Comparative Life Cycle Assessment of Ultra-High-Performance Concrete with Graphene Oxide ^†

Abstract

This study aimed to compare the environmental impacts of conventional concrete and ultra-high-performance concrete with graphene oxide. Four scenarios were considered: (1) samples comprising conventional concrete and (2, 3 and 4) comprising variations of ultra-high-performance concrete with graphene oxide at different doses. The environmental impact analysis was carried out using Life Cycle Assessment methodology. For impacts per MPa of compression strength, the scenarios showed a much lower environmental impact than scenario 1. Therefore, ultra-high-performance concrete with graphene oxide has the potential to support environmentally friendly construction if it results in less demand for concrete.

1. Introduction

Nanotechnology is an emerging field of research in which there is a high potential to support sustainable development in the building sector, as nanomaterials like graphene oxide (GO) present interesting physical properties that can be used to produce enhanced construction materials, including ultra-high-performance concrete (UHPC). UHPC can be defined as a cementitious material presenting high strength, toughness, and durability [1], mainly due to its very high packing density [2]. It is important to outline that UHPC can achieve compressive strength above 150 MPa by reducing the water−binder ratio [3]. In particular, UHPC, with the addition of graphene oxide, arises as a potential mix for high-performance concrete through the incorporation of nanomaterials in the concrete matrix. Indeed, the addition of graphene oxide seems to enhance the mechanical properties and chloride penetration resistance of UHPC [4]. Several studies have been conducted on ultra-high-performance concrete (UHPC) to enhance the mechanical properties of this construction material [4,5,6]. However, the benefits of this new material to the natural environment still need to be assessed.

In the context of environmental impact analysis, the use of Life Cycle Assessment (LCA) is a robust alternative, as this methodology adopts a systematic, comprehensive, and standardized process to assess the environmental impacts of a product or activity using a cradle-to-grave way of thinking [7,8]. LCA can be used to quantitatively estimate the environmental impacts involved in the production of construction materials, as it is a suitable tool to estimate the benefits or drawbacks of new types of concrete mixes.

So, this study aims to compare the environmental impacts of conventional concrete and UHPC with graphene oxide (GO) by applying Life Cycle Assessment (LCA).

2. Materials and Methods

2.1. Scenarios Considered

The analysis of environmental impacts was based on a comparative LCA, in which different concrete mix impacts were estimated and compared. Four scenarios were considered: (1) conventional concrete with a compression strength of 30 MPa, (2) UHPC without graphene, (3) UHPC with a low content of GO, and (4) UHPC with a high content of GO. The quantities of raw materials used and the mechanical properties considered for UHPC concrete mixes in each scenario were obtained in [9]. Based on the same reference, the compression strength used for scenarios 2 to 4 were 160 MPa, 160 MPa, and 180 MPa, respectively.

2.2. Life Cycle Assessment

LCA was conducted following the procedures recommended by the International Standards ISO-14040 [8] and ISO-14044 [10]. LCA was performed in four phases: goal and scope definition, Life Cycle Inventory (LCI), Life Cycle Impact Assessment (LCIA), and Interpretation. LCA was carried out using the software OpenLCA^®v2.2, described in [11]. Two functional units (FU) were adopted in order to compare the environmental impacts of the different concrete mixes in terms of the amount of concrete produced and performance. FU related to concrete amount was 1 m³ of concrete, and FU to represent performance was 1 MPa of compression strength.

2.2.1. Goal and Scope Definition

The goal and scope step aimed to depict the LCA’s objective and the system boundaries. This study aims to compare the environmental impact assessment of different concrete mixes, including UHPC with and without GO. The scope of this study comprises the extraction and manufacturing stages of the raw materials used in the production of concrete mixes used in each scenario.

2.2.2. Life Cycle Inventory

LCI is intended to estimate the input for resources used and output flows (emissions) for the analyzed system. The GO inventory was obtained in [12] and is presented in

Table 1. Inventory of input materials used for the production of 1 mg of graphene oxide using Hummer’s method according to [11].

Flow	Unit	Value
Graphite	mg	5.1
Electricity	kJ	1.21
Water	g	2.04
Potassium permanganate	mg	15.3
Sodium nitrate	mg	2.55
Sulfuric acid	mg	216
Hydrazine	mg	0.89
Hydrogen peroxide	mg	7.4

, assuming that it was produced using Hummer’s method [13]. This GO production approach is the most common approach and consists of the oxidation of graphite using potassium permanganate, sodium nitrate, and sulfuric acid [14]. The oxidized graphite is then reduced using hydrazine [12].

Flows involved in the production and processing of the materials used in each scenario were obtained in the LCI database Ecoinvent version 3.11, whose assumptions and methodological details are described in [15]. In terms of geographical representation, processes from the aforementioned LCI database were chosen to reflect technologies used in European Union (EU). In terms of electricity mix, it was adopted the EU average electricity mix in 2024.

The materials used for scenario 1, which refers to conventional concrete, were obtained in [15]. As mentioned in Section 2.1, inputs for scenarios 2 to 4 were obtained in [9]. So, the inputs used for each scenario are highlighted in Table 2.

Table 2. Inventory of input materials used for the 4 scenarios expressed in kg/m³ of concrete, based on [9,16].

Input Material	Unit	Scenarios
		Scenario 1 [16]	Scenario 2 [9]	Scenario 3 [9]	Scenario 4 [9]
Cement	kg	325	638.7	638.7	638.7
Water	kg	160	179.6	179.6	179.6
Sand	kg	660	1207	1207	1207
Gravel	kg	1300	0	0	0
Graphene oxide	kg	0	0	0.1996	0.3992
Plasticizer	kg	0	20	21	24.5

Table 2. Inventory of input materials used for the 4 scenarios expressed in kg/m³ of concrete, based on [9,16].

Input Material	Unit	Scenarios
		Scenario 1 [16]	Scenario 2 [9]	Scenario 3 [9]	Scenario 4 [9]
Cement	kg	325	638.7	638.7	638.7
Water	kg	160	179.6	179.6	179.6
Sand	kg	660	1207	1207	1207
Gravel	kg	1300	0	0	0
Graphene oxide	kg	0	0	0.1996	0.3992
Plasticizer	kg	0	20	21	24.5

2.2.3. Life Cycle Impact Assessment

Life Cycle Impact Assessment (LCIA) was performed using ILCD 2011 Midpoint+ [17]. The midpoint impact categories and respective units used in the LCIA are provided in

Table 3. List of midpoint impact categories and respective units used in the Life Cycle Impact Assessment [17].

Impact Category	Unit
Acidification	molc H+ eq
Climate change	kg CO2 eq
Freshwater ecotoxicity	CTUe
Freshwater eutrophication	kg P eq
Human toxicity, cancer effects	CTUh
Human toxicity, non-cancer effects	CTUh
Ionizing radiation HH	kBq U235 eq
Land use	kg C deficit
Marine eutrophication	kg N eq
Resource depletion	kg Sb eq
Ozone depletion	kg CFC-11 eq
Particulate matter	kg PM2.5 eq
Photochemical ozone formation	kg NMVOC eq
Terrestrial eutrophication	molc N eq
Water resource depletion	m3 water eq

.

2.2.4. Results Interpretation

The results were interpreted using tables and graphical representation. Moreover, a sensitivity analysis using the Monte Carlo simulation approach was performed regarding the background processes used in this study, using the uncertainty information available in the LCI database Ecoinvent 3.11 [15]. A total of 1000 iterations were carried out for each scenario and the sensitivity results were presented as Relative Standard Deviation for each impact category.

3. Results and Discussion

3.1. Impact Category Results

Table 4. Impact category results for each scenario per m³ of concrete produced.

Impact Category	Scenarios
	Scenario 1	Scenario 2	Scenario 3	Scenario 4
Acidification	7.13 × 10−1	1.51 × 100	2.28 × 100	3.09 × 100
Climate change	3.09 × 102	6.22 × 102	6.74 × 102	7.31 × 102
Freshwater ecotoxicity	1.52 × 103	3.44 × 103	5.22 × 103	7.13 × 103
Freshwater eutrophication	3.27 × 10−2	7.28 × 10−2	1.03 × 10−1	1.35 × 10−1
Human toxicity, cancer effects	2.80 × 10−5	4.89 × 10−5	6.34 × 10−5	7.93 × 10−5
Human toxicity, non-cancer	3.24 × 10−5	7.31 × 10−5	1.08 × 10−4	1.45 × 10−4
Ionizing radiation HH	1.05 × 101	2.01 × 101	3.74 × 101	5.50 × 101
Land use	4.15 × 102	3.87 × 102	4.32 × 102	4.82 × 102
Marine eutrophication	2.18 × 10−1	4.23 × 10−1	4.77 × 10−1	5.36 × 10−1
Resource depletion	1.97 × 10−3	5.27 × 10−3	7.04 × 10−3	9.10 × 10−3
Ozone depletion	1.13 × 10−6	3.17 × 10−6	3.94 × 10−6	4.87 × 10−6
Particulate matter	4.53 × 10−2	9.92 × 10−2	1.49 × 10−1	2.02 × 10−1
Photochemical ozone formation	6.64 × 10−1	1.32 × 100	1.49 × 100	1.67 × 100
Terrestrial eutrophication	2.46 × 100	4.70 × 100	5.12 × 100	5.59 × 100
Water resource depletion	7.13 × 101	1.16 × 102	1.98 × 102	2.82 × 102

and

Table 5. Impact category results for each scenario per MPa of concrete compression strength.

Impact Category	Scenarios
	Scenario 1	Scenario 2	Scenario 3	Scenario 4
Acidification	2.38 × 10−2	9.41 × 10−3	1.43 × 10−2	1.72 × 10−2
Climate change	1.03 × 101	3.89 × 100	4.22 × 100	4.06 × 100
Freshwater ecotoxicity	5.06 × 101	2.15 × 101	3.26 × 101	3.96 × 101
Freshwater eutrophication	1.09 × 10−3	4.55 × 10−4	6.45 × 10−4	7.50 × 10−4
Human toxicity, cancer effects	9.33 × 10−7	3.05 × 10−7	3.96 × 10−7	4.41 × 10−7
Human toxicity, non-cancer	1.08 × 10−6	4.57 × 10−7	6.73 × 10−7	8.04 × 10−7
Ionizing radiation HH	3.51 × 10−1	1.25 × 10−1	2.34 × 10−1	3.06 × 10−1
Land use	1.38 × 101	2.42 × 100	2.70 × 100	2.68 × 100
Marine eutrophication	7.26 × 10−3	2.64 × 10−3	2.98 × 10−3	2.98 × 10−3
Resource depletion	6.58 × 10−5	3.29 × 10−5	4.40 × 10−5	5.06 × 10−5
Ozone depletion	3.76 × 10−8	1.98 × 10−8	2.46 × 10−8	2.71 × 10−8
Particulate matter	1.51 × 10−3	6.20 × 10−4	9.31 × 10−4	1.12 × 10−3
Photochemical ozone formation	2.21 × 10−2	8.25 × 10−3	9.30 × 10−3	9.29 × 10−3
Terrestrial eutrophication	8.18 × 10−2	2.94 × 10−2	3.20 × 10−2	3.11 × 10−2
Water resource depletion	2.38 × 100	7.23 × 10−1	1.23 × 100	1.57 × 100

present the environmental impact category results for the four scenarios.

Table 4 shows that for impact assessed per m³ of concrete produced, scenarios with UHPC (scenarios 2, 3, and 4) led to a much higher environmental impact for most of the impact categories compared to conventional concrete results (scenario 1). This was already expected, as the rate of cement in UHPC was much higher than in conventional concrete, leading to an increase in environmental impacts directly related to cement consumption.

This can be seen in Figure 1, which shows the impact ratio for scenarios 2 to 4 compared to scenario 1, considering FU impacts per m³ of concrete. This explains the difference in the climate change impact category, in which the demand for cement plays an important role in the result of that category. Indeed, the climate change emissions for scenario 4 are 731 kg CO₂eq, which is 2.4 times higher than for scenario 1 (309 kg CO₂eq).

For mineral resource depletion, scenarios 2 to 4 also presented a much higher impact than scenario 1. This is also related to the higher cement rate in UHPC, and was even worse in scenarios 3 and 4, due to the additional demand for resources used in the production of GO. Regarding eutrophication, scenarios 3 and 4 presented a much higher impact due to phosphate emissions linked to chemicals required for GO production.

For acidification, impacts in this category were mainly related to nitrogen oxides and sulfur dioxides emissions during clinker production, followed by plasticizer manufacturing related flows. Concerning water depletion, it can also be seen that the scenarios including GO in concrete also resulted in 3 times more impact for that category than the baseline case (scenario 1), mainly due to the water demand related to GO production, as the water ratio from conventional concrete and UHPC is not very different, as shown in Table 2.

According to Table 5, when impacts are assessed per MPa of compression strength, the UHPC scenarios showed a much lower environmental impact than scenario 1. This can be seen in Figure 2, which shows the impact ratio for scenarios 2 to 4 compared to scenario 1, considering impacts per MPa of compression strength. Differently from what is shown in Figure 1, in this case, all impact categories have lower impacts in scenarios 2 to 4 than in scenario 1.

Actually, scenario 2, which considered UHPC without GO, resulted in equal or lower environmental impacts than scenarios 1, 3, and 4 in all impact categories. Scenarios 3 and 4 also had lower impacts than scenario 1 for all of the impact categories. Still, they also had higher values than scenario 2 for all impact categories. Notably, scenario 4, with a higher content of GO, resulted in a higher environmental burden than scenario 2 due to a higher increase in impacts through the addition of GO compared to the increase in strength (from 160 MPa to 180 MPa). Especially in terms of resource demand, the addition of GO in UHPC resulted in a high impact in resources depletion and water scarcity, as presented in Figure 2. This indicates that GO has the potential to contribute to the reduction in impacts for different categories as it enables an increase in concrete strength for UHPC, but the enhancement of the GO manufacturing process would be required mainly in terms of resources demanded for the production. Since the LCI data for GO production were based on small-scale laboratory tests, the scalability of GO manufacturing process could be supportive to reduce environmental impacts by considering commercial production of this material. However, the degree to which this contributes should be further investigated.

It is important to highlight that this study did not consider the effect of GO in the durability of concrete, which can also be another aspect that can contribute to lowering the impacts of UHPC, provided that it is expected that GO will enable increased concrete durability and, therefore, service life. For this reason, it is highly recommended to include durability studies in further studies in order to better compare the benefits of adding GO in UHPC.

On the one hand, a reduction in concrete demand for UHPC is expected compared to conventional concrete due to the increase in compression strength. On the other hand, the reduction in concrete demand would not necessarily be proportional to the increase in compression strength, as design codes and standards typically impose limitations in the design of concrete elements, which can undermine the benefit of the increased strength, mainly for the scenario with the higher strength values (scenario 4). Minimum cover, sectional dimension limits, and minimum reinforcement rates are just some examples of typical requirements defined in codes for reinforced concrete design that can limit the reduction in concrete demand when using UHPC. So, in order to better determine the real benefit of UHPC with GO, it is recommended that further research considering a specific structural design case in which the functional unit adopted will be impacts per unit of structural capacity. Anyways, the use of UHPC with GO is not only a solution for enhancing the mechanical properties of concrete, but also has the potential to contribute to more sustainable construction. This analysis should be conducted case by case, considering not only the concrete mixes but also the implications of those choices in structural design and the final project.

3.2. Sensitivity Analysis Results

Concerning the sensitivity analysis, the results of the Monte Carlo simulation resulted in the following variability, presented in

Table 6. Sensitivity analysis presented in terms of Relative Standard Deviation of results by impact category for each scenario.

Impact Category	Scenarios
	Scenario 1	Scenario 2	Scenario 3	Scenario 4
Acidification	10%	9%	7%	6%
Climate change	9%	8%	7%	7%
Freshwater ecotoxicity	22%	25%	21%	18%
Freshwater eutrophication	47%	45%	45%	49%
Human toxicity, cancer effects	38%	46%	46%	41%
Human toxicity, non-cancer	23%	22%	23%	19%
Ionizing radiation HH	123%	126%	159%	140%
Land use	46%	72%	60%	57%
Marine eutrophication	13%	13%	12%	11%
Resource depletion	29%	29%	24%	22%
Ozone depletion	9%	11%	9%	9%
Particulate matter	10%	13%	11%	10%
Photochemical ozone formation	12%	12%	11%	10%
Terrestrial eutrophication	13%	13%	13%	11%
Water resource depletion	4%	5%	3%	3%

. For most of the impact categories, sensitivity analysis resulted in a relative standard deviation below 20%. Notably, for climate change and acidification, the values were below 10%, indicating the reliability of the aforementioned discussion in which these categories were mentioned.

However, eutrophication, land use, human toxicity, and resource depletion impact categories have a relative standard deviation in the range of 20% to 50%, which indicates a significant degree in variability. In particular, for ionizing radiation, relative standard deviation was higher than 120%, for all scenarios, which means that the range of variation of values exceeded the average value of impact, indicating a high uncertainty in the results, which means that the results for this impact category must not be used as hotspot for comparison due to the high degree of variation. So, this indicates the need for further studies better addressing the sensitivity of results not only in terms of background processes, but also considering other aspects like energy sources, electricity mixes, cement types, and GO production processes.

4. Conclusions

This paper presented the results of a comparative LCA addressing different mixes of UHPC using graphene oxide. From the LCA results in terms of impact per volume of UHPC produced with or without GO does not seem to be a good choice regarding environmental protection. However, considering the increase in strength of UHPC, a decrease in the volume used is also expected to occur, which can lead to an overall reduction in environmental impacts. Compared to conventional concrete, UHPC with GO has a high potential to support more environmentally friendly construction in applications in which this type of concrete can result in a significant reduction in concrete demand that compensates for the increase in impact per volume of concrete products. However, additional studies are required to better compare the benefits of GO for the enhancement of UHPC itself. So, further research is also recommended to explore the following aspects:

• Carry out a similar analysis using a specific design using the impact per unit of structural capacity the Functional Unit in order to enable the identification of the break-even point, in which UHPC with GO starts to present a lower environmental impact than conventional concrete;
• Compare how the final LCA results of the UHPC will be impacted by considering other methods for the production of GO, as well as effects related to the production of GO at a commercial scale;
• Incorporate service life in LCA for the impact of UHPC with GO, as it can result in enhanced durability of concrete;
• Perform regionalized LCA for different regions worldwide in order to compare the dependence of UHPC with GO benefits on local characteristics.