Study On Supplementary Cementitious Material System Based On Manganese Slag

Manganese slag,a kind of granulated smelting slag formed by water quenching,can also be called Si Mn slag,which rapid cooling of molten slag emitted from electric furnace smelting Si Mn alloy.In this paper,firstly,the hydration characteristics and heavy metal ion leaching behavior of manganese slag-based supplementary cementitious materials were studied.Based on the problems of slow early hydration rate and low activity of manganese slag,circulating fluidized bed combustion ash and carbide slag were used as activators with their high sulfur and high calcium.Manganese slag-circulating fluidized bed combustion ash and manganese slag-carbide slag composite supplementary cementitious materials were prepared.Finally,C30 grade concrete was prepared by using manganese slag-based supplementary cementitious materials and composite supplementary cementitious materials.The main results are as follows:（1）Manganese slag has good activity and water-reducing effect.the addition of manganese slag powder can improve the fluidity of cement mortar;the 28d compressive strength of cement mortar mixed containing 30%and 40%manganese slag powder exceeds the reference group,and its activity index reaches 119.0%and 111.0%,respectively.The addition of manganese slag will accelerate the early hydration of C₃S in cement clinker,but at the same time reduce the accumulated hydration heat of cementitious material system.The leaching concentration of heavy metal ions of manganese slag in acid-base environment is low.In spite of this,the cement mortar mixed with manganese slag has a high risk of manganese ion leaching in a strong acidic environment.（2）Manganese slag-circulating fluidized bed combustion ash composite supplementary cementitious material was prepared,and the addition of circulating fluidized bed combustion ash will lead to the decrease of mortar fluidity.Compared with manganese slag powder,the activity index of manganese slag-circulating fluidized bed combustion ash composite supplementary cementitious material increased,and the activity index of 3 d and 7 d increased by 12.8%and 4.4%,respectively.With the addition of circulating fluidized bed combustion ash,the reaction start time of the secondary hydration of C₃A and pozzolanic reaction of manganese slag in the composite supplementary cementitious materials was delayed,and the hydration rate decreased in the later stage.The sulfate in circulating fluidized bed combustion ash can promote the formation of early ettringite and other hydration products.Under the excitation of circulating fluidized bed combustion ash,the activity of supplementary cementitious materials is improved,the pore structure is refined,the hardened paste is denser,and the proportion of harmless pores（<20nm）increases;when the amount of circulating fluidized bed combustion ash is too much,it will have a bad effect on the pore structure of the paste.（3）Manganese slag-carbide slag composite supplementary cementitious material was prepared,the addition of carbide slag leads to the decrease of mortar fluidity,and when the content of carbide slag is more than 25%,the mortar fluidity ratio is less than 95%.Carbide slag can stimulate the hydration of composite supplementary cementitious materials,and the activity index of manganese slag-carbide slag composite supplementary cementitious materials for 3 days and 7 days is 15.2%and 11.7%higher than that of manganese slag powder,respectively.The secondary hydration reaction of manganese slag in manganese slag-carbide slag composite cementitious material is ahead of schedule.Ca（OH）₂and carbonate in carbide slag can promote the formation of aluminate hydration products.Under the excitation of carbide slag,the hydration products of the gel increased,the compactness of the hardened paste increased,the pore structure refined and the proportion of harmless pores（<20nm）increased.（4）Compared with the C30 concrete prepared by adding 30%fly ash instead of cement.Although the 3 d and 7 d compressive strength of the concrete prepared with 30%manganese slag powder instead of cement decreased,the compressive strength at 28 d and90 d age increased.The compressive strength of the concrete prepared with manganese slag-based supplementary cementitious materials at the age of 7 d,28 d and 90 d is the same as or higher than that of the control group.The addition of manganese slag will decrease the frost resistance of concrete specimens,and the concrete will be destroyed after 150 freeze-thaw cycles;after manganese slag composite circulating fluidized bed combustion ash and carbide slag,the frost resistance index of concrete can meet the requirements of D200.The addition of manganese slag-based supplementary cementitious material deepens the carbonation depth of concrete in 3 days,but slows down the carbonization depth in 7～28 days.The shrinkage of concrete specimens with single manganese slag increases,and the shrinkage of concrete specimens can be effectively improved by composite circulating fluidized bed combustion ash and carbide slag.