Study On The Performance Of Solid Waste Steel Slag For Cement Stabilized Gravel Base

Steel slag is one of the largest piles of solid waste in China,and about 70 million tons of steel slag are piled up and discarded every year,so how to improve the resource utilization of steel slag has become a key research direction for solid waste disposal.In this thesis,steel slag,slag and desulfurization gypsum are used as raw materials to prepare steel slag-based cementitious materials in order to replace part of the cement in semi-rigid subgrade;at the same time,steel slag is considered as aggregate to replace part of the gravel to improve the resource utilization rate of steel slag and reduce the environmental problems caused by stone mining.The main findings of this thesis are as follows:(1)The physical properties of Tangshan Zunhua steel slag,which was used as an aggregate,are superior to those of crushed limestone,with a free calcium oxide content of 1.01%.Moreover,the soaking water swelling rate of the steel slag meets the required standard of ≤2%.Additionally,the alkalinity coefficient of the used steel slag is 3.12,indicating a high alkalinity slag with remarkable activity.The activity indices at 7d and28 d are 64.03% and 83.57%,respectively.(2)The utilization of steel slag,slag,and desulfurization gypsum in the preparation of steel slag-based cementitious materials can effectively achieve a synergistic hydration effect among the components.However,it should be noted that an increase in the dosing of steel slag may adversely affect the strength development of the cementitious system.Desulfurization gypsum,on the other hand,has a more prominent effect on the early strength of the stimulated steel slag-based cementitious materials.Notably,the mechanical strength of the cementitious sand specimens reached a peak at16% of desulfurization gypsum dosing.The 3d,7d,and 28 d compressive strengths of the mastic sand specimens prepared with steel slag: slag: desulfurization gypsum of30:54:16 were 12.17 MPa,28.87 MPa,and 48.31 MPa,respectively,with their late strengths being superior to those of conventional cement.(3)The addition of steel slag-based cementitious materials to the cement-stabilized gravel mix results in a reduction in unconfined compressive strength,indirect tensile strength,and compressive rebound modulus to varying degrees.Under 50% dosing,the performance of the mix with steel slag-based cementitious materials is comparable to that of the cement control group.The 7-day unconfined compressive strength and road performance of the cement-stabilized gravel mix with varying dosages of steel slag-based cementitious materials can meet the requirements of different road grade pavement subgrades.(4)In the semi-rigid subgrade material,the replacement of crushed stone with steel slag within a reasonable range has a positive effect on the strength improvement of the mixture.As the steel slag dosage increases,the unconfined compressive strength,indirect tensile strength,and compressive rebound modulus of the mixture increase accordingly.(5)The use of steel slag,either as a component of cementitious materials or as aggregate in semi-rigid subgrades,has been shown to have a significant inhibitory effect on the drying shrinkage deformation of the mixture.Increasing the amount of steel slag-based cementitious materials and the replacement rate of steel slag in the mixture can effectively reduce shrinkage deformation and improve the crack resistance of semi-rigid subgrade materials.