Pozzolanic Reactivity, Hydration and Microstructure Characteristics of Blended Cementitious Composites Comprising of Ultrafine Particles

Abstract

Performance of ultrafine fly ash (UFFA, 5–10 µm) and fly ash (FA, 45–50 µm) particles in cementitious composites was investigated individually as well as in combination. To study the physicochemical behaviour of blended cementitious composites, engineering properties and pozzolanic reactivity test were conducted. Further, characterization techniques such as thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX) were employed. The results showed good amplification in the development of early compressive strength and durability on admixing ultrafine particles of fly ash (UFFA) in cementitious system. Particle size and specific surface area of UFFA greatly influenced on the phase assemblages of cementitious composites, i.e. due to enriched pozzolanic reactivity which reduced Ca/Si atomic ratio (≤ 1.82) in the pore solution of cementitious matrix. On contrary, the presence of UFFA particles in cementitious composite mix developed disjoining pressure in addition to self-desiccation thereby induced early age cracks and also reduced the workability in correspondence to that of FA particles. Further, use of UFFA in conjunction with FA particles, cementitious composites showed much superior performance in terms of both physical and chemical characteristics, which necessitates the crucial need of admixing micron and submicron size particles in the design of sustainable and high-performance cementitious composites at this point of time. © 2022, The Author(s), under exclusive licence to Shiraz University.