An Investigation of the Effects of Thermo-Oxidative Aging and the Freeze–Thaw Cycle on the Performance of Polyester-Based, Self-Adhesive Asphalt Waterproofing Membranes

Abstract

Polyester-based, self-adhesive asphalt waterproofing membranes have garnered significant attention due to their extensive use in building-waterproofing projects, with their resistance to aging in complex environments being particularly crucial. This study evaluates the performance changes of these membranes under thermo-oxidative aging and freeze–thaw cycling conditions. The thermo-oxidative aging process was simulated using a thin-film oven and combined with freeze–thaw cycle tests to assess membrane performance at various aging stages. Changes in functional groups were analyzed via Fourier Transform Infrared Spectroscopy (FTIR), and tests for low-temperature flexibility, tensile properties, and peel strength were conducted. The results demonstrated that aging significantly reduced the membrane’s low-temperature flexibility and peel strength, accompanied by oxidative reactions and a loss of lightweight components. This study provides essential data on the aging behavior of the membrane and offers a theoretical foundation for its long-term application in practical engineering.

1. Introduction

Waterproofing membranes are flexible building materials extensively used in walls, roofs, tunnels, highways, landfills, and other construction projects. Their primary function is to prevent the infiltration of rainwater and groundwater [1]. Serving as the first line of defense between the foundation and the structure, waterproofing membranes are vital for ensuring the safety and longevity of construction projects. Given their broad applications and the need for complex substrate treatments, these membranes must exhibit excellent water resistance, stability under temperature fluctuations, and anti-aging properties [2,3].

Polyester tire self-adhesive asphalt waterproofing membranes (commonly referred to as self-adhesive membranes) are a new waterproofing material that has gained significant attention in recent years. The material incorporates a polyester tire base fabric as the reinforcement layer, which enhances the membrane’s strength and protects it from surface damage. Meanwhile, the self-adhesive asphalt on the membrane’s surface provides excellent creep resistance, allowing it to accommodate substrate deformations. The cold-application construction method ensures comprehensive adhesion between the membrane and the substrate without requiring specialized treatments for uneven surfaces, significantly reducing construction time and costs. This versatility renders it suitable for various construction environments. Due to its outstanding performance and ease of application, the self-adhesive membrane has been widely adopted in real-world projects. Its structure is shown in Figure 1.

Self-adhesive membranes are widely used in various applications, but their durability issues have attracted considerable attention from scholars both domestically and internationally. Li et al. [4] investigated the low-temperature cracking performance of asphalt under the combined influence of heat and light. They proposed using asphalt elongation after 15 days of joint aging as a key index for evaluating low-temperature cracking performance and emphasized that asphalt composition, particularly the instability of asphaltenes, plays a critical role in its low-temperature cracking behavior [5]. Yang et al. [6] investigated the changes in the chemical composition, molecular structure, and high- and low-temperature performance of various types of asphalt before and after hot-air aging using chromatographic column methods and Fourier transform infrared spectroscopy (FTIR). Their findings indicated that hot-air aging altered the distribution of organic compounds in asphalt. As the aging temperature increased, the low-temperature flexibility of asphalt decreased, and significant differences in aging resistance were observed across different types of asphalt. Additionally, higher temperatures were found to significantly accelerate the aging process [7]. Xiong Yuqin et al. [8] conducted thermal aging and durability tests on five polymer-based, self-adhesive waterproofing membranes at various time points, observing a continuous fluctuation in tensile strength and elongation throughout the testing process. However, the research on asphalt waterproofing membranes extends beyond thermal and optical aging. Song et al. [9] found that the combined effect of thermo-oxidative aging and UV aging had a greater impact on asphalt than all-weather aging through comparative tests of natural and artificial aging. Interestingly, thermo-oxidative aging improved asphalt’s resistance to deformation and its rutting performance at high temperatures. Wang et al. [10,11] evaluated the durability of asphalt waterproofing membranes through one- and four-year outdoor natural exposure tests, assessing changes in the physical and bonding properties of asphalt under natural conditions. Dong Wenlong et al. [12] investigated the low-temperature performance of SBS-modified asphalt in different aging states through low-temperature bending tests and found that short-term aging enhanced the low-temperature performance of SBS-modified asphalt. They used Fourier IR spectroscopy to quantitatively analyze the aging effects on functional groups. Similarly, Singh et al. [13] conducted short-term and long-term aging tests on base materials and asphalt binders using the Rolling Thin Film Oven Test (RTFOT) and Pressure Aging Vessel (PAV). By combining these tests with scanning electron microscopy (SEM) and FTIR, they investigated the effects of aging on asphalt properties and explored the underlying causes. Zhang Hui [14] prepared self-adhesive, polymer-modified asphalt waterproofing membranes using four different base asphalts and studied the changes in their low-temperature flexibility before and after thermo-oxidative aging. He also proposed an index system for evaluating the aging resistance of these membranes.

In addition, the issue of asphalt aging has garnered significant attention in the field of asphalt concrete roads and has been extensively studied [15,16]. Donchenko et al. [17] reviewed the aging of road asphalt and its potential solutions, proposing methods to mitigate the aging process. Guo et al. [18], using the Rolling Thin Film Oven (RTFO) test and Pressure Aging Vessel (PAV) test, investigated the effects of aging on the low-temperature properties of four types of asphalt and concluded that both aging and low-temperature conditions negatively impact their performance. Wang et al. [19] examined the mechanical properties of porous asphalt mixtures at low temperatures through low-temperature bending tests, finding that porosity had the greatest effect on their low-temperature performance. Pyshyev et al. [20] suggested that lignite-processed products could be used to improve the aging resistance of asphalt. Feng et al. [21] studied the effects of three anti-aging agents on enhancing asphalt properties.

The effects of aging caused by freeze–thaw cycles should not be overlooked. Huang et al. [22] investigated the evolution of the low-temperature properties of rubber-modified asphalt under freeze–thaw conditions through both water and salt freeze–thaw cycling tests. Shan et al. [23] analyzed the apparent morphology and mechanical properties of modified asphalt subjected to freeze–thaw cycles, concluding that these cycles reduce the low-temperature performance of asphalt binders, with salt freeze–thaw cycles causing more severe surface damage than water freeze–thaw cycles. Gebing et al. [24] studied the aging of SBS waterproofing membranes due to immersion and freeze–thaw cycles, finding that immersion aging significantly affects the performance of the polyester tire base. They also summarized the impact of these two aging forms on the tensile strength of the membrane.

In building-waterproofing projects, natural factors such as climate change, sunlight, and rain can accelerate the aging of self-adhesive membranes, leading to a decline in their impermeability, adhesion, low-temperature bending performance, and tensile strength [11,25]. While existing research has primarily focused on the aging performance of SBS-modified asphalt, there has been limited investigation into the aging of self-adhesive asphalt waterproofing membranes. In response to this gap, this paper simulates the natural aging process of self-adhesive membranes using a film oven and a freeze–thaw cycle test chamber to examine changes in their low-temperature flexibility and mechanical properties under the combined effects of thermo-oxidative aging and freeze–thaw cycles. The changes in functional groups of the self-adhesive membranes under different aging conditions were analyzed using Fourier Transform Infrared Spectroscopy (FTIR), while the surface changes after coupled aging were observed using a Scanning Electron Microscopey (SEM). Finally, this study summarizes the effects of different aging conditions and durations on the performance of self-adhesive membranes, providing a scientific basis for practical engineering applications.

2. Experimental

2.1. Materials

Polyester tire self-adhesive asphalt waterproofing membranes produced by ORIENTAL YUHONG (Beijing, China) was selected as the test material, specifically the SAM-polyester tire self-adhesive asphalt variant. The main performance indicators of the material are listed in

Table 1. Characteristics of self-adhesive asphalt waterproofing membranes.

Property	Measured Values
Thicknesses (mm)	3.0
Tensile strength (N/50 mm)	620/500
Elongation at maximum tension (%)	39
Soluble matter content (g/m2)	2208

. All test samples comply with the national standard GB 23441-2009, “Self-adhering Polymer Modified Bituminous Waterproof Sheet” [26].

2.2. Pilot Programme

(1)

Specimen Preparation

According to the specification requirements for specimen preparation, the specimens are to be cut evenly along the width of the membrane, with the long edge of the specimen aligned with the longitudinal direction of the web and at least 150 mm from the edge [27]. The cut specimens are classified into three types: A, B, and C. Type A specimens measure 25 mm × 150 mm and are used for low-temperature flexibility tests and Fourier infrared spectroscopy after thermo-oxidative and freeze–thaw cyclic aging. Type B specimens measure 50 mm × 300 mm and are used for tensile testing after thermo-oxidative and freeze–thaw cyclic aging. Type C specimens measure 50 mm × 200 mm and are used for peeling tests following thermo-oxidative and freeze–thaw cyclic aging.

(2)

Aging process

This paper examines the changes in the properties of self-adhesive membranes under two distinct aging conditions: thermo-oxidative aging and freeze–thaw cycle aging. The test uses a thin film oven (TFO) to simulate the high temperatures encountered by roofs and facades during summer, with aging duration as the test variable. Based on measurements of external wall temperatures during peak summer conditions [28], the test temperature was set at 80 °C, and the aging durations were 2, 5, 7, 14, and 28 days. After completing the thermo-oxidative aging test, the specimens were placed in a constant temperature and humidity incubator for 24 h before undergoing the freeze–thaw cycle aging test. The freeze–thaw cycle aging was conducted in a freeze–thaw cycle tester (FTCT), where the test conditions involved freezing at −20 °C for 12 h, followed by stabilization at a constant temperature of 23 °C (±2) for 12 h. The freeze–thaw cycle duration for each specimen corresponded to its thermo-oxidative aging time. Specimens that have undergone both thermo-oxidative aging and freeze–thaw cycles are to be subjected to low-temperature flexibility tests, Fourier infrared spectroscopy (FTIR), and mechanical property tests. The flowchart of the test is shown in Figure 2.

(3)

Test Methods

The tensile performance and seam peeling performance tests were conducted in accordance with the “Test Methods for Building Sheets for Waterproofing” (GB/T 328.8-2007 and GB/T 328.20-2007) [29,30]. An electronic universal testing machine was used as the testing instrument. The dimensions of the peeling specimen were 200 mm × 50 mm, with a seam width of 100 mm. The fixture spacing was set at 100 mm, and the fixture movement during the test was maintained at a constant rate of 100 mm/min. Fourier Transform Infrared Spectroscopy (FTIR) tests were performed using a Bruker B420 spectrometer (Bruker Corporation, Billerica, MA, USA) equipped with an attenuated total reflection (ATR) diamond accessory. The wavenumber range for the FTIR test was 4000 cm⁻¹ to 340 cm⁻¹, with 16 scans conducted for each measurement. The chemical properties of waterproofing membranes can be further analyzed by calculating the functional group index based on the following formula derived from the results of the infrared test spectra:

Carbonyl functional group index:

$$I_{C=O}={\displaystyle \frac{\mathrm{Carboniferous} \mathrm{peak} \left({\mathrm{Centred} \mathrm{at} 1700 \mathrm{cm}}^{-1}\right)\mathrm{area}}{{\mathrm{Peak} \mathrm{area} \mathrm{between} 600 \mathrm{and} 2000 \mathrm{cm}}^{-1}}}$$

(1)

Sulfoxide functional group index:

$$I_{S=O}={\displaystyle \frac{\mathrm{Sulfoxide} \mathrm{peak} \left({\mathrm{Centred} \mathrm{at} 1030 \mathrm{cm}}^{-1}\right)\mathrm{area}}{{\mathrm{Peak} \mathrm{area} \mathrm{between} 600 \mathrm{and} 2000 \mathrm{cm}}^{-1}}}$$

(2)

Butadiene double-bond functional group index:

$$I_{C=C}={\displaystyle \frac{\mathrm{Butadiene} \mathrm{Peak} \left({\mathrm{Centred} \mathrm{at} 966 \mathrm{cm}}^{-1}\right)\mathrm{area}}{{\mathrm{Peak} \mathrm{area} \mathrm{between} 600 \mathrm{and} 2000 \mathrm{cm}}^{-1}}}$$

(3)

Sulfide ether functional group index:

$$I_{R-S-R}={\displaystyle \frac{\mathrm{Sulfide} \mathrm{Peak}\left({\mathrm{Centred} \mathrm{at} 730 \mathrm{cm}}^{-1}\right)\mathrm{area}}{{\mathrm{Peak} \mathrm{area} \mathrm{between} 600 \mathrm{and} 2000 \mathrm{cm}}^{-1}}}$$

(4)

3. Results and Discussion

3.1. Apparent Appearance and SEM Analysis

A comparison of the unaged and coupled aging specimens is shown in Figure 3. It illustrates that the surface of the unaged specimen was smooth and flat, while with increased aging time, the surface became progressively rougher and glossier, with localized yellowing and asphalt oxidation spots. Additionally, the specimen’s profile morphology became more rounded due to thermal expansion as the aging time increased.

Figure 4 shows SEM photographs of unaged samples and those aged for 5, 14, and 28 days. As seen in Figure 4a, the surface texture of the unaged self-adhesive membrane was uniformly distributed and densely structured, with almost no impurities. After coupled aging, the surface of the samples exhibited noticeable folds, increased agglomerates, and uneven distribution, primarily due to the gradual conversion of lighter substances, such as aromatics and other asphalt components, into asphaltene. As the aging time increased, the asphalt became progressively harder and more brittle, leading to the formation of microcracks due to internal stress.

3.2. Quality Loss Rate

The changes in the mass of the original specimen and the specimens after each aging period were recorded, and the results are shown in Figure 5. As observed in the figure, when the aging times were 2 and 5 days, the rate of mass loss increased with the aging duration. This may be attributed to thermo-oxidative aging at high temperatures, which alters the internal chemical composition or causes the volatilization of surface substances. At 7 days of aging, the rate of mass loss decreased significantly. This was likely due to the application of putty powder on the internal platform of the thin-film oven (TFO) to prevent adhesion between the specimen and the platform during the thermo-oxidative aging test. As the aging time increased, the viscosity of the specimen’s surface also increased, causing putty powder to adhere to the specimen’s surface, which could not be completely removed during post-processing, thus resulting in an increase in the specimen’s mass. After 7 days, the rate of mass loss increased again, but more slowly than during the 2–5-day period, for the same reasons as the initial mass loss.

3.3. Low-Temperature Flexibility Analysis

The low-temperature flexibility of the self-adhesive membrane was tested in accordance with the requirements of GB 23441-2009, “Self-adhering Polymer Modified Bituminous Waterproof Sheet” [23]. Samples were prepared for both unaged and various-degrees-of-aged specimens to conduct the low-temperature flexibility limit test. The cracking temperature of the unaged specimen was −28.5 °C, which met the basic specification requirements [23]. The cracking temperatures of the specimens at each stage of aging in the low-temperature flexibility test are presented in

Table 2. Cracking temperature for low-temperature flexibility test.

Aging time (day)	0	2	5	7	14	28
Cracking temperature (°C)	−28.5	−26	−22	−21	−18	−15

.

As shown in Table 2, the cracking temperature in the low-temperature flexibility test increased with aging time. The cracking temperature of the specimen subjected to 28 days of combined thermo-oxidative aging and freeze–thaw cycle aging was −15 °C. Compared to specimens aged solely by thermo-oxidative aging [12], the self-adhesive membranes exposed to both thermo-oxidative aging and freeze–thaw cycle aging were more prone to cracking at low temperatures. This is because, during thermo-oxidative aging, the membrane undergoes an oxidation reaction, which accelerates phase separation, causing the modifier in the asphalt to separate from the asphalt. As freeze–thaw cycle aging continues, the deformation resistance of the membrane worsens, and its low-temperature ductility decreases, ultimately leading to an increase in the cracking temperature.

3.4. FTIR Analysis

Figure 6 shows the infrared spectra of the self-adhesive membrane specimens in their unaged state, as well as after 5, 7, 14, and 28 days of thermo-oxidative and freeze–thaw aging. The chemical bonds and functional groups present in the material can be identified by analyzing the position of the absorption peaks, as well as the shapes and intensities of the peaks in the infrared spectra. When the unaged and aged self-adhesive membrane specimens are compared, the characteristic peak areas near 2930 cm⁻¹ and 2846 cm⁻¹ significantly decreased with increasing aging time, which was attributed to the degradation and breakage of butadiene chain segments in bitumen, leading to a reduction in the content of C=C double bonds. Additionally, the characteristic peak area near 1400 cm⁻¹ increased due to the formation of oxygen-containing groups such as carbonyl (C=O) and sulfinyl (S=O) after oxidation at high temperatures, which resulted in an increase in the content of these groups. The aging mechanism and degree of different self-adhesive membranes can be analyzed by comparing and calculating the indices for double bonds, sulfoxide groups, carbonyl groups, and sulfide ether functional groups, with the results shown in

Table 3. A comparison of the functional group index of the self-adhesive membrane before and after aging.

Projects	Unaged	Aging 5 Days	Aging 7 Days	Aging 14 Days	Aging 28 Days
Carbonyl functional group index	0.22	0.046	0.026	0.022	0.018
Sulfoxide functional group index	0.06	0.115	0.135	0.172	0.187
Butadiene double-bond functional group index	0.06	0.115	0.132	0.172	0.187
Sulfide ether functional group index	0.16	0.012	0.003	0.001	0.001

.

As shown in Figure 6 and Table 3, the self-adhesive membrane subjected to the combined effects of thermo-oxidative aging and freeze–thaw cycle aging exhibited a decrease in the carbonyl index, alongside increases in both the sulfoxide index and the butadiene double-bond index. The sulfide index, however, decreased. This indicates that the specimen underwent oxidation reactions during the aging process, leading to a reduction in light components, such as the aromatic fraction of the asphalt. This also corroborates the presence of impurities observed on the surface in the SEM tests mentioned earlier.

3.5. Tensile Properties of Waterproofing Membranes

The tensile properties of the self-adhesive web specimens after unaged and coupled aging were tested, and the load–displacement curves of the self-adhesive web specimens under different aging conditions were obtained as shown in Figure 7, and the ultimate load and ultimate tensile displacements of the respective adhesive web specimens are shown in Figure 8.

According to Figure 7, the tensile load–displacement curves of self-adhesive membranes with different degrees of aging had approximately the same shape. When the tensile displacement was less than 20 mm, the load–displacement curve exhibited a linear trend, and the initial stiffness of all specimens remained almost identical. However, when the tensile displacement exceeded 20 mm, the specimens began to exhibit necking, resulting in a decreased slope of the curve and a reduction in stiffness. In the tensile displacement range of 20 mm to 40 mm, the load–displacement curves fluctuated. Observing the tensile test revealed that the fluctuation in the curves was due to the separation between the polyethylene film on the surface of the self-adhesive membrane and the membrane itself. Once the tensile displacement exceeded 20 mm, the polyethylene film began to separate from the membrane at the necking point, resulting in the up-and-down fluctuations in the load–displacement curve.

According to Figure 8, the ultimate load and ultimate displacement of the self-adhesive membrane exhibited a trend of increasing initially and then decreasing with aging time. When subjected to combined thermo-oxidative aging and freeze–thaw cycle aging for approximately 7 days, both the ultimate load and ultimate displacement of the self-adhesive membrane specimens reached their maximum values. This suggests that a certain degree of aging positively affects the tensile properties of the membrane when applied in real-world projects. However, prolonged aging ultimately reduces the tensile properties of the self-adhesive membrane.

3.6. Waterproofing Membrane Peeling Performance

The bonding performance of the membrane was evaluated through seam peeling tests, conducted in accordance with GB/T 328.20-2007. The loading process for the seam peeling performance test is illustrated in Figure 9.

According to the specification “Test Methods for Building Sheets for Waterproofing” GB/T 328.20-2007 [26], the maximum force during the peeling process was taken as the maximum peel strength of the specimen, with the results presented in Figure 10. The peel strength of the unaged specimen was higher than that of the aged specimens, and as aging time increased, the peel strength gradually decreased. After 28 days of aging, the peel strength of the specimens decreased by 21%. Upon observation, it was noted that the surface of the aged specimens exhibited a gully-like texture caused by asphalt aggregation, which reduced the surface adhesion performance during the peel test. Additionally, the flow and self-adhesive properties of the asphalt in the aged specimens were weakened, further contributing to the decrease in peel strength.

4. Conclusions

In this study, a self-adhesive asphalt waterproofing membrane was subjected to a coupling aging test, and the low-temperature properties, tensile properties, and peeling properties of the membrane after aging were investigated. The degradation of the specimens due to coupled aging was analyzed using FTIR and SEM, leading to the following main conclusions:

After 28 days of coupled aging, the low-temperature flexibility of the specimens decreased from −28.5 °C in the unaged condition to −15 °C, indicating that aging had a significant impact on their low-temperature properties. Additionally, the peel strength decreased by 21%, reflecting the deterioration of surface adhesion properties, particularly in cases in which asphalt aggregation was prominent.

FTIR analysis revealed a significant increase in oxygen-containing functional groups, such as carbonyl (C=O) and sulfinyl (S=O), during the coupled aging process. This indicates that oxidation reactions occurred in the asphalt, leading to a reduction in the light components and causing the hardening and embrittlement of the specimens. These chemical changes negatively affected the material’s mechanical properties, particularly its low-temperature flexibility and adhesion performance.

The self-adhesive asphalt waterproofing membrane demonstrated good mechanical properties after short-term aging (7 days), indicating its ability to adapt to moderate aging conditions. However, with prolonged aging (28 days), its mechanical properties significantly declined, particularly in extreme temperature environments, where its durability performance was notably poor. Therefore, for practical engineering applications, it is recommended to enhance the long-term stability and aging resistance of the membrane in harsh environments by improving the material formulation and optimizing structural design.