Abstract
Current demand for highly sustainable concrete, e.g. alkali-activated fly ash-slag (AAFS) concrete, urges understanding the links between microstructure and micromechanical properties of this binder. This paper presents a systematic investigation into the microstructure and micromechanical properties of AAFS paste from nano-scale to micro-scale. Nanoindentation was used to evaluate the micromechanical properties, while the microstructure was characterised using 29Si nuclear magnetic resonance, Fourier transform infrared spectroscopy, backscattered electron microscopy, and mercury intrusion porosimetry. The results indicate that N-A-S-H gels have a relatively low elastic modulus due to their high level of structural disorder and gel porosity, while the C-A-S-H gels and N-C-A-S-H gels with a low level of structural disorder and gel porosity have a relatively high elastic modulus. The elasticity of reaction products and their relative volumetric proportions mainly determine the macroscopic elasticity of AAFS paste, while the porosity and pore size distribution primarily condition its macroscopic strength.
Highlights
Alkali-activated materials (AAM), manufactured through the reaction of alkaline activator with aluminosilicate precursors, have been regarded as an environmentally friendly alternative to Portland cement (PC) because of the low CO2 emission and the low consumption of natural resources [1,2,3]
According to the experimental results obtained from nanoindentation, mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) tests as well as the theoretical results based on the self-consistent continuum micromechanics model, the macroscopic performance of activated fly ash-slag (AAFS) paste at Level II is dominated by two factors that exist at different scales: (1) the microscopic properties of reaction products at Level I, and (2) the characteristics of pore structure at Level II [26]
A series of tests including nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), MIP, SEM and nanoindentation were carried out to investigate the microstructure and micromechanical properties of AAFS paste cured at ambient temperature from nano-scale to micro-scale
Summary
Alkali-activated materials (AAM), manufactured through the reaction of alkaline activator with aluminosilicate precursors, have been regarded as an environmentally friendly alternative to Portland cement (PC) because of the low CO2 emission and the low consumption of natural resources [1,2,3]. AAF requires rigorous curing conditions with elevated temperature (60– 85 °C) to gain early-age strength, whereas AAS has some drawbacks including poor workability and quick setting [4,5,6]. To conquer these limitations, recent developments in the field of AAM have led to an increasing interest in the blended AAM, called alkali-activated fly ash-slag (AAFS), which can achieve the desired engineering properties under ambient curing conditions [6,7,8]. Regarding the effect of activator types, it was found that the AAFS mixture activated by a blend of sodium hydroxide (SH) solution and sodium silicate (SS) solution achieves a higher strength than that activated by SH or SS solution alone [19]
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