The objective of this review paper is to summarize the current status and identify the knowledge gaps in ceramic binder jetting additive manufacturing, with a particular focus on density. This paper begins with an overview of ceramic binder jetting. Then, it discusses different aspects of density, including various terminologies, measurement methods, and achieved values. Afterward, it reviews two categories of techniques to increase the part density: material preparation techniques (powder granulation, mixing powders of different sizes, using slurry feedstock, and mixing different materials) and postprocessing techniques (sintering, chemical reaction, infiltration, and isostatic pressing). Finally, it presents the knowledge gaps in the literature.

This paper reports a study on the effects of particle size distribution (tuned by mixing different-sized powders) on density of a densely packed powder, powder bed density, and sintered density in binder jetting additive manufacturing. An analytical model was used first to study the mixture packing density. Analytical results showed that multimodal (bimodal or trimodal) mixtures could achieve a higher packing density than their component powders and there existed an optimal mixing fraction to achieve the maximum mixture packing density. Both a lower component particle size ratio (fine to coarse) and a larger component packing density ratio (fine to coarse) led to a larger maximum mixture packing density. A threshold existed for the component packing density ratio, below which the mixing method was not effective for density improvement. Its relationship to the component particle size ratio was calculated and plotted. In addition, the dependence of the optimal mixing fraction and maximum mixture packing density on the component particle size ratio and component packing density ratio was calculated and plotted. These plots can be used as theoretical tools to select parameters for the mixing method. Experimental results of tap density were consistent with the above-mentioned analytical predictions. Also, experimental measurements showed that powders with multimodal particle size distributions achieved a higher tap density, powder bed density, and sintered density in most cases.

Additive manufacturing (AM) has had an enormous impact on the manufacturing sector. Its role has evolved from printing prototypes to manufacturing functional parts for a variety of applications in the automotive, aerospace, and medical industries. Recently, AM processes have also been applied in the infrastructure construction industry. Applications of AM processes could bring in significant improvements in infrastructure construction, specifically in the areas of productivity and safety. It is desirable to have a review on the current state of emerging AM processes for infrastructure construction and existing gaps in this field. This paper reviews the AM processes in infrastructure construction. It discusses the process principle, application examples, and gaps for each of the AM processes.

Agriculturally derived biowastes can be transformed into a diverse range of materials, including powders, fibers, and filaments, which can be used in additive manufacturing methods. This review study reports a study that analyzes the existing literature on the development of novel materials from agriculturally derived biowastes for additive manufacturing methods. A review was conducted of 57 selected publications since 2016 covering various agriculturally derived biowastes, different additive manufacturing methods, and potential large-scale applications of additive manufacturing using these materials. Wood, fish, and algal cultivation wastes were also included in the broader category of agriculturally derived biowastes. Further research and development are required to optimize the use of agriculturally derived biowastes for additive manufacturing, particularly with regard to material innovation, improving print quality and mechanical properties, as well as exploring large-scale industrial applications.

It is known that 3D printing can facilitate greater design flexibility in the printing of custom shapes for packaging and construction applications using biomass–fungi composite materials. The feasibility of this new method was demonstrated by a preliminary experiment, the results of which were reported in a journal publication in 2020. As a follow-up, this paper reports on an experimental study on the relationship between the mixture composition (i.e., the psyllium husk powder content) and print quality using this new method. Four mixtures were prepared by varying the amounts of psyllium husk powder (in grams) added to 400 mL of water. The ratios (g/mL) of psyllium husk powder weight (w_p) over volume of water (v_w) for the mixtures were 0, 1:40, 2:40, and 3:40. Each mixture also contained 100 g of biomass–fungi material and 40 g of whole wheat flour. The print quality of the samples was evaluated based on the extrudability and shape stability. The results showed that mixtures without any psyllium husk powder were not extrudable. An increase in the ratio of psyllium husk powder to water from 1:40 to 2:40 resulted in improved print quality; however, when the psyllium husk powder to water ratio was increased to 3:40, the extrudability became worse. This phenomenon was explained by analyzing the rheological properties of the mixtures.