Research On Activated Coal Gangue And Corrosion Behavior Of Steel Rebar In Gangue Based Mortars

Coal gangue is a complex industrial solid waste of coal industry. Comprehensive utilization of coal gangue has already become an important problem to be solved urgently. Gangue is used for preparation construction materials which have good prospects for comprehensive utilization. Current research is focused mainly on improving cementitious activity. However, the cementitious activity is currently insufficient for these materials to qualify as suitable for use in construction. Durability problems, especially the corrosion of reinforcement steel, limit the large-scale application of this byproduct in construction materials. Coal gangue from Beijing Fangshan was studied in this paper. Pozzolanic activity of coal gangue and reinforcement corrosion behavior in coal gangue-based mortars was analyzed to provide a reference for further extensive utilization of gangue in the field of building cementitious materials.In order to optimize the pozzolanic activity of coal gangue, the influence of simple calcination and co-calcination method on pozzolanic activity of coal gangue was studied, and pozzolanic activity optimization was achieved. Mechanism of activity optimization was investigated. Based on MAS NMR analysis technology, we proposed the concept of relative number of bridging oxygen （RBO） to evaluate [SiO₄] polymerization. It is found that [SiO₄] polymerization of coal gangue decreased during the aactivation process, while increase during the hydration process. There is obvious inverse correlation between RBO and cementitious activity.According to the difference of pore solution component between OPC and coal gangue based pastes, the corrosion behavior of steel bar in simulated pore solution was studied. The influence of ions in pore solution on corrosion behavior was analyzed. It is shown that the corrosion potential of reinforcement in coal gangue cementitious mortar is much higher than that in OPC which is mainly due to higher concrete resistance R_c from ACI analysis.The solidification for chloride is higher in coal gangue cementitious mortar than in OPC mortar. The solidification rate of chloride ion increased with coal gangue admixture. Phosphate improve solidification rate of chloride ion consolidate further during the activation process of coal gangue which benefit from chlorapatite product. （31）^P NMR results showed that （31）^P combine with silicon-oxide polyhedron and aluminum-oxygen polyhedron to form super phosphate structure. This is helpful to stable frame structure construction in mortar.The principal factor which affects diffusion rate of chloride ion is pore structure. Coal gangue has good solidification properties for chloride ion,which is helpful to decline the diffusion coefficient of chloride ion.Commercial experiments on production of coal gangue cementitious materials by co-calcination method were carried out at a clinker production line with capacity of 1200 tons per day. The experimented products has been used in construction of road works.