Effect of K₂O content on properties of sugar cane bagasse ash-cement-based systems

The influence of potassium oxide contamination of sugar cane bagasse ash (SCBA) on the hydration of cement-based pastes and the compressive strength of mortars was investigated. Three SCBAs with different potassium oxide contents (2.7–12.6%) were used. The SCBA samples were initially characterised by their particle size distribution, BET specific surface area (SSA), pore volume, mineralogy and pozzolanic activity based on the Chapelle method. The hydration of cement-based pastes containing 20 wt% of SCBA was investigated using isothermal calorimetry and chemical shrinkage. The compressive strength of the mortars was evaluated at 3, 7, 28 and 90 days. The pozzolanic activity of SCBA was found to increase with decreasing potassium oxide content due to the higher silicon dioxide content and SSA of the SCBA dosed with a low potassium oxide content in comparison with other samples. The potassium oxide dosage had a limited influence on the paste hydration, except for a slight increase in the induction period observed by calorimetry. Cement replacement with SCBA with a high potassium oxide dosage led to maintenance of the compressive strength in relation to the reference up to 90 days. The mortars with low and medium potassium oxide contents showed good performance in terms of compressive strength, with significant increases compared with the reference after 90 days of curing.