The Role Of Ferronickel Slag Powder In Cement-based Composite Binder

Ferronickel slag is a type of industrial residue from the manufacture of stainless steel and nickel alloys,which is a potential mineral admixture for concrete.In this paper,three electric arc furnace ferronickel slag powders?EFS?and two blast furnace ferronickel slag powders?BFS?were used,the aim was to study the role of ferronickel slag powder in the hydration process of composite binder and the differences in the roles of EFS and BFS in concrete under standard and high temperature curing conditions.Besides,the feasibility of using EFS in massive concrete structures was also investigated.The main research contents and relevant conclusions are listed as follows:?1?Both the specimen containing EFS and that containing BFS have qualified autoclave soundness and low leaching toxicity of Cr.The activities of EFS and BFS are very low under non-alkaline conditions.?2?BFS shows obviously higher pozzolanic activity than EFS and its reaction degree in composite binder system is also higher compared with EFS.BFS with higher CaO,Al₂O₃ contents and lower MgO,Fe₂O₃ contents exhibits higher pozzolanic activity.The differences in pozzolanic activity among different EFS powders are very small although their chemical compositions are different.?3?The addition of ferronickel slag powder slows the hydration rate of binder at early ages,but the hydration of the composite binder reaches greater development at late ages than plain cement due to the late pozzolanic reaction of ferronickel slag and its nucleation and dilution effects on cement hydration.High temperature curing can promote the early activity of ferronickel slag powder,and its promoting effect on BFS is more obvious.?4?No matter under standard condition or high temperature condition,replacing a portion of cement with ferronickel slag powder tends to decrease the Ca/Si ratio of C-S-H gel and increase the polymerization degree of silicate chains.The C-S-H in the paste containing EFS has a lower Ca/Si ratio and higher silicate polymerization degree than that in the paste containing BFS.The addition of EFS has a negligible influence on the Al/Si ratio of the C-S-H gel in cement-based paste,while the Al/Si ratio of the C-S-H gel in the paste containing BFS is larger than that in the plain cement paste.?5?The hardened paste containing EFS has a coarser microstructure than that of the plain cement paste.Replacing a portion of cement with EFS tends to decrease the compressive strengths of both mortar and concrete and increase the drying shrinkage of concrete.However,the addition of EFS decreases the chloride ion permeability grade of concrete due to its pozzolanic activity.Replacing a portion of cement with BFS does not increase the porosity of hardened paste but even improves its pore structure.The strength of the mortar,and the strength and drying shrinkage of the concrete containing BFS are also close to those of the plain cement specimens at late ages.The addition of BFS obviously improves the resistance of concrete to chloride ion penetration,and its improving effect is more obvious than that of EFS.The late strength of the concrete containing ferronickel slag powder under high temperature curing condition may be lower than that under standard condition.But the resistance to chloride ion penetration of the concrete containing ferronickel slag powder is not negatively influenced by high temperature curing.?6?The concrete containing 25%EFS and 25%phosphorus slag powder?HVFP concrete?has an adiabat temperature rise curve similar to that of the concrete containing50%fly ash?HVFA concrete?.Under temperature match curing condition,the late strength of HVFP concrete is slightly higher than that of HVFA concrete.The early elastic modulus and late resistance to chloride ion penetration of HVFP concrete are close to those of HVFA concrete.Therefore,it can be preliminarily concluded that HVFP concrete is suitable to be applied in massive concrete structures.