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. 2023 May 13;16(10):3712.
doi: 10.3390/ma16103712.

The Effect of Microwave Radiation on the Self-Healing Performance of Asphalt Mixtures with Steel Slag Aggregates and Steel Fibers

Carlos D A Loureiro  1 , Hugo M R D Silva  1 , Joel R M Oliveira  1 , Nuno L S Costa  1 , Carlos A O Palha  2
Affiliations

The Effect of Microwave Radiation on the Self-Healing Performance of Asphalt Mixtures with Steel Slag Aggregates and Steel Fibers

Carlos D A Loureiro et al. Materials (Basel). .

Abstract

Self-healing in asphalt mixtures is a property that can be enhanced by external heating, which causes a thermal expansion that increases the flow of bitumen with reduced viscosity through the cracks. Therefore, this study aims to evaluate the effects of microwave heating on the self-healing performance of three asphalt mixtures: (1) conventional, (2) with steel wool fibers (SWF), and (3) with steel slag aggregates (SSA) and SWF. After evaluating the microwave heating capacity of the three asphalt mixtures with a thermographic camera, their self-healing performance was determined with fracture or fatigue tests and microwave heating recovery cycles. The results demonstrated that the mixtures with SSA and SWF promoted higher heating temperatures and presented the best self-healing capacity during the semicircular bending test and heating cycles, with significant strength recovery after a total fracture. In contrast, the mixtures without SSA presented inferior fracture results. Both the conventional mixture and that containing SSA and SWF presented high healing indexes after the four-point bending fatigue test and heating cycles, with a fatigue life recovery of around 150% after applying two healing cycles. Therefore, the conclusion is that SSA greatly influences the self-healing performance of asphalt mixtures after microwave radiation heating.

Keywords: asphalt mixtures; microwave radiation heating; self-healing; self-healing assessment; steel slag aggregates; steel wool fibers.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the study’s design; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Different materials used in this study: (a) steel slag aggregates, (b) natural granite aggregates, (c) limestone filler, and (d) steel wool fibers.
Figure 2
Figure 2
Procedure for determining the surface temperature of specimens: (a) thermographic camera, (b) asphalt specimen in the microwave oven, and (c) thermal image of the specimen.
Figure 3
Figure 3
Cyclic setup of semicircular tests and microwave heating processes applied to assess the healing ratio.
Figure 4
Figure 4
Procedure for determining the surface temperature of specimens: (a) asphalt beam inside a wooden mold in the microwave oven and (b) thermal image of the beam.
Figure 5
Figure 5
Cyclic setup of fatigue tests and microwave heating applied to assess the healing index.
Figure 6
Figure 6
Evolution of surface temperature of the different asphalt mixtures with the heating time for three microwave power levels.
Figure 7
Figure 7
Thermal images of the different asphalt mixtures for the same radiation conditions (160 s and 900 W) in the microwave: (a) mixture A, (b) mixture B, and (c) mixture C.
Figure 8
Figure 8
Asphalt mixture specimen: (a) before the SCB test; (b) damaged after the fracture test; (c) after microwave healing.
Figure 9
Figure 9
Examples of load vs. displacement evolution of the different asphalt mixtures during the four fracture test repetitions: (a) 1st and 2nd SCB tests; (b) 3rd and 4th SCB tests.
Figure 10
Figure 10
Healing ratio values of the semicircular test specimens after the three healing cycles.
Figure 11
Figure 11
Mean temperatures of the mixtures induced by microwave heating in each healing cycle.
Figure 12
Figure 12
Evolution of the stiffness modulus (SM) and phase angle (PA) of the studied mixtures before healing (test 1) and after one (test 2) and two (test 3) healing cycles: (a) mixture A; (b) mixture B; (c) mixture C.
Figure 13
Figure 13
Stiffness modulus of the mixtures obtained in the test conditions mentioned in the standard (frequency of 8 Hz and temperature of 20 °C).
Figure 14
Figure 14
Evolution of the stiffness modulus during three fatigue tests performed before (intact beam) and after two healing cycles in the microwave: (a) mixture A; (b) mixture B; (c) mixture C; (d) comparison of all mixtures.
Figure 15
Figure 15
Healing index (HI) of each asphalt mixture in the fatigue test after two healing cycles.
Figure 16
Figure 16
Sporadic degradation of beams after some cycles of fatigue tests and microwave heating. (a) Mixture A, (b) Mixture B, (c) Mixture B, (d) Mixture C.
See this image and copyright information in PMC

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