An innovative methodology is presented for formulating geopolymer-based material for the requirements and demands of commercially available powder-based 3D printers. Different key powder parameters ...such as particle size distribution, powder bed surface quality, powder true/bulk densities, powder bed porosity, and binder droplet penetration behavior were used to quantitatively evaluate the printability of prepared geopolymer-based material. Results indicated the prepared geopolymer-based material achieved sufficient printability to be used in a powder-based 3D printer. 3D printed specimens from the geopolymer were assessed for printing accuracy, apparent porosity and mechanical property. All printed cubic specimens exhibited an anisotropic phenomenon in dimensional accuracies and mechanical properties. Before further post-processing, the printed cubic structure gained compressive strength of up to 0.9MPa with an acceptable low dimensional expansion of <4%. Post processing by immersion in saturated anhydrous sodium metasilicate solution at 60°C gained compressive strength of up to 16.5MPa.
Display omitted
•A new methodology is presented for formulating geopolymer for 3D printing process.•The study identified the essential characteristics for printability and dimensional accuracy.•Identified parameters for assessing the quality of the geopolymer printed shapes.•A new post-processing method for geopolymer to gain strength for construction application.
This paper evaluates the effect of different commercial superplasticizers (SPs) such as naphthalene, melamine and modified Polycarboxylate based on the workability and strength of a class F fly ash ...geopolymer paste activated by two different activator combinations, i.e. 8 M sodium hydroxide solution and a multi-compound activator composed of 8 M NaOH solution (28.6%) + Na2SiO3 (71.4%) with a SiO2/Na2O ratio of 2.0. These SPs at a dosage of 1% by mass of fly ash were added to the fresh paste and flowability of the activated fly ash paste was measured via mini slump test and compared with that of the paste without using any SP. The experimental results indicated that the effect of different SPs on the workability and strength of fly ash based geopolymer directly depends on the type of activator and the SP. In the case of using 8 M NaOH solution as the activator, naphthalene based SP was an effective type; whereas modified Polycarboxylate based SP was the most efficient type when the multi-compound activator was used.
•Effect of superplasticizers on the fly ash based geopolymer directly depends on the type of activator and the SP.•Naphthalene based SPs is an effective type for the fly ash based geopolymer activated by only NaOH solution.•Modified Polycarboxylates based SP is the most effective type for the fly ash based geopolymer activated by NaOH + Na2SiO3.
•Factors influencing the inter-layer strength in concrete 3D printing are studied.•The moisture level at the surface is identified as an important factor.•Low moisture level is linked to low ...inter-layer strength in 3D concrete printing.•The surface moisture level is affected by bleeding and evaporation rates.•Strengths of 3D printed concrete were different in x, y and z directions.
The extrusion-based 3D concrete printing is a new technology under development for construction of buildings and structures of complex geometries without the use of expensive formwork. The weak inter-layer strength between printed layers is one of the limitations of this technology when compared with cast-in-the-mold concrete. This study investigates effects of print-time interval on the inter-layer strength, along with compressive and flexural strengths of extrusion-based 3D printed concrete in different directions. Specimens were printed with 10, 20 and 30 min delay times (print-time intervals). Compressive, flexural and inter-layer strengths of the 3D printed concretes were measured. The inter-layer strengths of the specimens printed with 10 and 30 min delay times were comparable but higher than that of the specimens printed with 20 min delay time. A correlation was found between the results of inter-layer strength and the surface moisture content at the interface of the layers. The surface moisture content, in turn, depends on the bleed rate of the concrete and the rate of drying of moisture from the surface among other factors. The results also indicated that the compressive and flexural strengths of 3D printed concrete depended on the testing direction. The orthotropic phenomenon was more pronounced in compressive than flexural strength.
3D Construction Printing (3DCP) is a new and emerging technology that is set to revolutionise construction. Currently the technology is in its early stages of development and many hurdles are yet to ...overcome. Particularly in the field of extrusion 3DCP with cementitious materials, one of the primary hurdles is the weak interface bonds. The weakness in bonds is hypothesised to be present due to the layered fabrication of a stiff cementitious mix that creates a localised void structure. Due to the time gap intervals between depositions, the bond strength decreases due to lack of intermixing. This paper seeks to explore a method to strengthen the interlayer bonds, by applying a cementitious paste at the interface, to minimise voids and promote bond area. Using a flatbed scanner and a unique method of image processing on printed colour layers, a quantitative evaluation of the contact area, “effective bond” area, was determined. The application of these experimental and analytical methods shows that an increase in bond strength is achieved, which is proportional to the effective bond area.
Display omitted
•The application of a cementitious “glue” paste between layer depositions increases bond strength up to 60%.•Effective bond area was obtained by adding colour pigments to printed layers and image analysis of fractured interlayers.•Effective bond area was found to have strong correlation to bond strength of the interlayer.•Pastes containing a superplasticiser or retarder provide the largest increase in bond strength.
•Aligned fiber reinforced cementitious composite was proposed for 3D printing.•Mechanical behaviors of 3D printed samples exposed to various loadings were tested.•Mesoscale structures of printing ...material were detected through CT scanning.•Mechanical and acoustic indexes are proposed to evaluate the anisotropic properties.•Empirical relationships between the mechanical anisotropic properties and ultrasonic signals were established.
3D printing techniques are being researched extensively in the construction sector. However, the key issue lies in the development of cementitious materials with both favorable printability and enough mechanical capability by means of high strength and ductility. In this study, an optimal basalt fiber content was determined basing firstly on suitable printability and then on mechanical performance. A self-developed 3D printer was used for extrusion of the cementitious material and also for mechanical enhancement of fiber alignment along the print direction by keeping the nozzle diameter smaller than the length of the basalt fiber. The printing process deposits directional filaments, intrinsically resulting in laminated structures and mechanical anisotropy. Anisotropic performances of the printed material were evaluated by direction-based mechanical performance testing and confirmed by ultrasonic pulse velocity testing. The mechanical behaviors of 3D printed samples exposed to compressive, tensile, flexural and shearing loadings were experimentally investigated. The mesoscale structures of printed samples were detected through the advanced CT scanning technique. Both mechanical and acoustic indexes were proposed to evaluate the anisotropic properties of printed materials. In particular, empirical relationships between the mechanical anisotropic properties and ultrasonic signals were established. On the microstructural level, mechanical enhancement of fiber alignment, fiber pullout and fiber fracture were all probed through scanning electron microscope (SEM) imaging.
Yield strength development of 3D printable concrete by the early age activation reactions plays a vital role in the printability of geopolymer concrete. This study presents a rheo-chemical approach ...to investigate the early age strength development due to alkali reactions for the formulation of suitable 3D printable one-part geopolymer concrete. The influence of design parameters, including activator content, thixotropic additive (Magnesium Alumino Silicate -MAS), and retarder (sucrose) dosage, on the rheological properties of concrete were assessed. The shear stresses of geopolymer concrete were measured with the aid of a rotational rheometer for various shearing protocols that represent the major stages of printing operation (pumping, extrusion and building). The measured rheological properties were related to reaction kinetics of geopolymer mixes using FT-IR spectroscopy and calorimetry. The results revealed that, with MAS, activator and sucrose content of 0.75 wt%, 10 wt% and 1.5 wt% of the binder respectively, the formulated one-part geopolymer showcased enhanced printing properties. This is further demonstrated by printing laboratory-scale specimens and evaluating the hardened properties.
•Rheo-chemical characterisation of printable one-part geopolymer was conducted.•Total mixing time of 15 min is necessary for complete dissolution of solid activator.•Addition of retarders showed insignificant changes in dynamic rheological properties.•Open time of the concrete was significantly extended with prolonged shearing.•Chosen one-part geopolymer mix design showed buildability of more than 120 layers.
Geopolymers are generally believed to provide good fire resistance due to their ceramic-like properties. Previous experimental studies on geopolymer under elevated temperatures have mainly focused on ...metakaolin-based geopolymers. This paper presents the results of a study on the effect of elevated temperature on geopolymer paste, mortar and concrete made using fly ash as a precursor. The geopolymer was synthesized with sodium silicate and potassium hydroxide solutions. Various experimental parameters have been examined such as specimen sizing, aggregate sizing, aggregate type and superplasticizer type. The study identifies specimen size and aggregate size as the two main factors that govern geopolymer behavior at elevated temperatures (800
°C). Aggregate sizes larger than 10
mm resulted in good strength performances in both ambient and elevated temperatures. Strength loss in geopolymer concrete at elevated temperatures is attributed to the thermal mismatch between the geopolymer matrix and the aggregates.
•The dispersion of GO in water is independent of the sonication degree with only small amount of GO reagglomeration.•High alkalinity and calcium ions are key factors inducing the agglomeration of GO ...in cement system.•Polycarboxylate-based superplasticisers exhibits the most promising results to disperse GO in cement alkaline environment.•ADVA 210 can disperse GO better in the pore solution environment, which was preferable to preparing GO-ADVA 210 suspension.•The inclusion of 0.03% GO protected by cement weight increased the GO-cement composite flexural strength up to 67%.
Graphene oxide (GO) is a novel class of two-dimensional nanoscale sheet material due to its excellent dispersibility in water, high aspect ratio and good intrinsic strengths. In order to obtain a well-distributed GO-reinforced cement composites, the dispersion of GO in water, alkali and several ionic species are investigated with the aid of UV–vis spectroscopy. High alkalinity and calcium ions are key factors inducing the agglomeration of GO in cement system. Dispersion of GO in simulated pore solution is the culmination of the alkali and salt experiments. Agglomeration of GO occurred when GO contacted with the simulated pore solution, highlighting the necessity to protect GO against such aggressive media. The test on surfactant compatibility was then carried out to ensure GO was effectively dispersed in polycarboxylate, air-entrainment and Gum Arabic admixtures within the pore solution. Polycarboxylate-based superplasticisers gave the most promising results to disperse GO in cement alkaline environment. Flexural experiments was performed to highlight the importance of fabrication protocol on the mechanical properties of GO-cement composites. The result shows that the amount of 0.03% GO by weight of cement can increase the flexural strength of GO-cement composite up to 67%.
Display omitted
•Novel post-processing can increase strength to 30 MPa for 3D Printed Geopolymer.•This is a major improvement from the previously attained strength of 16 MPa.•Optimum cure temperature ...is 60 °C for post-processing.•Water is an ineffective post-processing medium for strength gain.•A specially formulated is found to be the most effective post-processing medium.
A previous study presented a method of formulating geopolymer for powder-based 3D concrete printing (3DCP) for construction applications. The highest strength achieved in using this method was 16 MPa. While this is sufficient for some special construction applications, a higher strength is necessary for the majority of the construction applications. The present study presents a number of curing methods to enhance the strength of 3D printed geopolymer parts. The effects of curing temperatures and curing mediums on the compressive strength of geopolymer samples produced via the 3DCP process have been evaluated. Curing of the printed samples has been carried out in tap water, three alkaline solutions and three fly ash-based geopolymer slurries at different temperatures (25 °C, 40 °C, 60 °C and 80 °C). Results showed that printed geopolymer samples cured in a combination solution of N Grade sodium silicate solution and sodium hydroxide solution (8.0 M) at 60 °C gained the highest compressive strength of 30 MPa. This strength is nearly double the strength achieved in the previous study. The higher strength achieved in this newly developed post-processing method opens up wider range of possible construction applications due to the significantly improved strengths.
•Summarizing the latest literature on CNTs and GO reinforced cement composites.•Cement fabrication focuses on separating and avoiding re-agglomeration of nanomaterials.•Preserving the workability of ...nanocomposites is accomplished by using admixtures.•The seeding of C–S–H gel occurs on the large surface area of nanomaterials.•Reinforcement and pore refinement by 1D and 2D nanomaterials strengthen cement.
Progress in the field of nanomaterials presents an invaluable opportunity to develop cementitious composites at the nanoscale. Engineered nanomaterials exist in three principal shapes, namely 0D nanoparticle, 1D nanofiber and 2D nanosheet. The application of 0D nanoparticle and 1D nanofiber, such as nanosilica and carbon nanotubes (CNTs), respectively, has been reported in literature. The discovery of 2D nanosheet known as graphene oxide (GO) provides an extra dimension to interact with cement and concrete matrix and has yet to gain widespread attention. In this paper, recent research studies in developing cement and concrete nanocomposites are comprehensively reviewed. Also highlighted herein are the effect of incorporating nanomaterials in low dosages to the fabrication, workability, hydration, microstructure, and mechanical properties of cement-based composites.
PDF
