SiC fiber reinforced geopolymer composites, part 2: Continuous SiC fiber

In this paper, unidirectional SiC fiber (SiCf) reinforced geopolymer composites (SiCf/geopolymer) were prepared and effects of fiber contents on the microstructure and mechanical properties of the composites in different directions were investigated. The XRD results showed that addition of SiCf retarded geopolymerization process of geopolymer matrix by weakening the typical amorphous hump. SiCf in all the composites were well infiltrated by geopolymer matrix, but microcracks which were perpendicular to the fiber axial direction were noted in the interface area due to the thermal shrinkage of matrix during the curing process. With the increases in fiber contents, although Young's modulus of the composites increased continuously, flexural strength, fracture toughness and work of fracture increased at first, reached their peak values and then decreased. And when fiber content was 20 vol%, the composites showed the highest flexural strength, fracture toughness and work of fracture, which were 14.2, 15.2 and 81.6 times as high as those of pristine geopolymer, respectively, indicating significant strengthening and toughening effects from SiCf. Meanwhile, SiCf/geopolymer composites failed in different failure modes in the different directions, i.e., tensile failure mode in the x direction (in-plane and perpendicular to the fiber axial direction) and shear failure mode in the z direction (laminate lay-up direction).