Modelling of fracture strength of functionally graded geopolymer

• Functionally graded geopolymers were produced from two different types of fly ashes.
• Mathematical model for evaluation of fracture strength.
• Load direction with respect to graded region plays an important role.

In the current paper, fracture strength of a functionally graded geopolymer was analytically modelled for crack propagation in two possible perpendicular situations with respect to the functionally graded region. Functionally graded geopolymer was produced by pouring and subsequent vibration of two layers of different alkali activated fly ash-based geopolymers into the moulds. The thickness of functionally graded region was determined equal to 18.6 mm through evaluating Si/Al ratio obtained from EDS. In modelling procedure of both crack configurations, the functionally graded region was considered to have 372 layers with the thickness of 50 μm and the fracture strength of the geopolymeric specimen in functionally graded region was related to the fracture strength of the constituent layers. To represent the variation of surface energy and elastic modulus in functionally graded region, three different functions including exponential, power-law and linear were considered. The obtained results from the proposed model show a good agreement with those of obtained through experimental procedure.