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Mechanical interlocking of 3D printed concrete layers
Thesis (PhD)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613959943618560 |
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| access_status_str | Open Access |
| author | Mostert, Jean-Pierre |
| author2 | Kruger, Jacques |
| author_browse | Kruger, Jacques Mostert, Jean-Pierre |
| author_facet | Kruger, Jacques Mostert, Jean-Pierre |
| author_sort | Mostert, Jean-Pierre |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134718 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:44:25.612Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134718 Mechanical interlocking of 3D printed concrete layers Mostert, Jean-Pierre Kruger, Jacques Van Zijl, Gideon Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. Three-dimensional printing Concrete -- Mechanical properties Additive manufacturing Thesis (PhD)--Stellenbosch University, 2025. Mostert, J. 2025. Mechanical Interlocking of 3D Printed Concrete Layers. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/923eb78b-be42-4c25-99ea-97a99e77fba5 ENGLISH ABSTRACT: Three-dimensional printed concrete (3DPC) is promoted as a pathway to affordable, resource-efficient, and geometrically flexible construction capable of meeting rapid urban growth. However, the adoption of 3DPC remains constrained by poor bonding between layers, which introduces anisotropy and undermines both mechanical and durability performance. To address this limitation, this research conducted a critical review of existing methods where mechanical interlocking was identified as the most practical and scalable approach. This strategy relies on the mechanical interlocking between printed filaments to enhance interlayer adhesion without relying on chemical additives or complex reinforcement. To implement this strategy, a custom 3D printed plastic nozzle with three grooves measuring 7×7 mm was designed to imprint rectangular, sinusoidal, and triangular tongue-and-groove profiles onto filament surfaces.The sinusoidal profile was most effective, increasing tensile strength perpendicular to the layers, also referred to as interlayer bond strength, by 213% and compressive strength by 45.1%. Further investigations into the anisotropic properties resulted in the tensile anisotropy index to reduce from 2.29 to 0.16, and the compressive index from 0.37 to 0.05, indicating near isotropic mechanical behaviour. Additional durability tests, following the Durability Index Procedure, further complimented these improvements, with the triangular profile reducing chloride conductivity through the interlayer region by 74.2% and improving the material’s classification from “very poor” to “good”. Optimising the interlocking geometry was a critical step in improving interlayer bonding performance. Due to the complex geometrical interactions and nonlinear material behaviour involved, analytical methods were insufficient to fully capture the intricacies of stress transfer and failure mechanisms. Therefore, a finite element analysis (FEA) approach was adopted to systematically evaluate the influence of groove geometry on interlayer bond performance. An interface-based finite element model was employed using DIANA to investigate the effect of groove depth, width, count, and fillet radius, which are key characteristics of the interlocking geometry. The model incorporated a combined cracking-shearing-crushing material model for the interlayer regions and a total strain-based cracking material model for the continuum (bulk material) to realistically capture the mechanical response under loading. Through this mesoscale simulation, an optimal configuration was identified, consisting of three grooves, each 7 mm deep and 7 mm wide, with a fillet radius equal to half the groove width. This arrangement resulted in a predicted 179.5% improvement in interlayer bond strength. To evaluate the structural performance benefits of filament interlocking in reinforced 3DPC beams, four-point bending tests were conducted on 2.5m long specimens under two shear-span-to-depth ratios (aᵥ/d = 2.75 and 5), representing shear- and bending-dominant conditions, respectively. Under the shear-dominant configuration, interlocked beams exhibited a 97.6% increase in peak load capacity (60.53 kN vs. 30.64 kN), along with substantial improvements in ductility (5.36 to 27.57) and yield stiffness (2.03 to 9.54 kN/mm). In the bending-dominant setup, interlocking still provided measurable gains, including a 10.7% increase in peak load and higher displacement capacity. Notably, cracking in interlocked beams propagated through the bulk material rather than along interlayer interfaces, indicating improved cohesion and mechanical continuity. Deterministic resistance predictions based on a modified Eurocode 2 model closely matched the behaviour of flat-layered beams (0.19% deviation in bending) but underestimated the flexural capacity of interlocked beams by 8.81%, providing a conservative design margin. For shear, predictions significantly overestimated resistance in the reference beams (up to 108%), whereas results for interlocked beams deviated by only 13.08%, demonstrating the accuracy and structural reliability enabled by interlayer interlocking. This research establishes mechanical interlocking of 3DPC layers as a viable and scalable method for enhancing the structural and durability performance of 3DPC. It demonstrates that tailored filament geometries can effectively mitigate anisotropy and improve mechanical and durability performance using standard printable materials and commercially available equipment. By integrating mesoscale experimental validation, computational optimisation, and structural-scale implementation, this work provides actionable design guidance and accessible tools for industry. The findings support digital construction as a sustainable, resilient, and high-performance solution for future infrastructure and housing needs. AFRIKAANSE OPSOMMING: Drie-dimensioneel gedrukte beton (3DGB) word bevorder as ‘n metode vir bekostigbare, hulpbroneffektiewe en geometries buigsame konstruksie wat vinnige stedelike groei kan ondersteun. Nietemin bly die aanvaarding van 3DGB beperk weens swak binding tussen opeenvolgende lae, wat beide meganiese en duursaamheidsprestasie benadeel sowel as aanleiding gee tot anisotropie. Om hierdie beperking aan te spreek, het hierdie navorsing ‘n kritiese oorsig van bestaande metodes uitgevoer en meganiese intervergrendeling geïdentifiseer as die mees praktiese en skaalbare benadering. Hierdie strategie maak staat op meganiese interaksie tussen gedrukte filamente om interlaag adhesie te verbeter sonder chemiese bymiddels of ingewikkelde versterkings. Om hierdie strategie uit te voer, is ‘n pasgemaakte 3D-gedrukte plastiek spuitstuk met drie groewe van 7×7 mm ontwerp om reghoekige, sinusvormige en driehoekige tong-en-groefprofiele op filamentoppervlaktes te druk. Die sinusvormige profiel was die doeltreffendste, met ‘n toename in treksterkte loodreg op die lae, bekend as interlaag-bindsterkte, van 213% en ‘n verhoging in druksterkte van 45.1%. Verdere ondersoeke na anisotropiese eienskappe het getoon dat die trek-anisotropie-indeks verminder het van 2.29 na 0.16 en die druk-indeks van 0.37 na 0.05, wat ‘n nagenoeg isotropiese meganiese gedrag aandui. Bykomende duursaamheidstoetse volgens die Duursaamheidsindeks-prosedure het hierdie verbeterings ondersteun, met die driehoekige profiel wat die chloriedgeleidingsvermoë deur die interlaaggebied met 74.2% verminder het, en die materiaal se klassifikasie verbeter het vanaf “baie swak” na “goed”. Optimering van die intervergrendelingsgeometrie was krities vir verdere verbetering van die interlaagbinding. Weens die komplekse geometriese interaksies en nie-lineêre materiaalgedrag was analitiese metodes onvoldoende om spanningsoordrag en falingsmeganismes volledig te beskryf. Daarom is ‘n eindige element-analise (EEA) benadering gevolg om die invloed van groefgeometrie op interlaagprestasie stelselmatig te evalueer. ‘n Koppelvlak-gebaseerde eindige elementmodel is met DIANA sagteware ontwikkel om die effek van groefdiepte, -breedte, -aantal en afrondingsradius te ondersoek, almal sleutelkenmerke van die intervergrendeling-geometrie. Die model het ‘n gekombineerde kraak-, skuif- en vergruisingsmateriaalmodel vir die interlaaggebiede gebruik en ‘n totale vervormingsgebaseerde kraakmodel vir die massamateriaal om realisties die meganiese reaksie onder las na te boots. Hierdie mesoskaalse simulasie het ‘n optimale konfigurasie geïdentifiseer wat bestaan uit drie groewe, elk 7 mm diep en 7 mm breed, met ‘n afrondingsradius gelyk aan die helfte van die groefbreedte. Hierdie konfigurasie het ‘n voorspelde verbetering van 179.5% in interlaag-bindsterkte opgelewer. Om die strukturele prestasievoordele van filament-intervergrendeling in versterkte 3DGB-balke te evalueer, is vierpunt-buigtoetse uitgevoer op 2.5 m lange balke onder twee skuifspan-tot-diepte-verhoudings (aᵥ/d = 2.75 en 5), onderskeidelik verteenwoordigend van skuif- en buigdominante toestande. In die skuifdominante opstelling het die intervergrendelde balke ‘n toename van 97.6% in maksimumlasvermoë getoon (60.53 kN teenoor 30.64 kN), tesame met aansienlike verbeterings in smeebaarheid (5.36 na 27.57) en styfheid by vloeipunt (2.03 na 9.54 kN/mm). Onder buigdominante toestande het intervergrendeling ook meetbare voordele gelewer, insluitend ’n toename van 10.7% in maksimumlas en hoër verplasingsvermoë. Merkwaardig genoeg het krake in intervergrendelde balke deur die massamateriaal versprei eerder as langs interlae, wat verbeterde kohesie en meganiese kontinuïteit aandui. Deterministiese weerstandvoorspellings gebaseer op ‘n aangepaste Eurokode 2-model het die gedrag van plat-laag balke noukeurig voorspel (0.19% afwyking in buiging), maar het die buigsterkte van intervergrendelde balke met 8.81% onderskat, wat ’n konserwatiewe ontwerpmarge verskaf. Vir skuifweerstand is voorspellinge aansienlik oorskat vir die verwysingsbalke (tot 108%), terwyl resultate vir intervergrendelde balke slegs met 13.08% afgewyk het, wat die akkuraatheid en strukturele betroubaarheid van interlaag-intervergrendeling demonstreer. Hierdie navorsing bevestig dat meganiese intervergrendeling van 3DGB-lae ‘n praktiese en skaalbare metode is om die strukturele- en duursaamheidsprestasie van 3DGB te verbeter. Dit toon aan dat aangepaste filamentgeometrieë anisotropie effektief verminder en verbeterde meganiese- en duursaamheidsprestasie lewer deur standaard drukbare materiale en kommersieël beskikbare toerusting te gebruik. Deur mesoskaalse eksperimentele validering, rekenaaroptimalisering en strukturele implementering te integreer, bied hierdie werk bruikbare ontwerpriglyne en toeganklike gereedskap vir die industrie. Die bevindings ondersteun digitale konstruksie as ‘n volhoubare, veerkragtige en hoëprestasie-oplossing vir toekomstige infrastruktuur- en behuisingsbehoeftes. Doctoral 2026-01-05T09:22:48Z 2026-01-05T09:22:48Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134718 Stellenbosch University xv, 132 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Three-dimensional printing Concrete -- Mechanical properties Additive manufacturing Mostert, Jean-Pierre Mechanical interlocking of 3D printed concrete layers |
| title | Mechanical interlocking of 3D printed concrete layers |
| title_full | Mechanical interlocking of 3D printed concrete layers |
| title_fullStr | Mechanical interlocking of 3D printed concrete layers |
| title_full_unstemmed | Mechanical interlocking of 3D printed concrete layers |
| title_short | Mechanical interlocking of 3D printed concrete layers |
| title_sort | mechanical interlocking of 3d printed concrete layers |
| topic | Three-dimensional printing Concrete -- Mechanical properties Additive manufacturing |
| url | https://scholar.sun.ac.za/handle/10019.1/134718 |
| work_keys_str_mv | AT mostertjeanpierre mechanicalinterlockingof3dprintedconcretelayers |