Geopolymers are new binding material made from mostly waste material by activating with an alkaline solution. This material has high early strength, excellent durability in acids and sulphates and also reported to be highly resistant to elevated temperatures. It is considered to be an alternative to portland cement binders. Geopolymer has, of late attracted a lot of attention from civil engineers and material scientists as well. With further research, this material can be expected to revolutionize the construction industry in the near future. This book is an outcome of an extensive experimental study on strength and durability of fly ash based geopolymer composites. Geopolymer pastes and mortars made with varying alkali and silica contents are exposed to different acids of varying concentrations.They are found to be highly resistant to acids on the basis of weight and strength changes, microstructural and mineralogical changes.