Properties of Concrete Reinforced with a Basalt Fiber Microwave-Absorbing Shielding Layer

Abstract

The purpose of this study was to propose a highly efficient, durable, and environmentally friendly method for the rapid removal of ice and snow. A microwave-absorbing functionality layer was placed between a conductive metal mesh and magnetite sand shielding layer, and ordinary cement concrete (OC). Microwave heating, mechanical strength determination, and indoor and outdoor de-icing tests were performed on the cement concrete specimens with the shielding layer. Basalt fibers were added to the absorbing functionality layer, and the formed specimens were tested for strength and durability. The microstructure was observed using SEM experiments. The results show that the temperature rise of microwave-absorbing cement concrete with a magnetite sand shielding layer (MCMS) and microwave-absorbing cement concrete with a conductive metal mesh shielding layer (MCMM) increased by approximately 17.2% and 27.1%, respectively, compared to that of microwave-absorbing concrete (MAC). After freeze–thaw cycles, the compressive strength and flexural strength of microwave-absorbing concrete with basalt fiber (MAB) increased by 4.35% and 7.90% compared to those of MAC, respectively. The compressive strength and flexural strength of microwave-absorbing concrete with a magnetite sand shielding layer and basalt fiber (MAMB) increased by 8.07% and 6.57%, respectively, compared to those of MCMS. Compared to specimens without basalt fiber, the wear rate per unit area of MAMB decreased by 8.8%, and the wear rate of MAB decreased by 9.4%. The water absorption rate of MAMB specimens decreased by 13.1% and 12.0% under the conditions of 20 and 40 microwave freeze–thaw cycles, respectively, compared to that of MCMS. The water absorption rate of MAB specimens decreased by 9.9% and 8.3% under the conditions of 20 and 40 microwave freeze–thaw cycles, respectively, compared to that of MAC. SEM analysis showed that the addition of basalt fibers improved the compactness and stability of the cement concrete structure as a whole. This study provides valuable references for the promotion and application of microwave de-icing technology.

1. Introduction

The formation of ice on roads threatens the safety of people, increasing the likelihood of vehicular accidents and having a detrimental effect upon society. Therefore, measures should be taken to remove ice and snow from road surfaces [1,2,3] to avoid traffic delays and economic losses [4,5]. Traditional de-icing methods primarily involve mechanical and chemical approaches to remove accumulated snow. However, in severe conditions, mechanical de-icing may not be feasible. These methods not only have low efficiency but can also cause chemical corrosion, thereby reducing the durability of the pavement [6]. Therefore, there is an urgent need for efficient and environmentally friendly methods to quickly remove ice and snow from road surfaces. Microwave heating, as an environmentally friendly snow melting and de-icing technology, has been applied in snow melting and de-icing [7]. Moreover, microwave technology has the unique advantage of selectively heating the road surface by penetrating the ice layer [8], offering broad prospects for rapid ice and snow removal on roads.

Micheli et al. [9,10] (2014, 2017) found that carbon nanotubes played a role in improving the electromagnetic properties of concrete, as they can shield electromagnetic waves. Wang et al. [11,12] discovered that magnetite improved the temperature increase performance of mortar materials under microwave irradiation. Liu et al. [13] used recycled cathode ray tube funnel glass as a substitute material for magnetite sand in radiation-shielding concrete. Concrete with fine aggregate replacement rates of 20–40% exhibited good performance. Guo et al. [14] designed a microwave-absorbing layer with a certain thickness of magnetite added to ordinary asphalt mixtures. The results showed that reducing the thickness of the absorbing layer did not lead to a loss in the surface temperature efficiency of the specimens. Gallego et al. [15] found that steel fibers could be used as absorbing materials to prepare absorbing asphalt concrete. After adding 10 mm long steel fibers with a mass fraction of 0.2% to asphalt concrete, the temperature reached 140 °C after 2 min of microwave heating. Lu et al. [16] incorporated carbon fiber materials into cement concrete to alter its electromagnetic characteristics. The research findings indicated that the thermal efficiency of microwave heating increased initially and then decreased with an increase in the carbon fiber content. Considering the de-icing effect and road performance of concrete, the optimal content of carbon fiber was determined to be 1‰. However, due to uneven concrete mixing, the uneven distribution of fibers in concrete significantly affected the temperature uniformity of the absorbing concrete. Liu et al. [17] investigated the effects of various factors, such as different materials and external conditions, on the efficiency of microwave de-icing. They found that the efficiency of microwave de-icing can be significantly improved by using a power of 7000 watts, a magnetic content of 60% by volume for the distributed microwave-absorbing surface, a shielding layer on the bottom surface, and wet conditions. Wang et al. [18,19] completely replaced limestone with magnetite. The results showed a significant improvement in the mechanical strength, dielectric loss, magnetic loss, and temperature increase performance of concrete. Magnetite exhibits excellent microwave-absorbing properties and has been widely applied in many studies on microwave de-icing. Zhao et al. [20] designed nucleus–shell structural microwave-enhanced aggregate (NSSA) consisting of an external microwave-absorbing and heat-collecting structure layer (ESL) to enhance the microwave absorption capacity of asphalt mixtures and improve the utilization rate of microwave energy. They also found that the NSSA architecture has better electromagnetic field distribution characteristics. Chung et al. [21] found that the shielding efficiency of transparent electromagnetic interference shielding films increased with a decrease in the aperture size and an increase in the height of the metal mesh electrode. Li et al. [22] found that a basalt fiber content of 1.5% in cement yielded good performance and improved durability. Wang et al. [23] studied the effects of three powders (Fe₃O₄, SiC, and graphite) on the efficiency of microwave heating and frost resistance. They found that all three powders can improve the efficiency of microwave heating, and SiC can improve the frost resistance of cement concrete. Fu et al. [24] explored an electromagnetic multifunctional asphalt pavement that can be heated for self-healing and snow melting through energy conversion.

Overall, research on microwave de-icing primarily focuses on improving the microwave absorption efficiency of road surfaces through the addition of coatings, selection of microwave-absorbing materials, and design of mix proportions. The goal is to effectively remove ice and snow from road surfaces. Additionally, studies on basalt fibers mainly concentrate on the dosage, fiber length, and distribution characteristics of the fibers. Research on the enhancement of strength and durability in microwave-absorbing cement concrete with basalt fibers is limited. In addition, research on improving microwave de-icing efficiency by modifying the road structure is scarce. Moreover, microwave-absorbing road surfaces undergo multiple cycles of freezing and melting in practical applications, which may result in inadequate strength and durability. Therefore, the aim of this study was to enhance microwave de-icing efficiency by introducing a microwave shielding layer beneath the microwave-absorbing functionality layer and investigating the reinforcement effect of basalt fibers on the mechanical strength and durability of concrete specimens.

Different materials were selected in order to prepare MAC specimens with microwave shielding layers. The de-icing performance of different structures was evaluated through temperature rise performance, mechanical properties, and indoor and outdoor de-icing tests. The addition of basalt fibers to the cement concrete specimens was also investigated, and tests were conducted to evaluate mechanical strength and durability. SEM analysis was employed to study the microstructure at the interface between basalt fibers and cement paste. This study provides references for the design of MAC road structures, improvement of microwave de-icing efficiency, and enhancement of structural durability. Furthermore, it promotes the application and popularization of microwave de-icing technology in road engineering.

2. Materials and Methods

2.1. Materials

2.1.1. Ordinary Materials

Silicate cement P.C.32.5 from Huaxia Cement Co., Ltd. (Huangshi, China) was used, and its performance indicators can be found in

Table 1. Properties of cement.

Model	Density (g/cm3)	Specific Surface Area (m2/kg)	Setting Time (min)		Compressive Strength (MPa)		Flexural Strength (MPa)
			Initial Setting	Final Setting	3 d	28 d	3 d	28 d
P.C.32.5	3.15	359	128	279	12.4	37.9	3.1	6.8

. A naphthalene-based water reducer was employed as the admixture, while limestone was used as the coarse aggregate, with performance indicators listed in

Table 2. Properties of limestone.

Apparent Density (g/cm3)	Crushing Value	Needle Flake Content (%)	Water Absorption (%)	Mud Content (%)	Firmness (%)
2.64	17	6	1.0	0.8	6

. The basalt fiber utilized in this study was provided by Shanghai Chenqi Chemical Technology Co., Ltd. (Shanghai, China). The basic properties of magnetite are presented in

Table 3. Properties of magnetite.

Apparent Density (g/cm3)	Bulk Content (%)	Mud Content (%)	Iron Content (%)	Mohs Hardness
3.78	2.77	0.2	65~85	6

, and the basic properties of basalt fiber can be found in

Table 4. Properties of basalt fiber.

Length (mm)	Single Fiber Diameter (μm)	Density (g/cm3)	Tolerance to Maximum Temperature (°C)	Elastic Modulus (G Pa)	Tensile Strength (MPa)
12	14	2.73	625	95~105.4	3250~3800

. Fine sand has an apparent density of 2603 kg/m³ and belongs to Zone II. All materials used in the study met the technical requirements specified in JTG D40—2011 [25].

2.1.2. Shielding Layer Material

In this study, a galvanized iron wire mesh with a diameter of 0.1 cm was chosen as the conductive metal grid for microwave shielding. The mesh was formed into a grid with a side length of 1 cm. The second type of electromagnetic wave shielding layer consisted of cement concrete prepared by combining hematite and magnetite sand. An optimal thickness of 5 cm is recommended for the shielding concrete layer. Magnetite sand was obtained by crushing and grinding magnetite ore and the properties of hematite ore can be found in

Table 5. Properties of hematite ore.

Needle Flake Particle Content (%)	Crushing Value Index	Alkali Activity (%)
2	19.5	0.06

.

2.2. Specimen Preparation

2.2.1. OC and MAC Specimens

According to the mix proportions (

Table 6. Material consumption per m³ of concrete.

Specimen Types	Cement (kg)	Water (kg)	Sand (kg)	Coarse Aggregate (kg)				Magnetite (16–19 mm) (kg)	Water-Reducing Agent (kg)
				4.75–9.5 (mm)	9.5–16.0 (mm)	16.0–19.0 (mm)	19.0–26.5 (mm)
OC	375	3.75	739	255	255	370	277	—	3.75
MAC	375	3.75	739	255	255	—	277	530	3.75

), standard compressive specimens with dimensions of 15 cm × 15 cm × 15 cm and standard flexural specimens with dimensions of 10 cm × 10 cm × 40 cm were prepared. The specimen preparation, curing, and testing followed the guidelines specified in JTG 3420–2020 [26].

First, well-mixed ordinary cement concrete was placed in a standard mold and compacted via vibration until a 5 cm thickness was achieved. Then, the MAC mixture was prepared according to the specified proportions and placed in the standard mold on top of the previously compacted layer. The mixture was compacted again via vibration to ensure density and prepare the MAC specimens.

2.2.2. Cement Specimens with a Shielding Layer

MCMM specimens: Firstly, well-mixed ordinary cement concrete material was placed in a mold and compacted via vibration to achieve density. Then, a 3 cm thickness was reserved for the microwave absorption functional layer. The preparation of the test specimens is shown in Figure 1a,b. A galvanized iron wire mesh was placed in the mold, followed by pouring and compacting the microwave-absorbing functionality layer containing magnetite material.

MCMS specimens: Firstly, cement concrete material with a magnetite sand shielding layer (Material consumption per m³ showed in

Table 7. Material consumption per m³ of magnetite sand.

Cement (kg)	Sand (kg)	Coarse Aggregate (kg)			Hematite (kg)		Magnetite Sand (kg)	Water Reducing Agent (kg)
		4.75–9.5 (mm)	9.5–16 (mm)	19–26.5 (mm)	9.5–16 (mm)	16–19 (mm)
375	622	255	182	197	141	715	644	3.75

) was prepared according to the specified mix proportions. It was then poured into the mold and compacted by vibration, reserving a 3 cm thickness. Subsequently, the microwave-absorbing functionality layer containing magnetite material was poured into the mold and compacted.

The preparation process for the flexural test standard specimens was the same as described above. After the preparation of the compressive strength test specimens and flexural strength test specimens, they were placed in a curing box for curing.

2.2.3. Specimen Preparation with Basalt Fibers

When preparing cement specimens containing basalt fibers, the basalt fibers were added to the microwave-absorbing functionality layer at a volume dosage of 0.2% and mixed. The remaining steps were the same as described above.

2.2.4. Ice Layer Preparation

Firstly, approximately 1.9 cm of water was poured into a rubber mold. The cured specimens were placed in the mold, and then the mold was securely placed in a freezer. After the cooling process was completed, the mold was removed, resulting in cement specimens with an ice layer (Ice preparation as shown in Figure 1d).

2.3. Methods

Based on the conventional microwave-absorbing road structure (Figure 2a), a microwave shielding layer was introduced between the absorbing layer and the road surface layer (Figure 2b) to enhance the utilization of microwaves. The research included tests on compressive strength and de-icing effectiveness. Basalt fiber (Figure 2c) was added to the absorbing layer to improve the compressive strength and durability of the road surface. Scanning electron microscopy experiments were conducted to analyze the microscopic mechanism.

2.3.1. Heating Effect

Each group of OC, MAC, MCMS, and MCMM specimens consisted of three parallel specimens. The experimental results were obtained by averaging the values. After the preparation of the standard specimens, they were heated in a microwave oven (Foshan, China) with a frequency of 2.45 GHz and a maximum power of 900 W. The dimensions of the microwave oven were 42 cm × 42 cm × 25 cm (length × width × height). During the heating process, temperature measurements were taken every minute using an infrared thermometer (FLUKE-62MAX model, Tuodapu, Dongguan, China). Three measurement points were selected on the surface of the cement specimens (Figure 3a) to calculate the average temperature and heating rate of the top surface of the specimens.

2.3.2. De-Icing Effect

For OC, MAC, MCMS, and MCMM pavement structures, standard specimens measuring 10 cm × 10 cm × 10 cm were prepared. A 2 cm thick ice layer was formed on the surface of each specimen. Each group consisted of three parallel specimens, and the experimental results were obtained by averaging the values. Subsequently, the specimens were placed on a support structure with a certain inclined angle (Figure 3c). The microwave oven door was closed, and the time required for the ice layer to detach from the surface of the specimen during microwave heating was recorded as the indicator for evaluating the microwave de-icing efficiency.

For outdoor de-icing experiments, OC, MAC, MCMS, and MCMM specimens were prepared, with each group consisting of three standard specimens. A 2 cm thick ice layer was formed on the surface of each specimen. A portable microwave vehicle was used for heating the standard specimens (Figure 3b), with the waveguide mouth positioned 2 cm away from the concrete specimen surface. The microwave vehicle was started, and the temperature changes of the specimens during the movement of the microwave vehicle were recorded using the SH-X multi-channel temperature recorder and temperature sensing wires. The heating rate of the concrete specimen surface was used as the indicator for evaluating the microwave de-icing efficiency of the pavement structure in outdoor de-icing experiments. The time required for the top surface of the specimen to reach 0 °C was recorded using temperature sensors.

2.3.3. Mechanical Properties

OC, MAC, MCMS, and MCMM specimens were prepared separately. Three parallel specimens were prepared for each group, and the experimental results were averaged. The experiments were conducted according to the current specifications for compressive strength testing methods.

Basalt fibers were added to the microwave-absorbing concrete specimens. For the OC, MAC, MCMS, MAB, and MAMB standard specimens for compressive strength and flexural strength (Figure 3d), three parallel specimens were prepared for each type, and the experimental results were averaged. The specimens underwent 50 cycles of freeze–thaw testing, and the strength variations before and after the freeze–thaw cycles were recorded for different structures. The experimental procedure followed the guidelines specified in JTG 3420-2020 [26], with a loading rate of 0.05 to 0.08 MPa/s for flexural strength testing.

2.3.4. Durability of Different Structures

In this study, a concrete abrasion testerYA-2000 (Tianjin Dongzheng Measurement and Control Technology Development Co., Ltd., Tianjing, China) was used. The specimens were prepared with dimensions of 15 cm × 15 cm × 15 cm. After curing under standard conditions for 28 days, the specimens were dried in an oven for 12 h until they reached a constant weight. Three parallel specimens were fabricated for each type, and the experimental results were averaged. Each structure was divided into two groups: one with 0.2% basalt fiber content and the other without basalt fibers (ordinary specimens). Three specimens were prepared for each group, and the results were averaged. After wiping off the surface dust from the specimens, they were placed on the turntable of the abrasion tester. The specimens were subjected to 30 rotations under a load of 200 N using a blade. The initial mass (m₁) was measured after wiping off the surface dust. Subsequently, the specimens were subjected to an additional 60 rotations under a load of 200 N, and the remaining mass (m₂) was measured after wiping off the surface dust. After completing the tests, the wear volume of each pavement structure specimen was calculated using Equation (1). The abrasion resistance of the specimens was characterized using the specific wear volume (Gc) per unit area.

$${\mathrm{G}}_{\mathrm{c}}=\frac{{\mathrm{m}}_1-{\mathrm{m}}_2}{\mathrm{A}}$$

(1)

In Equation (1), Gc represents the specific wear amount per unit area (kg/m²); m1 denotes the initial mass of the specimen (kg); m₂ refers to the mass of the specimen after wear (kg); and A represents the worn area of the specimen (m₂), where A = 0.0125 m² in this experiment.

The standard compressive strength specimens of different structures were placed in a freezer and frozen at a temperature of −20 °C. After 3 h, the specimens were removed from the freezer and heated in a microwave oven for 5 min. Then, the specimens were returned to the freezer for freezing. This cycle was repeated 40 times. Every 10 cycles, the water absorption rate of one specimen was tested and determined using Equation (2). Before measuring the water absorption rate of the specimens, they needed to be dried at 60 °C for 8 h and then at 80 °C for 8 h. The dried specimens were fully immersed in water, and the change in the water absorption rate over time was measured. The water absorption test was stopped after 6 h, and the specimens were air-dried at room temperature before continuing the cycle.

$$\mathsf{\alpha }=\frac{{\mathrm{m}}_{\mathrm{t}}-{\mathrm{m}}_0}{{\mathsf{\rho }}_{\mathrm{w}}{\mathrm{V}}_0}\times 100\%$$

(2)

In Equation (2), α represents the unit volume water absorption rate. The variables are defined as follows: m_t: the mass of the specimen after a certain immersion time, measured in grams (g); m₀: the mass of the specimen after drying, measured in grams (g); ${\rho }_w$: the density of water, measured in grams per cubic centimeter (g/cm³); V₀: the volume of the specimen before immersion, measured in cubic centimeters (cm³).

For this experiment, freeze–thaw cycle testing was conducted on the pavement specimens with and without fiber reinforcement using the rapid freezing method. The relative dynamic modulus of elasticity of the specimens was calculated every 25 cycles until reaching 200 cycles. Each group consisted of three specimens, and the average of the test results was taken.

2.3.5. SEM

A Zeiss GeminiSEM 360 scanning electron microscope (SEM, Carl Zeiss (Shanghai) Management Co., Ltd, Shanghai, China) was utilized. The coating materials used for the SEM sample preparation were gold (Au) and platinum (Pt). The acceleration voltage ranged from 0.02 kV to 30 kV, and the probe current ranged from 3 pA to 20 nA. MAB specimens were prepared, and after curing under standard conditions for 28 days, they were analyzed via SEM. The scanning electron microscope was used to study the cement paste and the fiber–cement paste interface transition zone.

3. Results and Discussion

3.1. Heating Effect

The experimental results, as shown in Figure 4a,b, demonstrate the microwave heating of the specimens. The analysis revealed that the heating rate of the top surface of different specimen structures gradually increased with the heating time. The ascending order of heating effectiveness among the four pavement structures is MCMM > MCMS > MAC > OC. The presence of shielding layers in two pavement structures enhances their heating performance compared to the ordinary absorbing concrete pavement structure. Specifically, MCMS and MCMM exhibited approximately 17.2% and 27.1% higher heating rates, respectively, compared to MAC. Although MAC demonstrated favorable heating performance, its microwave thermal conversion efficiency was slightly lower than that of the other two pavement structures with microwave shielding layers. The application of a conductive metal mesh shielding layer and magnetite sand shielding layer significantly improves the microwave thermal conversion efficiency [27]. This indicates that both shielding layers effectively shield and reflect microwaves, reducing microwave leakage to the underlying pavement structure and enhancing microwave heating efficiency [28].

3.2. De-Icing Effect

Due to the lower compressive strength of the conductive metal mesh structure, magnetite sand was chosen as the shielding layer. In this experiment, the MCMS structure was selected to test the de-icing effect. The experimental results were compared with those for the MAC structure.

3.2.1. Indoor De-Icing Test

The indoor experimental results are shown in Figure 4c. Specimens 1–3 represent the MCMS structure, while specimens 4–6 represent the MAC structure.

From Figure 4c, it can be observed that the relative sliding time of the ice layer for MCMS and MAC specimens occurred at around 220 s and 260 s, respectively. The complete detachment of the ice layer from the specimen surface took place at approximately 260 s for MCMS and 300 s for MAC. Based on the indoor de-icing test results, the de-icing efficiency of the MCMS structure is approximately 14% higher compared to that of the MAC structure. Additionally, the MCMS structure is capable of reflecting microwaves that are not absorbed by the absorbing concrete. The magnetite sand reabsorbs the reflected microwaves and converts them into heat, thereby improving the microwave thermal conversion efficiency.

3.2.2. Outdoor De-Icing Test

The outdoor de-icing test results are shown in Figure 4d. The analysis revealed that under an initial temperature of −20 °C, it takes approximately 193 s for the surface temperature of the MCMS structure specimen to rise to 0 °C, with a heating rate of 6.25 °C/min. However, it takes approximately 257 s for the surface temperature of the MAC structure specimen to reach 0 °C, with a heating rate of 4.68 °C/min. In the outdoor de-icing test, the heating rate of the specimens was significantly lower compared to that in the indoor de-icing test. This phenomenon can be attributed to the heating conditions in the indoor de-icing test, where the specimens were placed inside a microwave cavity. The microwaves that were not absorbed by the specimens underwent reflection within the cavity and were reabsorbed by the specimens. Additionally, the microwave cavity is a closed environment, which reduces heat loss. As a result, the heating rate of the specimens in the indoor de-icing test was much higher than that in the outdoor de-icing test. Furthermore, the presence of ice layers on the specimen surfaces also had a significant impact on the heating rate.

Due to the stronger heating performance of the MCMS structure, the time required for the surface temperature to rise to 0 °C was shorter, and the heating rate was faster. After the ice layer on the surface of the MCMS structure specimen began to melt, the heating rate was approximately 7.45 °C/min, while for the MAC structure specimen, it was around 6.13 °C/min. The heating rates of both pavement structure specimens significantly increased after the ice layer started to melt. This is because the melting ice layer produced liquid water, which can better absorb microwaves and generate heat, leading to an increase in the surface temperature rise rate of the specimens. However, the heating performance of the MCMS structure was still superior to that of the MAC structure.

3.3. Mechanical Properties

3.3.1. Undoped Basalt Fiber

The compressive strength of four types of specimens, namely, OC, MAC, MCMM, and MCMS, was tested, and the specific experimental results are shown in Figure 5a. As shown in Figure 5a, the compressive strength of the four specimens can be ranked from high to low as MCMS ≈ MAC > OC > MCMM. The compressive strength of the MCMS and MAC specimens increased by 8.0% and 9.0%, respectively, compared to that of the OC specimen. However, the compressive strength of the MCMM specimen decreased by 14.1% compared to that of the OC specimen. The significant decrease in the compressive strength of the MCMM specimen compared to that of the MCMS and MAC specimens is due to the presence of the conductive metal mesh at the interlayer interface, which reduces the bond strength between the two layers of concrete, and thus decreases its compressive strength. The compressive strength test results of the MAC specimens have a strong correlation with their structural characteristics. This is because the concrete containing magnetite has been fully vibrated and has a small thickness of the absorbing layer. Moreover, magnetite has higher hardness and strength than ordinary limestone aggregate, which can cause magnetic blocking during the compressive strength test process and thus exhibit higher compressive strength. Magnetite sand was chosen as a shielding layer material for experimental purposes.

The compressive strength of different absorbing concrete structures was tested for their resistance to multiple “microwave freeze–thaw” cycles, and the experimental results are shown in Figure 5b. As shown in Figure 5b, the compressive strength of MCMS specimens decreased by 2.59 MPa, or 6.22%, after 50 freeze–thaw cycles; and the compressive strength of MAC specimens decreased by 2.52 MPa, or 5.92%, after 50 freeze–thaw cycles; and the compressive strength of OC specimens decreased by 1.88 MPa, or 4.73%, after 50 freeze–thaw cycles. From the perspective of the compressive strength loss rate, MCMS > MAC > OC. The volume expansion and contraction degree between different aggregates in the road structure specimens containing magnetite was different, and the heating rate of magnetite was greater than that of cement mortar and limestone aggregate. In addition, the heating performance of MCMS specimens was slightly stronger than that of OC specimens, and the shielding layer contained magnetite sand and hematite aggregate, which caused large differences in internal aggregate volume changes, and thus resulted in the fastest decrease in compressive strength for this specimen. Chen et al. [29] studied the mechanical strength of polyurethane elastomers under different environmental conditions and curing times for performance testing.

3.3.2. Incorporated Basalt Fiber

The results of compressive strength tests before and after 60 cycles of freeze–thaw exposure for concrete specimens of different structural types are shown in Figure 6a. The results of flexural strength tests are presented in Figure 6b.

The experimental results of the microwave-absorbing concrete specimens without basalt fiber are shown above the 0-axis in Figure 6a, while those for the specimens with basalt fiber are shown below the 0-axis. The right axis represents the strength loss rate of the specimen structure type before and after the freeze–thaw cycles. First, we analyze the change in compressive strength of the specimens before and after the freeze–thaw cycles. The compressive strength of the OC specimen after freeze–thawing decreased by 2.51 MPa, or about 6.0%, compared to before freeze–thawing. The compressive strength of the MCMS structure cube specimen decreased by 3.95 MPa, or about 8.5%, compared to before freeze–thawing. The compressive strength of the MAMB specimen decreased by 3.56 MPa, or about 7.3%, after experiencing microwave freeze–thaw cycles. The compressive strength of the MAC structure cube specimen without fiber decreased by 3.55 MPa, or about 7.9%, after freeze–thawing compared to before freeze–thawing. The compressive strength of the MAB specimen decreased by 2.59 MPa, or about 5.5%, after experiencing microwave freeze–thaw cycles. Afroz and Shu et al. [30,31] discovered that basalt fibers exhibit good compatibility with cement. When added to concrete, these fibers can significantly enhance strength and elastic modulus while also increasing toughness and improving durability.

Figure 6b shows that the flexural strength of the OC standard specimen (c-1) after freeze–thawing decreased by 0.64 MPa, or about 12.0%, compared to before freeze–thawing. The flexural strength of the MCMS (a-1) specimen decreased by 0.79 MPa, or about 14.3%, compared to before freeze–thawing. The compressive strength of the MAMB (a-2) specimen decreased by 0.66 MPa, or about 11.6%, after experiencing microwave freeze–thaw cycles. The flexural strength of the MAC standard specimen (b-1) after freeze–thawing decreased by 0.73 MPa, or about 13.2%, compared to before freeze–thawing. The compressive strength of the MAB (B-2) specimen decreased by 0.54 MPa, or about 9.4%, after experiencing microwave freeze–thaw cycles. Nguyen et al. [32] found that incorporating 1.5% basalt fibers into concrete can enhance its compressive and flexural strength.

The compressive and flexural strength loss rates of specimens containing basalt fibers were significantly lower than those of specimens without fibers, and the strength loss rate of specimens without fibers was significantly higher than that of ordinary concrete specimens. This is because during the freeze–thaw cycle, basalt fibers compensate for the defects generated inside the concrete due to volume changes and delay the expansion of cracks; after the specimen cracks, the high elastic modulus of basalt fibers plays a connecting role, so the strength of the specimen can be improved. In addition, basalt fibers can improve the mechanical properties of absorbing concrete under freeze–thaw cycles. Adding basalt fibers can compensate for the strength loss caused by cracks generated inside absorbing concrete due to temperature changes.

3.4. Durability of Different Structures

The results of the abrasion resistance experiment for the OC, MAMB, MAC, MAB, and MCMS specimens, as well as the relative dynamic modulus of elasticity after different numbers of freeze–thaw cycles, are shown in Figure 7a. A total of 200 freeze–thaw cycles were conducted on the specimens, and the relative dynamic modulus of elasticity was recorded every 50 cycles, as shown in Figure 7a. When the specimens of different types underwent 0 freeze–thaw cycles, the water absorption rate varied over time, as shown in Figure 7b. After 20 freeze–thaw cycles, the water absorption rate varied over time, as shown in Figure 7c. After 40 freeze–thaw cycles, the water absorption rate varied over time, as shown in Figure 7d. Ogut et al. [33] found that adding basalt fibers can enhance the durability of concrete.

3.4.1. Wear Resistance

According to the analysis of Figure 7a, the wear loss mass of MCMS and MAC specimens was lower than that of OC specimens. Specifically, compared with ordinary concrete specimens, the wear amount per unit area of MCMS specimens decreased by 10.7%, and that of MAC specimens decreased by 13.6%. The wear resistance of the two types of pavement structure specimens was significantly improved. This change is due to the fact that the absorbing surface layer of MCMS and MAC specimens contains magnetite, whose hardness and strength are superior to those of ordinary limestone gravel aggregate. The hardness of magnetite can reach about 6.5, while that of limestone is only about 4. Therefore, the wear resistance performance of the two pavement structure specimens was much higher than that of ordinary concrete specimens. The wear resistance performance of MCMS and MAC specimens before and after adding basalt fibers also changed. The wear amount per unit area of MAMB decreased by 8.8%, and that of MAB decreased by 9.4%. Therefore, adding basalt fibers to the absorbing concrete pavement structure can effectively improve its wear resistance performance. Alkali-activated materials (AAMs), an alternative to Portland cement, have demonstrated favorable wear performance compared to Portland cement [34]. Ahmed et al. [35] discovered that an optimal content of 1% by weight of cement demonstrated improved abrasion resistance and durability, and met the main requirements of concrete highway pavement, including strength and workability.

3.4.2. Freeze–Thaw Cycle

The analysis of Figure 7a showed that the relative dynamic modulus of elasticity of the four specimens decreased, and the decrease rate of the dynamic modulus of elasticity of the specimens in the early stage of freeze–thaw cycle was relatively slow. When the freeze–thaw cycle had occurred 150 times, the decrease rate increased significantly. The relative dynamic modulus of elasticity of MAC specimens decreased at a lower rate than that of MCMS, indicating that MAC has better frost resistance than MCMS. The frost resistance of MCMS and MAC specimens was improved after adding basalt fibers. The reason for this is that adding basalt fibers to concrete can effectively fill voids, and microwave-absorbing concrete has a denser internal structure. Therefore, the relative dynamic modulus of elasticity of specimens with fibers added decreased slowly in the early stage of freezing and thawing. As hydration inside the concrete progresses, damage caused by freezing and thawing gradually accumulates, and the dynamic modulus of elasticity of specimens decreases rapidly in the later stage. Li et al. [36] analyzed the properties and microstructure of concrete after adding basalt fibers to it. They found that basalt fibers can improve the crack resistance and freeze–thaw resistance of concrete.

3.4.3. Water Absorption

According to the analysis of Figure 7b–d, the water absorption rate of the four structural specimens changed consistently over time, with a significant increase in water absorption rate within the first hour of immersion, followed by a slower increase in water absorption rate over the next five hours. Under the same freeze–thaw cycle conditions, MCMS had a higher water absorption rate than MAC. This may be due to the fact that the lower layer of MCMS specimens contains magnetite and hematite, which have different volume changes from cement materials under microwave freeze–thaw cycle conditions, resulting in cracks and pores and thus increasing the water absorption rate. In addition, the water absorption rate of MAMB specimens decreased after adding basalt fibers. The 6-h water absorption rates under 0, 20, and 40 microwave freeze–thaw cycles decreased by 13.9%, 13.1%, and 12.0%, respectively. Similarly, the 6-h water absorption rate of MAB specimens decreased by 10.8%, 9.9%, and 8.3% under 0, 20, and 40 microwave freeze–thaw cycles, respectively. Therefore, adding basalt fibers to MAC can effectively reduce internal pores in concrete and lower the water absorption rate of pavement structures, thereby reducing cracks caused by liquid water freezing in low-temperature environments. Cui et al. [37] investigated the effects of material composition, porosity, and solute factors on the water absorption of soft rock in their study. Zhang et al. [38] examined the influence of silica fume admixture on the water absorption of hydrophobic concrete.

3.5. SEM

SEM experiments were conducted on specimens containing basalt fibers, and the results are shown in Figure 8.

According to the analysis of Figure 8, the basalt fibers were not tightly connected to the cement slurry, and no chemical reaction occurred between the basalt fibers and the cement slurry. Cement hydration produces flocculent and needle-shaped hydration products. There are gaps between the hydration products of cement hydration, and basalt fibers can fill these gaps, increase the compactness of cement specimens, and enhance the impermeability and durability of cement. C-S-H hydration products of cement hydration adhere to the surface of basalt fibers, increasing the roughness of the surface of basalt fibers. At the same time, a hard shell can be formed on the surface of basalt fibers, which can better transmit stress and improve the overall mechanical properties of cement concrete [22,39].

4. Conclusions

• After incorporating a microwave shielding layer into microwave-absorbing cementitious concrete structures, the heating and temperature rise effects of MCMM and MCMS structures were improved by 27.1% and 17.2%, respectively, compared to those of the MAC structure. However, the compressive strength of MCMM and MCMS decreased by 14.1% and increased by 8%, respectively, compared to that of OC.
• MCMS exhibited a 14% improvement in indoor de-icing effectiveness compared to the MAC structure. In outdoor de-icing experiments, by comparing the rate of temperature rise before and after ice melting and the time required for the specimen surface to reach 0 °C, MCMS consistently demonstrated superior performance. Therefore, considering the comprehensive comparison, magnetite sand material was selected as the microwave shielding layer material for microwave de-icing of cementitious concrete pavement to improve de-icing efficiency.
• After incorporating basalt fibers into cementitious concrete specimens and subjecting them to freeze–thaw cycles, the compressive strength loss rate of MCMS decreased by 1.2%, and the flexural strength attenuation decreased by 2.7%. The strength loss rate of MAB decreased by 2.4%, and the flexural strength rate decreased by 3.8%. Moreover, the addition of basalt fibers also led to certain improvements in the durability performance of cementitious concrete specimens.
• The microstructure between basalt fibers and the cement matrix was observed and analyzed using SEM, providing microscopic evidence for the enhancement of mechanical strength and durability of cementitious concrete by incorporating basalt fibers. Therefore, a volume fraction of 0.2% of basalt fibers was selected to enhance the mechanical strength and durability of microwave-absorbing cementitious concrete pavement.
• In this study, MCMB and MAB specimens were formed at room temperature. Further research is needed to investigate the performance of specimens formed with the addition of basalt fibers under low-temperature conditions. Additionally, a comprehensive evaluation method and system for the performance of MAC pavement have not yet been established. Future studies could focus on scientifically and systematically researching microwave de-icing technology considering climate conditions and economic factors.