Preparation And Mechanical Properties Of Cobalt Slag And Steel Slag Cementitious Materials

The reuse of solid waste has received more and more attention.It is very important for environmental protection and efficient utilization of resources by using solid waste with pozzolanic reactivity as raw materials for the preparation of cementitious materials.On the one hand,it can reduce the environmental problems caused by the accumulation of solid waste.On the other hand,the cementitious materials can be applied to the building materials and thereby reduce the consumption of cement and the emission of CO₂.In this paper,modified slag powder,cobalt slag and steel slag were used as main raw materials to prepare cementitious materials.The mechanical properties,microstructure and hydration reaction process of modified slag cobalt slag composite cementitious materials?short for containing cobalt slag cementitious materials?and modified slag steel slag composite cementitious materials?short for containing steel slag cementitious materials?were studied by universal testing machine,X-ray fluorescence?XRF?,scanning electron microscope?SEM?and energy dispersive spectroscopy?EDS?.In the preparation of cementitious materials,the mechanical properties of cementitious materials were studied by changing the amount of cobalt slag?steel slag?,the water cement ratio and the cement sand ratio of the materials.By adding cement and increasing the specific surface area of cobalt slag and steel slag,the effect of specific surface area of raw materials on the mechanical properties of modified slag cobalt slag cement composite cementitious materials?short for containing cobalt slag cement cementitious materials?and modified slag steel slag cement composite cementitious materials?short for containing steel slag cement cementitious materials?ware studied.The finds in the preparation and characterization of containing cobalt slag cementitious materials listed as follows:1)When the cement sand ratio and the water cement ratio were 1:1.5 and 0.5 respectively,the 3 d compressive and bending strength of cobalt slag cementitious materials decreased firstly,then increased and decreased finally with the increase of the amount of cobalt slag.The optimized 3 d compressive and bending strength of 23.0 MPa and 5.5 MPa were obtained when the amount of cobalt slag was 30%.However,the 28 d compressive strength and bending strength decreased with the increase of the amount of cobalt slag.2)With the increase of water cement ratio,the 3 d and 28 d compressive and bending strength gradually reduced when the content of cobalt slag and the cement sand ratio of were set as 30%and 1:1.5.The cementitious materials exhibited the optimized mechanical properties as the water cement ratio was 0.45.3)When the amount of cobalt slag was 30%and the water cement ratio was 0.45,the compressive and bending strengths at the 3 d and 28 d ages gradually decreased as the ratio of the grit increased,but the reduction degree was different.4)The SEM photographs of containing cobalt slag cementitious materials samples at different ages?3 d,7 d,28 d?showed that the generated AFt was small at the 3 d stage.With the increasing age,the amount of AFt increased and the size of AFt also increased.The finds in the preparation and characterization of containing steel slag cementitious materials listed as follows:1)When the cement sand ratio and the water cement ratio was fixed 1:1.5 and 0.5,the best mechanical properties of the samples were obtained when the amount of steel slag was 35%.The compressive and bending strength of containing steel slag cementitious materials increased firstly and decreased with the increase of steel slag content at the age 3 d and 28 d.2)With the amount of steel slag added increase,the water absorption was decreased gradually.When the steel slag addition amount was less than30%,the water absorption ratio of the sample decreased rapidly.When the steel slag addition amount was more than 30%,the water absorption rate of the sample decreased slowly.3)When the amount of steel slag was 40%and the cement sand ratio was 1:1.5,with the increase of water cement ratio,the compressive and bending strengths of containing steel slag cementing material increased firstly and then decreased.The sample exhibited the optimized mechanical properties as the water cement ratio was 0.55.4)C-S-H gel was formed by Si?OH?₄ and Ca²⁺when the vitreous body was dissociated due to the mutual excitation between steel slag and modified blast furnace slag.Subsequently,the generated AFt was enwrapped by Ca?OH?₂ and CaSO₄×2H₂O.Finally,the amount of AFt increased and the size of AFt enlarged gradually with the prolonging of hydration time.The finds in the preparation and characterization of containing cobalt slag cement and containing steel slag cement cementitious materials listed as follows:1)As the specific surface area of cobalt slag increased,the compressive and bending strength of the sample increased gradually.When the specific surface area of cobalt slag was 638 m²/kg,the compressive and bending strength of the sample reached the maximum.The 3 d compressive and bending strength were 29.2 MPa and 5.2 MPa,respectively.The 28 d compressive and bending strength were 39.1 MPa and 8.7 MPa,respectively.2)The compressive and bending strength of the sample increased with the increase of the specific surface area of the steel slag at 3 d and 28 d,but the increased degree was different.When the specific surface area was 544 m²/kg,the sample had the best mechanical properties.3)With the respectively increase of the specific surface area of cobalt slag and steel slag,the water consumption of the standard consistency of the sample increased gradually and the setting time decreased accordingly.