Lightweight ultrathin overlay asphalt mixture and preparation method thereof

Abstract

The invention discloses a light ultrathin overlay asphalt mixture and a preparation method thereof, and aims to solve the technical problems that SBS modified asphalt is poor in compatibility with waste rubber powder and is easy to layer and separate. According to the mixture, cement, SBS modified asphalt, waste rubber powder, a silane coupling agent, a water reducing agent and nano silicon dioxide are used as main components, and structural optimization is achieved through the synergistic effect of the multiple components. The preparation method comprises the steps of surface activation of rubber powder, multi-component dry mixing, wet mixing and shearing and the like. By utilizing a rigid framework of the cement, the flexibility of the SBS modified asphalt and the enhancement effect of the waste rubber powder, and combining a silane coupling agent bridging interface, a water reducing agent optimizing dispersion and nano silicon dioxide filling pores, the freeze-thaw splitting strength, the immersion Marshall residual stability, the dynamic stability and the crack resistance of the asphalt mixture are remarkably improved; high-temperature layering and segregation are effectively inhibited, and the ultrathin overlay material which is light in weight, high in strength, flexible and durable is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt mixtures, and particularly to a lightweight ultra-thin wearing course asphalt mixture and a preparation method thereof. Background Art

[0002] Due to its good plasticity and durability, asphalt materials are widely used in engineering such as road construction and airport runways. With the increase in traffic volume, the durability and service performance of traditional asphalt are facing increasing challenges. Especially under high temperature and extreme climate conditions, the performance of asphalt materials may decline significantly. In order to improve the performance of asphalt, modified asphalt has gradually become a research and application hotspot. As a common modifier, SBS (styrene-butadiene-styrene) triblock copolymer is widely used in asphalt modification due to its good high-temperature resistance, anti-aging property, and elasticity. Chinese Patent (CN115215610B) discloses a high-performance anti-skid thin wearing course asphalt mixture containing steel slag and a preparation method thereof. Aiming at the problem of insufficient water stability of the wearing course material caused by free calcium oxide in steel slag, by adding highly polymerized and matured modified waste rubber powder and cement, the surface voids of steel slag are sealed, thereby improving its water stability. However, there is thermodynamic incompatibility between the linear segments of styrene-butadiene block copolymer in SBS modified asphalt and the vulcanized cross-linked network of waste rubber powder. Specifically, the difference in solubility parameters between the two leads to hindered diffusion of interfacial molecular chains; at high temperature, the thermal motion of the butadiene segments of SBS intensifies, and the dissociation rate of its entanglement points is higher than the relaxation rate of the cross-linked network of rubber powder, resulting in a decrease in the shear stress transfer efficiency at the two-phase interface. At the same time, the sulfides and fillers such as ZnO remaining on the surface of waste rubber powder form a polar barrier, hindering the binding of the rigid styrene segments of SBS to the aromatic components of rubber powder through π-π interaction, resulting in the formation of a micron-level weak bonding zone at the interface, which preferentially generates crazes and expands into delamination cracks under shear loads. These factors jointly lead to a significant decrease in the bonding strength at the two-phase interface, and ultimately may cause delamination and segregation phenomena at high temperature. Such delamination or segregation phenomena may lead to problems such as accelerated aging and fatigue cracking during the long-term use of asphalt materials, thereby reducing the service life of roads. Summary of the Invention

[0003] The molecular structures of SBS modified asphalt and waste rubber powder are different, resulting in weak interaction between them. Especially at high temperature, the polymer chains of SBS are not tightly combined with the particle interface of waste rubber powder, which is easy to cause delamination and segregation. The poor dispersibility of rubber powder in asphalt will form large particle agglomerates, which will further affect the uniformity and stability of asphalt. Such delamination or segregation phenomena may lead to problems such as accelerated aging and fatigue cracking during the long-term use of asphalt materials, thereby reducing the service life of roads.

[0004] In view of the above technical problems, the present application provides a lightweight and ultra-thin wearing asphalt mixture, which, by mass fraction, includes: 30 to 40 parts of cement, 5 to 8 parts of SBS modified asphalt, 10 to 15 parts of waste rubber powder, 0.5 to 1.2 parts of silane coupling agent, 0.8 to 1.5 parts of water reducing agent, and 0.3 to 0.8 parts of nano-silica, wherein the water-cement ratio is 0.18 to 0.22.

[0005] It should be noted that the lightweight and ultra-thin wearing asphalt mixture of the present application realizes structural optimization through the synergistic effect of multiple components: taking cement (30-40 parts) as the rigid skeleton, the styrene-butadiene copolymer of SBS modified asphalt (5-8 parts) exerts a dual function through the microphase separation structure - the butadiene soft segment forms a dense three-dimensional physical crosslinking network with the unsaturated carbon chains on the surface of waste rubber powder (10-15 parts) through segment diffusion - entanglement at high temperature. At the same time, the benzene ring at the end of the styrene hard segment and the high-concentration Ca released by the cement hydration product Ca(OH)2 2+ Construct chemical bridge points between the C-S-H gel and the asphalt phase through π-cation chelation coordination to inhibit high-temperature plastic flow, thereby inhibiting delamination and segregation phenomena at high temperature; nano-silica (0.3-0.8 parts) reduces the water-cement ratio (0.18-0.22) by filling cement-based micropores and synergistically with polycarboxylate water reducing agent (0.8-1.5 parts), reducing pore defects; the cement hydration product and the asphalt film interpenetrate and crosslink, the silane coupling agent bridges the organic-inorganic interface, and the nanoparticles strengthen the transition zone, forming a lightweight, high-strength and flexible ultra-thin dense layer.

[0006] As a preferred technical solution of a lightweight and ultra-thin wearing asphalt mixture, the silane coupling agent is KH-550.

[0007] It should be noted that the present application selects KH-550 (γ-aminopropyltriethoxysilane) as the coupling agent. The amino group (-NH2) in its molecule can form a hydrogen bond with the carboxyl group on the surface of the waste rubber powder. At the same time, the silanol group (-Si-OH) generated by the hydrolysis of the ethoxy group can undergo a condensation reaction with Ca(OH)2 in the cement hydration product to form a Si-O-Ca chemical bond. This bifunctional characteristic can effectively bridge the organic rubber powder and the inorganic cement interface, form a transition layer with reactive activity on the surface of the rubber powder, and enhance the synergistic effect between the SBS modified asphalt and the cement matrix.

[0008] As a preferred technical solution of a lightweight and ultra-thin wearing asphalt mixture, the water reducing agent is a polycarboxylate water reducing agent.

[0009] It should be noted that the polycarboxylate superplasticizer is used in this application. The carboxylic acid groups (-COOH) on the main chain of its molecule and the side-chain polyether structure (-O-R) can form steric hindrance and electrostatic repulsion effects by adsorbing on the surface of cement particles, significantly reducing the water-binder ratio and improving the fluidity of the slurry.

[0010] A preparation method of asphalt mixture includes the following technical steps:

[0011] Step S1. Add silane coupling agent to the pretreated waste tire rubber powder in proportion and stir at high speed to form surface-activated rubber powder;

[0012] Step S2. Dry-mix cement and nano-silica evenly, add the pretreated rubber powder and SBS modified asphalt, and continue dry-mixing for 30 minutes to ensure uniform dispersion of components;

[0013] Step S3. Slowly add mixing water to the dry materials, and at the same time add polycarboxylate superplasticizer. Use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculent structure, and then transfer it to a high-speed shearing machine for shearing for 10 minutes to break the flocs and optimize the dispersion.

[0014] It should be noted that in step S1, the amino group (-NH2) of the silane coupling agent (KH-550) binds to the carboxyl group (-COOH) on the surface of the waste rubber powder through hydrogen bonds. At the same time, the hydrolyzed silanol group (-Si-OH) condenses with the subsequent cement hydration product Ca(OH)2 to form a Si-O-Ca bond, endowing the surface of the rubber powder with chemical activity and reducing the interfacial energy between it and the inorganic phase. In step S2, nano-silica improves the density of the cement matrix through nano-filling effect and pozzolanic reaction (generating C-S-H gel with Ca(OH)2). Its surface hydroxyl groups bond with the residual silanol groups of KH-550 to form a "rubber powder - nano-particle - cement" multi-level interfacial transition zone; the styrene-butadiene block structure of SBS modified asphalt forms an interpenetrating network with the activated rubber powder through physical entanglement and van der Waals forces, enhancing the elastic recovery ability. In step S3, the carboxyl group and ether chain of the polycarboxylate superplasticizer inhibit the agglomeration of cement particles through adsorption-dispersion action. It cooperates with KH-550 to regulate the distribution of water molecules at the rubber powder-cement interface. Low-speed stirring induces the initial hydration products of cement to wrap the rubber powder to form a spatial framework, while the turbulent flow field generated by high-speed shearing depolymerizes the flocs through mechanical-chemical synergistic action, promoting the uniform embedding of nano-silica and rubber powder into the cement-asphalt composite phase, and finally forming a multi-scale enhanced structure with chemical bonds as the core and physical entanglement as the shell, realizing the simultaneous improvement of rutting resistance and fatigue resistance.

[0015] As a preferred technical solution of a preparation method of asphalt mixture, in step S1, the waste tire rubber powder is crushed to a particle size of ≤80 mesh and pretreated in an oven at 120°C for 2 hours to dry to a moisture content of ≤3%.

[0016] It should be noted that when the waste tire rubber powder is pretreated, it is crushed to a particle size of ≤80 mesh, which can increase the contact area with the silane coupling agent and promote the directional bonding of amino groups to the carboxyl groups on the surface of the rubber powder; drying at 120 °C for 2 hours can remove the adsorbed water and low-molecular volatile substances inside the rubber powder (moisture content ≤ 3%), avoiding the hydrolysis and condensation reaction of the silane coupling agent from being interfered by water and becoming ineffective, and at the same time eliminating the micropore defects at the rubber powder-asphalt interface caused by water evaporation.

[0017] As a preferred technical solution of a method for preparing an asphalt mixture, in step S2, the uniformly mixed cement and nano-silica are ground to a specific surface area of ≥400 m 2 / kg.

[0018] It should be noted that after the dry mixing of cement and nano-silica and grinding to a specific surface area of ≥400 m 2 / kg, the surface of the particles is activated by mechanochemical action, increasing the density of hydroxyl groups (-Si-OH) on the surface of nano-silica, and after the cement particles are deagglomerated, more Ca 2+ active sites are exposed. The high specific surface area not only enhances the pozzolanic reaction rate of nano-silica, but also forms -Si-O-Si- bridging bonds with the residual silanol groups of KH-550 in step S1, strengthening the three-phase interface of rubber powder-cement-nano-particles; at the same time, the cement particles are refined to fill the pores of the rubber powder, expanding the initial hydration contact area of the mixture and providing a structural basis for the subsequent uniform coating of the hydration products on the rubber powder.

[0019] As a preferred technical solution of a method for preparing an asphalt mixture, in step S2, after the dry mixing of cement and nano-silica, the order of adding the pretreated rubber powder and SBS modified asphalt is: first add the rubber powder, and then add the SBS modified asphalt.

[0020] It should be noted that adding the pretreated rubber powder first can preferentially utilize the amino groups (-NH2) of the silane coupling agent on its surface to form coordination bonds with Ca 2+ and -Si-OH of the cement-nano-silica mixture, forming a "rubber powder-cement" pre-crosslinked skeleton; adding the SBS modified asphalt later forms an elastic coating layer through the physical entanglement of styrene segments with the rubber powder and the dissolution and penetration of the butadiene phase, avoiding premature wrapping of the rubber powder by asphalt and hindering the inorganic phase interface reaction. This order anchors the rubber powder to both the cement matrix (chemical bond) and the asphalt phase (van der Waals force) at the same time, constructing a "hard-elastic" gradient transition interface.

[0021] As a preferred technical solution of a method for preparing an asphalt mixture, in step S3, after adding the mixing water, the pH is adjusted to 10.5 to 11.5.

[0022] It should be noted that adjusting the pH to 10.5 to 11.5 helps the benzene ring at the end of the styrene hard segment to chelate and coordinate with the high-concentration Ca released by the cement hydration product Ca(OH)2. 2+ Through π-cation chelation coordination.

[0023] The beneficial effects of this application are as follows. Through the synergistic action of multiple components such as cement, SBS modified asphalt, waste rubber powder, silane coupling agent, water reducer, and nano-silica, the structural optimization and performance improvement of the lightweight ultra-thin wearing asphalt mixture are achieved. Specifically, a rigid framework is constructed using cement, a flexible reinforcement phase is formed by SBS modified asphalt and waste rubber powder, the organic-inorganic interface is bridged by a silane coupling agent, nano-silica fills the pores and synergistically reduces the water-cement ratio with the water reducer, and finally a lightweight, high-strength and flexible ultra-thin dense layer is constructed. This multi-component system not only effectively inhibits the delamination and segregation phenomena at high temperatures, significantly improves the key performance indicators such as the freeze-thaw splitting strength ratio, immersion Marshall residual stability, dynamic stability, and anti-cracking strength of the asphalt mixture, but also realizes the simultaneous improvement of rutting resistance and fatigue resistance, providing a new solution for the performance upgrade and sustainable development of road wearing materials. Detailed implementation manners

[0024] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the detailed implementation manners of the present invention in conjunction with the embodiments of the specification.

[0025] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0026] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or selectively exclusive embodiments from other embodiments.

[0027] Embodiment

[0028] Embodiment 1

[0029] Embodiment 1 provides a lightweight ultra-thin wearing asphalt mixture and a preparation method thereof. Among them, the lightweight ultra-thin wearing asphalt mixture, by mass, includes: 30 parts of cement, 6 parts of SBS modified asphalt, 10 parts of waste rubber powder, 0.5 part of KH-550, 1.2 parts of polycarboxylate water reducer, and 0.8 part of nano-silica, where the water-cement ratio is 0.20;

[0030] Preparation method of asphalt mixture, comprising the following technical steps:

[0031] Step S1. Pulverize waste tire rubber powder to a particle size ≤ 80 mesh, and pre-treat it in an oven at 120 °C for 2 hours to dry to a moisture content ≤ 3%. Add 10 parts of the pre-treated waste tire rubber powder to 0.5 part of silane coupling agent (KH-550) in proportion, and stir at high speed to form surface-activated rubber powder;

[0032] Step S2. Dry-mix 30 parts of cement and 0.8 part of nano-silica evenly, grind the evenly mixed cement and nano-silica to a specific surface area ≥ 400 m 2 / kg, add the pre-treated rubber powder and 6 parts of SBS modified asphalt, and continue dry-mixing for 30 minutes to ensure uniform dispersion of components; wherein, the cement is P.O52.5R ordinary Portland cement, and the softening point of SBS modified asphalt is 85 °C and the penetration is 40 dmm;

[0033] Step S3. Slowly add mixing water to the dry materials, with a water-cement ratio of 0.20 (mass ratio of mixing water to cement), adjust the pH to 10.5, and at the same time add 1.2 parts of polycarboxylate water reducer. Use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculent structure, and transfer it to a high-speed shearer for shearing for 10 minutes to break the floccules and optimize the dispersion.

[0034] Example 2

[0035] Example 1 provides a light and ultra-thin wearing course asphalt mixture and its preparation method. Among them, the light and ultra-thin wearing course asphalt mixture, by mass, includes: 40 parts of cement, 8 parts of SBS modified asphalt, 12 parts of waste rubber powder, 0.8 part of KH-550, 1.5 parts of polycarboxylate water reducer, and 0.5 part of nano-silica, wherein the water-cement ratio is 0.18;

[0036] Preparation method of asphalt mixture, comprising the following technical steps:

[0037] Step S1. Pulverize waste tire rubber powder to a particle size ≤ 80 mesh, and pre-treat it in an oven at 120 °C for 2 hours to dry to a moisture content ≤ 3%. Add 12 parts of the pre-treated waste tire rubber powder to 0.8 part of silane coupling agent (KH-550) in proportion, and stir at high speed to form surface-activated rubber powder;

[0038] Step S2. Dry-mix 40 parts of cement and 0.5 part of nano-silica evenly, grind the evenly mixed cement and nano-silica to a specific surface area ≥ 400 m 2 / kg, add the pre-treated rubber powder and 8 parts of SBS modified asphalt, and continue dry mixing for 30 minutes to ensure uniform dispersion of the components; among them, the cement is P.O52.5R ordinary Portland cement, the softening point of the SBS modified asphalt is 95 °C, and the penetration is 60 dmm;

[0039] Step S3. Slowly add mixing water to the dry materials, with a water-cement ratio of 0.18 (the mass ratio of mixing water to cement), adjust the pH to 11.5, and at the same time add 1.5 parts of polycarboxylate water reducer. Use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculated structure, and transfer it to a high-speed shearer for shearing for 10 minutes to break the flocs and optimize the dispersion.

[0040] Example 3

[0041] Example 3 provides a lightweight ultra-thin wearing asphalt mixture and its preparation method. Among them, the lightweight ultra-thin wearing asphalt mixture, by mass, includes: 35 parts of cement, 5 parts of SBS modified asphalt, 15 parts of waste rubber powder, 1.0 part of KH-550, 0.8 part of polycarboxylate water reducer, and 0.3 part of nano-silica dioxide, among which the water-cement ratio is 0.18;

[0042] The preparation method of the asphalt mixture includes the following technical steps:

[0043] Step S1. Crush the waste tire rubber powder to a particle size of ≤80 mesh, and pre-treat it in an oven at 120 °C for 2 hours to dry to a moisture content of ≤3%. Add 15 parts of the pre-treated waste tire rubber powder to 1.0 part of silane coupling agent (KH-550) in proportion, and stir at high speed to form surface-activated rubber powder;

[0044] Step S2. Dry mix 35 parts of cement and 0.3 part of nano-silica dioxide evenly, and grind the evenly mixed cement and nano-silica dioxide to a specific surface area of ≥400 m 2 / kg, add the pre-treated rubber powder and 5 parts of SBS modified asphalt, and continue dry mixing for 30 minutes to ensure uniform dispersion of the components; among them, the cement is P.O52.5R ordinary Portland cement, the softening point of the SBS modified asphalt is 85 °C, and the penetration is 40 dmm;

[0045] Step S3. Slowly add mixing water to the dry materials, with a water-cement ratio of 0.18 (the mass ratio of mixing water to cement), adjust the pH to 11.0, and at the same time add 0.8 part of polycarboxylate water reducer. Use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculated structure, and transfer it to a high-speed shearer for shearing for 10 minutes to break the flocs and optimize the dispersion.

[0046] Example 4

[0047] Example 4 provides a lightweight and ultra-thin wearing asphalt mixture and a preparation method thereof. The lightweight and ultra-thin wearing asphalt mixture, by mass, comprises: 40 parts of cement, 5 parts of SBS modified asphalt, 13 parts of waste rubber powder, 1.2 parts of KH-550, 1.0 part of polycarboxylate water reducer, and 0.5 part of nano-silica dioxide, wherein the water-cement ratio is 0.22;

[0048] The preparation method of the asphalt mixture comprises the following technical steps:

[0049] Step S1. Crush the waste tire powder to a particle size ≤ 80 mesh, and pre-treat it in an oven at 120 °C for 2 hours to dry to a moisture content ≤ 3%. Add 1.2 parts of silane coupling agent (KH-550) to 13 parts of the pre-treated waste tire powder in proportion, and stir at high speed to form surface-activated powder;

[0050] Step S2. Dry-mix 40 parts of cement and 0.5 part of nano-silica dioxide evenly, grind the evenly mixed cement and nano-silica dioxide to a specific surface area ≥ 400 m 2 / kg, add the pre-treated powder and 5 parts of SBS modified asphalt, and continue dry-mixing for 30 minutes to ensure uniform dispersion of the components; wherein, the cement is P.O52.5R ordinary Portland cement, and the softening point of the SBS modified asphalt is 85 °C and the penetration is 50 dmm;

[0051] Step S3. Slowly add mixing water to the dry materials, with a water-cement ratio of 0.22 (mass ratio of mixing water to cement), adjust the pH to 11.0, and at the same time add 1.0 part of polycarboxylate water reducer, and stir at low speed for 3 minutes using a planetary mixer to form a preliminary flocculated structure, and transfer it to a high-speed shearer for shearing for 10 minutes to break the floccules and optimize the dispersion.

[0052] Example 5

[0053] Example 5 provides a lightweight and ultra-thin wearing asphalt mixture and a preparation method thereof. The lightweight and ultra-thin wearing asphalt mixture, by mass, comprises: 10 to 60 parts of cement, 6 parts of SBS modified asphalt, 13 parts of waste rubber powder, 1.2 parts of KH-550, 1.0 part of polycarboxylate water reducer, and 0.6 part of nano-silica dioxide, wherein the water-cement ratio is 0.22;

[0054] The preparation method of the asphalt mixture comprises the following technical steps:

[0055] Step S1. Crush the waste tire powder to a particle size ≤ 80 mesh, and pre-treat it in an oven at 120 °C for 2 hours to dry to a moisture content ≤ 3%. Add 1.2 parts of silane coupling agent (KH-550) to 13 parts of the pre-treated waste tire powder in proportion, and stir at high speed to form surface-activated powder;

[0056] Step S2. Dry-mix 10 parts, 20 parts, 30 parts, 40 parts, 50 parts or 60 parts of cement with 0.6 parts of nano-silica evenly, and grind the evenly mixed cement and nano-silica to a specific surface area ≥ 400 m 2 / kg, add the pre-treated rubber powder and 6 parts of SBS modified asphalt, and continue dry-mixing for 30 minutes to ensure uniform dispersion of the components; among them, the cement is P.O52.5R ordinary Portland cement, and the softening point of the SBS modified asphalt is 85°C and the penetration is 50 dmm;

[0057] Step S3. Slowly add mixing water to the dry materials, with a water-cement ratio of 0.22 (mass ratio of mixing water to cement), adjust the pH to 11.0, and at the same time add 1.0 part of polycarboxylate superplasticizer, and use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculated structure, and transfer it to a high-speed shearer for shearing for 10 minutes to break the flocs and optimize the dispersion.

[0058] Example 6

[0059] Example 6 provides a light and ultra-thin wearing course asphalt mixture and its preparation method. Among them, the light and ultra-thin wearing course asphalt mixture, by mass, includes: 40 parts of cement, 7 parts of SBS modified asphalt, 10 parts of waste rubber powder, 0.8 part of KH-550, 1.0 part of polycarboxylate superplasticizer, and 0.6 part of nano-silica, among which the water-cement ratio is 0.20;

[0060] The preparation method of the asphalt mixture includes the following technical steps:

[0061] Step S1. Crush the waste tire rubber powder to a particle size ≤ 80 mesh, and pre-treat it in an oven at 120°C for 2 hours to dry to a moisture content ≤ 3%, and add 0.8 part of silane coupling agent (KH-550) to the pre-treated 10 parts of waste tire rubber powder according to the proportion, and stir at high speed to form surface-activated rubber powder;

[0062] Step S2. Dry-mix 40 parts of cement with 0.6 parts of nano-silica evenly, and grind the evenly mixed cement and nano-silica to a specific surface area ≥ 400 m 2 / kg, add the pre-treated rubber powder and 7 parts of SBS modified asphalt, and continue dry-mixing for 30 minutes to ensure uniform dispersion of the components; among them, the cement is P.O52.5R ordinary Portland cement, and the softening point of the SBS modified asphalt is 85°C and the penetration is 50 dmm;

[0063] Step S3. Slowly add mixing water to the dry materials, with a water-cement ratio of 0.20 (mass ratio of mixing water to cement), adjust the pH to 9.5 to 12.5, and at the same time add 1.0 part of polycarboxylate superplasticizer, and use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculated structure, and transfer it to a high-speed shearer for shearing for 10 minutes to break the flocs and optimize the dispersion.

[0064] Comparative Example

[0065] Comparative Example 1

[0066] The difference between Comparative Example 1 and Example 1 is that lignosulfonate is used to replace the polycarboxylate water reducer in equal amounts.

[0067] Comparative Example 2

[0068] The difference between Comparative Example 1 and Example 1 is that after dry mixing cement and nano-silica, the order of adding the pretreated rubber powder and SBS modified asphalt is: first add SBS modified asphalt, and then add the rubber powder.

[0069] Performance Test Method

[0070] Freeze-Thaw Splitting Strength Test: According to "Test Procedures for Bitumen and Bituminous Mixtures for Highway Engineering" JTGE20 - 2011, the strength ratio in the freeze-thaw splitting test is used as the evaluation means; cylindrical specimens are made from the micro-surfacing asphalt mixtures prepared in Examples 1 - 6 and Comparative Examples 1 - 2. The size of the specimens is a diameter of 101.6 ± 0.25 mm and a height of 63.5 ± 1.3 mm. The experimental conditions are a temperature of 25°C ± 0.5°C and a loading rate of 50 mm / min for the freeze-thaw splitting test.

[0071] Immersion Marshall Residual Stability Test: The immersion Marshall residual stability of the micro-surfacing asphalt mixtures prepared in Examples 1 - 6 and Comparative Examples 1 - 2 is tested according to the method in "Technical Specifications for Construction of Highway Asphalt Pavements" (JTGF40 - 2004). The higher the freeze-thaw splitting strength and the immersion Marshall residual stability, the higher the water stability of the micro-surfacing asphalt mixture.

[0072] High Temperature Durability: The rutting test of the micro-surfacing asphalt mixtures prepared in Examples 1 - 6 and Comparative Examples 1 - 2 is determined according to the method in "JTGE20 - 2011" to test the dynamic stability of the asphalt mixture.

[0073] Cracking Resistance Performance: The uniaxial compression test of the micro-surfacing asphalt mixtures prepared in Examples 1 - 6 and Comparative Examples 1 - 2 is carried out according to the method in "JTGE20 - 2011" to determine the cracking resistance strength of each test block.

[0074] The test results are shown in Table 1 below.

[0075] Table 1 Experimental Data of Examples 1 to 4 and Comparative Examples 1 to 2

[0076]

[0077] Table 2 is the experimental data of Example 5

[0078]

[0079]

[0080] Table 3 shows the experimental data of Example 6

[0081]

[0082] It can be seen from Examples 1 to 4, Comparative Examples 1 to 2 and Table 1 that the lightweight and ultra-thin wearing asphalt mixtures of Examples 1 to 4 exhibit excellent comprehensive performance. Their freeze-thaw splitting strength ratios reach 85.3%-89.1%, the retained stability of immersion Marshall is 86.5%-90.1%, the dynamic stability range is 4,200-4,800 times / mm, and the anti-cracking strength is 2.6-3.0 MPa. In this application, the silane coupling agent KH-550 is used to strengthen the cement-asphalt interface bonding, the polycarboxylate superplasticizer is used to optimize the cement dispersibility, and the SBS / waste rubber powder composite modification is used to improve the flexibility, effectively balancing the brittleness risk caused by a high cement dosage (60-70 parts). Comparing the data of Example 1 and Comparative Example 1, it can be found that the performance of Example 1 is significantly better than that of Comparative Example 1, especially the improvement in the freeze-thaw splitting strength ratio, anti-cracking strength and dynamic stability. The freeze-thaw splitting strength ratio of Example 1 is 86.7%, the anti-cracking strength is 2.8 MPa, and the dynamic stability is 4500 times / mm, while the freeze-thaw splitting strength ratio of Comparative Example 1 is 76.2%, the anti-cracking strength is only 1.5 MPa, and the dynamic stability is 2300 times / mm. These differences are mainly attributed to the different superplasticizers used. In Example 1, a polycarboxylate superplasticizer is added, which has strong dispersibility and the function of optimizing the hydration reaction. The polycarboxylate superplasticizer molecule contains multiple negatively charged carboxyl groups (-COOH), which can effectively reduce the mutual attraction between cement particles, improve the cement dispersibility, reduce the agglomeration phenomenon of cement particles, and enhance the density and strength of the mixture. In addition, the polycarboxylate superplasticizer can also promote the smooth progress of the cement hydration process, optimize the cement hydration products, and enhance the anti-cracking and freeze-thaw stability of the mixture. In contrast, the lignosulfonate superplasticizer used in Comparative Example 1, although it also has a certain water-reducing effect, its dispersibility and the charge repulsion force between cement particles are weak, resulting in easy aggregation of cement particles, affecting the uniformity and density of the mixture, and thus reducing the overall performance. Therefore, Example 1 significantly improves the performance of the mixture by using the polycarboxylate superplasticizer. Comparing the data of Example 1 and Comparative Example 2, it can be found that the performance of the asphalt mixture in Example 1 is significantly better than that in Comparative Example 2. This is mainly due to the different addition sequences of rubber powder and SBS modified asphalt. In Example 1, the rubber powder and SBS modified asphalt are added first. The advantage of this sequence is that adding the rubber powder first can preferentially absorb the light components in the asphalt, swell, and form an expanded rubber particle network. This pre-swollen rubber particle network can provide better dispersion and anchoring points for the subsequently added SBS modified asphalt, promote the full compatibility and effective modification of SBS and asphalt, and thus improve the overall performance of the asphalt mixture. On the contrary, if the addition sequence is improper, such as adding SBS first or adding them simultaneously, the rubber powder may not swell sufficiently, and the dispersibility of SBS will also be affected, resulting in a reduced modification effect.Therefore, in Example 1, by optimizing the addition sequence of crumb rubber and SBS, more excellent asphalt modification effects are achieved, thus showing better performance in asphalt mixtures.

[0083] Combined with Example 5 and Table 2, it can be seen that when the amount of cement is relatively low, the performance indicators of the lightweight ultra-thin wearing course asphalt mixture are relatively poor, mainly because the insufficient cement content results in insufficient Ca 2+ concentration, which cannot form an effective π-cation chelation coordination with the benzene ring at the end of the styrene hard segment in the SBS modifier. As the amount of cement gradually increases, all the performance indicators of the lightweight ultra-thin wearing course asphalt mixture show an obvious upward trend. However, when the amount of cement continues to increase to 50 parts and 60 parts, the performance indicators begin to decline instead. Excessive addition of cement will cause the mixture to be too rigid, increasing the risk of brittleness, thus reducing the water damage resistance, high-temperature stability and low-temperature crack resistance.

[0084] Combined with Example 6 and Table 3, it can be seen that the pH value has a significant impact on the performance of the lightweight ultra-thin wearing course asphalt mixture. As the pH value increases from 9.5 to 11.0, all the performance indicators show an obvious upward trend: the freeze-thaw splitting strength ratio increases from 72.0% to 92.0%, the residual stability of the soaked Marshall test increases from 75.0% to 94.0%, the dynamic stability increases from 3200 times / mm to 4800 times / mm, and the cracking strength increases from 2.1 MPa to 3.2 MPa. When the pH value reaches a suitable alkaline environment of about 11.0, the benzene ring at the end of the styrene hard segment in the SBS modifier can form the most effective π-cation chelation coordination with Ca 2+ released by the cement hydration products, significantly enhancing the interfacial adhesion between asphalt and aggregates and improving the overall structural stability and durability of the mixture.

[0085] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lightweight ultra-thin overlay asphalt mixture, characterized in that: Calculated by mass, it includes: 30 to 40 parts of cement, 5 to 8 parts of SBS modified asphalt, 10 to 15 parts of waste rubber powder, 0.5 to 1.2 parts of silane coupling agent, 0.8 to 1.5 parts of water reducing agent and 0.3 to 0.8 parts of nano silicon dioxide, wherein the water-cement ratio is 0.18 to 0.

22.

2. The lightweight ultra-thin overlay asphalt mixture according to claim 1, characterized in that: The silane coupling agent is KH-550.

3. The lightweight ultra-thin overlay asphalt mixture according to claim 1, characterized in that: The water reducer is a polycarboxylate water reducer.

4. The method for preparing asphalt mixture according to claim 1, characterized in that: The technical steps include: Step S1. Add the pretreated waste tire rubber powder to the silane coupling agent in proportion, and stir at high speed to form a surface activated rubber powder; Step S2. Dry-mix cement and nano-silica evenly, add pretreated rubber powder and SBS modified asphalt, and continue dry-mixing for 30 minutes to ensure that the components are evenly dispersed; Step S3. Slowly add mixing water to the dry material, and add polycarboxylate water reducer at the same time, use a planetary mixer to stir at low speed for 3 minutes to form a preliminary flocculation structure, and transfer to a high-speed shearing machine for shearing for 10 minutes to destroy the floccules and optimize dispersion.

5. The method for preparing asphalt mixture according to claim 4, characterized in that: In step S1, the waste tire rubber powder is crushed to a particle size of ≤80 mesh, and pre-treated in an oven at 120° C. for 2 hours to dry to a moisture content of ≤3%.

6. The method for preparing asphalt mixture according to claim 4, characterized in that: In step S2, the uniformly mixed cement and nano-silicon dioxide are ground to a specific surface area of ​​≥400m 2 / kg.

7. The method for preparing asphalt mixture according to claim 4, characterized in that: In step S2, after cement and nano-silicon dioxide are dry-mixed, the order of adding pre-treated rubber powder and SBS modified asphalt is: first adding rubber powder, and then adding SBS modified asphalt.

8. The method for preparing asphalt mixture according to claim 4, characterized in that: In step S2, the cement is P.O52.5R ordinary Portland cement, the softening point of SBS modified asphalt is 85-95°C, and the needle penetration is 40-60dmm.

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