Evaluating the Environmental Impacts and Social Risks of Limestone Calcined Clay Cement (LC³) Mortars

Abstract

Cement production significantly contributes to global CO₂ emissions. Limestone Calcined Clay Cement (LC³)—a mixture of limestone, calcined clay, cement clinker, and gypsum—offers a promising alternative by significantly reducing clinker contents without compromising mechanical performance. This study assesses the environmental and social hotspots of various LC³ mortars produced in Germany, a context not yet explored in previous research. While prior studies have mostly focused on LC³ in concrete applications and in low- to middle-income countries, this is the first to evaluate LC³-based mortar in a high-income, highly industrialized context using both Life Cycle Assessment (LCA) and Social Risk Assessment (SRA) to determine the main environmental and social drivers of this material. The LCA revealed that LC³ mixtures achieve substantial reductions in key impact categories compared to conventional Ordinary Portland Cement (OPC) mixes, including Climate Change (up to 42.6% reduction) and Particulate Matter (up to 15.8% reduction). The SRA highlights significant social risks related to corruption, fair competition, and workers’ rights, including fair wages, discrimination, and safe working conditions. This study underscores LC³ as a promising sustainable solution in cement applications while emphasizing the importance of region-specific assessments to address unique environmental and social considerations.

1. Introduction

Portland cement contributes significantly to global environmental challenges, particularly climate change. Roughly 7% of global CO₂ emissions originate from cement production, primarily due to the clinkering process [1]. As cement is an indispensable building material for the construction industry, various efforts are underway to reduce the CO₂ emissions of this material by changing its formulation [2].

Research on alternatives with a potentially improved environmental performance includes a broad range of binder systems and technologies, including waste valorization approaches such as fly ash- and slag-based geopolymers [3,4], and emerging technologies like three-dimensional concrete printing [5]. In this landscape, Limestone Calcined Clay Cement (LC³) emerges as a viable solution, combining two abundantly available supplementary cementitious materials (SCM), limestone and calcined clay, with cement clinker and gypsum [6]. Replacing part of the cement clinker with limestone and calcined clay can lower CO₂ emissions and energy use in comparison to Ordinary Portland Cement (OPC) while preserving structural integrity and functionality [7].

In contrast to OPC, which is composed of over 90% Portland clinker phases, LC³ could replace 50% or more of these phases with the aforementioned SCMs [8]. The calcination of clays, primarily kaolinitic, occurs at a temperature that is half of that used for OPC production [9]. Furthermore, this process does not emit any inherent chemically bound CO₂, which is the primary emitter during the clinkering process for OPC production.

Thermally activated kaolinitic clays, otherwise known as calcined clays, comprise metakaolin, an aluminosilicate phase characterized by high pozzolanic reactivity [10]. When combined with natural limestone, gypsum, and a portion of OPC, these clays are capable of achieving performance levels similar to those of a conventional OPC system [11]. In particular, clays with as little as 40% kaolinite in the raw state and dolomite-rich limestone, which is often discarded during clinker production, can be used in LC³ formulations without compromising the mechanical or durability characteristics [12].

Various physical and chemical interactions within this ternary binder system contribute to its mechanical performance. Physically, incorporating calcined clay and limestone facilitates the formation of additional nucleation sites, enhancing the degree of hydration of OPC [13]. Moreover, as these SCMs undergo a chemical reaction subsequent to the primary binder, a substantial volume of space is available for OPC to precipitate its hydrates, thereby exerting dilutive effects [14]. These two phenomena, also known as the filler effect of added SCMs, play a key role in the development of early-age strength in the LC³ blends [15]. Chemically, the hydration of OPC yields portlandite (CH), which enables the pozzolanic traits of metakaolin from calcined clay, forming C-(A)-S-H. Additionally, a synergistic reaction occurs in LC³ blends between alumina from metakaolin and carbonates from limestone with the portlandite from OPC hydration, yielding space-filling carboaluminate (AFm) phases [16,17]. LC³ also forms a greater quantity of ettringite (AFt) phases than OPC due to the presence of excess alumina (from metakaolin) and added sulfates (gypsum) [18]. These physicochemical interactions result in a dense microstructure within LC³ systems.

The most extensively investigated LC³ system is LC³-50. Nevertheless, several studies have explored the potential of exceeding 50% OPC replacement levels. Many of these studies involved the design of fiber-reinforced cement-based materials using LC³ and resulted in the desired mechanical response for the targeted applications [19,20,21,22]. Exceeding 50% OPC replacement seems to be a promising strategy for enhancing the environmental performance of cementitious materials. Consequently, our analysis also considers the LC³-35 and LC³-25 systems, containing 35% and 25% OPC by weight of the binder, respectively.

The environmental impacts of products along their life cycle can be quantified through the implementation of Life Cycle Assessment (LCA) according to ISO 14040 and ISO 14044 [23,24]. LCA enables the evaluation of the environmental impacts of products along their life cycle [25] and has been used in several studies to determine the environmental performance of LC³ in different contexts—cement, mortar, concrete, and components.

Despite the evident global interest in this material, no study has yet addressed the environmental and social performance of LC³ production in Germany. Furthermore, the influence of certain assumptions on the environmental assessment of LC³ remains unexplored, as do the social hotspots in the LC³ supply chain. Studies on LC³-based mortars are particularly underrepresented compared to research on cement and concrete, with previous investigations largely focusing on the incorporation of industrial by-products. Alghamdi et al. [26] investigated LC³-based mortars incorporating recycled waste and ferrochrome slag, but only assessed the impact category of Climate Change. Similarly, Zhou et al. [19] examined LC³ mortars with fly ash cenosphere (FAC). The incorporation of such materials is not within the scope of the present work.

This investigation addresses these gaps by identifying the main environmental and social hotspots of LC³ mortars produced in Germany. Particularly, it identifies the most relevant impact categories, life cycle stages, and processes, and examines how data sources and assumptions affect LCA results. Finally, this study highlights the social hotspots in impact subcategories associated with LC³ production in Germany by conducting a Social Risk Assessment (SRA) based on generic data obtained in the Product Social Impact Life Cycle Assessment (PSILCA) database, offering guidance on critical social considerations and laying the foundation for a more comprehensive Social Life Cycle Assessment (S-LCA).

2. Literature Review

Relevant scientific literature was reviewed to create an overview of existing studies on the sustainability performance of LC³. Relevant studies were identified in databases including Scopus, Web of Science, and Google Scholar. The review targeted studies investigating the environmental, economic, and/or social impacts of LC³ using life-cycle-based methods such as LCA, S-LCA, Life Cycle Costing (LCC), or Life Cycle Sustainability Assessment (LCSA). The overview of the selected studies is found in

Table 1. Reviewed studies.

No.	Source	Object	Sustainability Dimension(s)	Method(s)	Goal of Study
1	[27]	Cement	Environmental	LCA	Determine the cradle-to-gate environmental impact of LC3 cements produced with kaolinitic waste in Brazil, and quantify the associated carbon footprint and energy requirements of their production.
2	[28]	Cement	Environmental	LCA	Develop a life cycle inventory framework and a tool (MKC-LCA Tool) to evaluate the cradle-to-gate environmental impacts of metakaolin manufacturing, and assess the carbon emissions and energy requirements of ternary cement blends (clinker–metakaolin–limestone) with conventional ones.
3	[29]	Cement	Environmental	LCA	Investigate the combined influence of various SCMs in thirteen blended cement systems, across four blend series combining slag, calcined clay, limestone filler, and fly ash, by evaluating compressive strength over time and relating it to GHG emissions through LCA.
4	[30]	Cement	Environmental	LCA	Analyze the mechanical and environmental performance of LC3 cements produced from various Brazilian natural and waste clay materials by conducting a cradle-to-gate LCA, comparing their environmental benefits and performance against OPC.
5	[31]	Cement	Environmental, economic, and social	LCSA	Conduct the first Cuban LCSA implementation through a practical example on introducing LC3, developing a tailored framework to evaluate sustainability impacts specific to the cement industry.
6	[26]	Mortar	Environmental	LCA	Evaluate the thermophysical, mechanical, fire resistance properties, and carbon emissions of LC3-based mortars incorporating recycled waste and ferrochrome slag as substitutes for traditional materials.
7	[19]	Mortar	Environmental	LCA	Develop a sustainable lightweight engineered cementitious composite (LW-ECC) incorporating LC3 and FAC, and evaluate its material and environmental performance at varying LC3 replacement levels compared to conventional ECC.
8	[32]	Concrete	Environmental	LCA	Evaluate the environmental profile of using an LC3-based material for 3D concrete printing to determine its potential for reducing the environmental performance associated with this technology.
9	[33]	Concrete	Environmental and economic	LCA, LCC	Evaluate the economic and environmental impacts of concrete mixes produced with OPC, Portland Pozzolana Cement (PPC), and LC3 through optimized mix design, considering strength, workability, durability, and material availability.
10	[34]	Concrete	Environmental	LCA	Investigate the effects of replacing OPC with LC3 on the performance of concrete made with 100% recycled aggregate concrete (RAC) made with 100% RAC, focusing on mechanical strength, chloride resistance, hydration behavior, pore structure, reinforcement corrosion risk, and environmental impact through LCA.
11	[35]	Concrete	Environmental	LCA	Provide a holistic assessment of LC3 concrete’s suitability by combining service life estimates (based on chloride ingress and corrosion initiation data) with CO2 footprint analysis, comparing it to OPC concrete and OPC blended with 30% fly ash of similar strength grades.
12	[36]	Component–slabs	Environmental	LCA	Evaluate the decarbonization potential of using LC3-based concrete with steel fibers as an alternative to conventional OPC concrete with steel rebars using one-way slabs as the case study. Eurocode guidelines were applied to assess structural performance, and an LCA was conducted to quantify environmental impacts.
13	[37]	Component–beam	Environmental and economic	LCA, LCC	Assess the environmental and economic performance of LC3-based concrete and structural elements incorporating seawater, sea sand, RAC, and fiber-reinforced polymer bars.
14	[38]	Component–beam	Environmental	LCA	Evaluate the shear capacity of beams made with LC3 concrete beams implementing American, Chinese, and Eurocode standards, and assess their carbon emissions and environmental impact.
15	[39]	Component–building	Environmental and economic	LCA, Economic Value Added (EVA)	Assess the impacts of substituting OPC/PPC with LC3 in the Cuban context through an eco-efficiency analysis combining LCA and EVA, evaluating three construction methods under scenarios of partial and full LC3 substitution.

.

At the level of cement, comparisons between LC³ and OPC have demonstrated significant reductions in emissions and energy demand [28,29]. Similarly, Arruda Junior et al. [27] and Malacarne et al. [12] demonstrated the environmental performance of LC³ in Brazil, considering kaolinitic residues and other clay-based materials.

For mortars, Alghamdi et al. [26] determined that LC³-based mixtures with natural and recycled aggregates had Climate Change values 38% to 45% lower than OPC-based mixes. Similar results were reported in other assessments. Fiber-reinforced composites based on LC³ showed reductions across eight out of twelve impact categories compared to OPC-based counterparts [19]. Despite clay calcination being energy-intensive, the study demonstrates that energy demand remains approximately 40% lower than that of clinkering, making LC³ a more environmentally friendly option.

Several LCA studies have evaluated LC³ in concrete mixes. Notably, 3D printed LC³ concrete displayed a 36–46% reduction in Climate Change impacts compared to the OPC counterpart [32]. However, Ozone Depletion, Ionizing Radiation, Eutrophication (freshwater), Land Use, and Energy Demand presented increases ranging between 16% and 300% [32]. Guo et al. [34] reported similar trends, finding that LC³ mixtures using recycled aggregates reduced Climate Change impacts by up to 42% and energy consumption by 31% compared to OPC. Moreover, Pillai et al. [35] reported that LC³-based mixes showed 16–30% lower overall Climate Change impacts than those based on OPC and fly ash.

Finally, the use of LC³ has also been studied at the component level. The LCA of one-way steel-reinforced concrete slabs demonstrated that the use of LC³ led to reductions of up to 25% in Climate Change impacts [36]. Huang et al. [38] studied LC³ concrete beams and found reductions of 30–70% in several impact categories compared to OPC-based components. However, increases ranging from 50% to 300% in Ozone Depletion, Ecotoxicity, and Eutrophication impacts were observed. Furthermore, Cancio Díaz et al. [39] assessed two buildings where LC³ substituted traditional cement, resulting in 30% lower CO₂ emissions.

Further studies explored the holistic sustainability of LC³. Huang et al. [37] found that LC³ mixes containing recycled concrete aggregate reduced Climate Change impacts by up to 42% and costs by 26%. Similarly, Kanagaraj et al. [33] estimated a 46% decrease in Climate Change impacts and 9% reduction in production costs. In an LCSA conducted in Cuba, Sánchez Berriel et al. [31] found that LC³ outperformed OPC in both the environmental and economic dimensions, with reductions of up to 38% and 46%, respectively. The social dimension was evaluated through selected indicators, which mostly showed a moderate or significant potential for improvement.

While the aforementioned studies have demonstrated environmental advantages of LC³ compared to OPC in various contexts, including Brazil, India, and Cuba, most assessments focus on cement and concrete mixes rather than mortar, and few reflect the conditions of high-income, industrialized settings like Germany. To date, no study has performed an LCA of LC³-based mortar within the German context, nor has any combined this with an SRA to identify social risks along the supply chain. This is a critical gap, given the increasing relevance of social sustainability in public procurement and EU-level policy. By combining environmental and social assessments tailored to a German production scenario, this study provides a novel, location-specific perspective on the broader sustainability implications of adopting LC³ as an alternative to OPC in mortars. Therefore, this study not only extends the material-specific literature to new geographies and product types but also contributes a more holistic sustainability analysis that integrates environmental and social considerations.

3. Materials and Methods

3.1. Scenarios

All raw materials of the OPC and LC³ mortar mix designs were locally sourced and commercially available. This study examines three LC³ formulations–LC³-50, LC³-35, and LC³-25–with 50%, 35%, and 25% OPC relative to the binder content, based on a previous study by Ahmed et al. [14] and transformed into fine-grained mortars in the present investigation. For detailed physical, chemical, and mineralogical characterizations of the binder constituents, readers are referred to the aforementioned study by Ahmed et al. [14].

The selected primary binder was a high-strength, rapid-hardening, sulfate-resistant OPC (CEM I 52.5 R-SR3/NA). The clay, produced via industrial calcination, is of low kaolinite content, with up to 25 wt.% kaolinite. Saxodol 90 LE, a white marble-derived limestone powder with a carbonate content of 98 wt.%, was used. High-purity, precipitated gypsum was used to ensure proper sulfation in the LC³ mixes, while fine quartz (particle size range of 60–200 µm) was incorporated as a fine inert aggregate. To enhance the workability, a viscosity-modifying agent (VMA, Unterwasser-Compound 100, Sika^®, Stuttgart, Germany) and a polycarboxylate (PCE)-based superplasticizer (MasterGlenium ACE 460, Master Builders Solutions, Mannheim, Germany) were incorporated. The water-to-binder ratio was 0.4 across all compositions, while the calcined clay-to-limestone ratio was 2:1. Gypsum was added in 3 wt.% binder in all LC³ mixes. The detailed mix compositions are depicted in

Table 2. Composition of reference and LC³ mixtures.

Material	Unit	OPC	LC3-50	LC3-35	LC3-25
CEM I 52.5 R-SR3/NA	g/L	1206	584	404	286
Quartz sand	g/L	271	262	259	257
Limestone	g/L	-	187	245	282
Calcined clay	g/L	-	375	490	564
Gypsum	g/L	-	18	12	9
Water	g/L	484	467	462	458
Superplasticizer	g/L	8	8	8	8
VMA	g/L	4	4	4	4

.

3.2. Life Cycle Assessment

The environmental performance of the OPC and LC³ mixtures was assessed with the LCA method according to the standards ISO 14040 and ISO 14044 [23,24]. The implementation of the LCA phases is described below.

3.2.1. Goal and Scope

This assessment identifies the main environmental hotspots of LC³ in Germany. Specifically, the most influential life cycle stages and processes were identified, and possible environmental impact reductions of LC³ compared to OPC were investigated.

Four mixtures were studied–one OPC-based reference mixture and three LC³ mixes with reducing clinker factors. The corresponding 28-day strengths of the mixtures are 69 MPa, 52 MPA, 34 MPa, and 25 MPa for OPC, LC³-50, LC³-35, and LC³-25 mortars, respectively. Notably, even the lowest strength values fall within the 25–35 MPa range typically specified for structural applications in many developed countries [40]. Given the broad range of applications of the studied material (see below), the selected functional unit is 1 L of mortar. The method Environmental Footprint, version 3.0 (EF 3.0) was chosen for the impact assessment. The software ©GaBi ts 10.6.2.9, and the databases ©GaBi Professional 2022.2 and Ecoinvent 3.8 were utilized.

The system boundaries, presented in Figure 1, were defined according to EN 15804 [41]. The processes in orange and their respective transport are specific to the LC³ mixes. The extraction of raw materials (Module A1) includes the extraction, pre-processing, and production of each raw material, as well as electricity generation and transmission. Module A2 covers the transport of the raw materials to the production site, while Module A3 comprises the energy use during the mixing of the materials. Module A4 represents the transport of the finished mortar mix to the construction site via road transport. The use and end-of-life stages were excluded from the system boundaries due to the wide variability of mortar applications—such as masonry work, plastering, rendering, tile adhesives, concrete repair, joint filling, and grouting—where OPC consumption is typically higher than in conventional concrete and reinforced concrete [42]. Covering all potential uses of mortars would require application-specific assessments, which fall beyond the scope of this study.

Beyond their direct applications, LC³ mortars also serve as the basis for fine-grained matrix design in fiber-reinforced composites, including strain-hardening cementitious composites (SHCC) and textile-reinforced composites (TRC) [43]. Another promising avenue is fine-grained 3D-printed concrete, which inherently reduces material use and can potentially lower the material’s carbon footprint [44,45,46]. Nevertheless, and as previously mentioned, a comprehensive evaluation of all potential mortar applications would require application-specific LCAs, which fall beyond the scope of this study.

Given the extensive secondary data used and the variety of datasets available for some materials, the influence of dataset selection on the results was explored through sensitivity analyses.

3.2.2. Life Cycle Inventory

The bill of quantities was based on primary data stemming from the Institute of Construction Materials of the Technische Universität Dresden, while the rest of the data was secondary. German datasets were prioritized, and when unavailable, regional data were preferred. Otherwise, global datasets were used.

For most materials, no specific LCA datasets were available. Therefore, generic datasets were used in the model. The selected datasets for the baseline scenario are presented in Table S1 (Supplementary Materials). When multiple datasets were available, the most conservative option in terms of Climate Change was chosen.

For cement production, a dataset was chosen covering CEM I 52.5 production, including raw material extraction, clinker production, and cement grinding. The dataset depicts the situation in Germany, and uses country-specific data for the background system. The dataset for quartz sand covered elutriation and sieving, and included drying. Moreover, the superplasticizer was modeled with a dataset representing a sectoral Environmental Product Declaration (EPD) according to EN 15804 of the German association Deutsche Bauchemie (DBC). The dataset uses the product with the highest environmental impacts as a representative product and covers raw material extraction, transport, and manufacture (including packaging materials).

Limestone was modeled with a dataset depicting limestone flour (20 μm grain size), covering open pit mining, blasting, conveying, sizing, and crushing. Gypsum was modeled with a dataset representing its recovery as a by-product from coal power plants, including transport by train, drying, purifying, and heating to obtain the final product.

For the VMA, no generic datasets were available, and a proxy was selected. The main component of the VMA is listed as cellulose ether, a water-soluble polymer derived from cellulose, but no further composition details are provided by the manufacturer [47]. Literature on similar commercial products indicates that cellulose ethers such as methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) are commonly used as VMA [48]. Among these, MC is often used in the construction sector to improve material properties [49] and was used as a proxy, as it reflects the chemistry of cellulose-ether-based commercial products used in similar applications.

Ecoinvent provides a dataset for calcined clay production [50], based on Brazilian data, which may not reflect the German context. The dataset references petroleum coke, which is not the most common energy source in Germany. Furthermore, no information related to the type of clay used as input in the process is provided. The chosen dataset is mainly based on primary data for the German context and covers clay mining, wet processing, as well as grinding and drying of the material. In this regard, the process was adjusted to reflect German conditions. In particular, the German electricity mix was used, and lignite dust was assumed to be the thermal energy source for the calcination process due to its wide use in the German sector of stones and soils [51]. The resulting CO₂ emissions of the process were adjusted using the emission factors from the German Ministry of Environment [52]. The input and output parameters and datasets used to model 1 kg of calcined clay are presented in

Table 3. Calcined clay modeling. Adapted from Ecoinvent [50].

Material	Amount	Unit	Dataset	Comment
Inputs
Kaolinitic clay	1.03	kg	DE: Kaolin Sphera	Proxy for kaolinitic clay
Electricity	0.09	MJ	DE: Electricity grid mix (2020) Sphera
Lignite	0.0901	kg	DE: Lignite mix Sphera	Proxy for lignite dust
Outputs
Carbon dioxide	0.208	kg	Flow	The CO2 emissions were adjusted to represent the adjusted energy source.
Methane	6.15 × 10−6	kg	Flow
Nitrous oxide	1.23 × 10−6	kg	Flow
Water	0.0003	m3	Flow

.

Considering that the mixes were produced under laboratory conditions with no industrial production site, and to avoid bias from site-specific transport distances, a conservative hypothetical transport distance of 500 km was assumed for all raw materials (Module A2). Furthermore, no site-specific construction site is defined, the delivery of the mortar to the construction site (Module A4) is set as 100 km based on conservative assumptions from experts. The mixing process, based on the Hobart HSM-20 machine [53] and the mixing procedure described in Ngo et al. [54], resulted in an energy consumption of 0.23 kWh/m³, modeled with the German electricity mix.

3.2.3. Life Cycle Impact Assessment

All EF 3.0 impact categories were reported. The characterized values for each category were presented, while the normalization (per person equivalent) and weighting factors of EF 3.0 were used to identify the most relevant impact categories.

3.2.4. Interpretation

The environmental hotspots of the mixtures were identified for life cycle stages and processes. Furthermore, the most relevant impact categories were identified and are emphasized in the discussion.

Several sensitivity analyses evaluated the influence of assessment choices and established a performance range for the mixes. Alternative scenarios were explored for clay and cement production, as well as the energy source for clay calcination.

For clay production, two scenarios were explored. The first, a best-case scenario for Climate Change, used a European dataset from the ©GaBi Professional database. This dataset is based on several production sites across Europe, with electricity and upstream processes reflecting European averages. It covers both wet and dry extraction routes, as well as drying (mechanical and thermal), extrusion, and milling. The second, represents the worst-case scenario in terms of Acidification, Ecotoxicity, Eutrophication, Human Toxicity, and other impact categories. In this case, an Ecoinvent dataset is used based on a single European producer and covers wet processing, including mining, mineral separation, beneficiation, storage, and transport.

Similarly, two alternative scenarios were assessed for cement production. The first represents the best-case scenario for Climate Change, using an Ecoinvent dataset covering the representative production mix of CEM I 42.5 and CEM I 52.5 in Switzerland (as a proxy for Germany). This dataset begins with the clinker in the silo and includes electricity consumption for grinding and thermal energy for drying. The second alternative dataset is product-specific and depicts production in Germany [55]. It covers the extraction and processing of raw materials (limestone, clay, marl), clinker production in a rotary kiln at 1450 °C, and grinding of clinker into cement with the addition of a sulfate carrier. The dataset was developed in accordance with the German Product Category Rules for cement [56].

Furthermore, an energy demand value for the mixing process was adopted from literature to better reflect typical industrial conditions. Additionally, the sensitivity of the energy source for calcination was tested by exploring scenarios where natural gas and electricity from renewable energy (via electric kiln) were explored. Finally, the influence of transport distance for the most impactful materials was studied. An overview of the scenarios is presented in Table S2 (Supplementary Materials).

3.3. Social Risk Assessment

S-LCA is a method that assesses the potential negative and positive social impacts of a product system throughout its life cycle [57]. While adopting a stakeholder perspective, S-LCA follows a structure similar to LCA with goal and scope definition, social life cycle inventory analysis (S-LCI), impact assessment, and interpretation [58]. The method is standardized by ISO 14075 [57]. The impact assessment phase, according to ISO 14075, has two alternatives: Social Life Cycle Impact Assessment (S-LCIA) and Social Life Cycle Performance Assessment (S-LCPA). The S-LCIA, based on impact pathways, faces challenges due to the limited availability of characterization methods [59]. Alternatively, in the S-LCPA, the outcomes of the S-LCI are transformed into a score using predefined reference scales [57]. Furthermore, S-LCA is highly context-dependent and requires extensive primary data to accurately compute results that capture the impacts of products on humans.

Given the lack of impact pathways and the necessity of primary data in S-LCPA, an SRA can help identify potential social risks using secondary data [58]. The results highlight social issues that appear to be the most known at the current state of the art. However, SRA is not product-specific, but focuses on economic sectors associated with the product. Secondary databases such as Social Hotspot Database (SHDB) [60] and PSILCA [61] can be used to conduct an SRA. The databases differ in how the information is structured, which indicators are used, and how the social risk is calculated.

SRA Procedure

An SRA for LC³ production in Germany was performed for the system boundaries shown in Figure 1 to identify key social risks associated with the relevant economic sectors. The aim is not to compare social risks related to OPC- and LC³-based mortar mixtures, as such a comparison is not feasible with secondary data.

The SRA used the PSILCA database, which visualizes social risks for selected sectors in a particular country using a color scale, where each color represents risks going from very low to very high. The economic sectors are classified according to the Eora database [62]. Therefore, LC³ production processes are allocated to the Eora harmonized sectors.

LC³ production is divided into several processes similar to conventional cement production, which include: (1) preparation of raw materials, (2) chemical conversion, and (3) grinding [63]. Clay is also fired for the manufacturing of LC³.

The preparation of raw materials includes quarrying, homogenization, and grinding of limestone and clay. The processed raw materials are delivered to the cement plant, where the chemical conversion occurs. Limestone and clay are calcined at their respective temperatures. Then, in the grinding process, the burning products of limestone (clinker) and clay (calcined clay), are ground along with low-quality unburned limestone and mixed with gypsum to produce LC³. In 2022, coal, including lignite and hard coal, accounted for the largest fuel source in Germany [64]. Furthermore, electricity is required during the various production processes [65]. Accordingly, lignite, hard coal, and electricity supply are also considered in the SRA.

Based on these processes, the raw material extraction and processing are assigned to the sector “Quarrying of Stone & Soil”, while material transport is modeled as the “Road and Pipeline Transport” sector. The burning, grinding, and mixing fall under the “Manufacture of Non-Metallic Mineral Products” sector. The electricity is modeled with the “Electricity & District Heat” sector, while the fuel is modeled by the “Mining of Coal & Lignite” sector. A graphical representation can be found in Figure 2.

After identifying the relevant sectors, the social risks can be computed. For this assessment, relevant risks are those considered “high” and “very high”.

4. Results

4.1. LCA

The characterized LCA results for all life cycle stages corresponding to the OPC and the LC³ mixtures for the baseline scenario are presented in

Table 4. LCA results for baseline scenario.

Impact Category	Unit	OPC	LC3-50	LC3-35	LC3-25
Climate Change (total)	kg CO2 eq.	1.13	8.04 × 10−1	7.11 × 10−1	6.49 × 10−1
Acidification	Mole of H+ eq.	1.12 × 10−3	7.86 × 10−4	6.89 × 10−4	6.26 × 10−4
Ecotoxicity (freshwater)	CTUe	1.86	1.59	1.50	1.44
Eutrophication (freshwater)	kg P eq.	6.63 × 10−6	6.51 × 10−6	6.48 × 10−6	6.45 × 10−6
Eutrophication (marine)	kg N eq.	3.56 × 10−4	2.72 × 10−4	2.47 × 10−4	2.31 × 10−4
Eutrophication (terrestrial)	Mole of N eq.	3.74 × 10−3	2.82 × 10−3	2.55 × 10−3	2.38 × 10−3
Human toxicity (cancer)	CTUh	7.22 × 10−11	6.30 × 10−11	6.01 × 10−11	5.83 × 10−11
Human toxicity (non-cancer)	CTUh	6.88 × 10−9	4.85 × 10−9	4.24 × 10−9	3.85 × 10−9
Ionizing radiation (human health)	kBq U235 eq.	1.32 × 10−2	1.00 × 10−2	9.08 × 10−3	8.46 × 10−3
Land Use	Pt	1.30	1.08	1.02	9.80 × 10−1
Ozone depletion	kg CFC-11 eq.	2.80 × 10−9	2.80 × 10−9	2.80 × 10−9	2.80 × 10−9
Particulate matter	Disease incidences	2.08 × 10−8	1.85 × 10−8	1.79 × 10−8	1.75 × 10−8
Photochemical ozone formation	kg NMVOC eq.	9.56 × 10−4	6.92 × 10−4	6.15 × 10−4	5.66 × 10−4
Resource use (fossils)	MJ	4.26	5.12	5.36	5.53
Resource use (minerals and metals)	kg Sb eq.	2.81 × 10−7	2.72 × 10−7	2.69 × 10−7	2.67 × 10−7
Water use	m3 world eq.	3.30 × 10−2	2.79 × 10−2	2.64 × 10−2	2.54 × 10−2

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The results show significant improvement in most environmental impacts due to the decreased clinker content, with reductions ranging from 0.02% for Ozone Depletion to 44.0% for Human Toxicity (non-cancer), as shown in Table S3 (Supplementary Materials). However, Resource Use (fossils) exhibits an increase for the LC³ mixtures.

Table 5. Normalized results by compressive strength at 28 days.

Impact Category	Unit	OPC	LC3-50	LC3-35	LC3-25
Climate Change (total)	kg CO2 eq./MPa	1.64 × 10−2	1.54 × 10−2	2.07 × 10−2	2.64 × 10−2
Acidification	Mole of H+ eq./MPa	1.62 × 10−5	1.51 × 10−5	2.00 × 10−5	2.54 × 10−5
Ecotoxicity (freshwater)	CTUe/MPa	2.69 × 10−2	3.04 × 10−2	4.35 × 10−2	5.83 × 10−2
Eutrophication (freshwater)	kg P eq./MPa	9.59 × 10−8	1.25 × 10−7	1.88 × 10−7	2.62 × 10−7
Eutrophication (marine)	kg N eq./MPa	5.15 × 10−6	5.22 × 10−6	7.20 × 10−6	9.40 × 10−6
Eutrophication (terrestrial)	Mole of N eq./MPa	5.41× 10−5	5.41 × 10−5	7.44 × 10−5	9.68 × 10−5
Human toxicity (cancer)	CTUh/MPa	1.04 × 10−12	1.21 × 10−12	1.75 × 10−12	2.37 × 10−12
Human toxicity (non-cancer)	CTUh/MPa	9.96 × 10−11	9.29 × 10−11	1.23 × 10−10	1.56 × 10−10
Ionizing radiation (human health)	kBq U235 eq./MPa	1.92 × 10−4	1.92 × 10−4	2.64 × 10−4	3.43 × 10−4
Land Use	Pt/MPa	1.88 × 10−2	2.08 × 10−2	2.96 × 10−2	3.98 × 10−2
Ozone depletion	kg CFC-11 eq./MPa	4.06 × 10−11	5.37 × 10−11	8.14 × 10−11	1.14 × 10−10
Particulate matter	Disease incidences/MPa	3.01 × 10−10	3.55 × 10−10	5.21 × 10−10	7.12 × 10−10
Photochemical ozone formation	kg NMVOC eq./MPa	1.38 × 10−5	1.33 × 10−5	1.79 × 10−5	2.30 × 10−5
Resource use (fossils)	MJ/MPa	6.16 × 10−2	9.82 × 10−2	1.56 × 10−1	2.24 × 10−1
Resource use (minerals and metals)	kg Sb eq./MPa	4.06 × 10−9	5.21 × 10−9	7.82 × 10−9	1.09 × 10−8
Water use	m3 world eq./MPa	4.78 × 10−4	5.36 × 10−4	7.66 × 10−4	1.03 × 10−3

presents the results normalized by the 28-day compressive strength of the mixtures.

Although the characterized results show a clear advantage of the LC³-based mixes in comparison to OPC, the normalized results (per MPa) show that this advantage disappears at lower clinker contents. Only LC³-50 presents slightly better results in some impact categories. Climate Change and Acidification present reductions of around 6%, Human Toxicity (non-cancer) is reduced 7%, while Photochemical Ozone Formation decreases 4%. For the rest of the impact categories, there is a clear worsening of impacts per MPa at lower clinker levels, with increases of up to 264% (Resource Use (fossils)).

The normalized and weighted results (using the normalization and weighting factors of the EF3.0) are presented in Table S4 (Supplementary Materials). Based on this, the most relevant impact categories can be determined, i.e., the categories accounting for at least 80% of the overall environmental impact. The most relevant impact categories for all mixtures are Climate Change, Particulate Matter, and Resource Use (fossils), with a total contribution of 86.4%. The contribution of each life cycle stage to these categories is presented in Figure 3, with Module A1 being the greatest, followed by Module A2. The contributions of Modules A3 and A4 are minimal.

A contribution analysis of the most relevant impact categories is shown in Figure 4. The most influential process in the OPC mixture is cement production, contributing 92.0% to Climate Change, 88.5% to Particulate Matter, and 69.5% to Resource Use (fossils). However, other processes, like VMA production, are key drivers in categories such as Eutrophication (freshwater) (91.0%), Ozone Depletion (99.6%), and Resource Use (minerals and metals) (79.7%). VMA, along with diesel (for transport) and cement production, is also a hotspot for Land Use. Furthermore, sand and VMA production are also major contributors to Water Use.

While cement production remains a key factor, clay calcination emerges as a significant hotspot in LC³ mixes. Calcined clay production contributes between 25.3% (LC³-50) and 47% (LC³-25) to Climate Change. Similar trends are observed in Particulate Matter and Resource Use (fossils), with contributions ranging from 30.9% to 49.1% and 45.1% to 62.8%, respectively. Additionally, sand, VMA, and diesel production play significant roles in other impact categories.

Sensitivity Analysis

Two alternative datasets were explored for clay production: One representing the best-case scenario for Climate Change, and the other the worst-case scenario for several other impact categories. The results were compared to the baseline scenario, as shown in Figure 5 and Figure 6.

The best-case dataset leads to reductions in most impact categories compared to OPC, except for Ecotoxicity (freshwater), Eutrophication (freshwater), Ionizing Radiation, Ozone Depletion, and Water Use. In the case of the worst-case dataset, most impact categories present increases, except for Climate Change, Particulate Matter, and Resource Use (fossils)–the most relevant in the baseline scenario.

Similarly, two further datasets were explored for cement production: one generic with the most favorable Climate Change value, and the other specific to the product used in the mixtures. The relative differences compared to the baseline are presented in Figure 7 and Figure 8. Toxicity-related categories and Land Use are unreported, as they are not part of the specific dataset.

In the best-case scenario, reductions are observed only in Climate Change, Human Toxicity (non-cancer), Land Use, and Particulate Matter, while other categories increase by 1% to 1592%. In contrast, the context-specific scenario shows more moderate changes.

Two additional scenarios were examined, considering alternative energy sources for clay calcination: natural gas and electricity from renewable sources. The relative results are shown in Figure 9. In the natural gas scenario, only the impact category of Climate Change presented reductions (up to 7%), while other categories, such as Human Toxicity (non-cancer) and Resource Use (fossils) increased by up to 67% and 112%, respectively. For the renewable electricity scenario (via electric kiln), Climate Change, Ionizing Radiation, and Resource Use (fossils) were reduced by up to 17%, 8%, and 10%, respectively. However, several impact categories increased substantially, such as Human Toxicity (cancer) (up to 56%) and Land Use (up to 146%).

The sensitivity of the outcomes to the energy demand for the mixing process was analyzed (Figure 10). Using a literature value representative of industrial conditions, the results show increased impacts. However, the contribution of Module A3 to the overall results remains minimal.

Module A3 has the highest contribution to the results for LC³-25, except for Resource Use (fossils), where the OPC substitution with calcined clay led to an increased contribution from Module A1 and a smaller contribution from Module A3. Despite this, LC³-25 has the lowest overall impacts. Nevertheless, in most cases, the influence of Module A1 increases as OPC content also increases. Thus, the share of Module A3 is the highest in the LC³-25 mix.

A sensitivity analysis was conducted on cement and calcined clay transport distance, assuming the longest distance that can be driven in Germany (Figure S1, Supplementary Materials). Despite the increased influence of Module A2, it is still not an environmental hotspot.

4.2. SRA

The SRA results are presented in

Table 6. SRA results for LC³ production in Germany.

Stakeholder Category	Sub-Category	Social Issue	Risk Indicator	Economic Sectors
				Q	T	E	L	M
Value Chain Actors	Corruption	Active involvement of enterprises in corruption and bribery	Active involvement of enterprises in corruption and bribery	VH	VH		VH
	Fair Competition	Anti-competitive behavior or violation of anti-trust and monopoly legislation	Presence of anti-competitive behavior or violation of anti-trust and monopoly legislation	VH			VH
Workers	Freedom of association and collective bargaining	Association and bargaining rights	Right of Collective bargaining			H
			Right to Strike			H
	Fair Salary	Fair Salary	Living wage, per month	VH	VH	VH	VH	VH
	Discrimination	Gender wage gap	Gender wage gap					H
	Health and Safety	Non-fatal accidents	Rate of non-fatal accidents at workplace	H	H	H	H	H
		Safety measures	Presence of sufficient safety measures			H		H
Local Community	Access to material resources	Biomass consumption	Extraction of biomass (related to area)	VH	VH	VH	VH	VH
		Certified environmental management system	Certified environmental management systems		VH			H
		Industrial water depletion	Level of industrial water use (related to renewable water resources)	VH	VH	VH	VH	VH
			Level of industrial water use (related to total withdrawal)	VH	VH	VH	VH	VH
	Safe and healthy living conditions	Contribution to environmental load	Contribution of the sector to environmental load, CO2-equiv, I-Greenhouse Gases (GHG)-CO2eTOTAL_agg		H	H	H
			Contribution of the sector to environmental load, NMVOC, I-AIR-NMVOC_agg				H
			Contribution of the sector to environmental load, CO, I-AIR-CO_agg		H
	Migration	International migrant stock	International Migrant Stock	H	H	H	H	H
Society	Contribution to economic development	Education	Public expenditure on education	H	H	H	H	H

Q = quarrying of stone and soil, T = road and pipeline transport, E = electricity and district heat, L = mining of coal and lignite, M = manufacture of non-metallic mineral products. H = high risk, VH = very high risk.

, focusing on the most relevant risks. The main social sub-categories associated with LC³ production are corruption and fair competition, freedom of association, fair salary, discrimination, health and safety, access to material resources, safe and healthy living conditions, migration, and contribution to economic development.

5. Discussion

5.1. LCA

In the present study, the LCA results for OPC- and LC³-based mixtures were presented. The characterized results indicate lower environmental impacts for LC³ mixtures compared to OPC, with LC³-25 exhibiting the greatest reductions (up to 44%) across most categories (except for Resource Use (fossils)), due to its low cement content. The results were also normalized and weighted using factors of the EF 3.0 method. It should be emphasized that normalization and weighting were applied solely to identify the most relevant impact categories–namely, Climate Change, Particulate Matter, and Resource Use (fossils)–and do not constitute the sole basis for the conclusions of this study. The contribution and sensitivity analyses, as well as their interpretation, are based on the unweighted results.

Significant reductions are observed in Human Toxicity (non-cancer), Acidification, Climate Change, and Photochemical Ozone Formation across all LC³ mixtures, with Climate Change impacts decreasing by 28.9% (LC³-50), 37.1% (LC³-35), and 42.6% (LC³-25). However, Resource Use (fossils) increases by 20.3% (LC³-50) to 29.8% (LC³-25), which is linked to the higher proportion of calcined low-grade kaolinitic clay in the mixture. In particular, the increase in this impact category is driven by clay extraction and the thermal energy required for clay calcination, modeled using lignite as fuel. This increase represents a trade-off with the reductions in clinker-related impacts in the other impact categories. Notably, higher clinker substitution amplifies this trade-off: while LC³-25 achieves the largest reduction in the rest of categories, it also leads to a significant increase in fossil resource consumption. This increase could be mitigated through the replacement of lignite with alternative, non-fossil energy sources, such as biomass or green hydrogen [66]. Furthermore, the integration of waste heat recovery systems could lead to a reduced use of fossil fuels.

While LC³ mixtures demonstrate improved environmental performance compared to OPC, further improvements may be possible. This case study used commercial products. However, past studies on LC³ considered waste materials, such as low-grade clays and discarded limestone [26,27,30,67], which could affect the environmental profile of LC³ mixtures. This scenario, however, is not addressed in this study.

The results were also normalized by compressive strength (i.e., expressed per MPa). While the characterized results indicated substantial improvements in most impact categories for all LC³ mixes compared to OPC, the normalized results revealed an opposing trend. Specifically, the lower clinker mixes (LC³-35 and LC³-25) displayed higher impacts per MPa. Specifically, the lower compressive strength of LC³-35 and LC³-25 outweighed the environmental benefits of the lower clinker amount under the system boundaries of this study (cradle-to-gate plus transport to the construction site). In contrast, LC³-50 maintained a balance between reduced clinker content and strength, performing comparably or even more favorably than OPC in impact categories such as Climate Change, Acidification, Human Toxicity (non-cancer), and Photochemical Ozone Formation. These results highlight ongoing discussions on the choice of appropriate functional units and the context in which construction materials are compared. On the one hand, the way material performance is defined directly LCA outcomes. On the other hand, robust comparisons can only be achieved within an application context (e.g., the role of a material in a building), consistent with the comparability principles established in EN 15804.

The most relevant impact categories for all mixtures are Climate Change, Particulate Matter, and Resource Use (fossils). For Climate Change, the contribution decreases with reduced cement content, from 66.5% in the OPC mix to 55.0% in LC³-25. In contrast, Particulate Matter and Resource Use (fossils) increase from 7.1% to 8.6% and from 12.3% to 23.0%, respectively, as a result of incorporating calcined clay, limestone, and gypsum.

These findings present an important trade-off: the reduced cement content in LC³ mixtures leads to mostly lower impacts compared to OPC, but the impact of the second most relevant impact category–Resource Use (fossils)–increases due to higher rates of calcined clay and limestone. In this regard, the integration of renewable energy into LC³ production, in particular for calcined clay, could help mitigate this impact.

The most relevant life cycle stage is Module A1, with cement production being the most influential process. In the LC³-mixes, calcined clay production was the second most relevant process. Considering the other impact categories, VMA and diesel production considerably influence the environmental profile of the LC³ mortars. Although the LC³ mixes present an overall lower environmental impact than OPC, the change in composition causes a shift in the environmental loads. In this regard, the environmental performance of LC³ mixtures could be improved by using alternative admixtures and fuels.

Module A2 is the second most influential stage, with impact contributions ranging between 4.33% to 7.15% for Climate Change, 4.17% to 4.70% for Particulate Matter, and 10.96% to 15.03% for Resource Use (fossils). For Climate Change and Particulate Matter, the lowest values correspond to the OPC mixture and the highest to LC³-25. In this instance, the reduction in environmental impacts in Module A1 leads to burden-shifting towards Module A2, thus increasing the relative importance of this life cycle stage. For Resource Use (fossils), the highest value corresponds to OPC, and the lowest to LC³-25 due to increased calcined clay. For Climate Change and Particulate Matter, the main driver is cement transport, while diesel production is the main hotspot for Resource Use (fossils). The results suggest that, as the impacts of Module A1 decrease, greater attention should be paid to transport-related processes since their relevance increases. Effective measures to reduce the impacts of Module A2 include sourcing material from closer suppliers and using high-capacity, low-emission trucks, particularly for cement and calcined clay transport, which are the main contributors to this stage. Finally, the contribution of Module A3 is very low, ranging from 0.01% to 0.02%.

Given the reliance on secondary data, several sensitivity analyses were conducted to explore how dataset choice, energy-related aspects, and transport distance affect the LCA results. First, dataset selection was studied for clay extraction and cement production.

Table 7. Relative difference from the baseline scenario for LC³ mixtures. The highest reductions and increases are highlighted in green and red, respectively.

Impact Category	Clay (Best Case)	Clay (Worst Case)	Cement (Best Case)	Cement (Ökobaudat)
Climate Change (total)	−16%	−11%	−7%	−8%
Acidification	−2%	45%	47%	5%
Ecotoxicity (freshwater)	3%	55%	132%	−20%
Eutrophication (freshwater)	4%	645%	572%	−2%
Eutrophication (marine)	−8%	4%	36%	1%
Eutrophication (terrestrial)	−9%	1%	42%	4%
Human toxicity (cancer)	−25%	5%	7%	−31%
Human toxicity (non-cancer)	−20%	−8%	−5%	−47%
Ionizing radiation (human health)	23%	217%	116%	6%
Land Use	−12%	12%	−11%	−25%
Ozone depletion	3%	377%	136%	0%
Particulate matter	−34%	−27%	−18%	−26%
Photochemical ozone formation	−8%	5%	41%	3%
Resource use (fossils)	−34%	−18%	1%	0%
Resource use (minerals and metals)	−2%	94%	93%	−6%
Water use	23%	300%	138%	7%

presents the relative difference between the average values for the LC³ mixtures of the alternative scenarios and the baseline.

The worst-case scenario for clay generates significant changes in several categories, notably Eutrophication (freshwater), Water Use, and Ozone Depletion, which are now among the most relevant in this scenario. As noted in Section 3.2.4, the dataset for the worst-case scenario represents clay production from a single European producer and, like the baseline, covers wet processing. Despite using the same general production route, several factors could explain the differing results. For example, mining can be performed open-pit (for shallow deposits) or underground (for deeper deposits), while the degritting can be achieved using classifiers, hydrocyclones or screens. Beneficiation may involve flotation, magnetic separation, chemical leaching or sedimentation. Additional post-treatments can be performed depending on the producer. Each of these technological choices can substantially influence energy and water consumption, as well as emissions and waste generation, leading to significantly different results.

In contrast, the best-case scenario reflects European averages and includes both wet and dry extraction technologies. By integrating data from multiple sites with varying efficiencies and reflecting average production practices, lower estimated impacts may be obtained in comparison to a single, higher-impact producer. Moreover, dry extraction generally uses less water and energy than wet extraction, possibly further contributing to the reduced impacts in most categories.

In the best-case scenario for cement, considerable differences are observed, with a slight reduction in Climate Change, but substantial increases in other impact categories, like Eutrophication (freshwater) (despite the fact that the alternative dataset excludes clinker production). Here, the most relevant impact categories also change. The differences may be due to assumed technologies and process efficiencies, such as older grinding and handling technologies, higher energy consumption, and conservative emission factors. These outcomes illustrate an important aspect: reductions in one category can lead to increased contribution to other impacts, highlighting the need to consider trade-offs across multiple impact categories when assessing environmental performance.

Further sensitivity analyses were conducted regarding energy-related parameters for clay calcination and LC³ mixing. Clay calcination was modeled with lignite as a fuel. Another common fuel used in this context is natural gas, which was chosen for the sensitivity analysis. Results show moderate improvements in Climate Change, but significant increases for the rest of the categories, reinforcing the importance of assessing all environmental impacts.

An additional scenario was modeled in which calcination occurs in an electric kiln powered by electricity from renewable sources. Studies from the cement industry suggest that the electrification of the clay calcination process using green electricity could reduce CO₂ emissions by up to 50% [68]. In line with this, the results of the sensitivity analysis revealed improvements in the impact categories Climate Change, Ionizing Radiation, and Resource Use (fossils). However, several other impact categories showed increases, most notably Land Use. The chosen electricity mix combines energy from wind, photovoltaic, biogas, hydro, biomass, waste, and geothermal sources. This combination helps explain the observed trade-offs. For instance, the high share of wind energy (52%) contributes to Land Use impacts due to spatial requirements, while the production of wind turbines and photovoltaic panels requires considerable amounts of metals, driving the increase in Resource Use (minerals and metals). Moreover, the manufacturing of these technologies involves the use of substances that lead to higher results in the Human Toxicity categories. These findings show that the use of renewable electricity, although beneficial for Climate Change due to lower CO₂ emissions, does not automatically translate into lower impacts across all categories in the context of LC³ production. Instead, the environmental performance strongly depends on the specific composition of the energy mix, which must be assessed on a case-by-case basis.

The LC³ mixing process was modeled based on laboratory conditions, which may differ from industrial-scale production. Therefore, a sensitivity analysis was conducted using a value almost 40 times higher than the baseline (representing industrial values). This increase led to a maximum increase of 2.5% in the environmental impacts. This outcome suggests that the results are robust and that the lab-scale assumptions regarding energy consumption do not significantly bias the conclusions. However, it should be noted that lab-scale mix proportions may differ from those used in industrial practice, introducing some uncertainty in the results.

A final sensitivity analysis was conducted with the transport distance of cement and calcined clay, where the maximum transport distance in Germany was assessed (100% higher than in the baseline scenario). This change led to increases ranging from 3.5% and 4.3% for Climate Change, 2.8% and 3.4% for Particulate Matter, and 6.6% and 12.2% for Resource Use (fossils). Furthermore, the proportion of impacts of Module A2 increased by 1.8% in Climate Change, 1.4% in Particulate Matter, and 3.7% in Resource Use (fossils), demonstrating the limited sensitivity of the LCA results to changes in transport distance.

Table S5 (Supplementary Materials) summarizes the average relative differences in LCA results between the baseline and alternative scenarios. Overall, using the Ecoinvent dataset to model cement production, which represents the best-case scenario for Climate Change, results in the largest increases across most impact categories. However, this trend does not hold in one of the most relevant categories, Particulate Matter, which presents a reduction of around 28.5%. Furthermore, Resource Use (fossils) presents a less pronounced increase of 2.3%.

The results of similar studies were compared to the obtained LCA values. Two studies on LC³-based mortar mixtures were found. However, while both present cradle-to-gate results, the LCAs excluded transport processes. Furthermore, Alghamdi et al. [26] used natural siliceous sand and recycled aggregates and did not consider any admixtures, while the mixtures by Zhou et al. [19] included high-range water-reducing admixtures, FAC, and polyethylene fibers. Additionally, the mixtures showed different compressive strengths at 28 days. Nevertheless, the results for Climate Change normalized for compressive strength are still compared to the outcomes of this study, as shown in

Table 8. Climate Change results for LC³ mixtures from literature and the current study.

Source	Compressive Strength at 28 Days [MPa]	Climate Change [kg CO2 eq./m3]	Relative Climate Change [kg CO2 eq./m3/MPa]	Comment
[26]	45.5	265	5.82	LC3 mixture with natural siliceous sand
[26]	49.2	301	6.12	LC3 with ferrochrome slag (recycled material)
[19]	38	980	25.79	OPC substitution of 35%
[19]	36	850	23.61	OPC substitution of 50%
[19]	31	700	22.58	OPC substitution of 65%
Current study	52.2	804	15.42	OPC substitution of 50%
Current study	34.4	711	20.67	OPC substitution of 35%
Current study	24.6	649	26.38	OPC substitution of 25%

.

The results of the current study are in the same order of magnitude as in Zhou et al. [19], whereas Alghamdi et al. [26] reported considerably lower values. These differences can be attributed to several factors, including the mix designs. This study used low kaolinite clays, yielding lower compressive strength. In turn, Alghamdi et al. [26] used recycled material in one of their mixtures, while Zhou et al. [19] used different admixtures than those used in this study. Additionally, variations in energy consumption and fuel types due to the different geographical contexts (i.e., Egypt, China, and Germany) may also contribute to the disparities. Nevertheless, the main hotspots were similar across the studies–OPC and calcined clay production. Comparisons across other impact categories were not feasible due to the use of different impact assessment methods.

5.2. SRA

The SRA results indicate that all sectors present similar levels of risk, with 9 to 11 indicators identified as “high” and “very high risk”. It is important to highlight that these risks are based on sector- and country-specific data, which may not entirely represent the reality of a particular supply chain. As outlined in Section SRA Procedure, the objective of this SRA was not to compare the OPC and LC³ supply chains. However, the results serve as guidance for more detailed assessments (e.g., an S-LCA), and can support improving the social performance of LC³ by addressing the identified social hotspots.

Several social issues were found to be of common risk for all sectors: living wage, non-fatal accidents, biomass consumption, industrial water depletion, international migrant stock, and public expenditure on education.

Fair salary was depicted as “very high risk” in the worker stakeholder category. PSILCA measures fair salary by comparing the sector’s average wage to the country’s living wage. The results point to the salary in these sectors being possibly not sufficient to cover the living costs of the workers, which could negatively affect their quality of life and that of their families.

Another common issue related to workers is health and safety, particularly the non-fatal accident rate, depicted as “high risk” across all sectors. Recent data from the German Social Accident Insurance shows that industries involved in the manufacture of glass and glassware, ceramics, processing of stone and soil (NACE code C, which includes manufacturing of clay, limestone, sand, cement, and mixing of mortars), as well as to transport and storage (NACE code H, which includes road transport) show non-fatal accident shares of 1.3% and 10.3%, respectively [69]. A comparison to other sectors suggests that the accident rate in raw material extraction and manufacture is relatively low, while that of transport is one of the highest [69]. This indicates that material transport may be a major social hotspot for non-fatal accidents.

Other identified social issues—biomass consumption, industrial water depletion, and migrant stock, and public expenditure on education—are determined at the country level in PSILCA and are not necessarily directly associated with the specific social risks of LC³ production. However, the LCA in this study revealed that sand extraction and cement production significantly contribute to water depletion. Regarding migrant stock, migrants are an essential part of the construction sector, including raw material extraction and production. This group is usually socially and economically vulnerable due to suboptimal working conditions, disproportionate representation, and immigration laws making migrants highly dependent on their employer [70].

In the LCSA by Sánchez Berriel et al. [31], the social impacts of LC³ production are assessed by evaluating potential changes in selected indicators. Some sub-categories in their study overlap with those identified here, namely health and safety for workers, access to material resources and safe and healthy living conditions (local community), and contribution to economic development (society). However, the indicators used to evaluate these aspects differ. For instance, health and safety addresses the incidence of diseases attributable to cement production, while the corresponding indicator in the SRA was not considered relevant for any of the economic sectors addressed, and the hotspot pointed to accident rates instead. Similarly, access to material resources is assessed by the number of infrastructure projects benefitting the community, while this indicator is not considered in PSILCA. These differences highlight the particularity of different geographical contexts when addressing social impacts and hotspots.

Regarding the possible adoption of LC³ production in Germany, the SRA revealed several topics that could affect the dissemination and establishment of the material. Specifically, fair salary and work accidents may be critical for the social performance of LC³.

As previously noted, it should be emphasized that this SRA relied on secondary data from the PSILCA database. Consequently, the conclusions on social risks were derived from sector- and country-level data rather than product- and location-specific information due to the absence of industrial LC³ production in Germany. This type of data limits the granularity and specificity of the outcomes, which is a common constraint in SRAs and social assessments based on secondary sources.

Table 9. LC³ processes, corresponding Eora sectors, and aspects requiring primary data or higher data resolution.

Process	Eora Sector	Primary Data/Higher Data Resolution Needs
Fuel production (for clay calcination)	Mining of coal and lignite	Type and origin of fuel; deviation from sector averages
Clay extraction	Quarrying of stone and soil	Origin of clay Extraction and processing methods (e.g., wet versus dry extraction)
Calcination process	Manufacture of non-metallic mineral products	Calcination technology (e.g., static, rotary, flash calcination)
Dried quartz sand production	Quarrying of stone and soil	Origin and extraction methods
Gypsum production	Manufacture of non-metallic mineral products	Origin and production route
Cement production	Manufacture of non-metallic mineral products	Origin and production technology
Limestone production	Quarrying of stone and soil	Origin of limestone
Raw material transport	Road and pipeline transport	Transport mode, vehicle type and capacity, fuel, distance
Electricity generation and transmission	Electricity and district heat	Electricity mix and supplier-specific conditions
LC3 manufacture	Manufacture of non-metallic mineral products	Mixing and batching operations; variations not captured by sector-level data
LC3 transport	Road and pipeline transport	Transport mode, vehicle type and capacity, fuel, distance

contrasts the main processes in LC³-based mortar production with Eora sectors (the country basis and sector-level data in PSILCA), highlighting processes that may require more granular data in future site- or supplier-specific SRAs or S-LCAs. These are steps where the standard sector-level data may mask variations that could meaningfully affect social risk and impact outcomes, such as extraction methods, calcination technology, or transport modes.

It is emphasized that certain LC³ processes may be oversimplified in sector-level data, which may not sufficiently reflect reality. For example, differences in clay extraction methods or calcination technology may lead to variations in labor conditions and exposure to hazards, or impacts on the local community that are not captured by coarser data. Similarly, transport and electricity sourcing could influence outcomes if supplier practices differ from the averages represented in the implemented database.

Future LC³ studies addressing social sustainability, such as S-LCA, should incorporate primary data to more accurately capture potential social impacts on the relevant stakeholder categories. Primary data would allow for validation of whether the identified social hotspots identified using country- and sector-level data, remain consistent, particularly for unit processes that differ between OPC and LC³. Moreover, primary data could reveal additional hotspots unique to specific locations or suppliers. Given that collecting such data requires significant time and resources, a pragmatic approach for a future S-LCA would be to prioritize the stakeholders and sub-categories highlighted in this SRA. At the same time, the use of primary data could uncover additional hotspots that are not identifiable at the sector- and country-level.

6. Conclusions

This study presents the first LCA and SRA of LC³-based mortar production in Germany, identifying key environmental and social hotspots. The LCA compared the environmental performance of OPC and LC³ mixtures with varying clinker content, highlighting the most relevant impact categories, life cycle stages, and processes. Additionally, the study explores the influence of dataset selection, assumptions on energy consumption and source, and transport distances in LCA results.

The LCA results indicate that LC³ mixtures significantly reduce environmental impacts across most impact categories. However, when results were normalized by compressive strength, an opposing trend emerged: the lower-strength mixes (LC³-35 and LC³-25) showed higher environmental impacts per MPa, as the benefits of clinker substitution were outweighed by reduced material performance. In contrast, LC³-50 maintained a balance between strength and reduced clinker, performing comparably or more favorably than OPC in categories such as Climate Change, Acidification, Human Toxicity (non-cancer), and Photochemical Ozone Formation. These findings emphasize the importance of evaluating construction materials within their application context, consistent with EN 15804 principles for comparability.

Raw material extraction was the most crucial life cycle stage, with OPC and calcined clay production being the most influential processes for Climate Change, Particulate Matter, and Resource Use (fossils). Clinker reduction in LC³ led to impact reductions ranging from 0.03% (Ozone Depletion) to 44.0% (Human Toxicity, non-cancer) in the mix with the lowest clinker content. However, Resource Use (fossils) increased by up to 29.8% for LC³-25, primarily due to the fuel used in clay calcination.

The SRA identified key social issues within the LC³ supply chain in Germany, including corruption, fair competition, freedom of association, fair salary, discrimination, worker health and safety, access to material resources, safe and healthy living conditions for the local community, and economic development contributions. Fair salary and non-fatal worker accidents were deemed particularly critical and should be closely monitored in LC³ production.

Future LCA studies should expand system boundaries to component-level impacts. Additionally, primary data would provide a more accurate representation of the environmental impacts of LC³. A comprehensive S-LCA study, building on the SRA findings, would quantify the actual social performance of LC3 and identify possible positive impacts based on supply chain-specific data.

The LCA and SRA in this study had several limitations. A key challenge was the reliance on secondary data, which may differ from industrial conditions. The SRA, conducted with PSILCA, provides country- and sector-level data only, meaning that the actual social conditions within specific supply chains may differ from those assessed.