Fracture Parameters of Alkali-Activated Aluminosilicate Composites with Ceramic Precursor

Abstract

This paper deals with selected alkali-activated aluminosilicate composites with a ceramic precursor in terms of their characterization using mechanical fracture parameters. Three composites were studied. They were manufactured using brick powder as a precursor and an alkaline activator with a dimensionless silicate modulus of Ms = 1.0, 1.2 and 1.4. The test specimens were nominally 40 × 40 × 160 mm in size and had a central edge notch with a depth of 1/3 of the specimen’s height. At least 6 specimens made of each composite were tested at the age of 28 days. The specimens were subjected to three-point bending tests, during which diagrams showing force vs. deflection at midspan (F–d diagrams) and force vs. crack mouth opening displacement (F–CMOD diagrams) were recorded. After the processing of these diagrams, values were determined for the static modulus of elasticity, effective fracture toughness (including its initiation component from the analysis of the first part of the F–CMOD diagrams), effective toughness and specific fracture energy using the effective crack model, Work-of-Fracture method, and Double-K fracture model. After the fracture experiments had been performed, compressive strength values were determined for informational purposes from one part of each specimen that remained after testing. In order to obtain visual information about the internal structure of the composites before and after the mechanical testing, the selected specimen was examined via X-ray microtomography. Tomographic measurements and image processing were performed for the qualitative and quantitative evaluation of internal structural changes with an emphasis on the calculation of porosimetry parameters as well as the visualization of the fracture process zone. The fractal dimension of the fracture surface and fracture process zone was determined. The porosity and microstructure images of selected samples taken from specimens were assessed.