3D　concrete　printing　(3DCP)　faces　challenges　in　the　automated　integration　of　reinforcement.　The　use　of　strain-hardening　cementitious　composites　(SHCCs)　with　high　ductility　offers　a　promising　solution　to　this　issue.　However,　the　high　cement　content　in　printable　SHCC　increases　the　carbon　footprint,　contributing　to　heavy　environmental　burden.　This　study　investigates　using　diatomite　(DE),　a　natural　sedimentary　rock,　to　develop　sustainable　SHCC　for　3DCP.　Diatomite　partially　replaces　ordinary　Portland　cement,　and　the　effects　of　various　DE　replacement　ratios　(10　%,　20　%,　30　%)　on　fresh　properties,　mechanical　properties,　hydration,　and　microstructure　are　experimentally　examined.　Sustainability　analysis　is　conducted　using　life　cycle　assessment　(LCA).　Results　show　that　a　30　%　DE　replacement　ratio　increases　the　dynamic　yield　stress,　static　yield　stress,　and　plastic　viscosity　by　31.7　%,　79.7　%,　and　239.5　%,　respectively.　A　10　%　DE　replacement　achieves　the　highest　mechanical　properties,　with　tensile,　compressive,　and　flexural　strengths　increased　by　54.6　%,　14.0　%,　and　27.4　%,　respectively,　compared　to　the　reference　group.　A　10　%　DE　replacement　ratio　enhances　the　hydration　process　with　increased　calcium　silicate　hydrate　gels　formation　and　refines　the　microstructure.　DE　replacement　ratio　above　20　%　negatively　impacts　hydration　due　to　insufficient　portlandite,　while　the　porous　structure　of　unhydrated　DE　increases　the　total　porosity　by　18.4　%.　LCA　results　show　a　25.8　%　reduction　in　global　warming　potential　can　be　achieved.　The　findings　reveal　that　the　developed　DE-SHCC　has　the　potential　to　facilitate　sustainability　and　enhance　the　mechanical　properties　in　construction　3D　printing.　©　2025