Grouting material for horizontal drilling of airport pavement base and preparation method thereof

Abstract

The application discloses an airport pavement base horizontal drilling grouting material and a preparation method thereof, and relates to the technical field of grouting materials. The application is based on the airport non-stop construction characteristics and engineering needs, and focuses on the contradiction between the liquidity, setting time and compressive strength of the material. A grouting material suitable for the airport non-stop construction is prepared through a large number of tests. The raw materials of the grouting material include cement, water reducing agent, aggregate and tap water. The cement is silicate cement and sulphoaluminate cement. The water reducing agent is polycarboxylic acid water reducing agent. The proportion of the silicate cement and the sulphoaluminate cement is 9:1-1:9, the sand-cement ratio is 1:1, the water-cement ratio is 0.45-0.6, and the water reducing agent content is 0.5%-0.7%. When the mixing proportion of the grouting material is PC:SAC=7:3, the sand-cement ratio is 1:1, the water-cement ratio is 0.6, and the water reducing agent content is 0.6%, the initial setting time of the material is 95 min, the final setting time is 118 min, the liquidity is 196 mm, the liquidity after 30 min is 88 min, and the 1d compressive strength is 2.93 MPa. Under the mixing proportion, the PC and SAC composite cement mortar has excellent stability.

Description

Technical Field

[0001] This invention relates to the field of grouting materials technology, and in particular to a grouting material for horizontal drilling of airport pavement base course and its preparation method. Background Technology

[0002] With the continuous growth of passenger and cargo throughput at my country's transport airports, flight schedules are becoming increasingly tight, and more and more flights are taking off and landing at night. Existing facilities and equipment can no longer meet the normal operation needs of airports. The "Technical Specifications for Civil Airport Pavement Evaluation and Management" and "Technical Standards for Civil Airport Flight Areas," issued in 2019, have placed higher demands on the operation and management of transport airport flight areas. Among the existing facilities and equipment requiring upgrades, the most urgent and important issue is the densification of runway centerline lights to better ensure the safe takeoff and landing of flights at night.

[0003] Currently, the common practice in civil airport navigation lighting upgrade projects is to groove and cut sections in cement concrete pavements or mill asphalt pavements, followed by laying pipelines. However, this method damages the pavement, posing significant safety hazards and economic losses. This leads to a further exploration of this issue. Referring to subway tunnel excavation technology, horizontal directional drilling (WDD) is used to drill directional holes in the runway subbase for pipeline installation, replacing traditional surface grooving and avoiding damage to the surface layer. This technology has already been applied in the construction of centerline lights on the taxiway at Mangshi Airport in Dehong Prefecture, reducing the pavement construction area and lowering the risk of restoring airworthiness, demonstrating significant social and economic benefits. However, drilling in the runway subbase using WDD inevitably affects the subbase structure, potentially causing runway pavement underside delamination and a series of other defects. Therefore, grouting and backfilling of the horizontally drilled holes are necessary to stabilize the pavement structure and prevent support deterioration.

[0004] Currently, there is no unified standard for the selection of grouting materials in airport engineering. In other engineering fields, combining the advantages of silicate cement (PC) and sulfoaluminate cement (R·SAC) to prepare grouting materials with performance suitable for specific projects has become a research direction for scholars at home and abroad. Zhang Xin et al. used a novel experimental method to study the time-varying viscosity and setting deformation characteristics of silicate-sulfoaluminate composite cement slurry with different blending ratios, and analyzed the microscopic characteristics to provide theoretical support for practical engineering applications. Yang Qing et al. conducted a comprehensive analysis of the setting time and compressive strength of silicate-sulfoaluminate composite cement using isothermal calorimetry, thermal analysis (TG-DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that when the SAC content was only 10%, the setting time, early and late compressive strength were improved, and the early hydration rate and heat release of the composite cementitious system were higher than those of single-component cement. Wang Bo et al. conducted research on the addition of silica fume and silica slag to the silicate-sulfoaluminate composite cement gel system, which can significantly improve the compressive strength, flexural strength and fluidity of the composite cementitious system in the later stage, providing the optimal mix ratio for actual construction. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a grouting material for horizontal drilling of airport pavement base courses and its preparation method. Based on the actual needs of airport horizontal grouting materials, composite silicate cement (PC) and sulfoaluminate cement (R·SAC) are compounded, supplemented with river sand, water, and a polycarboxylate superplasticizer to prepare a silicate-sulfoaluminate composite cement mortar suitable for airport non-stop construction and for horizontal drilling of airport pavement base courses. Related indoor tests are conducted to study the various performance characteristics of the grouting material, obtaining a specific mix proportion that meets the engineering requirements. This material can be widely applied to horizontal drilling grouting and backfilling projects in airport pavement base courses. The objective of this invention is mainly achieved through the following scheme:

[0006] A grouting material for horizontal drilling of airport pavement base course is characterized in that the grouting material comprises the following raw materials: cement, water-reducing agent, aggregate and tap water, wherein the sand-cement ratio is 1:1, the water-cement ratio is 0.45-0.6, and the water-reducing agent dosage is 0.5%-0.7%.

[0007] Furthermore, the cement includes silicate cement and sulfoaluminate cement; the ratio of silicate cement to sulfoaluminate cement is 9:1 to 1:9.

[0008] Furthermore, the water-reducing agent is a polycarboxylate water-reducing agent.

[0009] Furthermore, the aggregate is medium-fine sand with a diameter of less than 0.5 mm.

[0010] Furthermore, the ratio of silicate cement to sulfoaluminate cement is 7:3, the sand-cement ratio is 1:1, the water-cement ratio is 0.6, and the water-reducing agent dosage is 0.6%.

[0011] Furthermore, the composition of the sulfoaluminate cement by mass percentage is 8.15% SiO2, 22.47% Al2O3, 2.66% Fe2O3, 42.7% CaO, 2.08% MgO, 14.98% SO3, and 1.36% TiO2.

[0012] The above-mentioned method for preparing grouting material for horizontal drilling of airport pavement base course is characterized by comprising the following steps:

[0013] S1: Place silicate cement, sulfoaluminate cement, and aggregate into the grouting machine at a ratio of 7:3 for silicate cement to sulfoaluminate cement and a 1:1 ratio for sand to cement.

[0014] S2: Stir at a speed of 300-800 r / min, add an appropriate amount of tap water at a water-cement ratio of 0.6, and continue stirring;

[0015] S3: After stirring for 3 minutes, add polycarboxylate superplasticizer at a ratio of 0.6% and stir for another 3 minutes to obtain the mixture, which is the grouting material for horizontal drilling of airport pavement base course.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] (1) It can meet the needs of airport construction without interruption. From the start of construction to the final setting of the grouting material in the horizontal borehole, the time does not exceed 6 hours. Even for airports with large throughput, it will not affect the normal operation of aircraft the next day.

[0018] (2) Since directional drilling is a horizontal drilling technique, the fluidity of the grouting material is required to be high. Once the grouting pressure is determined, the better the fluidity of the grouting material, the shorter the grouting time, which saves construction time, improves efficiency, and leaves enough time for subsequent tasks.

[0019] (3) A series of indoor tests and on-site inspections have proven that the present invention can achieve the compressive strength specified by the base layer in a short time, and the bearing capacity and structure of the pavement after grouting are restored and improved. Attached Figure Description

[0020] Figure 1 The effect of the PC to SAC ratio on flowability and 1-day compressive strength;

[0021] Figure 2 The effect of the PC and SAC ratio on setting time at a water-cement ratio of 0.45;

[0022] Figure 3 Comparison of setting time and initial setting time for different water-cement ratios;

[0023] Figure 4 The effect of water-reducing agent ratio on the performance of composite cement mortar;

[0024] Figure 5 Drilling and grouting for embedded parts with a diameter of 2cm;

[0025] Figure 6 The strength changes before and after grouting at different hole diameters;

[0026] Figure 7 This is the test section site;

[0027] Figure 8 The change in impact stiffness modulus before and after drilling and after grouting;

[0028] Figure 9 For ground-penetrating radar detection. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Non-stop construction refers to engineering work carried out within the flight area of ​​an airport without closing or for a specific period of time, while aircraft continue to take off and land according to flight schedules. For horizontal directional drilling and grouting projects at airports, it is necessary to conduct them without affecting normal airport operations; therefore, non-stop construction can only be carried out at night. Due to the short construction time and heavy workload, strict requirements are placed on the performance parameters of the grouting materials, and the selection of materials needs to consider multiple factors such as the strength of the solidified body, fluidity, and setting time.

[0031] 1. The effective working time for project construction is short.

[0032] Due to varying flight schedules at airports across the country, construction work also differs, typically commencing after midnight. At busier airports with high passenger and cargo volumes, construction may begin after 1:00 AM or even later. One hour before aircraft takeoff or landing, the construction unit must clear and restore the site, fill and compact trenches, and evacuate personnel, equipment, and vehicles. Therefore, the non-stop construction work only lasts 6-7 hours. A horizontal directional drilling rig can drill from the shoulder to the runway centerline in approximately 4 hours, followed by immediate grouting and backfilling after drilling.

[0033] 2. High safety requirements

[0034] The primary function of the base course in airport pavements is to enhance the structural bearing capacity of the pavement. By improving the stress state of the subgrade, delaying cumulative plastic deformation, and improving the stress conditions of the surface layer, the base course receives uniform and stable support, ensuring safe aviation operations. After ABAQUS finite element simulation calculations, it was decided to use drilling grouting in the base course. The horizontal grouting holes are 30 meters deep. This requires a certain pressure from the grouting machine and high fluidity of the grout to complete. If the fluidity is low, the grout is prone to clogging in the base course, and continued grouting can easily cause surface bulging.

[0035] For grouting materials used in airport construction that does not require uninterrupted operation, the following basic requirements must be met:

[0036] (1) Setting time: The initial setting time is 60-90 minutes and the final setting time is within 120 minutes. The interval between the initial setting time and the final setting time should be as short as possible, within 30 minutes, to achieve "right-angle thickening" and meet the special requirement that the airport can immediately take off and land after the non-stop construction is completed.

[0037] (2) Flowability: The horizontal grouting distance for the airport pavement base course is 30m. Poor flowability can easily cause pore blockage. Therefore, when using a truncated cone mold to measure the flowability of the material, it is necessary to ensure that the mortar flowability meets the grouting requirements. Since the grouting time is about 30 minutes, the grouting material needs to still have a certain flowability after 30 minutes to avoid pore blockage.

[0038] (3) Compressive strength: The "Design Specification for Cement Concrete Pavement of Civil Airports" requires that when the flight zone index II is E and the base layer material is cement-stabilized aggregate, the 7-day immersion compressive strength should not be less than 2.5 MPa. Since the airport will be open to traffic the day after grouting, the 1-day compressive strength of the consolidated body is tested to determine if it reaches 2.5 MPa. Subsequent testing can be conducted by preparing base layer strength specimens, filling them with embedded parts, drilling holes, and grouting to assess the change in base layer strength. Since the grouting material is silicate-sulfoaluminate composite cement mortar, the compressive strength is determined according to the "Test Method for Compressive Strength of Cement Grout for Foundation Engineering Grouting," and the test mold is a 70.7mm x 70.7mm x 70.7mm cube.

[0039] (4) Stability: The stability of grouting materials mainly includes two parts: water separation rate and stone formation rate. A water separation rate of less than 10% meets the grouting conditions, but the lower the water separation rate, the more stable the material.

[0040] Based on the characteristics of cement hydration, cement-based grouting materials generally suffer from a contradiction between fluidity, setting time, and compressive strength. When the water-cement ratio of the grouting material is high, cement particles can be better dispersed, the resistance between cement particles decreases, and the fluidity of the material increases accordingly. However, with a high water-cement ratio, the spacing between cement particles increases, the time for the hydration reaction products to form a network flocculated structure increases, and the porosity increases, leading to a prolonged setting time and a decrease in compressive strength. Under the premise of uninterrupted airport construction, the preparation of grouting materials for horizontal drilling into the airport pavement base course and the control of the balance between various performance characteristics to meet engineering requirements has become a research focus. This invention, starting from the characteristics and engineering needs of uninterrupted airport construction, focuses on considering the inherent contradictions in materials and, through extensive experiments, prepares a grouting material universally suitable for uninterrupted airport construction.

[0041] A grouting material for horizontal drilling of airport pavement base course comprises cement, water-reducing agent, aggregate and tap water, wherein the cement is silicate cement and rapid-hardening sulfoaluminate cement; the water-reducing agent is polycarboxylate water-reducing agent; and the aggregate is medium-fine sand less than 0.5mm.

[0042] A method for preparing grouting material for horizontal drilling of airport pavement base course, the specific operation is as follows:

[0043] S1: Place silicate cement, sulfoaluminate cement, and aggregate into the grouting machine in the optimal ratio of silicate cement to sulfoaluminate cement and the optimal sand-cement ratio (mass ratio of aggregate to cement).

[0044] S2: Stir at a speed of 300-800 r / min, add an appropriate amount of tap water according to the optimal water-cement ratio (mass ratio of water to cement), and continue stirring;

[0045] S3: After stirring for 3 minutes, add polycarboxylate superplasticizer according to the optimal ratio of superplasticizer dosage (superplasticizer as a percentage of cement mass), and stir for another 3 minutes to obtain a mixture. The well-stirred mixture is the grouting material for horizontal drilling of the airport pavement base course.

[0046] The formulation of the above-mentioned grouting material for horizontal drilling of airport pavement base course was optimized, and its performance was tested. The specific process is as follows:

[0047] 1 experiment

[0048] 1.1 Experimental Raw Materials

[0049] The cement used in the experiment was composite silicate cement (P.C42.5R) and rapid-hardening sulfoaluminate cement (R·SAC42.5), the water-reducing agent was polycarboxylate high-efficiency water-reducing agent, and other common materials were medium and fine river sand with a particle size of less than 0.5 mm and tap water; the mineral composition of SAC is shown in Table 1.

[0050] Table 1 Mineral composition of sulfoaluminate cement

[0051]

[0052] Adding river sand to composite cement can improve the fluidity of grouting materials. However, if the sand particle size is too large, it can cause grout blockage in the 30-meter-long pores of the base layer. In this experiment, medium-fine sand with a particle size of less than 0.5 mm was selected as the aggregate. In cement mortar construction, the ratio of cement to sand is usually around 1:3. Increasing the proportion of sand can actually reduce the compressive strength of the grouting material. Therefore, in this experiment, the ratio of cement to sand was set to 1:1. Adding a certain amount of river sand can appropriately reduce the amount of cement used, which is economical in engineering.

[0053] Currently, the development of new water-reducing agents remains a research hotspot both domestically and internationally. Their excellent characteristics, such as reducing mortar water consumption, improving mortar durability, and achieving significant effects with low dosage, have led to their widespread application in grouting materials. Water-reducing agents effectively improve mortar fluidity, perfectly meeting the needs of long-distance grouting for airport pavement base courses. Under the same conditions, the dosage order of different series of high-performance water-reducing agents is: polycarboxylate-based < aminosulfonic acid-based ≤ melamine-based ≈ naphthalene-based. From the perspectives of economy and workability, polycarboxylate-based water-reducing agents were selected in this experiment.

[0054] 1.2 Experimental Design

[0055] When preparing horizontal borehole grouting materials for airport pavement base courses, the experiments considered the effects of variations in the ratio of silicate cement and sulfoaluminate cement, the water-cement ratio, and the dosage of water-reducing agent on the workability of the grouting material. In studying the effect of the ratio of silicate cement to sulfoaluminate cement on the workability of the grouting material, nine ratios were set from 9:1 to 1:9. When studying the water-cement ratio, the ratios were set to 0.45, 0.5, 0.55, and 0.6, respectively; the water-reducing agent dosages were 0.5%, 0.55%, 0.6%, 0.65%, and 0.7%, respectively. For the water-cement ratio of 0.6, some orthogonal experimental schemes are shown in Table 2 when studying the two types of cement dosages; the schemes for studying the water-reducing agent dosage are shown in Table 3.

[0056] Table 2 Test Scheme for Cementitious Material Proportioning at a Water-Cement Ratio of 0.6

[0057]

[0058] Table 3. Test scheme for water-reducing agent dosage when water-cement ratio is 0.6

[0059]

[0060] 1.3 Test Methods

[0061] Setting time: The setting time of grouting material used for horizontal drilling of airport pavement base course is determined by referring to the "Test Method for Standard Consistency Water Requirement, Setting Time and Soundness of Cement" (GB / T 1346-2011) Cement Paste Setting Time Test Method. The time required for the initial setting needle and final setting needle to sink to a certain depth is used to test the initial setting time and final setting time of the grout.

[0062] Flowability: The flowability of the slurry is determined by referring to the "Test Method for Homogeneity of Concrete Admixtures" (GBT8077-2012). After the truncated cone mold is lifted, the maximum diameter of the slurry flowing on the glass plate in two mutually perpendicular directions after 30 seconds is calculated, and the average value is taken as the flowability of the slurry.

[0063] Stability: The grout separation rate was determined according to the "Technical Specification for Cement Grouting Construction of Hydraulic Structures" (SLT 62-2020). 100ml of grout was poured into a graduated cylinder, and when it approached 100ml, it was accurately added to the 100ml mark using a pipette. After standing for 2 hours, the corresponding mark at the interface between the separated clear water and the lower grout was read for calculation.

[0064] Compressive strength: The compressive strength was determined in accordance with the "Test Method for Compressive Strength of Cement Grout for Grouting in Foundation Engineering". The test mold was a cube of 70.7mm×70.7mm×70.7mm. The test was performed using a pressure testing machine after 24 hours.

[0065] 2. Experimental Results and Analysis

[0066] 2.1 Effect of PC to SAC ratio on grouting material properties

[0067] Based on the experimental results, the effects of the proportions of the two types of cement on fluidity and 24-hour compressive strength were plotted, as follows: Figure 1 As shown.

[0068] Depend on Figure 1 As shown in (a), with the increase of the proportion of sulfoaluminate cement, the fluidity of composite cement mortar at different water-cement ratios shows a slow decreasing trend. The higher the amount of sulfoaluminate cement, the more significant its effect on the fluidity of composite cement mortar. The fluidity of composite cement mortar is mainly related to the fineness of cement particles. Compared with silicate cement, sulfoaluminate cement has a larger fineness and a larger specific surface area, resulting in poorer fluidity at the same water-cement ratio. Therefore, at the same water-cement ratio, the fluidity of composite cement mortar decreases with the increase of the proportion of sulfoaluminate cement. Taking a water-cement ratio of 0.6 as an example, the fluidity remains between 166mm and 228mm. Overall, the study shows that the proportion of the two types of cement has little effect on the fluidity of composite cement mortar.

[0069] With the increase of SAC proportion, the 1-day compressive strength of composite cement mortar continuously increases. The strength increase is more pronounced when the PC / SAC ratio is between 7:3 and 4:6. This is because the early strength of composite cement mortar mainly comes from SAC hydration. As a major active admixture, SAC can increase the early strength and durability of concrete while reducing heat generation and cracking tendency. Sulfate ions in sulfoaluminate cement and hydroxide ions in silicate cement can react to form silicates and generate corresponding heat of chemical reaction, thereby accelerating the hardening process and improving the early strength of concrete.

[0070] The ratio of PC to SAC has a significant impact on the setting time of mortar. Taking a water-cement ratio of 0.45 as an example, when the SAC ratio is 90%, the initial setting time can be as low as 8 minutes, while when the SAC ratio is 10%, the initial setting time is the highest, reaching 292 minutes. Therefore, the setting time can be precisely controlled by adjusting the PC and SAC ratio according to different engineering conditions. As the SAC ratio increases, the setting time decreases continuously, and the interval between the initial setting time and the final setting time also shortens. Figure 2 As shown; when PC:SAC = 7:3, the time interval between initial and final setting is within 30 minutes; when the SAC ratio is the same as or higher than PC, the time interval between initial and final setting is within 10 minutes.

[0071] This phenomenon mainly occurs because the retarding components in PC react with the calcium sulfoaluminate in SAC through hydration to form ettringite, which accelerates the hydration and setting process of the composite cement mortar, generating aluminum hydroxide gel. The aluminum hydroxide gel then rapidly reacts with the calcium hydroxide hydration product of PC to form ettringite, further accelerating the setting of the composite cement mortar.

[0072] 2.2 Effect of water-cement ratio on the properties of grouting materials

[0073] The fluidity of mortar is a crucial indicator in engineering construction, and different water-cement ratios exhibit corresponding effects on the fluidity of composite cement mortar. Through comparative experiments and... Figure 1 Data (a) shows that at a water-cement ratio of 0.45, the mortar exhibits poor fluidity and workability. However, as the water-cement ratio increases to 0.5, the mortar's fluidity significantly improves. This is because at a high water-cement ratio, the resistance between cement particles is lower, allowing them to disperse freely in the solution. This weakens the interaction forces between particles and reduces the filling of voids between them, further decreasing the cohesion and internal friction of the composite cement mortar, thus improving its fluidity. In actual engineering projects, it is necessary to select an appropriate water-cement ratio based on specific circumstances and requirements to achieve the optimal fluidity performance of the composite cement mortar. Furthermore, selecting the optimal water-cement ratio level through experiments provides a basis and guarantee for engineering construction.

[0074] Increasing the water-cement ratio weakens the compressive strength of composite cement mortar. Higher water content reduces the interaction forces between cement particles, making it harder for particles to stay together. This increases the number of capillary pores and porosity after hydration, leading to a decrease in compressive strength. Furthermore, the increased water content restricts the hydration reaction, potentially preventing some cement particles from fully hydrating and ultimately reducing the mortar's strength. At water-cement ratios of 0.45 and 0.5, the 1-day compressive strength of the mortar is almost the same, but decreases with increasing ratio. At a water-cement ratio of 0.6, the lowest 1-day compressive strength is 2.93 MPa, which still meets the compressive strength requirements for the runway subbase.

[0075] Figure 3 This study primarily investigated the effect of different water-cement ratios on the setting time of composite cement mortar, with (d) representing a comparison of initial setting times. The graph shows that the effects of different water-cement ratios on setting time exhibit roughly similar trends. When the water-cement ratio is too high, excessive water dilutes the composite cement mortar paste, reducing its viscosity and consequently slowing down the cement hydration reaction. However, the addition of sulfoaluminate cement leads to a faster hydration reaction rate, thus offsetting the effect of the water-cement ratio and making its influence on setting time negligible. Therefore, the effect of different water-cement ratios on the setting time of composite cement mortar can be balanced by adding an appropriate amount of sulfoaluminate cement.

[0076] 2.3 Effect of admixture ratio on the performance of grouting materials

[0077] In studying the effect of water-reducing agent dosage on composite cement mortar, the ratio of composite silicate cement to sulfoaluminate cement was 7:3, the water-cement ratio was 0.6, and the water-reducing agent proportion was set at five levels: 0.5%, 0.55%, 0.6%, 0.65%, and 0.7%. The experimental results are as follows: Figure 4 As shown.

[0078] When the PC, SAC ratio and water-cement ratio are determined, the fluidity gradually increases with the increase of the water-reducing agent ratio. Its working principle is to change the surface charge of the cement material, reducing the mutual repulsion between cement particles, thereby reducing the attraction between cement particles, making the particles more dispersed, forming a higher specific surface area, thus affecting the chemical reaction between cement and water and the arrangement of cement particles, thereby improving the fluidity of cement mortar. However, when the water-reducing agent ratio exceeds 0.6%, the fluidity of the composite cement mortar no longer changes, and the development law of fluidity retention after 30 minutes is the same as that of overall fluidity. When the water-reducing agent ratio exceeds 0.6%, the effect is not obvious, indicating that the water-reducing agent dosage has exceeded the optimal mixing ratio at this point.

[0079] Adding an appropriate amount of water-reducing agent can improve the fluidity and pumpability of grouting materials and reduce the water content, thus lowering the water-cement ratio and improving the strength and hardening properties of the grouting material. Figure 4 It was found that as the proportion of water-reducing agent increased, the 24-hour compressive strength of the composite cement mortar also increased. However, when the proportion of water-reducing agent exceeded 0.7%, the strength decreased instead. This is because excessive water-reducing agent dosage negatively impacted the material's bonding performance. Therefore, in practical applications, it is necessary to select the appropriate type of water-reducing agent and dosage based on the specific application environment and material properties to maximize the effect of the water-reducing agent, improve the strength of the grouting material, and meet engineering requirements.

[0080] 2.4 Determination of the optimal mix ratio

[0081] Based on the comprehensive experimental results, as shown in Tables 4-6, the optimal mix proportion for the grouting material used in horizontal drilling of airport pavement base courses was determined to be: PC:SAC = 7:3, sand-cement ratio 1:1, water-cement ratio 0.6, and water-reducing agent ratio 0.6%. The initial setting time was 95 min, the final setting time was 118 min, the fluidity was 196 mm, and the fluidity after 30 min was 88 min; the 1-day compressive strength was 2.93 MPa. The optimal mix proportion of silicate-sulfoaluminate composite cement mortar for small-diameter horizontal grouting in airports is listed in Table 4, and its workability is shown in Table 5.

[0082] Table 4 Optimal Grouting Material Mix Ratio

[0083]

[0084] Table 5. Performance of Optimal Grouting Materials

[0085]

[0086] Under this grouting material mix design, the composite cement mortar exhibits excellent fluidity and maintains stable fluidity for 30 minutes after mixing. This ensures that the grout will not cause pore blockage due to loss of fluidity during grouting. However, there is a certain trade-off between the fluidity of the grouting material and its setting time. If the setting time is continuously shortened for efficiency, the fluidity of the material will also be affected within a short period. To ensure smooth grouting, a PC to SAC ratio of 7:3 is recommended. Under this condition, the final setting time will still be kept within two hours, meeting the requirements of on-site construction.

[0087] Table 6 shows the orthogonal test results when the ratio of P.C to SAC is 9:1-1:9, the water-cement ratio is 0.45-0.6, and the proportion of water-reducing agent is 0.6%.

[0088]

[0089]

[0090] 3. Evaluation of Grouting Effect 3.1 Simulated Base Horizontal Drilling Specimen

[0091] To better test the effect of composite cement mortar grouting on the compressive strength of the pavement subbase, this invention starts from the mix design of the subbase, prepares cylindrical compressive strength specimens and uses embedded parts to fill them to simulate the drilling process, grouting is carried out on the sixth day of curing of the strength specimens, and the compressive strength is tested on the seventh day.

[0092] Table 7. Relevant parameters for unconfined compressive strength test

[0093]

[0094] This method can not only test the effect of drilling on compressive strength, but also test the grouting effect of composite cement mortar after 1 day. In this experiment, the diameters of the embedded parts selected were 2cm, 4cm, 6cm and 8cm. Figure 5 The process of drilling and grouting a 2cm diameter hole.

[0095] Figure 6 To investigate the strength changes of specimens before and after grouting with different hole diameters, the "Design Code for Cement Concrete Pavement of Civil Airports" requires that when the flight zone index II is E or F, the 7-day water immersion compressive strength of the cement-stabilized aggregate in the lower base layer should not be less than 2.5 MPa. The original strength of the specimens in this test was 2.71 MPa. As the hole diameter increased, the compressive strength of the specimens continuously decreased, but after grouting, the compressive strength of specimens with all hole diameters recovered and improved. When the hole diameter was 8 cm, the strength was completely lost, decreasing to 0.7 MPa; however, after the composite cement mortar grouting was completed, it recovered to 2.53 MPa, meeting the code requirements. When the hole diameter was 2 cm, the strength was 2.59 MPa when tested without grouting, showing a relatively small strength loss. Therefore, during on-site construction, to protect the structure and strength of the lower base layer, the hole size should be minimized as much as possible. This not only reduces the damage to the base layer caused by drilling but also reduces the amount of composite cement mortar material used, resulting in certain economic benefits.

[0096] 3.2 On-site testing and inspection

[0097] To better verify the practicality and grouting effect of the composite cement mortar material, a simulated drilling and grouting process with a diameter of 10cm was carried out on the base layer of the field test section. Figure 7 The test section is shown by an arrow indicating the transverse half of the runway, with the direction from the shoulder to the runway centerline. The lower base layer is divided into three types: cement-stabilized crushed stone, lime-stabilized crushed stone, and lime-fly ash-stabilized crushed stone.

[0098] 1. Heavy Weight Deflectometer (HWD)

[0099] A weighted deflectometer is a device used to measure pavement deformation and settlement. After the weight falls freely, it senses the degree of pavement deformation. Sensors record and measure the rebound height of the weight at different test points. Based on the changes in rebound height, the pavement settlement and deformation can be inferred, and the impact stiffness modulus at the current location can be obtained, thereby calculating the reaction modulus of the base course surface. In this experiment, tests were conducted before and after drilling, and after grouting, to verify the grouting effect of composite cement mortar.

[0100] Figure 8 The changes in impact stiffness modulus before and after drilling and after grouting indirectly reflect the stability of the pavement structure. After backfilling and grouting, the pavement quality was improved. At a position 2.25m from the runway centerline, the impact stiffness modulus before drilling was 1137.5 KN / mm², which decreased to 1066.9 KN / mm² after drilling. After grouting with composite cement mortar, the impact stiffness modulus was 1175.3 KN / mm², showing some recovery compared to before and after drilling. At positions 6.75m, 11.25m, and 15.75m from the runway centerline, the impact stiffness modulus after grouting increased by 2.1%, 1.6%, and 0.2% respectively compared to before drilling. This data also indirectly reflects the improved pavement bearing capacity after grouting.

[0101] However, at a distance of 20.25 meters from the center of the runway, near the shoulder, the impact stiffness modulus decreased. This is because this location is close to the start of grouting, and drilling and sealing operations are required during the grouting process. This damages the original material structure and interaction of the pavement, resulting in incomplete filling of the composite cement mortar and a decrease in the impact stiffness modulus.

[0102] 2. Ground Penetrating Radar

[0103] Ground-penetrating radar (GPR) is a non-destructive testing device that uses electromagnetic wave technology to detect the structure and characteristics of underground materials. Its working principle involves emitting high-frequency electromagnetic waves and receiving their reflected signals. By analyzing the signal reflection parameters, it obtains information on the spatial distribution and morphology of the underground materials. In this experiment, GPR equipment used for airport pavement inspection was used after grouting to assess the filling condition of the underlying base layer after grouting and whether grouting would cause problems such as voids in the underlying base layer, thus providing reliable support for airport pavement engineering.

[0104] Figure 9 This refers to the test results before and after drilling and after grouting at a certain location during field testing. Figure 9 (a) shows the pre-test inspection, which proved that the pavement condition was good. After drilling small-diameter holes, the scanned image showed convex peaks, indicating that holes did indeed exist in the lower base layer. Figure 9 (b). However, after grouting with composite cement mortar, the grouting effect at the lower base layer was good, and the filling was dense. Figure 9 (c) After grouting with composite cement mortar, the defects generated before drilling were effectively repaired, and the structural support and load-bearing capacity of the subbase were also strengthened. This test result confirms the effectiveness and feasibility of composite cement mortar in reinforcing the subbase structure of pavement.

[0105] 4. Conclusion

[0106] (1) Silicate-sulfoaluminate composite cement mortar has the advantages of short setting time, adjustable within a certain range, good fluidity and stability, and high early compressive strength. It is a universal material that meets the requirements of airport non-stop construction and is suitable for horizontal grouting of pavement base.

[0107] (2) Sulfoaluminate cement has a fast hydration reaction rate, and controlling the ratio of silicate cement to sulfoaluminate cement becomes a key factor affecting the setting time of composite cement mortar. When PC:SAC = 7:3, the final setting time of composite cement mortar is within 2 hours, and the time interval between the initial setting and the final setting does not exceed 30 minutes.

[0108] (3) The water-cement ratio and the proportion of water-reducing agent have a significant impact on the fluidity of composite cement mortar. To ensure its applicability to horizontal grouting, composite cement mortar should have the highest possible fluidity. However, the increased fluidity of the mortar will also have a certain impact on its setting time. Finally, under the premise of ensuring the horizontal grouting effect, the water-cement ratio is controlled at 0.6 and the proportion of water-reducing agent is 0.6%. At this time, the fluidity of composite cement mortar is 196 mm, and the fluidity is maintained at 88 mm for 30 minutes.

[0109] (4) Through the simulated drilling grouting of cylindrical strength specimens and the HWD and ground-penetrating radar detection of the field test section, it was shown that the silicate-sulfoaluminate composite cement mortar was filled densely, which played a certain role in improving the strength and structure of the underground base layer, and successfully ensured the safety of the airport opening the next day.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A grouting material for horizontal drilling of airport pavement base course, characterized in that, The grouting material includes the following raw materials: cement, water-reducing agent, aggregate, and tap water; The cement comprises silicate cement and sulfoaluminate cement; the ratio of silicate cement to sulfoaluminate cement is 7:3, the sand-cement ratio is 1:1, the water-cement ratio is 0.6, and the water-reducing agent dosage is 0.6%. The aggregate is medium-fine sand with a diameter of less than 0.5 mm; The water-reducing agent dosage is the percentage of the water-reducing agent by mass of the cement, and the water-reducing agent is a polycarboxylate water-reducing agent.

2. The method for preparing grouting material for horizontal drilling of airport pavement base course as described in claim 1, characterized in that, Includes the following steps: S1: Place silicate cement, sulfoaluminate cement, and aggregate into the grouting machine at a ratio of 7:3 for silicate cement to sulfoaluminate cement and a 1:1 ratio for sand to cement. S2: Stir at a speed of 300-800 r / min, add an appropriate amount of tap water at a water-cement ratio of 0.6, and continue stirring; S3: After stirring for 3 minutes, add polycarboxylate superplasticizer at a ratio of 0.6% and stir for another 3 minutes to obtain the mixture, which is the grouting material for horizontal drilling of airport pavement base course.

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