Hydration and Setting Behavior of Cement Pastes Modified with Swine-waste Biochar

The purpose of this study was to investigate the effect of swine-waste biochar (SB) on the hydration and setting behavior of cement pastes using real-time Fourier Transform Infrared Spectroscopy—Attenuated Total Reflectance (FTIR-ATR) and Raman spectroscopic techniques, as well as the Vicat needle test. Results indicated that SB is not an inert material in cement pastes, as the gradual shifts in the frequencies as well as the intensity changes of characteristic peaks in the Raman and FTIR spectra indicated accelerated polymerization as a result of hydration reactions. In addition to typical cement hydration products (calcium-silicatehydrate, calcium hydroxide, and calcium-aluminate-sulfatehydrate), characteristic peaks for calcium-carboxylate-salts (C-C-S) were detected. In all of the SB modified pastes, C-C-S was observed before C-S-H in the FTIR spectra; this explained the lower setting times obtained for SB-modified cement pastes. As early as 15 minutes after water was added to the dry binder mix of ordinary Portland cement with a 20% SB replacement by mass, C-C-S was observed and accelerated the setting of the cement pastes. The shorter setting times of the modified pastes was a result of chemical reactions between the calcium cations from Portland cement and carboxylate anions from SB, leading to the development of C-C-S. The presence of C-C-S also created additional nucleation sites, which accelerated the development of the typical calcium-silicate-hydrates (C-S-H). For acceptable setting times, the highest SB replacement percentage in this research study was 15% at a water/binder ratio of 0.28. Shifts to lower Raman wavelengths for C-S-H in SBmodified pastes provided an indication that C-C-S may have interfered with C-S-H polymerization during the setting period.