A method for repairing a non-intumescent fire-retardant coating base layer local hollowing grouting

Abstract

The application discloses a kind of non-intumescent fireproof coating base layer partial hollow grouting repair method, it is related to hollow grouting repair technical field, comprising: S1, coating surface inspection, the coating surface of hollow area is observed, and the distribution and width of coating surface crack are investigated;The application is filled with the minimally invasive operation mode of debonding cavity by being provided with small hole in hollow area and using pressure grouting, without large-area cutting breaking original fireproof coating, realize low-damage repair to base hollow defect, effectively retain the integrity of coating internal reinforcing net, improve the structural strength of repaired coating, the consistency of fireproof performance and the overall appearance integrity, through the operation logic of intermittent grouting cooperates overflow grouting hole exhaust plugging, in combination with percussion detection real-time master grout penetration state, realize the controllable regulation of grouting pressure, avoid coating to crack due to pressure overload, guarantee cavity filling dense uniform.

Description

Technical Field

[0001] This invention relates to the field of grouting repair technology for hollow areas, specifically a method for grouting repair of localized hollow areas in non-expansive fireproof coating substrates. Background Technology

[0002] Fire-retardant coating delamination refers to a quality defect where, after the fire-retardant coating has cured, the bonding interface between the coating and the steel structure substrate separates, creating a cavity between the two. This defect causes the coating to lose its adhesive constraint from the substrate, making it highly susceptible to detachment under environmental erosion or external forces. This directly reduces the fire resistance and heat insulation capacity of the components and weakens the fire resistance limit of the steel structure. Therefore, timely repair of delamination is essential to ensure the fire resistance performance of buildings. Grouting repair of delamination falls under the category of minimally invasive repair techniques. It does not require large-scale destruction of the original intact coating; instead, adhesive cementitious material is injected into the delaminated cavity through small channels to restore the adhesion between the coating and the substrate. This method preserves the structural integrity of the original coating to the greatest extent possible and is superior to traditional destructive recoating processes in terms of repair efficiency, material consumption, and molding effect.

[0003] Non-intumescent fire-retardant coatings, also known as thick-film fire-retardant coatings, primarily use inorganic cementitious materials such as gypsum and cement as their core substrate. After application, they form a dense fire-resistant and heat-insulating layer with a fire resistance rating of over 2.5 hours, making them the mainstream fire protection material for high-fire-resistance steel structural components. These coatings have a large coating thickness and high structural strength after application. In many projects, reinforcing mesh is added inside the coating to improve crack resistance. Therefore, when defects such as hollow areas appear in the base layer, repairing them by cutting and breaking them not only easily severs the internal reinforcing mesh but also generates a large amount of solid waste and dust. The construction difficulty and material loss are significantly higher than with thin-film coatings. Grouting repair, on the other hand, only requires creating small holes in the coating surface. It is well-suited to the thick, high-strength, and mesh-containing structural characteristics of these coatings, completing defect repairs with minimal coating damage and preserving the original fire-retardant performance to the greatest extent possible.

[0004] In current engineering practice, the common method for repairing hollow areas in the substrate of non-intumescent fire-retardant coatings is to use handheld cutting equipment to remove the hollow sections, clean the substrate interface, and then re-spray or scrape the coating. This process is cumbersome, consumes a lot of materials, and has a long repair cycle. Furthermore, the cutting process can easily damage the reinforcing mesh inside the coating, resulting in insufficient bonding strength between the repaired area and the original coating, poor overall appearance, and the large amount of dust and waste generated during construction can cause environmental pollution. In construction scenarios near railways, residential areas, or other areas sensitive to construction disturbances, additional protective facilities are required, further increasing construction costs and operational complexity. Therefore, developing a grouting repair method for localized hollow areas in the substrate of non-intumescent fire-retardant coatings is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for repairing local hollow areas in non-expansive fireproof coating substrates by grouting. This method can achieve efficient repair of hollow defects through minimally invasive pressure grouting, simplifying construction procedures, reducing construction costs, reducing environmental pollution, and improving the integrity of the repaired coating while ensuring repair quality.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for repairing localized hollow areas in a non-intumescent fire-retardant coating substrate by grouting, the method comprising the following steps:

[0007] S1. Coating surface inspection: Observe the coating surface in the hollow areas to check the distribution and width of cracks on the coating surface; remove damaged areas with through cracks in advance to avoid the construction risk of large-area cracking and damage to the coating caused by grouting pressure transmission.

[0008] S2. Mark the hollow area and lay out the hole positions. Use a hollow hammer to tap and determine the boundary of the hollow area and mark the outline of the area. According to the shape of the hollow area, lay out the grouting holes at the bottom of the area and the overflow holes at the top of the area. Relying on the staggered arrangement of the grouting holes and overflow holes, a complete fluid flow channel is constructed to ensure that the air inside the cavity can be completely discharged and eliminate the dead corners of grout filling.

[0009] S3. Drill and clean the ducts. Use drilling equipment to drill grouting holes and overflow holes at the marked positions. Clean the paint debris and dust in the ducts. After removing the debris in the ducts, ensure smooth flow of grout and avoid solid debris blocking the ducts and interrupting the grouting operation.

[0010] S4. Install the grouting needle. Screw the water-stopping grouting needle into the grouting hole. The outer wall of the needle should fit tightly against the hole wall. Use the elastic rubber structure of the needle to seal the gaps in the hole wall and prevent the grout from leaking out of the borehole sidewall during the grouting process.

[0011] S5. Prepare grouting slurry and perform pressure grouting. Prepare interface gelling slurry compatible with non-intumescent fireproof coatings. Inject the slurry into the hollow cavity using intermittent grouting. After the slurry overflows from the overflow hole, seal it. Stop grouting after all overflow holes are sealed. The special interface gelling agent can be matched with gypsum-based and cement-based non-intumescent fireproof coatings to maintain the fire resistance parameters of the repaired section and the original coating. The intermittent grouting mode evenly distributes the internal pressure of the cavity to prevent single-point high-pressure cracking of the thick fireproof coating.

[0012] The matching interface cementitious grout consists of the following components by weight: 20-35 parts inorganic silicate adhesive powder, 40-55 parts quartz fine powder, 8-15 parts fire retardant modifier, 0.5-2 parts water-based dispersant, 0.1-0.5 parts retarder, and the balance is mixing water. The water-cement ratio is controlled at 0.40-0.55. The quartz powder is graded in two stages: 40 mesh and 80 mesh, with a mass ratio of 1:1.2-1.8. The retarding regulator is sodium gluconate or tartaric acid retarder. Under the premise of ensuring the slurry fluidity ≥220mm, the working time can be controlled between 12-18min, which has good time sequence matching with the 10min grouting operation window and 20min initial setting characteristics of a single area. The tensile bond strength between the hardened slurry and the two types of non-expansive fireproof coatings, namely gypsum-based and cement-based, can reach more than 0.4MPa, and the loss of fire resistance performance can be controlled within 5%.

[0013] S6. Static curing: After grouting, allow the grout to cure statically at a set temperature and wait for it to solidify. Constant temperature curing controls the shrinkage and deformation of the grout, reducing the probability of cracking and voiding again after repair.

[0014] S7. Remove the needle and complete the acceptance and duct restoration. After curing, remove the grouting needle and sealing parts. Conduct two tests on the hollow repair status. After passing the test, fill the duct with the original coating material. Two phased tests are conducted to verify the bonding strength of the grout. The duct is repaired with the same mix ratio to eliminate the appearance color difference and thickness difference at the repair point, so as to achieve a unified overall appearance of the coating.

[0015] Furthermore, in step S2, for rectangular or near-rectangular hollow areas, grouting holes are evenly distributed along the bottom contour of the area, with the lateral coverage of a single grouting hole not exceeding 300mm. Overflow holes are evenly distributed along the top contour of the area, with the spacing between adjacent overflow holes being 150-200mm, and the vertical spacing between overflow holes and grouting holes being 180-200mm. For circular or elliptical hollow areas, grouting holes are set at the bottom of the area, and overflow holes are horizontally arranged above the grouting holes. When the height of the hollow area exceeds 200mm, a bottom-up layered grouting operation is adopted. Layered grouting fills the cavity step by step from low to high, avoiding air retention inside high-level hollow areas, and is suitable for the repair of hollow areas in various irregular steel structure components such as vertical steel columns and horizontal steel beams.

[0016] Furthermore, in step S3, the drilling operation is carried out using a hand drill. The diameter of the grouting hole is 14mm, and the diameter of the overflow hole is 6mm. During the drilling process, the drill rod is kept perpendicular to the coating surface, and the hole depth extends into the hollow cavity, so that the grouting hole and the overflow hole form a connecting passage through the hollow cavity. After the hole is opened, a fine brush is inserted into the hole to clean the coating debris and dust adhering to the inner wall of the hole. Vertical drilling ensures that the hole straight through the hollow interlayer, and the differential design of the hole diameter adapts to the two different functional requirements of grouting and air venting.

[0017] Furthermore, in step S4, the grouting needles are made of aluminum. The grouting needles are assembled sequentially from a stainless steel nozzle, an aluminum rod, a gasket, an elastic rubber, and a connecting screw. The total length of the needle is 10cm, and the diameter of the needle tip is 13mm. The installation is carried out using a T-type socket wrench. The needle is screwed into the grouting hole until the end of the connecting screw is in contact with the surface of the base layer. Grouting is carried out after all the grouting needles in a single hollow area are installed. The 10cm total length is suitable for a conventional 25-50mm thick fireproof coating. The lightweight aluminum body is easy to install manually, and the stainless steel nozzle is resistant to high-pressure grout and is not easily deformed or damaged.

[0018] Furthermore, in step S5, the grouting operation is carried out using a high-pressure grouting machine, with the grouting pressure controlled within the range of 0.3-0.5 MPa. An intermittent injection mode is adopted, with each grouting session lasting 3-5 seconds. After each grouting session, there is a short pause to allow the internal pressure of the duct to be released before continuing to inject grout. This injection and pause process is repeated until the grouting is completed. The 0.3-0.5 MPa low-pressure range is suitable for thick-layer fireproof coatings with wire mesh, taking into account both the grout penetration capacity and the upper limit of the coating structure's load-bearing capacity. The intermittent pressure relief operation balances the pressure distribution inside the cavity.

[0019] Furthermore, in step S5, when multiple grouting holes are set in a single hollow area, alternating grouting is used or multiple grouting machines are used for simultaneous grouting. During the grouting process, a hollow hammer is used to tap the coating surface, and the penetration range of the grout is judged based on the tapping echo. The state changes of the coating surface are observed throughout the process. Alternating grouting avoids local stress concentration in the coating caused by continuous pressure on one side. The tapping echo provides real-time feedback on the grout filling progress, and the repair density can be intuitively judged without disassembling the coating.

[0020] Furthermore, in step S5, when the overflow hole overflows with a continuous and full amount of grout, the overflow hole is sealed with a rubber stopper or a wooden stopper. All grouting operations for a single hollow area are completed within 10 minutes. If new cracks are observed in the coating during the grouting process, the grouting operation is immediately terminated and the internal pressure of the duct is released. The 10-minute operation time is matched with the initial setting cycle of the grout to prevent the grout from solidifying prematurely and losing its flow and filling properties. The pressure is released immediately when cracks appear to control the damage range to be limited to a small area.

[0021] Furthermore, in step S6, the ambient temperature and base layer temperature during the grouting process and curing stage are maintained within the range of 5-35℃. After grouting, the grout completes initial setting in about 20 minutes. The minimum curing time is set to 24 hours. No external disturbance is applied to the coating during the curing period. The 5-35℃ temperature range covers indoor ambient temperature and outdoor open-air conventional construction environments. The 24-hour curing cycle ensures that the interface cementitious agent forms complete bonding strength. Static and undisturbed curing prevents the uncured grout from shifting and debonding.

[0022] Furthermore, in step S7, two inspections are conducted at the 24h and 72h curing nodes, respectively. The inspection uses a hollow hammer to tap and check for hollow areas, and a magnifying glass to observe the coating cracks. Areas with secondary hollow areas are removed and recoated. The initial inspection at 24h checks the bonding effect of the grout base, and the re-inspection at 72h verifies the long-term bonding performance after the grout has fully cured. The dual inspection mechanism screens out and repairs failed points, and distinguishes between defects that can be repaired by grouting and those that must be removed and recoated.

[0023] Furthermore, in step S7, the duct filling is carried out using fire-retardant coating with the same mixing ratio as the original coating. The filling operation fills the inside of the duct densely. After the filling is completed, the coating surface around the duct is repaired, and the surface height of the repaired part is aligned with the surface of the surrounding coating, so that the repaired part and the original coating surface are smoothly transitioned. The same proportion of coating is used to repair the duct to eliminate the weak points in fire resistance. After the surface is leveled and repaired, there are no obvious repair marks, which is suitable for construction scenarios with high appearance requirements such as facades and public passages.

[0024] Compared with existing technologies, this method for repairing localized hollow areas in non-intumescent fire-retardant coating substrates via grouting has the following advantages:

[0025] This invention utilizes a micro-repair method by creating small holes in the hollow areas and filling the debonded cavities with pressure grouting. This eliminates the need for large-area cutting and removal of the original fireproof coating, achieving low-damage repair of hollow defects in the substrate. It effectively preserves the integrity of the internal reinforcing mesh of the coating, improving the structural strength, fire resistance consistency, and overall appearance of the repaired coating. Through intermittent grouting combined with overflow hole venting and sealing, and combined with tapping detection to monitor the grout penetration status in real time, the grouting pressure can be controlled and adjusted to prevent the coating from cracking due to pressure overload. This ensures that the cavity is filled densely and uniformly. The standardized and streamlined operation simplifies the repair process, shortens the construction period, reduces dust and waste generation, and reduces construction costs and controls environmental impact. At the same time, it can adapt to the construction needs of sensitive areas without the need for additional large-scale protective facilities.

[0026] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0028] Figure 1 A flowchart of a method for repairing localized hollow areas in a non-intumescent fire-retardant coating substrate using grouting;

[0029] Figure 2 This is a flowchart illustrating the steps of a method for repairing localized hollow areas in a non-intumescent fire-retardant coating substrate using grouting. Detailed Implementation

[0030] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0031] Example 1

[0032] This embodiment addresses the repair of rectangular hollow defects in the cement-based non-expansive fireproof coating substrate on the surface of steel beams in a factory building. The hollow area measures 420mm × 190mm, with a coating thickness of 30mm and an internal galvanized steel wire reinforcing mesh. A grouting layout with injection holes at the bottom and overflow holes at the top, combined with intermittent low-pressure grouting, fills the debonded cavities. This minimally invasive repair of the hollow defect is achieved without damaging the internal reinforcing mesh, ensuring consistency between the fireproof performance of the repaired coating and the structural strength.

[0033] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0034] S1. Coating surface inspection: The coating surface of the hollow area was observed by visual inspection combined with a magnifying glass. It was found that there were no through cracks in the area, only two shallow hairline cracks with a width of less than 0.1mm at the edge. There was no risk of grouting construction, and grouting repair work could be carried out directly.

[0035] S2. Mark the hollow areas and lay out the holes: Use a hollow hammer to tap around the perimeter of the hollow area point by point, determine the boundary of the hollow area based on the echo difference, and mark the rectangular outline with a marker. Evenly lay out two grouting holes along the bottom outline of the area, with the horizontal coverage of each grouting hole being 210mm, meeting the requirement of not exceeding 300mm; evenly lay out two overflow holes along the top outline of the area, with the spacing between adjacent overflow holes being 200mm, and the vertical spacing between the overflow holes and the grouting holes being 190mm, forming corresponding fluid channels at the top and bottom.

[0036] S3. Drilling and Cleaning the Holes: Use a hand drill with a special drill bit to drill holes. The diameter of the grouting hole is controlled at 14mm, and the diameter of the overflow hole is controlled at 6mm. When drilling, keep the drill rod perpendicular to the coating surface. The hole depth should penetrate the coating and extend into the hollow cavity, confirming that the grouting hole and the overflow hole are connected through the cavity. After drilling, use a fine brush to reach into the hole and repeatedly sweep and clean the coating debris and dust adhering to the inner wall to prevent debris from clogging the hole.

[0037] S4. Install the grouting needle: Select an aluminum water-stopping needle with a total length of 10cm and an end diameter of 13mm. This needle is assembled sequentially from a stainless steel nozzle, an aluminum rod, a gasket, an elastic rubber, and a connecting screw. Use a T-type socket wrench to screw the needle into the grouting hole until the end of the connecting screw is in contact with the surface of the steel structure base, so that the elastic rubber on the outer wall of the needle is tightly and tightly fitted to the hole wall. After completing the installation of two grouting needles, prepare for grouting operations.

[0038] S5. Prepare grout and perform pressure grouting: Prepare an interface gelling grout compatible with the cement-based non-expansive fireproof coating, and stir until uniform and lump-free. Use a high-pressure grouting machine to carry out grouting operations, with the grouting pressure stably controlled at 0.4 MPa. Use an intermittent injection mode, with each injection lasting 4 seconds, followed by a 2-second pause to allow the internal pressure of the duct to release before continuing grouting. During grouting, gently tap the coating surface with a hollow hammer and judge the grout penetration range based on the echo changes. When the upper overflow hole overflows with continuous and full grout, immediately seal the overflow hole with a rubber plug. Stop grouting after both overflow holes are completely sealed. The total grouting operation time for a single area is 7 minutes.

[0039] S6. Static Curing: The ambient temperature at the work site is 22℃, and the base layer temperature is 20℃, which is within the suitable range of 5-35℃. After grouting, allow the grout to cure statically. The grout will complete its initial setting in 18 minutes. The entire curing process takes 24 hours. During the curing period, do not touch or knock the coating, and avoid external disturbance.

[0040] S7. Remove the needle and complete acceptance and duct restoration: After 24 hours of curing, conduct the first inspection. Use a hollow hammer to tap the original hollow area to confirm there is no hollow echo. Observe the coating surface with a magnifying glass; the original shallow cracks have not expanded, and no new cracks have appeared. After 72 hours of curing, conduct a second inspection. The adhesion is stable, and there is no secondary hollowing. After passing the inspection, remove the grouting needle and rubber plug. Fill the duct with cement-based fireproof coating with the same mix ratio as the original coating. After filling and compacting, repair the surface to ensure the repaired area is flush with the surrounding coating, with a smooth transition and no obvious repair marks.

[0041] In summary, this embodiment demonstrates minimally invasive grouting repair for small rectangular hollow areas. Testing showed that the tensile bond strength between the repaired coating and the substrate reached 0.42 MPa, meeting the standard requirement of 0.3 MPa. The hollow area repair pass rate was 100%. The internal galvanized steel wire mesh was not damaged throughout the construction process, and the coating structure integrity retention rate exceeded 98%. The total operation time for a single hollow area was approximately 35 minutes, only one-fifth of the traditional demolition and recoating process. Material consumption was less than 8% of the traditional process. The repaired appearance was excellent, with no obvious color difference or repair marks. This method is suitable for the rapid repair of small-scale hollow defects on the surface of steel beams.

[0042] Example 2

[0043] This embodiment addresses the repair of large-area vertical hollow defects in the gypsum-based non-expanding fireproof coating substrate on the surface of a building's steel structure column. The hollow area measures 580mm × 460mm, with a vertical height of 460mm, exceeding the 200mm layering threshold. The coating thickness is 40mm, and a fiberglass mesh reinforcement is installed internally. A bottom-up, layered grouting operation mode is employed, with alternating grouting at multiple points combined with layered overflow control to achieve dense filling of the high-level cavities, preventing air retention and the formation of filling dead zones, thus ensuring the repair quality of large-sized hollow defects.

[0044] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0045] S1. Coating surface inspection: A comprehensive inspection of the coating surface in the hollow area revealed a longitudinal non-through crack with a width of 0.15mm in the middle of the area. There was no damage or detachment at the edge. After assessment, the crack width was within the safe range and the grouting pressure was controllable, so repair work could be carried out.

[0046] S2. Marking the hollow areas and laying out the holes: Use a hollow hammer to tap and determine the boundary of the hollow area, and mark the outline of the vertical rectangular area. Since the vertical height of the hollow area exceeds 200mm, a layered hole placement scheme is adopted: the bottom layer has 3 grouting holes along the bottom outline, with each grouting hole covering a horizontal range of approximately 190mm; the middle and top layers each have 2 sets of overflow holes, with an adjacent overflow hole spacing of 180mm. The vertical spacing between the bottom layer grouting holes and the middle layer overflow holes is 190mm, and the vertical spacing between the middle layer overflow holes and the top layer overflow holes is 180mm, forming a three-level filling channel from bottom to top, suitable for layered grouting operations.

[0047] S3. Drilling and Cleaning the Channels: Use a hand drill to drill vertically. The grouting hole diameter is 14mm, and the overflow hole diameter for each layer is 6mm. The channel depth penetrates the coating and enters the hollow cavity, confirming that all channels are interconnected through the cavity. After drilling, use a fine brush to clean the plaster coating debris from the inner wall of each channel, and use compressed air to gently blow out the dust from the channel to ensure smooth grout flow.

[0048] S4. Install grouting needles: Screw three 10cm long aluminum water-stopping needles into the bottom grouting holes respectively, and tighten them with a T-type socket wrench until the connecting screw is in contact with the base layer and the elastic rubber is fully expanded to seal the hole wall. After checking that all needles are installed firmly and without looseness, prepare for layered grouting operation.

[0049] S5. Prepare grout and perform pressure grouting: Prepare an interface gelling grout compatible with the gypsum-based fireproof coating, stir evenly, and set aside. Use a high-pressure grouting machine, controlling the grouting pressure at 0.35 MPa, and adopt a bottom-up layered grouting method: First, use an alternating grouting mode for the bottom layer grouting holes, with a single grouting time of 3 seconds, followed by a 3-second pause to release pressure, and repeat this cycle until continuous grout overflows from the middle layer overflowing holes, then seal the middle layer overflowing holes; continue intermittent grouting to the bottom layer grouting holes until the top layer overflowing holes are full of grout, then seal the top layer overflowing holes and stop grouting. Throughout the grouting process, use a hollow hammer to tap and monitor the grout filling height. The total grouting time for a single area is 9 minutes, and no new cracks are generated in the coating during the process.

[0050] S6. Static Curing: The ambient temperature at the construction site is 25℃, and the substrate temperature is 23℃, which meets the construction temperature requirement of 5-35℃. After grouting, allow the grout to cure statically. The grout will initially set in about 20 minutes. Continue curing for 24 hours. During the curing period, avoid external disturbances such as collisions and vibrations to the coating.

[0051] S7. Remove needles and complete acceptance and channel restoration: After 24 hours of curing, conduct the first inspection. Tapping tests show that the original hollow areas have a dense echo with no hollow sounds. Magnification examination shows no expansion of the original cracks. After 72 hours of curing, conduct a second inspection. The coating adhesion is stable, with no secondary hollowing or detachment. After passing the inspection, remove all needles and sealing plugs. Use the same proportion of gypsum-based fire-retardant coating to fill all channels in layers. After surface finishing and smoothing, seamlessly connect with the original coating, with no obvious repair marks on the surface.

[0052] In summary, this embodiment utilizes a layered grouting process to repair large-area vertical hollow areas. Testing revealed that the repaired coating achieved a tensile bond strength of 0.38 MPa, with a filling density of over 96% in the hollow areas and no residual cavities. The internal fiberglass mesh was not cut throughout the process, maintaining a coating structural integrity retention rate of over 95%. The total construction time for a single hollow area was approximately 50 minutes, representing a 75% reduction in construction time and an 85% reduction in material waste compared to traditional demolition and recoating processes. The repaired coating exhibited excellent fire resistance consistent with the original coating, making it suitable for repairing large-sized hollow defects in vertical components such as steel columns.

[0053] Example 3

[0054] This embodiment addresses the repair of elliptical hollow defects in the cement-based non-expansive fireproof coating substrate on the surface of circular column joints in steel structures. The hollow area has a major axis of approximately 260mm, a minor axis of approximately 180mm, and a coating thickness of 50mm. A double-layer galvanized steel wire reinforcing mesh is added internally. An irregular hole layout with a single grouting hole at the bottom and two overflow holes at the top, combined with a low-pressure intermittent grouting process, is employed to adapt to the hollow shape of curved components, achieving low-damage repair of the curved coating and ensuring the integrity of the fireproof protection at the joint.

[0055] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0056] S1. Coating surface inspection: The coating surface of the hollow area was observed segment by segment along the curved surface. No through cracks were found in the area. Only very fine shallow cracks were found at the corners of the curved surface. There was no risk of damage or peeling. The prerequisite for grouting repair was met.

[0057] S2. Marking the hollow area and setting up the holes: Use a hollow hammer to tap along the curved surface to determine the boundary of the elliptical hollow area and mark the outline. For the hollow shape of the circular curved surface component, set one grouting hole at the bottom of the area, and set two overflow holes horizontally above the grouting hole. The overflow holes are spaced 160mm apart, and the vertical distance between the grouting hole and the overflow hole is 200mm, which is adapted to the vertical dimension of the elliptical hollow area to form a bottom-up air venting and filling channel.

[0058] S3. Drilling and Cleaning: Use a hand drill to drill holes along the normal direction of the curved surface, keeping the drill rod perpendicular to the coating surface. The grouting hole diameter is 14mm, and the overflow hole diameter is 6mm. The hole depth penetrates 50mm of coating and extends into the hollow cavity. Confirm that the grouting hole and the two overflow holes are connected through the cavity. After drilling, use a fine brush to clean the paint debris in the hole, repeatedly cleaning until there is no floating dust or debris in the hole.

[0059] S4. Install the grouting needle: Screw one 10cm long aluminum water-stopping needle into the bottom grouting hole. Use a T-type socket wrench to tighten it until the end of the connecting screw is in contact with the surface of the circular steel node base. The elastic rubber ring is fully tightened to seal the gap in the hole wall. After checking that the needle is installed securely, prepare for grouting.

[0060] S5. Prepare grout and perform pressure grouting: Prepare an interface gelling grout suitable for cement-based thick-coat fireproof coatings and mix thoroughly. Use a high-pressure grouting machine for grouting, controlling the grouting pressure at 0.3 MPa, and adopt an intermittent injection mode. Each grouting session lasts 5 seconds, followed by a 2-second pause to release pressure, and repeat the process. During grouting, gently tap the curved coating surface with a hollow hammer and judge the diffusion range of the grout along the curved surface based on the echo. After two overflow holes have overflowed continuously and fully with grout, seal the overflow holes one by one with wooden plugs. Stop grouting after all holes are sealed. The grouting operation time for a single area is 6 minutes, and no new cracks appeared in the coating throughout the process.

[0061] S6. Static Curing: The ambient temperature is 20℃, and the substrate temperature is 19℃, which is within the suitable construction range of 5-35℃. After grouting, allow the grout to cure statically. The grout will initially set in about 21 minutes. Continue curing for 24 hours. During the curing period, do not touch the joint coating and avoid external disturbance.

[0062] S7. Remove the grouting needle and complete acceptance and duct restoration: After 24 hours of curing, an initial inspection is conducted. Tapping tests show that the hollow areas have a uniform and dense echo with no abnormal hollow sounds. Magnification examination reveals no new cracks in the coating, and existing shallow cracks have not expanded. A second inspection is conducted after 72 hours of curing. The coating is firmly bonded, with no secondary hollowing. After passing the inspection, the grouting needle and wooden plug are removed. Cement-based fireproof coating with the same mix ratio as the original coating is used to fill the ducts. After compaction, the curved surface is smoothed to ensure a smooth transition between the repaired area and the surrounding coating, with consistent curvature and no obvious repair marks.

[0063] In summary, this embodiment demonstrates a minimally invasive grouting repair method for elliptical hollow areas in circular steel nodes. Testing revealed that the tensile bond strength of the repaired coating reached 0.45 MPa, the hollow area repair pass rate was 100%, and the coating filling density on the curved surface reached 97%. The double-layer galvanized steel wire mesh remained intact throughout the process, and the coating structural integrity retention rate reached 99%. The total construction time for a single node was approximately 30 minutes, demonstrating high construction precision, extremely low material waste, excellent overall appearance of the repaired curved surface, and no reduction in fire resistance. This method is suitable for the repair of localized hollow areas in various irregularly shaped curved steel structural components.

[0064] Comparative Example

[0065] This comparative example uses the traditional cutting, removal, and recoating process commonly used in engineering to repair a rectangular hollow defect in a steel beam of the same size as in Example 1. The repair is completed by cutting and removing the paint from the hollow section, cleaning the base layer, and re-spraying fireproof paint. It serves as a control group to compare and verify the comprehensive advantages of the grouting repair process.

[0066] The specific implementation process is as follows:

[0067] Marking and Cutting: After determining the boundary of the hollow area using a hollow hammer, mark and cut a 50mm area outside the boundary. Use a handheld cutter to cut the fireproof coating along the marked line, with the cutting depth penetrating the coating to the surface of the base layer. A large amount of dust is generated during the process.

[0068] Demolition and Cleaning: Use a chisel to remove all hollow coatings within the cutting range. During the cleaning process, cut the internal galvanized steel wire reinforcing mesh, remove the detached paint residue, and then use a wire brush to grind the surface of the steel structure base layer to remove residual dust and failed adhesive layers. Collect the generated solid waste.

[0069] Interface treatment and recoating: Apply an interface agent to the cleaned base surface. After the interface agent is surface dry, apply the same type of cement-based non-expanding fireproof coating as the original coating in 3 coats. Each coat should not exceed 10mm in thickness. Apply the next coat after the previous coat has initially set, until the coating thickness is flush with the surrounding original coating.

[0070] Curing and acceptance: After recoating, cure at room temperature for 72 hours. After the coating is fully cured, use a hollow hammer to tap and test the adhesion. Observe the surface cracks with a magnifying glass.

[0071] In summary, this comparative example uses the traditional cutting and recoating process to repair hollow areas of the same size. Testing showed that the tensile bond strength of the repaired coating was 0.32 MPa, just meeting the acceptable standard. However, the overall crack resistance of the repaired area decreased due to the cutting of the reinforcing mesh. The total construction time for a single area was approximately 180 minutes, which is relatively long. The construction process generated approximately 1.2 kg of solid waste and a large amount of dust, resulting in significant material loss. The repaired area showed obvious splicing marks, poor overall appearance, and required additional dust protection facilities, leading to high overall construction costs.

[0072] Comparison Projects Example 1 Example 2 Example 3 Comparative Example Total construction time for a single section Approximately 35 minutes Approximately 50 minutes Approximately 30 minutes Approximately 180 minutes Material loss level Low lower Extremely low high Enhanced network integrity retention rate More than 98% More than 95% More than 99% 0% Post-repair tensile bond strength 0.42MPa 0.38MPa 0.45MPa 0.32MPa Hollow drum repair pass rate 100% More than 96% 100% 90% Overall Appearance Rating excellent good excellent Difference Construction dust and waste generation Very few few Very few Extremely many Comprehensive construction cost rating Low lower Low high Overall Performance Rating excellent good excellent generally

[0073] In summary, the above comparisons show that the three grouting repair solutions are significantly superior to the traditional cutting and recoating process in terms of construction efficiency, structural integrity, appearance, and environmental friendliness. The grouting repair solution for small-area flat surfaces and irregular curved surfaces exhibits the best overall effect, achieving a 100% success rate in repairing voids and a very high coating integrity retention rate, maximizing the preservation of the original coating's fire resistance and structural strength. The large-area layered grouting solution is effectively adaptable to large-sized vertical void scenarios, avoiding air resistance in high-level cavities through graded filling, ensuring stable filling density and repair quality. While the traditional cutting and recoating process can repair basic defects, it suffers from numerous drawbacks, including lengthy construction periods, high material consumption, damage to the internal reinforcing mesh, poor appearance, and severe dust pollution. In sensitive areas, additional protective facilities are required, further increasing construction costs. The grouting repair process proposed in this invention, through a micro-creation work model, significantly improves construction efficiency and reduces environmental impact while ensuring repair quality. It possesses significant technical advantages and engineering application value, allowing for flexible selection of the appropriate grouting solution based on the size, shape, and component type of the void.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for repairing localized hollow areas in a non-expansive fire-retardant coating substrate using grouting, characterized in that, The method includes the following steps: S1. Coating surface inspection: Observe the coating surface in the hollow areas and check the distribution and width of coating surface cracks. S2. Mark the hollow areas and set up the hole positions. Use a hollow hammer to tap and determine the boundary of the hollow area and mark the outline of the area. According to the shape of the hollow area, set up grouting holes at the bottom of the area and grout overflow holes at the top of the area. S3. Drilling and cleaning: Use drilling equipment to drill grouting holes and overflow holes at the marked positions, and clean the paint debris and dust in the ducts. S4. Install the grouting needle. Screw the water-stopping grouting needle into the grouting hole, ensuring that the outer wall of the needle fits tightly against the hole wall. S5. Prepare grouting slurry and perform pressure grouting. Prepare interface gelling slurry that is compatible with non-expansive fireproof coating. Inject slurry into the hollow cavity using intermittent grouting. After the slurry overflows from the overflow hole, seal it. Stop grouting after all overflow holes are sealed. S6. Static curing: After grouting is completed, allow the grout to solidify under a set temperature environment. S7. Remove the needle and complete the acceptance and duct restoration. After curing, remove the grouting needle and sealing parts. Conduct two tests on the hollow repair status. After passing the test, fill the duct with the original coating material.

2. The method for repairing localized hollow areas in a non-expansive fire-retardant coating substrate according to claim 1, characterized in that, In step S2, for rectangular or near-rectangular hollow areas, grouting holes are evenly distributed along the bottom contour of the area, with the lateral coverage of a single grouting hole not exceeding 300mm. Overflow holes are evenly distributed along the top contour of the area, with the spacing between adjacent overflow holes being 150-200mm. The vertical spacing between overflow holes and grouting holes is 180-200mm. For circular or elliptical hollow areas, grouting holes are set at the bottom of the area, and overflow holes are horizontally arranged above the grouting holes. When the height of the hollow area exceeds 200mm, a bottom-up layered grouting operation is adopted.

3. The method for repairing localized hollow areas in a non-intumescent fireproof coating substrate according to claim 1, characterized in that, In step S3, the drilling operation is carried out using a hand drill. The diameter of the grouting hole is 14mm and the diameter of the overflow hole is 6mm. During the drilling process, the drill rod is kept perpendicular to the coating surface. The hole depth extends into the hollow cavity, so that the grouting hole and the overflow hole form a connecting passage through the hollow cavity. After the hole is opened, a fine brush is inserted into the hole to clean the paint debris and dust adhering to the inner wall of the hole.

4. The method for repairing localized hollow areas in a non-expansive fireproof coating substrate according to claim 1, characterized in that, In step S4, the grouting needles are made of aluminum. The grouting needles are assembled from a stainless steel nozzle, an aluminum rod, a gasket, an elastic rubber, and a connecting screw. The total length of the needle is 10cm and the diameter of the needle end is 13mm. The installation is carried out using a T-type socket wrench. The needle is screwed into the grouting hole until the end of the connecting screw is in contact with the surface of the base layer. Grouting is carried out after all the grouting needles in a single hollow area are installed.

5. The method for repairing localized hollow areas in a non-expansive fireproof coating substrate according to claim 1, characterized in that, In step S5, the grouting operation is carried out using a high-pressure grouting machine. The grouting pressure is controlled within the range of 0.3-0.5MPa. An intermittent injection mode is adopted, with a single grouting time of 3-5 seconds. After a single grouting is completed, there is a short pause to allow the internal pressure of the duct to be released before continuing to inject grout. The above injection and pause process is repeated until the grouting is completed.

6. The method for repairing localized hollow areas in a non-intumescent fireproof coating substrate according to claim 1, characterized in that, In step S5, when multiple grouting holes are set in a single hollow area, alternating grouting is used or multiple grouting machines are used for synchronous grouting. During the grouting process, a hollow hammer is used to tap the coating surface, and the penetration range of the grout is judged based on the tapping echo. The state changes of the coating surface are observed throughout the process.

7. The method for repairing localized hollow areas in a non-intumescent fireproof coating substrate according to claim 1, characterized in that, When the overflow hole overflows with continuous and full grout in step S5, the overflow hole is sealed with a rubber stopper or a wooden stopper. All grouting operations for a single hollow area are completed within 10 minutes. If new cracks are observed in the coating during the grouting process, the grouting operation is immediately terminated and the internal pressure of the duct is released.

8. The method for repairing localized hollow areas in a non-intumescent fireproof coating substrate according to claim 1, characterized in that, In step S6, the ambient temperature and the base layer temperature during the grouting operation and curing stage are maintained within the range of 5-35℃. After the grouting is completed, the grout will complete the initial solidification in about 20 minutes. The minimum curing time is set to 24 hours. No external disturbance is applied to the coating during the curing period.

9. The method for repairing localized hollow areas in a non-intumescent fireproof coating substrate according to claim 1, characterized in that, In step S7, two tests are conducted at 24h and 72h of curing, respectively. The tests use a hollow hammer to tap and check for hollow areas, and a magnifying glass to observe the coating cracks. Areas with secondary hollow areas are removed and recoated.

10. The method for repairing localized hollow areas in a non-intumescent fireproof coating substrate according to claim 1, characterized in that, In step S7, the duct filling is carried out using fire-retardant coating with the same mixing ratio as the original coating. The filling operation fills the inside of the duct tightly. After the filling is completed, the coating surface around the duct is trimmed, and the surface height of the repaired part is aligned with that of the surrounding coating so that the repaired part transitions smoothly with the original coating surface.

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