Hydration Performance And Life Cycle Assessment Of Nickel Slag Cementitious Materials

Cement is the most widely used cementitious material in the world.Since cement production will consume a lot of non-renewable resources and energy,it is urgent to find alternative materials.At present,the most commonly used measure is to use industrial solid waste as supplementary cementing materials(SCMs)to replace cement.Fly ash is a classic example.Nickel slag is the waste residue in the process of smelting nickel from laterite nickel ore.The production of 1t nickel will produce 6t ～ 16 t nickel slag.Most of the nickel slag produced over the years is in the open-air accumulation state,occupying many land resources,and may cause heavy metal pollution to the ecological environment.In view of the precedent of industrial waste as SCMs,the feasibility of nickel slag as SCMs was been explored from two aspects of performance and environmental impact,which provided reference for the study of its reuse.It is important to study its pozzolanic activity for studying SCMs.In this paper,the mechanical activation method was been used to improve the activity of nickel slag,then the effect of the proportion of nickel slag replacing cement(10% to 40%)and the fineness of nickel slag on the strength of nickel slag cement mortar was studied.The test found that the nickel slag was inactive in the early stage.When the age was 7 days,the strength of the 7d mortar decreased with increased content of the nickel slag.Then the strength of the mortar was similar to that of the pure cement mortar when the nickel slag content was 10% at 210 day,but the strength decreases obviously after the increase of nickel slag.Moreover,the reduction of flexure strength is higher than that of compressive strength,and the addition of nickel slag will lead to a great increase in the porosity of the mortar.Due to the low activity of nickel slag,this article attempts to use steam curing to improve the early performance of nickel slag cementitious materials and stimulate the activity of nickel slag.Experiments have found that steam curing temperature and nickel slag content are the main factors affecting the 14 d performance of cement paste containing nickel slag.Steam curing can improve the14 d performance of cement paste containing nickel slag,and stimulate the activity of nickel slag.However,increasing the temperature from 60°C to 80°C,steam curing,found by thermal analysis,has little effect on nickel slag activity.C-S-H gel with high content of Mg was found in the pictures of scanning electron microscope and energy spectrum analysis,indicating that Mg in nickel slag underwent secondary hydration reaction and C-M-S-H gel was formed,which proved that nickel slag has certain activity.After life cycle assessment of mortar containing nickel slag,it is found that the addition of nickel slag can effectively reduce the energy consumption and various waste gas emissions in the mortar production process,but from the perspective of combined strength,when the addition of nickel slag is 10%,a win-win situation can be achieved between strength and environmental impact.