Flexural properties of fiber-reinforced alkali slag-red mud geopolymer

To improve the flexural performance of alkali slag-red mud geopolymer (AS-RG), polypropylene fiber was uniformly mixed into AS-RG, and a three-point bending test was carried out on fiber-reinforced AS-RG under different conditions; this was done to carry out the structural performance improvement and control test of composite materials. Based on the degradation control technology of fiber structure and properties, the ductility strengthening mechanism of composites was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) at the microscopic level. Particle flow numerical simulation software (PFC3D5.0) was used to simulate the whole process of three-point bending failure of the specimen, and the crack evolution law of the specimen was explained. The results show that the flexural strength of AS-RG can be effectively improved by adding a proper amount of polypropylene fiber, and the ability of resisting instability and failure of the material will be improved with the increase of fiber length, which will first strengthen, then weaken, and finally decrease with the increase of the water-binder ratio. Therefore, the combination of fiber length of 9 mm, fiber content of 4 parts per thousand, and water-binder ratio of 0.26 has the best effect on improving the fracture performance of the material. The three-point bending PFC3D numerical test results of samples under different fiber content are basically consistent with the indoor test results. After adding fiber, the formation of the crack zone of the samples obviously lags, and the total number of cracks that the samples can bear under the peak strength increases significantly. This study results can provide a theoretical basis for the flexural performance of fiber reinforced AS-RG.