Comparing conventional concrete to high performance concrete through life cycle assessment

In this study, conventional concrete is compared to high performance concrete in terms of environmental performance. The Open LCA software along with the Ecoinvent database 3.1 and data from a literature review were used. The ReCiPe life cycle impact assessment methodology was applied. Results show better environmental performance for high performance concrete. Regarding climate change and water depletion results, conventional concrete turned out to have almost twice the impact of high performance concrete, while for the fossil depletion and human toxicity indicators results were even higher. In addition, it must be noted that high performance concrete also results in benefits regarding dematerialization since it is needed 0.654 m 3 less than in the conventional concrete case for the same function. Nevertheless, further analysis should be conducted using primary data.


Introduction
A life cycle assessment (LCA) is the assessment of the environmental impact of a given product throughout its lifespan (International Organization for Standardization, 2006aStandardization, , 2006b)).LCA has been used in the building sector since 1990 (Fava, 2006), and it is now a widely used methodology (Häfliger et al., 2017).
LCA compares different solutions that will provide the same function and identifies opportunities to improve the environmental performance of products and services in various phases of their life cycle.The term "life cycle" refers to the idea that for a fair, holistic assessment the raw material production, manufacture, distribution, use and disposal need to be assessed.
LCA is essential in order to compare the environmental performance of concrete mixes.Usually, LCA are implemented for 1 m 3 of concrete when comparing concrete mixes.In this study, a LCA is carried out considering a structural element.This is a step further on the life cycle of concrete which include raw materials extraction, concrete production, concrete use and end of life for a structural element.
The objective of this study is to compare conventional concrete to high performance concrete (HPC) -which is a relatively new type of concrete with compressive strength of 50 MPa or more and a set of standards above those of the most common concretes (Malier, 2018).This is for a specific structural element with a specific load.These results should be complemented with a life cost analysis in order to assess the viability of the implementation of high performance concrete towards sustainable development.

Literature review
A literature review was conducted in order to contextualize life cycle assessment for concrete and identify data for the study (Rowley;Slack, 2004).The literature review includes relevant material published in scientific journals, books and conference proceedings from bibliographic databases such as Google Scholar, Web of Science and Scopus which are the largest abstract and citation databases.Papers and bibliography were selected according to their relevance.Four LCA studies on conventional concrete, high performance concrete, ultra-high performance concrete, frost-resistance concrete and admixtures such as superplasticizers were studied in detail.

Life cycle assessment
The Open LCA version 1.4 was used along with the Ecoinvent database 3.1 and data from the literature review.The four phases of LCA were performed according to the ISO 14040 standard.In addition, a comparison between the study and reviewed papers was made.
The goal of the present LCA is to compare the environmental performance of conventional concrete and high performance concrete for a 3 m tall square section concrete column (structural element) supporting a 18750 KN load.High performance concrete demands less materials for a single structural element; however, it uses admixtures (superplasticizers) in its composition in order to increase compressive strengths, workability and to maintain a low water/cement ratios (Yuan et al., 2023).As a result, using these high performance additives may imply greater environmental impacts.
The system boundaries comprise life cycle assessment for processes from raw material extraction to placing concrete into a clean truck, all these processes occurring inside the concrete plant.The use phase and end of life phase of the product are excluded in this study since this is a cradle to gate LCA.The chosen functional unit is a 3 m tall square section concrete building column (structural element) supporting a 18750 KN load.Table 1 shows properties, dimensions and volume for two concrete options.The two concrete options, even if they do not have exactly the same dimensions, correspond to the functional unit and can therefore be compared.Four midpoints indicators were selected: climate change, fossil depletion, human toxicity and water depletion.These indicators will be explained along with their respective units.
Both product systems consist of two processes: "concrete production" and "placing concrete into truck" (see Figure 1, Figure 2 and Figure 3).In order to create the product system, the Ecoinvent version 3.1 database was imported to the Open LCA software.For the product system some of the flows and processes were used directly from the Ecoinvent version 3.1 database, as in the case of the "concrete production" process while other flows and processes had to be created and fed by literature data, such as "placing into concrete truck" process.In the case of the "concrete production" process even though the process was available in the Ecoinvent version 3.1 database, the amounts were adjusted to fit this study.Concrete has as components: aggregates, water, cement and chemical admixtures.During the concrete production process, the different components come together to form a uniform mass which can be molded into different shapes.Conventional concrete comprises compression strengths under 50 MPa while high performance concrete is defined by Lafarge (2013) as concrete with compressive strength greater than 50 MPa.High performance concrete composition includes superplasticizer admixtures which increases its workability and keeps low water/cement ratios.
Inventory data for conventional concrete (35 MPa) and high performance concrete (59 MPa) is presented in Table 8 and Table 9 respectively.For conventional concrete (35 MPa), inventory data was compiled from the PCA Environmental Life Cycle Inventory of portland cement concrete in its majority and also from the Ecoinvent database 3.1.For conventional concrete (59 MPa), inventory data was compiled from the PCA Environmental Life Cycle Inventory of Portland cement concrete, Chapter 17 from Design and Control of Concrete Mixtures engineering bulletin (Kosmatka et al., 2003), and Ecoinvent database 3.1.
The chosen life cycle impact assessment method for the study is ReCiPe Midpoint (E).ReCiPe integrates midpoint and endpoint approach.It has regional validity for Europe, Global for Climate change, Ozone layer depletion and resources and time horizon of 20 years, 100 years or indefinite, depending on the cultural perspective (JRC European Commission, 2010).Converting the extensive compilation of Life Cycle Inventory results into a handful of indicator scores is the main goal of the ReCiPe approach.The relative severity of an environmental impact category is expressed by these indicator ratings.ReCiPe bases its modeling on an environmental mechanism, which may be seen as a set of interrelated impacts that cumulatively have the potential to cause a specific amount of harm to, say, ecosystems or human health.In ReCiPe the indicators are determined at two levels: 1. Eighteen midpoint indicators

Three endpoint indicators
A midpoint indicator can be defined as a parameter in a cause-effect chain or network (environmental mechanism) for a particular impact category that is between the inventory data and the category endpoints.Endpoint characterization factors (or indicators) are calculated to reflect differences between stressors at an endpoint in a cause-effect chain and may be of direct relevance to society's understanding of the final effect.Both midpoint and endpoint methods requires building a proper inventory and hence using an impact method to transform emissions to potential environmental impact.Endpoint characterization is more complex and relatively more uncertain and midpoint results being more robust and certain.The choice between midpoints and endpoints is mainly driven by the goal of the LCA and who is the LCA for.For this study midpoint methodology was chosen since the study correspond to research purposes.
Each method (midpoint, endpoint) contains factors according to the three cultural perspectives: • Individualist: short term, optimism that technology can avoid many problems in future.Considers the proven environmental impacts.
• Hierarchist: consensus model, as often encountered in scientific models.
• Egalitarian: long term based on precautionary principle thinking.Considers all environmental impacts proven or not.
These perspectives represent a set of choices on issues like time or expectations that proper management or future technology development can avoid future damages (Characterisation -ReCiPe, n.d.).For this study Egalitarian (E) cultural perspective was chosen.
For the present LCA the next four impact categories were selected as they are considered to be relevant for concrete production LCIA.Cementitious materials industry generates significant environmental impacts in terms of CO2 emissions and energy consumption for this reason these impacts must be properly quantified and assessed.Water consumption is an environmental impact that has been relatively ignored in the production of cementitious materials either because of lack of data or because they are considered to be insignificant.However nowadays due to the water scarcity problems, this impact has gained great relevance and is being assessed in a more meticulous way.As for human toxicity, in this study is considered very important aspect because it directly affects people.
Equivalent carbon dioxide (CO2 eq) is a functionally equivalent amount or concentration of CO2 as the reference to measures how much global warming a given type and amount of greenhouse gas may cause.The carbon dioxide equivalency for a gas is obtained by multiplying the mass and the Global Warming Potential (GWP) of the gas.
Kilogram(s) of oil equivalent is a normalised unit of energy equivalent to the approximate amount of energy that can be extracted from one kilogram of crude oil.This unit has an assigned net calorific value of 41 868 kilojoules/kg and may be used to compare the energy from different sources.
C6H4Cl2 is the formula for the chemical compound 1,4-dichlorobenzene.Humans who inhale 1,4-dichlorobenzene over a brief period of time experience irritation of their eyes, throat, and skin.Humans who breathe in 1,4-dichlorobenzene over an extended period of time may experience consequences on their liver, skin, or central nervous system (CNS).EPA has classified 1,4-dichlorobenzene as a Group C, possible human carcinogen.For each toxic substance human toxicity potentials are expressed using the reference unit, kg 1,4-dichlorobenzene (1,4-DB) equivalent.
For the water depletion a midpoint indicator of cubic meter (m 3 ) expresses the total amount of water used and considers water flows such as: water from rivers and lakes, water from wells and water from unspecified natural origin.This indicator consist of summation of all different water flows.
The four impact categories correspond to ReCiPe midpoint methodology.

Literature review
Four LCA studies on conventional concrete, high performance concrete, ultra-high performance concrete, frost-resistance concrete and admixtures such as superplasticizers are presented.(Sjunnesson, 2005)

Goal and scope
The study focuses particularly on the superplasticizers used as admixtures and is conducted for two types of concrete: ordinary and frost-resistant concrete.Since the sort of structure for which the concrete is utilized is not specified, the utilization phase is not covered in this study.The functional unit is 1 m 3 of concrete.

Inventory data
The composition of the two types of concrete used in this study is presented in Table 2. Energy demands and emissions for cement, aggregates, admixtures, concrete production are presented in Table 3. (methane); HC (hydrocarbon).Source: Author, 2024.

Global warming Potential
The primary source of the global warming potential (GWP) in the concrete life cycle is the raw material production.It contributes about 85% of the GWP overall.Because of the cement factory's calcination process, the manufacture of cement generates the most greenhouse gas emissions among raw materials.The calcination process accounts for about 69% of the factory's CO2 emissions, with fossil fuel use accounting for the remaining 31%.

Energy consumption
Cement production has the highest energy demand both as electricity and fossil fuels.Superplasticizers use 2% of both electricity and fossil fuel in ordinary concrete and 4% of electricity and 3% fossil fuel in frost-resistant concrete.

Toxicity
In a worst-case scenario, the study indicates that roughly 15-25% of sulphonated naphthalene polymers (SNP), lignosulphonate, and polycarboxylates, and 30-60% of sulphonated melamine polymers (SMP), were leached.This may sound like a lot, but further testing revealed that superplasticizers are only responsible for a portion of the overall amount of leached organic chemicals; the remainder originates from other goods like adhesives and coatings.

Conclusions
The environmental impact of frost-resistant concrete is between 24-41 % higher than that of ordinary concrete due to its higher content of cement.Superplasticizers contribute with approximately 0.4-10.4% of the total environmental impact of concrete, the least to the global warming potential (GWP) and the most to the photochemical ozone creation potential.
3.1.2Reducing environmental impact by increasing the strength of concrete: quantification of the improvement to concrete bridges (Habert et al., 2012)

Goal and scope
This study evaluates the environmental consequences of using high performance concrete instead of ordinary concrete for a bridge.In this study, the chosen functional unit is the crossing of a four-lane divided highway with a two-lane road over a one-hundred year time period.

Inventory data
The components for different concretes are presented in Table 2. Source: Habert et al. (2012).

Life cycle impact assessment and results
The findings indicate that, overall, using high performance concrete instead of ordinary concrete for bridge construction is more environmentally beneficial.

Conclusions
The present study shows that choosing a high performance bridge construction solution to cross a four lane divided highway with a two-lane road is always more environmentally friendly than a traditional concrete bridge solution, regardless of the observed environmental impact and the geographic context.

Goal and scope
The paper presents the results of life cycle assessments (LCA) performed for three bridges in which UHPC was an essential part of the structure.The results comprise only the assessment of the materials used for the bridges including the raw materials and the infrastructure necessary for production.Heat treatment of UHPC, transport to the construction, maintenance as well as disposal of the bridges has not yet been considered.The functional unit is one section of each bridge without foundation.Due to lack of information, the bridge railing is not considered in this study.

Inventory data
Materials used and origin if materials data are presented in (Table 5).The life cycle inventory analysis and impact assessment were carried out using SimaPro version 7.1 software.The data required to construct a product were retrieved from the econinvent database as well as from our own data compilation.

Life cycle impact assessment and results
The ecological effects of global warming (GWP100), depletion of the stratospheric ozone (ODP), photo-oxidant formation (POCP), acidification (AP) and eutrophication (NP) were adopted as impact category indicators.

Conclusions
The results show that UHPC used in the Sherbrooke footbridge and the Gärtnerplatz footbridges causes approximately 60 to 85% of the environmental impact.The Wapello road bridge has a somewhat smaller contribution from UHPC to the environmental impact, ranging from 44 to 74%.As well as UHPC, in particular normal concrete in the bridge deck, the steel reinforcement of the bridge deck and the prestressing of the UHPC contribute appreciably to the effect on the environment.(Fiala et al., 2013)

Goal and scope
A LCA approach from cradle to the gate is presented in environmental analysis of three alternatives of experimentally verified subtle columns.Relevant LCA is based on local environmental data collected within the inventory phase of the LCA procedure.Environmental assessment was evaluated for three selected alternatives of subtle columns.The environmental analysis covers transport of the raw material to the concrete plant and production of prefabricated elements in the plant.

Inventory data
Aggregated impact data of construction life phase is presented in (Table 6).Source: Fiala et al. (2013).

Life cycle impact assessment and results
The life cycle impact assessment results are presented in Table 7 for the different impact categories.

Conclusions
The first solution labeled V1 presents higher impact assessment results.It can be seen that major part of these impacts comes from steel fibers used in high performance concrete composition, cement and admixtures also increase environmental impacts for high performance concrete.

Conventional concrete (35 Mpa) vs High performance concrete
Table 8 and Table 9 gather the life cycle inventory for conventional concrete and high performance concrete respectively.Source: Author, 2024.
Figure 4 shows a comparison of the two concrete solutions for the different impact categories.For the four selected impact categories the conventional concrete (35 MPa) resulted in greater environmental impacts than high performance concrete (59 MPa).However, further analysis should be conducted using primary data.
Compared to the "Reducing environmental impact by increasing the strength of concrete" study by Habert et al. (2012), the result of this study agrees that the use of concrete with high and ultra-high performance characteristics results in lower environmental impacts than conventional concrete.As for the "Methodology of life-cycle assessment or RC structures using high performance concrete" study by Fiala et al. (2013) this study concludes that the use of HPC results in higher environmental impact due to the use of steel fibers which is not the case of our study.It must be clarified that the comparison between the present study and others from literature is very difficult and not always possible since the functional unit, system boundaries, product composition and other aspects of the LCA are different.Carefully attention must be paid to the interpretation of the water depletion indicator which include water flows for all background processes.

Conclusions
Results show better environmental performance for high performance concrete in all four studied indicators (climate change, fossil depletion, human toxicity and water depletion).In addition to better environmental performance, it must be noted that high performance concrete also results in benefits regarding dematerialization since it is needed less volume of high performance concrete than in the conventional concrete case for the same function.It can be said that using high performance concrete represents an opportunity to improve environmental performance in civil construction.Nevertheless, the effective application and quality of results of LCA are dependent on the availability of relevant input data obtained using a detailed inventory analysis, based on specific regional data sources.

Acknowledgments
The author acknowledges the support of the Sistema Nacional de Investigación (SNI) of Panamá.

Authors' Contributions
Yazmin Lisbeth Mack-Vergara: research, conceptualization, writing of the article and publication.

Conflicts of Interest
No conflicts of interest.

Ethics Approval
Not applicable.

Figure 1 .
Figure 1.Graphic representation of the product system.Source: Author, 204.

Table 1 .
Properties, dimensions and volume for two concrete options.

Table 3 .
Energy demand and emissions to air.

Table 2 .
Concrete mix designs used during the life cycle of both bridges solutions.

Table 3 .
Concrete composition for each bridge.

Table 6 .
Balance of input data of construction life phase.

Table 7 .
Aggregated impact data of construction life phase.

Concrete production process data inventory Placing concrete into truck process data inventory
The life cycle inventory results are presented in Table including different activities and materials for concrete production.