Microwave healing properties and moisture sensitivity of asphalt mixture containing iron powder filler

Abstract

Through experimental tests, this paper investigated the effectiveness of microwave healing on asphalt mixtures containing iron powder (IP) filler to improve durability and enhance mechanical properties. The moisture sensitivity of the asphalt mixes with varying iron powder filler contents was measured using the modified Lottman test. For evaluating the asphalt mixture healing ability, two complementary methods were used: the fatigue-based method, derived from the ability of microwave healing of asphalt mixture samples damaged up to 50% level of indirect tensile fatigue (ITF), and the fracture-based method, obtained from the strength recovery rate of broken semi-circular samples by applying consecutive breaking-healing cycles. The results showed that the greater the quantity of iron powder filler in the asphalt sample, the greater the sample's indirect tensile strength and TSR ratio, indicating that IP had a positive effect on moisture sensitivity. The findings also indicated that utilizing iron powder as a filler positively strengthens the fatigue life, increases the toughness, and increases the microwave healing indices (both fatigue and failure approaches). Finally, according to the study results, substituting 70% iron powder as the filler is the most suitable option for improving the mechanical and self-healing characteristics of asphalt mixes.

Keywords: Asphalt mixture; Iron powder filler; Microwave healing; Moisture susceptibility.

Fig. 1

The gradation of selected aggregates.

Fig. 2

Hydrophobic surface (left), hydrophilic surface (right), θ: contact angle.

Fig. 3

Scheme of healing assessment using ITFT.

Fig. 4

The procedures for recovering the strength of the semi-circular samples: (a) a sample of asphalt cut in a semicircular shape, (b) the fractured asphalt sample after testing, (c) the microwave heat treatment and healing of the cracked specimen, and (d) the healed sample before beginning a new cycle.

Fig. 5

SEM images of (a) limestone filler at 1000× magnification, (b) iron powder filler at 1000× magnification, and (c) iron powder filler at 5000× magnification.

Fig. 6

(a) A water droplet on the mineral mastic surface, (b) a water droplet on the iron powder mastic surface, (c) Contact angle results and work of adhesion between liquid (water) and solid surfaces (asphalt mastics).

Fig. 7

Indirect tensile strength and the ratio of the tensile strength of the asphalt mixes.

Fig. 8

The fatigue lines of asphalt mixtures contain different iron powder fillers.

Fig. 9

Fatigue life extensions of the asphalt mixture with 70% IP + 30% LF filler (IR70) at a 180 kPa stress level.

Fig. 10

The healing performance of mixtures based on ITFTs.

Fig. 11

Comparing the fracture toughness of different asphalt mixtures.

Fig. 12

The healing process of SC samples: (a) Setup for the semi, (b) A fractured specimen under the SCB test, (c) Microwave heating, (d) Some healed samples are ready to begin a new breaking-healing cycle.

Fig. 13

Healing indices of the asphalt mixtures during cyclic breaking-healing using the SCB test at −20 °C for (a) CLs and (b) IR70s.

Fig. 14

Comparison of healing indices for asphalt mixtures using the SCB test.