Mix Design of 3D-Printable Carbon-negative Concrete Recipes
Abstract
The construction sector faces urgent pressure to improve sustainability amid persistent labour shortages. Conventional energy- and material-intensive practices are increasingly incompatible with net-zero emission targets for 2050. This study introduces a performance-based approach to develop 3D-printable mixes composed entirely of industrial slags, without cement, virgin aggregates, or hydraulic activation. Strength is achieved exclusively through mineral carbonation curing, enabling both CO₂ sequestration and by-product valorisation. Optimised formulations exhibited compressive strengths of up to 22 MPa after seven days of curing under 3% CO₂, 20 °C, and 60% relative humidity. These findings highlight a pathway toward ultra-low-carbon, cement-free concretes for compression-dominant, deconstructable structures.
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MIX DESIGN OF 3D-PRINTABLE CARBON-NEGATIVE CONCRETE RECIPES Denis Ayena Lorika, Yi Zhang, Kim Van Tittelboom, and Stijn Matthys Magnel-Vandepitte Laboratory, Department of Structural Engineering and Building Materials 1. Introduction The construction industry faces urgent demands to improve sustainability while addressing enduring labour shortages. Current energy-rooted approaches and material-intensive practices are increasingly misaligned with emerging environmental targets, such as the 2050 net-zero emissions. Consequently, a comprehensive upgrade to the sector’s design philosophy and technological framework is both timely and essential. www.ugent.be Universiteit Gent @ugent Ghent University FEARS 2025, Sint-Pietersabdij, Sint-Pietersplein 9, 9000 Gent October 13, 2025 Metal Oxide-rich byproduct Carbon capture and utilization (CCU/S) Digital fabrication Dumping-Human Toxicity Potential (HTP) Long construction duration, labor shortage, material wastage, need for formwork GHG emission - Global Warming Potential (GWP) 2. Materials and test matrix •Binder –Carbinox Fine stainless-steel slag fraction Particle size: 0.25 mm max •Aggregates - Stinox Coarser blended slag fraction Particle size: 2 mm max. Aggregates and binder are supplied by Orbix, Belgium •Additives SP: Polycarbonate Ether Superplasticizer (BASF) VMA: Hydroxypropyl Methylcelulose, Tylose (Shin-Etsu) Compression-dominant system Dry-jointed 3D-printed carbon-cured blocks Fig 1: schematic idealization of the study framework This study employs a performance-based approach to innovate formations that; •Incorporate 100% secondary constituents solely based on industrial slags (no cement and virgin aggregates) •Are not hydraulically or alkali-activated •Are 3D-printable •Solely rely on mineral carbonation curing for full strength development •Meet mechanical and durability performance criteria suitable for compression-dominant, deconstructable structures mix A/B ratio W/B ratio SP/B ratio (%) VMA/B ratio (%) M0.5_0.25 0.5 0.25 0.80 0.056 M0.5_0.30 0.5 0.30 0.25 0.056 M0.5_0.35 0.5 0.35 0.00 0.075 M0.7_0.25 0.7 0.25 1.00 0.080 M0.7_0.30 0.7 0.30 0.50 0.080 M0.7_0.35 0.7 0.35 0.00 0.045 M1.0_0.25 1.0 0.25 1.75 0.090 M1.0_0.30 1.0 0.30 1.00 0.090 M1.0_0.35 1.0 0.35 0.50 0.090 A/B - Aggregate-to-binder ratio W/B - Water-to-binder ratio SP/B - Superplasticizer-to-binder ratio VMA/B - VMA-to-binder ratio Mixing time, 2.5 min rotary mixer Mix M-0.5_0.25 considered reference mix for the first 3D-print test, its performance reported here as key result. 3. Methods 4. Key results Fig 4: Flow retention Fig. 5: Yield stress evolution Fig. 6: First 3D-printing test Fig. 7: 3D-printed & carbon-cured block 5. Conclusions Denis Ayena Lorika PhD Fellow E: [email protected] T: +32 466 493 511 ➢Flow optimization enabled achievement of a printable rheology using non-activated industrial slags with additives ➢Achieved up to 22 MPa compressive and 6 MPa flexural strength after 7 days of carbonation curing (3% CO2,20°C Temp, 60% RH) ➢successful first 3D-print trial with one-component (1k) system Demonstration of potential for ultra-low-carbon waste-based materials in 3D concrete printing (3DCP). Rheology Optimization Carbonation Curing of Specimens Printing of Small-scale Specimens Mechanical Performance Assessment Flowability –ASTM 1437-20 Slow penetration tests Carbonation chamber (3% CO2,20°C Temp, 60% RH) Automated 2D mortar gun. Compression and flexural strength tests 3D Print Trial Reference mix 3D-printed - 6-axis robotic arm Fig 2: Loading sign convention for mechanical testing Fig 3: Mechanical performance 5.9 6.2 0.0 2.0 4.0 6.0 8.0 M-0.5_0.25 Flexural Strength, MPa w-direction v-direction 21.2 19.3 0.0 5.0 10.0 15.0 20.0 25.0 M-0.5_0.25 Compressive Strength, MPa w-direction v-direction 015 30 45 60 140 145 150 155 160 165 Spread diameter (mm) Time (min) Extrudability threshold 0200 400 600 2000 4000 6000 8000 10000 Yield Stress,y0 (Pa) Time (s) y0=7899.8Pa