A seamless expansion joint mixture suitable for medium expansion and a method of making the same

Abstract

This invention discloses a seamless expansion joint compound suitable for medium expansion and contraction and its preparation method, comprising 22-28 parts polyurethane and 100 parts aggregate and rubber particles. By adjusting the proportion of rubber particles, it can accommodate seamless expansion joints with medium expansion and contraction of 50mm-80mm and tensile deformation rate of 5%-8%. In this invention, polyurethane provides excellent elastic recovery and adhesion, rubber particles contribute high toughness and damping properties, and aggregates of specific particle sizes provide skeletal support and compressive strength. The three components work synergistically, enabling the compound to flexibly absorb stress and prevent cracking under medium expansion and contraction, while rigidly resisting traffic loads and preventing rutting and permanent deformation. By adjusting the proportions of the three components, the elastic modulus of the seamless expansion joint compound can be precisely controlled, placing it between that of highly elastic pure polyurethane and rigid cement-based materials, thereby achieving better modulus matching with adjacent pavement structures, reducing stress concentration at joints, and extending service life.

Description

Technical Field

[0001] This invention relates to the field of highway bridge technology, and in particular to a seamless expansion joint compound suitable for medium expansion and contraction and its preparation method. Background Technology

[0002] Currently, the most widely used seamless expansion joint materials are modified asphalt seamless expansion joint materials and polyurethane seamless expansion joint materials. Among them, modified asphalt seamless expansion joint materials are prone to wear and rutting at high temperatures, and their high-temperature and low-temperature properties conflict, resulting in weak deformation performance. They are generally only used in seamless expansion joints for bridges with small expansion amounts of less than 30mm.

[0003] Polyurethane seamless expansion joint material is a seamless expansion joint material made of polyurethane (PU). This material has good high and low temperature performance, fatigue resistance, and deformation performance. Polyurethane seamless expansion joints are divided into polyurethane concrete type and polyurethane filled type. Polyurethane concrete type seamless expansion joints are limited by the rigidity of mineral powder and fine aggregates, and their deformation performance is also somewhat lacking, so they are only used in bridge seamless expansion joints with small to medium expansion ranges of less than 50mm. Polyurethane filled type seamless expansion joints utilize the hardness of polyurethane itself to withstand vehicle loads and bridge deformation, and can be used in bridge seamless expansion joints with medium to large expansion ranges of 50mm to 100mm. However, seamless expansion joint devices made of pure polyurethane are expensive, have complicated construction processes, and are difficult to implement, making them less economical for seamless expansion joints with medium expansion ranges of 50mm to 80mm.

[0004] Therefore, there is an urgent need for a seamless expansion joint compound that is both economical and has excellent performance, and is suitable for medium expansion joints with an expansion range of 50mm to 80mm. This has important practical significance and application value. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a seamless expansion joint compound suitable for medium expansion and contraction and its preparation method. The seamless expansion joint compound suitable for medium expansion and contraction and its preparation method reduce engineering costs and improve the toughness and deformation resistance of the compound by using rubber particles, provide skeleton support and compressive strength by using aggregates of specific particle sizes, and improve the service life of the compound by using polyurethane adhesive to encapsulate the rubber particles and fine aggregates.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A seamless expansion joint compound suitable for medium expansion and contraction includes the following components and parts by weight: 22-28 parts of polyurethane, and 100 parts of aggregate and rubber granules.

[0008] By adjusting the proportion of rubber particles, it can adapt to seamless expansion joints with a medium expansion range of 50mm~80mm and a tensile deformation rate of 5%~8%.

[0009] The mass fraction of rubber granules is 40-60 parts, and the rubber granule content is positively correlated with the tensile deformation rate of the mixture.

[0010] The rubber granules are in the form of 40 or 60 parts by weight.

[0011] The polyurethane uses PTMG1000 as the soft segment polyol, with an isocyanate index R value of 2.5~3.3; PTMG1000 is a polytetrahydrofuran with a molecular weight of 1000.

[0012] The polyurethane uses PTMG1000 as the soft segment polyol, with an isocyanate index R value of 2.9.

[0013] Methods for obtaining the optimal mass fraction of polyurethane include:

[0014] Step 1: Adjust the mass fraction of polyurethane to make the porosity of the mixture within the range of 3%-6%;

[0015] Step 2: After meeting the requirements of Step 1, adjust the mass fraction of polyurethane again to make the compression recovery rate of the mixture reach more than 98%.

[0016] Step 3: Perform Marshall stability tests on different polyurethane mass fractions that meet the requirements of Step 2, and select the polyurethane mass fraction with the highest stability as the optimal polyurethane mass fraction.

[0017] The rubber granules have a particle size of 1~3mm, and the aggregates have a particle size of 0.3~4.75mm.

[0018] The mixture exhibits a tensile deformation rate of ≥9% at -10℃, a dynamic stability of ≥5000 cycles / mm, and a low-temperature bending tensile strain of ≥190,000 με.

[0019] A method for preparing a seamless expansion joint compound suitable for medium expansion and contraction includes the following steps.

[0020] S1. Collective material is screened and dried;

[0021] S2. Aggregates and rubber granules are premixed at 60°C.

[0022] S3. Add polyurethane to the premixed material from S2 and mix thoroughly.

[0023] S4. Place the mixture completed in S3 in a 120°C oven to cure for 3 hours, and then place it in a 90°C oven to cure for 48 hours.

[0024] In S3, polyurethane is prepared by a semi-prepolymer method.

[0025] The present invention has the following beneficial effects:

[0026] (1) The seamless expansion joint mixture used in this invention provides excellent elastic recovery and adhesion through a polyurethane matrix, high toughness and damping properties through rubber particles, and skeleton support and compressive strength through aggregates of a specific particle size. These three components work synergistically to enable the mixture to flexibly absorb stress and prevent cracking when subjected to moderate expansion and contraction deformation, while also rigidly resisting traffic loads to prevent rutting and permanent deformation. By adjusting the proportions of these three components, the elastic modulus of the seamless expansion joint mixture can be precisely controlled, placing it between that of highly elastic pure polyurethane and rigid cement-based materials. This results in better modulus matching with adjacent pavement structures, reducing stress concentration at joints and extending service life.

[0027] (2) By adjusting the proportion of rubber particles, the present invention can precisely control the tensile deformation rate of the mixture to meet the medium expansion and contraction requirements of 50–80 mm for different bridges.

[0028] (3) The dynamic stability of the mixture of the present invention is ≥5000 times / mm and the low temperature bending tensile strain is ≥190,000 με, which meets the requirements for use in high-grade highways.

[0029] (4) Compared with existing seamless expansion joint materials, the present invention has both rigid and flexible mechanical properties, and also has excellent fatigue resistance and crack resistance. When the rubber particle content is 40 parts, the maximum tensile deformation rate of the mixture should not exceed 8%; when the rubber particle content is 60%, the maximum tensile deformation rate of the mixture should not exceed 9%, which can ensure that it can withstand more than 50 design deformations within 10 years.

[0030] (5) The present invention shows through CCD and SEM analysis that the polyurethane adhesive phase effectively bonds the mineral material and rubber particles, forming a gradient modulus interface, avoiding stress concentration, and improving the overall coordinated deformation capability of the material.

[0031] (6) The seamless expansion joint mixture used in this invention forms an integral seamless and cohesive structure after curing, without weak interfaces, thus avoiding the problems of component aging and falling off in traditional modular expansion joints. Attached Figure Description

[0032] Figure 1 The diagram shows the gradation curves of aggregates with different rubber particle content in this invention.

[0033] Figure 2 A schematic diagram showing the room temperature tensile properties of the PPG-type polyurethane material in this invention is displayed.

[0034] Figure 3A schematic diagram showing the room temperature tensile properties of the PTMG-type polyurethane material in this invention is displayed.

[0035] Figure 4 The graph shows the Marshall stability variation of the PTUR-60 material in this invention under different rubber ratios.

[0036] Figure 5 The diagram shows the flexural strain and flexural strength of mixtures with different rubber particle content.

[0037] Figure 6 The stress-strain curves of PTUR material with different rubber particle content mixtures at -10℃ are shown.

[0038] Figure 7 The tensile properties of mixtures with different rubber particle content at -10℃ are shown in the graph.

[0039] Figure 8 The phase distribution diagram of the mixture after CCD scanning is shown.

[0040] Figure 9 The microstructure of the mixture interface obtained by SEM testing is shown.

[0041] Figure 10 The figure shows the stress peak decay curve in the fatigue test of the mixture of the present invention; (a) is PTUR-40; (b) is PTUR-60.

[0042] Figure 11 The graphs show the relationship between the cumulative energy dissipation and the number of cycles of the mixture of the present invention; wherein, (a) is PTUR-40; and (b) is PTUR-60. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

[0044] A seamless expansion joint compound suitable for medium expansion and contraction includes the following components and parts by weight: 22-28 parts of polyurethane, and 100 parts of aggregate and rubber granules.

[0045] I. Selection of Particle Size of Mixture

[0046] The above-mentioned aggregates and rubber particles together form a mixed aggregate mixture.

[0047] The aggregates are preferably minerals such as basalt and limestone; in this embodiment, basalt is preferred, with a particle size of 0.3~4.75mm. The sieving results are shown in Table 1 below.

[0048] Table 1 Results of water washing and screening of aggregates

[0049]

[0050] As shown in Table 1, the screening results indicate that over 16% of the aggregate consists of dust particles smaller than 0.075 mm, and over 25% is fine material in the 0.075-0.3 mm range. This indicates a significant portion of the aggregate contains fine particles. An excessively high proportion of fine particles can negatively impact the workability of the mixing process, leading to agglomeration, uneven mixing, and the generation of substantial amounts of dust. Therefore, this paper screened out fine materials smaller than 0.3 mm during the mix design process, using aggregate with a particle size of 0.3-4.75 mm as the aggregate skeleton structure for the polyurethane seamless expansion joint mixture.

[0051] The aforementioned rubber granules are preferably desulfurized rubber granules, recycled rubber granules, or EPDM rubber; in this embodiment, EPDM rubber granules are preferred, with a particle size of 1-3 mm. The rubber granules are sieved using a dry sieve method, and the sieve results are shown in Table 2 below, wherein the content of long and flat particles is less than 10%.

[0052] Table 2. Sieving results of rubber particles

[0053]

[0054] The aggregate of this invention has a particle size of 1-3 mm, which is comparable to that of mineral aggregate (0.3-4.75 mm). This avoids the situation where larger mineral aggregate particles are replaced by smaller rubber particles. The amount of rubber particles incorporated is adjusted by mass substitution, with a 20% interval gradient. Rubber particles are added to the mixture at 0%, 20%, 40%, 60%, 80%, and 100% of the total mass of mineral aggregate and rubber particles, respectively. The effect of rubber particle incorporation on the performance of polyurethane seamless expansion joint mixture is studied.

[0055] Based on Tables 1 and 2 and the mass ratio of mineral aggregate to rubber granules, the gradation curve of the "mineral aggregate + rubber granules" mixed aggregate was calculated, as follows: Figure 1 As shown, from Figure 1 It can be seen that as the amount of rubber granules added increases, the particle size of 1-4 mm in the mixed aggregate gradually increases. This will result in more voids in the aggregate with a higher rubber content during the mixing process, potentially weakening the mixture's density, strength, and resistance to water damage. The density of the added rubber granules is approximately 1.15 g / cm³. 3 The density is much lower than that of mineral aggregates. This requires further increasing the amount of polyurethane binder when molding high-content rubber granule mixtures. By utilizing the good fluidity of polyurethane binder and the good oil absorption of rubber granules, the polyurethane binder can fully fill the gaps between "rubber-mineral aggregate", "rubber-rubber", and "mineral aggregate-mineral aggregate", so that the molded mixture has a low porosity.

[0056] II. Selection of Polyurethane Type

[0057] This invention selects one binder with the best performance from both PPG-type polyurethane and PTMG-type polyurethane for the preparation of the mixture. For ease of expression and identification, the polyurethane with a PPG soft segment molecular weight of 1000 is named PU1, the polyurethane with a PPG soft segment molecular weight of 2000 is named PU2, the polyurethane with a PTMEG soft segment molecular weight of 1000 is named TPU1, and the polyurethane with a PTMEG soft segment molecular weight of 2000 is named TPU2.

[0058] For PPG-type polyurethanes, such as Figure 2 As shown, its tensile strength first increases and then decreases with the increase of R value, while the elongation at break gradually decreases.

[0059] Furthermore, as the R-value increases, the hardness of the polyurethane binder rises. The increase in R-value simultaneously promotes an increase in elastic components and a decrease in viscous components, significantly impacting the viscoelastic properties of polyurethane materials. Optimization of the R-value significantly improves the mechanical strength and thermal stability of the material.

[0060] For both polyurethane materials, the polyurethane with a soft segment polyol molecular weight of 1000 exhibits better tensile strength and elongation at break than that with a soft segment polyol molecular weight of 2000. Comprehensive analysis results indicate that among various PPG-type polyurethane materials, the material with the best tensile properties is PU1 prepared using PPG1000 as the soft segment polyol with an R value of 2.9. PPG1000 is polypropylene glycol with a molecular weight of 1000. Similarly, among various PTMG-type polyurethane materials, the material with the best tensile properties is TPU1 prepared using PTMG1000 as the soft segment polyol with an R value of 2.9. PTMG1000 is polytetrahydrofuran with a molecular weight of 1000.

[0061] III. Polyurethane Adhesive Ratio

[0062] The polyurethane mentioned above is the binder in the mixture. The ratio of polyurethane to the aggregate mixture (the sum of aggregate and rubber particles) is called the binder ratio. For ease of expression and identification, PPG-type polyurethane mixtures are named PPUR. Based on the amount of rubber particles in the mixture from low to high, the mixtures are named as follows: PPUR-0, PPUR-20, PPUR-40 (the mass ratio of polyurethane to aggregate mixture is 40%, and so on), PPUR-60, PPUR-80, and PPUR-100. Similarly, PTMG-type polyurethane mixtures are named as PTUR-0, PTUR-20, PTUR-40, PTUR-60, PTUR-80, and PTUR-100.

[0063] Taking PTUR-60 as an example, this invention introduces the process of determining the optimal rubber compound ratio of the mixture. With 2% intervals, the proposed rubber compound ratios are 20%, 22%, 24%, 26%, 28%, and 30%. For each rubber compound ratio, four standard Marshall specimens are molded to carry out Marshall tests.

[0064] Considering that seamless expansion joint compounds are mainly used in bridge structures of busy highways, urban roads, and expressways, their porosity should be controlled between 3% and 6%. Within this porosity range, the compound can meet load-bearing capacity requirements while avoiding the adverse effects of excessively low porosity on the elasticity and crack resistance of the expansion joint. Furthermore, this porosity helps ensure the compound's resistance to water damage. Therefore, the optimal binder-to-mortar ratio should be between 22% and 28%.

[0065] The preferred method for obtaining the optimal mass fraction of the aforementioned polyurethane includes the following steps.

[0066] Step 1: Adjust the mass fraction of polyurethane to make the porosity of the mixture within the range of 3%-6%.

[0067] Step 2: After satisfying the requirements of Step 1, adjust the mass fraction of polyurethane to achieve a compression recovery rate of over 98% for the mixture.

[0068] Step 3: Perform Marshall stability tests on different polyurethane mass fractions that meet the requirements of Step 2, and select the polyurethane mass fraction with the highest stability as the optimal polyurethane mass fraction.

[0069] Using the above-described method, the optimal mass fraction (optimal binder ratio) of the polyurethane in this invention is preferably 24%. At this value, the Marshall stability and flow value of the PTUR-60 material are the highest. Among these, as shown... Figure 4 As shown, the Marshall strength reached 9.19 kN.

[0070] IV. Rubber Particle Content

[0071] The preferred mass fraction of rubber granules is 40-60 parts, and the rubber granule content is positively correlated with the tensile deformation rate of the mixture.

[0072] Under low-temperature conditions in winter, the expansion joints will experience significant tensile deformation due to the shrinkage and deformation of structures such as bridge decks connected by seamless expansion joints. Simultaneously, repeated vehicle loads can easily lead to damage such as low-temperature cracking. To investigate the effect of different rubber particle dosages on the low-temperature performance of two polyurethane blends (PPUR and PTUR), this section uses low-temperature beam bending tests for analysis.

[0073] During the low-temperature bending test of small beams, it was found that the mid-span displacement corresponding to the peak test force of the PPUR and PTUR mixture small beam specimens at -10℃ exceeded 35mm, which indicates that the two types of mixtures still have extremely strong flexibility in low-temperature environments.

[0074] Figure 5 This diagram shows the flexural strain and flexural strength of mixtures with different rubber particle content. Figure 5 The calculated tensile strength and strain of the beam show that the tensile strain gradually increases with the increase of rubber particle content in the mixture. Specifically, the tensile strain of the PPUR mixture increases from 198,323 με in PPUR-0 to 241,397 με in PPUR-100, an increase of 43,074 με. The tensile strain of the PTUR mixture increases from 209,379 με in PTUR-0 to 244,565 με in PTUR-100, an increase of 35,186 με. The results indicate that both PPUR and PTUR mixtures exhibit excellent tensile deformation capacity, and the increase in rubber particle content significantly improves their deformation performance. This is because rubber particles themselves have high elasticity and flexibility, enabling them to undergo large deformations under external forces. Therefore, when rubber particles are incorporated into the mixture, they effectively absorb and disperse externally applied stress and strain, delaying crack initiation and propagation, thereby enhancing the overall deformation capacity of the material. Meanwhile, as the amount of rubber particles increases, the interaction between particles becomes more significant. At higher dosages, a certain network structure is formed between the rubber particles, which is more conducive to the transfer and dispersion of loads, thereby improving their bending deformation capacity.

[0075] from Figure 5The test results of the flexural tensile strength of the materials also revealed that the flexural tensile strength of both PPUR and PTUR blends gradually decreased with the increase of rubber particle content in the blend. Furthermore, under the same rubber particle content, the flexural tensile strength of the PTUR blend was higher than that of the PPUR blend, and the strength difference between the two gradually decreased with the increase of rubber particles. Specifically, the PPUR blend with the highest flexural tensile strength was PPUR-0, at 3.86 MPa, while the lowest was PTUR-100, at 2.00 MPa. For the PTUR blend, the highest flexural tensile strength was PTUR-0, at 5.51 MPa, while the lowest was PTUR-100, at 2.23 MPa. The test results indicate that the increase of rubber particles reduced the strength of the blend and, to some extent, weakened the strength difference between the PPUR and PPUR blends. This is because while the incorporation of rubber particles improves the flexibility and deformability of the blend, its high toughness and low rigidity lead to a decrease in the blend's strength. Secondly, the superior mechanical strength of TPU1 compared to PU1 also contributes to the difference in flexural strength between PPUR and PTUR blends. However, as the number of rubber particles increases, the proportion of rigid mineral components in the material gradually decreases, partially "balancing" the difference in flexural strength, thus gradually reducing the gap in flexural strength between the two.

[0076] Under the same rubber particle content, the flexural strain and flexural strength of PTUR material are consistently higher than those of PPUR material. This indicates that TPU1 material has stronger adhesion to the interface with rubber particles, and compared to PU1 material, TPU1 can more effectively maintain the stability of the interfacial bond. Therefore, PTUR material exhibits better performance in low-temperature resistance.

[0077] Stress-strain curves of mixtures with different rubber particle contents at different temperatures are shown below. Figure 6 The figure shows the stress-strain variation of PTUR mixture at -10℃. As can be seen from the figure, under different temperature conditions, the stress-strain curves of the mixture exhibit characteristics similar to those of metallic materials, and can be roughly divided into three stages: "elastic-yield," "stress decay," and "fracture."

[0078] The first stage is the elastic-yield stage. In this stage, the stress and strain of the material initially increase linearly, consistent with the characteristics of elastic deformation. However, as the strain continues to increase, the stress growth begins to slow down, entering a yield stage similar to that of metallic materials, until the stress gradually increases to its peak. During this stage, the components in the mixture form a complete whole under the bonding action of the binder. Simultaneously, the phenomenon that the stress value of the material gradually increases with increasing strain indicates that no significant internal damage occurs in the material during this stage.

[0079] Taking the stress-strain diagram of PTUR mixture at -10℃ as an example, the strain range of the mixture in the first stage gradually widens with the increase of rubber particle content. This is because rubber particles themselves have high elastic deformation capacity. When the mixture undergoes large deformation under external force, they can play a good role in deformation coordination, effectively extending the stress growth range of the mixture. Therefore, when rubber particles are added to the mixture, the overall elastic deformation capacity of the material is enhanced, allowing it to maintain elastic deformation within a larger strain range. At the same time, the elasticity and flexibility of rubber particles help the material absorb more strain, enabling the mixture to enter the yield state under greater strain, and making the yielding phenomenon more gradual and smooth. Secondly, rubber particles reduce stress concentration in local areas, making the stress distribution of the mixture in the first stage more uniform.

[0080] The second stage is the stress decay stage. In this stage, the stress in the material no longer increases continuously with increasing strain, but instead enters a gradually decreasing stress decay stage. The stress-strain change law in this stage is similar to the "necking" stage of metallic materials. However, unlike metallic materials, PTUR mixtures do not exhibit localized abrupt shrinkage leading to necking; therefore, this stage is named the stress decay stage. In this stage, although no obvious damage occurs on the surface of the mixture as the deformation further increases, the stress decay indicates that irreversible micro-damage must have occurred inside the mixture, causing the stress value to gradually decrease with further increases in deformation.

[0081] The third stage – the fracture stage. In this stage, the stress in the material rapidly decreases with increasing strain until fracture occurs. At this stage, the deformation of the material has reached its limit, and the binder can no longer provide good adhesion, causing the mixture to fracture.

[0082] In summary, when determining the tensile strength and tensile deformation rate of a mixture based on the stress-strain curve, the tensile strength at fracture and elongation at fracture cannot be used as the final result, as is the case with tensile tests on cementitious materials. Considering the stress attenuation phenomenon caused by irreversible damage within the structure during the second stage, the stress value at which the mixture reaches its peak stress should be selected as its tensile strength, and the strain at that moment should be used as its tensile deformation rate.

[0083] The tensile properties of PPUR and PTUR mixtures obtained by the above method under different rubber particle contents are as follows: Figure 7 As shown, Figure 7The experimental results show that the tensile strength of PPUR and PTUR blends gradually decreases with increasing rubber particle content. The tensile strength of the PPUR blend decreased from 2.19 MPa for PPUR-0 to 0.85 MPa for PPUR-100, a decrease of 61%; the tensile strength of the PTUR blend decreased from 2.78 MPa for PTUR-0 to 0.90 MPa for PTUR-100, a decrease of 68%. Secondly, with increasing rubber particle content, the tensile deformation rate of the blends gradually increases. The tensile deformation rate of the PPUR blend increased from 2.78% for PPUR-0 to 10.69% for PPUR-100, an increase of 2.8 times. The tensile deformation rate of the PTUR blend increased from 5.99% for PTUR-0 to 11.28% for PTUR-100, an increase of 0.88 times. This phenomenon indicates that rubber particles play a significant role in improving the material's deformation properties within the blend system. The addition of rubber granules alters the mechanical structure of the mixture. The rubber granules increase the proportion of variable components in the mixture, which to some extent disperse external loads and mitigate stress concentration. Simultaneously, with the increase in rubber granules, the material's mechanical structure shifts towards greater flexibility, which also reduces the tensile strength of the mixture to some extent. However, this structural change enhances the material's deformation capacity during tensile testing, resulting in a significant increase in the tensile deformation rate of the mixture.

[0084] In addition, the tensile deformation rate of the mixture at -10℃ is ≥9%, the dynamic stability is ≥5000 cycles / mm, and the low-temperature bending tensile strain is ≥190,000 με.

[0085] Tensile properties of PPUR and PTUR blends at 25℃ and 60℃. Test results show that the tensile properties of both blends exhibit similar trends to those at -10℃. Tensile strength gradually decreases with increasing rubber particle content, while tensile deformation rate gradually increases with increasing rubber particle content.

[0086] The tensile strength of PPUR mixtures at 25℃ decreased by 67% from 0.85 MPa for PPUR-0 to 0.28 MPa for PPUR-100; the tensile deformation rate increased from 7.59% for PPUR-0 to 10.39% for PPUR-100. Similarly, the tensile strength of PTUR mixtures at 25℃ decreased by 69% from 1.33 MPa for PTUR-0 to 0.41 MPa for PTUR-100; the tensile deformation rate increased from 7.88% for PTUR-0 to 11.15% for PPUR-100.

[0087] The tensile strength of PPUR mixtures at 60℃ decreased by 79% from 0.39 MPa for PPUR-0 to 0.08 MPa for PPUR-100; the tensile deformation rate increased from 2.15% for PPUR-0 to 4.85% for PPUR-100. The tensile strength of PTUR mixtures at 25℃ decreased by 77% from 0.56 MPa for PTUR-0 to 0.13 MPa for PTUR-100; the tensile deformation rate increased from 4.50% for PTUR-0 to 6.31% for PPUR-100.

[0088] The research results on the road performance and deformation performance of the mixture show that among the PPUR and PTUR mixtures that meet the road performance requirements, PTUR-40 and PTUR-60 have better deformation performance. Their tensile deformation rates at -10℃ are 9.01% and 9.94%, respectively. This ensures that they can be applied in seamless expansion joints with medium expansion range of 50mm-80mm and tensile deformation rate of 5%-8%.

[0089] A method for preparing a seamless expansion joint compound suitable for medium expansion and contraction includes the following steps.

[0090] S1. Collective material is screened and dried.

[0091] S2. Aggregates and rubber granules are premixed at 60°C.

[0092] S3. Add polyurethane to the premixed material from S2 and mix thoroughly.

[0093] S4. Place the mixture completed in S3 in a 120°C oven to cure for 3 hours, and then place it in a 90°C oven to cure for 48 hours.

[0094] In S3, polyurethane is prepared by a semi-prepolymer method.

[0095] This invention, by adjusting the proportion of rubber particles, can adapt to seamless expansion joints with a medium expansion range of 50mm to 80mm and a tensile deformation rate of 5% to 8%.

[0096] Figure 8 The image shows the phase distribution of the mixture after CCD scanning, from Figure 8 As can be seen, the seamless expansion joint mixture containing rubber particles is a complex multiphase system, in which the mineral phase, polyurethane adhesive phase, and rubber particle phase are interspersed. Furthermore, as the amount of rubber particles increases, the proportion of the mineral phase in the mixture gradually decreases, while the proportion of the rubber particle phase gradually increases, and the proportion of the polyurethane adhesive phase remains relatively stable.

[0097] Figure 9 The SEM images show the microstructure of the mixture interface. Figure 9 As can be seen, the polyurethane adhesive phase forms an intermediate transition zone between rubber particles, mineral aggregates, and other particles. This prevents direct contact between the aggregate particles and provides a deformation buffer space for the mixture. Secondly, the interface shape between the rubber particles and the mineral aggregates shows that the boundary of the mineral aggregate interface is complex and varied, while the rubber particle interface is relatively smooth. This indicates that there is stronger mechanical interlocking between the mineral aggregate interface and the polyurethane adhesive, which to some extent strengthens the bonding between the polyurethane adhesive and the mineral aggregates.

[0098] Furthermore, it can be observed that the thickness of the polyurethane adhesive transition zone between aggregate particles is inconsistent, generally exhibiting a trend of rubber-rubber > rubber-mineral aggregate > mineral aggregate-mineral aggregate. This is due to several factors: First, the rubber particles are slightly larger than the mineral aggregate, allowing for larger gaps between them and enabling more polyurethane adhesive to remain. Second, during the compaction process of the mixture, the rubber particles, due to their deformation capacity, easily form cavities, which can retain more polyurethane adhesive. This phenomenon is also the main reason why seamless expansion joint mixtures with high rubber particle content have better deformation performance and a larger optimal adhesive ratio.

[0099] Optical scanning CCD and SEM observations show that the seamless expansion joint compound with rubber particles is composed of three phases: a mineral phase, a polyurethane mortar phase, and a rubber particle phase. The polyurethane mortar phase acts as an intermediate transition zone between the other two phases, and its excellent bonding ability tightly binds them together, forming a complete compound network. This allows the seamless expansion joint compound with rubber particles to withstand both load and tensile deformation, making it a promising candidate for application in seamless expansion joints with moderate expansion ranges.

[0100] Figure 10 This diagram displays the stress peak decay curve of the mixture in the fatigue test of the present invention. The stress peak values ​​of PTUR-40 and PTUR-60 materials during each cyclic tensile process are extracted from the stress-strain curve of the fatigue test. The stress decay of the mixture after 10 cyclic tensile deformations under different deformation rates is also shown. Figure 10It can be seen that the stress decay process of the PTUR-40 and PTUR-60 mixtures in the fatigue test can be divided into two stages. The first stage is the rapid stress decay stage; in the first four cycles of the fatigue test, the stress decay of the mixtures exhibits a significant nonlinear decreasing trend, and this trend becomes more prominent with the increase of the deformation rate. This indicates that in the initial stage of cyclic tensile testing, the mixtures experience significant stress decay due to plastic deformation and adaptive reorganization of the internal structure. As the tensile deformation rate increases during the cycle, the deformation and damage of the mixtures in the early stage intensify, leading to a greater magnitude of stress decay. The second stage is the uniform stress decay stage. In the fourth to tenth cycles, the stress decay of both mixtures changes to a linear decreasing trend. This indicates that after four cycles, the stress decay of the mixtures tends to stabilize, the rate of damage accumulation slows down, and it enters a relatively stable fatigue state. This phenomenon indicates that after the initial rapid damage, the fatigue damage rate of both mixtures gradually stabilizes, and the stress enters a uniform decay stage. PTUR-40 and PTUR-60 materials can still be used normally after 10 cycles of tensile testing in seamless expansion joints with a design maximum tensile deformation rate of 5% to 9%. To ensure that the seamless expansion joint mixture has a service life of more than 10 years, the design maximum tensile deformation rate of PTUR-40 material should not exceed 8%, and the design maximum tensile deformation rate of PTUR-60 material should not exceed 9%.

[0101] Figure 11 The graph showing the relationship between the cumulative dissipated energy of the mixture of the present invention and the number of cycles is displayed. Figure 11 The cumulative energy dissipation curves of PTUR-40 and PTUR-60 mixtures at different tensile deformation rates show that the cumulative energy dissipation generally increases linearly. Once the cumulative energy dissipation reaches a certain level, fatigue failure occurs. The slope of the curve can be considered the rate of increase of the cumulative energy dissipation. This indicates that the energy dissipation rate of both mixtures gradually increases with the maximum tensile deformation rate. This suggests that at higher deformation rates, the mixture is more likely to reach the critical point of cumulative energy dissipation, which is the main reason for the significant reduction in fatigue life of the mixture under higher tensile deformation rates.

[0102] After a certain number of cyclic tensile tests, both PTUR-40 and PTUR-60 blends enter a fatigue stability stage, and energy loss tends to stabilize. The blends are designed to withstand more than 50 cycles of maximum design tensile deformation within 10 years. When designing seamless expansion joint dimensions, the maximum design tensile deformation rate for PTUR-40 should not exceed 8%, and for PTUR-60, it should not exceed 9%.

[0103] The present invention was verified through experiments using the following two comparative examples.

[0104] Comparative Example 1:

[0105] A comparative example of a seamless expansion joint compound for medium-amplitude expansion and contraction and its preparation method specifically includes the following components: by weight, 100 parts aggregate and 20 parts polyurethane. The diisocyanate in the polyurethane is selected as diphenylmethane diisocyanate, and the polyol is polytetrahydrofuran (molecular weight 2000), with a diisocyanate:polyol ratio of 2:1. The chain extender is selected as 1,4-butanediol and 1,4-cyclohexanediol, with a 1,4-butanediol:1,4-cyclohexanediol ratio of 2:1. The comparative example uses the same polyurethane formulation and preparation method as the example, as shown below.

[0106] Step 1: Use a standard vibrating screen to remove fine powder minerals with a particle size of less than 0.3 mm from the mineral material. Place the remaining mineral material in an oven at 105±5°C and dry it for 4 hours for later use.

[0107] Step 2: Add the dried mineral material and rubber granules to the mixing pot in a certain amount and premix at 60°C for 60 seconds to make the rubber granules and mineral material evenly dispersed.

[0108] Step 3: After stirring, add a certain amount of polyurethane prepolymer and curing agent to the mixing pot, and continue stirring at 60°C for 120 seconds to obtain the polyurethane seamless expansion joint mixture.

[0109] Step 4: After the mixture is mixed and formed, place it in a 120°C oven to cure for 3 hours, and then place it in a 90°C oven to cure for 48 hours.

[0110] Comparative Example 2:

[0111] This comparative example describes a seamless expansion joint compound for medium expansion and contraction and its preparation method, specifically comprising the following components: by weight, 0 parts aggregate, 100 parts rubber granules, and 26 parts polyurethane.

[0112] Example 1:

[0113] This embodiment provides a seamless expansion joint compound for medium expansion and contraction and its preparation method, which specifically includes the following components: by weight, 80 parts of aggregate, 20 parts of rubber granules, and 22 parts of polyurethane.

[0114] Example 2:

[0115] This embodiment provides a seamless expansion joint compound for medium expansion and contraction and its preparation method, which specifically includes the following components: by weight, 60 parts of aggregate, 40 parts of rubber granules, and 24 parts of polyurethane.

[0116] Example 3:

[0117] This embodiment provides a seamless expansion joint compound for medium expansion and contraction and its preparation method, which specifically includes the following components: by weight, 40 parts of aggregate, 60 parts of rubber granules, and 24 parts of polyurethane.

[0118] Example 4:

[0119] This embodiment provides a seamless expansion joint compound for medium expansion and contraction and its preparation method, which specifically includes the following components: by weight, 20 parts of aggregate, 80 parts of rubber granules, and 26 parts of polyurethane.

[0120] The road performance and tensile properties of the seamless expansion joint mixtures in the examples and comparative examples are shown in Tables 3 and 4.

[0121] Table 3 Road performance of seamless expansion joint mixture

[0122]

[0123] Table 4 Tensile properties of seamless expansion joint mixture

[0124]

[0125] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A seamless expansion joint compound suitable for medium expansion and contraction, characterized in that: Includes the following components and parts by weight: 22-28 parts of polyurethane 100 parts of aggregate and rubber granules By adjusting the proportion of rubber particles, it can adapt to seamless expansion joints with a medium expansion range of 50mm~80mm and a tensile deformation rate of 5%~8%.

2. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 1, characterized in that: The mass fraction of rubber granules is 40-60 parts, and the rubber granule content is positively correlated with the tensile deformation rate of the mixture.

3. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 2, characterized in that: The rubber granules are in the form of 40 or 60 parts by weight.

4. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 1 or 3, characterized in that: The polyurethane uses PTMG1000 as the soft segment polyol, with an isocyanate index R value of 2.5~3.3; PTMG1000 is a polytetrahydrofuran with a molecular weight of 1000.

5. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 4, characterized in that: The polyurethane uses PTMG1000 as the soft segment polyol, with an isocyanate index R value of 2.

9.

6. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 1, characterized in that: Methods for obtaining the optimal mass fraction of polyurethane include: Step 1: Adjust the mass fraction of polyurethane to make the porosity of the mixture within the range of 3%-6%; Step 2: After meeting the requirements of Step 1, adjust the mass fraction of polyurethane again to make the compression recovery rate of the mixture reach more than 98%. Step 3: Perform Marshall stability tests on different polyurethane mass fractions that meet the requirements of Step 2, and select the polyurethane mass fraction with the highest stability as the optimal polyurethane mass fraction.

7. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 1, characterized in that: The rubber granules have a particle size of 1~3mm, and the aggregates have a particle size of 0.3~4.75mm.

8. The seamless expansion joint compound suitable for medium expansion and contraction as described in claim 1, characterized in that: The mixture exhibits a tensile deformation rate of ≥9% at -10℃, a dynamic stability of ≥5000 cycles / mm, and a low-temperature bending tensile strain of ≥190,000 με.

9. A method for preparing a seamless expansion joint compound suitable for medium expansion and contraction, characterized in that: Includes the following steps: S1. Collective material is screened and dried; S2. Aggregates and rubber granules are premixed at 60°C. S3. Add polyurethane to the premixed material from S2 and mix thoroughly. S4. Place the mixture completed in S3 in a 120°C oven to cure for 3 hours, and then place it in a 90°C oven to cure for 48 hours.

10. The method for preparing a seamless expansion joint compound suitable for medium expansion and contraction according to claim 9, characterized in that: In S3, polyurethane is prepared by a semi-prepolymer method.

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