Application of powdered bio-composites in the field of self-compacting concrete: A review

Cement manufacture accounts for 5% of worldwide carbon dioxide emissions, resulting in significant environ-mental issues, and using supplemental cementitious materials (SCM) is an efficient strategy to minimise cement consumption. Self-compacting concrete (SCC) often relies on high amounts of binder and chemical additives to maintain workability. Thus, reducing the embodied carbon of SCC materials becomes essential for its wider application. Powdered bio-composites (PBCs), such as rice husk ash (RHA), bagasse ash (BA), palm oil fuel ash (POFA), groundnut shell ash (GSA), and eggshell ash (ESA), can be utilised as SCM for SCC. This paper sys-tematically reviewed the physical properties, chemical properties, and heat treatment methods of five types of PBCs and their impacts after replacing cement in SCC. The review disclosed that heat treatment could effectively reduce the value of loss on ignition (LOI), thus ensuring the activity of PBCs. High-temperature, short-duration incineration or low-temperature incineration for a long time can be effective. The review revealed that adding the five types of PBCs will reduce the workability of SCC, and RHA has the greatest negative impact. Segregation occurs when the cement replacement rate with RHA exceeds 20%. All five types of PBCs improve the mechanical properties of SCC to a certain extent after replacement. The preferred replacement rates are 5%-20% for RHA, BA and GSA, while for POFA the preferred rate could exceed 30%. The preferred rate is not conclusive for Eggshell ash, as it may lead to either positive or slightly negative impacts regarding compressive strength. In addition, adding an appropriate amount of PBCs will increase the durability of hardened SCC. The summarised impacts were also correlated with the microstructure of SCC through various analysis tools. The paper reveals the current gaps in applying PBCs in SCC and proposes strategies to design environmentally friendly SCC containing PBCs.