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.

Fly ash is a waste product from thermal power plants where pulverised coal is used for the generation of electricity. Fly ash is being utilised in the blended cements, additive for concrete and manufacturing of concrete blocks and bricks. Fly ash-lime-gypsum bricks are being manufactured and marketed throughout the country. The literature review on fly ash-lime-gypsum (FALG) mixtures as intended to manufacture bricks or blocks for masonry applications indicates several gaps in understanding the various aspects of the technology. The present thesis is an attempt to understand the behaviour of compacted stabilised fly ash mixtures for the manufacture of fly ash bricks and characteristics of masonry using such bricks. A brief introduction to the technology of compacted stabilised fly ash bricks for structural masonry is provided. Review of the literature on fly ash-lime and fly ash-lime-gypsum mixtures, and fly ash bricks is provided in chapter 1. Chapter 2 gives details of the experimental programme, properties of raw materials used in the experimental investigations, methods of preparing different types of specimens and their testing procedures. Chapter 3 deals with the strength and absorption characteristics of compacted stabilised fly ash mixtures in greater detail. The main focus of the investigations is on arriving at the optimum stabilizer-fly ash mixtures considering density, stabilizer-fly ash ratio, curing conditions, etc. as the variables. Therefore the parameters/variables considered in the investigation include: (a) density of the compacted fly ash mixture, (b) stabilizer-fly ash ratio, (c) curing duration (normal curing and steam curing) and (d) dosage of additives like gypsum. Some of the major conclusions of the investigations are (a) compressive strength of compacted stabilised fly ash mixtures is sensitive to dry density of the specimens and the strength increases with increase in density irrespective of stabiliser content and type of curing, (b) Optimum limefly ash ratio yielding maximum strength is 0.75, (c) addition of gypsum accelerates rate of strength gain for compacted fly ash-lime mixtures (d) for 28 days wet burlap curing optimum gypsum content yielding maximum strength is 2% and maximum compressive strength is achieved for lime contents in the range of 10 – 17%, (e) steam curing (at 80 °C for 24 hours) gives highest compressive strength for compacted fly ash-lime mixtures. Characteristics of compacted fly ash-lime, fly ash-lime-gypsum and fly ash-cement bricks and their masonry are presented in chapter 4. Compressive strength, elastic modulus, water absorption, initial rate of absorption, dimensional stability and durability of the bricks were examined. Compressive strength, flexure bond strength and stress strain relationship for the fly ash brick masonry using cement-lime mortar were evaluated. The investigations clearly show the possibility of producing bricks of good quality using compacted fly ash-lime gypsum mixtures. Wet compressive strengths of 8- 10 MPa was obtained for compacted fly ash-lime-gypsum bricks at the age of 28 days. Wet strength to dry strength ratio for these bricks is in the range of 0.55 – 0.67. Initial tangent modulus for the fly ash-lime-gypsum bricks in saturated condition is in the range of 8000 – 12000 MPa. There is a large scope for selecting optimum mix ratios of fly ash, sand, lime and other additives to obtain a specific designed strength for the brick. The thesis ends with Chapter 5 highlighting major conclusions of the investigations.