Study On The Performance Of Granular Blast Furnace Nickel Slag Powder As Concrete Admixture

Granulated blast furnace nickel-iron slag is an industrial solid waste discharged during the pyrometallurgical nickel smelting process.It has been accumulated in large quantities in Luoyuan Bay and other places in Fujian Province,causing land occupation and environmental pressure.In view of the current situation of shortage of concrete mineral admixtures in Fujian Province,nickel slag is used as an admixture in concrete to promote environmental protection and benefit the green and healthy development of the concrete industry.This paper mainly studies the effect of partial replacement of cement with nickel slag on the hydration characteristics and pore structure of composite cementitious materials,and the influence of nickel slag on the mechanical properties,durability and volume stability of concrete.The main work is as follows:1.Study on the effect of nickel slag on the hydration process of the paste.Using a microcalorimeter to measure the hydration heat release curve of the paste for 168 h.in order to study the effect of nickel slag on the laws of hydration heat release of the composite cementitious material at different substitution rates*And the effect of nickel slag on the overall hydration process of the cementitious material system was studied by measuring the chemically bound water content of the paste.It was found that the replacement of cement with nickel slag lowers the degree of hydration in early age of the cementitious material system,but its contribution to later hydration can not be ignored,and the results of the test are analyzed.2.Study on the effect of nickel slag on the hydration product and mesostructure of the paste.X-ray diffractometer was used to measure the type of hydration product in the paste powder samples.The Ca(OH)2 content of the hardened paste was measured by a simultaneous thermal analyzer,and the pore structure of the hardened paste at different ages was measured by a mercury porosimeter.It was found that the replacement of cement with nickel slag does not change the type of hydration product of cementitious material.The increase of Ca(OH)2 content of hardened paste is almost stagnant when the substitution rate of nickel slag is 15%after 7 d,and the substitution rate continues to increase,which causes the Ca(OH)2 content to decrease significantly after 28 d.Nickel slag has an adverse effect on the pore structure of hardened paste before 7 days,but it has a good effect on the pore structure of hardened paste in the long age.Through the comprehensive analysis of different test results,the effect of nickel slag on the composite cementitious material system and its action mechanism were discussed.3.Study on the effect of single-doping nickel slag at different water binder ratio and the composite powder mixed nickel slag with silica fume or slag on the mortar strength.The application about using nickel slag as concrete admixture under lower water binder ratio(0.35)and higher water binder ratio(0.5)without affecting the strength was proposed.Under the low water binder ratio,cement can be partiaclly replaced by nickel slag,and the substitution rate should be controlled within 25%;under high water binder ratio,only mixing nickel slag with silica fume or slag can maintain the strength of the mortar,and reasonable mix alternatives and the optimal ratio of compounding were given.4.Study on the effect of nickel slag on the shrinkage and chloride ion permeability of concrete at lower water binder ratio(0.35)and higher water binder ratio(0.5),and the application of nickel slag as concrete admixture in engineering is promoted by the evidence provided.It was found that the autogenous shrinkage of concrete at all ages has the tendency of increasing by partially replacing cement with nickel slag,but nickel slag has little effect on the total shrinkage of the concrete;both single doped nickel slag and blended composite powder can effectively lower the electric flux of the concrete,and the longer the age,the better the effect.Theoretical and practical basis for the application of nickel slag as a concrete admixture in engineering is provided through these research,and feasible suggestions that the application of nickel slag as concrete admixture under lower water binder ratio and higher water binder ratio are proposed.