Microstructure of Calcium Carbide Residue–Ground Fly Ash Paste

Abstract

Microstructures of calcium carbide residue (CCR) and CCR–ground fly ash (CCR-GFA) pastes were examined. A ratio of CCR to GFA of 30 to 70 by weight was used as a binder without portland cement. CCR-GFA pastes with three different water-to-binder (W/B) ratios of 0.3, 0.4, and 0.5 were prepared. Scanning electron microscopy (SEM) was used to study the morphology of the CCR-GFA pastes. X-ray diffractometry (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to provide fundamental information about the specimens. Microstructures of CCR-GFA pastes were studied at 60 days. The compressive strengths of CCR-GFA pastes were determined at 7, 14, 28, 42, and 60 days. The morphology of CCR-GFA paste was composed of gelatinous particles of different sizes. The fracture surface was inhomogeneous with rough textures. Calcium silicate hydrate (CSH) product as Ca5(SiO4)2(OH)2 was found in all CCR-GFA pastes. This new compound was also found by FTIR analysis at wavelengths of 435 and 970 cm-1. Results from this work illustrate that the formation of CSH products is most likely the reaction of SiO2 from GFA, and Ca(OH)2 from CCR. This chemical reaction is possibly similar to the pozzolanic reaction. The compressive strengths of all samples increased with age and were almost constant after 42 days.