A partitioned progressive repair method for mortar falling off of an old stone masonry river channel

Abstract

An old stone river channel mortar peeling off partition progressive repair method, comprising the following steps: step one, comprehensive diagnosis and accurate partition; step two, differential material preparation and pretreatment; step three, partition progressive repair; step four, ecological restoration and long-term monitoring; Realize the accurate diagnosis of old stone river channel mortar disease, avoid hidden disease omission; Special repair materials and processes are matched for different grades of diseases to improve the durability of repair; While ensuring the safety of the structure, the historical style of the river channel is maximized; After repair, the ecological function of the river channel is restored, and a long-term monitoring mechanism is established to realize the whole life cycle management.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of water conservancy engineering and ancient building restoration. Specifically, it involves a construction method for scientifically diagnosing, classifying and zoning stone masonry riverbanks with long service life and mortar spalling defects, and implementing progressive restoration using differentiated materials and processes. It is applicable to the maintenance and restoration of old stone masonry riverbanks that have both water conservancy functions and historical and cultural value. Background Technology

[0002] Old stone-paved river channels are an important part of historical water conservancy engineering heritage, while also undertaking modern water conservancy functions such as flood control, drainage, and ecological water conveyance. However, due to long-term rainwater erosion, freeze-thaw cycles, microbial corrosion, and load changes, the mortar used for riverbank wall construction generally suffers from three major types of defects: first, surface powdering, which reduces the surface strength of the mortar and makes it easy to be eroded and peeled off by water flow; second, the development of cracks, with micro-cracks extending from the surface to internal through-cracks, leading to a decrease in the overall structural integrity; and third, hollowing and loosening, where the mortar separates from the stone interface to form cavities, which in severe cases can lead to stone misalignment, riverbank wall leakage, and even the risk of partial collapse.

[0003] Current industry methods for repairing this type of disease have significant technical shortcomings, as detailed below: 1. The repair strategy is "one-size-fits-all" and lacks specificity: Regardless of the degree of mortar loss (minor powdering or severe hollowing), the traditional process of "manually chiseling away the damaged mortar → filling the entire surface with ordinary cement mortar" is used, without differentiating treatment based on the severity of the damage. This approach leads to over-construction in slightly weathered areas that only require surface protection, resulting in material waste and financial losses. Furthermore, the "surface covering" of severely hollow areas does not address the internal cavity problem, making them prone to secondary cracking in the short term after repair, resulting in poor durability.

[0004] 2. Disease diagnosis relies on subjective experience and lacks accuracy: Current diagnosis relies mostly on workers to observe surface diseases with their naked eyes, supplemented by simple hammering and listening to the sound to judge hollowness. It cannot identify hidden hollowness inside (such as deep cavities inside the stone) and fine cracks (width <0.2mm), and is easy to miss key disease points, resulting in incomplete repair.

[0005] 3. Disconnect between materials and appearance / ecology: The ordinary silicate cement mortar used in the restoration differs greatly in color and texture from the traditional lime mortar of the old stone-lined river channel. After restoration, the surface of the bank wall is clearly "new and old", which destroys the integrity of the historical appearance. At the same time, the dense and hard surface of cement mortar is not conducive to the attachment of vegetation on the riverbank, blocks the interaction channel between aquatic and terrestrial organisms, and affects the continuity of the river ecosystem.

[0006] 3. Lack of quantitative control during construction, resulting in large quality fluctuations: During grouting repair, the grouting pressure and material ratio are adjusted entirely based on the workers' experience, without unified technical standards. Excessive pressure can easily crack the original stones or widen cracks, while insufficient pressure leads to incomplete filling of internal cavities; moreover, there are no systematic monitoring methods after repair, making it impossible to detect subsequent structural deformation in a timely manner, and making it difficult to achieve full life cycle management.

[0007] In summary, existing technologies cannot simultaneously address the three core needs of "structural safety restoration, preservation of historical features, and restoration of ecological functions," and there is an urgent need for a systematic restoration method that combines scientific diagnosis, precise zoning, and matching of materials and processes. Summary of the Invention

[0008] This invention aims to overcome the technical shortcomings of existing old stone-masonry river channel mortar detachment repair methods, which are characterized by "extensive diagnosis, simple processes, damage to appearance, and ecological disruption," and to provide a repair method that is scientific, economical, and eco-friendly.

[0009] The technical solution of this invention is as follows: A zoned, progressive repair method for mortar loss in old stone-lined river channels includes the following steps: Step 1, Comprehensive Diagnosis and Precise Zoning: Using a drone equipped with a high-definition camera and thermal imager to generate orthophotos and thermal maps, combined with hammer impact and mechanical wave detection methods for verification, the repair area is divided into Class I, Class II and Class III areas, where Class I is a severely damaged area, Class II is a moderately cracked area and Class III is a slightly weathered area. As one implementation method, the initial drone detection is as follows: a multi-rotor drone equipped with a 4K high-definition camera and an infrared thermal imager is used to fly at a constant speed along the riverbank, with a flight altitude of 5-8m above the bank and an overlap of ≥80%, to generate an orthophoto map and a thermal distribution map of the bank.

[0010] Among them, the orthophoto image is used to identify surface cracks (the location, length and width of cracks are automatically marked by image recognition algorithms); the thermal image uses the physical property that "the thermal inertia of the air layer in the hollow area is lower than that of the dense mortar" to mark the suspected hollow areas inside (areas with abnormally low temperatures in the thermal image).

[0011] On-site verification involved using two complementary methods to verify suspected hollow areas and cracked areas marked by drones: ① Hammering method: Lightly tap the mortar surface with a rubber hammer to make a preliminary distinction between "crisp sound (hollow)" and "dull sound (dense)" and mark the areas with abnormal sound; ② Mechanical wave detection method: Using a non-metallic ultrasonic detector, the transmitting probe and the receiving probe are placed on both sides of the marked area. The range of hollow areas is determined by the difference in ultrasonic wave propagation speed (wave speed ≥3000m / s in dense mortar, wave speed <2000m / s in hollow areas). Areas with wave speed <2000m / s are divided into hollow areas.

[0012] The three-level zoning standard is as follows: Based on the diagnostic results, the repair area is divided into three levels: Class I severely damaged area: Determined if any of the following conditions are met: The area where mortar has fallen off accounts for ≥30% of the total area of ​​the region; Hollow depth ≥50mm (ultrasonic detection); The displacement of the stones is ≥10mm (measured by drone photography), and there is leakage.

[0013] Class II moderate crack zone: surface crack width 0.2-5mm, crack length ≥500mm; no obvious hollow areas (ultrasonic wave velocity ≥2800m / s); no displacement of stones, and the structure is basically stable.

[0014] Class III Slightly Weathered Area: Only the mortar surface is powdery (powdering depth < 10 mm), with no obvious cracks (crack width < 0.2 mm); ultrasonic testing shows no hollow areas, and the structural integrity is good.

[0015] This step is the core invention point of this invention. It adopts a multi-method integrated diagnosis + three-level zoning standard to achieve accurate diagnosis of mortar defects in old stone masonry river channels, avoid omission of hidden defects, and lay a good foundation for subsequent zoning repair.

[0016] Step 2: Differentiated material preparation and pretreatment: Prepare high-fluidity composite grouting material for Class I areas, high-permeability modified cement-based grout for Class II areas, and eco-friendly surface protective agent for Class III areas; As one implementation method, the material for Zone I is a high-flow composite structural grout, with the following formula: P.O42.5R cement (40%), ultrafine fly ash (25%), quartz sand (20%, particle size 0.1-0.3mm), micro-expansion agent (5%, ettringite type), polycarboxylate superplasticizer (1.5%), and water (8.5%). This material has an initial flowability ≥300mm, a 28-day compressive strength ≥40MPa, and a bond strength ≥3.5MPa, meeting the requirements for dense filling and structural reinforcement of the hollow area.

[0017] Category II materials: High-permeability modified cement-based grout, with the following formula: P.O32.5 cement (35%), silica fume (10%), nano-silica (3%), acrylate copolymer emulsion (8%), and water (44%). The grout permeability coefficient is ≤1×10⁻⁶. -8cm / s, 28d flexural strength ≥5MPa, can penetrate into micro-cracks and form an elastic gel, adapting to temperature deformation.

[0018] Category III materials: Eco-friendly surface protectant, composed of traditional lime paste (40%), nano silica sol (15%, particle size 20-50nm), iron oxide pigment (2%, matching the original mortar color), water-based resin (5%), and water (38%). After drying, the surface hardness is ≥3H, the water absorption rate is reduced by ≥60%, and the color difference with the original mortar is ΔE<3, ensuring consistency in appearance.

[0019] The pretreatment process for high-pressure water vapor cleaning and crack diversion channel excavation in the repair area is as follows: Surface cleaning: Use a high-pressure water-air mixture cleaner (pressure 0.8-1.2MPa, water-air ratio 1:3) to rinse along the mortar surface at a 45° angle to remove loose mortar debris, moss, oil stains and other dirt, and avoid vertical impact damage to the original stone surface by high-pressure water flow.

[0020] Crack pretreatment: For cracks in Class II zones, use a diamond grinding wheel (thickness 0.5-1mm) to carve a "V-shaped guide groove" along the crack direction. The groove is 5-8mm wide and 3-5mm deep, with both ends extending 50mm to facilitate grout injection. After the guide groove is carved, use compressed air (pressure 0.3MPa) to blow away the dust.

[0021] This step is the second core inventive point of this invention: different material formulations are used for repairing different zones.

[0022] Step 3, Gradual Repair by Zone: First, use low-pressure slow grouting method to grout the Class I area and scrape it level. Then, use a manual grouting device to inject grout into the Class II area. Finally, apply a protective agent to the Class III area. As one implementation method, the repair of Class I areas should be prioritized to prevent the spread of the disease, specifically: Drilling layout: Use a handheld electric drill (8-10mm in diameter) to lay grouting holes 50mm from the edge of the hollow area, with a hole spacing of 200-300mm. The hole depth should penetrate the hollow layer to the surface of the stone (leaving a 5mm protective layer). Vent holes (6mm in diameter) are installed at the highest point of the void area to ensure that air is discharged during grouting.

[0023] Low-pressure slow injection: Use an electric grouting pump (maximum pressure 1.0MPa), connect it to the grouting hole, and inject grout from bottom to top hole by hole. Control the grouting pressure to be stable at 0.2-0.5MPa through the pump body pressure sensor (adjust according to the volume of the void: 0.2-0.3MPa when the volume is <0.1m³, and 0.3-0.5MPa when the volume is ≥0.1m³). Control the grouting speed of each hole at 50-100mL / min until uniform grout (no air bubbles) overflows from the vent hole. Close the grouting valve and maintain the pressure for 10-15min.

[0024] Surface treatment: 24 hours after grouting is completed (after the grout has initially set), use a trowel to scrape off the excess grout on the surface so that the repaired surface is 2-3mm lower than the original stone surface, leaving space for the ecological vegetation layer.

[0025] Remediation work in Class II areas shall be carried out within 72 hours after remediation work in Class I areas, specifically as follows: Grout injection: Using a portable manual grout injector (capacity 500mL), draw the modified cement-based grout into the syringe, insert the needle into one end of the guide channel, and slowly push the grout until the other end of the guide channel overflows with grout. Seal the overflow end with a cotton strip, continue to push and maintain pressure for 5 minutes to ensure that the crack is fully filled.

[0026] Surface finishing: 12 hours after grouting, wipe off any residual grout on the surface with a damp cloth to keep the cracked area flush with the surrounding mortar surface.

[0027] Construction will be carried out last in Class III areas to avoid pollution from earlier construction, specifically as follows: Application of protective agent: Use a wool brush (50mm wide) to apply the eco-friendly surface protective agent in one direction along the mortar surface. The coating thickness should be controlled at 0.2-0.3mm. Apply two coats (apply the second coat after the first coat has dried for 6 hours) to ensure that the protective agent penetrates evenly into the mortar surface (penetration depth ≥5mm).

[0028] This step is the third core inventive point of this invention: a phased and differentiated construction process to avoid a one-size-fits-all repair strategy.

[0029] Step 4: Ecological restoration and long-term monitoring: Spray vegetation slurry on Class I areas, pre-embed stress and strain sensors, and establish monitoring records.

[0030] As one implementation method, the plant slurry is composed of 5% local herb seeds, 3% water-retaining agent, 10% coconut shell fiber, 20% decomposed organic fertilizer, and 62% river sand, with a spray thickness of 2-3mm.

[0031] After spraying the slurry, cover it with non-woven fabric to keep it moist until the seeds germinate.

[0032] The sensor is pre-embedded at the junction of rocks in Class I area, in areas with a hollow area > 0.5m².

[0033] In addition, monitoring archives can be established by combining regular aerial photography with drones.

[0034] Through the above design, the present invention provides a zoned, progressive repair method for mortar loss in old stone-masonry river channels, which has the following technical effects: 1. Significant structural repair effect and improved durability: Through differentiated materials and processes, the void filling rate after grouting in Class I areas is ≥98% (ultrasonic testing), and the permeability coefficient of the repaired revetment wall is reduced to 1×10⁻⁶. -7 Below cm / s (original impermeability coefficient 1×10) -4 (cm / s); After repair of Class II areas, no secondary cracking occurred after more than 50 freeze-thaw cycles (-20℃→20℃); After protection of Class III areas, the surface hardness of the mortar increased by more than 40%, the water absorption rate decreased by more than 65%, and the service life of the structure is expected to be extended by 20-30 years after repair.

[0035] 2. The historical features are well preserved: the color difference between the ecological surface protectant and the original mortar is ΔE<3, making it difficult to distinguish between the old and new areas with the naked eye; the repair surface covered by the vegetation slurry blends with the natural riverbank vegetation, avoiding "artificial repair traces". According to the assessment of cultural relics protection experts, the preservation rate of the historical features is over 90%.

[0036] 3. Good restoration of ecological function: After the vegetative slurry is sprayed, the seed germination rate is ≥80%, and the vegetation coverage reaches more than 60% after 3 months. It provides a habitat for small aquatic organisms (such as snails and aquatic insects), and the dissolved oxygen content in the water surrounding the restored area increases by 5%-8%, thus restoring the continuity of the ecosystem.

[0037] 4. Economic and efficiency advantages: Compared with the traditional "one-size-fits-all" repair, this method reduces material usage by 35%-40% (avoiding over-repair of slightly weathered areas) and reduces labor costs by 25% (zoning construction reduces repetitive work); taking a 100m long and 3m high stone riverbank wall as an example, the traditional repair period is about 30 days, while this method shortens the period to 20 days, and the overall cost is reduced by 30%.

[0038] 5. Strong monitoring and controllability: Through stress and strain sensors and drone photography and measurement, the stress changes of the repair body (such as the stress increment when the water level rises during the flood season) and the development of cracks can be monitored in real time. Once an abnormality occurs (such as strain exceeding 1000με or crack width increasing by 0.5mm), timely warnings can be issued and repair measures can be taken to avoid sudden accidents. Detailed Implementation

[0039] Example The stone-built bank wall of an ancient canal was built in 1865. It is 500m long and 2.5m high. It is constructed using "block stone + lime mortar". Currently, it has defects such as mortar falling off (the local area of ​​falling off reaches 40%), hollow areas (the hollow area is 60mm deep in some areas), and cracks (the longest crack is 1.2m and the width is 0.5-3mm). It needs to be repaired.

[0040] To address the above situation, this embodiment provides a zoned, progressive repair method for mortar loss in old stone-masonry river channels. The specific implementation steps are as follows: Step 1: Comprehensive Diagnosis and Precise Zoning (2 days) Drone detection: A DJI M300RTK drone, equipped with a Zenmuse P14K camera and XT2 thermal imager, was used to fly along the shore wall (6m altitude, 2m / s speed, 85% overlap) to generate a 500m orthophoto map of the shore wall, automatically identifying 23 surface cracks (total length 18.5m); and marking 12 suspected areas of hollowness (total area approximately 35m²) on the thermal map.

[0041] On-site verification: For the 12 suspected hollow areas, a rubber hammer was first used to tap and mark 8 hollow areas with a crisp sound; then, an NM-4B non-metallic ultrasonic detector with a probe spacing of 200mm was used to measure the wave velocity of the hollow areas as 1500-1800m / s, and finally 8 hollow areas were identified (total area 32m²).

[0042] Based on the above diagnostic results, the 500m revetment was divided into zones. The zoning results are as follows: Category I area: 8 hollow areas + surrounding mortar spalling areas, totaling 45m²; Class II area: 23 cracks and a 100mm radius around them, with a total area of ​​60m²; Category III area: The remaining area, with a total area of ​​1145m².

[0043] Step Two: Material Preparation and Pre-treatment (3 days) Material preparation: Mix the following according to the formula: 5 m³ of high-flow composite grout for Zone I, 0.8 m³ of high-permeability modified cement-based grout for Zone II, and 200 L of eco-friendly surface protectant for Zone III. After mixing, test the following: grout flowability 310 mm, grout permeability coefficient 8 × 10⁻⁶. -9 cm / s and color difference of the protective agent ΔE=2.5 both meet the requirements.

[0044] Pretreatment: Clean the entire surface of the bank wall with a high-pressure water vapor cleaner (pressure 1.0MPa) to remove about 0.3m³ of loose mortar; chisel V-shaped diversion channels (6mm wide and 4mm deep) in 23 cracks and blow away the dust with compressed air.

[0045] Step 3: Gradual Repair by Zone (10 Days) Category I area repair (4 days): A total of 120 grouting holes and 32 venting holes were drilled in 8 hollow areas. Grouting was carried out using an electric grouting pump (pressure 0.3-0.4MPa, speed 80mL / min). After grouting in each hollow area, the pressure was maintained for 12 minutes. The final hollow filling rate was 99% as measured by ultrasonic testing. After leveling, the repaired surface was 2mm lower than the original stone.

[0046] Class II area repair (3 days): Modified grout was injected into 23 cracks using a manual grouting device. Pressure was maintained for 5 minutes after each crack was grouted. The crack filling saturation was 100% after repair (inspection by cutting).

[0047] Class III area repair (3 days): Apply the protective agent twice with a wool brush. After application, the penetration depth was tested by core drilling and reached 6mm. The surface hardness was 3.2H.

[0048] Step 4: Ecological Restoration and Long-Term Monitoring (Construction period: 5 days; monitoring to continue indefinitely) Ecological restoration: Prepare 500 kg of vegetation slurry and spray it on the surface of 45 m² Class I area and the perimeter of 60 m² Class II area with a thickness of 2.5 mm. Cover with non-woven fabric to retain moisture. After 8 days, the seed germination rate is 85%.

[0049] Monitoring setup: Ten vibrating wire strain sensors (model BGK-4000) were pre-embedded at key locations in Class I areas (where stones meet and areas with hollow areas > 0.5m²), connected to a data acquisition instrument (model GPR-100). Sensor data were collected once a day, and aerial photography was conducted once a quarter using a drone. The monitoring data for the first year showed that the maximum strain was 850με (flood season), cracks did not propagate, and the water absorption rate in Class III areas decreased by 68%.

[0050] Implementation effect verification Six months after restoration, on-site inspection revealed: no leakage or displacement of stones in Area I; no cracks after 50 freeze-thaw cycles in Area II; no powdering on the surface in Area III; vegetation coverage reached 65%; dissolved oxygen in surrounding water bodies increased by 7%; the cultural relics protection department assessed the preservation rate at 92%; and the overall project cost was reduced by 32% compared to traditional methods, achieving the expected technical goals.

Claims

1. A zoned, progressive repair method for mortar loss in old stone-masonry river channels, characterized in that, Includes the following steps: Step 1, Comprehensive Diagnosis and Precise Zoning: Using a drone equipped with a high-definition camera and thermal imager to generate orthophotos and thermal maps, combined with hammer impact and mechanical wave detection methods for verification, the repair area is divided into Class I, Class II and Class III areas, where Class I is a severely damaged area, Class II is a moderately cracked area and Class III is a slightly weathered area. Step 2, Differentiated Material Preparation and Pretreatment: Prepare high-fluidity composite grouting material for Class I areas, high-permeability modified cement-based grout for Class II areas, and eco-friendly surface protective agent for Class III areas; High-pressure water and steam cleaning and crack diversion channel excavation were carried out in the repair area; Step 3, Gradual Repair by Zone: First, use low-pressure slow grouting method to grout and scrape the surface of Class I area; then use manual grouting device to inject grout into Class II area; finally, apply protective agent to Class III area. Step 4: Ecological restoration and long-term monitoring: Spray vegetation slurry on Class I areas, pre-embed stress and strain sensors, and establish monitoring records.

2. The method according to claim 1, characterized in that, In step one, the criteria for determining Class I areas are: mortar spalling area ≥ 30% of the total area, and / or, hollow depth ≥ 50mm, and / or, stone displacement ≥ 10mm; The criteria for class II areas are: crack width 0.2-5mm and length ≥500mm, with no hollow areas; The criteria for class III areas are: mortar surface powdering depth <10mm, no obvious cracks.

3. The method according to claim 1, characterized in that, In step one, the drone flies at an altitude of 5-8 meters above the shore wall, with an overlap of ≥80%. Mechanical wave detection uses a non-metallic ultrasonic detector, and the area with a wave velocity <2000m / s is divided into a hollow zone.

4. The method according to claim 1, characterized in that, In step two, the high-pressure water-steam cleaning pressure is 0.8-1.2 MPa, and the water-steam ratio is 1:2-4; The guide channel is 5-8mm wide and 3-5mm deep, extending more than 30mm at both ends.

5. The method according to claim 1, characterized in that, In step three, the grouting pressure in Class I area is controlled at 0.2-0.5MPa, the grouting speed is 50-100mL / min, the pressure is maintained for 10-15min, and the repaired surface is scraped flat and 2-3mm lower than the original stone surface.

6. The method according to claim 1, characterized in that, In step three, after grouting in the Class II area, pressure should be maintained for at least 5 minutes, and the protective agent in the Class III area should be applied at least twice, with a penetration depth ≥ 5 mm.

7. The method according to claim 1, characterized in that, In step four, the thickness of the vegetation slurry spray is 2-3mm.

8. The method according to claim 1, characterized in that, In step four, after the sap is sprayed, it is covered with non-woven fabric to keep it moist until the seeds germinate.

9. The method according to claim 1, characterized in that, In step four, the sensor is pre-embedded at the junction of rocks in Class I area and in areas with a hollow area > 0.5m².

10. The method according to claim 1, characterized in that, Step four also incorporates regular drone aerial photography to establish monitoring archives.