Effect of curing condition and carbonization enhancement on mechanical properties of fly ash -desulfurization gypsum - steel slag blocks

Abstract

This research demonstrates the effect of curing conditions and carbonization enhancement on mechanical properties of fly ash (FA) - desulfurization gypsum (FGD) - steel slag (SS) gelation blocks. Five curing conditions, including dry-air curing, hot and humid curing, autoclave curing, hot and humid+autoclave curing, autoclave+hot and humid curing, were studied. The experimental results showed that the gelation block under the hot and humid+autoclave curing condition had the highest compressive strength, reaching 35.8MPa. The microstructural characterization of the gelation block by X-ray diffraction (XRD), Fourier-transfer infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA) and Scanning electron microscopy (SEM) indicated that the hot and humid + autoclave curing was favorable for producing more C-S-H gels and promoting the conversion of C-S-H gels to tobermorite crystals on the gelation block. Under the hot and humid+autoclave curing condition, both the tobermorite crystals and C-S-H gels resulted in more compact gelation blocks and thus their higher mechanical properties. The cured gelation block was subjected to enhanced carbonation, which resulted in a more compact gelation block with its pores filled with nano-size calcium carbonate and thus further improvement in its compressive strength by 19.6 %. The physical effect of enhanced carbonation on the gelation block is increased mass by 1.95 %, indicating that approximately 1.95 % of CO2 of the mass of the respective gelation block can be absorbed.