Varieties of masonry units such as burnt clay bricks, stones and concrete products are used for masonry construction. Even though these materials are durable, they are considered as unsustainable options because of the issues concerning energy, environment and conservation of natural resources. The walling materials are consumed in bulk quantities and hence large quantities of natural resources are depleted. There is a need for energy efficient and environment friendly alternative materials for masonry. Fly ash is an industrial by-product from the coal based thermal power plants which can be exploited for manufacturing of masonry units such as fly ash blocks/bricks, which are an alternative for conventional masonry units. Fly ash-Lime-Gypsum (FaL-G) bricks can be manufactured by compaction of a mixture of fly ash-lime-gypsum and water. The behaviour of FaL-G brick masonry is inadequately explored area and hence the thesis is focused on understanding the flexural behaviour of FaL-G brick masonry and bond development phenomenon at FaL-G brick-mortar interface. A brief introduction to the fly ash-based masonry units and literature review with respect to utilizing fly ash in manufacturing masonry units are presented. Characteristics of raw materials used and the procedure followed in casting of masonry units/compacts, mortar and their assemblages including testing methods have been discussed. Characteristics of FaL-G brick, mortars, FaL-G brick masonry are presented. Apart from determining the stress-strain relationships for these materials shear strength parameters of FaL-G compact, mortar and brick-mortar joint were determined. Mohr-Coulomb failure envelopes for FaL-G compact and mortar are presented. The mechanism of bond development in masonry is discussed. FaL-G brick masonry shows considerably higher bond strength when compared with the bond strength of conventional brick masonry. Results of micro-structure analysis (SEM, XRD and TGA) of the FaL-G brick-mortar interfaces confirm the formation of chemical bond in addition to mechanical interlocking of cement hydration products into brick pores. Flexural behaviour of FaL-G brick masonry wallettes in the two orthogonal directions was studied. The flexural strength, displacement profiles and load-displacement curves were determined, and moment-curvature relationships were established. Linear elastic analysis performed closely predicted the cracking flexural stress in FaL-G brick masonry. A brief introduction to the computational modelling of masonry using different approaches has been presented. Literature review with respect to simplified micro-modelling approach has been discussed. The flexural behaviour of FaL-G brick masonry panels under lateral loads was predicted using a non-linear 3D finite element analysis. The finite element model reasonably predicted the flexural behaviour of FaL-G brick masonry panels. The thesis ends with summary of research work with a note on scope for further research.