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Abstract

The design of proper mixes for 3D concrete printing has been already a subject of many studies. Modification to mixes aim to obtain certain properties (extrudability, workability, flowability, open time or buildability) which allow for proper printing of the material. There are different types of reactive or non-reactive mineral additives that were already used to modify the mixes for 3D concrete printing. Studies have already shown the usefulness of fly ash, silica fume, metakaolin, limestone powder or quartz powder. The properties of the mix can also be changed with different chemical admixtures such as plasticizer, accelerators or retarders and viscosity modifying agents. Use of different admixtures can however significantly increase the cost of designed mixes. The study determined the influence of non-reactive limestone powder on the properties of the mix. The mixes were modified with 10% to 50% of additive, that replaced the fine aggregate. Rheological properties of the mixes were studied in this research. The stiffness and load-bearing capacity of mixes (t ≤ 45 min) were tested. Chosen mixes were printed out to experimentally verify the results. The study has shown that the limestone powder can successfully be used to improve the properties of printing mixes with simultaneous reduction of cement content. The results are promising regarding the sustainable development attitude in modern constructions.
... A high binder content has a positive effect on the rheological properties of the printing compound, which is one of the key parameters [17]. Modification of a mix to reduce its environmental impact can be done in two main ways: changing the composition and amount of binder [10,16,[18][19][20] or changing the composition and type of aggregate [16,21]. Today, due to the increasing production of concrete and mortar, the consumption of natural aggregates is increasing and has become one of the biggest environmental problems [22,23]. ...
... There are also different types of tests that allow to inspect the print while it is in progress [36], or to check the change of stress in the pump [37]. Less advanced methods are usually based on the spreading table test [16,21,32,38,39], which in a large number of situations is sufficient to check the printability of a mix. Another important parameter regarding 3D printing is the so-called "buildability," which can be defined as "resistance to failure during printing" [35]. ...
... Another important parameter regarding 3D printing is the so-called "buildability," which can be defined as "resistance to failure during printing" [35]. The way in which this criterion is assessed can vary from simple tests involving the loading of fresh concrete mixes [28,40], to precise tests determining the relationship between stresses and strains (unconfined uniaxial compression [41] or squeezing test [21,42]), to the printing of entire walls [9,14,41] or columns [16,43]. A detailed description of this problem can be found, inter alia, in [12,35]. ...
Article
3D concrete printing technology of cementitious materials is challenging in many aspects. Despite the workability and mechanical properties of a mix and hardened concrete or mortar, the researchers need to face problems with environmental impact and durability of printed elements. Furthermore, today thousands of tons of waste are produced and natural aggregates which are most used resources by volume in the construction sector are on the verge of exhaustion. To date, limited knowledge about utilized of artificial aggregate (including Polyethylene terephthalate (PET) in 3D printed mortar is available. The main objective of this study is to develop 3D printed mortar with PET granules as the replacement of natural aggregate (10 vol-% to 50 vol-%). The paper contributes to knowledge of properties of 3D printed composites with plastic aggregate. Four printable mixes were made: one reference mix and three mixes in which natural aggregate was replaced by PET granulate in quantities amounting to 10%, 30% and 50% (by volume), respectively. The replacement ratios were chosen on the base of literature review for ordinary cementitious mortars. Several strength tests were carried out for standard and printed specimens. In addition, a freeze–thaw resistance test and high temperature performance test were conducted to evaluate to validate the properties of artificial aggregate. The results show that PET granulate is useful in 3D printing owing to their buildability and extrudability properties. Furthermore, printed mixes with high amount of PET (30% and 50%) granulate shows high decreases in strength (up to 75%). Unfortunately, after the freeze–thaw resistance test specimens with a high amount of PET granulate (30% and 50%) indicated high strength reduction (up to 80%). Exposure to a temperature exceeding the melting point of PET results in significant reduction of compressive strength for printed specimens (up to 68.8 % for 50 % PET addition). In addition, mixes with up to 10% PET can be used for most structural elements even under varying thermal conditions (even under extreme cold temperature).
... Due to the recent changes in smelting technology, its market availability is gradually decreasing [1]. Ground granulated blast furnace slags have been traditionally used in the production of concretes and binders, along with other slags and waste materials from various metal processing branches and different mineral additives of industrial origin [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Slags with a high crystalline phase content, such as shaft slags, are used mainly as aggregates in road construction. ...
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Abstract: In this study, ground granulated blast furnace slag was activated with a wide variety of sodium salts to compare the effects of their pH and anion size on the hydration progress and compressive strength development of GGBFS pastes. Research was carried out on samples activated with twelve different sodium salts and cured for one year. Changes in their phase composition (XRD), loss on ignition at different temperatures, expansion and microstructure (SEM + EDS) were examined over the entire curing period. The results showed that the presence of sodium ions is more important than the pH of the system, as activation took place even in the case of compounds whose solutions are characterized by a low pH, such as sodium tartrate or phosphate. The compressive strength of the pastes ranged from approximately 8 to 65 MPa after one year of curing.
... Additional binders and admixtures are commonly used in 3DPC to modify the thixotropy of the mixture, which improve the properties of extrudability, pumpability and buildability. Moreover, supplementary cementitious materials (SCMs) such as silica fume or limestone powder are used to modify the rheological properties of mixtures along with decreasing the cement content in the mixtures Skibicki et al. 2020). Additionally, nanomaterials have gathered particular attention due to their unique physical properties as well as significant chemical reactivity, which is the result of their ultra-fine size and high-specific surface area (Sikora et al. 2018). ...
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Additive manufacturing (AM), also referred as 3D printing, is a technology that enables building automated three-dimensional objects in a layer-by-layer manner. AM of cement-based and alkali-activated composites has gathered attention over the last decade and is one of the most rapidly developing civil engineering fields. Development of proper mixture compositions which are suitable in fresh and hardened state is one of the key challenges of AM technology in construction. As the behaviour of cement-based materials (CBM) and alkali-activated materials (AAM) is determined by chemical and physical processes at the nano-level, incorporation of nano-and micro-sized admixtures has great influence on the performance of printable composites. These modifications are attributed to the unique reactivity of nanoparticles associated with their small size and large surface area. This review paper summarizes recent developments in the application of nano-and micro-particles on 3D printable cementitious composites and how they influence the performance of 3D-printed construction materials. The research progress on nano-engineered CBM and AAM is reviewed from the view of fresh and hardened properties. Moreover, comparison between nano-and micro-sized admixtures including nanosilica, graphene-based materials, and clay nanoparti-cles as well as chemical admixtures such as viscosity-modifying admixtures and superplasticizers is presented. Finally, the existing problems in current research and future perspectives are summarized. This review provides useful recommendations toward the significant influence of nano-and micro-sized admixtures on the performance of 3D printable CBMs.
... The SP content in mortars was adapted to achieve the comparable consistency of the printable mortar. Similar to other studies [32][33][34] the consistency was determined using a flow-table method (conforming EN 1015-3) with targeted flow between 140 and 155 mm. In all the mixtures tested, the water-to-solid ratio was set to 0.14, which corresponds to a water-to-cement ratio of w/c = 0.52. ...
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This study presents the experimental results of an investigation on the effects of nanosilica (NS) on the material characteristics of printable mortars used for additive manufacturing. Printable cement mortars based on Ordinary Portland Cement, limestone filler and silica sand were modified with different dosages of nanosilica (from 2% to 6% by weight of binder) and its influence on their hydration, rheological, mechanical and transport properties was assessed. The study showed that NS accelerates significantly the setting and hardening of printable mortar, while reducing its open time. Moreover, an increment of yield stress, together with an increment in NS dosage, was found to have occurred. The incorporation of an optimal NS dosage results in a noticeable increase in the compressive strength and alteration of the pore structure as determined by the MIP measurements. Moreover, transport properties of the produced mortar are significantly improved due to incorporation of NS. In addition to the microstructure refinement, Micro-CT and scanning electron microscopy (SEM) studies revealed that 3D printed mortars exhibit pore anisotropy in accordance with the printing direction. However, incorporation of NS in the mixture resulted in improved buildability, thus decreasing pore anisotropy.
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This study determines the effect of spent garnet as a replacement for natural sand in 3D-printed mortar at early ages. Five mixes with different spent garnet amounts were prepared (0%, 25%, 50%, 75% and 100% by volume). The ratio of binder to aggregate remained unchanged. In all mixes the water/binder ratio was assumed as a constant value of 0.375. Tests were performed to confirm the printability of the mix (a path quality test using a gantry robot with an extruder). Determinations of key buildability properties of the mix (green strength and Young’s Modulus) during uniaxial compressive strength at 15 min, 30 min and 45 min after adding water were conducted. A hydraulic press and the GOM ARAMIS precision image analysis system were used to conduct the study. The results showed that an increase in spent garnet content caused a decrease in green strength and Young’s Modulus (up to 69.91% and 80.37%, respectively). It was found that to maintain proper buildability, the recommended maximum replacement rate of natural sand with garnet is 50%. This research contributes new knowledge in terms of using recycled waste in the 3D printing technology of cementitious materials.
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Few studies have focused on determining the Young’s modulus of 3D printed structures. This study presents the results of experimental investigations of Young’s modulus of a 3D printed mortar. Specimens were prepared in four different ways to investigate possible application of different methods for 3D printed structures. Study determines the influence of the number of layers on mechanical properties of printed samples. Results have shown a strong statistical correlation between the number of layers and value of Young’s modulus. The compressive strength and Young’s modulus reduction compared to standard cylindrical sample were up to 43.1% and 19.8%, respectively. Results of the study shed light on the differences between the current standard specimen used for determination of Young’s modulus and the specimen prepared by 3D printing. The community should discuss the problem of standardization of test methods in view of visible differences between different types of specimens.
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Proper quality assessment of ready-mixed concrete, which is currently the principal material for construction, land engineering and architecture, has an impact on the optimisation and verification of correct functioning of individual stages of the production process. According to the European Standard EN 206 “Concrete–Specification, performance, production and conformity”, obligatory conformity control of concrete is carried out by the producer during its production. In order to verify the quality of concrete, investors generally commission independent laboratory units to perform quality assessment of both concrete mix and hardened concrete, which guarantees a high quality of construction works. One of the essential tools for ensuring the quality of test results is the participation of laboratories in the so-called proficiency testing (PT) or inter-laboratory comparisons (ILC). Participation in PT/ILC programmes is, on the one hand, a tool for demonstrating the laboratory’s performance, on the other hand an aid for maintaining the quality of available concrete tests and validating test methods. Positive evaluation is a confirmation of the laboratory’s capability for performing the tests. The paper presents the results of laboratory proficiency tests carried out by means of inter-laboratory comparisons, as shown in the example of quality assessment of ready-mixed concrete for nine participating laboratories. The tests were performed for concrete of the following parameters: strength class C30/37, consistency S3, frost resistance degree F150, and water resistance degree W8. This involved determining consistencies, air content and density of the concrete mix, and compressive strength of hardened concrete. For the evaluation of laboratory performance results, z-score, ζ-score and En-score were applied. The innovation of the proposed study lies in employing both classical and iterative robust statistical methods. In comparison with classical statistical methods, robust methods ensure a smaller impact of outliers and other anomalies on the measurement results. Following the analyses, clear differences were found between the types of detected discrepancy of test results, which occurred due to the nature of individual parameters. For two laboratories, two scores revealed unsatisfactory results for concrete mix consistency. The main reasons can be pouring into the cone-shaped form a concrete mixture that is too dry, or incorrect use of a measuring tool also creating a possibility that the obtained value can be wrongly recorded. Other possible reasons are discussed in the paper. Participation in inter-laboratory comparison programmes is undoubtedly a way to verify and raise the quality of tests performed for concrete mix and hardened concrete, whereas individual analysis of the results allows the laboratory quality system to be improved.
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One of the fields in the construction industry where 3D printing of cementitious composites can play a significant role is associated with manufacturing of lightweight structures. Thanks to 3D printing, structural self-weight can be reduced by topology optimization of printed elements. Moreover, further decrements of self-weight and improvement of thermal insulating properties can be achieved by the mixture design and introduction of materials of low thermal conductivity. To date, limited knowledge on lightweight printable mixtures is available. The main objective of this study is to develop 3D printed lightweight concrete (3DPLWC) mixture, with the intention of replacing natural aggregate with waste glass (WG) by 50 vol.-% and 100 vol.-%. Moreover, expanded thermoplastic microspheres (ETM) were incorporated into the mixture. This led to a reduction in density of the mixtures as well as the thermal conductivity by up to 40 %. Comprehensive evaluation of material's fresh properties revealed that the addition of ETM results in 3D printable material with lower yield shear stress and higher plastic viscosity by 28 % and 66 %, respectively, compared to the mixes without ETM. Moreover, improvement of shape retention, flowability, setting times, and early-hardened mixtures' properties was observed. The mechanical properties of 3DPLWC showed that the replacement of natural aggregate by 50 vol.-% WG led to enhanced flexural and compressive strength of the composite, while full replacement resulted in retaining or slight reduction of the mechanical properties.
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Foundation piles that are made by concrete 3D printers constitute a new alternative way of founding buildings constructed using incremental technology. We are currently observing very rapid development of incremental technology for the construction industry. The systems that are used for 3D printing with the application of construction materials make it possible to form permanent formwork for strip foundations, construct load-bearing walls and partition walls, and prefabricate elements, such as stairs, lintels, and ceilings. 3D printing systems do not offer soil reinforcement by making piles. The paper presents the possibility of making concrete foundation piles in laboratory conditions using a concrete 3D printer. The paper shows the tools and procedure for pile pumping. An experiment for measuring pile bearing capacity is described and an example of a pile deployment model under a foundation is described. The results of the tests and analytical calculations have shown that the displacement piles demonstrate less settlement when compared to the analysed shallow foundation. The authors indicate that it is possible to replace the shallow foundation with a series of piles combined with a printed wall without locally widening it. This type of foundation can be used for the foundation of low-rise buildings, such as detached houses. Estimated calculations have shown that the possibility of making foundation piles by a 3D printer will reduce the cost of making foundations by shortening the time of execution of works and reducing the consumption of construction materials.
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Despite the rapid development of 3D printing technology for cement composites, there are still a number of unsolved issues related to extrusion printing. One of them is proper mix design that allows for meeting criteria related to the printing of cementitious materials, such as pumpability, buildability, consistency on the materials, flowability and workability, simultaneously incorporating sustainable development ideas. In the case of mixes for 3D printing, the modification of the composition which increases the overall performance does not always go hand in hand with the reduction of negative environmental impact. The article presents the results of tests of eight mixtures modified with reactive and inert mineral additives designed for 3D printing. The mixes were evaluated in terms of their rheological and mechanical properties as well as environmental impact. Initial test results were verified by printing hollow columns up until collapse. Later, the differences between the compressive strength of standard samples and printed columns were determined. In order to summarize the results, a multi-faceted analysis of the properties of the mixes was carried out, introducing assessment indicators for its individual parameters. The article proves that appropriate material modification of mixes for 3D printing can significantly reduce the negative impact on the environment without hindering required 3D printing properties.
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Developments in the automation of construction processes, observable in recent years, is focused on speeding up the construction of buildings and structures. Additive manufacturing using concrete mixes are among the most promising technologies in this respect. 3D concrete printing allows the building up of structure by extruding a mix layer by layer. However, the mix initially has low capacity to transfer loads, which can be particularly troublesome in cases of external components that need to be placed on top such as precast lintels or floor beams. This article describes the application of additive manufacturing technology in the fabrication of a building wall model, in which the door opening was finished with automatic lintel installation. The research adjusts the wall design and printing process, accounting for the rheological and mechanical properties of the fresh concrete, as well as design requirements of Eurocode. The article demonstrates that the process can be planned precisely and how the growth of stress in fresh concrete can be simulated, against the strength level developed. The conclusions drawn from this research will be of use in designing larger civil structures. Furthermore, the adverse effects of concrete shrinkage on structures is also presented, together with appropriate methods of control.
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This contribution studies failure by elastic buckling and plastic collapse of wall structures during extrusion-based 3D printing processes. Results obtained from the parametric 3D printing model recently developed by Suiker (Int J Mech Sci, 137: 145–170, 2018), among which closed-form expressions useful for engineering practice, are validated against results of dedicated FEM simulations and 3D concrete printing experiments. In the comparison with the FEM simulations, various types of wall structures are considered, which are subjected to linear and exponentially decaying curing processes at different curing rates. For almost all cases considered, the critical wall buckling length computed by the parametric model turns out to be in excellent agreement with the result from the FEM simulations. Some differences may occur for the particular case of a straight wall clamped along its vertical edges and subjected to a relatively high curing rate, which can be ascribed to the approximate form of the horizontal buckling shape used in the parametric model. The buckling responses computed by the two models for a wall structure with imperfections of different wavelengths under increasing deflection correctly approaches the corresponding bifurcation buckling length. Further, under a specific change of the material properties, the parametric model and the FEM model predict a similar transition in failure mechanism, from elastic buckling to plastic collapse. The experimental validation of the parametric model is directed towards walls manufactured by 3D concrete printing, whereby the effect of the material curing rate on the failure behaviour of the wall is explored by studying walls of various widths. At a relatively low curing rate, the experimental buckling load is well described when the parametric model uses a linear curing function. However, the experimental results suggest the extension of the linear curing function with a quadratic term if the curing process under a relatively long printing time is accelerated by thermal heating of the 3D printing facility. In conclusion, the present validation study confirms that the parametric model provides a useful research and design tool for the prediction of structural failure during extrusion-based 3D printing. The model can be applied to quickly and systematically explore the influence of the individual printing process parameters on the failure response of 3D-printed walls, which can be translated to directives regarding the optimisation of material usage and printing time.
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The goal of this study is to investigate the effects of different grades of calcined clay on the extrudability and early-age strength development under ambient conditions. Four mix designs were proposed. Three of them contained high, medium, and low grades of calcined clay, respectively, and one was the reference without calcined clay. In terms of extrudability, an extrusion test method based on the ram extruder was introduced to observe the quality of extruded material filaments, and to determine the extrusion pressure of tested materials at different ages. For evaluating the very early-age strength development, the penetration resistance test, the green strength test, and the ultrasonic pulse velocity test were applied. Furthermore, the mechanical properties of the developed mix designs were determined by the compressive strength test at 1, 7 and 28 days. Finally, the main finding of this study was that increasing the metakaolin content in calcined clay could significantly increase the extrusion pressures and green strength, shorten the initial setting time and enhance the compressive strength at 1, 7, and 28 days.
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This contribution investigates the effects of seawater and colloidal silica (NS) in the amounts of 1, 3 and 5 wt%, respectively, on the hydration, strength development and microstructural properties of Portland cement pastes. The data reveal that seawater has an accelerating effect on cement hydration and thus a significant contribution to early strength development was observed. The beneficial effect of seawater was reflected in an improvement in compressive strength for up to 14 days of hydration, while in the 28 days compressive strength values were comparable to that of cement pastes produced with demineralized water. The combination of seawater and NS significantly promotes cement hydration kinetics due to a synergistic effect, resulting in higher calcium hydroxide (CH) production. NS can thus react with the available CH through the pozzolanic reaction and produce more calcium silicate hydrate (C-S-H) gel. A noticeable improvement of strength development, as the result of the synergistic effect of NS and seawater, was therefore observed. In addition, mercury intrusion porosimetry (MIP) tests confirmed significant improvements in microstructure when NS and seawater were combined, resulting in the production of a more compact and dense hardened paste structure. The optimal amount of NS to be mixed with seawater, was found to be 3 wt% of cement.
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The 3D Printing of cement composites is one of the fastest developing technologies of modern concrete. The 3D printing involves concretes with high amounts of microfillers. The study analyses the influence of curing conditions on the development of strength of concretes applicable in 3D printing. Ten mixes were tested in the study. In the studied cases cement constituted to 50% of the mass, while microfillers such as lime stone powder, kaolin, quartz powder and sand (up to 2 mm) constituted to the rest of the mass. Samples were cured for 7 days in exothermic conditions at 5°C, 20°C, 35°C. Standard mortar samples of 4x4x16 cm and cylinders with 46.5 mm and height of 35 mm that simulate the printed 3D path were made. The compressive strength was tested after 12h, 24h, 48h, 72h, 168 h and 28 days. Based on the acquired results the temperature development function was formulated and activation energy was determined. The results showed that the proposed method is useful in evaluation of printed concrete curing. It can be also used to determine the time of loading the wall which can speed up the process of constructing while maintaining degree of safety.
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The article presents overview of additive manufacturing for concrete structures. Study focuses on specific tests used to determine suitability of high performance mixes for 3D printing. The tests include determination of compressive strength and evaluation of printing speed, extrudability and overall surface quality. Tests were performed on a High-Performance Concrete mix with fine natural aggregate up to 2 mm. Mineral additives such as silica fume and fly ash, and superplasticizer were added to obtain proper consistency. The tests were performed using specially designed site consisting of Cartesian robot and pumping module. The design of printed paths were tailored for specific tests. The evaluation of pump performance was made by measuring pumped mix volume in time. The determination of correct pumping speed was made based on the visual quality of the printed layers. Study determines also the ability to print multilayered structures and printability window of proposed mix.
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3D printing, or additive manufacturing, is a technology which adopts layer-by-layer additive deposition process to build three-dimensional objects. Over the past decade, 3D printing has been attracting more and more attention in the building and construction industry. Compared with conventional concrete casting techniques, 3D printing contributes to higher efficiency with freeform construction, greatly reduced labor and much less construction waste. However, 3D printable cementitious materials are different from conventional concrete in terms of rheology, printability, and mechanical performances. This paper aims to systematically bridge the gap between the requirement and research and development of 3D printable cementitious materials to date. Guided by 3D printing process and multi-level design of cementitious materials, the requirements for 3D printable cementitious material at different material development levels are discussed. This paper provides insights for the future development of 3D printable cementitious materials for building and construction by controlling the basic inputs of materials to obtain desired structural performance.
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The current study deals with a yield stress based mixture design approach for 3D printable concretes. The mixtures were evaluated based on buildability, extrudability, robustness and tests for structural build-up. For the print parameters (such as pump type, nozzle size and extrusion velocity) used in the study, it was found that both extrudability and buildability could be achieved only when the material yield stress was within a range of 1.5–2.5 kPa. Below this range, the material lacked enough strength to achieve shape stability, while above this range, the extrudabilty of the material was difficult. The robustness of the mixtures was quantified in terms of a variability factor defined in terms of the variation in yield stress with small changes in the superplasticizer dosage. Inclusion of 10% of silica fume, 0.1% of viscosity modifying agent (VMA) and 0.1–0.3% addition of nanoclay resulted in decreasing the variability factor, hence improving the robustness. The structural changes due to thixotropy and cement hydration increased the yield stress with time. This structural build-up was assessed by measuring the yield stress with increasing rest duration. The mixture with silica fume showed the maximum structural build-up while the mixture with VMA showed the least. Heat curves from semi-adiabatic calorimetry and penetration curves were also used to assess the structural build-up. They showed a similar trend to that of the yield stress vs time plots.
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This paper reports the fresh and hardened properties of an ambient temperature cured 3D printable geopolymer suitable for extrusion-based 3D concrete printing process. Effects of several key geopolymer synthesis parameters including type of alkaline activator (sodium (Na)-based versus potassium (K)-based), mass ratio of silicate to hydroxide solutions, viscosity and SiO2/M2O ratio (where M = Na or K) of silicate solution on extrudability, open time, shape retention ability and compressive strength of the 3D printable geopolymers were investigated. The results revealed that the type of alkaline activator solution and SiO2/Na2O ratio of the silicate solution had a significant influence on the open time and shape retention ability of the mixtures. The parameters investigated in this study did not have significant effect on the extrudability of the mixtures. The Na-based activators resulted in higher compressive strength of 3D printed geopolymer than the K-based activators. The 3D printable geopolymer mixture made by 8.0 M NaOH solution (25% w/w) and Na2SiO3 solution (75% w/w) with a SiO2/Na2O ratio = 2.0 exhibited the highest compressive strength of 16.6 MPa when cured for only 3 days in the ambient temperature.