The effects of four typical activators on the early hydration of sintering flue gas desulphurisation ash-steel slag-cement composite cementitious material

Millions of tons of steelmaking solid wastes are produced every year worldwide, such as steel slag (SS) and sintering flue gas desulphurisation ash (DA). As using DA directly in building materials is difficult due to its high CaSO3 content, it was combined with SS and ordinary Portland cement (OPC) into desulphurisation ash-steel slag-cement (DASSC) composite cementitious material. The effects of NaOH, Na2SO4, tri-isopropanolamine (TIPA), and silica fume (SF) on the early hydration of DASSC were investigated based on the workability of fresh pastes, compositions, structures, and properties of hardened pastes. Heat release indicated the hydration of SS and OPC were both inhibited in DASSC, but DA promoted their hydration, increasing the 72 h heat release from 113.62 J/g to 120.84 J/g. TIPA, Na2SO4, and SF showed improvements of 39.4%, 23.3%, and 14.8% on 14 d compressive strength of DASSC, respectively. TIPA accelerated the hydration of C2F in SS by complexation to Fe3+, producing large amounts of C–S–H and C-(A)-S-H, contributing to a decrease in porosity of DASSC from 33.14% to 26.06%, while average pore size decreased from 23.64 nm to 15.98 nm.