Efflorescence and leaching behaviour of fly ash-slag based alkali-activated materials

Efflorescence and leaching behaviour of fly ash-slag based alkali-activated materials

Over the past few decades, alkali-activated materials (AAMs) have shown the potential as alternative construction materials because of their high mechanical performance, low CO2 emissions, and the utilisation of industrial wastes as raw material such as fly ashn(FA). However, the curing conditions, reaction mechanisms, and durability or long-term performance of AAMs over ordinary Portland cement materials (OPC) are still under exploration. In addition, AAMs are required to exhibit adequate/superior durability to match OPCs. A wide range of precursor materials, different chemical compositions, lack of standard code of practices, complex reaction mechanisms, and variable experimental methodologies in the AAM field, have led to complexities in engineering and application and assessing durability.

This body of work aims at understanding efflorescence, leaching properties and the mechanical properties of low, intermediate, and high-calcium-based AAMs. AAMs with different calcium contents in the FA precursor, with sodium silicate, sodium hydroxide, and sodium carbonate were used as activators. Representative molecular models of geopolymer were developed and molecular dynamics (MD) simulations were performed on AAMs with alkaline solvents, aimed to understand the underlying atomistic interactions.

The primary objective was to understand the FA-slag based AAMs phases deterioration under efflorescence and leaching exposure, with a detailed physical and chemical analysis of the process. The research conducted was multidisciplinary and broadly classified into three parts. The first part of the work was to understand the effect of mixed activators on phase deterioration of AAMs. The second part of the work was to understand the effect of FA-slag ratio and Na2O content on reaction products. Specifically focused to understand the changes in 27Al and 23Na environment before and after efflorescence exposure. The third part of the research work discusses the effect of FA-slag ratio and Na2O content on the reaction products under leaching exposure.

The outcomes of this research have contributed to the knowledge of efflorescence and leaching behaviour of alkali-activated materials. The parametric formulations of
precursors and activators discussed in this work can be optimised to develop stable AAMs under various conditions.

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