Ternary gypsum-cement-pozzolan (GCP) binders represent a promising low-carbon alternative to traditional Portland cement-based systems for additive 3D printing (3DP). This study presents a systematic three-stage experimental framework for the development of printable and durable GCP mixtures: (i) optimisation of gypsum-cement-metakaolin binder proportions based on a ternary diagram for 25 formulations, (ii) comparative evaluation of different pozzolanic additives and secondary gypsum sources alongside comprehensive durability testing, and (iii) adaptation of the optimised mixtures for 3DP, focusing on rheological properties. The optimal composition was determined with 55 wt% gypsum, 22.5 wt% Portland cement, and 22.5 wt% metakaolin, achieving a 28-day wet compressive strength of 36.2 MPa and a softening coefficient of 0.85. Successful integration of secondary gypsum sources was demonstrated. The GCP 3DP mixtures were developed with water/binder ratios of 0.38-0.45 and sand/binder ratios of 0.5-1.4, with an open time of 20-40 min. The mixtures exhibit pronounced thixotropic behaviour, characterised by increasing yield stress over time and relatively stable plastic viscosity. Printability tests confirmed the stable application of 29-39 layers before structural buckling. 3DP under laboratory conditions successfully demonstrated the feasibility of producing architectural and structural elements from sustainable GCP compositions.

Development of sustainability systems for assessment of environmental impacts remains a paramount challenge for green and circular manufacturing of polymers. In this study, a comprehensive life cycle assessment (LCA) framework is developed for European polymeric waste by integrating OpenLCA, Ecoinvent v3.11, and Python-based machine learning (ML) algorithms. Cradle-to-gate, service-life, and cradle-to-grave assessments are performed for representative thermoplastic composite systems, including PP-PET-cotton, HDPE-glass fiber, and PEEK-carbon fiber composites, covering domestic, engineering, and high-performance polymer categories. The results demonstrate that raw material extraction and manufacturing stages dominate environmental impacts, contributing the highest shares to climate change, ecotoxicity, and non-renewable energy consumption. PP-based composite systems exhibit the lowest overall environmental burdens due to lower processing energy and simpler molecular structures, while HDPE-based systems show moderate impacts. PEEK-based composites present the highest impacts per unit mass, driven by energy-intensive synthesis and high processing temperature. Environmental impacts are evaluated using EF v3.1 and ReCiPe methodologies, supported by Monte Carlo simulations and ML-assisted uncertainty quantification. Monte Carlo simulations and ML-assisted LCA provide probabilistic ranges, uncertainty quantification, and predictive insights into impact indicators, enabling the development of a quantitative sustainability system based on probability-impact relationships. A Europe-wide assessment of 57 Mt of polymeric waste highlights that environmental burdens are concentrated in countries with high polymer production and consumption, emphasizing the importance of energy mix, recycling efficiency, and waste management strategies. Overall, this work demonstrates that digitalized LCA coupled with ML offers a powerful decision-support framework for sustainable polymer design, recycling optimization, and circular economy policy development, supporting the transition toward low-carbon and resource-efficient polymer systems in Europe.

This study investigates the effect of accelerated carbonation on fine and coarse recycled concrete aggregates (RCA) obtained from a controlled precast concrete production source and their suitability for application in conventional and 3D printed concrete. Six mixtures with different RCA fractions, replacement levels were developed and evaluated in terms of fresh-state behavior, mechanical performance, and environmental impact. Aggregate carbonation was performed at 20 vol% CO2, 20°C ± 2 °C, and 70% ± 5% relative humidity for 7 days. XRD and DSC analyses confirmed portlandite consumption and limited bulk formation of calcium carbonate, while FTIR showed intensified carbonate bands and reduced hydroxyl-related vibrations. SEM observations revealed a denser and more compact adhered mortar microstructure after carbonation, indicating pore refinement and densification of the adhered mortar. Microstructural changes after carbonation resulted in a 28.7% and 23.8% reduction in water absorption for fine and coarse RCA, respectively, and improved flow retention in fresh mixtures. The incorporation of RCA reduced compressive strength by 13.2%, 7.8%, and 21.8% for 50% coarse RCA, 100% coarse RCA, and combined 100% coarse and 50% fine RCA replacement, respectively. Carbonation improved compressive strength by 4.6%–8.4% and reduced capillary water absorption. The mixture containing 100% carbonated coarse RCA achieved mechanical and water transport properties comparable to the reference concrete. The influence of carbonation in 3D-printed specimens was limited, suggesting that interlayer porosity dominates mechanical and capillary water absorption performance. All 3D printed mixtures proved suitable for 3D printing applications, where immediate extrusion can minimize the workability loss associated with the high water absorption of RCA during transport and prolonged handling. Life cycle assessment (LCA) showed that replacing NA with RCA reduced the global warming potential (GWP) of concrete mixtures, although the environmental benefit of carbonation depended strongly on the energy demand of the carbonation process.

This paper investigates wood fiber and cement binder composites to propose a novel method for predicting their physical and thermal properties. These materials hold significant potential for applications in wood-wool cement boards designed for ecological and passive buildings. Three composites with varying compositions and properties were studied. Initial analyses included testing the densities, porosities, and thermal conductivities of the dry composites. The materials exhibited bulk densities ranging from 0.312 to 0.392 g/cm3, true densities from 1.986 to 2.135 g/cm3, and open and total porosities of 58.0-61.8 % and 81.6-84.3 %, respectively. Their thermal conductivities, measured over temperatures from 13 to 33 degrees C, ranged from 0.0549 to 0.0649 W/m/K, with a linear increase observed with increasing temperature. These experimentally determined properties were employed to develop and tune the micro-scale numerical model of heat transfer in bio-based composites and the method for predicting their physical and thermal properties. The model used micro-computed tomography data to capture the complex and highly anisotropic microstructure of the composites. The main novelty of the proposed method is its ability to predict the anisotropic thermal conductivity tensor of highly heterogeneous composites, including the temperature dependence of their components. Another advantage is that it can also predict other physical properties of composites, such as density and porosity. The method demonstrated high prediction accuracy, with relative errors below +/- 5.4 % for all materials studied, together with high computational efficiency. This method is of significant relevance for the field, as it enables the prediction and optimization of properties in similar bio-based composites, the calculation of properties in directions not typically measured (i.e., along the width and length of boards), and the generation of input data for macro-or wall-scale models.

Circularity (CE) is a powerful instrument to contrive sustainability. However, CE entails innovation. Current research discovers advanced technological solutions for operational implementation of CE in polymeric manufacturing industries. Based on spectroscopic characterization, mechanical testing, tribological investigations, Python-based computation, and PyCharm machine learning algorithms, the traditional, engineering, high performance, and ultra-high performance manufacturing systems are developed fundamentally rely on coefficient of friction (COF), wear rates, plastic deformation, and fracture mechanism. The designed COF values of strategic, conventional, and domestic manufacturing systems are standardized in the range of 0.03-0.09, 0.10-0.22, and 0.30-0.47, respectively. Experimental manufacturing systems are evinced on the fabrication of polypropylene-based composites with facilities of Vickers hardness and thermal stability in the ranges of 1000-1800 HV10 and 400-2400 degrees C. Tensile, bending, and impact tests are standardized according to American standards for industrial production and commercialization. The conceptual framework of silicon nitride, zirconia, tungsten carbide, steel, alumina hard materials, titanium aluminum nitride, and titanium carbo-nitride coatings manufacturing systems are propounded to process all possible polymers and waste. Additionally, diversity in experimental and computational results can be introduced for automation, digitalization, implementation of the concept of circularity, and sustainability in view of reverse engineering concepts. (c) 2025 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

This study addresses a research gap in upcycling complex organic-mineral residues by investigating the thermal reactivation of sanding dust (SD) generated during the production of wood-wool cement panels. Its novelty lies in establishing a low-temperature pathway that recovers hydraulic capacity without triggering CO2 release from carbonated phases. The research design involved heating raw SD at 450 ℃ for five hours - a temperature selected to maximize portlandite dehydration while remaining below the 600 ℃ decarbonation threshold - followed by comprehensive chemical, mineralogical, and physical characterization (XRD, TGA, SEM). This reactivated binder was then utilized to produce novel, low-density biocomposites using manufacturing-line waste as filler. Major findings confirmed that heat treatment reduced average particle size from 29.21 μm to 19.11 μm and successfully restored hydraulic activity, increasing binder compressive strength from 1.59 to 13.05 MPa. The resulting biocomposites achieved compressive strengths up to 185 kPa and a low thermal conductivity of 0.068 W/(m·K) with a density of 369-415 kg/m3. These results indicate that 450 ℃ serves as an optimal "thermal window" for this waste, effectively transforming industrial residues into functional secondary raw materials for sustainable building insulation.

Reducing CO2 emissions is a critical priority in the construction industry. This study investigates CO2 storage in 3D-printed hempcrete while achieving sufficient mechanical properties for envelope or shell element applications. The use of hemp shives as bio-based aggregates with cement, hydrated lime, and hydraulic lime-based binders was investigated to develop low carbon 3D-printable hempcrete. The mixtures were evaluated for printability, fresh-state properties, mechanical performance, thermal conductivity, and CO2 emissions. Hydrated lime mixtures exhibited lower compressive strength than cement and hydraulic lime-based mixtures after 7, 28, and 90 days of curing. Hemp shives reduced compressive strength by up to 80.1% compared with the corresponding cement mortar. Hydraulic lime-based hempcrete showed the lowest CO2 emissions, reaching 15.15 kg CO2-eq/MPa of compressive strength. These results demonstrate the potential of hydraulic lime-based binders for extrusion-based 3D printing of sustainable hempcrete envelope or shell elements.

To meet 2050 climate targets, the construction sector must reduce CO2 emissions and transition toward circular material flows. Recycled aggregates (RA) derived from construction and demolition waste (CDW) and industrial byproducts such as oil shale ash (OSA) show potential for use in concrete, although their application remains limited by standardisation and performance limitations, particularly in structural uses. This study aims to develop and evaluate low-strength, resource-efficient concrete mixtures with full replacement of natural aggregates (NA) by CDW-derived aggregates, and partial or full replacement of cement CEM II by OSA-metakaolin (MK) binder, targeting non-structural 3D-printing applications. Mechanical performance, printability, cradle-to-gate life cycle assessment, eco-intensity index, and transport-distance sensitivity for RA were assessed to quantify the trade-offs between structural performance and global warming potential (GWP) reduction. Replacing NA with RA reduced compressive strength by similar to 11-13% in cement-based mixes, while the aggregate type had a negligible effect in cement-free mixtures. In contrast, full cement replacement by OSA-MK binder nearly halved compressive strength. Despite the strength reductions associated with the use of waste-derived materials, RA-based cement-free 3D-printed specimens achieved similar to 30 MPa in compression and similar to 5 MPa in flexure. Replacing CEM II with OSA-MK and NA with RA lowered GWP by up to 48%, with trade-offs in the air-emission, toxicity, water and resource categories driven by the OSA supply chain. The cement-free RA mix achieved the lowest GWP and best eco-intensity, whereas the CEM II mix with RA offered the most balanced multi-impact profile. The results show that regionally available OSA and RA can enable eco-efficient, structurally adequate 3D-printed concrete for construction applications.

The increasing generation of wood ash (WA) from biomass combustion presents both an environmental challenge and an opportunity for sustainable resource utilization. This review provides a comprehensive assessment of recent advances in the valorization of WA for the development of sustainable engineering materials within a circular economy framework. Unlike previous studies that primarily focus on isolated applications of WA, this work integrates multiple technical dimensions, including material characterization, advanced manufacturing technologies, mechanical performance evaluation, computational modelling, and industrial commercialization pathways. Wood ash typically exhibits alkaline characteristics (pH 9-13.5) and particle sizes ranging from 1 to 1000 µm, enabling its application in a wide range of material systems. In cementitious materials, partial replacement of cement with WA (0.10-20%) generally improves mechanical performance, whereas excessive incorporation may reduce structural integrity. The high silica content (>62%) in certain WA types also enables its utilization in lightweight glass systems and radiation-shielding materials. Furthermore, WA has emerged as a promising functional filler in polymeric and ceramic composites, where additions above 0.5% can enhance dynamic mechanical properties and thermal stability. The review also examines standardized inspection and testing procedures, including quality control (QC) and quality assurance (QA) frameworks based on American Society for Testing and Materials (ASTM), Canadian Standards Association (CSA), and European standards, to ensure the reliability of WA-derived materials. Recent developments in artificial intelligence, machine learning, and computational modelling are highlighted for predicting mechanical behavior, optimizing processing parameters, and enabling digitalized manufacturing systems. In addition, circular manufacturing strategies and economic evaluation models, including break-even analysis, are discussed to assess the industrial feasibility of WA-based products. By integrating circular economy principles with materials engineering, digital technologies, and economic assessment, this review establishes a holistic framework for transforming wood ash from an industrial residue into value-added sustainable materials for construction, energy, and advanced composite applications.

This study examines the feasibility and environmental performance of extrusion-based 3D-printed bio-based composite wall elements combining a structural outer shell with a hempcrete insulation core. To address the critical gap in process-level life cycle impacts for digital bio-construction, this work introduces a novel multi-scale evaluation that couples fresh-state printability and mechanical performance with a comprehensive CO2 footprint assessment. Three printable bio-based mixtures were developed using alternative binders—magnesium oxychloride cement (MOC), calcium sulfoaluminate cement (CSA), and a gypsum-based binder (BG)—and evaluated across material, printing-process, and wall-assembly levels. Green strength, density, and compressive and flexural strengths were measured on both printed and moulded specimens. Concurrently, a cradle-to-gate life cycle assessment was conducted, utilizing strength-normalized climate indicators and comparisons with conventional insulated wall systems. The CSA mix delivered the highest printed compressive strength exceeding 5MPa, followed by MOC and BG; printed specimens consistently exhibited slightly lower strength and density than moulded counterparts due to extrusion-induced porosity. At the material scale, BG achieved the lowest global warming potential (GWP) per cubic meter due to the low-impact nature of gypsum, whereas CSA and MOC have higher environmental impacts associated with their respective binders. When normalized by compressive strength, BG also emerged as the most eco-efficient binder, while MOC exhibited the highest impact per MPa. At the component scale, all three 3D-printed configurations achieved net-negative GWP, storing 123 to 171kg CO2-eq per square meter of wall at an insulation performance of U = 0.105W/(m2·K), significantly outperforming mineral wool and EPS-insulated reference masonry. These results demonstrate that combining 3D-printed bio-based skins with carbon-sequestering cores provides a mechanically robust, thermally efficient, and truly carbon-negative alternative to conventional building envelopes.

Recycling concrete at the end of its service life has become increasingly important for sustainable construction, but the use of recycled aggregates (RA) remains limited because their properties are generally inferior to those of natural aggregates. This shortcoming is mainly due to the porous adhered mortar and weak interfacial transition zones, which reduce their physical properties and durability. Microbially Induced Calcite Precipitation (MICP) has recently emerged as a promising bio-based treatment method for improving RA properties by precipitating calcite (calcium carbonate, CaCO3) within surface pores and microcracks. This study presents a comprehensive systematic review, focusing exclusively on experimental research that applied MICP to enhance RA properties. Thirty-one relevant studies were identified, and their findings were analyzed and synthesized to determine the influence of bacterial strain, cell concentration, calcium source and concentration, treatment duration, temperature, and pH on RA performance. Across the standalone MICP datasets, water-absorption reductions of up to 64% and mass gains of up to 13% were reported. Sodium-alginate-assisted MICP achieved water-absorption reductions of up to 88%, but these assisted datasets were analyzed separately because the contribution of the alginate could not be isolated from the MICP effect. The synthesis identified independently derived literature-informed candidate ranges, including Sporosarcina pasteurii as the most extensively investigated strain, cell concentrations 108-109 cells/mL, calcium-source concentrations of 0.333 - 0.666 mol/L, soaking for approximately seven days, controlled temperatures of 20 - 25°C, and initial bulk-solution pH values of 9 - 10. These parameters were not evaluated together and should not be interpreted as a validated combined protocol. Additionally, research gaps, remaining challenges, and future work in MICP treatment for RA are outlined.

This research proposes an alternative low-cement multicomponent binder for extrusion-based 3D concrete printing to reduce CO2 emissions associated with high Portland cement content. Due to the extremely low Portland cement content (100 kg/m3), the proposed mixture presents several limitations, making it unsuitable for 3D printing without additional activation. To overcome these limitations, chemical and physico-chemical activation methods were applied to promote rapid early-age structuration, partly associated with accelerated ettringite formation, thereby improving compliance with the printing process requirements. The results demonstrate that both activation methods positively affect Portland cement hydration and improve printing-related properties. The research focuses primarily on the hardened properties of 3D-printed concrete, showing that activation reduces macroscopic porosity and increases density and compressive strength. The applied activation methods also increase overall shrinkage compared to the nonactivated low-cement mixture. However, the absolute shrinkage remains approximately 25-30 % lower than that of a conventional reference mortar with a high Portland cement content. The suitability of the components used in the multicomponent binder was evaluated through pozzolanic activity testing. In contrast, the effects of chemical and physico-chemical activation on binder phase composition were investigated by X-ray diffraction, and the hardened properties of concrete were assessed using X-ray computed tomography, mercury intrusion porosimetry, shrinkage measurements, density, and compressive strength testing. The results demonstrate that chemical and physico-chemical activation enables the effective use of low-cement multicomponent binders in extrusion-based 3D concrete printing, providing a more sustainable alternative to conventional high-cement mixtures.

This paper presents the design, fabrication, and verification workflow used to realise LABLAB 2.0, a large-scale multi-part 3D concrete printed sculpture installed on the Riga Technical University campus. Developed through a student design competition with support from researchers, designers, industry partners, and mentors, the project explores how a complex digital geometry can be translated into printable, transportable, and assemblable concrete components. The workflow combined constraint-based geometry development, parametric segmentation, material verification, extrusion-based fabrication, crane-assisted assembly, and scan-based assessment. The sculpture was produced from 13 printed concrete components using a one-component dry-mix material containing oil shale ash and metakaolin. In the printing campaign, 3.7 t of dry mix material was consumed within 26 h of machine printing time, and total production took ˜59 h. Assembly required ˜130 person-hours, with manual alignment, sanding, drilling, lifting, and connection detailing remaining major sources of labour. Scan-based dimensional verification showed a ˜5% higher volume than the fabrication-ready digital model, with dimensional deviations of ˜2%, 5%, and 3% along the principal axes. The results demonstrate that multi-part 3D concrete printing depends not only on material and printing performance, but also on segmentation logic, handling strategy, tolerance management, and workflow organisation.

This study examines the feasibility and environmental performance of extrusion-based 3D-printed biobased composite wall elements, which combine a structural outer shell with a hempcrete insulation core. Three printable bio-based mixtures were developed using alternative binders – magnesium oxychloride cement (MOC), calcium sulfoaluminate cement (CSA) and a gypsum-based binder (BG) – and evaluated in terms of fresh properties, mechanical performance and life-cycle impacts. Green strength, density, compressive and flexural strength were measured on both printed and moulded specimens, while a cradle-to-gate carbon footprint assessment was carried out at material, printing-process and wall-assembly levels, including strength-normalised indicators and comparison with conventional insulated wall systems. CSA delivered the highest compressive strength of the printed composites (>5 MPa), followed by MOC and BG, with printed specimens showing slightly lower strength and density than their moulded counterparts. At the material level, BG exhibited the lowest global warming impact (GW) per cubic metre due to the intrinsically low impact of gypsum, whereas CSA and MOC were penalised by their calcined components. When normalised by compressive strength, CSA emerged as the most environmentally efficient binder, while MOC showed the highest GW per MPa. At wall level, all three 3D-printed outer layers combined with a low-density hempcrete core achieved net-negative GW, storing approximately 123–171 kg CO₂-eq per square metre of wall at U = 0.105 W/(m²·K), and clearly outperforming mineral wool and EPS-insulated reference walls. The results demonstrate that 3D-printed bio-based envelopes with hempcrete infill can provide mechanically robust, thermally efficient and carbon-negative alternatives to conventional building envelope solutions.

Steel slag aggregates (SSA) offer a potential route for reducing reliance on natural aggregates (NA) and diverting steelmaking by-products from landfill. However, facility-specific life cycle data for SSA production in Abu Dhabi, United Arab Emirates, remain limited. This study quantifies the cradle-to-gate greenhouse gas footprint of SSA produced at two recycling facilities in Abu Dhabi. The assessment follows ISO 14040/14044 and uses a functional unit of 1 tonne of SSA. Primary 2024 operational data were combined with emission factors from the UK Government 2024 dataset, Intergovernmental Panel on Climate Change default values, and published literature. The combined emissions for 500,000 tonnes of SSA were 3,270.22 t CO2eq, corresponding to an average intensity of 6.54 kg CO2eq/tonne SSA. Al Fayah emitted 2,007.88 t CO2eq for 250,000 tonnes of output, equivalent to 8.03 kg CO2eq/tonne SSA, while KEZAD B emitted 1,262.33 t CO2eq for 250,000 tonnes of output, equivalent to 5.05 kg CO2eq/tonne SSA. Inbound material transportation dominated the footprint at both plants, particularly last-mile road transport. Compared with the NA benchmark of 7.75 kg CO2eq/tonne, the average SSA intensity was approximately 16% lower. Under the stated boundary and assumptions, SSA showed lower cradle-to-gate emissions than NA. The way forward should prioritize primary metering, carrier data, and the development of a third-party-verified Environmental Product Declaration to strengthen comparability and market uptake.

This study investigates the feasibility of incorporating wood-based waste in cementitious composites for extrusion-based three-dimensional (3D) printing through the production of artificial aggregates. Because lignocellulosic residues can retard cement hydration, wood dust was chemically modified with a calcium nitrate-based accelerator and granulated into aggregates using disc granulation. The resulting aggregates were characterized for mechanical robustness, and their influence on cement hydration and microstructural development was evaluated using X-ray diffraction (XRD) and thermogravimetric/differential scanning calorimetry (TG/DSC). The modified aggregates were then incorporated into 3D printable cementitious mixtures to assess fresh-state properties, printability, and mechanical performance. The accelerator affected hydration by increasing bound water content and altering the development of hydration products. The produced aggregates exhibited sufficient crushing resistance for practical handling. The incorporation of artificial aggregates resulted in reduced compressive and flexural strengths compared to the reference mixture. However, the differences between mechanical properties measured in different loading directions were reduced, indicating a more uniform structural response in printed elements. The findings demonstrate that chemically treated wood-based aggregates can be successfully integrated into 3D printable cementitious systems, offering a promising pathway toward more sustainable construction materials.

Cement production significantly contributes to greenhouse gas emissions and depletes limited natural resources. Sustainable methods are needed to mitigate the environmental impact, including carbon capture, alternative fuels, and supplementary cementitious materials. Recycling waste aggregates or processed cement can reduce the carbon footprint of cement production. This research investigates the mechanical recovery of residual material fines fraction generated during wood–cement particleboard manufacturing to create a new sustainable binder with unhydrated and hydrated cement particles. This approach could lead to the development of more environmentally friendly building materials. This study offers the application of the recovered binder and residual materials generated during wood–cement particleboard manufacturing to produce a new bio-based building material. The residual material fines fraction, consisting of partially hydrated and unhydrated cement particles and wood fibers, is processed by milling to break up the conglomerates. The resulting fines fraction is used as a binder in mortar samples tested for mechanical compressive strength. The developed binder was combined with different wood wool residual material streams and used as the filler material. Lightweight bio-based building material was created with a 245 kg/m3 density and thermal conductivity of 0.0796 W/(mK). The study highlights the potential of using residual resources to produce sustainable construction materials.

This paper discusses the flexural and tensile strength properties of 3D printed concrete, based on the results of a RILEM TC 304-ADC interlaboratory study on mechanical properties. These properties are determined using different testing techniques, including 3- and 4-point flexural tests, splitting tests, and uniaxial tension tests, on specimens extracted from large 3D printed elements in accordance with a prescribed study plan. The relationship between compressive and flexural or tensile strengths, cast or printed samples, different types of tests, and different loading orientations, are analysed to understand the influence of 3D printing. As expected, the strength can reduce significantly when the main tensile stress is acting perpendicular to the interface between layers. The role of deviations from the standard study procedure, in terms of the time interval between the placing of subsequent layers, or the adoption of a different curing strategy, are also assessed. While the increased time interval significantly impacts the strength in the critical direction, the use of variable curing conditions does not seem to have a clear-cut effect on the strength ratios of the printed to cast specimens. Additionally, the paper looks at the variability in the results for the printed specimens, in order to emphasize the need for multiple replicates for obtaining a proper result. An extensive insight into the aspects affecting the variability is presented in the paper. Finally, with the limited dataset available for specimens tested at a larger scale, it is difficult to arrive at a clear understanding of the role of specimen size (i.e., greater number of layers).

The two major themes in the current construction industry are digital construction and low environmental impact. As a prominent digital construction technology, concrete 3D printing has attracted increasing attention. However, the current understanding of the durability of 3D printed cement-based materials (3DPCM) remains limited, which hinders its wider application, especially as load-bearing, reinforced concrete structures. This work shares the knowledge acquired during a broad interlaboratory study regarding the durability of 3DPCM with 15 laboratories from 13 countries participating, under the framework of TC 304-ADC ‘Assessment of Additively Manufactured Concrete Materials and Structures’. Anisotropy in water absorption capacity, carbonation and chloride ingress resistance of 3DPCM were evaluated by 15 institutes with their own printable materials and printing equipment. Additionally, the impacts of cold joints on these properties were investigated and a comparison between printed and cast samples was carried out. The outcome of this study indicates that the water absorption test provides information on the bulk porosity of the samples, while the carbonation and chloride ingress tests are more effective and visually reflect the local defects, especially the layer interfaces and cold joints. The water ingress depth of cast samples prepared with printable mixtures is an order of magnitude higher compared to conventional concrete, while their carbonation and chloride ingress resistance are comparable. The sorptivity and estimated water ingress height of printed samples measured in the direction parallel to the filaments is generally higher than that measured in the perpendicular direction and in cast samples. Similarly, the carbonation and chloride ingress depth and rate of printed samples measured in the direction parallel to the filaments is generally higher than that measured in the perpendicular direction or in cast samples. The overall durability of 3DPCM is weakened by anisotropy, these effects can be addressed with targeted mixture design and processing strategies. Due to the variations in printers, printing parameters and materials, three types of cross-section geometries were observed in printed samples with cold joints. The carbonation depth that measured from the maximum carbonation ingress point near the cold joint to the sample edge effectively captures the effect of cold joints in all these three types of cross-section geometries of printed samples. Finally, the participants identified areas of improvement in the methodology and suggestions were made to refine the procedure for adoption in future research.

Cities and their inhabitants are among the largest consumers of energy and contributors to environmental pollution, accounting for 70 % of global greenhouse gas emissions. One of the European Union’s key strategies for addressing this issue is the development of Positive Energy Districts (PEDs). Although some PEDs already exist, the concept remains an emerging field of study that goes beyond achieving neighborhoods with net-zero energy imports – or even net-positive energy production. It also emphasizes sustainability and the reduction of greenhouse gas (GHG) emissions. This article explores solutions for implementing PEDs, focusing on energy flow analysis and Life Cycle Assessment (LCA) to inform decision-making. Developing PEDs is a multifaceted process that involves improving building energy efficiency, assessing existing energy sources, exploring opportunities for on-site energy generation, integrating renewable energy systems, and ensuring efficient storage of generated energy. A significant aspect of LCA is calculating embodied emissions for all PED-related implementations, particularly in existing districts where substantial improvements are needed to meet PED goals. In such cases, LCA plays a crucial role in ensuring not only net-zero energy imports but also meaningful GHG emission reduction. Although LCA is not yet widely applied in the development of PEDs, this article highlights its importance in addressing key aspects of achieving climate neutrality goals, when transforming urban areas to PEDs.