Reactivity Assessment of Residual Rice-Husk Ashes

The production of rice-husk ash without controlled burning results in pozzolans with different physicochemical characteristics. The amorphous content of residual rice-husk ash (RRHA) is related to the temperature and exposure time during burning, whereas the BET specific surface area depends on the siliceous structure formed during plant growth, in addition to burning and grinding methods. In this study, amorphous content was quantified by X-ray diffraction (Rietveld refinement) in three RRHA samples randomly collected from rice mills located in southern Brazil, in which the burning process was not controlled. Pozzolanic activity evolution of RRHA samples in lime paste was monitored by thermogravimetry for 182 days in order to determine the influence of the lime:pozzolan ratio, BET specific surface area, and average particle size. The results show that lime consumption is not significantly affected by the BET specific surface area or average particle size of RRHA samples with a high amorphous content (>66%). The reaction rate of RRHA depends on the lime: pozzolan ratio. Lime consumption per unit surface area of RRHA declines with an increase in the BET specific surface area. Because the proposed shape factor connects the BET specific surface area and average particle size of RRHA and indirectly includes the amorphous content of RRHA samples, it can therefore be used as an indicator of RRHA reactivity. (C) 2017 American Society of Civil Engineers.