Carbon Footprint Assessment: Case Studies for Hemp-Based Eco-Concrete Masonry Blocks

Abstract

In recent times, climate change has become more evident than ever, and measures to slow down its negative effects are imperative for the future of the world. The scientific and economic communities of countries around the world, under the force of international climate agreements, are identifying solutions to reduce greenhouse gas (GHG) emissions by establishing appropriate measures and developing new strategies. In the context of these objectives, the effort to identify eco-sustainable practices for the construction industry is growing significantly. Recently, much research has focused on solutions for producing green building materials, as well as applying circular economy principles to achieve a balance between anthropogenic emissions and absorptions by greenhouse gas absorbers. The relevant indicators of the level of achievement of these major objectives can be identified, already from the construction design phase, with the help of Life Cycle Assessment (LCA) analysis. This paper presents a series of environmental impact analyses for an eco-friendly solution of precast concrete masonry blocks. Ecological concrete is manufactured with aggregates from biological waste resulting from hemp crops. Impact assessments were performed with the SimaPro 9.5 software application. Research has shown that in the production chain, which includes the materials resulting from the recycling and reuse of hemp concrete blocks, the contribution to the effort to achieve neutrality in terms of global warming is significant. The Cradle-to-Cradle scenario revealed that the recycling of hemp concrete masonry blocks at the end of their use, for a functional unit of 0.5 m³, has a GHG emission of 33.5228 [kg CO₂-eq] and CO₂ uptakes can reach the negative value of −53.8397 [kg CO₂-eq]. Thus, the balance of GHG emissions is negative, with values of approximately −20.3169 [kg CO₂-eq]. The LCA analyses also reflect a decreased damage to human health, natural resources, and biodiversity when hemp concrete is used for masonry blocks.

1. Introduction

The European Climate Law (ECL) [1] has a main target of zero emissions by 2050, the first step being the reduction in GHG emissions by at least 55% until 2030, compared to levels in 1990. The ECL includes a recognition of the need to enhance the EU’s carbon sink through a more ambitious Land Use, Land Use Change and Forestry (LULUCF) regulation, and a commitment to negative emissions after 2050 [1]. The rules governing the accounting and reporting of greenhouse gas emissions from LULUCF under the Kyoto Protocol are contained in several decisions of the Conference of Parties under the United Nations Framework Convention on Climate Change (UNFCCC). The Kyoto Protocol is an international treaty that expands the UNFCCC from 1992 and obliges states to reduce GHG emissions. The Kyoto Protocol was adopted in Kyoto, Japan, in 1997 and entered into force in 2005. The Commission’s proposal for a revised LULUCF regulation brings to the fore the need to increase the carbon sequestration potential to eliminate GHGs in the current decade [2]. EU institutions and member states are making sustained efforts to implement the necessary measures for the achievement of this major objective, both at the European and national levels.

The data report published by the EU Commission in 2023 [3] highlights that global GHG emissions show an upward trend, mainly due to their increase in countries with emerging economies. The data recorded show that GHG emissions have increased dramatically, with the side effect of global warming. Global temperatures have accelerated over the past 30 years and are now at their warmest since records began. The substantial increase in atmospheric concentrations of greenhouse gases, with obvious consequences in global warming, can negatively affect life on Earth. Scientists agree that GHGs are the cause of climate change [4,5].

The main contributor to global GHG emissions is CO₂, which continues to rise worldwide, despite climate change mitigation agreements. The report [3] and the databases from [4] reveal that CO₂ emissions, globally estimated by economic sectors, have an increasing trend in the period 2003–2022, as is shown in Figure 1.

The graphs presented in Figure 1, in accordance with the data reported in [2,3,4], highlight without a doubt that, globally, CO₂ emissions, the main contributor to GHGs, have positive values in a trend of annual growth.

The arguments presented in the previous analyses show that the prevention of global warming requires a sustained effort through measures and strategies applied worldwide. The mandatory objective of zero net emissions by 2050 requires the identification of solutions for clean energy systems, as well as solutions for the decarbonization of practices with high emissions—such as construction, energy production, and transport. In the fields of energy production and transport, in recent decades important steps have been taken to replace fossil fuel emissions with environmentally friendly alternatives. The construction sector cannot be appreciated in the same way.

The construction sector is by far the largest emitter of greenhouse gases, accounting for a staggering 37% of global emissions. The production and use of materials such as cement, steel, and aluminum have a significant carbon footprint [6]. Much of the sector’s progress has focused on reducing carbon emissions from building operations—these emissions are valued at 75% of the total, and come from heating, cooling, and lighting. It is estimated that these operational emissions will decrease to 50% of the construction sector’s total emissions in the coming decades [6]. In order to lower the contribution to carbon dioxide emissions even further, it is necessary to identify solutions to mitigate the carbon emissions embedded in buildings, which come from the manufacturing processes of the materials used or from the construction technologies of the buildings.

Building materials are responsible for 11% of global carbon emissions [7] and as the building industry continues to look for ways to lower its carbon footprint, scientists, architects, and manufacturers alike are turning to natural materials. Studies have focused, in recent years, on identifying solutions for the manufacture of ecological construction materials, as well as on the application of the principles of the circular economy, which extends the life cycle of products and ensures the minimization of waste. In addition to the significant impact on the annual reduction in total GHG emissions, some solutions can favor carbon sequestration, known as “carbon sinks”.

To effectively address this challenge, cross-cutting research actions and multidisciplinary collaborations need to be rapidly developed to identify valid solutions to reduce CO₂ emissions throughout the construction life cycle. This is crucial to mitigating the environmental impact of the construction industry. The carbon footprint of the construction industry can be significantly reduced by adopting sustainable practices, such as the efficient use of resources, local sourcing of materials, waste reduction, and the application of circular economy principles. Concepts such as a passive design methodology and the use of ecological materials, together with the integration of modern technology in buildings’ facilities for operations, are often mentioned in strategies for greening the built environment, achieving the target of reducing carbon dioxide emissions, and aligning with the global climate objectives by mid-century.

Hemp concrete is a bio-composite material fabricated as a mixture of hemp hurds (shives) and lime, cement, sand, or pozzolana, with some additives or additions. The potential of hemp as a natural aggregate has been known for centuries. The strength properties of hemp concrete do not show high performance, but, as a composite material, it has multiple possibilities for its characteristics’ improvement [8,9,10]. Hemp concrete is a light material, with high thermal and acoustic insulation properties and a positive impact on the environment [11,12]. Hemp concrete blocks are also very suitable for use in masonry construction. The blocks have an increased assembly productivity due to their large dimensions, favored by the very low density of the material. The mechanical, thermal, acoustic, and fire resistance properties of hemp concrete are appropriate for masonry walls in simple or hybrid structural compositions and in buildings for various uses, private or public [13].

Figure 2 shows examples of buildings where hemp concrete is used [14,15], highlighting the architectural potential of this eco-material.

Researchers at the University of Nebraska-Lincoln have developed a solution for the hemp-based concrete block that could support green construction. According to the team, innovation goes beyond simple construction, focusing on building a sustainable future [16]. Green constructions are also subjects of analysis in studies [17,18], in which the use of 3R principles is evaluated to determine future research opportunities to achieve a circular economy in the construction industry. The results of these studies offer interdisciplinary research perspectives on the use of hemp-based waste and materials.

One of the green advantages of hemp concrete is its ability to bind the greenhouse gas carbon dioxide (CO₂). Research in [19,20] reveals that when hemp concrete is used in precast masonry blocks, it acts as a carbon sink throughout its lifetime. Studies presented in [20,21,22] indicate higher values for carbon sequestration than the CO₂ produced during production and transportation, meaning that hemp concrete has a negative carbon footprint. James Vosper in his report entitled “The Role of Industrial Hemp in Carbon Farming” [23], presented in the Australian Parliament, mentioned that every ton of industrial hemp stems contains 0.445 tons of carbon absorbed from the atmosphere (44.46% of stem dry weight) [23]. These values bring out that industrial hemp is unmatched as a means of sequestering carbon dioxide and binding it permanently in the building elements manufactured using hemp concrete. The aim of the research presented in [24] was to assess the sustainability of hemp, quantified by an LCA, and particular attention was given to the CO₂ emissions of the whole process, and the CO₂ uptake of hemp was considered. In the technical literature, there are studies built on LCA analyses, which present the beneficial effect of hemp and hemp-based products on the global warming potential (GWP), assessed by the CO₂ emissions [25,26,27,28]. The study [25] evaluates the carbon content of hemp concrete used for construction and emphasizes the importance of considering the carbon incorporated in similar building materials to support a greener built environment. Also, in paper [24], the sustainability of hemp for construction applications is quantified by evaluating the life cycle of a construction panel, paying particular attention to the amount of CO₂-eq from the entire process, highlighting the result negative for GWP100 in the case of hemp use. The ability of hemp to absorb CO₂ during the photosynthesis process during its growth period is analyzed from the point of view of agricultural practices [26] and the environmental impact of the different fertilizer used is highlighted. An energy and environmental assessment of the hemp crop in France, carried out through a Life Cycle Assessment approach, is presented in paper [27], showing the positive and negative contributions related to the different phases of the hemp crop life cycle. The work [27] picked out that the total carbon footprint, for products that include hemp in various forms, is influenced not only by the CO₂ uptake, but also by the biogenic carbon captured and stored during the growth of hemp. The results from paper [28] support the idea that the production chain, which includes hemp, can be sustainable and carbon neutral, when all parts of the plant (especially the woody stem, usually considered as residue) are used in products manufacturing.

The study presented in this article was developed in an extensive research project and is focused on highlighting the contribution of hemp concrete, used in the production of prefabricated masonry blocks, to the reduction in carbon dioxide emissions, the emphasis being also on carbon sequestration, in various scenarios of LCA. Achieving building energy efficiency imperatives, while ensuring a reduction in the environmental impact of materials and technologies used in the construction sector, is a central concern in the sustainable design and operation of buildings. This study aims to explore, through methodologies implemented in dedicated software programs, the benefits that this ecological concrete brings to the problem of global warming. Computational evaluations were based on the statistical information found in current scientific reports to evaluate the environmental impact indicators of hemp concrete blocks.

This paper presents indicators, attached to the environmental impact analysis, for an original solution of prefabricated eco-concrete masonry blocks, manufactured with aggregates from hemp biological waste. The relevant indicators of the achievement level of these major objectives can be evaluated, even in the building design phase, with the support of an LCA methodology. The analysis of the potential impact on the environment of the products and services used that define a construction is carried out throughout its life cycle. Research has shown that in the production chain, which includes the materials resulting from the recycling and reuse of hemp concrete blocks, after the dismantling of buildings, the contribution to the effort to achieve neutrality in terms of global warming is significant.

This research highlights the multi-criteria approach required to achieve both reduced CO₂ emissions and the achievement of the decarbonization target. Increasing the implementation level of the solutions developed through this study, related to the use of ecological materials, complementary to the solutions obtained from the application of the circular economy principles, can lead to obtaining reduced parameter values, which generate the graphs presented previously (Figure 1), as defined by worldwide regulations.

2. Materials and Methods

In the first part of this study, information is presented regarding the composition of the hemp concrete used for the masonry blocks and the parameters’ values that were researched if they met the required performance in use: block’ compression strength, masonry compression strength, and average thermal conductivity.

The carbon footprint assessment for the hemp-based eco-concrete masonry blocks was then deepened, using the accredited software application SimaPro 9.5 [29], based on the LCA, and according to international standards ISO 14040 [30] and ISO 14044 [31]. The integration of this software tool enabled a comprehensive examination of how hemp concrete blocks influence the dynamics of carbon dioxide emissions in different usage scenarios. The environmental impact of hemp concrete masonry blocks was analyzed in two case studies: Case Study 1 was conducted applying the IPCC (Intergovernmental Panel on Climate Change) methodology and Case Study 2 used the ReCiPe 2016 Midpoint (H) V1.08 methodology.

2.1. Description of the Masonry Blocks Made of Hemp Concrete

The hemp concrete mixture used for casting the masonry blocks has the following components: hemp shredding, calcium oxide, Portland cement, water, and additives. The composition, presented in Figure 3, comprises quantities, for 1 m³ of hemp concrete, which are detailed in

Table 1. Composition of hemp concrete for hollow masonry blocks.

No.	Materials	Mass
		[kg]
1	Hemp shredding	110
2	Lime	80
3	Portland cement 42.5 R	80
4	Water	390
6	Sodium silicate Na2SiO3	11.25

. The ecological hemp-based concrete masonry blocks obtained by pressing the composition in the mold are presented in Figure 4b. The method of placing the blocks to obtain the masonry wall is shown in Figure 4a. The hardening period of the blocks was 28 days, and thermal conductivity, λ, and compressive strengths, f_b, were measured after, according to standard procedures. The property values are shown in

Table 2. Properties of hemp concrete masonry blocks.

No.	Properties	U.M.	Values
1	Dimensions—L × l × h	mm	570 × 200 × 230
2	Block weight	kg	13.20
3	Compressive strength of the block—fb	N/mm2	0.2683
4	Characteristic compressive strength of masonry—fk fk = K(fb)0.7(fm)0.3 where K = 0.7 (acc. to [33])	N/mm2	0.556
5	Average thermal conductivity of the block—λechiv	W/mK	0.2661

, based on experimental measurements. The characteristic compressive strength for masonry, f_k, is evaluated according to Eurocode no. 6 [32], as f_k = K(f_b)^0.7(f_m)^0.3, where K = 0.7 and the mortar compressive strength, f_m, is 10 N/mm². The low values for compressive strengths and the reasonable values for thermal conductivity recommend the use of hemp masonry blocks as thermal insulation layer filling elements in the wall structure.

From the composition presented in Table 1, 38 blocks were fabricated. It is observed that the hemp concrete blocks, as a result of the manufacturing technology by pressing in the mold, have a reduced density compared to the fresh material obtained after mixing the components. The weight, for 1 m³ of concrete, after the hardening period decreased from 671.25 kg to 503.43 kg due to the evaporation loss of approximately 168 kg of water. The coefficient of thermal conductivity was evaluated as the average of the values obtained differentiated for areas with and without hollows.

2.2. Carbon Footprint Assessment for Hemp-Based Eco-Concrete Masonry Blocks

The LCAs of hemp concrete, used as masonry blocks, are performed using the SimaPro 9.5 software [29] in two scenarios as follows:

• Cradle-to-Grave-scenario LCA from the production of hemp concrete to the end of the use period [34]. The Cradle-to-Grave scenario ends when the building, after the standard period of operation (100 years), is demolished, and the resulting waste is deposited at a landfill.
• Cradle-to-Cradle-scenario LCA from the production of hemp concrete to the end of the period of use, considering the recycling and reuse of newly obtained raw materials [33]. The Cradle-to-Cradle scenario means that the building, after its normal service life (100 years), is dismantled and the hemp concrete is reused as a recycled product (e.g., as recycled aggregates) in a new construction.

The results obtained were differentiated according to the impact evaluation method used:

• IPCC 2021 GWP100 V1.02 method—a global warming potential analyzing GWP100-fossil; GWP100-biogenic; GWP100-land transformation; and GWP100-CO₂ uptake [35];
• ReCiPe 2016 Midpoint (H) V1.08 method analyzing the potential pollutants with an effect on reducing the ozone layer, changing the soil structure, human health, diminishing mineral resources, consumption and water pollution from marine or continental ecosystems, land use, etc. [36].

The functional unit (FU) chosen for the LCA analyses was 0.5 m³ of hemp concrete in the form of masonry blocks detailed previously. The manufacturing technology of masonry blocks has the following steps:

• Step 1—The hemp shreds are hydrated in a sodium silicate–water solution for 24 h;
• Step 2—The hydrated hemp shreds are mixed with a calcium oxide–water solution and a cement–water solution;
• Step 3—The composition is poured into a mold and pressed.

The quantities of materials used in manufacturing stages are analyzed to determine the environmental impact of the hemp concrete; the indicators evaluated by the methods specified above are as follows:

• Sodium silicate (5.625 kg) mixed with water (55 kg);
• Calcium oxide (40 kg) mixed with water (120 kg) as a mineral binder;
• Cement (40 kg) mixed with water (20 kg) as a hydraulic mineral binder;
• Hemp shredding (55 kg), the ecological base material.

The environmental impact of hemp concrete masonry blocks was analyzed in two case studies:

➢

Case Study 1 was carried out applying the IPCC 2021 GWP100 V1.02 methodology;

➢

Case Study 2 was conducted applying the ReCiPe 2016 Midpoint (H) V1.08 methodology.

The LCA was performed by using the SimaPro software V9.5.0.2. To assess the environmental impacts of the hemp concrete masonry blocks examined, critical datasets were required. Background inventory data were drawn from the Ecoinvent database, version 3.9.1., specifically for the European Region (RER). The environmental impact was measured using the global warming potential (GWP) indicator, which estimates the contribution of emissions to global warming over 100 years, as defined by the Intergovernmental Panel on Climate Change. The impact of GHG emissions was quantified in terms of relative carbon dioxide and reported as an equivalent mass of carbon dioxide [kg CO₂-eq] [37]. The ReCiPe method allows for the assessment of ecological impact at two distinct levels: the midpoint (intermediate level, e.g., the amount of CO₂ emissions) and endpoint (final level, such as effects on human health and ecosystems). This dual approach provides a more detailed and comprehensive evaluation, enhancing the understanding of impact and critical intervention points.

3. Results

3.1. Case Study 1—The Results Obtained in the Assessment of Environmental Impact Indicators Applying the IPCC Methodology

The IPCC Working Group on Climate Change Mitigation develops methodologies for estimating anthropogenic and greenhouse gas emissions. One methodology includes the formulation and evaluation of the factors used to link the emission of a greenhouse gas, for a given source, to the amount of activity (products or services) that causes the emission. The methodology and software are internationally agreed upon for calculating and reporting greenhouse gas emissions [38]. Method used: IPCC 2021 GWP100 (incl. CO₂ uptake) V1.02, SimaPro 9.5 [29]. The obtained values are measured in [kg CO₂-eq].

In the Cradle-to-Grave scenario, presented in Figure 5, the values obtained for GWP indicators highlight a maximum value of 151.3181 [kg CO₂-eq] for GWP100-fossil, a value of 11.2959 [kg CO₂-eq] for GWP100-biogenic, while only a value of 1.3158 [kg CO₂-eq] for GWP100-land transformation. As a crop, hemp can capture atmospheric carbon more effectively than other plants/trees during its growing period. Also, in hemp concrete there is carbon stored via the carbonation of the binders. In this scenario, the sequestrated carbon is evaluated as the GWP100-CO₂ uptake indicator, and a negative value of –56.3215 [kg CO₂-eq] is obtained.

In the Cradle-to-Cradle scenario, presented in Figure 6, the values for GWP Indicators have significantly reduced, highlighting values of 14.3336 [kg CO₂-eq] for GWP100-fossil, 18.1019 [kg CO₂-eq] for GWP100-biogenic, 1.0872 [kg CO₂-eq] for GWP100-land transformation, and a value of –53.8397 [kg CO₂-eq], for GWP100-CO₂ uptake, which represents the sequestrated carbon.

3.2. Case Study 2—The Results Obtained in the Assessment of Environmental Impact Indicators Applying the ReCiPe Methodology

ReCiPe is a method of impact assessment (LCIA) in an LCA [39]. According to the presentation [39], an LCIA translates emissions and resource extraction into a limited number of environmental indicators or characterization factors.

There are two main ways to analyze environmental influences, namely: at the midpoint level and at the endpoint level. The ReCiPe methodology, based on midpoint indicators, calculates endpoint indicators by aggregation. Midpoint indicators refer to unique environmental issues, for example, climate change or acidification. The endpoint indicators, which show the impact on the environment, are evaluated for the effect on human health, biodiversity, and resource scarcity. Converting midpoints to endpoints simplifies the interpretation of LCIA results. Based on the aggregation scheme presented in [39], the values for the endpoint indicators are obtained.

Midpoint indicators are presented as percentages (%) in Figure 7. Their values were obtained from a Cradle-to-Grave scenario of hemp concrete masonry blocks. The SimaPro 9.5 software generated 18 midpoint indicators, shown graphically in Figure 7.

The results of the midpoint impact indicators for the materials used in manufacturing 0.5 m³ of hemp concrete reveal significant differences in environmental impacts across various categories. Calcium hydroxide and the silicate–water solution generally exhibit higher impacts across most environmental categories compared to the cement–water solution, hemp, and low-voltage electricity. Hemp shows notably higher water consumption and impacts in eutrophication and land use, while low-voltage electricity consistently presents lower impacts across the board:

• Silicate–water solution exhibits moderate impacts (under 30%) in categories like ionizing radiation and various ecotoxicity measures;
• Calcium hydroxide shows elevated impacts (over 50%) in several critical categories, including global warming, ionizing radiation, fine particle formation, and ecotoxicity;
• Cement–water solution has significant impacts on global warming and ozone formation, though it does not reach the highest thresholds (under 30%);
• Hemp shows considerable impacts (over 70%) in water consumption, marine eutrophication, and land use. These high values indicate the need for sustainable practices in hemp cultivation;
• Low-voltage electricity consumption has the lowest impact (under 1.5%) across all environmental categories considered, indicating that it is the least environmentally detrimental.

One distinct result that stands out is the negative 17% impact that hemp has regarding human non-carcinogenic toxicity. The negative value indicates that hemp, in comparison to other materials, has a positive impact on human non-carcinogenic toxicity. This can be attributed to the lower potential for hemp to cause non-cancerous health issues, which might be due to its natural composition and the absence of harmful chemicals typically associated with other materials. In this context, hemp offers health benefits by reducing potential non-carcinogenic toxicity and is visually represented on the axis in Figure 7.

In

Table 3. The endpoint indicators with the corresponding midpoint indicators in the LCIA-ReCiPe method.

No. Crt.	Endpoint Impact Indicators LCIA-ReCiPe Method	Midpoint Impact Indicators LCIA-ReCiPe Method
1	Damage to human life	Global warming
		Stratospheric ozone depletion
		Ionizing radiation
		Ozone formation, human health
		Formation of fine particles
		Human carcinogenic toxicity
		Human non-carcinogenic toxicity
		Water consumption
2	Damage to ecosystems	Ozone formation, terrestrial ecosystems
		Terrestrial acidification
		Eutrophication of fresh water
		Marine eutrophication
		Terrestrial ecotoxicity
		Ecotoxicity of fresh water
		Marine ecotoxicity
		Land use
3	Damage to resources availability	Lack of mineral resources
		Lack of fossil resources

, three endpoint indicators are presented, evaluated according to [39] from midpoint indicator values shown in Figure 7 as follows:

• Damage to human life from midpoint indicators;
• Damage to ecosystems from midpoint indicators;
• Damage to resources availability from midpoint indicators.

Regarding an overall view with respect to possible damage, the endpoint impact indicators summarized in Table 3 provide a comprehensive assessment of the environmental impacts associated with the materials used in the production of 0.5 m³ of hemp concrete masonry blocks. These indicators, derived from the Life Cycle Impact Assessment (LCIA) and using the ReCiPe method, offer insights into the potential damage these materials can inflict on human health, ecosystems, and resource availability.

Calcium hydroxide is the most detrimental to human life among the materials, with a notably high impact of almost 45%.

Regarding ecosystems, calcium hydroxide leads to the highest damage (over 38%), followed by hemp (31%). The cement–water solution and silicate–water solution have moderate impacts, while electricity has a negligible effect.

Calcium hydroxide, the silicate–water solution, and the cement–water solution have high impacts (especially calcium hydroxide at 47%) on resource availability, with hemp showing a relatively low impact (4%).

Figure 8 highlights the percentage contribution of materials used in hemp concrete masonry blocks to environmental impact indicators at the endpoint level. Hemp performs relatively well in terms of resource availability but shows moderate impacts on ecosystems. In contrast, calcium hydroxide exhibits the highest impacts across all categories, indicating significant environmental concerns, shown as red in Figure 8.

4. Discussion

The analysis of the carbon footprint generated by the production of hemp concrete masonry blocks aimed to highlight the advantages they have in multiple areas. The studies presented in this paper, carried out by two methods that can be developed through LCA analyses, were performed concerning an innovative solution of masonry blocks, based on extensive research about the optimization of resource consumption used in their manufacture. Also, the innovative solution, made in the form of hollow blocks, is part of the general optimization objective applied to masonry blocks (Figure 5), by designing a hemp concrete composition that meets both the requirements of energy efficiency and of resistance, imposed by the technical norms. The research depicted emphasizes the hemp contribution to global warming by measuring CO₂ emissions in the production chain of masonry blocks with two end-of-life scenarios, with and without recycling the materials.

The results obtained with the SimaPro 9.5 software, used for the LCA of masonry blocks, confirmed the advantages of using hemp-based ecological concrete to achieve climate neutrality. The results were evaluated for a functional unit of 0.5 m³ hemp concrete.

The analyses carried out in Case Study 1, based on the IPCC method, within the limits of the Cradle-to-Grave (CtG) and Cradle-to-Cradle (CtC) scenarios, (Figure 6 and Figure 7), contribute to estimate the impact that the waste hemp can produce through its uses in the construction sector, associated with the global warming potential (GWP), as CO₂ emissions, with the GWP100-fossil, GWP100-biogenic, or GWP100-thermal transformation indicators. Also, the LCA highlighted, in both the CtG and CtC scenarios, the existence of sequestered carbon, expressed through the CO₂ uptake indicator, which is given by absorption of CO₂ during the hemp growth period, and by the carbonation that occurs over the time periods of use, established in the analyzed scenarios.

The comparative analysis of the results obtained in the two scenarios, CtC/CtG, presented in Figure 9, highlights the positive influence regarding the reduction in the GWP indicators in the case of adopting a circular economy model—the CtC scenario. Thus, it is found that in the CtC scenario, when the reused materials represent 95% of the hemp concrete used for masonry blocks (functional unit), the indicators have values as follows: the GWP100-fossil reduces from 151.2524 to 14.3336 [kg CO₂-eq], the GWP-biogenic indicator increases from 11.2941 to 18.1019 [k kg CO₂-eq], and the GWP100-land transformation reduces from 1.3158 to 1.0872 [kg CO₂-eq], while the influence of the GWP100-CO₂ uptake indicator is still negative with a value of −53.8397 from −56.3215 [kg CO₂-eq].

A summation of the emission values expressed by the four indicators shows that in the CtG scenario, the total GWP impact has a positive value of 107.6084 [kg CO₂-eq], while in the CtC scenario, the total GWP impact has a negative value of −20.3168 [kg CO₂-eq]. This result found in the CtC scenario shows that more GHG emissions are absorbed than emitted into the atmosphere. The benefit is brought by the combined contribution of the CO₂ sequestered in the hemp concrete (resulting from the absorption during the hemp crop growth, and by binding it through the carbonation of the binder) as well as the application of the circularity principle, the recycling of materials at the end of the life cycle for masonry blocks. The increase in GWP100-biogenic is due to the municipality waste, especially (5% of initial materials used).

In Case Study 2, using the ReCiPe method, the midpoint and endpoint indicators are analyzed for hemp concrete in the CtG scenario.

The midpoint indicator results presented in Figure 7 highlight that hemp has a negative percentage contribution to the human non-carcinogenic toxicity midpoint indicator, of −17.0731%, while all other materials have high positive influences, for example, of 56.5298%, as pointed out for calcium hydroxide, or 14.4162% in the case of the cement–water solution.

The endpoint impact indicator values, shown in Table 3 and Figure 8, emphasize that hemp has a lower influence than the contributions of the other materials used. For the damage to human life endpoint impact indicator, it is found that the influence of hemp is 15.712% out of 100%, the remaining 84.288% being caused by the other materials used in the composition of hemp concrete. The damage to resources availability endpoint impact indicator is influenced by hemp in the percentage of 4.0595% of 100%, in comparison with 95.9405% due to the other materials used.

The LCIA analyses in the ReCiPe method show the reduced contribution of endpoint indicators, generated by the presence of hemp in the composition of hemp concrete. The positive, but much reduced, and in some cases even negative, values brought on by hemp compared to other materials reflect a decreased damage to human health, natural resources, and biodiversity when this ecological material is used.

5. Conclusions

Research has shown that in the production chain, which includes the materials resulting from the recycling and reuse of hemp concrete blocks, after the dismantling of buildings, the contribution to the effort to achieve neutrality in terms of global warming is significant.

The research carried out and presented in this paper highlighted the following aspects:

• Hemp concrete has been used successfully in various multi-purpose buildings and renovation projects. Solutions for masonry blocks based on hemp concrete, with their proven thermo-mechanical performances, can expand the range of applications. Its versatility and adaptability demonstrate the potential of this eco-sustainable material for widespread use in the construction industry.
• Masonry blocks made of hemp concrete have low values of compressive resistance, which, however, ensure shape stability and maneuverability during assembly. These characteristics, combined with the reasonable thermal conductivity values, constitute an advantage for their use as filling elements of the thermal insulation layer in the wall structure.
• Hemp concrete has a significantly lower carbon footprint compared to traditional concrete materials.
• Hemp crops absorb carbon dioxide, making hemp a carbon-negative material, and its use as a building material has a positive influence by reducing GHG emissions and reaching the decarbonization target in the construction sector.
• The LCA research emphasized that, for 0.5 m³ of hemp concrete used in masonry blocks, there are CO₂ uptake values of −53.8397 [kg CO₂-eq] in the Cradle-to-Cradle scenario and of −56.3215 [kg CO₂-eq] in the Cradle-to-Grave scenario.
• Recycling and the use of shredded hemp in masonry blocks have a significant contribution, and positively influence the balance in CO₂ emissions, according to the GWP indicators.
• According to the Cradle-to-Cradle analysis, using the IPCC methodology, it was found that recycling hemp concrete masonry blocks at the end of their lifespan, for a functional unit of 0.5 m³, results in GHG emissions of 33.228 [kg CO_2-eq]. Additionally, the blocks have the capacity to sequester carbon dioxide, with an uptake value of −53.8397 [kg CO₂-eq]. Therefore, the overall GHG balance is negative, totaling approx. −20.3168 [kg CO₂-eq].
• Balancing the indicators’ values, it is observed that for the Cradle-to-Cradle scenario the results show a negative carbon footprint of −20.3168 [kg CO₂-eq], and in the Cradle-to-Grave scenario the result is a positive carbon footprint of 107.6084 [kg CO₂-eq].
• The environmental evaluation of the ReCiPe method offers both midpoint and endpoint indicators. This dual-level approach affords a detailed analysis (midpoints) or a more simplified, overarching view of environmental impacts (endpoints). The method targets environmental impact assessment to convert LCIA goals to a limited number of impact scores at a midpoint or endpoint level.
• The LCIA analyses in the ReCiPe method reflect a decreased damage to human health, natural resources, and biodiversity when hemp concrete is used for masonry blocks.
• Economic circularity in the construction sector is possible if capacities are developed for the dismantling and recycling of hemp concrete construction elements after the end of the building’s life, so that at least 95% of the materials are reused (as aggregates for example) to obtain new eco-sustainable hemp concrete masonry blocks.
• Hemp concrete is emerging as a viable solution for sustainable construction. As the environmental impact of traditional concrete becomes apparent, innovative alternatives such as hemp concrete in various forms of use are gaining importance. Its environmental benefits and structural advantages place hemp concrete in the category of materials that can bring changes in the practices and principles in the construction industry. Using hemp concrete can help reduce the carbon footprint, creating healthier environments for future generations. Multidisciplinary research and collaborations are crucial to the widespread adoption of hemp concrete and the achievement of a sustainable built infrastructure.