Material Design and Performance Study of a Porous Sound-Absorbing Sound Barrier

Abstract

A new type of porous sound-absorbing sound barrier was developed with quartz sand and self-developed polysiloxane resin. The forming process of the material was studied. The test specimens of the porous sound-absorbing sound barrier were prepared with different mesh numbers of quartz sand and different proportions of resin, and the void properties, compressive strength, durability, and acoustic performance were investigated. Based on the mix design results, it is suggested that 20-mesh quartz sand and a 10:1 mass ratio of quartz sand are used to prepare the porous sound-absorbing sound barrier. The durability study showed that the porous sound-absorbing sound-barrier material had good salt and alkali resistance, poor acid resistance, good water stability, and freeze–thaw stability. The laboratory acoustic test and practical engineering application results showed that the porous sound-absorbing sound barrier had excellent acoustic performance and good noise-reduction effects.

1. Introduction

The expansion of the road traffic network in China has brought great convenience to people’s daily lives. However, road traffic noise has also negatively impacted residents’ lives, especially in areas close to highways and urban railways. According to the 2021 China Environmental Noise Pollution Prevention Report [1], the night-time compliance rate of noise near traffic arteries is only 62.9%. As urbanization in China continues to rise, urban residents’ awareness of noise pollution is gradually increasing. Residents realize that noise pollution not only disrupts the tranquility and harmony of cities but also causes adverse effects such as sleep disorders, hypertension, and myocardial infarction [2]. In terms of noise pollution, effective sound insulation solutions are crucial for enhancing the comfort of living and working environments. Researchers have explored various types of sound-insulation walls and their studies focused on soundproof materials and structures. By analyzing silicate bricks, hollow materials, composites, and innovative metamaterials, they have studied new technologies and materials to improve acoustic effects and mitigate the impact of noise on human life.

Jagniatinskis et al. [3] analyzed cavity wall structures made of silicate bricks, hollow silicates, gypsum, and aerated concrete blocks. They explored the acoustic insulation performance of non-load-bearing cavity walls composed of two masonry leaves. The study results showed that cavity walls can replace homogeneous walls to reduce the load on ceiling structures while ensuring compliance with architectural acoustics requirements. Porous concrete layers can serve as perforated materials on the noise-incident surface of road noise barriers. Galip et al. [4] studied the pore structure of porous concrete and the results revealed that the thickness of the porous concrete, as well as the use of two-layer and multi-layer configurations, played a crucial role in improving low-frequency sound absorption. They proposed a mixture for producing porous layers with excellent sound-absorption performance. Laxmi et al. [5] utilized a composite material made of fly ash, waste tire rubber particles, and cement as sound-absorbing panels for noise barriers. This composite material was cost-effective and exhibited favorable engineering properties. It reduce waste through recycling, required no chemical treatments, and mitigated noise pollution via sound barriers. Arenas et al. [6] evaluated the acoustic performance of a porous layer placed on the noise-incident surface. The porous layer was made of bottom ash produced from traditional coal powder combustion at a semi-industrial scale. They assessed the sound-absorption coefficients and air insulation effects in a reverberation chamber. Ramírez-Solana et al. [7] found that sound-wave crystals, a relatively novel type of sound barrier, can enhance insulation performance by incorporating cavity resonators within the crystal scatterers. Fredianelli et al. [8] investigated the practical application of sound-wave crystals as acoustic barriers including hollow scatterers, wood or recycled materials, and porous coatings. Zhuo et al. [9] proposed a sound-insulation barrier with a nonlocal acoustic metastructure which adjusted sound wave transmission through the connection of a pair of spatially separated microphones and speakers to achieve non-reciprocal sound-insulation. Mir et al. [10] studied the MetaWall noise barrier which is a supermaterial wall designed for industrial sound insulation. The MetaWall is a rubber–metal–concrete composite. Their studies revealed that the proposed MetaWall could filter approximately 60% of the original sound energy, converting the filtered sound energy back into electrical potential. Bundo et al. [11] explored the impact of reflecting sound barriers on energy production of roadside-integrated bifacial solar power systems. Thakre et al. [12] proposed a unique design and development methodology for sound-insulation barriers, utilizing novel composite materials with sound-absorbing panels and plant coverings. This design accommodated various materials in sound-absorbing panels and movable noise caps at multiple angles, enhancing noise attenuation and aesthetic appeal. Lee et al. [13] conducted a study on the noise assessment of elevated rapid transit lines and the acoustic performance of various noise barriers. The results indicated that the simulated noise-reduction barriers decreased the noise levels reaching residential apartments by 5–12 dB. Zahra et al. [14] explored the acoustic applications of diatomaceous-earth aerogel-based materials. Their study demonstrated the effectiveness of the materials in sound absorption and sound insulation. Xiang et al. [15] proposed a design for a ventilation sound-insulation barrier with a variable cross-section spiral channel. The barrier could achieve efficient broadband attenuation of low-frequency sounds (<1000 Hz) through Fano-like interference while maintaining free airflow. Kwon [16] developed a novel sound-insulation barrier panel with an inclined mechanism that remained closed under wind speeds below a certain threshold and opened during sudden strong winds, which significantly reduced wind load. Zheng et al. [17] analyzed the characteristics of solid transmission noise from full-enclosure sound barriers made of engineered cementitious composites on high-speed railway bridges, and their impact on the acoustic environment. They introduced a new type of low-viscosity, high-strength concrete sound-barrier panel that offers advantages in noise reduction and cost-effectiveness. Wrona et al. [18] proposed a novel semi-active control method for noise barriers which involved installing switchable bistable links between double-layer soundproof panels. This method adjusted the structural response according to the noise spectrum, achieving significant noise-reduction effects.

In this study, a new type of porous sound-absorbing sound-barrier material was developed using polysiloxane resin and quartz sand. The raw materials, mix design, volume characteristics, durability, and acoustic performance of this material were investigated.

2. Raw Materials and Specimen Forming

The new sound-barrier material studied in this paper was mainly composed of quartz sand and polysiloxane resin. The polysiloxane resin was composed of two components, A and B. In the forming mixture, quartz sand formed the material’s skeleton structure, while the polysiloxane resin acted as a binder, enhancing the overall material strength by bonding the quartz-sand particles. The resin did not completely block the pores between the quartz-sand particles, allowing the final material to maintain the characteristics of a porous material, thus possessing good sound-absorbing properties. Four parallel samples were tested in the volume-index test and compressive-strength test and the mean value was used as the test result.

2.1. Raw Materials

(1)

Polysiloxane resin

The polysiloxane resin used in this study was self-developed and consisted of two components, A and B, as shown in Figure 1. Both components were liquids; component A was milky white, while component B was yellowish and semi-transparent, with stronger fluidity compared with component A.

(2)

Quartz sand

Natural quartz sand available in the market is generally classified by mesh size. This study used quartz sand with mesh sizes of 10, 20, and 40, as shown in Figure 2. The sand was gray–white, granular, smooth, and hard, with silicon dioxide as the main component.

2.2. Forming Process

To facilitate the performance study of this material, Marshall specimens were prepared as cylindrical specimens, following the compaction method from Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011) [19]. The main preparation process is shown in Figure 3. The forming process of the specimens is summarized as follows:

(1) Material preparation. The two components of the polysiloxane resin were mixed at a mass ratio of 3:1. Quartz sand and resin were then mixed at a certain mass ratio and stirred for 10 min.

(2) Specimen molding and compaction. The well-mixed quartz sand and resin was added to the Marshall mold. The diameter of the mold was 101.6 mm and the height of the mold was 63.5 mm, as shown in Figure 4. The mixture was then compacted using the Marshall compaction device, as shown in Figure 5. The Marshall compaction device consists of a hammer, a round compactor head, and a guide bar. It is automatically operated. During compaction, the hammer was lifted and dropped down along the guide bar from a height of 457.2 mm. The weight of the hammer was 4536 g.

(3) Specimen curing and demolding. To accelerate the curing process and shorten the curing time, the specimens were placed in an oven at 110 °C for 90 min. The specimens were then demolded using a demolding machine, as shown in Figure 6. The demolding machine was manually operated. During the demolding operation, the Marshall mold was fixed on the rack first and then the bar was manually lifted until the specimen was ejected from the mold.

3. Mix Design

3.1. Quartz-Sand Parameters

(1)

Gradation curve

Quartz sand constituted the main body of the porous sound-absorbing sound-barrier material. Considering the different mesh sizes of quartz sand, its gradation composition was crucial for this study. According to the fine-aggregate sieving test method in Test Procedures for Aggregates in Highway Engineering (JTG E42-2005) [20], the gradation curve was obtained, as shown in Figure 7. A larger mesh number indicates smaller particle size. As shown in Figure 7, the proportion of 10- to 20-mesh quartz sand in the 10-mesh quartz sand was 90.5%, the proportion of 20- to 30-mesh quartz sand in the 20-mesh quartz sand was 67.1%, and the proportion of 40- to 50-mesh quartz sand in the 40-mesh quartz sand was 44.1%.

(2)

Density

Density tests were conducted according to Test Procedures for Aggregates in Highway Engineering (JTG E42-2005) [20]. The main procedures for the density test were as follows:

(1) The quartz sand was soaked in water for 24 h and the moisture was removed by a dryer. The saturated-surface dry test mold was used to determine whether the saturated-surface dry state had been reached.

(2) The quartz sand at the saturated-surface dry state was then placed in the volumetric flask and the total weight was measured, as shown in Figure 8. The quartz sand was finally removed from the volumetric flask and dried in the oven.

(3) The apparent relative density and gross relative density can be, respectively, computed by Equations (1) and (2):

$${\gamma }_{\mathrm{a}}={\displaystyle \frac{m_0}{m_0+m_1-m_2}}$$

(1)

$${\gamma }_b={\displaystyle \frac{m_0}{m_3+m_1-m_2}}$$

(2)

where ${\gamma }_{\mathrm{a}}$ is the apparent relative density; ${\gamma }_b$ is the gross relative density; $m_0$ is the dried weight of quartz sand; $m_1$ is the total weight of the water and volumetric flask; $m_2$ is the total weight of the water, volumetric flask, and quartz sand at the saturated-surface dry state; and $m_3$ is the weight of quartz sand at the saturated-surface dry state.

The apparent relative density and gross relative density of the 10-mesh, 20-mesh, and 40-mesh quartz sand were tested, and the results are shown in

Table 1. Quartz-sand density.

Quartz-Sand Types	Apparent Relative Density	Gross Relative Density
10-mesh	2.849	2.780
20-mesh	2.893	2.857
40-mesh	2.844	2.806

. The density data were used to compute the volume parameters of the sound-barrier specimens.

3.2. Experimental Design

This study aimed to select the most suitable quartz sand for engineering applications and to determine the optimal ratio of quartz sand to resin. Based on the ratio of quartz sand to resin and the mesh size of quartz sand, an orthogonal experiment was designed and a total of 15 experimental combinations were determined, as shown in

Table 2. Orthogonal experimental combinations.

Quartz-Sand Mesh	Ratio of Quartz Sand to Resin
	8:1	9:1	10:1	11:1	12:1
10-mesh	√	√	√	√	√
20-mesh	√	√	√	√	√
40-mesh	√	√	√	√	√

.

4. Volume Index and Mechanical Strength

4.1. Porosity

The material used in this study was similar to an asphalt mixture. Therefore, the method for calculation of porosity refers to that of an asphalt mixture, as shown in Equation (3):

$$VV=\left(1-{\displaystyle \frac{{\gamma }_f}{{\gamma }_t}}\right)\times 100$$

(3)

where $VV$ is the porosity of the specimen, ${\gamma }_f$ is the gross relative density of the specimen, and ${\gamma }_t$ is the theoretical maximum relative density of the material.

The gross relative density of the specimen was measured using the volumetric method specified in Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011) [19]. The theoretical maximum relative density of the material was calculated by Equation (4):

$${\gamma }_t={\displaystyle \frac{100+P_a}{\frac{100}{{\gamma }_{se}}+\frac{P_a}{{\gamma }_c}}}$$

(4)

where ${\gamma }_t$ is the maximum theoretical relative density of the material, $P_a$ is the mass ratio of resin to quartz sand, ${\gamma }_{se}$ is the effective relative density of quartz sand, and ${\gamma }_c$ is the relative density of resin.

Figure 9 shows the porosity of the sound-barrier specimens with different mesh sizes and different mix ratios. As shown in Figure 9, the porosity of the specimens increased with the decrease in the proportion of resin. With the same resin proportion, the porosity of the specimen made of 10-mesh quartz sand was the greatest while the porosity of the specimen made of 20-mesh quartz sand was the lowest.

4.2. Connected Porosity

The voids in the material included closed voids and open pores. To study the void characteristics of the material, the connected porosity test method in Technical Specification for Permeable Asphalt Pavement (CJJ/T 190-2012) [21] was used. The measured connected porosity is shown in Figure 10. The figure shows that there were significant differences in the connected porosity of the specimens made of different mesh quartz sand. For the specimens made of 10-mesh, 20-mesh, and 40-mesh quartz sand, the connected porosity was highest when the ratio of quartz sand to resin was 10:1. Compared with porosity, the effect of quartz-sand mesh size and resin proportion on the connected porosity was more significant.

4.3. Compressive Strength

The compressive strength of the specimens was measured using the unconfined compressive strength test method specified in Test Methods of Materials Stabilized with Inorganic Binders for Highway Engineering (JTG E51-2009) [22]. It was used as a design and quality control index for porous sound-absorbing sound-barrier material. The automatic servo compression machine was used to conduct the compressive test, as shown in Figure 11. The maximum pressure of the machine was 2000 kN. Considering that the performance of this new resin binder was better than that of ordinary inorganic binders, a loading rate of 0.1 MPa/s was selected for the test. Figure 12 shows the test results. As shown in Figure 12, the smaller the proportion of resin, the lower the compressive strength. With the same resin proportion, the compressive strength of the specimen made of 20-mesh quartz sand was highest.

Based on the test results of porosity, connected porosity, and compressive strength, the specimen made of 20-mesh quartz sand had good porosity, connected porosity, and the highest compressive strength. Therefore, it is recommended that sound-barrier material is prepared with 20-mesh quartz sand and a 10:1 mass ratio of quartz sand to resin.

5. Durability of Sound-Barrier Material

The sound barrier is a traffic facility exposed to the air for a long time. Its corrosion resistance and durability have a significant impact on service life. Therefore, the sound-barrier material must have properties such as strength, corrosion resistance, and water stability. The corrosion resistance of the porous sound-absorbing barrier material was evaluated through acid-immersion, alkali-immersion, and salt-immersion tests. The water stability was evaluated through water-immersion and freeze–thaw-cycle tests. These tests were designed to verify whether the material maintained stability under extremely harsh environmental conditions.

5.1. Corrosion Resistance

Referring to the test methods in Technical Conditions for Anti-corrosion of Steel Components in Highway Traffic Engineering (GB/T 18226-2015) [23], optimization of the test scheme for the sound-barrier material was conducted. The material was soaked in 20% sulfuric acid solution, 20% sodium hydroxide solution, and 10% sodium chloride solution for 7, 14, 21, and 28 days. During the tests, one group of specimens was placed at room temperature as a control group while the experimental group was placed in the solution. The compressive strength was tested at the specified dates.

Figure 13 shows the specimens soaked in sulfuric acid solution, sodium hydroxide solution, and sodium chloride solution for 28 days. As shown in Figure 13, from the appearance, the specimens soaked in salt and alkali solutions did not show significant changes in shape or color. However, in the specimens soaked in acid solution, bright white or dark yellow colors appeared.

Figure 14 and

Table 3. Compressive strength of specimens soaked in 10% sodium chloride solution.

Salt-immersion days (d)	7	14	21	28
Compressive strength of control group (MPa)	10.57	10.33	9.54	9.38
Compressive strength of experimental group (MPa)	8.41	9.68	8.96	8.49

show the compressive strength of specimens soaked in the salt solution. As shown in Figure 14 and Table 3, the compressive strength of specimens soaked in the salt solution generally decreased. With the increase in the soaking time, the compressive strength first increased and then decreased. However, the decrease in the compressive strength was relatively small. This demonstrates that the porous sound-absorbing sound-barrier material had good salt resistance.

Figure 15 and

Table 4. Compressive strength of specimens soaked in 20% sodium hydroxide solution.

Alkali-immersion days (d)	7	14	21	28
Compressive strength of control group (MPa)	10.57	10.33	9.54	9.38
Compressive strength of experimental group (MPa)	9.47	10.47	9.40	9.09

show the compressive strength of specimens soaked in the alkali solution. As shown in Figure 15 and Table 4, the strength of specimens soaked in the alkali solution was lower than that of the control group. However, the decrease in the compressive strength was relatively small. This demonstrates that the porous sound-absorbing sound-barrier material had good alkali resistance.

Figure 16 and

Table 5. Compressive strength of specimens soaked in 20% sulfuric acid solution.

Acid-immersion days (d)	7	14	21	28
Compressive strength of control group (MPa)	10.57	10.33	9.54	9.38
Compressive strength of experimental group (MPa)	6.09	5.17	5.10	3.97

show the compressive strength of specimens soaked in the acid solution. As shown in Figure 16 and Table 5, the strength of specimens soaked in the sulfuric acid solution was significantly lower than that of the control group, with a maximum reduction of up to 57%. This demonstrates that the porous sound-absorbing sound-barrier material had poor acid resistance.

5.2. Water Stability

During the tests, the specimens of experimental group were placed in water at a constant temperature of 25 °C for a certain number of days. Figure 17 and

Table 6. Compressive strength of specimens soaked in water.

Water-immersion days (d)	7	14	21	28
Compressive strength of control group (MPa)	10.57	10.33	9.54	9.38
Compressive strength of experimental group (MPa)	10.14	9.81	8.88	8.65

show the compressive strength of specimens soaked in water. As shown in Figure 17 and Table 6, the compressive strength of the specimens gradually decreased with the soaking time. However, the strength reduction in the experimental group did not exceed 14%. And compared with the control group, the strength reduction did not exceed 7%. The results indicate that the material had good water stability.

5.3. Freeze–Thaw Stability

The freeze–thaw tests were conducted referring to the freeze–thaw splitting test in Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering (JTG E20-2011) [19]. The specimens were divided into control and experimental groups. The experimental group was placed in a vacuum-saturated water environment for 15 min, then placed in a constant-temperature freezer at −18 °C for 24 h and, finally, placed in a constant temperature water bath at 60 °C for 24 h. The control group was placed at normal temperature. The compressive strength of the two groups was tested and the results are shown in Figure 18 and

Table 7. Compressive strength of specimens before and after one freeze–thaw cycle.

Quartz-sand mesh	10	20	40
Compressive strength of control group (MPa)	9.15	12.04	10.13
Compressive strength of experimental group (MPa)	7.49	11.52	8.88

. As shown in Figure 18 and Table 7, after one freeze–thaw cycle, the compressive strength of specimens made of the three mesh numbers of quartz sand did not decrease greatly. Furthermore, the specimens made of 20-mesh quartz sand had the best freeze–thaw stability.

6. Acoustic Performance

Referring to the technical requirements and test methods for the acoustic performance of sound-barrier materials specified in Highway Sound Barriers Part 4: Technical Requirements and Test Methods for Acoustic Materials (JT/T 646.4-2016) [24], the noise-reduction coefficient and weighted sound-insulation index were tested. The sound-absorbing sound-barrier slab was prepared with the 20-mesh quartz sand and a 10:1 mass ratio of quartz sand to resin. The acoustic tests were conducted using the reverberation-room method. The test data are shown in Figure 19 and

Table 8. Acoustic performance of the sound-barrier material.

Frequency (Hz)	100	200	400	500	800	1000	1600	2000	4000	5000
Absorption coefficient	0.42	0.61	0.70	0.86	0.73	0.70	0.71	0.75	0.92	0.90
Sound insulation (dB)	30.0	31.3	33.9	35.2	39.0	41.0	44.4	47.5	54.7	56.2

.

According to the above data and referring to the calculation method of the noise-reduction coefficient in Classification of Sound Absorption Performance of Building Sound Absorption Products (GB/T 16731-1997) [25], the noise-reduction coefficient of the material was 0.7. Referring to the calculation method of the weighted sound-insulation index in the Evaluation Standard for Building Sound Insulation (GB/T 50121-2005) [26], the weighted sound-insulation index of the material was 40 dB. The noise-reduction coefficient should not be less than 0.6 and the weighted sound-insulation index should not be less than 26 dB according to Chinese highway sound-barrier standard [24]. Therefore, the porous sound-absorbing sound-barrier material had excellent acoustic performance.

7. Engineering Application

This porous sound-absorbing sound barrier has been used in Gengche town section of the Ningsuxu expressway in China, as shown in Figure 20. The Gengche town section is one of the noise-sensitive points along the Ningsuxu expressway. Residential houses and the Liuwei primary school are near the expressway. The nearest distance between the houses and the expressway is 60 m. The distance between the Liuwei primary school and the expressway is 35 m.

The sound-pressure levels of the noise-sensitive points were detected before and after installation of the porous sound-absorbing sound barrier. Three detection points were selected as shown in Figure 21. The first point, Z1, was located at the northeast corner of the Liuwei primary school, the second point, Z2, was inside Liuwei village, and the third point, Z3, was located at the Liuwei village park. The sound-pressure levels at the three detection points during the day and at night were recorded. The vehicle-flow data during the detection period were also recorded. The detection data are shown in

Table 9. Detection data during the day before installation of the sound barrier.

Date	Detection Point	Time	Sound-Pressure Level in the Day (dB)	Vehicle Flow (Vehicles/5 min)
				Large Vehicles	Medium and Small Vehicles
2 September 2021	Z1	10:23	71.7	22	43
		13:49	69.3	19	40
		16:10	72.2	18	69
	Z2	11:01	70.3	22	43
		14:25	69.1	19	40
		16:32	70.6	18	69
	Z3	11:25	62.6	22	43
		15:24	61.2	19	40
		17:00	62.9	18	69

,

Table 10. Detection data at night before installation of the sound barrier.

Date	Detection Point	Time	Sound-Pressure Level at Night (dB)	Vehicle Flow (Vehicles/5 min)
				Large Vehicles	Medium and Small Vehicles
3 September 2021	Z1	0:48	59.6	23	11
	Z2	00:18	60.1	25	13
2 September 2021	Z3	23:55	52.8	20	14

,

Table 11. Detection data during the day after installation of the sound barrier.

Date	Detection Point	Time	Sound-Pressure Level in the Day (dB)	Vehicle Flow (Vehicles/5 min)
				Large Vehicles	Medium and Small Vehicles
15 May 2023	Z1	10:24	56.7	41	103
		13:49	51.5	29	88
		16:09	49.7	42	89
	Z2	10:54	53.8	39	87
		14:24	54.1	31	117
		16:35	53.4	44	112
	Z3	11:21	52.3	34	101
		15:26	50.0	47	117
		17:00	50.4	40	98

and

Table 12. Detection data at night after installation of the sound barrier.

Date	Detection Point	Time	Sound-Pressure Level at Night (dB)	Vehicle Flow (Vehicles/5 min)
				Large Vehicles	Medium and Small Vehicles
15 May 2023	Z1	00:48	47.0	35	40
	Z2	00:18	51.7	41	46
	Z3	23:54	42.8	69	21

.

The mean of the detection data at different times for the same detection point was computed and was used to represent the sound-pressure level of this point. Figure 22 shows the mean sound-pressure level during the day at the three detection points before and after installation of the sound barrier. As shown in Figure 22, the noise reduction at the three detection points Z1, Z2, and Z3 was 18.5 dB, 16.2 dB, and 11.3 dB, respectively, during the day after installation of the sound barrier. Figure 23 shows the mean sound-pressure level at night at the three detection points before and after installation of the sound barrier. As shown in Figure 23, the noise reduction at night was 12.6 dB, 8.4 dB, and 10 dB, respectively. Therefore, the porous sound-absorbing sound barrier had good noise-reduction effects.

8. Conclusions

A new type of porous sound-absorbing sound-barrier material was prepared using quartz sand and self-developed polysiloxane resin. Specimens were prepared with quartz sand with different mesh numbers and with different resin ratios. The porosity, compressive strength, durability, and acoustic performance of the material were investigated. The main conclusions are as follows:

(1) Based on the test results of porosity, connected porosity, and compressive strength, the specimen made of 20-mesh quartz sand had good porosity, connected porosity, and the highest compressive strength. It is recommended that the sound-barrier material be prepared with 20-mesh quartz sand and a 10:1 mass ratio of quartz sand to resin.

(2) The corrosion resistance of the porous sound-absorbing barrier material was evaluated through acid-immersion, alkali-immersion, and salt-immersion tests. The results showed that the material had good salt resistance, good alkali resistance, and poor acid resistance. The water stability was evaluated through water-immersion and freeze–thaw-cycle tests. The results showed that the material has good water stability and freeze–thaw stability.

(3) The porous sound-absorbing sound-barrier material had excellent acoustic performance with a noise-reduction coefficient of 0.7 and a weighted sound-insulation index of 40 dB, which are far above the standard requirements.

(4) This porous sound-absorbing sound barrier has been used in the Gengche town section of Ningsuxu expressway in China. The sound-pressure levels at three detection points were measured before and after installation of the porous sound-absorbing sound barrier. The detection results showed that the porous sound-absorbing sound barrier had good noise-reduction effects.