Post-Cyclic Monotonic Behavior of Steel Slags Materials Modified By Geogrid and Tire Chips As Railway Ballast and Sub Ballast

This paper presents post-cyclic-monotonic behavior of BOF and EAF steel slags as ballast and subballast layers with and without geogrid or tire chips, and comparing their behavior with limestone material. Tests were carried out by the large scale triaxial equipment. The confining pressures are chosen with respect to the stress levels in typical rail road track. The tested specimens were prepared by maximum dry density. The used square shape geogrid has aperture sizes of 25*30.5 mm and the depth of placement about 5cm above and middle of subballast. Size of tire chips was 12.7-25 mm and mixed 7% by weight, only in ballast layer. Maximum deviatoric stress, secant modulus, unloading-reloading modulus, friction angle and particle breakage are investigated. Results indicated that performing cyclic loading on ballast layer before the post cyclic-monotonic tests decreases the axial strain corresponding to maximum deviatoric stress. Post-cyclic-monotonic friction angle of ballast and subballast with and without geogrid ranges from 57-65°. The friction angles of the steel slag of ballast, subballast and ballast/subballast specimens are similar to traditional ballast materials. The values of and decrease as moisture of specimen increases. Average poison ratio for mention layers is about 0.3. Marsal breakage index (Bg) of the single layered steel slag ballast is almost two times of the limestone ballast. Presence of steel slag subballast increases Bg of the steel slag ballast to about 2 times. According to fouling and breakage indexes of steel slag ballast under post cyclic-monotonic loading is relative clean. Saturation of ballast specimen causes increase of particle breakage, therefore the drainage of ballast materials is necessary. Usage of tire chips is not recommended in ballast due to high rate of decreasing of modulus and friction angle. Results indicated that the steel slag particle may be used as natural aggregate in ballast and subballast layers.