Study On Corrosion Resistance Of Granulated Blast Furnace Nickel Slag Concrete In Chloride Environment

Nowadays,the total generation of nickel slag at present in China is up to 100 million tons,but only about 12%of which has been recycled and the rest is landfilled resulting in serious environmental pollution.Incorporation of the nickel slag in cement concrete can not only reduce the cost,but also have good environmental benefits.The feasibility of the application of nickel slag in cement concrete has been widely confirmed by scholars at home and abroad.However,little study has been carried out on chloride penetration and reinforcement corrosion in nickel slag blended concretes.In this thesis,nickel slag is used as a main mineral admixture partially replace cement in concrete.A range of blended mixtures were prepared,including nickel slag（replacing 20～70%OPC（ordinary Portland cement）by weight）,combined nickel slag and fly ash（replacing 50%of total OPC,ratio being 3:7,5:5 and 7:3）,and combined nickel slag and silica fume（30%nickel slag and10%silica fume、50%nickel slag and 10%silica fume、70%nickel slag and 10%silica fume）.The influences of these blended mixtures on concrete slump,compressive strength,chloride penetration and reinforcement corrosion were studied.The above macro-properties of concrete was investigated by means of MIP、XRD、SEM and TG.The main conclusions are drawn as follows:1.When OPC is partially replaced by nickel slag or by combined nickel slag and 10%silica fume,a higher amount of nickel slag leads to an increase of the concrete slump.However,when nickel slag is added together with fly ash,the concrete slump decreases with a higher nickel slag-to-fly ash ratio.2.For concrete with a higher addition of nickel slag,the compressive strength decreases obviously in the first 7d,followed by an increase and again a decrease at the later ages of 28d,56d and 180d.An appropriate amount of nickel slag is favorable to the compressive strength.When the nickel slag addition is 20%（an optimal amount）,the highest compressive strength of 61.3 MPa at 180d is 8.5%higher that of the OPC concrete.In the case of combined addition of nickel slag and fly ash,an increase of the nickel slag-to-fly ash ratio results in an increased compressive strength at early age（7d）and an increased first and then decreased ones at later ages,with a best combination ratio of 5:5.When nickel slag is added in combination with 10%silica fume,the compressive strength of concrete decreases with the increase of nickel slag content.3.Compared with the OPC concrete,the concretes blended with nickel slag,combined nickel slag and fly ash,or combined nickel slag and 10%silica fume exhibit a significantly lower chloride penetration.Both the charge passed and the D_RCM（chloride diffusion coefficient）experience an increase and then a decrease with the increase of nickel slag content.When the nickel slag content is set at 50%,charge passed and D_RCM is just 211.7 C and 1.3×10^-12 m²/s,smaller than those of the OPC concrete by 85.5%and 77.4%,respectively.When incorporating with both nickel slag and fly ash,with a higher nickel slag-to-fly ash ratio,the charge passed and D_RCMare increased.The optimal ratio for nickel slag-to-fly ash ratio is 7:3.When incorporatating with both nickel slag and 10%silica fume,a higher amount of nickel slag results in decreasing charge passed and the D_RCM,with the optimal proportion of 50%nickel slag and 10%silica fume.4.Compared with the OPC concrete,the addition of nickel slag,combined nickel slag and fly ash,or combined nickel slag and silica fume can significantly enhance the corrosion resistance of the reinforcing steel in concrete.The corrosion rate decreases with the increase of nickel slag content.In the presence of nickel slag and fly ash,the corrosion rate is decreased at first and then increased with the increase of the nickel slag-to-fly ash ratio.When the ratio is 5:5,the steel corrosion resistance is the highest.For combined addition of nickel slag and 10%silica fume,the corrosion rate also decreases at first and then increases,and the highest corrosion resistance is found when 50%nickel slag and 10%silica fume are used.5.The concrete blended nickel slag exhibit better durability in chloride environment.For example,when concrete cover is 60mm,the service life of concrete structure can be prolonged nearly 1.4 times as long as that of the the OPC concrete.6.The addition of nickel slag can reduce the crystallinity of the Ca（OH）₂ in concrete,increase the compactness of the interface transition zone between cement paste matrix and aggregate,and refine the capillary pore structure,leading to the higher resistance to chloride penetration and reinforcement corrosion.