The main objective of this article is to develop ceramic-based materials for additive layer manufacturing (3D printing technology) that are suitable for civil engineering applications. This article is focused on fly ash-based fiber-reinforced geopolymer composites. It is based on experimental research, especially research comparing mechanical properties, such as compressive and flexural strength for designed compositions. The comparison includes various composites (short fiber-reinforced geopolymers and plain samples), different times of curing (investigation after 7 and 28 days), and two technologies of manufacturing (casted and injected samples—simulations of the 3D printing process). The geopolymer matrix is based on class F fly ash. The reinforcements were green tow flax and carbon fibers. The achieved results show that the mechanical properties of the new composites made by injection methods (simulations of 3D technology) are comparable with those of the traditional casting process. This article also discusses the influence of fiber on the mechanical properties of the composites. It shows that the addition of short fibers could have a similar influence on both of the technologies.

SYNOPSISIn order to increase the chemical bonding force between fiber and resin, several kinds of organometallic coupling agent (such as titanate, zirconate, and zircoaluminate) were chosen and added in the BMI resin formulation, which possess the same solvent system with those coupling agents. The DSC analysis technique was used to find the best curing condition, and TGA was used to investigate the thermal stability property of the best curing condition. For the purpose of analyzing the bonding structure, ESCA surface element analysis techniques was applied in this study. Beside that, the mechanical properties of tensile, flexural, and short-beam shear strengths were measured for the effect of adding coupling agents, and the SEM of fracture surfaces were taken to study the fractural analysis. The results showed that composites with the application of organometallic coupling agents of [ RO-Ti ( OX-R'NH2)3] structure in the treatment of BMI resin were highly thermal stable. Also, it was shown that the mechanical strengths of composites fabricated by pretreatment of the carbon fibers with coupling agents were higher than those fabricated by adding coupling agents in resins, but there was no obvious improvement of mechanical properties with higher concentration of coupling agents. However, the SEM showed that the adhesion between fiber and resin can actually be improved by adding proper amount of coupling agents in the BMI resin formulation. INTRODUCTIONIn general, synthetic resin, ceramic, metal, and carbon are used as the matrix of carbon fiber composites. Epoxy resin is the most popularly used one. Bismaleimide (BMI) contains an imide group, so it possesses a better heat resistance than epoxy resin. The crosslinking of BMI is an addition reaction in which no small molecular evaporative substances is produced, so that nonvoid material can be obtained.' Therefore, the use of BMI in advanced composite material is worth developing.Because the manufacturing techniques of composites are constantly improved, the mechanical properties of composites are becoming better and better. Accordingly, the study on adhesion between fiber and resin is becoming very i m p~r t a n t .~.~ The study on improving the adhesion between epoxy * To whom correspondence should be addressed. resin and carbon fiber, which has been treated by coupling agent (such as Ti, Zr, and Zr/Al) , is already in~estigated.~.~ The resulting composites possess excellent physical properties, except for the wet-hot resistance. To address this disadvantage, some new types of organometallic coupling agents were selected that contains an amine functional group with better heat resistance. This functional group will easily react with an unsaturated double bond of BMI. Solvent of the selected coupling agent is the same as that of BMI, thus, not only the chemical bonding between carbon fiber and BMI is i n~r e a s e d~.~ but the wet-hot resistance and the mechanical properties of composites can be improved. EXPERIMENTAL MaterialsThe following materials were used Car...