Recycling of switchgrass combustion ash in cement: Characteristics and pozzolanic activity with chemical accelerators

Biomass combustion produces renewable energy, but generates hazardous ash that must be disposed. High-volume of fine ash from the biomass combustion could be a harmful pollutant which causes lung cancer. Recycling the ash in cement is an environmentally-friendly solution especially for the cement industry. The objectives of this paper were to (1) characterize the ash from switchgrass combustion in a lab-designed furnace and (2) evaluate the material properties of cement containing switchgrass combustion ash. Cement-ash blends tested in this study contained 10% and 20% of ground ash (by weight) and chemical accelerators (5% Na2SO4 or 5% CaCl2·2H2O). Switchgrass combusted at 411 °C generated 5% ash by weight. After grinding for 30 s, ground ash had a porous structure with 65.0 μm of mean particle size and 41.2 m2/g of BET surface area. Ground ash consisted of 67.2% of SiO2 and its structure contained 72.2% of amorphous crystal. This ash was a good pozzolan in blended cement, and its pozzolanic activity was improved by adding chemical accelerators (5% Na2SO4 and 5% CaCl2·2H2O were equally effective). Blended cement with 10% ash and either 5% Na2SO4 or 5% CaCl2·2H2O had similar material properties (strength and expansion resistance) as conventional Portland cement. Hence, recycling the switchgrass ash in the cement proved to be technically applicable.