Suitability of fly ash brick masonry as infill in reinforced concrete frames

Past experimental studies have shown that fly ash bricks are softer and weaker in comparison with burnt clay bricks and mortar generally used on site. Thus, mechanics of masonry under compression is altered such that the softer bricks are under tri-axial compression and mortar is under bilateral tension. An experimental study was carried out to understand the lateral load response of reinforced concrete (RC) frame infilled with fly ash brick masonry. Results showed that the frame provided reasonably good results in terms of lateral strength, stiffness, deformation, and energy dissipation. Using an analytical model developed from the experimental results a parametric study was carried out to compare the influence of using both fly ash and burnt clay brick masonry as infill in RC frames. Though frames infilled with fly ash brick masonry exhibited slightly lesser lateral strength and stiffness, the degradation in lateral load carrying capacity in post peak regime was significantly more gradual due to soft nature of fly ash bricks. Finally, to understand the possible reasons for the weak and soft nature of fly ash bricks, three types of analyses were carried out to evaluate their chemical and mineralogical composition: X-ray fluorescence analysis, scanning electron microscope associated with energy dispersive spectrometer, and powder X-ray diffraction technique. It was concluded that due to incomplete pozzolanic reaction, fly ash bricks exhibited weak and soft nature. Addition of activators was recommended to improve their stiffness and compressive strength, in case it is required.