# Performance Evaluation of Steel Slag Asphal Mixtures for Sustainable Road Placement Rehabilitation
## 2 Materials and Methods
### Test Methods  
An experimental program was developed to evaluate the effects of the incorporation of SSA in the performance of the asphalt mixtures. Firstly, the bonding between the binder (bitumen) and aggregate was evaluated through the affinity test, and following, the asphalt mixtures were tested to characterize the Marshall properties, fatigue resistance, permanent deformation, and water sensitivity. The test methods were selected according to European and Portuguese specifications [32]. The affinity between binder and aggregate was assessed through the rolling bottle method as described by EN 12697-11 [35]. The test consists of a visual evaluation of the degree of binder coverage on loose (uncompacted) binder-coated aggregates after a determined period of mechanical stirring in the presence of water. According to the test specification, the samples of aggregates were previously sieved, and only the fraction from 8 to 11.2 mm was used for the test. Bitumen was added to the aggregate and mixed until all surface of the aggregate particles were totally covered by bitumen. The amount of bitumen added was calculated, and corrected according to the respective aggregate density, to be 3.0% (by mass of mixture). After preparation and a resting period of 24 h, 150 g of the bitumen coated aggregates were transferred to the glass bottle previously filled with distilled water at 5 \({}^{\circ}\)C, a standardized glass rod was introduced in the bottle and the test was initiated. The affinity tests were conducted at a constant ambient temperature, 25 \({}^{\circ}\)C, and a fixed bottle rotation speed of 60 rpm. The degree of binder coverage of the aggregate particles was evaluated after 6 and 24 h of rotation. For each mixture, three tests (i.e., three individual bottles) were conducted. The Marshall test, described in EN12697-34 [36], comprises the determination of stability, flow, and Marshall quotient (MQ). In this test, cylindrical specimens (100 mm diameter and 63.5 mm height) conditioned at 60 \({}^{\circ}\)C were placed in the Marshall test head and then loaded at a constant deformation rate of 50 mm/min until rupture. Prior to the Marshall test, the bulk density of each compacted specimen was determined according to EN12697-6 [37]. After the Marshall test, the specimens were disaggregated, and maximum density was determined according to EN12697-5 [38]. With these results other volumetric properties, namely voids content and voids in the mineral aggregate (VMA) were calculated as indicated in EN12697-8 [39]. Stiffness and fatigue resistance were evaluated by the four-point bending beam method as indicated by EN 12697-26--Annex B [40] and EN12697-24--Annex D [41], respectively. In these tests, the outer clamps of the equipment fix the prismatic specimen (400 mm \(\times\) 50 mm \(\times\) 50 mm) to the frame, allowing free rotation and horizontal translation, while the inner clamps apply a cyclic vertical load that induces a bending strain. All tests were carried out under strain-controlled conditions. The loading was applied in a sinusoidal configuration where load amplitude (bending strain), frequency, and tempera  
Figure 3: Prismatic specimens: (**a**) general view; (**b**) detail of the cutting face. ture were kept constant during the test. In the case of fatigue tests, three strain levels were used. The selected strain levels were 150, 250, and 400 \(\upmu\)m/m. Within each mixture, for each strain level, three specimens were tested. The loading frequency was 10 Hz and the test temperature was 20 \({}^{\circ}\)C. The criterion to terminate the test was a 50% reduction of the initial stiffness modulus. Before the fatigue tests, the stiffness tests were conducted under low strain, 50 \(\upmu\)m/m, to avoid premature fatigue damage to the specimens. The stiffness was evaluated at 20 \({}^{\circ}\)C and for the loading frequencies of 1, 3, 5, 10, 20, and 30 Hz. A total of nine specimens per mixture were tested. Permanent deformation was assessed through the wheel-tracking test.