Preparation and properties of optimized waterborne epoxy resin mixed with SBR modified emulsified asphalt

ABSTRACT

This study recommended a micro-surfacing cold-mix binder with good water stability, high- and low-temperature property and fast curing rate. Additionally, a dynamic water disturbance experiment method to evaluate the adhesion of composite modified emulsified asphalt was developed. Initially, the optimal SBR content is determined through performance tests, followed by selected a suitable WER system via film-forming experiments. Various WER-SBR composite-modified emulsified asphalt formulations are prepared by adjusting WER concentrations. The properties of WER-SBR modified emulsified asphalt were comprehensively evaluated using methods including penetration, softening point, ductility, Brookfield viscosity, storage stability, dynamic water disturbance experiment, dynamic shear rheometer, scanning electron microscopy, and fluorescence microscopy, and the appropriate range of WER content was discussed. The results of the study showed that when the SBR content was 3%, the comprehensive performance of the modified emulsified asphalt was optimal. The addition of WER could improved the high-temperature performance and adhesion of SBR modified emulsified asphalt, but it gradually weakened the low-temperature performance and storage stability. Based on the comprehensive evaluation of the experiments, if the modified emulsified asphalt is for immediate use, the recommended WER content is 6%–9%. If the modified emulsified asphalt needs to be stored for one day, the recommended WER content is below 4%.

Keywords:
Micro-surfacing binder; Composite-modified emulsified asphalt; Performance evaluation; Microcosmic mechanism; Modifier dosage

1. INTRODUCTION

Emulsified asphalt is a road construction material with low viscosity and good fluidity at room temperature. Its main production principle involves heating viscous asphalt, which is then mechanically stirred with water under the action of an emulsifier to form a water-in-oil emulsion [¹]. The primary advantages of emulsified asphalt include its usability at ambient temperatures and its ability to bond with cold and wet aggregates, making it particularly suitable for road construction requiring cold mixing. This characteristic provides emulsified asphalt with significant advantages in road construction, such as energy savings, reduced environmental pollution, minimized health hazards for workers, improved construction efficiency, and shortened road opening times [²]. However, emulsified asphalt is an unstable physical-chemical system [³], and the composition of conventional emulsified asphalt can no longer meet the growing demands of transportation. Therefore, polymer modification is an important means to enhance its service performance. In recent years, researchers have added styrene-butadiene-styrene (SBS) and SBR to emulsified asphalt, resulting in composite-modified emulsified asphalt with excellent high- and low-temperature performance [⁴]. XU et al. [⁵] studied waterborne acrylate and polyurethane as novel modifiers to further enhance the performance of SBS-SBR modified asphalt emulsions. Tests on storage stability and high-temperature performance indicating that waterborne cationic acrylate had a better modification effect on SBS-SBR asphalt emulsions, providing a new method for preparing high-performance cold adhesives. MO [⁶] prepared graphene oxide (GO)-SBS composite modified emulsified asphalt and studied the effect of GO on the performance of SBS modified emulsified asphalt. The results show that the addition of GO improves the high-temperature performance, aging resistance, and storage stability of SBS modified emulsified asphalt. The mixture made with GO-SBS composite modified emulsified asphalt exhibits excellent low-temperature crack resistance and can extend the service life of the pavement. In addition, experiments have shown that WER has a significant effect on improving the high-temperature performance and adhesion property of emulsified asphalt. As a result, research on WER modified emulsified asphalt has made considerable progress.

Waterborne epoxy resin is a thermosetting material [⁷], which is nontoxic and possesses the dual advantages of both waterborne materials and epoxy resins, such as low volatility, safety, environmental protection, and high bond strength after curing. WER can form a network structure within the emulsified asphalt system, significantly enhancing the high-temperature stability of the emulsified asphalt [⁸]. HAN et al. [⁹] prepared a WER modified emulsified asphalt for micro-surfacing mixtures. Through wet wheel abrasion tests and load wheel tests, they determined the optimal dosage range of aggregates and asphalt, and evaluated indicators such as interlayer adhesion and skid resistance, finding that the optimal WER content was 12%. WANG et al. [¹⁰] studied the effect of epoxy value on the high- and low-temperature performance and water stability of WER modified emulsified asphalt mixtures, showing that the mixture with an epoxy value of 20 and triethylenetetramine (TETA) as the curing agent had the best overall performance. However, due to the poor ductility and high-brittleness of waterborne epoxy resin after curing, it is prone to layer cracking in cold conditions when used as a bonding layer [¹¹]. Therefore, enhancing the toughness of WER modified emulsified asphalt has become a research focus.

ZHANG et al. [12] attempted to mix SBR latex with WER to prepare modified emulsified asphalt. They first determined the SBR latex content using the bonding method and differential scanning calorimetry, then established the WER content through storage stability tests. Further research on the three major indicators of evaporated residues of the composite-modified emulsified asphalt (i.e., penetration, softening point, and ductility), Brookfield viscosity tests, and 45-degree shear tests showed that the combined use of WER and SBR could improve the high- and low-temperature performance as well as the shear strength of the emulsified asphalt. YAO et al. [¹³] studied the modification effect of combined WER and SBR on emulsified asphalt and found that SBR improved the ductility, softening point, and penetration of evaporated residues of emulsified asphalt. When the WER content was 6% and the SBR content was 3%, the enhancement effect was significant, however, when the WER content exceeded 6%, it negatively impacted the cross-linked structure of SBR. LIU et al. [¹⁴] introduced a composite-modified emulsified asphalt using WER and SBR as a binder for micro-surfacing technology, addressing issues like peeling, flaking, and poor water stability. Through pavement performance and durability testing, they demonstrated that WER and SBR composite-modified emulsified asphalt micro-surfacing exhibited good water stability and durability.

Existing research has extensively discussed the effects of WER and SBR combination on the high- and low-temperature performance of emulsified asphalt [¹²,¹²,¹³,¹⁴,¹⁵], proving that under certain dosage conditions, their combined use has a beneficial improvement effect. However, the selection of waterborne epoxy resin when preparing WER-SBR modified emulsified asphalt still lacks evaluative criteria, and research on the adhesion of modified emulsified asphalt to aggregates is relatively scarce. Furthermore, the study of the reasonable dosage of modifiers is not sufficient, thus, comprehensive performance evaluation and mechanism analysis of WER-SBR composite-modified emulsified asphalt require substantial further research. Firstly, this paper sets up a film-forming experiment based on the paint film and putty film drying time determination method [¹⁶] to provide a method for screening waterborne epoxy systems. Secondly, it establishes modified emulsified asphalt with varying SBR dosages based on the highway engineering asphalt and asphalt mixture testing regulations [¹⁷], employing three major indicators, Brookfield rotational viscosity, and storage stability experiments to select an appropriate SBR dosage. Finally, based on the determined SBR dosage, it explores the mutual blending with different concentration gradients of WER and provides recommendations for suitable WER dosage based on macro and micro performance evaluations. This paper proposes a dynamic water disturbance test method for evaluating asphalt adhesion under specific conditions, combining the three major indicators of evaporated residues of modified emulsified asphalt, Brookfield viscosity, dynamic shear rheological experiments, and storage stability experiments to comprehensively assess the improvement effect of WER-SBR on the performance of emulsified asphalt. The distribution characteristics of WER-SBR in the evaporated residues of asphalt are observed using scanning electron microscopy (SEM), and the physicochemical reaction state of WER-SBR modified emulsified asphalt is studied using fluorescence microscopy to analyze the microscopic characteristics of WER-SBR composite-modified emulsified asphalt and elucidate the modification mechanism.

2. MATERIALS AND EXPERIMENTAL SCHEME

2.1. Raw materials

2.1.1. Matrix asphalt

Matrix asphalt is the main material for producing emulsified asphalt. In this study, 90# matrix asphalt is used for the experiments, and its performance parameters are shown in Table 1.

Table 1
Main parameters of 90# matrix asphalt.

ITEMS	PENETRATION (25°C,100 g,5 g)	SOFTENING POINT	DUCTILITY (15°C, 5 cm/min)	DYNAMIC VISCOSITY (60°C)
UNITS	0.1 mm	°C	cm	(Pa·s)
MEASURED VALUE	86.7	54.5	>100	186
REQUIREMENT	80–100	≥45	>100	≥160
PRINCIPLE	T0604	T0606	T0605	T0620

2.1.2. Emulsifier, stabilizer and defoamer

Emulsifier, stabilizer, and defoamer are primarily used for the laboratory preparation of matrix emulsified asphalt. In this study, a cationic slow-cracking fast-setting emulsifier was used, which has a dark brown appearance and a pH value of 0.5. The stabilizers used were anhydrous calcium chloride (CaCl₂) and polyvinyl alcohol (PVA). Anhydrous calcium chloride appears as white granules and is easily soluble in water, polyvinyl alcohol appears as a white powder and is difficult to dissolve in water at room temperature. The defoamer mainly consists of non-ionic surfactants such as organic fluorine and hydroxyl compounds, and has a milky white viscous fluid appearance.

2.1.3. SBR latex

This study used a specialized cationic SBR latex for modified emulsified asphalt, which has a milky white appearance and a measured pH value of 3.5, demonstrating good compatibility with emulsified asphalt.

2.1.4. WER and curing agent

This study initially selected three different types of waterborne epoxy systems, which include waterborne epoxy resin and curing agents. The role of the curing agent is to react with the waterborne epoxy resin, resulting in curing and forming strength [¹⁸]. The basic performance parameters of the three waterborne epoxy systems are shown in Table 2.

Table 2
Basic parameters of WER system.

(a) WERS-1
ITEMS	APPEARANCE	EPOXY EQUIVALENT	ROTATIONAL VISCOSITY	SOLID CONTENT	PH VALUE	PROPORTION
UNITS	–	(G/EQ)	(mPa·s)	(%)
WERA1	Milky white	400–800	<1000	50 ± 3	4.3	1.01–1.08
CURING AGENT B1	Faint yellow	–	>2000	44 ± 2	10.2	1.00–1.08
MIX RATIO	WERA1: Curing agent B1 = 2:1
(b) WERS-2
UNITS		mol/100g	(mPa·s)	(%)
WER A2	Milky white	0.26	1500–2000	50 ± 2	7.4	1.03–1.10
CURING AGENT B2	Faint yellow	–	>2000	44 ± 3	11.3	1.03–1.08
MIX RATIO	WERA2: Curing agent B2 = 1:1
(c) WERS-3
UNITS		mol/100g	(mPa·s)	(%)
WER A3	Milky white	0.52	<1000	50 ± 3	6.8	1.03–1.05
CURING AGENT B3	Faint yellow	–	6500–9000	50 ± 1	10.6	1.05–1.08
MIX RATIO	WER A3: Curing agent B3 = 100:85

2.2. Experimental scheme

2.2.1. Preparation of matrix emulsified asphalt

After heated 400g of distilled water to 80°C, 0.6g of polyvinyl alcohol (PVA) and 0.6g of anhydrous calcium chloride (CaCl₂) are added separately, and stirred with a glass rod until the PVA dissolves. Then, a cationic slow-cracking fast-setting emulsifier is added, and stirring continues for 5 minutes. Finally, 0.05g of defoamer is added, and after thorough mixing, an emulsifier solution is obtained, which is kept warm at around 65°C for later use. Meanwhile, 600g of 90# base asphalt is heated in an oven to 150°C and maintained for 1 hour. Once all materials are prepared, boiling water is poured into a colloid mill, and the mill is operated for about 2 minutes for preheating. The emulsifier solution is then added to the colloid mill and mixed for 30 seconds, followed by slowly pouring in the base asphalt. After shearing the asphalt and solution in the colloid mill for 5 minutes, the outlet of the colloid mill can be opened, producing a dark brown base emulsified asphalt. The basic performance tests of the prepared emulsified asphalt are shown in Table 3.

Table 3
Basic performance of matrix asphalt.

ITEMS	UNITS	TEST RESULTS
PENETRATION(25°C)	0.1mm	94.2
SOFTENING POINT	°C	55.7
DUCTILITY(15°C)	cm	58.6
ROTATIONAL VISCOSITY	mPa·s	561.15
SOLID CONTENT	%	60.2
5D STORAGE STABILITY	%	4.87
RESIDUAL CONTENT ON THE SIEVE	%	0.02

2.2.2. Preparation and dosage determination of SBR modified emulsified asphalt

SBR latex was added to the matrix emulsified asphalt in concentration gradients of 1%, 2%, 3%, 4%, and 5%, respectively. The mixture was stirred for 5 minutes using an emulsifying shear machine to prepare SBR modified emulsified asphalt [¹⁹]. The prepared SBR modified emulsified asphalt was tested for the three main indices, Brookfield rotational viscosity, and storage stability. Based on the performance test results, the optimal SBR content was determined.

2.2.3. Preparation of WER-SBR modified emulsified asphalt

2.2.3.1. Selection of the waterborne epoxy system

The performance of the waterborne epoxy resin system directly affects the quality of the modified emulsified asphalt [²⁰]. Since the curing rate of the modified emulsified asphalt influences its early strength and setting time [²¹], this study uses a film-coating experiment to select a waterborne epoxy system, with a fast curing rate as an additive for the modified emulsified asphalt.

The room-temperature film-coating experiment was conducted to screen the three waterborne epoxy systems listed in Table 2. The process involved evenly applying each of the three systems onto clean glass plates, marking them, and storing them at room temperature (25°C). The drying time of the coating was measured following the GB-T 1728-2020 test procedure (GB/T 1728-2020 2020), and the initial and final setting times were determined using the finger-touch and blade methods. The waterborne epoxy system with the fastest curing reaction was selected for this study.

2.2.3.2. Preparation of WER-SBR composite modified emulsified asphalt

SBR modified emulsified asphalt is prepared using the determined SBR dosage first. Subsequently, varying concentrations of 1%, 2%, 3%, 4%, 5%, 6%, 9%, and 12% of WER are added to the SBR modified emulsified asphalt, and the mixture is mechanically stirred for 2 minutes using a shear mixer, next preparing the WER-SBR composite modified emulsified asphalt with different WER contents.

2.3. Performance study of WER-SBR modified emulsified asphalt

2.3.1. Basic performance tests

Evaporated residues of WER-SBR composite-modified emulsified asphalt with varying WER dosages were prepared. These residues underwent tests for three main indicators [²²] and Brookfield rotational viscosity at 135°C to evaluate their high- and low-temperature performance.

2.3.2. Dynamic shear rheological performance

This study utilizes a Dynamic Shear Rheometer (DSR) to perform temperature scanning on the evaporation residues of WER-SBR modified emulsified asphalt. Evaporation residues of modified asphalt with 3%, 6%, 9%, and 12% WER and 3% SBR were set as the experimental group, the 3% SBR modified emulsified asphalt without WER was set as the control group. The temperature range for the experiments was set between 52°C and 82°C, with data collected at 6°C intervals. The variations of the complex shear modulus (G*) and phase angle (δ) with temperature are analyzed, and the rutting resistance of the modified emulsified asphalt under high-temperature conditions is evaluated using the rutting factor (G*/sinδ).

2.3.3. Adhesion

The existing method for evaluating asphalt adhesion primarily involves the boiling water method, where coarse aggregates coated with an asphalt film are immersed in boiling water. The adhesion between asphalt and aggregate is assessed by evaluating changes in the weight of the aggregates and the morphology of the asphalt film after immersion [²³]. A limitation of the boiling water method is that the water’s action on the aggregates is static, however, in actual operation, water flow on asphalt pavements has an erosive effect. Therefore, this study references the boiling water method and designs a dynamic water disturbance test. The experimental principle involves using a mechanical device to induce movement in the boiling water within the container, flushing the coarse aggregates coated with emulsified asphalt. Adhesion performance of the modified emulsified asphalt is assessed by evaluating the morphology and detachment rate of the asphalt film on the aggregate surface after flushing with boiling water [²⁴, ²⁵].

The experimental process is as follows: Coarse aggregates are cleaned, dried, and weighed, then suspended using fine string. After immersion in modified emulsified asphalt for 45 seconds, they are removed, hung, dried, and weighed for later use. A beaker filled with distilled water is placed on an electric stove and heated to a gentle boil, with a mechanical stirrer submerged to create water movement. The prepared aggregates are then suspended and immersed in the moving water for 3 minutes, after which they are removed, hung to dry, and weighed again. The adhesion of the aggregates to the asphalt film is evaluated by calculating the detachment rate index, using the following formula:

(1) $$\text{α}=\frac{(m_2-m_3)}{(m_2-m_3)}\times 100\%$$

In the equation, α represents the asphalt detachment rate, m₁ is the weight of the dry aggregate without asphalt coating, m₂ is the weight of the aggregate after being coated with asphalt, and m₃ is the weight of the asphalt and aggregate after being subjected to dynamic water disturbance. The adhesion index of the aggregate is typically represented as (1 – α). This study utilizes a shear machine to generate dynamic water, the experimental equipment is shown in the Figure 1.

Figure 1
Schematic of dynamic water disturbance experiment: (a) schematic diagram of the experiment apparatus; (b) experimental condition of the aggregate.

Different dosages of composite modified emulsified asphalt with varying WER content are subjected to dynamic water disturbance experiments. The condition of the asphalt film wrapping the aggregate surface is observed, and changes in aggregate weight are measured to calculate the asphalt film detachment rate, thereby evaluating the adhesion of the composite modified emulsified asphalt [²⁶].

2.3.4. Storage stability

Take 100g of WER-SBR composite modified emulsified asphalt with varying WER contents and pour them into sealed transparent sample cups. Set SBR modified emulsified asphalt as the control group. Let the samples stand at room temperature (25°C) for one day, and periodically record the state of the modified emulsified asphalt to evaluate its storage stability [²⁷].

2.3.5. Micro-morphology test

WER-SBR composite modified emulsified asphalt residues with WER concentrations of 4%, 9%, and 12% were prepared. Scanning electron microscopy (SEM) was used to observe the distribution of WER and SBR within the modified asphalt and evaluate their compatibility [²⁸]. Additionally, an Olympus IX73 fluorescence microscope captured images of WER-SBR composites at WER concentrations of 0%, 3%, 6%, 9%, and 12%, analyzed the micro-structure and physical-chemical reactions to clarify the modification mechanism [²⁹,³⁰,³¹].

3. RESULTS AND DISCUSSION

3.1. Determination of SBR dosage

3.1.1. Basic performance

Penetration, softening point, and ductility tests were conducted on the evaporation residues of SBR modified emulsified asphalt with SBR dosages of 1%, 2%, 3%, 4%, and 5%. The ductility at 5°C for the specimen with 1% SBR latex was 89.7 cm, while the ductility results for specimens with 2% or more SBR latex were all greater than 100 cm. This indicates that SBR modified emulsified asphalt with the above dosages exhibits excellent low-temperature ductility and plasticity. The penetration and softening point test results are shown in Figure 2.

Figure 2
Softening point and penetration of SBR modified emulsified asphalt.

Figure 2 shows that as the SBR latex content increased, the softening point temperature of the modified emulsified asphalt gradually rose, indicating an effective improvement in the high-temperature stability of the emulsified asphalt. Because SBR is a block copolymer material, when it is used as a modifier and added to emulsified asphalt, the SBR particles are evenly and stably dispersed within the asphalt components. This dispersion fills the spaces between asphalt molecules and forms a cross-linked structure, which enhances the asphalt’s resistance to deformation at high temperatures, thereby increasing the softening point of the modified emulsified asphalt. Furthermore, the base emulsified asphalt prepared in this study is a cationic emulsified asphalt. Since its charge type is similar to that of cationic SBR latex, the two exhibit good compatibility, which improves the overall performance of the emulsified asphalt. Meanwhile, the penetration of the modified emulsified asphalt decreases, suggesting that with the addition of SBR latex, the modified emulsified asphalt becomes more viscous at room temperature.

In summary, SBR latex significantly enhances the high-temperature stability of emulsified asphalt.

3.1.2. Brookfield viscosity

Rotational viscosity tests at 135°C were conducted using a Brookfield viscometer on modified emulsified asphalt with different SBR contents. Results are shown in Figure 3.

Figure 3
Brookfield viscosity of SBR modified emulsified asphalt.

Figure 3 shows that as the SBR latex content increased, the Brookfield viscosity of the modified emulsified asphalt also increased, with a particularly significant rose observed at a 5% SBR content.

3.1.3. Storage stability

Samples of modified emulsified asphalt with SBR contents of 0%, 1%, 2%, 3%, 4%, and 5% were placed in sealed sample cups and stored at room temperature for one day. The state changes of the emulsified asphalt were observed to evaluate its storage stability. The experimental results are shown in Table 4.

Table 4
Storage stability evaluation of SBR modified emulsified asphalt.

PHENOMENON ANALYSIS	PICTURE PRESENTATION
Initial State: All six groups of modified emulsified asphalt are brownish-black liquids with no signs of coagulation or sedimentation. After two hours of standing, there are no changes observed in any of the modified emulsified asphalt groups, as shown in the figure on the right.
After 8 hours of standing, slight oil-water separation was observed in all sample groups. After 14 hours, the modified emulsified asphalt with 5% SBR dosage exhibited wall clinging, indicating the occurrence of phase separation of the SBR modifier. After 24 hours of storage, as shown in the figure on the right, white precipitates appeared on the surface of the modified emulsified asphalt containing SBR latex, with the amount of precipitate increasing with higher SBR dosages. Additionally, the separation of asphalt from water became more pronounced with increasing SBR content, particularly evident in the samples with 4% and 5% SBR modified emulsified asphalt.

Table 4 indicates that as the SBR dosage increases, the storage stability of the modified emulsified asphalt gradually decreases, suggesting that the SBR content should not exceed 3%.

Based on a comprehensive analysis of the three key parameters, Brookfield rotational viscosity, and storage stability experimental results, this study selects a 3% SBR latex dosage combined with WER for composite modification of the emulsified asphalt.

3.2. Selection of waterborne epoxy resin system

This study used three types of water-based epoxy resins and curing agents to observe the initial and final curing times through film coating experiments, in order to selected the water-based epoxy system with a fast curing reaction speed. This experiment used the waterborne epoxy resin system mentioned earlier, Labeled from left to right as: WERS-1, WERS-2, WERS-3. The experimental samples are shown in Figure 4.

Figure 4
Film coating experiment of water-based epoxy system: (a) WERS-1, WERS-2, WERS-3 before curing, (b) cured WERS-1, WERS-2, WERS-3.

After completed the film application of the water-based epoxy system, the samples were observed every 10 minutes, and the curing status was checked by gently touching the surface of the glass plate with a finger. The curing times of the three water-based epoxy systems are shown in Figure 5.

Figure 5
Result of the waterborne epoxy system film application experiment.

As shown in Figure 4, the film-forming effect of WERS-1 is denser than that of the other two groups. Figure 5 indicates that WERS-1 has the fastest curing rate, with an initial curing time of a hour and 20 minutes and a final curing time of 5 hours and 20 minutes. These results demonstrated that WERS-1 not only cures quickly but also has a superior curing structure. Therefore, this study selected WERS-1 as the modifier for the WER-SBR composite modified emulsified asphalt.

Through the coating film experiment, the initial and final setting times of the waterborne epoxy resin (WER) can be easily observed and recorded, allowing the assessment of its curing and setting speed. This served as a simple experimental method for evaluating WER performance, with the curing reaction speed of WER used as an indicator for performance evaluation.

3.3. Performance study of WER-SBR composite modified emulsified asphalt

3.3.1. Basic performance

The evaporation residues of WER-SBR composite modified emulsified asphalt with WER contents of 1%, 2%, 3%, 4%, 5%, 6%, 9%, and 12% (labeled as WER-1, WER-2, WER-3, WER-4, WER-5, WER-6, WER-9, WER-12) were subjected to the three major index experiments. The results for penetration and softening point are shown in Figure 6, while the results for ductility are presented in Table 5.

Figure 6
Penetration and softening point of WER-SBR composite modified emulsified asphalt.

Table 5
5°C ductility of WER-SBR composite modified emulsified asphalt.

WER DOSAGE (%)	0	1	2	3	4	5	6	9	12
DUCTILITY (CM)	>100	>100	>100	>100	>100	>100	>100	>100	5.5

As shown in Figure 6, the penetration of the composite modified emulsified asphalt gradually decreased with the increasing content of water-based epoxy resin. This is attributed to the formation of a cross-linked network structure after the curing of the water-based epoxy resin, which enhanced the stiffness of the evaporation residue of the emulsified asphalt, resulted in a sharp decrease in the penetration. Meanwhile, due to the excellent high-temperature performance of WER, the softening point of the modified emulsified asphalt increased with the rising concentration of WER.

As shown in Table 5, the 5°C elongation of modified emulsified asphalt with 12% WER content is only 5.5 cm, indicating high stiffness and poor ductility. This is because the high WER content leads to the formation of a continuous network structure within the asphalt after the epoxy resin cures, encapsulated the asphalt and significantly reducing its ductility, resulted in brittleness. The 5°C elongation of WER-SBR composite modified emulsified asphalt with WER content below 9% exceeds 100 cm, showing good ductility.

3.3.2. Evaluation of high-temperature rheological performance

Samples of WER-SBR composite modified emulsified asphalt with WER content of 0%, 3%, 6%, 9%, and 12% were prepared, and their evaporative residues were subjected to Dynamic Shear Rheometer (DSR) tests. The changes in complex shear modulus (G*) and phase angle (δ) with temperature were analyzed, and the rutting factor (G*/sinδ) was calculated to evaluate the deformation resistance of different modified emulsified asphalts under high-temperature conditions. The test results are shown in Figure 7.

Figure 7
DSR test results of WER-SBR composite modified emulsified asphalt.

As shown in Figure 7, with the increased in WER content, the phase angle of the modified emulsified asphalt decreased at each test temperature, while the complex shear modulus and rutting factor increase. This indicates an improvement in the asphalt’s elastic recovery and a significant enhancement in its high-temperature deformation resistance. When the WER content is below 6%, the phase angle reduction exhibits some delay, but when the content reaches 9% or higher, this delay becomes less apparent, and the phase angle decreases sharply as the temperature rises. This suggests that increasing the WER content enhances the asphalt’s temperature stress response. When the WER content reaches 12%, the complex shear modulus and rutting factor of the modified emulsified asphalt increase significantly, which correlates with the earlier finding of increased stiffness. The analysis shows that adding WER effectively improves the high-temperature performance of SBR modified emulsified asphalt, consistent with the results of the penetration and softening point tests.

3.3.3. Brookfield rotational viscosity test

Rotational viscosity tests at 135°C were conducted on WER-SBR composite modified emulsified asphalt with WER contents of 1%, 2%, 3%, 4%, 5%, 6%, 9%, and 12%. The test results are shown in Figure 8.

Figure 8
Brookfield viscosity of WER-SBR composite modified emulsified asphalt.

As shown in Figure 8, the Brookfield viscosity of the composite modified emulsified asphalt initially increases and then decreases as the WER content increases. At lower WER contents, a continuous cross-linked structure cannot form, resulting in a relatively small increase in viscosity. As the WER content increased, sufficient curing occurs to form a continuous cross-linked network, which raises the viscosity of the modified emulsified asphalt. However, an excessive amount of WER not only alters the physical state of the emulsified asphalt but also impairs its performance, leading to incomplete curing between WER and SBR, which reduces the viscosity. Therefore, the WER content should not exceed 9%.

3.3.4. Adhesion evaluation

Prepare base emulsified asphalt, modified emulsified asphalt with 3% SBR content, and composite modified emulsified asphalt with combined SBR and WER contents of 3%, 6%, 9%, and 12%. Use the dynamic water disturbance test method to conduct adhesion tests on the modified emulsified asphalts, calculating the asphalt stripping rate index and adhesion rate. The results are shown in Figure 9, and the appearance of the aggregate coated with asphalt after the dynamic water disturbance test is shown in Figure 10.

Figure 9
Stripping rate and adhesion rate of asphalt.

Figure 10
Morphology of asphalt-aggregate attachment after dynamic water disturbance test: (a) matrix emulsified asphalt, (b) 0%WER+3%SBR, (c) 3%WER+3%SBR, (d) 6%WER+3%SBR, (e) 9%WER+3%SBR, (f) 12%WER+3%SBR.

The dynamic water disturbance test revealed that the ordinary emulsified asphalt film on the surface of the aggregate exhibited significant peeling, especially at the edges, where the asphalt nearly completely detached, resulting in a detachment rate index of 56.7%, indicating poor adhesion and water stability. The aggregate coated with 3% SBR emulsified asphalt showed considerable improvement in appearance, the damage to the asphalt film was less pronounced, with a honeycomb-like structure observed and only minor wear at the edges. The detachment rate index for this sample was 36.37%. For aggregates coated with WER modified emulsified asphalt, the asphalt film remained relatively intact after the dynamic water disturbance test, and the detachment rate significantly decreased. When the WER content reached 9%, the detachment rate was only 14.29%, reflecting a 42.41% improvement over ordinary emulsified asphalt. However, when the WER content increased to 12%, the wear and detachment of the asphalt film became severe again, with the detachment rate rising to levels comparable to those at 3% WER, indicating that the WER content should not exceed 9%. The incorporation of WER effectively enhanced the adhesion and water stability of the emulsified asphalt.

3.3.5. Storage stability test

Different WER content composite modified emulsified asphalts were placed in open containers and kept at room temperature for one day. The state changes of the emulsified asphalt were observed to evaluate the storage stability of the WER-SBR composite modified emulsified asphalt. The experimental results are shown in Table 6.

Table 6
Assessment of the storage stability of WER-SBR composite modified emulsified asphalt.

PHENOMENON ANALYSIS	PICTURE PRESENTATION
Initial State:All groups of composite modified emulsified asphalt are dark brown liquids with no signs of coagulation or precipitation, as shown in the figure on the right.
After two hours of storage, the modified emulsified asphalt with 12% WER content exhibited significant coagulation and precipitation, making it unusable. After eight hours, the 12% WER sample had completely solidified, while the 9% WER sample showed wall adhesion, other groups displayed light yellow precipitates. After fourteen hours, the 9% WER sample experienced considerable coagulation and sedimentation, and the 5% and 6% WER samples also showed wall adhesion. After one day of storage, the modified emulsified asphalts displayed light yellow precipitates, as shown in the right image. The samples with 4%–6% WER content exhibited wall adhesion, and those with 5% and 6% WER also showed sedimentation. In contrast, the samples with 1%–3% WER content only exhibited light yellow precipitate.

3.3.6. SEM experimental Analysis

Samples of evaporated residue from WER-SBR composite modified emulsified asphalt with 4%, 9%, and 12% WER content were selected for SEM observation to analyze the micro-structure. The results are shown in Figure 11.

Figure 11
SEM results of composite modified emulsified asphalt with different WER contents: (a) 4% WER dosage, (b) 9%WER dosage, (c)12% WER dosage.

The SEM results indicate that when the WER content is at 4%, a large number of irregular folds form within the SBR modified emulsified asphalt. This is due to the breaking of the emulsion and the cross-linking structure formed between the cured WER and SBR. At 9% WER content, the spatial three-dimensional structure of the modified asphalt becomes more pronounced, indicating a stronger bond between WER and SBR. However, when the WER content reaches 12%, there is a fractured three-dimensional structure between WER and SBR, attributed to the rapid curing of excessive WER, which prevents the formation of a complete cross-linked structure in the asphalt, leading to the breakage of some SBR particles. Combined with the ductility test results, it is evident that 12% WER content is excessive, compromising the cross-linked structure of the emulsified asphalt and thus degrading its performance.

3.3.7. Fluorescence microscopy analysis

In this experiment, fluorescence microscopy was performed on WER-SBR composite modified emulsified asphalts with WER contents of 0%, 3%, 6%, 9%, and 12%. The results are shown in Figure 12.

Figure 12
Fluorescence images of composite modified emulsified asphalt with different WER contents: (a) 0%WER dosage, (b) 3%WER dosage, (c) 6%WER dosage, (d) 9%WER dosage, (e) 12%WER dosage.

The results of the fluorescence microscopy experiment showed that the SBR modified emulsified asphalt with 0% WER content exhibits no visible network structure, with SBR particles randomly distributed throughout the asphalt. In the composite modified emulsified asphalt with 3% WER, due to the lower WER content and smaller particle size, a limited and scattered network structure is formed in the asphalt. For the composite modified emulsified asphalt with 6% WER, a clear three-dimensional cross-linked network structure is visible, with a more uniform and dense distribution. In the modified emulsified asphalt with 9% WER, the WER distribution becomes denser, though slightly less uniform. Overall, the 9% WER composite modified emulsified asphalt exhibits a very clear and tighter cross-linked network. In contrast, the composite modified emulsified asphalt with 12% WER shows a looser WER distribution compared to those with 6% and 9% WER, indicating that the higher concentration of WER results in incomplete curing, which negatively affects its cross-linking and causes the asphalt to become brittle. As a result, the toughness of the asphalt with 12% WER content significantly declines compared to other concentrations.

To further investigate the distribution of WER in modified emulsified asphalt, a binarized conversion of the fluorescence images was performed, as shown in Figure 13.

Figure 13
Binarized images of the composite modified emulsified asphalt with different WER contents: (a) 0%WER dosage, (b) 3%WER dosage, (c) 6%WER dosage, (d) 9%WER dosage, (e)12%WER dosage.

To more intuitively analyze the distribution and structural state of WER in the emulsified asphalt, the area of the binarized fluorescence microscopy images of the modified emulsified asphalt was measured. The fractal dimension of the binarized images was calculated using the box-counting method [³²], with the formula as follows [³³]:

(2) $$D\text{=}\underset{\epsilon =0}{\text{lim}}\frac{\log (N(\epsilon ))}{\log (1/\epsilon )}$$

In the formula: D represents the fractal dimension, which describes the complexity of the structure. The larger the fractal dimension, the denser the micro-structure of the modified emulsified asphalt. N(ε) is the number of boxes that can cover the entire fractal object, and ε is the side length of the boxes, approaching zero.

The fluorescence area ratio and fractal dimension of the modified emulsified asphalt are shown in Figure 14.

Figure 14
Fluorescence area ratio and fractal dimension of modified emulsified asphalt.

The results in Figure 14 show that as the WER content increases, both the fluorescent area ratio and fractal dimension of the emulsified asphalt initially increase and then decrease. From the figure, it can be observed that when the WER content is between 3% and 6%, the area ratio of WER increases the most significantly. This is because at lower WER contents, a compact cross-linked network structure cannot form in the emulsified asphalt, resulting in a more dispersed distribution of WER. As the WER content increases, the fluorescent area of the asphalt increases, and the fractal dimension also rises, indicating a more uniform and dense WER distribution. When the WER content is between 6% and 9%, the increase in both the fluorescent area ratio and fractal dimension slows down, suggesting that at 6% WER content, the curing reaction is sufficiently effective, and further increases in WER content do not significantly enhance the internal curing reaction. When the WER content reaches 12%, both the fluorescent area ratio and fractal dimension begin to decrease, indicating a reduction in the cross-linked network structure within the asphalt. This analysis suggests that WER contents of 6% to 9% allow for a uniform distribution in the emulsified asphalt and result in a well-formed cross-linked network structure.

4. CONCLUSION

This study prepared high-performance composite modified emulsified asphalt using a method of emulsification followed by modification, which can be used as a cold-mix binder. The paper first determined the appropriate dosage of the SBR modifier and then conducted comprehensive testing and micro-structural analysis on the properties of WER-SBR composite modified emulsified asphalt with different WER contents. Main research conclusions are summarized as follows:

• (1)

  When only SBR emulsion is added to the base emulsified asphalt, the modified emulsified asphalt showed significant improvements in low-temperature ductility, high-temperature stability, and viscosity. However, the storage stability decreased as the SBR content increased. After comprehensive analysis, it was determined that the optimal SBR content is 3%. When the WER is additionally incorporated into the SBR modified emulsified asphalt, the composite modified emulsified asphalt exhibited further improvement in high-temperature performance and resistance to water stripping. However, when the WER content increases to 12%, the low-temperature ductility of the modified emulsified asphalt deteriorated significantly. It was concluded that the optimal WER content for the best performance is 9%.

• (2)

  The micro-structure of composite modified emulsified asphalt with different WER contents was analyzed through SEM and fluorescence microscopy experiments. The results indicating that when the WER content is 6% and 9%, the WER and SBR form a well-developed network structure in the modified emulsified asphalt, and the WER is distributed more evenly. However, when the WER content reaches 12%, cracks appeared on the surface of the emulsified asphalt, and the fluorescent area of WER decreased. This suggests that at high WER contents, the curing rate is too fast, preventing proper reaction with the curing agent and leading to incomplete reactions within the waterborne epoxy system. This, in turn, results in a deterioration of the performance of the modified emulsified asphalt.

• (3)

  The workability time of WER-SBR composite modified emulsified asphalt was evaluated through storage stability experiments. The results show that as the WER content increased, the curing rate of the modified emulsified asphalt accelerated, leading to a gradual deterioration in the storage stability of the composite modified emulsified asphalt. For immediate-use applications, it is recommended to choose a WER content of 6% to 9%, while for applications requiring one day of storage, the WER content should be below 4%.

5. ACKNOWLEDGMENTS

This project was supported by the Technology Application of Liaoning province (NO.2023JH2/101300140), National Natural Science Foundation of China (No.52108402), Basic Science Foundation of Liaoning (No.LJKMZ20220833).

6. BIBLIOGRAPHY

• ^[1] ZIARI, H., KEYMANESH, M.R., ZALNEZHAD, H., “Effect of emulsifying agent on rheological properties of bitumen emulsion modified with different techniques of adding SBR latex polymer”, Road Materials and Pavement Design, v. 23, n. 3, pp. 639–655, 2022. doi: http://doi.org/10.1080/14680629.2020.1835695.
  » https://doi.org/10.1080/14680629.2020.1835695
• ^[2] ZOU, G., ZHANG, J., LIU, X., et al, “Design and performance of emulsified asphalt mixtures containing construction and demolition waste”, Construction & Building Materials, v. 239, pp. 117846, 2020. doi: http://doi.org/10.1016/j.conbuildmat.2019.117846.
  » https://doi.org/10.1016/j.conbuildmat.2019.117846
• ^[3] LIU, B., LIANG, D., “Influence of SBS and SBR on the properties of emulsified asphalt”, Petroleum Science and Technology, v. 35, n. 10, pp. 1008–1013, 2017. doi: http://doi.org/10.1080/10916466.2017.1303720.
  » https://doi.org/10.1080/10916466.2017.1303720
• ^[4] MENG, Y., CHEN, J., KONG, W., et al, “Review of emulsified asphalt modification mechanisms and performance influencing factors”, Journal of Road Engineering, v. 3, n. 2, pp. 141–155, 2023. doi: http://doi.org/10.1016/j.jreng.2023.01.006.
  » https://doi.org/10.1016/j.jreng.2023.01.006
• ^[5] XU, L., LI, X., ZONG, Q., et al, “Chemical, morphological and rheological investigations of SBR-SBS modified asphalt emulsions with waterborne acrylate and polyurethane”, Construction & Building Materials, v. 272, pp. 121972, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2020.121972.
  » https://doi.org/10.1016/j.conbuildmat.2020.121972
• ^[6] MO, Z., “Study on the performance and aging low temperature performance of GO/SBS modified asphalt”, Matéria (Rio de Janeiro), v. 28, n. 1, pp. e20230151, 2023. doi: http://doi.org/10.1590/1517-7076-rmat-2023-0151.
  » https://doi.org/10.1590/1517-7076-rmat-2023-0151
• ^[7] LIU, F., ZHENG, M., FAN, X., et al, “Properties and mechanism of waterborne epoxy resin-SBR composite modified emulsified asphalt”, Construction & Building Materials, v. 274, pp. 122059, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2020.122059.
  » https://doi.org/10.1016/j.conbuildmat.2020.122059
• ^[8] ÇUBUK, M., GÜRÜ, M., ÇUBUK, M.K., “Improvement of bitumen performance with epoxy resin”, Fuel, v. 88, n. 7, pp. 1324-1328, 2009. doi: http://doi.org/10.1016/j.fuel.2008.12.024.
  » https://doi.org/10.1016/j.fuel.2008.12.024
• ^[9] HAN, S., YAO, T., HAN, X., et al, “Performance evaluation of waterborne epoxy resin modified hydrophobic emulsified asphalt micro-surfacing mixture”, Construction & Building Materials, v. 249, pp. 118835, 2020. doi: http://doi.org/10.1016/j.conbuildmat.2020.118835.
  » https://doi.org/10.1016/j.conbuildmat.2020.118835
• ^[10] WANG, L., ZHANG, Z., LIU, W., et al, “Effects of epoxy resin value on waterborne-epoxy-resin-modified emulsified asphalt mixture performance”, Applied Sciences (Basel, Switzerland), v. 14, n. 4, pp. 1353, 2024. doi: http://doi.org/10.3390/app14041353.
  » https://doi.org/10.3390/app14041353
• ^[11] CAI, X., HUANG, W., LIANG, J., et al, “Study of pavement performance of thin-coat waterborne epoxy emulsified asphalt mixture”, Frontiers in Materials, v. 7, pp. 88, 2020. doi: http://doi.org/10.3389/fmats.2020.00088.
  » https://doi.org/10.3389/fmats.2020.00088
• ^[12] ZHANG, Q., XU, Y., WEN, Z., “Influence of water-borne epoxy resin content on performance of waterborne epoxy resin compound SBR modified emulsified asphalt for tack coat”, Construction & Building Materials, v. 153, pp. 774-782, 2017. doi: http://doi.org/10.1016/j.conbuildmat.2017.07.148.
  » https://doi.org/10.1016/j.conbuildmat.2017.07.148
• ^[13] YAO, X., TAN, L., XU, T., “Preparation, properties and compound modification mechanism of waterborne epoxy resin-styrene butadiene rubber latex modified emulsified asphalt”, Construction & Building Materials, v. 318, pp. 126178, 2022. doi: http://doi.org/10.1016/j.conbuildmat.2021.126178.
  » https://doi.org/10.1016/j.conbuildmat.2021.126178
• ^[14] LIU, F., ZHENG, M., LIU, X., et al, “Performance evaluation of waterborne epoxy resin-SBR composite modified emulsified asphalt fog seal”, Construction & Building Materials, v. 301, pp. 124106, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2021.124106.
  » https://doi.org/10.1016/j.conbuildmat.2021.124106
• ^[15] LIU, F., ZHENG, M., FAN, X., et al, “Performance evaluation of waterborne epoxy resin-SBR compound modified emulsified asphalt micro-surfacing”, Construction & Building Materials, v. 295, pp. 123588, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2021.123588.
  » https://doi.org/10.1016/j.conbuildmat.2021.123588
• ^[16] CHINESE STANDARD, GB/T 1728-2020: Determination of drying time of coating and putty films, Beijing, China, National Standards of the People’s Republic of China, 2020.
• ¹⁷ [17] CHINESE STANDARD, JTG E20-2011: Standard test methods of bitumen and bituminous mixtures for Highway Engineering, Beijing, China, National Standards of the People’s Republic of China, 2011.
• ^[18] LI, R., LENG, Z., ZHANG, Y., et al, “Preparation and characterization of waterborne epoxy modified bitumen emulsion as a potential high-performance cold binder”, Journal of Cleaner Production, v. 235, pp. 1265–1275, 2019. doi: http://doi.org/10.1016/j.jclepro.2019.06.267.
  » https://doi.org/10.1016/j.jclepro.2019.06.267
• ^[19] ZHANG, Y.J., CAO, D.W., ZHANG, H.Y., et al, “The study of curing characteristics of epoxy asphalt”, Advanced Materials Research, v. 785, pp. 295–299, 2013. doi: http://doi.org/10.4028/www.scientific.net/AMR.785-786.295.
  » https://doi.org/10.4028/www.scientific.net/AMR.785-786.295
• ^[20] YAO, X., XU, H., XU, T., “Mechanical properties and enhancement mechanisms of cold recycled mixture using waterborne epoxy resin-styrene butadiene rubber latex modified emulsified asphalt”, Construction & Building Materials, v. 352, pp. 129021, 2022. doi: http://doi.org/10.1016/j.conbuildmat.2022.129021.
  » https://doi.org/10.1016/j.conbuildmat.2022.129021
• ^[21] SHENG, X., MO, R., MA, Y., et al, “Waterborne epoxy resin-polydopamine modified zirconium phosphate nanocomposite for anticorrosive coating”, Industrial & Engineering Chemistry Research, v. 58, n. 36, pp. 16571–16580, 2019. doi: http://doi.org/10.1021/acs.iecr.9b02557.
  » https://doi.org/10.1021/acs.iecr.9b02557
• ^[22] YANG, J., ZHANG, Z., FANG, Y., et al, “Performance characterization of waterborne epoxy resin and styrene-butadiene rubber latex composite modified asphalt emulsion (WESAE)”, Coatings, v. 10, n. 4, pp. 352, 2020. doi: http://doi.org/10.3390/coatings10040352.
  » https://doi.org/10.3390/coatings10040352
• ^[23] ZHANG, X., WEI, Y., GAO, Y., et al, “Laboratory evaluation on performance of emulsified asphalt modified by reclaimed ion exchange resin”, Construction & Building Materials, v. 364, pp. 129994, 2023. doi: http://doi.org/10.1016/j.conbuildmat.2022.129994.
  » https://doi.org/10.1016/j.conbuildmat.2022.129994
• ^[24] YANG, G., WANG, C., FU, H., et al, “Waterborne epoxy resin-polyurethane-emulsified asphalt: Preparation and properties”, Journal of Materials in Civil Engineering, v. 31, n. 11, pp. 04019265, 2019. doi: http://doi.org/10.1061/(ASCE)MT.1943-5533.0002904.
  » https://doi.org/10.1061/(ASCE)MT.1943-5533.0002904
• ^[25] ZHANG, Y.J., WU, W.M., CAO, H.S., et al, “Investigation and evaluation of the emulsified asphalt with waterborne epoxy resin”, Key Engineering Materials, v. 842, pp. 337–345, 2020. doi: http://doi.org/10.4028/www.scientific.net/KEM.842.337.
  » https://doi.org/10.4028/www.scientific.net/KEM.842.337
• ^[26] GU, Y., TANG, B., HE, L., et al, “Compatibility of cured phase-inversion waterborne epoxy resin emulsified asphalt”, Construction & Building Materials, v. 229, pp. 116942, 2019. doi: http://doi.org/10.1016/j.conbuildmat.2019.116942.
  » https://doi.org/10.1016/j.conbuildmat.2019.116942
• ^[27] WANG, T., DRA, Y.A.S.S., CAI, X., et al, “Advanced cold patching materials (CPMs) for asphalt pavement pothole rehabilitation: State of the art”, Journal of Cleaner Production, v. 366, pp. 133001, 2022. doi: http://doi.org/10.1016/j.jclepro.2022.133001.
  » https://doi.org/10.1016/j.jclepro.2022.133001
• ^[28] LI, H.P., ZHAO, H., LIAO, K.J., et al, “A study on the preparation and storage stability of modified emulsified asphalt”, Petroleum Science and Technology, v. 30, n. 7, pp. 699–708, 2012. doi: http://doi.org/10.1080/10916466.2010.490812.
  » https://doi.org/10.1080/10916466.2010.490812
• ^[29] SHENG, X., WANG, M., XU, T., et al, “Preparation, properties and modification mechanism of polyurethane modified emulsified asphalt”, Construction & Building Materials, v. 189, pp. 375–383, 2018. doi: http://doi.org/10.1016/j.conbuildmat.2018.08.177.
  » https://doi.org/10.1016/j.conbuildmat.2018.08.177
• ^[30] CHEN, M., GENG, J., XIA, C., et al, “A review of phase structure of SBS modified asphalt: affecting factors, analytical methods, phase models and improvements”, Construction & Building Materials, v. 294, pp. 123610, 2021. doi: http://doi.org/10.1016/j.conbuildmat.2021.123610.
  » https://doi.org/10.1016/j.conbuildmat.2021.123610
• ^[31] FU, H., WANG, C., NIU, L., et al, “Composition optimisation and performance evaluation of waterborne epoxy resin emulsified asphalt tack coat binder for pavement”, The International Journal of Pavement Engineering, v. 23, n. 11, pp. 4034–4048, 2022. doi: http://doi.org/10.1080/10298436.2021.1932878.
  » https://doi.org/10.1080/10298436.2021.1932878
• ^[32] LIU, M., HAN, S., PAN, J., et al, “Study on cohesion performance of waterborne epoxy resin emulsified asphalt as interlayer materials”, Construction & Building Materials, v. 177, pp. 72–82, 2018. doi: http://doi.org/10.1016/j.conbuildmat.2018.05.043.
  » https://doi.org/10.1016/j.conbuildmat.2018.05.043
• ^[33] FOROUTAN-POUR, K., DUTILLEUL, P., SMITH, D.L., “Advances in the implementation of the box-counting method of fractal dimension estimation”, Applied Mathematics and Computation, v. 105, n. 2-3, pp. 195–210, 1999. doi: http://doi.org/10.1016/S0096-3003(98)10096-6.
  » https://doi.org/10.1016/S0096-3003(98)10096-6

Publication Dates

• Publication in this collection
  10 Feb 2025
• Date of issue
  2025

History

• Received
  25 Oct 2024
• Accepted
  04 Jan 2025