Composition design and performance evaluation of rubber-particle cement-stabilized gravel

Abstract

To improve the mechanical properties and durability of the cement-stabilized base, rubber particles of three different sizes and with three different contents were optimally selected, the evolution laws of the mechanical strength and toughness of rubber-particle cement-stabilized gravel (RCSG) under different schemes were determined, and the optimal particle size and content of rubber particles were obtained. On this basis, the durability of the RCSG base was clarified. The results show that with an increase in the rubber particle size and content, the mechanical strength of RCSG gradually decreased, whereas the toughness and transverse deformation ability gradually increased. 1% content and 2–4 mm sized RCSG can better balance the relationship between mechanical strength and toughness. The 7 d unconfined compressive strength was 17.7% higher than that of the 4–8 mm RCSG. The 28 d toughness index and ultimate splitting strain can be increased by 9.8% and 6.3 times, respectively, compared with ordinary cement-stabilized gravel (CSG). In terms of durability, compared with CSG, RCSG showed a 3.7% increase in the water stability property of cement-stabilized base with 1% content and 2–4 mm rubber particles, 5.5% increase in the frozen coefficient, and 80.6% and 37.9% increase in the fatigue life at 0.70 and 0.85 stress ratio levels, respectively.

Graphical abstract

Keywords

pavement materials / cement-stabilized gravel / rubber particles / material components / mechanical property / durability performance

1 Introduction

As a common type of base in China, the cement-stabilized base has the advantages of strong integrity and high bearing capacity; however, its excessive rigidity easily causes cracking and blowup, among other issues, which affect the driving quality and service life of pavements [1–5]. By contrast, rubber-particle cement-stabilized base has the characteristic of high toughness, which can effectively alleviate the internal stress caused by dry shrinkage and temperature shrinkage and reduce cracking [6–9]. Meanwhile, it reduces the environmental pollution caused by waste tires [10–14]. In recent years, it has gradually become the research focus of scholars in the field of road construction.

Pettinari and Simone [15] found that the incorporation of rubber particle reduces the indirect tensile stiffness modulus (ITSM) and indirect tensile strength of cement-stabilized materials, the effect on the ITSM being more significant. Saberian and Li [16] studied the permanent deformation of rubber cement-stabilized base. The results show that excessive increases in the rubber particle size and content lead to the instability of the permanent deformation of the material. Lv et al. [17] prepared cement-stabilized macadam with strength meeting the specifications and modulus adjustable by adjusting the content of rubber particles, and the maximum splitting and flexural-tensile strains of the materials increased significantly. Sun et al. [18] systematically studied the dry shrinkage performance of crumb rubber-modified cement-stabilized macadam, and the results show that the crumb rubber can provide more volume shrinkage space for cement-stabilized macadam, thus preventing the formation and expansion of initial cracks. Chen et al. [19] analyzed the road performance of rubber particles and basalt fibers mixed with cement-stabilized materials and found that the mechanical strength and durability of the mixture can be complemented. Yang et al. [20] evaluated the unconfined compressive strength of rubber-particle cement-stabilized macadam specimens formed by the vibrating compaction and static pressure methods. The results show that the former is 300% higher than the latter. Farhan et al. [21] mixed rubber particles with cement and then added graded crushed stone to the mixture to ensure a uniform distribution of the rubber particles in cement-stabilized macadam. Based on repeated load triaxial tests. Zhao et al. [22] analyzed the meso-cracking characteristics of rubber particle cement-stabilized aggregate using the discrete element method and found that rubber particles can absorb the crack-tip stress and redistribute it, thus improving the deformation limit of cement-stabilized materials. Using X-rays, Farhan et al. [23] observed the internal crack propagation law of rubber-particle cement-stabilized material and found that the rubber particles in the crack path can delay the crack development through their own deformation and improve the cracking limit of the base. Using scanning electron microscopy and pore structure analysis, Wang et al. [24] found that the structure of the interfacial transition zone between rubber particles and cement matrix is loose with obvious gaps, resulting in the formation of a weak stress zone inside the composite material. In conclusion, relevant research has been conducted on the single mechanical performance index analysis, preparation process optimization, and microstructure revelation of rubber-particle cement-stabilized materials, and certain results were obtained. However, the variation of the mechanical properties of rubber-particle cement-stabilized materials with rubber particle sizes and contents is not clear. Toughness evaluation indicators have not been unified, and the research on the durability of rubber-particle cement-stabilized materials is insufficient.

Hence, in this study, rubber particles of three different sizes and with three different contents were selected to design the composition of rubber-particle cement-stabilized gravel (RCSG). Based on uniaxial compression, compression modulus of resilience, and splitting tests, the effects of the different sizes and contents of the rubber particles on the mechanical properties of cement-stabilized gravel (CSG) were compared and evaluated, and the particle size and content scheme resulting in the optimal comprehensive performance were determined. On this basis, the durability of the optimal scheme was verified using water stability, freeze–thaw, and fatigue tests to lay a foundation for further popularization and application of rubber particle cement-stabilized base. The main research points of this paper are shown in Fig.1.

2 Materials and methods

2.1 Materials

PO42.5 cement was used, and the aggregate comprised pebbles and manufactured sand produced in southern Xinjiang, China. Rubber particles of 1–2, 2–4, and 4–8 mm sizes were processed from waste tire inner tubes. As the tire rubber contained hydrophobic substances such as zinc stearate, soaking in NaOH solution (5% concentration) is used to improve the hydrophilicity of rubber particles, to improve the adhesive property of rubber particles and CSG [25,26]. The technical indicators of the rubber particles are presented in Tab.1.

2.2 Specimen preparations

2.2.1 Material composition design

The aggregate satisfied the C-B-1 gradation recommended by China’s JTG/T F20-2015. To reduce the influence of the rubber particles on the aggregate intersqueezing, the proportion of coarse aggregate was appropriately increased in the range of the C-B-1 gradation [27,28]. The aggregate and C-B-1 gradations are presented in Fig.2.

Considering the resilience space and the integrity of aggregate structure, the 2–4 mm rubber particles were selected as the main research object [17,21] and compared with the adjacent 1–2 and 4–8 mm rubber particles. The content of rubber particles comprised 0.5%, 1%, and 2% of the dry weight of the aggregate. The dosage of cement comprised 4.5% of the dry weight of the aggregate. To ensure that the gradation of the RCSG mixture was similar to that of the CSG, equal volume blending was adopted, the 1–2 and 2–4 mm rubber particles were used to replace 0–5 mm aggregate with equal volume, and the 4–8 mm rubber particles were used to replace 5–10 mm aggregate with equal volume. The specific blending scheme of the rubber particles is presented in Tab.2. The optimum water content and maximum dry density of different rubber particle content schemes were determined by compaction test. The test results are presented in Tab.3.

2.2.2 Preparation of specimen

A number of cylindrical specimens with a height of 150 mm and a diameter of 150 mm were prepared according to the T0843-2009 test method in JTG E51-2009, and five specimens were tested in each group, taking the average of three valid test results as the final test result. The preparation process is illustrated in Fig.3, and the specific steps are as follows.

1) To ensure that the rubber particles are evenly distributed in the CSG, they were first dry-mixed with fine aggregate below 4.75 mm for 30 s, then dry-mixed with coarse aggregate for 30 s, finally mixed with water for 60 s, and placed in a plastic bag for 24 h.

2) Cement was added to the mixture, water was added up to the optimal water content, and the whole was mixed for 60 s.

3) The mixture was added to the mold in three layers and molded by a pressure testing machine for 6 h.

4) The molded specimens were demolded, wrapped in plastic bags, and moved to a curing box at a temperature of (20 ± 2) °C and a humidity of ≥ 98%.

2.3 Test methods

2.3.1 Methods of mechanical property testing

1) Uniaxial compression test

In accordance with T0805-1994 in JTG E51-2009, a uniaxial compression test was performed by a Universal Testing Machine (UTM). After the test, the stress–strain curve was drawn, and the ratio of the curve area corresponding to 0.8 times the peak stress after the peak to that corresponding to the peak stress was considered as the toughness index [29], which was calculated using Eq. (1), and the calculation diagram is shown in Fig.4.

(1)I=\frac{S_{\mathrm{A}}+S_{\mathrm{B}}}{S_{\mathrm{A}}},

where I is the toughness index, S_{\mathrm{A}} is the corresponding curve area of peak stress, and S_{\mathrm{B}} is the corresponding curve area of 0.8 times the peak stress after the peak.

2) Compression modulus of resilience

Referring to T0808-1994 in JTG E51-2009, the compression modulus of resilience of the RCSG was determined by the UTM. After the test, the compressive resilient modulus was calculated according to Formula T0808-2.

3) Splitting test

The splitting test was performed according to T0806-1994 in JTG E51-2009. After the test. The splitting strength was calculated according to Formula T0806-5, and the ultimate splitting strain was calculated according to Eq. (2).

(2){\epsilon }_{max}=\frac{\mathrm{\Delta }l}{l}\times {10}^6,

where {\epsilon }_{max} is the ultimate splitting strain (N), \mathrm{\Delta }l is the lateral deformation corresponding to the peak load (mm), and L is the diameter of the specimen (mm).

2.3.2 Durability test methods

1) Water stability test

The RCSG specimens with 28 d curing were placed into a water tank for 7 d, with the water surface exceeding the top surface of the specimens by approximately 2.5 cm. After soaking, the specimens were taken out, the surface water was absorbed with a towel, and the unconfined compressive strength was then measured.

2) Freeze–thaw test

The splitting test was performed according to T0858-2009 in JTG E51-2009. After completing the specified number of freeze–thaw cycles, the compressive strength of the freeze–thaw specimens was measured. The frozen coefficient of the specimens was calculated according to Formula T0858-1.

3) Splitting fatigue test

To simulate the long-term load of the vehicle, a splitting fatigue test was performed using an Mechanical Testing & Simulation (MTS) universal material testing machine [30]. Stress ratio levels of 0.7, 0.75, 0.8, and 0.85 were selected for the test. The fatigue data was dispersed. The Weibull distribution was used for reliability analysis [31–33], and a linear fitting of -\mathrm{l}\mathrm{n}\mathrm{l}\mathrm{n}\left(1/p\right) and \mathrm{l}\mathrm{n}{N}_i was performed with reference to Eq. (3). The fatigue life of 50% guarantee rate in the fitting line was considered as the equivalent fatigue life at a specific stress level, and then the fatigue life was linearly regressed according to Eq. (4) to analyze the effect of the rubber particles on the fatigue characteristics of the CSG.

(3)-\mathrm{l}\mathrm{n}\mathrm{l}\mathrm{n}\left(1/p\right)=m\mathrm{l}\mathrm{n}{N}_i-\mathrm{l}\mathrm{n}{t}_0,

(4)\mathrm{l}\mathrm{o}\mathrm{g}{N}_i=a+b\sigma /S,

where N_i is the number of repeated loads, p is the probability of material failure, \sigma /S is the stress ratio, m is the shape parameter, t₀ is the size parameter, and a and b are the regression coefficients.

3 Results and discussion

3.1 Mechanical properties

3.1.1 Effect of the rubber particle size on the mechanical properties

To clarify the influence of the rubber particle size on the mechanical properties of the CSG base, the rubber particle content in this section was fixed at 1%, and three particle sizes of 1–2, 2–4, and 4–8 mm were selected. Based on the uniaxial compression, compression modulus of resilience, and splitting tests, the mechanical properties of the CSG were explored for different rubber particle sizes.

1) Compressive strength

The top surface of the base mainly bears the vertical load from the pavement surface and should have sufficient compressive capacity. To determine the evolution law of the compressive strength of the RCSG for different rubber particle sizes, the unconfined compressive strength of 7, 14, and 28 d was measured based on the uniaxial compression test. The test results are shown in Fig.5.

As can be observed from Fig.5, the data of all ages indicate that the compressive strength of the RCSG gradually decreased with an increase in the rubber particle size. Taking the age of 7 d as an example, the reductions in the compressive strengths of the 1–2 and 2–4 mm RCSG were similar, 54.4% and 55.7%, respectively, but still met the requirement of 3–5 MPa for the medium and light traffic intensities of the expressway and first-class highway base in China. The decline in the strength of the 4–8 mm RCSG was significant, up to 73.4%. This was due to the poor adhesion between the rubber particles and cement and stone, forming a weak interface in the RCSG. In addition, the modulus of the rubber particles was small, the bearing capacity was low, and the specimen was easy to crack starting from the position of rubber particles when compressed. The 4–8 mm rubber particles would also affect the intersqueezing between aggregates, destroying the CSG skeleton structure and resulting in a decrease in strength. Furthermore, the compressive strength ratio of 2–4 mm RCSG to CSG was 44.3% at 7 d and increased to 50.9% at 28 d, indicating that the influence of the rubber particles on the strength of the CSG was gradually weakened with an increase in age.

2) Toughness index

The toughness index is used to measure the post-peak bearing capacity of the material. To explore the change law of toughness of RCSG under different rubber particle sizes, based on the uniaxial compression test, the stress–strain relationship of the mixture at different ages was clarified, as shown in Fig.6–Fig.8, and the toughness index is shown in Fig.9.

Fig.6–Fig.8 show that the strain at all ages of the RCSG at the peak stress was greater than that of the CSG and that the stress decline rate after the peak load was significantly lower, indicating that the rubber particles improved the post-peak bearing capacity of the CSG. It can be observed from Fig.9 that the toughness index of the RCSG was significantly higher than that of the CSG. Considering the 28 d age as an example, the toughness indexes of the 1–2, 2–4, and 4–8 mm RCSG increased by 6.5%, 9.8%, and 13%, respectively, indicating that the rubber particles effectively improved the deformation capacity of the CSG. When the crack extended to the rubber particles, these could relieve the crack-tip stress through their own rebound deformation, promote the redistribution of stress, prevent stress concentration, and delay the development of cracks. The larger the rubber particle size, the larger the space for rebound deformation, and therefore the stronger the stress absorption capacity at the crack tip [22]. The toughness index of the CSG with 4–8 mm rubber particles at 7 d age was lower than that with the other particle sizes. The analysis showed that the 4–8 mm rubber particles affected the intersqueezing between aggregates and that the strength growth was slow. At the age of 7 d, the strength had not formed yet, and it was easy to destabilize under loading, resulting in a low toughness index.

3) Compression modulus of resilience

The compression modulus of resilience is often used to evaluate the strength of the cement-stabilized base. Based on the compression modulus of resilience test, the influence of the rubber particle size on the compression modulus of resilience of the CSG was investigated. The test results are shown in Fig.10.

Fig.10 shows that the incorporation of rubber particles significantly reduced the compression modulus of resilience of the CSG and that the law of decline was similar to that of the compressive strength. At the age of 7 d, the compression modulus of resilience of the 1–2 and 2–4 mm RCSG decreased by 31.6% and 33.5%, respectively, whereas that of the 4–8 mm RCSG decreased by 63.8%, indicating that the bearing capacity decreased while the deformation capacity increased. This was due to the strong elasticity of rubber particles, which maked the base easy to deform when bearing the load, and promoted the rebound of the base after unloading; the larger the size of rubber particles, the larger the space of the rebound deformation inside the material, and the compression modulus of resilience decreased more noticeably.

4) Splitting strength and ultimate splitting strain

Splitting strength and ultimate splitting strain are important indexes to evaluate the tensile strength and transverse deformation ability of RCSG. The 28 d splitting strength and ultimate splitting strain of the mixture were measured based on the splitting test. The test results are shown in Fig.11 and Fig.12.

Fig.11 and Fig.12 show that with an increase in particle size, the splitting strength of the RCSG gradually decreased. The splitting strength of the CSG with 1–2, 2–4, and 4–8 mm rubber particles decreased by 27.6%, 31.7%, and 34.1%, respectively. The bonding strength between the rubber particles and cement-based materials was low, and the mixture around the rubber particles was easy to deform and crack under tensile stress. During the crack development, rubber particles could partially absorb the tip stress. At the same time, the deformation of the rubber particles made the coarse aggregate form a new intersqueezing effect and promoted stress redistribution. The larger the size of rubber particles, the stronger the absorption capacity of stress and the stronger the ability to delay the development of cracks.

3.1.2 Effect of the rubber particle content on the mechanical properties

The rubber particle size was fixed at 2–4 mm, and three contents of 0.5%, 1%, and 2% were selected. Based on the uniaxial compression, compression modulus of resilience, and splitting tests, the mechanical properties of the CSG under different rubber particle contents were determined.

1) Compressive strength

Based on the uniaxial compression test, the 7, 14, and 28 d unconfined compressive strength of the CSG under different rubber particle sizes were measured. The test results are shown in Fig.13.

Fig.13 shows that the unconfined compressive strength loss of the CSG was more significant with an increase in the rubber particle content. Considering the 7 d age as an example, the unconfined compressive strength of the CSG with 0.5%, 1%, and 2% rubber particles was 40.5%, 55.7%, and 77.2% lower than that of the CSG. With an increase in the rubber particle content, the weak interface in the CSG increased, and the specimen was more likely to crack during compression. When the content of rubber particles was increased to 2%, the 7 d unconfined compressive strength was reduced to 1.8 MPa, which did not meet the requirement of 3–5 MPa for the base of the expressway and first-class highway in China. This indicates that too much rubber particle content would lead to a significant reduction in compressive strength, which did not meet the strength requirements of the specification, so the rubber particle content should not be too high, so as not to affect the base load capacity.

2) Toughness index

Based on the uniaxial compression test, the corresponding stress–strain data of the CSG were measured for different rubber particle contents, as shown in Fig.14–Fig.16, and the toughness index was calculated, as shown in Fig.17.

Fig.14–Fig.16 show that the peak strain of most of the RCSG was located on the right side of the CSG and that the deformation capacity was generally improved. The peak strains of the 0.5% and 2% RCSG at 28 and 14 d ages were lower than those of the CSG. In contrast, the 1% rubber particles had a more stable effect on improving the deformation capacity of the CSG. As can be observed from Fig.17, the toughness index increased with an increase in the rubber particle content, the improvement effect of the 0.5% content was not clear, and the 28 d toughness index increased only by 1.6%, whereas the 1% and 2% rubber particle contents increased by 9.8% and 17.9%, respectively, indicating that the rubber particle content should not be excessively low. This was due to the lack of rubber particles around most cracks when the rubber particle content was 0.5%, which could not absorb the tip stress. When the rubber particle content was further increased, the probability of micro-cracks encountering rubber particles was improved, and crack development was inhibited.

3) Compression modulus of resilience

Fig.18 shows the compression modulus of resilience test results for the 0.5%, 1%, and 2% RCSG at each age.

As shown in Fig.18, with an increase in rubber particle content, the compressive modulus of resilience of the RCSG gradually decreased. When the rubber particle content increased from 0.5% to 1%, the compressive modulus of resilience decreased slowly, and the 7 d compressive modulus of resilience decreased by only 2.4%, whereas that of 2% rubber particle content decreased by 33.7%, compared with 1%. The analysis showed that with an increase in the rubber particle content, the number of rubber particles between the CSG aggregates increased, and the load was partially transferred from the aggregate to the rubber particles, resulting in increased rebound deformation and reduced compressive modulus of resilience.

4) Splitting strength and ultimate splitting strain

Based on the splitting test, the 28 d splitting strength and ultimate splitting strain of the CSG were measured for different rubber particle contents. The test results are shown in Fig.19 and Fig.20.

It can be observed from Fig.19 and Fig.20 that the variation of splitting strength and ultimate splitting strain of the RCSG with the rubber particle content were similar to that of rubber particle size, which showed that the splitting strength decreased gradually while the ultimate splitting strain increased greatly. Compared to that of the CSG, the splitting strength of the CSG with 0.5%, 1%, and 2% rubber particles decreased by 17.9%, 16.8%, and 25%, and the ultimate splitting strain increased by 1.4, 6.3, and 16.6 times, respectively. This was because, with an increase in the rubber particle content, the number of rubber particles in the micro-crack propagation area increased, which could better absorb the crack-tip stress, promote the stress redistribution, and reduce the rate of crack development, thus increasing the ultimate splitting strain.

The above research showed that compared to RCSG with other particle sizes and contents, the 2–4 mm and 1% RCSG met the compressive strength requirements of the base, and exhibited great post-peak bearing capacity and lateral deformation capacity. The performance of each age was stable, and the comprehensive application effect was optimal.

3.2 Durability performance

3.2.1 Water stability

Long-term water erosion easily destroys the internal bond strength of CSG. To determine the water damage resistance of the RCSG base, the 7 d soaking compressive strengths of the CSG and RCSG were measured based on the water stability test. The test results are shown in Fig.21.

As can be observed from Fig.21, the overall strength of the RCSG before and after soaking was lower than that of the CSG; however, the compressive strength of the RCSG decreased by 8.6%, which was less than that of the CSG, 12.3%, indicating that rubber particles weaken the influence of water on the material. Rubber particles, whose sealing performance is better than that of fines, are distributed in the skeleton structure of the aggregate, which can effectively prevent water from penetrating into the interior of the mixture. In addition, rubber particles can absorb a small amount of invading water, thus reducing the damage to the overall bond strength of the CSG.

3.2.2 Freezing resistance

To determine the influence of freeze–thaw cycles on the performance of the RCSG base, the compressive strengths of 5, 10, and 15 freeze–thaw cycles were measured based on the freeze–thaw test, and the frozen coefficient was calculated. The test results are shown in Fig.22 and Fig.23.

The changes in the compressive strength under different freeze–thaw cycles are shown in Fig.22. The compressive strengths of the RCSG and CSG decreased rapidly during 0–5 freeze–thaw cycles and tended to be moderate during 5–15 freeze–thaw cycles. When water was added to the mixture, the volume increased after freezing, resulting in expansion stress inside the mixture. The water absorption in the mixture was limited. In the first five freeze–thaw cycles, the water absorption was close to saturation; therefore, the expansion stress caused by the subsequent freeze–thaw action gradually decreased. Fig.23 shows the changes in the frozen coefficient of materials under different freeze–thaw cycles. The frozen coefficient of the RCSG was always larger than that of the CSG. The difference in the frozen coefficient between the two was 5.5% at 5 freeze–thaw cycles. When the number of freeze–thaw cycles increased to 15 times, the difference in the frozen coefficient decreased to 2.2%, indicating that rubber particles can significantly improve the freezing resistance of the CSG and that excessive freeze–thaw cycles would weaken the optimization effect of the rubber particles. Rubber particles are highly elastic materials, which can alleviate the expansion stress generated by freeze–thaw cycles. When the number of freeze–thaw cycles was excessive, the cyclic loading of expansion stress aggravated the fatigue damage of the rubber particles, resulting in insufficient elasticity of the rubber particles and the decline of the stress absorption effect.

3.2.3 Fatigue property

Based on the splitting fatigue test, the fatigue life of the RCSG material was measured. The Weibull distribution of the fatigue test data under four stress ratios is shown in Tab.4, where Y=-\mathrm{l}\mathrm{n}\mathrm{l}\mathrm{n}\left(1/p\right) and x=\mathrm{l}\mathrm{n}{N}_i. The linear fitting of the stress ratio-fatigue life and the comparison of the fatigue life of the two materials are shown in Fig.24 and Fig.25.

The fitting correlation coefficient R² of the fatigue test data was above 0.9 for the CSG and RCSG, indicating that the fatigue test results obeyed the Weibull distribution. Therefore, this distribution model can be used to predict the fatigue life of the two materials.

The stress ratio-fatigue life linear regression is shown in Fig.24. Under different stress ratios, the correlation coefficient R² of fatigue life in the RCSG and CSG was larger than 0.94, showing a good linear relationship. In the range of the test stress ratio, the fatigue life of the RCSG was greater than that of the CSG, indicating that rubber particles can significantly reduce the fatigue damage of cement-stabilized base under cyclic loading. Under the action of driving load, rubber particles with high elasticity absorbed the high-frequency vibration transmitted by the road surface, dissipated the internal strain energy of the CSG, hindered the generation and development of micro-cracks inside the material, and weakened the loading damage to the integrity and bond strength of the base, thereby improving the durability of the base. The slope of the fitting line indicates that as the stress ratio increased, the improvement effect of the rubber particles on fatigue life continued to decrease. Fig.25 shows that the fatigue life increased by 80.6%, 65.1%, 50.8%, and 37.9% at the stress ratio levels of 0.70, 0.75, 0.80, and 0.85, respectively. When the load increase, some rubber particles would be directly compressed, resulting in excessive deformation. The CSG material around the rubber particles would form initial cracks due to stress concentration, thus affecting the fatigue life.

4 Conclusions

1) With an increase in the particle size or content of the rubber particles, the compressive strength, splitting strength, and compression modulus of resilience of CSG decreased gradually, whereas the toughness index and ultimate splitting strain increased significantly.

2) Compared with other blending schemes, 2–4 mm and 1% RCSG better balanced the relationship between the mechanical strength and toughness properties. The 7 d unconfined compressive strength satisfied the requirements of the medium and light traffic intensity at the base of China’s expressway and first-class highway. The 28 d toughness index and ultimate splitting strain increased by 9.8% and 6.3 times, respectively.

3) The durability of the 2–4 mm and 1% RCSG improved significantly. The water stability increased by 3.7%; freezing coefficient under 5,10, and 15 freeze–thaw cycles increased by 5.5%, 4.7%, and 2.2%, respectively; and the fatigue life under 0.70, 0.75, 0.80, and 0.85 stress ratio levels increased by 80.6%, 65.1%, 50.8, and 37.9%, respectively.

4) This study clarifies the development law of the mechanical properties and durability of RCSG with different sizes and contents of rubber particles. However, the shrinkage performance of RCSG is not clear, and the crack resistance under dry and low temperature environment can be further studied to comprehensively evaluate the road performance of RCSG.

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