Influence of nano-silica particles on fracture features of recycled aggregate concrete using boundary effect method: Experiments and prediction models

The aim of this investigation is to assess the impact of using nano-silica (Na) at varying weight percentages of 0%, 1.5%, 3%, 4.5%, and 6% as partial cement substitute on fracture parameters of recycled aggregate concrete (RAC). A servo-controlled testing system was employed to carry out three-point flexure tests on 90 notched beams. Boundary effect method was used in order to interpret the fracture features. The results illustrate that adding Na increases the size-independent fracture energy, fracture toughness and initial fracture energy of RAC by 29%, 32%, and 24% compared to that without Na, respectively. The maximum values of these parameters occur at 4.5% Na. The reference crack length ((Formula presented.)) decreases from 6% to 22% by adding 1.5% to 6% Na. This shows that the RAC gets more brittle by the addition of Na. Moreover, the RAC behavior moves towards linear elastic fracture mechanics criteria by adding Na. Finally, according to the mechanical properties and test variables, multivariable models were suggested for prediction of the fracture parameters of the RAC containing Na. The models predictions were compared with experimental findings of the previous research.