The relevance of ultrafine fly ash properties and mechanical properties in its fly ash-cement gelation blocks via static pressure forming

Two fly ash samples, collected from the circulating fluidized bed (CFBFA) and pulverized boiler (PCFA) were ultrafine grinded and characterized by the scanning electron microscopy (SEM), the X-ray diffractometer (XRD) and the fourier transform infrared spectroscopy (FT-IR). The characterizations revealed the ultrafine grinding of fly ash resulted in not only the increase of their specific surface areas, also the decrease of crystallinity degree and the anion polymerization degree of silicates and aluminates. In comparison to CFBFA, PCFA showed a higher anion polymerization degree of silicates and aluminates. This was followed by strength behavior studies of the fly ash-cement gelation blocks. The mixing ratio of tested fly ash and cement was 1:1 (by wt%), and the fly ashes included those before and after ultrafine grinding. The results showed that ultrafine fly ash (UFFA)-cement blocks exhibited higher compressive strength as compared to that of original fly ash (OFA)-cement blocks, especially at their early stage. Compared with PCFA, CFBFA was more significant in improvement of mechanical properties of fly ash-cement block at its early age for the gelation block. Studies on the water absorption and the thermal weight loss revealed the effectiveness of UFFA in increasing the density and producing more C-S-H in order to improve the mechanical properties in gelation blocks. Due to the difference of CFBFA and PCFA in chemical and mineral compositions, the enhancement of CFBFA in producing C-S-H was greater at its early age but lower at its late age than those of PCFA.