Studies on alkali activated compressed earth bricks for structural masonry

Abstract

Earth based construction materials are acknowledged as low carbon and low embodied energy materials. The investigations dealt in the thesis were mainly focused on exploring the geopolymer and lime-ground slag binders for the stabilised compressed earth bricks. A brief summary of the literature review on geopolymer and lime-pozzolana binders is presented. The thesis work is mainly based on experimental investigations. The initial part of the thesis presents the results of the investigations on the geopolymer stabilised compressed earth specimens and the brick specimens. Locally available red soil and pure clay minerals (kaolinite and montmorillonite) were used to cast the geopolymer stabilised compressed earth specimens. The investigations examine the role of clay and the alkali content on the strength of the geopolymer stabilised earth and pure clay specimens. Also, the influence of pozzolanas (ground slag and fly ash) on the strength of the specimens was examined. The results revealed the optimum mix proportions. The strength of the ground slag/fly ash based geopolymer specimens was nearly double that of non-ground slag/fly ash based geopolymer stabilised specimens. The characteristics of the geopolymer stabilised bricks such as strength, absorption, durability, and the stress-strain characteristics were examined in greater detail. The results showed the possibility of high strength (>20 MPa in wet state) bricks using a geopolymer binder. Investigations on using lime-pozzolana binder in the manufacturing process of the lime stabilised compressed earth bricks forms the next part of the thesis. The influence of clay, lime, and the pozzolana (ground granulated blast-furnace slag, i.e., GGBS) content on the strength of the specimens was examined in greater detail. The strength of the lime-pozzolana stabilised specimens increased with the increase in the pozzolana (ground slag) content. The long-term strength of the lime-pozzolana stabilised specimens was monitored. The results showed nearly 20% higher strength at the end of 365 days when compared to the strength of 28-day cured specimens. The investigations on the lime-GGBS stabilised compressed earth bricks showed that there is potential to obtain good quality bricks using lime-GGBS blended binders. The bricks showed satisfactory durability characteristics meeting the acceptable limits provided by the standards. The last part of the thesis deals with the investigations on the masonry using geopolymer and lime-GGBS stabilised compressed earth bricks. The strength (compressive strength and the flexure bond strength) and stress-strain characteristics of the masonry were examined through tests on masonry prisms. The results showed that the masonry bond strength increased with the increase in the surface porosity of the bricks. The results showed a linear relationship between brick strength and the masonry modulus. The thesis ends with a summary of the research outcome, contributions made to the knowledge domain, and the future work.