Green reaction-type nucleation seed accelerator prepared from coal fly ash ground in water environment

•A novel reaction-type nucleation seed accelerator with D50 of 512 nm was prepared.•Early compressive strength was significantly increased by 50% at 12 h.•The secondary reaction of WFA seed occurs as early as 12 h.•MCL and Al/Si ratio of C-S-H gel were increased by WFA seed.•Pore structure of cement was refined by the addition of WFA seed. Fly ash is the main waste generated from coal production. The application of fly ash in building materials helps reduce pollution. In the present work, a novel reaction-type nucleation seed accelerator with D50 of 512 nm was prepared from coal fly ash using wet-grinding technology, denoted as WFA seed. The physical and chemical performances of WFA seed and its promotion effect on hydration, strength and microstructure of Portland cement (PC) were studied. With the addition of WFA seed, compressive strength was significantly increased by 50% and 16% at 12 h and 28 days. The hydration heat peak was also clearly increased by WFA seed. The hydration and strength promotion by WFA seed is attributed to the dual function of secondary reaction (which occurs as early as 12 h) and nucleation induction, which is different from the single function of nucleation site effect of some existing nano-materials. Furthermore, the main chain length and Al/Si ratio of C-S-H gel were increased, and the pore structure of cement was refined by the addition of WFA seed.