A cerf compressible material, its method of manufacture and use

Abstract

The application discloses a CERF compressible material and a preparation method and application thereof, and comprises the following raw materials in parts by weight: modified polypropylene foam particles 8-12 parts, cement 319-531 parts, water 124-191 parts, medium sand 425-766 parts, rubber powder 60-90 parts, polymer fiber material 2.58-15.48 parts, and water reducing agent 3.19-5.31 parts; the modified polypropylene foam particles are polypropylene foam particles coated with a cement shell layer; the compatibility of the polypropylene foam particles in the concrete is improved by adding the modified polypropylene foam particles coated with the cement shell layer, so that the toughness and ductility of the concrete are significantly improved, the compressibility of the concrete is ensured, and the brittleness of the concrete is reduced; the toughness and ductility of the concrete are further improved through the synergistic effect of the added polymer fiber material and rubber powder and the modified polypropylene foam particles, so that the CERF concrete has more excellent compressibility and is more suitable for large-scale production and application.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a CERF compressible material, its preparation method, and its application. Background Technology

[0002] As the construction of highways and high-speed railways in my country shifts towards the central and western regions, the number of tunnels in high-stress soft rock areas, such as the Sichuan-Tibet Railway, is increasing. Most high-stress soft rocks exhibit rheological properties, with surrounding rock creep posing a significant threat to operational tunnels. Investigations have revealed that several highway and railway tunnels, including a long highway tunnel in western Sichuan, a railway tunnel between Kunming and Dali in western Yunnan, and a highway tunnel at the border of Shaanxi and Sichuan, have experienced secondary lining cracking and floor heave due to surrounding rock creep during operation, severely impacting operational safety. Currently, many tunnel projects still employ a "strong support and hard roof" support method. However, soft rock remains in a rheological state, and its strength and other mechanical parameters gradually weaken over time after construction, leading to increased rheological displacement of the surrounding rock in the later stages of tunnel construction or operation. Rigid support structures in tunnels have poor adaptability to surrounding rock deformation and exhibit inconsistent deformation, making them unable to accommodate long-term creep deformation of the tunnel's surrounding rock.

[0003] Under high ground stress conditions, traditional methods such as "strengthened support" and "strong support and hard roof" for soft rock tunnels, which rely on increasing the strength and stiffness of the support structure and timely or advanced support, cannot completely solve the problem of large deformations caused by creep in soft rock tunnels. Therefore, based on the experience of rigid support, flexible support and combined support, scholars at home and abroad have taken a different approach and carried out theoretical, experimental and applied research on energy-absorbing and pressure-relieving support set between the surrounding rock and the initial support or between the initial support and the secondary lining. The current research status is to use the formwork method to cast compressible modified concrete with certain energy-absorbing and pressure-relieving properties between the secondary lining and the initial support of tunnels constructed by drill and blast method.

[0004] Existing compressible modified concretes mainly include: polystyrene foam (EPS) concrete, polyurethane foam (PU) concrete, ethylene-vinyl acetate copolymer rubber (EVA) foam concrete, polyethylene chemically cross-linked high-expansion (PEF) concrete, and polypropylene foam (EPP) concrete. Modification methods mostly employ substitution, using foam particles of equal volume to replace coarse aggregates to achieve the compressibility of foam concrete under certain pressure. However, the added foam materials such as EPS, PU, ​​EVA, PEF, and EPP in existing compressible modified concretes have problems such as low thermal sensitivity, poor degradation, water pollution, and high cost, which severely limit the large-scale application of these compressible modified concretes.

[0005] To address these shortcomings, researchers proposed using polypropylene (EPP) foam particles to prepare compressible modified concrete. However, studies have shown that while compressible modified concrete prepared using EPP foam particles improves upon these issues, it exhibits significant brittleness, high strength with limited compressibility, and insufficient toughness and ductility, which are clearly detrimental to the development and application of polypropylene foam concrete. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of insufficient toughness and ductility in existing polypropylene foam concrete, and to propose a CERF (C: cement; E: polypropylene particles; R: rubber powder; F: fiber) compressible material, its preparation method and application.

[0007] To achieve the above-mentioned objectives, this invention proposes a CERF compressible material, which is prepared from the following raw materials in parts by weight: 8-12 parts modified polypropylene foam particles, 319-531 parts cement, 124-191 parts water, 425-766 parts medium sand, 60-90 parts rubber powder, 2.58-15.48 parts polymer fiber material, and 3.19-5.31 parts water-reducing agent; wherein the modified polypropylene foam particles are polypropylene foam particles with a cement shell coating on the surface.

[0008] This invention discloses a CERF compressible material that not only improves the compatibility of PVC foam particles in concrete by adding modified PVC foam particles coated with a cement shell, thereby significantly improving the toughness and ductility of concrete and ensuring compressibility while reducing brittleness; but also further enhances the toughness and ductility of concrete through the synergistic effect of added polymer fiber materials and rubber powder with the modified PVC foam particles, making CERF concrete more compressible and more suitable for large-scale production and application.

[0009] Preferably, in the modified polypropylene foam particles, the ratio of the radius of the polypropylene foam particles to the thickness of the cement shell is not less than 5; the preferred thickness of the cement shell significantly improves the compatibility of the polypropylene foam particles in concrete without significantly increasing the strength of the polypropylene foam particles, thus ensuring that the polypropylene foam particles still have good compressibility after being subjected to stress, and the resulting concrete has significantly improved toughness and ductility without affecting compressibility; more preferably, the ratio of the radius of the polypropylene foam particles to the thickness of the cement shell is 8-12.

[0010] Preferably, the polypropylene foam particles have a diameter of 3-5 mm, a bulk density of 10-15 kg / m3, an apparent density of 18-22 kg / m3, and a porosity of 20-25%. These preferred polypropylene foam particle parameters provide better dispersibility and compressibility, and are also more conducive to controlling the thickness of the cement shell layer.

[0011] Preferably, the preparation method of the modified polypropylene foam particles includes: impregnating the polypropylene foam particles with an adhesive solution, and then coating and curing them with cement (dry powder); the preparation method is simple and reliable, and suitable for large-scale production of modified polypropylene foam particles.

[0012] Preferably, the adhesive solution is an aqueous solution of redispersible adhesive powder with a mass percentage of 45-55%; it has moderate adhesion, which is more conducive to the formation and thickness control of the cement shell layer.

[0013] Preferably, the cement is silicate cement, such as P.O42.5R cement.

[0014] Preferably, the apparent density of the medium sand is 2600-2700 kg / m3, and the fineness modulus is 2.5-2.7.

[0015] Preferably, the rubber powder has a particle size of 30-50 mesh, a bulk density of 300-350 kg / m³, and an apparent density of 700-800 kg / m³; it has better dispersibility and can better improve the toughness and ductility of the material.

[0016] Preferably, the polymer fiber material has a length of 3-18 mm, an elongation at break of ≤30%, a tensile strength of ≥1550 MPa, a density of 1.28-1.31 g / cm³, an initial modulus of ≥35 GPa, and an equivalent diameter of 15-31 μm. With the preferred polymer fiber material performance parameters, the resulting CERF compressible material has better toughness and ductility.

[0017] More preferably, the polymer fiber material is polyvinyl alcohol fiber material; the preferred fiber type has low cost, good environmental affinity, and excellent performance, which is more conducive to the large-scale production and application of CERF compressible materials.

[0018] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent; it has better water-reducing performance and better overall properties of the CERF compressible material.

[0019] To achieve the above-mentioned objectives, this invention further proposes a method for preparing a CERF compressible material, comprising the following steps:

[0020] (1) After mixing the medium sand and cement evenly, add rubber powder, modified polypropylene foam particles and polymer fiber materials, and mix evenly to obtain the mixture;

[0021] (2) Add water and water-reducing agent to the mixture and continue to stir and mix evenly to obtain CERF compressible material.

[0022] Preferably, the stirring speed in the preparation method is 20-35 r / min, and the time is not less than 60 s.

[0023] To further achieve the above-mentioned objectives, this invention proposes an application of CERF compressible material in high-stress soft rock tunnels.

[0024] Preferably, the CERF compressible material is used in prefabricated tunnel segments.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The CERF compressible material of this invention improves the compatibility of polypropylene foam particles in concrete by adding modified polypropylene foam particles coated with a cement shell, thereby significantly improving the toughness and ductility of concrete, ensuring compressibility, and reducing the brittleness of concrete.

[0027] 2. The CERF compressible material of this invention further improves the toughness and ductility of concrete through the synergistic effect of the added polymer fiber material and rubber powder with modified polypropylene foam particles.

[0028] 3. The raw materials in the CERF compressible material of this invention have good environmental compatibility, will not pollute water sources, and have low production costs, making them suitable for large-scale promotion and application.

[0029] 4. The preparation method of the CERF compressible material of the present invention is simple and reliable, and the obtained CERF compressible material has good performance and is suitable for large-scale production of CERF compressible materials. Attached Figure Description

[0030] Figure 1 This is a curve showing the lateral confined compressive stress-volume strain relationship of the CERF compressible material in Embodiment 1 of the present invention.

[0031] Figure 2 This is a curve showing the lateral confined compressive stress-volume strain relationship of the CERF compressible material in Embodiment 2 of the present invention.

[0032] Figure 3 This is a curve showing the lateral confined compressive stress-volume strain relationship of the CERF compressible material in Embodiment 3 of the present invention.

[0033] Figure 4This is a curve showing the lateral confined compressive stress-volume strain relationship of the CERF compressible material in Comparative Example 1 of the present invention.

[0034] Figure 5 This is a curve showing the lateral confined compressive stress-volume strain relationship of the CERF compressible material in Comparative Example 2 of the present invention.

[0035] Figure 6 This is a curve showing the lateral confined compressive stress-volume strain relationship of the CERF compressible material in Comparative Example 3 of the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention. Example 1

[0037] A CERF compressible material is prepared from the following raw materials in parts by weight: 8 parts modified polypropylene foam particles, 531 parts cement, 191 parts water, 766 parts medium sand, 90 parts rubber powder, 15.48 parts polymer fiber material, and 5.31 parts water-reducing agent.

[0038] The preparation method of modified polypropylene foam particles is as follows: Polypropylene foam particles (EPP particles with a diameter of approximately 4 mm and a bulk density of 12 kg / m³) are prepared. 3 The apparent density is 20 kg / m³. 3 The modified polypropylene foam particles are obtained by impregnating them with an adhesive solution (50% by mass of redispersible adhesive powder aqueous solution) with a porosity of 22%, and then coating and curing them with cement (P.O42.5R cement); the thickness of the cement shell layer of the modified polypropylene foam particles is about 0.4 mm.

[0039] The apparent density of medium sand is 2660 kg / m³. 3 The fineness modulus is 2.6;

[0040] The polymer fiber material is polyvinyl alcohol fiber, with a length of about 10 mm, a breaking elongation of about 18%, a tensile strength of about 1580 MPa, a density of 1.29 g / cm³, an initial modulus of about 36.4 GPa, and an equivalent diameter of about 20 μm;

[0041] The rubber powder has a particle size of 40 mesh, a bulk density of 314 kg / m³, and an apparent density of 750 kg / m³.

[0042] The water-reducing agent is a polycarboxylate water-reducing agent.

[0043] The specific preparation method includes the following steps:

[0044] (1) Mix medium sand and cement evenly (30 r / min, 60 s), then add rubber powder, modified polypropylene foam particles and polymer fiber materials, and mix evenly (30 r / min, 120 s); to obtain a mixture;

[0045] (2) Add water and water-reducing agent to the mixture and continue stirring (30r / min, 60s) until the mixture is homogeneous to obtain CERF compressible material. Example 2

[0046] A CERF compressible material is prepared from the following raw materials in parts by weight: 10 parts modified polypropylene foam particles, 443 parts cement, 155 parts water, 685 parts medium sand, 75 parts rubber powder, 6.5 parts polymer fiber material, and 4.43 parts water-reducing agent.

[0047] The preparation method of modified polypropylene foam particles is as follows: Polypropylene foam particles (EPP particles with a diameter of approximately 5 mm and a bulk density of 10 kg / m³) are prepared. 3 The apparent density is 22 kg / m³. 3 The modified polypropylene foam particles are obtained by impregnating them with an adhesive solution (45% by mass of redispersible adhesive powder aqueous solution) with a porosity of 25%, and then coating and curing them with cement (P.O42.5R cement); the thickness of the cement shell layer of the modified polypropylene foam particles is about 0.25 mm.

[0048] The apparent density of medium sand is 2600 kg / m³, and the fineness modulus is 2.5.

[0049] The polymer fiber material is polyvinyl alcohol fiber, with a length of about 18 mm, a breaking elongation of about 30%, a tensile strength of about 1620 MPa, a density of 1.28 g / cm³, an initial modulus of about 35.4 GPa, and an equivalent diameter of about 31 μm;

[0050] The rubber powder has a particle size of 50 mesh, a bulk density of 350 kg / m³, and an apparent density of 800 kg / m³.

[0051] The water-reducing agent is a polycarboxylate water-reducing agent.

[0052] The specific preparation method includes the following steps:

[0053] (1) Mix medium sand and cement evenly (30 r / min, 60 s), then add rubber powder, modified polypropylene foam particles and polymer fiber materials, and mix evenly (30 r / min, 90 s); to obtain a mixture;

[0054] (2) Add water and water-reducing agent to the mixture and continue stirring (30r / min, 60s) until the mixture is homogeneous to obtain CERF compressible material. Example 3

[0055] A CERF compressible material is prepared from the following raw materials in parts by weight: 12 parts modified polypropylene foam particles, 319 parts cement, 124 parts water, 425 parts medium sand, 60 parts rubber powder, 2.58 parts polymer fiber material, and 3.19 parts water-reducing agent.

[0056] The preparation method of modified polypropylene foam particles is as follows: Polypropylene foam particles (EPP particles with a diameter of approximately 3 mm and a bulk density of 15 kg / m³) are prepared. 3 The apparent density is 18 kg / m³. 3 The modified polypropylene foam particles are obtained by impregnating them with an adhesive solution (55% by mass of redispersible adhesive powder aqueous solution) with a porosity of 20%, and then coating and curing them with cement (P.O42.5R cement); the thickness of the cement shell layer of the modified polypropylene foam particles is about 0.18 mm.

[0057] The apparent density of medium sand is 2700 kg / m³, and the fineness modulus is 2.7.

[0058] The polymer fiber material is polyvinyl alcohol fiber, with a length of about 3 mm, a breaking elongation of about 5%, a tensile strength of about 1550 MPa, a density of 1.31 g / cm³, an initial modulus of about 36.8 GPa, and an equivalent diameter of about 15 μm;

[0059] The rubber powder has a particle size of 30 mesh, a bulk density of 300 kg / m³, and an apparent density of 700 kg / m³.

[0060] The water-reducing agent is a polycarboxylate water-reducing agent.

[0061] The specific preparation method includes the following steps:

[0062] (1) Mix medium sand and cement evenly (30 r / min, 60 s), then add rubber powder, modified polypropylene foam particles and polymer fiber materials, and mix evenly (30 r / min, 120 s); to obtain a mixture;

[0063] (2) Add water and water-reducing agent to the mixture and continue stirring (30r / min, 60s) until the mixture is homogeneous to obtain CERF compressible material.

[0064] Comparative Example 1:

[0065] Compared with Example 2, the only difference is the preparation method of the modified polypropylene foam particles: the polypropylene foam particles are impregnated with adhesive and then cured (without being coated with cement).

[0066] Comparative Example 2:

[0067] The only difference from Example 2 is that the amount of modified polypropylene foam particles added is 15 parts.

[0068] Comparative Example 3:

[0069] The only difference from Example 2 is that the cement shell thickness of the modified polypropylene foam particles is 1 mm.

[0070] Experimental example:

[0071] 1. The CERF compressible materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to slump (GB / T50080-2016) and apparent density tests (GB / T50080-2016). The test results are shown in Table 1:

[0072] Table 1. Experimental results of slump and apparent density of CERF compressible materials

[0073] Slump (mm) 129 137 136 125 160 150 Apparent density (kg / m³) 1145.25 990.29 803.20 901.33 813.60 1072.29

[0074] 2. The CERF compressible materials prepared in Examples 1-3 and Comparative Examples 1-3 were made into specimens and subjected to Poisson's ratio, confined compression and other tests (GB / T-50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete"). The test results are shown in Tables 2, 3 and 4. The confined compression stress-volume strain relationship curve was plotted based on the experimental results. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 ).

[0075] Table 2 Specimen Performance Test Results

[0076] Example 1 4.03 0.83 0.0048 3.50 0.034 0.039 0.244 Example 2 2.66 0.64 0.0029 2.32 0.015 0.010 0.260 Example 3 1.71 0.38 0.0010 1.67 0.014 0.015 0.383 Comparative Example 1 1.93 0.45 0.0016 2.17 0.022 0.012 0.212 Comparative Example 2 1.50 0.27 0.0009 1.77 0.013 0.011 0.297 Comparative Example 3 3.38 0.90 0.0043 3.17 0.016 0.024 0.303

[0077] Table 3 Basic Data Statistics Table

[0078] Example 1 0.039 0.122 1.503 9.81 0.317 Example 2 0.014 0.028 1.243 8.12 0.285 Example 3 0.011 0.020 1.476 8.081 0.412 Comparative Example 1 0.006 0.010 1.174 7.26 0.321 Comparative Example 2 0.008 0.025 0.943 6.05 0.343 Comparative Example 3 0.026 0.030 1.276 8.95 0.246

[0079] In the table: W1, W2, W3 – strain energy density at each compression stage; σm – compaction stress (MPa) corresponding to the compaction strain of concrete; εm – compaction strain value of concrete.

[0080] Table 4 Statistical Table of Energy Absorption Performance Evaluation Indicators

[0081] Example 1 1.664 17.0 1.453 0.415 5.249 31.7 Example 2 1.285 15.8 1.298 0.559 4.509 28.5 Example 3 1.507 18.6 1.876 1.124 3.658 41.2 Comparative Example 1 1.190 14.4 1.220 0.446 3.707 32.1 Comparative Example 2 0.976 16.1 1.200 0.930 2.845 34.3 Comparative Example 3 1.272 14.9 1.242 0.392 5.415 24.6

[0082] In the table: W – strain energy density (MJ / m³); η – energy absorption efficiency; SEA – specific energy absorption (MJ / kg); STE – specific total efficiency (kg⁻¹); σp – average stress (MPa); Xd – effective compression stroke of concrete (mm).

[0083] Analysis of the experimental data shows that the CERF compressible materials in Examples 1-3 of this invention exhibit excellent toughness and ductility. In Comparative Example 1, the lack of cement coating on the polypropylene foam particles significantly reduces their compatibility with concrete, resulting in a significant decrease in the toughness and ductility of the CERF compressible material. In Comparative Example 2, the addition of excessive modified polypropylene foam particles increases the volume content of the polypropylene foam particles, leading to thinner pore walls between the EPP particles inside the concrete. Therefore, its compressive strength, tensile strength, and confined compressive strength are lower than those in Example 2. However, the increased EPP volume content improves the compressibility of the concrete. In Comparative Example 3, the increased coating thickness of the polypropylene foam particles enhances the interfacial adhesion with the concrete matrix material but affects the volume content of the polypropylene foam particles, resulting in a decrease in compressibility. Therefore, its compressive strength, tensile strength, and confined compressive strength are all greater than those in Example 2, but the reduced compressibility leads to a decrease in energy absorption.

Claims

1. The application of a CERF compressible material in high-stress soft rock tunnels, characterized in that, The CERF compressible material is prepared from the following raw materials in parts by weight: 8-12 parts modified polypropylene foam particles, 319-531 parts cement, 124-191 parts water, 425-766 parts medium sand, 60-90 parts rubber powder, 2.58-15.48 parts polymer fiber material, and 3.19-5.31 parts water-reducing agent; the modified polypropylene foam particles are polypropylene foam particles with a cement shell coating on the surface; the ratio of the radius of the polypropylene foam particles to the thickness of the cement shell is not less than 5; the preparation method of the modified polypropylene foam particles includes: impregnating the polypropylene foam particles with an adhesive solution, then coating them with cement and curing them.

2. The application of the CERF compressible material according to claim 1 in high-stress soft rock tunnels, characterized in that, The polypropylene foam particles have a diameter of 3-5 mm and a bulk density of 10-15 kg / m³. 3 The apparent density is 18-22 kg / m³. 3 Porosity 20-25%.

3. The application of the CERF compressible material according to claim 1 in high-stress soft rock tunnels, characterized in that, The adhesive solution is an aqueous solution of redispersible adhesive powder with a mass percentage of 45-55%.

4. The application of the CERF compressible material according to claim 1 in high-stress soft rock tunnels, characterized in that, The rubber powder has a particle size of 30-50 mesh, a bulk density of 300-350 kg / m³, and an apparent density of 700-800 kg / m³.

5. The application of the CERF compressible material according to claim 1 in high-stress soft rock tunnels, characterized in that, The polymer fiber material has a length of 3-18 mm, an elongation at break of ≤30%, a tensile strength of ≥1550 MPa, a density of 1.28-1.31 g / cm³, an initial modulus of ≥35 GPa, and an equivalent diameter of 15-31 μm.

6. The application of the CERF compressible material according to claim 1 in high-stress soft rock tunnels, characterized in that, The polymer fiber material is polyvinyl alcohol fiber material.

7. The application of the CERF compressible material according to claim 1 in high-stress soft rock tunnels, characterized in that, The method for preparing the CERF compressible material includes the following steps: (1) After mixing the medium sand and cement evenly, add rubber powder, modified polypropylene foam particles and polymer fiber materials, and mix evenly to obtain the mixture; (2) Add water and water-reducing agent to the mixture and continue to stir and mix evenly to obtain CERF compressible material.

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