.01 2.18 CFA60 2.23 2.21 0.69 1.84 2.82 2.16 BFA60 2.23 2.21 0.69 1.69 2.80 2.07 CFA49.5HL0.5 2.75 2.53 0.84 2.22 3.55 2.77 CFA49.5BFA0.5 2.96 2.77 0.94 2.51 4.20 3.31 CFA48.8BFA1.3 2.99 2.85 0.95 2.54 4.26 3.36 CFA45BFA5 2.75 2.59 0.85 2.22 3.57 2.73 CFA48.8BFA0.6HL0.6 2.73 2.57 0.83 2.18 3.46 2.64 Table 4. Values obtained for the different environmental impacts. Formulations GWP100 ODP AP EP POCP ADP_FF [kg CO2 eq] [kg CFC-11 eq] [kg SO2 eq] [kg PO4 eq] [kg C2H4 eq] [MJ eq] REF 0.00 0.24 0.00 0.01 0.18 0.50 CFA20 0.32 0.44 0.30 0.26 0.42 0.62 BFA20 0.32 0.44 0.31 0.32 0.43 0.65 CFA40 0.66 0.72 0.65 0.54 0.71 0.78 BFA40 0.66 0.72 0.65 0.66 0.71 0.82 CFA50 0.83 0.86 0.82 0.68 0.85 0.85 CFA50b 0.64 0.20 0.32 0.16 0.20 0.20 BFA50 0.83 0.86 0.83 0.83 0.86 0.91 CFA60 1.00 0.99 0.99 0.82 0.99 0.93 BFA60 1.00 1.00 1.00 1.00 1.00 1.00 CFA49.5HL0.5 0.71 0.47 0.52 0.37 0.49 0.46 CFA49.5BFA0.5 0.59 0.09 0.21 0.04 0.04 0.03 CFA48.8BFA1.3 0.58 0.00 0.17 0.00 0.00 0.00 CFA45BFA5 0.71 0.37 0.50 0.38 0.47 0.49 CFA48.8BFA0.6HL0.6 0.72 0.41 0.54 0.42 0.55 0.56 Table 5. Normalized values of the studied environmental impact categories [4]. results are presented in Table 5. This enables a bet- ter perception of which of the concretes has a bet- ter environmental performance. It is observed that, concrete in which 60% BFA had the best environmen- tal performance, being REF and CFA48.8BFA1.3 the mixes that presented the lowest environmental per- formance. Figure 1 present the sustainability profiles and the overall environmental performances. At the level of each impact category, the best concrete is the one that has the value closest to one. It is verified that the BFA60 concrete presented the best environmen- tal performance (NDA = 1.00) and plain cement con- crete (REF) presented the worst performance (NDA = 0.12) [4]. Therefore, these results allow the conclusion that using a high content of BFA significantly increases the environmental performance of concrete produc- tion, since the overall environmental performance of concrete is improved. Additionally, the usage of these materials contributes to a better compatibility be- tween the construction sector and the goals of Sus- tainable Development [4]. 4. Conclusions BFA used alone or blended displayed a capability to reduce the environmental impacts of concrete, when compared to conventional concrete. The re- sults showed that 60% of BFA presented the best results. Besides the good results observed, it is im- portant to refer that the concrete formulations with 0.5 and 1.3%wt of BFA presented a low environmen- tal performance, but better than that of plain ce- ment concrete. The environmental issues related with 614 vol. 33/2022 Biomass Fly Ash on the Concrete Sustainability Figure 1. Normalized values that described the sustainability profile. these two concrete formulations are due to the use of a higher content of superplasticizer when compared with the other formulations. The effect of superplas- ticizer on the environmental indicators is known, but the results showed that it is possible to slightly re- duce the content of SP, without having a significant effect on the workability, maintaining the values sim- ilar to those of the concrete formulation with 5%wt of BFA [4]. The decrease of the content of SP has an important contribution on the improvement of envi- ronmental performance of these two concrete mixes. Acknowledgements The authors wish to thank the Portuguese Foundation for Science and Technology (FCT) and the Eco-Construction and Rehabilitation Doctoral Program for supporting the PhD scholarship (reference PD/BD/ 52661/2014). This work was partly financed by FCT/MCTES through na- tional funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. References [1] R. Rajamma, L. Senff, M. J. Ribeiro, et al. 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