Circulating fluidized bed fly ash based multi-solid wastes road base materials: Hydration characteristics and utilization of SO3 and f -CaO

Circulating fluidized bed fly ash (CFBFA) is a harmful by-product of CFB boiler in power plant, which is difficult to be treated because it contains f-CaO and SO3. In this research, CFBFA based multi-solid wastes road base materials (CRM) composed of CFBFA, Bayer red mud (RM), OPC and coal gangue aggregate are produced. It is interesting to see that SO3 and f-CaO are utilized in CRM. The durability of CRM is improved by the synergistic effect of CFBFA and RM. The results proves that CFBFA containing SO3 makes the unrestricted compressive strength (UCS) of CRM reach the highest (6.14 MPa) at 7 days when (Ca + Na)/(Al + Si) mass ratio is 0.39, which satisfies the road base strength requirements. Meanwhile, CRM37 has the best volume stability because f-CaO compensates for CRM37 vol shrinkage. The main hydration gel products of CRM are C/N-A-S-H gel and ettringite, which are beneficial to amelioration of the UCS and durability. The densest microstructure and optimal [Si (Al)O4] polymerization structure is embodied in CRM37. The leaching results showed that Na+ and heavy metals satisfies the WHO drinking water safety standard. Therefore, this work presents a feasible reference for the comprehensive utilization of CFBFA and multi-solid wastes.

Automated summary

The study found that road base materials composed of circulating fluidized bed fly ash and Bayer red mud performed well in improving durability, achieving the required compressive strength. The prepared CRM showed good volume stability and improvements in UCS and durability through the synergistic effect between specific materials. The research also demonstrated the microstructure and hydration gel products of CRM, showing their positive role in enhancing material performance.