Study on the Fracture Performance of Carbon Fiber Reinforced Recycled Powder-Based Geopolymer Composites

To overcome the common shortcomings such as high brittleness, low toughness, and susceptibility to cracking in geopolymers, a three-point bending fracture test was conducted to study the effects of carbon fiber (CF) length (6 and 12 mm) and different contents (0.3, 0.6, 0.9, 1.2, and 1.5%) on the fracture performance of a recycled powder-based geopolymer (RPG). Parameters such as Load-CMOD curve, peak load, initial fracture toughness, unstable fracture toughness, and critical effective crack were used as evaluation indicators. The results show that the addition of CF within a certain dosage range can improve the fracture performance of RPG; After adding CF to geopolymer, the peak load, initial fracture toughness, unstable fracture toughness, and critical effective crack of the specimen can be significantly increased. These fracture parameters show a trend of first increasing and then decreasing as the CF content gradually increases, reaching their maximum value at a CF volume fraction of 0.9%. At this point, the load–crack opening displacement curve of the specimen was the highest, and the envelope area between the coordinate axes was the largest. Compared with the 12 mm fibre, the 6 mm CF has a stronger enhancement effect on the fracture toughness of the geopolymer.