Material applied to pavement repair at negative temperature and preparation method thereof

Abstract

The invention discloses a material applied to pavement repair at negative temperature and a preparation method thereof. The material is prepared from dead burned magnesium oxide, monopotassium phosphate, borax, light burned magnesium oxide, nano silicon dioxide, fly ash, a polycarboxyl water reducer and water, the water-binder ratio is 0.16-0.18, the mass of the light burned magnesium oxide is 4.3%-6% of that of the dead burned magnesium oxide, the doping amount of the nano silicon dioxide is 3% of the total mass of the cementing material, the doping amount of the borax is 4%-6% of the total mass of the cementing material, and the doping amount of the fly ash is 4%-6% of the total mass of the cementing material. The molar ratio of dead burned magnesium oxide to monopotassium phosphate is 5: 1, the doping amount of fly ash is 20% of the total mass of the cementing material, and the doping amount of the polycarboxyl water reducer is 1% of the total mass of the cementing material. According to the invention, through compound doping of dead burned magnesium oxide, light burned magnesium oxide and nano-silica, balance of rapid hardening early strength and low temperature resistance stability is realized, excellent mechanical properties and freeze-thaw resistance stability are shown, and construction requirements in a negative temperature environment in winter are met.

Description

Technical Field

[0001] This invention belongs to the field of road repair materials technology, and relates to a material for road repair at negative temperatures and its preparation method. Background Technology

[0002] In cold regions, winter temperatures often drop below 0°C, making road surfaces prone to cracks, potholes, and spalling under vehicle loads and freeze-thaw cycles. Failure to repair these defects promptly will exacerbate road damage, impacting traffic safety and efficiency. Therefore, the core requirements for road surface repair materials at sub-zero temperatures focus on two aspects: rapid hardening and early strength, and low-temperature stability. Materials need to quickly develop strength at sub-zero temperatures to allow for short-term road reopening; simultaneously, they need to maintain stable mechanical properties during service at sub-zero temperatures to resist freeze-thaw damage.

[0003] Magnesium phosphate cement (MPC) has become a potential material for road repair in sub-zero temperatures due to its unique rapid hardening, early strength, low-temperature resistance, and corrosion resistance. Compared with traditional cement, MPC can still undergo hydration reactions in environments below 0°C, and its early strength development is faster, which can meet the needs of rapid road repair in cold regions to a certain extent. Therefore, it has gradually attracted attention in the engineering field in recent years.

[0004] Currently, for MPC pavement repair materials used in sub-zero temperatures, existing technologies mostly employ a single modifier to adjust performance, such as adding only lightly calcined magnesium oxide (LBM) or only nano-silica (Nano-SiO2). This single modification method cannot simultaneously meet the multiple requirements of sub-zero temperature pavement repair: when only LBM is added, although its high activity can accelerate the early hydration reaction and improve short-term strength, if the dosage is not properly controlled, the long-term strength of the material is prone to decline at sub-zero temperatures, and it is difficult to optimize the internal pore structure of the material, resulting in insufficient flexural strength and freeze-thaw resistance; when only Nano-SiO2 is added, although it can fill the micropores of the material and improve the microstructure, its nucleation effect is suppressed at sub-zero temperatures, which cannot effectively improve early strength, and excessive addition can easily cause particle agglomeration, which can create defects inside the material and reduce the overall mechanical properties. Furthermore, existing technologies have not developed a complete preparation scheme for negative temperature pavement repair scenarios. There is no clear synergistic optimization relationship between water-cement ratio and LBM and Nano-SiO2 compounding ratio, nor is there a lack of material preparation, mixing, and curing processes adapted to negative temperature environments. As a result, the prepared materials either have poor construction fluidity and unsuitable setting time, or their mechanical properties cannot be stabilized in the long term. The repaired pavement is still prone to secondary damage in the short term, making it difficult to truly meet the actual engineering needs of pavement repair under negative temperatures. Summary of the Invention

[0005] This invention provides a material for road repair at sub-zero temperatures and its preparation method. It solves the problems that a single modifier cannot simultaneously meet the requirements of rapid hardening and early strength as well as low-temperature stability in road repair at sub-zero temperatures. Adding only lightly calcined magnesium oxide can easily lead to long-term strength degradation and insufficient freeze-thaw resistance. Adding only nano-silica can hardly improve early strength and is prone to particle agglomeration. Furthermore, there is a lack of complete preparation schemes, no clear synergistic optimization relationship between water-cement ratio and compounding ratio, and no suitable batching, mixing, and curing processes for sub-zero temperatures. This results in poor material flowability during construction, unsuitable setting time, or inability to maintain long-term stable mechanical properties, and the road surface is prone to secondary damage in a short period of time after repair.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] The material used for road repair at sub-zero temperatures consists of calcined magnesium oxide, potassium dihydrogen phosphate, borax, light-calcined magnesium oxide, nano-silica, fly ash, polycarboxylated water-reducing agent, and water. The water-cement ratio is 0.16~0.18. The mass of light-calcined magnesium oxide is 4.3%~6% of the mass of calcined magnesium oxide, the amount of nano-silica is 3% of the total mass of the cementitious material, the amount of borax is 4%~6% of the total mass of the cementitious material, the molar ratio of calcined magnesium oxide to potassium dihydrogen phosphate is 5:1, the amount of fly ash is 20% of the total mass of the cementitious material, and the amount of polycarboxylated water-reducing agent is 1% of the total mass of the cementitious material.

[0008] Furthermore, the amount of borax added is 5% of the total mass of the cementitious material.

[0009] Furthermore, the purity of the recalcined magnesium oxide is ≥92%, the particle size is 200 mesh, and it is obtained by calcining magnesite at 1600℃.

[0010] Furthermore, the purity of potassium dihydrogen phosphate is ≥98%.

[0011] Furthermore, the purity of borax is 98%.

[0012] Furthermore, the lightly calcined magnesium oxide has a purity of ≥91.6%, a particle size of 200 mesh, and an activity of 70, and is obtained by calcining magnesite at 1000℃.

[0013] Furthermore, the particle size range of nano-silica is 5~20 nm.

[0014] The preparation method of the above-mentioned material for road surface repair at negative temperatures includes the following steps:

[0015] According to the formula, pre-cooled calcined magnesium oxide, potassium dihydrogen phosphate, borax, fly ash, light-calcined magnesium oxide and nano silica are dry-mixed, and then water and polycarboxylated water-reducing agent pre-cooled at 0~1℃ are added. The mixture is wet-mixed to obtain a uniform slurry, which is then shaped and finally cured at -5℃ or below.

[0016] Furthermore, the pre-cooling treatment involves placing the solid raw materials and water in a -5°C environment for at least 24 hours under constant temperature conditions.

[0017] Furthermore, the rotation speed for dry mixing and wet mixing is 300 r / min to 500 r / min, the dry mixing time is 1 to 2 min, and the wet mixing time is 2 to 3 min.

[0018] Furthermore, the molding method is vibration, with 100 vibrations, an amplitude of 5mm, and a frequency of 50Hz.

[0019] Furthermore, during the maintenance period, the ambient temperature fluctuation should be kept within ±2℃.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) This invention solves the problem that the existing single modifier is difficult to take into account multiple properties by compounding calcined magnesium oxide, dihydrogen phosphate, borax, light-calcined magnesium oxide and nano silica. Light-calcined magnesium oxide can accelerate early hydration at negative temperature and improve short-term strength, while nano silica can fill micropores and optimize microstructure. The two work together to achieve a balance between rapid hardening and early strength and low-temperature stability; thus, the material achieves a synergistic improvement in early strength development and long-term durability under negative temperature conditions.

[0022] (2) The material of this invention exhibits excellent mechanical properties and freeze-thaw stability. Its compressive strength can reach 18~25 MPa after 8 hours of curing at -5℃. The nano-silica effectively fills the micropores and optimizes the microstructure, so that the compressive strength reaches 65~70 MPa after 28 days. After 300 freeze-thaw cycles, the strength loss rate is less than 10% and the mass loss rate is less than 5%.

[0023] (3) Through the optimization of the formula, the water-binder ratio of the present invention is 0.16~0.18, the mass of lightly calcined magnesium oxide is 4.3%~6% of the mass of heavily calcined magnesium oxide, and the nano silica content is 3%. Under these conditions, the compressive strength of the material in the negative temperature environment is increased by more than 30% compared with the unmodified system after 7 days. It also has good construction performance, with an initial flowability of 190~220 mm. The setting time can be adjusted to 15~26 minutes by the amount of borax, which is suitable for construction requirements in the negative temperature environment in winter. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of materials used in road repair at sub-zero temperatures. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. The following description is used to explain the present invention, not to limit its scope of protection.

[0026] In the following examples, the raw materials used are: calcined magnesium oxide: purity ≥92%, particle size 200 mesh, obtained by calcining magnesite at 1600℃; light-calcined magnesium oxide: purity ≥91.6%, particle size 200 mesh, obtained by calcining magnesite at 1000℃; potassium dihydrogen phosphate, purity ≥99%; retarder, industrial grade borax decahydrate; nano-silica, particle size range 5~20nm; and mixing water, tap water.

[0027] Before conducting the negative temperature environment test, all solid raw materials and mixing water were placed in a -5℃ environment for no less than 24 hours of constant temperature treatment, and the temperature of the mixing water was controlled at 0~1℃.

[0028] In the following embodiments, the relevant parameters of magnesium phosphate cement based on brucite were tested according to the following criteria:

[0029] Material strength testing was performed using the GB / T17671-2020 standard "Test Method for Strength of Cement Mortar (ISO Method)" to form specimens.

[0030] The setting time test shall be performed in accordance with the "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement" (GB / T1346-2011).

[0031] Example 1

[0032] The material for road repair at sub-zero temperatures consists of calcined magnesium oxide, potassium dihydrogen phosphate, borax, fly ash, polycarboxylated water-reducing agent, light-burned magnesium oxide, nano-silica, and water. The molar ratio of potassium dihydrogen phosphate to calcined magnesium oxide is 3:1; the amount of borax is 5% of the total mass of the cementitious material; the amount of fly ash is 20% of the total mass of the cementitious material; the amount of polycarboxylated water-reducing agent is 1% of the total mass of the cementitious material; the mass ratio of light-burned magnesium oxide to calcined magnesium oxide is 4.3%; the amount of nano-silica is 3% of the total mass of the cementitious material; and the amount of mixing water is such that the water-cement ratio of the system is 0.16. The material is prepared through the following steps:

[0033] Pre-cooled calcined magnesium oxide, potassium dihydrogen phosphate, borax, fly ash, light-calcined magnesium oxide, and nano-silica were added to a mixer and dry-mixed at 400 r / min for 1.5 minutes. Then, mixing water at 0-1℃ and polycarboxylated water-reducing agent were added, and wet-mixed at the same speed for 2.5 minutes to obtain a uniform slurry. The slurry was quickly poured into a pre-cooled 40 mm × 40 mm × 160 mm mold and placed on a vibrating table to compact it 100 times. The surface was then smoothed. Finally, the molded mold was immediately transferred to a constant temperature curing chamber at -5℃ ± 1℃ and cured for 24 hours before demolding. The specimens were then cured at the same temperature until the test age.

[0034] Performance test results: initial setting time was 31 minutes; 8-hour compressive strength was 19.3 MPa; 1-day compressive strength was 28.5 MPa; 3-day compressive strength was 38.7 MPa; 28-day compressive strength was 62.3 MPa; 7-day flexural strength was 8.5 MPa; after 300 rapid freeze-thaw cycles, the mass loss rate was 0.7%, and the relative dynamic modulus of elasticity retention rate was 88.5%.

[0035] Example 2

[0036] This embodiment is largely the same as Embodiment 1, except that: the mass ratio of lightly calcined magnesium oxide to heavily calcined magnesium oxide is 6%, the amount of nano-silica is 3% of the total mass of the cementitious material, and the amount of mixing water is such that the water-cement ratio of the system is 0.16.

[0037] Performance test results: initial setting time was 22 minutes; 8-hour compressive strength was 23.3 MPa; 1-day compressive strength was 31.2 MPa; 3-day compressive strength was 41.4 MPa; 28-day compressive strength was 55.1 MPa; 7-day flexural strength was 7.9 MPa. After 300 rapid freeze-thaw cycles, the mass loss rate was 1.2%, and the relative dynamic modulus of elasticity retention rate was 79.5%.

[0038] Example 3

[0039] This embodiment is largely the same as Embodiment 1, except that: the mass ratio of lightly calcined magnesium oxide to heavily calcined magnesium oxide is 5%, the amount of nano-silica is 3% of the total mass of the cementitious material, and the amount of mixing water is such that the water-cement ratio of the system is 0.18.

[0040] Performance test results: Initial setting time was approximately 27 minutes; 8-hour compressive strength was 16.8 MPa; 1-day compressive strength was 25.6 MPa; 3-day compressive strength was 37.5 MPa; 28-day compressive strength was 65.1 MPa; 7-day flexural strength was 8.3 MPa. After 300 rapid freeze-thaw cycles, the mass loss rate was 0.5%, and the relative dynamic modulus of elasticity retention rate was 87.3%.

[0041] Comparative Example 1

[0042] This comparative example is largely the same as Example 1, except that the water-to-binder ratio of the system is 0.14.

[0043] Performance test results: The 7-day compressive strength can reach 52 MPa, but the 28-day compressive strength is only 59 MPa, and the long-term strength is significantly affected.

[0044] Comparative Example 2

[0045] This comparative example is largely the same as Example 1, except that the water-to-binder ratio of the system is 0.22.

[0046] Performance test results: The 7-day compressive strength is only 37 MPa, while the 28-day compressive strength reaches 62 MPa, which has a significant impact on its early and long-term strength.

[0047] Comparative Example 3

[0048] This comparative example is largely the same as Example 1, except that the mass ratio of lightly calcined magnesium oxide to heavily calcined magnesium oxide is 3%.

[0049] Performance test results: The 1-day compressive strength showed almost no significant improvement.

[0050] Comparative Example 4

[0051] This comparative example is largely the same as Example 1, except that the mass ratio of lightly calcined magnesium oxide to heavily calcined magnesium oxide is 8%.

[0052] Performance test results: The 1-day compressive strength not only did not increase, but actually decreased by 20% of the original strength.

[0053] Comparative Example 5

[0054] This comparative example is largely the same as Example 1, except that the amount of nano-silica added is 6% of the total mass of the cementitious material.

[0055] Performance test results: The compressive strength decreased by 95% after 7 days.

[0056] In summary, this invention addresses the problem of existing technologies where a single modifier cannot simultaneously achieve multiple properties by combining recalcined magnesia, dihydrogen phosphate, borax, light-calcined magnesia, and nano-silica. Light-calcined magnesia accelerates early hydration at sub-zero temperatures, enhancing short-term strength, while nano-silica fills micropores and optimizes the microstructure. Together, they achieve a balance between rapid hardening, early strength, and low-temperature stability. Furthermore, by clearly defining the water-cement ratio and the mass ratio of light-calcined to recalcined magnesia, the invention solves the problem of insufficient proportion optimization. The invention also establishes a complete preparation scheme through staged mixing (dry mixing followed by wet mixing), standardized vibration molding, and -5℃ constant temperature curing, avoiding issues such as poor flowability and unsuitable setting time. The final material can rapidly develop strength at sub-zero temperatures to meet short-term traffic opening requirements, exhibits stable long-term mechanical properties and freeze-thaw resistance, reducing secondary damage to the road surface after repair, and is suitable for the actual needs of sub-zero temperature road repair projects.

Claims

1. A material for road surface repair at sub-zero temperatures, characterized in that, It is composed of deburned magnesium oxide, potassium dihydrogen phosphate, borax, light-burned magnesium oxide, nano-silica, fly ash, polycarboxylated water-reducing agent and water, with a water-cement ratio of 0.16~0.

18. The mass of light-burned magnesium oxide is 4.3%~6% of the mass of deburned magnesium oxide, the amount of nano-silica is 3% of the total mass of cementitious materials, the amount of borax is 4%~6% of the total mass of cementitious materials, the molar ratio of deburned magnesium oxide to potassium dihydrogen phosphate is 5:1, the amount of fly ash is 20% of the total mass of cementitious materials, and the amount of polycarboxylated water-reducing agent is 1% of the total mass of cementitious materials.

2. The material according to claim 1, characterized in that, The amount of borax added is 5% of the total mass of the cementitious materials.

3. The material according to claim 1, characterized in that, The purity of calcined magnesium oxide is ≥92%, the particle size is 200 mesh, and it is obtained by calcining magnesite at 1600℃; the purity of light-calcined magnesium oxide is ≥91.6%, the particle size is 200 mesh, the activity is 70, and it is obtained by calcining magnesite at 1000℃.

4. The material according to claim 1, characterized in that, The purity of potassium dihydrogen phosphate is ≥98%, and the purity of borax is 98%.

5. The material according to claim 1, characterized in that, The particle size range of nano-silica is 5~20 nm.

6. The method for preparing the material according to any one of claims 1 to 5, characterized in that, Includes the following steps: According to the formula, pre-cooled calcined magnesium oxide, potassium dihydrogen phosphate, borax, fly ash, light-calcined magnesium oxide and nano silica are dry-mixed, and then water and polycarboxylated water-reducing agent pre-cooled at 0~1℃ are added. The mixture is wet-mixed to obtain a uniform slurry, which is then shaped and finally cured at -5℃ or below.

7. The preparation method according to claim 6, characterized in that, Pre-cooling treatment involves placing the solid raw materials and water in a -5°C environment for at least 24 hours under constant temperature.

8. The preparation method according to claim 6, characterized in that, The rotation speed for dry mixing and wet mixing is 300r / min~500r / min, the dry mixing time is 1~2min, and the wet mixing time is 2~3min.

9. The preparation method according to claim 6, characterized in that, The molding method is vibration, with 100 vibrations, a vibration amplitude of 5mm, and a vibration frequency of 50Hz.

10. The preparation method according to claim 6, characterized in that, During the maintenance period, keep the ambient temperature fluctuations within ±2℃.

Images