{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,26]],"date-time":"2026-01-26T23:47:03Z","timestamp":1769471223061,"version":"3.49.0"},"reference-count":119,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,1,24]],"date-time":"2026-01-24T00:00:00Z","timestamp":1769212800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Riga Technical University 2024 Project for Scientist","award":["RTU-ZG-2024\/1-0008"],"award-info":[{"award-number":["RTU-ZG-2024\/1-0008"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Compos. Sci."],"abstract":"<jats:p>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\u2013metakaolin (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 ~11\u201313% 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 ~30 MPa in compression and ~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.<\/jats:p>","DOI":"10.3390\/jcs10020062","type":"journal-article","created":{"date-parts":[[2026,1,26]],"date-time":"2026-01-26T12:41:16Z","timestamp":1769431276000},"page":"62","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Low-CO2 Concrete from Oil Shale Ash and Construction Demolition Waste for 3D Printing"],"prefix":"10.3390","volume":"10","author":[{"ORCID":"https:\/\/orcid.org\/0009-0007-1221-2026","authenticated-orcid":false,"given":"Alise","family":"Sapata","sequence":"first","affiliation":[{"name":"Institute of Sustainable Building Materials and Engineering Systems, Faculty of Civil and Mechanical Engineering, Riga Technical University, 6A Kipsalas, LV-1048 Riga, Latvia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0745-9634","authenticated-orcid":false,"given":"Ella","family":"Spurina","sequence":"additional","affiliation":[{"name":"Institute of Sustainable Building Materials and Engineering Systems, Faculty of Civil and Mechanical Engineering, Riga Technical University, 6A Kipsalas, LV-1048 Riga, Latvia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7864-7889","authenticated-orcid":false,"given":"Mohammed H.","family":"Alzard","sequence":"additional","affiliation":[{"name":"Institute of Sustainable Building Materials and Engineering Systems, Faculty of Civil and Mechanical Engineering, Riga Technical University, 6A Kipsalas, LV-1048 Riga, Latvia"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-7291-8296","authenticated-orcid":false,"given":"Peteris","family":"Slosbergs","sequence":"additional","affiliation":[{"name":"Institute of Sustainable Building Materials and Engineering Systems, Faculty of Civil and Mechanical Engineering, Riga Technical University, 6A Kipsalas, LV-1048 Riga, Latvia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9349-350X","authenticated-orcid":false,"given":"Hilal","family":"El-Hassan","sequence":"additional","affiliation":[{"name":"Department of Civil and Environmental Engineering, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2332-1347","authenticated-orcid":false,"given":"Maris","family":"Sinka","sequence":"additional","affiliation":[{"name":"Institute of Sustainable Building Materials and Engineering Systems, Faculty of Civil and Mechanical Engineering, Riga Technical University, 6A Kipsalas, LV-1048 Riga, Latvia"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,24]]},"reference":[{"key":"ref_1","unstructured":"(2025, July 10). The European Green Deal: Striving to Be the First Climate-Neutral Continent. Available online: https:\/\/commission.europa.eu\/strategy-and-policy\/priorities-2019-2024\/european-green-deal_en."},{"key":"ref_2","unstructured":"(2025, July 10). Circular Economy Action Plan. Available online: https:\/\/environment.ec.europa.eu\/topics\/circular-economy-topics\/first-circular-economy-action-plan_en."},{"key":"ref_3","unstructured":"(2025, July 10). Net Zero by 2050. 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