Partial or total replacement of blast furnace slag with palm oil fuel ash in high-volume slag cement: hydration characteristics, compressive strength, and carbonation resistance

With the emergence of new electric arc furnace technology, the long-term supply of blast furnace slag (BFS) may decline. To address this potential shortage, this study proposes partial or total replacement of BFS with palm oil fuel ash (POFA), an agricultural by-product from the oil palm industry, in high-volume slag cement. The hydration characteristics, compressive strength development, and carbonation resistance of the resulting binary/ternary cementitious systems containing BFS or POFA are thoroughly evaluated. The results indicate that POFA is less reactive than BFS at an early stage (2 d or 3 d). However, as the curing time increased, the pozzolanic reaction of POFA became pronounced, significantly reducing the calcium hydroxide content in the hardened paste at later ages. The reactions of POFA and BFS further contribute to the increase in mechanical strength. This study revealed that incorporating 15% POFA in high-volume slag cement paste results in 8.6% greater compressive strength than cement paste without any supplementary cementitious materials (SCMs) after 56 d of curing. However, the addition of POFA diminishes the carbonation resistance of such ternary cementitious systems. Specifically, the carbonation rate increases by 16.9% to 95.0% when the proportion of POFA in high-volume ternary cement increases from 15% to 60%. This work provides valuable insights into a ternary cementitious system containing POFA and BFS, promoting the sustainable use of POFA as an SCM in cement-based materials.