Preparation And Properties Of Alkali-Ativated/Heat-Activated Coal Gangue Cementing Materials

In this paper,using coal gangue powder（CG）,fly ash（FA）,and blast furnace slag powder（GGBS）as the main raw materials,using sodium hydroxide,sodium sulfate,and sodium silicate as alkali activators,a coal gangue based cementitious material was prepared through the process of alkali activation and thermal activation of coal gangue,and its mechanical properties and working properties were analyzed and studied.When the content of NaOH is 3%,the content of Na₂SO₄is 2%,and the ratio of microwave activated coal gangue:mineral powder:fly ash is 5:4:1,the compressive strength at 28d reaches 30.92 MPa.The 28 d unconfined compressive strength of the cementitious material prepared by the calcination process reached an extreme value of 47.52 MPa.Compared with the two thermal activation methods,the microwave activation process was highly efficient.When the modulus of sodium silicate is 1.2,the alkali content is 5%,and the ratio of coal gangue:mineral powder:fly ash is 5:4:1,the compressive strength of 28d reaches45.40 MPa.By X-ray diffraction（XRD）,Fourier infrared spectroscopy（FTIR）and scanning electron microscopy（SEM）.The main hydration products in the system are C-S-H,C（N）-A-S-H,AFt,AFm,C₄AF,Zeolite,hydrotalcite like,Anhydrite and Illite.The hydration products of Ettringite and hydrated calcium silicate and other gel phases in the products form a dense chimeric structure to provide mechanical properties for the materials.The mechanical properties,dry-wet cycle durability and heavy metal ion detection of the cementitious material prepared by alkali-activated thermal activation of coal gangue and red mud were studied.With the increase of the content of red mud,the 28d compressive strength shows a trend of increasing first and then decreasing.The 28d compressive strength of the microwave coal gangue red mud quaternary system is 26.33MPa,and the 28d compressive strength of the calcined coal gangue red mud quaternary system is 38.70 MPa.Based Based on Gibbs free energy minimization,the results of hydration and then the change trend of C-S-H was simulated.The precursor constitutes a Ca O-Al₂O₃-Si O₂-Fe₂O₃system,which promotes the diversification of hydration products.Through this study,coal gangue can be activated by two thermal activation methods to activate silicon and aluminum active substances,and under the action of alkali excitation,it can solidify and harden with other industrial solid wastes to form inorganic cementing materials,It provides some theoretical and technical guidance for further developing the large-scale application of solid waste bulk.