Search Results (105)

The successful application of extrusion-based 3D-printed geopolymer mortars largely depends on precursor chemistry, activator composition, mixture proportions, and fresh-state behavior, which is highly sensitive to time-dependent structural build-up. This review examines the relationships among mix design, geopolymerization chemistry, rheological properties, and printability requirements for 3D-printed geopolymer mortars. Particular emphasis is placed on the effects of precursor type, alkaline activator characteristics, liquid-to-solid ratio, additives, and fibers on flowability, yield stress, viscosity, extrudability, buildability, shape retention, and interlayer bonding. The review further discusses how geopolymerization kinetics influence the evolution of fresh-state properties, the printable time window, and the transition from extrusion to structural stability. In addition, early-age performance is evaluated in terms of setting behavior, green strength development, and layer-interface integrity. Current challenges, including the lack of standardized test methods, limited comparability among published studies, and the complex coupling between material design and process parameters, are also highlighted. Finally, the review identifies key research gaps and proposes future directions for developing robust, printable, and sustainable geopolymer mortar systems for additive manufacturing in construction. Full article

This study investigates the interlayer shear performance of 3D-printed concrete (3DPC) using direct shear tests. Three nominal layer heights, 5 mm, 10 mm, and 15 mm, were considered, and specimens were loaded parallel to the printing path (x direction) and perpendicular to the printing path (y direction). The results show that the interlayer nominal shear strength decreased with increasing layer height. When the layer height increased from 5 mm to 10 mm and then to 15 mm, the nominal shear strength decreased from 9.18 MPa to 7.01 MPa and 4.88 MPa in the x direction, and from 7.87 MPa to 5.29 MPa and 2.68 MPa in the y direction. At the same layer height, the x-direction specimens exhibited higher nominal shear strength than the corresponding y-direction specimens, with increases of approximately 17%, 33%, and 82% for the 5 mm, 10 mm, and 15 mm series, respectively. DIC analysis indicated that tensile–shear damage was the main local failure characteristic. The loading-direction effect was related to different shear-transfer paths: the L-x specimens mainly followed a “continuous filaments-mortar matrix-interlayer bonding” path, whereas the L-y specimens were more controlled by weak interlayer-edge regions and local stress concentration. The effective shear-area analysis showed that the effective bonded area decreased with increasing layer height. After area correction, the corrected shear strengths of the x-direction specimens were 9.18 MPa, 8.76 MPa, and 8.13 MPa for L-5-x, L-10-x, and L-15-x, respectively, while those of the y-direction specimens were 7.87 MPa, 6.61 MPa, and 4.47 MPa, respectively. This indicates that a larger layer height not only reduced the effective bonded area but also weakened filament compaction and bonding quality. The findings provide a mechanism-oriented basis for understanding the anisotropic interlayer shear behavior of 3DPC. Full article

Cementitious materials in the fresh state are commonly regarded as viscoplastic. That is, below a given yield stress, they exhibit solid-like behavior, whereas above this threshold, they behave as fluids. In this context, the shear strength of such materials has traditionally been analyzed from a rheological standpoint, considering them as fluids and using time as the primary state variable. From a structural perspective, however, relatively few studies have treated the material as a solid. With the advent of 3D printing technology, this trend has persisted. Within this framework, the present research aims to evaluate the shear strength of a structural mortar for 3D printing in its solid-like regime, by applying the Mohr–Coulomb failure criterion. Furthermore, in a novel approach, the degree of hydration of Portland cement is proposed as a state variable to replace time, enabling a more comprehensive and objective description of the material’s mechanical evolution. Thus, addressing this gap in the state of the art, a chemo-mechanical coupling is developed. To obtain the necessary data, direct shear, uniaxial compression, and isothermal calorimetry tests are performed. The results indicate that the friction angle remains constant, at approximately 33°, and that cohesion, the parameter governing strength gain, exhibits the same linear rate of increase with hydration in both mechanical tests, indicating an intrinsic relationship within the material. Full article

The study presents an approach to the synthesis of micro- and nano-sized biosilica from rice husk ash (RHA) and describes its effective incorporation into cementitious composites for 3D concrete printing (3DCP). It is demonstrated that the calcination of rice husk at 700 °C, followed by sonochemical treatment, leads to the formation of a nanoscale silica phase with high pozzolanic reactivity. X-ray powder diffraction (XRD), infrared spectroscopy (IR), differential thermogravimetric analysis (DTG), and scanning electron microscopy (SEM) show that the incorporation of nano-biosilica (NBS) into the cementitious composites accelerates the hydration process through a nucleation effect and pozzolanic reaction. This, in turn, densifies the hardened cement microstructure and improves compressive strength significantly. Laboratory 3D concrete printing tests demonstrate that adding 1.72 wt.% NBS improves shape retention, decreases layer slump, and improves interlayer bond strength. The results indicate the viability of rice husk ash-derived biosilica as a supplementary cementitious material (SCM) in 3DCP due to its positive influence on the concrete mortar properties and parameters. Full article

This study investigates the reuse of mussel shell waste as a secondary raw material in bio-cement mortars designed for the additive manufacturing of artificial reefs for marine habitat restoration. The novelty of the research lies in combining a high recycled shell content (60 wt.%), low-clinker cement, and two 3D-printing techniques: Extruded Material Systems (EMS) and Powder-Based Systems (PBS). Mechanical performance was evaluated through flexural and compressive tests after 7, 28, and 91 days under both air and freshwater curing conditions, while environmental impacts were assessed through Life Cycle Assessment (LCA). The LCA evaluated both the environmental performance of shell-based mixtures compared with conventional materials and the impacts associated with the investigated fabrication techniques. The best-performing bio-mixtures achieved compressive strengths up to 46.01 MPa and flexural strengths up to 9.91 MPa after freshwater curing, demonstrating the suitability of shell-based mortars for submerged applications. LCA results showed reduced impacts in land use and mineral resource depletion compared with conventional mixtures, despite slightly higher energy and water demands associated with shell pre-treatment. The results demonstrate the technical and environmental feasibility of integrating aquaculture waste into sustainable 3D-printed marine restoration solutions. Full article

Three-dimensional concrete printing (3DCP) offers an accurate, formwork-free, and resource-efficient construction process; however, the absence of vibration and compaction often results in increased porosity and reduced durability. This study investigates the influence of nano-calcium carbonate (NC), acting as a nano pore-filler, on the durability and other physical properties of 3DCP. NC was incorporated at dosages of 0–3% by weight of cement, and specimens were fabricated using a laboratory-scale 3D printing machine. Durability performance was evaluated after 120 days under plastic-wrapped curing, sulfuric acid exposure, and magnesium sulfate immersion. In addition, thermal conductivity and sound absorption were measured to identify the effect of pore structure modification by NC. The results show that NC enhances matrix densification and mechanical performance up to an optimal dosage of approximately 2%, beyond which its effectiveness decreases. Under magnesium sulfate immersion, the strength decreased slightly but improved with increasing NC content up to about 2%. In the case of sulfuric acid exposure, the strength decreased significantly after 120 days; however, it still increased with increasing NC content. Incorporating NC into 3DCP appears to provide improved resistance to both magnesium sulfate and sulfuric acid exposure. Thermal conductivity increased with NC addition, indicating improved solid-phase continuity, whereas sound absorption decreased due to the reduction in porosity. These findings demonstrate that nano-calcium carbonate can effectively refine pore structure and improve durability-related performance, contributing to extended service life and more sustainable 3D-printed cementitious materials in the built environment. Full article

To address the accumulation of construction and demolition waste (W&D), this study recycled it into regenerated fine aggregate and prepared 3D-printed mortars with replacement ratios ranging from 0% to 100%. The mechanical properties of hardened specimens were tested, and the degradation mechanisms of mechanical performance were investigated through SEM, MIP, and microhardness analysis. The carbon emissions of the materials were evaluated. The results indicated that while the 3D-printed mortar exhibited excellent buildability, its compressive strength, flexural strength, and interlayer bond strength gradually decreased with increasing replacement ratio. MIP results showed that as the replacement ratio of the W&D increased from 0% to 100%, the total porosity of the 3D-printed specimens significantly increased from 14.7433% to 27.5903%. SEM and microhardness images confirmed severe ITZ deterioration, and the average ITZ width increased from 31 to 79 μm. As the W&D replacement ratio increased from 0% to 100%, the total GWP decreased from 0.4043 to 0.3800 kg CO₂-eq/kg mortar. Maximizing the utilization of W&D is key to achieving efficient utilization of solid waste. Considering printability, mechanical performance, interlayer behavior, microstructural characteristics, and environmental impact in a comprehensive manner, the 80% W&D replacement ratio can be regarded as a relatively balanced and promising selection. This work not only suggests the technical feasibility of recycling W&D in 3D printing mortar, but also proposes a sustainable pathway to reduce carbon emissions in construction. Full article

To enhance the utilization rate and mechanical performance of recycled sand (RS) in extrusion-based 3D printing, this study investigates the influence of varying incorporation ratios of RS across two particle size fractions: 0.075–1.18 mm (RS01) and 1.18–2.36 mm (RS12). The RS utilization rate was determined via the material balance method, while microstructural mechanisms were analyzed using scanning electron microscopy and Vickers microhardness testing. The results indicate that: a combination of 75% RS01 and 25% RS12 achieves the maximum RS utilization rate of 84.3%. At an RS12/RS01 ratio of 1:3, the printed specimens exhibit the smallest tilt angles in bidirectional buildability tests, measuring 7.6° and 7.2°, with corresponding tan θ values of 0.066 and 0.063. Compared to mortar with 100% RS01, this optimized mixture yields average increases of 36.5% in compressive strength, 40.7% in flexural strength, and 6.8% in interlayer splitting strength. Analysis of variance indicates that different particle size combinations have a significant effect on the mechanical properties. Microhardness analysis reveals that the combination of 75% RS01 and 25% RS12 achieves a minimum interfacial transition zone width of 46 µm. Utilizing larger-particle-size RS in 3D printing effectively enhances its utilization rate while maintaining satisfactory printability and mechanical properties. Full article

Three-dimensional printing (3DP) has gained increasing attention in construction as a means of addressing labor shortages and improving efficiency. Various studies have investigated fiber-reinforced mortars for 3DP. However, only a few studies have examined mixture design strategies aimed at controlling early structural build-up, and the relationships between early structural build-up, printability, and interlayer stability remain largely unexplored. This study aimed to establish a practical method for evaluating the static yield stress and early buildability of 3DP mortars under construction-site conditions. Vane shear and 15-stroke flow tests were conducted to assess the static and dynamic behavior of mortars incorporating polyvinyl alcohol (PVA) fibers, and their compressive and flexural strengths were also evaluated. According to the results, the vane shear test sensitively captured the rheological changes associated with variations in fiber content and superplasticizer dosage. The addition of PVA fibers increased the maximum shear stress of the mortar, resulting in atypical static yield stress development compared to fiber-free mortars. While the 15-stroke flow test further elucidated flowability, the vane shear test revealed a stronger correlation between mechanical properties and overall buildability. Thus, vane shear testing can be reliably used to assess early-age structural build-up and interlayer stability in 3DP mortars for optimizing print performance. Full article

The paper presents the results of a study focused on technological parameters that ensure the effectiveness of using concrete powders obtained from crushed concrete waste as an active mineral additive in construction mixtures used for 3D printing. The efficiency of using a complex polyfunctional additive to cement pastes and mortars based on it is experimentally demonstrated. This additive includes a naphthalene–formaldehyde-based superplasticizer and a water-retaining additive, hydroxyethyl methylcellulose. Using the mathematical experiment planning methodology, polynomial models of the cement pastes and mortars’ mechanical properties were obtained. The models showed a positive effect of the complex additive on the cement pastes’ normal consistency and viscosity. Additionally, the results of the study demonstrate the possibility of regulating the cement pastes’ setting time and the plastic strength of mortars based on them using a complex additive. Analysis of the experimental–statistical models shows that using the complex additive allows regulation of water separation as well as the compressive and flexural strength of cement–sand mortars based on the investigated cement pastes within the required limits. Improving the key properties of building mixtures containing crushed concrete waste for 3D printing using complex polyfunctional modifier additives opens up new opportunities for increasing their economic and environmental efficiency. Full article

This study addresses the technical challenges of using construction residue sand (CRS) with high mud content in 3D printing by developing a novel sustainable mortar system. The key novelty lies in optimizing the mix design with calcium sulfoaluminate cement (CSA) and defining a quantitative printability window. Results show that at a CSA dosage of 10–15% and a sand–binder ratio of 1.4–1.5, the mortar achieves excellent printability, with a fluidity of 165–195 mm and a slump of 10–40 mm. Mechanistically, CSA promotes AFt formation, refining pore structure, and enhancing mechanical strength. This work provides a high-value pathway for recycling construction waste and advancing green intelligent construction. Full article

As 3D printing emerges as a transformative technology in construction, the structural performance of 3D-printed mortar (3DPM) has become a key research focus. This study conducted shear tests on reinforced specimens combining 3D-printed mortar (3DPM) and normal mortar (NM). Four different shapes of interfacial locking design (I-shaped, K-shaped, C-shaped, S-shaped) were examined, comparing reinforced (CR) and non-reinforced (NR) specimens. The investigation analyzed failure modes, crack propagation patterns, and shear transfer mechanisms at CR series specimens under direct shear loading. CR-S specimens exhibited a shear peak load value 14.0% higher than CR-K specimens, 33.2% higher than CR-C specimens, and 42.9% higher than CR-I specimens. CR-I specimens exhibited pure adhesive failure. CR-K, CR-C, and CR-S specimens showed composite failure patterns combining adhesive and shear failure mechanisms. Strain analysis revealed the maximum horizontal strain ε_xx across all specimen shapes. CR-C and CR-S specimens recorded strain values exceeding CR-I and CR-K specimens by over 50%. Reinforcement produced pronounced increases in ultimate bearing capacity for I-shaped and C-shaped specimens, achieving gains of 51.9% and 60.4%, respectively. Reinforcement substantially enhanced energy dissipation capacity. Compared with NR series specimens, the performance improvements ranked as follows: CR-C (+164.67%) > CR-S (+70.70%) > CR-I (+52.05%) > CR-K (+9.42%). Full article

Concrete 3D printing (3DCP) combines materials science with material processing technologies to enable automated, additive construction. This review summarizes findings from the literature and industrial practice on 3DCP mortar formulation with emphasis on the material processing chain. The workflow is examined from raw material storage through handling, mixing, and deposition. The roles of binders, aggregates, dispersed reinforcement, and chemical admixtures are discussed in relation to rheological behavior, buildability, and early-age mechanical performance. The analysis covers storage, dosing, and mixing strategies with respect to mix consistency and overall process reliability, while mortar pumping and extrusion are addressed alongside nozzle-injected additives and automation. Finally, limitations and scalability challenges are outlined with research directions such as continuous mixing, in-line monitoring, and adaptive mix formulation for on-site applications. Full article

With the rise in additive manufacturing in construction, particularly 3D printing using extrusion-based mortars, there is an increasing need to optimize material properties. This study compares the mechanical performance of mortar specimens produced by traditional casting and 3D printing, with a focus on flexural behavior. A high-durability mortar with very low chloride and sulfate content, which produces less CO₂ than standard Portland cement, was used. This study also explores the impact of varying water–cement (w/c) ratios to obtain a valid mix for both fabrication methods. The results show that the samples obtained by traditional processes and those produced through 3D printing exhibit distinctly different behaviors under bending stresses. In the case of the molded samples, the maximum stress ranged from 1.23 to 1.78 MPa, indicating good strength and uniformity within these materials. In contrast, the 3D-printed samples showed higher values but with greater variation, ranging between 2.77 and 3.76 MPa. This variation highlights the influence of the fabrication technique in 3D printing, which may contribute to either the superiority or limitations of these samples. In terms of deformation, molded specimens exhibited brittle failure with limited post-peak energy dissipation (0.11–0.22 kN.mm), whereas 3D-printed samples displayed a mixed brittle–ductile response and enhanced energy absorption (1.70–2.82 kN.mm). These findings suggest that traditionally obtained specimens are suitable for applications requiring predictable stiffness, while 3D-printed mortars are advantageous for applications demanding greater flexibility and energy absorption. Full article

The use of recycled materials and locally sourced alternative binders in 3D concrete printing (3DCP) has significant potential to reduce carbon emissions in concrete construction. This study examines the effect of sugarcane bagasse ash (SCBA), a byproducts from the sugarcane industry, as a sustainable binder in 3DCP. SCBA was oven-dried at 105 °C, sieved to 250 µm, and used to replace up to 25% of the total binder by weight in a supplementary cementitious material (SCM) blended system. The impact of polypropylene (PP) and steel (ST) microfibres on SCBA-based mixes was also investigated. The fresh properties of the mortar were evaluated using the flow table, Vicat needle, shape retention, buildability, and rheometer tests. The mortar was 3D printed using a small-scale robotic setup with a RAM extruder. Mechanical properties were then tested, including compressive and flexural strengths, and interlayer bonding, along with microstructure analysis. The results showed that increasing the SCBA content led to greater slump and improved flowability, as well as a slower rate of static yield stress development, with up to a 90 percent reduction compared to the control mix. The addition of PP fibres doubled the static yield stress in the mixes containing 20 percent SCBA. The 10 percent SCBA mix achieved the highest mechanical strength, both in compression and flexure, due to its denser microstructure and enhanced pozzolanic reaction. Full article