Polymer-modified phase change fireproof construction for rooftop eVTOL tarmac and methods thereof

Abstract

The application discloses a polymer modified phase change fireproof structure for a roof eVTOL apron and a method thereof, and belongs to the technical field of low-altitude traffic infrastructure safety. The structure is laid on an existing or newly built building reinforced concrete floor, and sequentially comprises a thermal barrier insulation layer, a phase change heat absorption bearing layer and a grid fireproof isolation flow guide component from bottom to top. The phase change bearing layer is packaged with phase change aggregates by using high-performance polymer cement mortar, and has the characteristics of fire resistance, high toughness and active heat absorption. The isolation flow guide component is made of high-temperature and corrosion-resistant material and is used for blocking the flowing fire. The application also discloses a quantitative design method based on the "heat-power-flow" coupling theory, which accurately calculates the thickness of the functional layer and the groove parameters, and gives a standardized construction process. The application effectively solves the problems of fire spread and structure collapse caused by the extremely hot impact of lithium batteries and the flowing fire of the roof apron through passive structure protection.

Description

Technical Field

[0001] This invention relates to the fields of civil engineering materials, low-altitude transportation infrastructure construction, and fire safety technology. Specifically, it relates to a composite structure that integrates phase change temperature control, flow fire blocking, and high load-bearing capacity for non-ground eVTOL helipads such as building roofs, multi-story parking garage top floors, and elevated platforms, as well as its design and construction method based on the thermo-mechanical-fluid coupling theory. Background Technology

[0002] With the rise of urban air mobility (UAM), utilizing the rooftops of new or existing buildings to construct eVTOL takeoff and landing fields has become mainstream. However, eVTOLs are generally equipped with high-energy-density lithium batteries, whose fire characteristics pose a serious challenge to elevated structures.

[0003] Fires are difficult to extinguish: Unlike fuel-powered aircraft, the lithium-ion batteries in eVTOLs have the characteristic of "self-generating oxygen" during thermal runaway, making traditional foam firefighting methods ineffective. Fires typically last 1-4 hours. Compared to electric vehicles (EVs), eVTOLs have much higher combustion intensity due to the higher specific energy and discharge rate requirements of their batteries, making rescue efforts much more difficult.

[0004] Significant structural safety risks: Unlike ground-based airports, where runways are built directly on a foundation, fires only damage the surface layer with no risk of collapse, relying primarily on active fire suppression and having lower requirements for structural fire resistance. However, the area beneath an eVTOL rooftop helipad is typically a building functional area. In the event of a fire, the combustion center temperature of lithium batteries exceeds 1000℃ (extreme thermal shock). Ordinary concrete slabs soften steel reinforcement and crack at 500℃, easily burning through the slab and triggering secondary disasters such as continuous collapses.

[0005] High risk of flowing fire: If the high-temperature electrolyte (containing organic solvents and hydrofluoric acid) ejected from the battery during a deflagration is not effectively blocked, it will flow everywhere and ignite adjacent units.

[0006] The materials have a narrow range of applicability: for example, asphalt is flammable and promotes combustion, and it will undergo static creep (rutting) under the heavy pressure of long-term fixed-point parking in eVTOL, making it unsuitable; traditional thickened solutions for ordinary concrete are too heavy and unsuitable for the renovation of existing buildings; thin-layer mortar is too brittle and prone to cracking under heavy landing impact. Therefore, there is an urgent need for a lightweight, high-strength and tough, dedicated passive protection system that can actively absorb heat and block flowing fire. Summary of the Invention

[0007] The present invention aims to solve the above problems and provides a polymer-modified phase change fireproof structure and method for rooftop eVTOL helipads.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0009] The eVTOL rooftop helipad uses a polymer-modified phase change fireproof structure, laid on the reinforced concrete floor slab of a building roof or elevated structure, and includes, from bottom to top:

[0010] A thermal barrier layer is laid on the surface of the floor slab base layer to block heat conduction;

[0011] The phase change heat-absorbing load-bearing layer, cast on top of the thermal barrier insulation layer, is a polymer-modified cement-based composite material containing aggregates encapsulated with phase change material PCM.

[0012] The fireproof isolation and diversion components are distributed in a grid pattern and penetrate the thermal barrier insulation layer and the phase change heat absorption load layer, dividing the apron surface into several independent fire-resistant zones.

[0013] The top surface of the phase change heat absorption bearing layer is provided with a flow guiding slope i of the fireproof isolation flow guiding component, and the flow guiding slope i ≥ 1.5%.

[0014] The matrix material of the phase change heat-absorbing load-bearing layer is high-performance polymer-modified cement mortar, including:

[0015] Special cementitious materials: rapid-hardening sulfoaluminate cement or high-grade silicate cement;

[0016] Polymer modifier: The dosage is 3%-15% of the mass of the special cementitious material, and it is selected from one of water-based epoxy resin emulsion, acrylic emulsion or redispersible latex powder.

[0017] Phase change energy storage aggregate: The dosage is 30%-50% of the mass of special cementitious materials. It is made by adsorbing phase change materials with porous lightweight aggregate and then encapsulating them on the surface.

[0018] Toughening and crack-resistant fiber: The volumetric dosage is 0.5%-1.5% of the high-performance polymer-modified cement mortar, and it is selected from either polyvinyl alcohol fiber or basalt fiber.

[0019] Fireproof isolation and diversion components include:

[0020] The prefabricated double-layer bottom fire-resistant groove is embedded in the thermal barrier insulation layer and the phase change heat absorption bearing layer. It has a horizontal outer bottom plate and an internal flow guiding bottom plate with an internal drainage slope S. An air insulation cavity is formed between the inner and outer bottom plates.

[0021] A rigid heat insulation pad is prefabricated and integrated or laid under the outer bottom surface of a prefabricated double-bottom fire-resistant channel. The prefabricated double-bottom fire-resistant channel sits directly on the reinforced concrete floor slab base through this rigid heat insulation pad.

[0022] Mechanical anchors vertically penetrate the bottom of the prefabricated double-layer fire-resistant channel and the rigid heat insulation pad, anchoring the fireproof isolation and diversion components into the reinforced concrete floor slab base.

[0023] High-temperature resistant and corrosion-resistant inner lining is coated on the inner wall of the prefabricated double-bottom fire-arresting tank.

[0024] Heavy-duty liquid-permeable cover plates are placed over the prefabricated double-layer bottom fire-arresting tank. Their load-bearing capacity meets the eVTOL wheel pressure requirements, and the opening ratio is not less than 30%.

[0025] The top surface guiding slope i of the phase change heat absorption bearing layer and the internal drainage slope S of the prefabricated double-layer bottom fire-resistant trough satisfy the synergistic relationship of i > S.

[0026] The internal drainage slope S ranges from 0.5% to 1.0%.

[0027] The thermal barrier insulation layer uses a high-temperature resistant insulation material with a thermal conductivity of less than 0.05 W / (m·K), selected from one of silica aerogel felt, nanoporous insulation board or ceramic fiber board.

[0028] The design method for polymer-modified phase change fireproof structures for rooftop eVTOL helipads includes the following steps:

[0029] S1. Local Impact Pressure Calculation: Based on the impulse principle, calculate the impact pressure during the eVTOL's hard landing. And check the compressive strength of the phase change heat absorption bearing layer material. Does it meet safety requirements?

[0030] S2. Determine the thickness H1 of the phase change heat-absorbing load-bearing layer: Based on the first law of thermodynamics, the thickness is calculated according to the balance relationship between the net heat flow input of the fire and the total enthalpy change capacity of the sensible heat and latent heat of the phase change heat-absorbing load-bearing layer material, so as to ensure that the interface temperature at the bottom of the layer does not exceed the set value during the design fire duration.

[0031] S3. Determine the thickness H2 of the thermal barrier layer: Based on the steady-state heat conduction formula, and according to the maximum allowable safe temperature of the reinforced concrete floor slab base. Calculated;

[0032] S4. Determine the parameters of the fireproof isolation and diversion component: Based on the Manning formula of fluid mechanics, calculate the minimum water passage section and internal drainage slope S of the fireproof isolation and diversion component according to the total amount of battery electrolyte leakage and time, and determine the surface layer diversion slope i.

[0033] In step S2, the thickness H1 of the phase change heat absorption bearing layer is calculated according to the following formula:

[0034] ,

[0035] in, Net heat flux density in a fire. The duration of intense burning in the fire, The mixing density of the phase change heat absorption support layer, The average specific heat capacity of the phase change heat absorption support layer. This is the ultimate design temperature at the bottom of the phase change heat absorption support layer. The initial ambient temperature is φ, the mass content of the phase change aggregate is φ, and ΔH is the effective latent heat of phase change of the phase change aggregate.

[0036] In step S3, the thickness H2 of the thermal barrier layer is calculated according to the following formula:

[0037] ,

[0038] in, The thermal conductivity of the insulation material is... This is the interface design temperature at which the phase change heat absorption support layer fails. This refers to the maximum safe temperature allowed for the reinforced concrete floor slab base. Design limits for the residual heat flux density that can be transferred to the base layer.

[0039] The construction method for polymer-modified phase change fireproof structures for rooftop eVTOL helipads includes the following steps:

[0040] Step 1, Substrate Treatment: Clean, level, and apply interface agent to the reinforced concrete floor slab substrate;

[0041] Step 2, laying the thermal barrier layer: lay the thermal barrier layer on the prepared base layer and seal its joints;

[0042] Step 3: Installation of fireproof isolation and diversion components: Cut grooves in the laid thermal barrier insulation layer, place the fireproof isolation and diversion components into the grooves and place them on the base layer, fix them to the base layer with mechanical anchors, then coat the inner wall of the groove with a high-temperature resistant and anti-corrosion lining, and temporarily shield and protect the groove opening.

[0043] Step 4: Pour and slope the phase change heat-absorbing load-bearing layer: Pour polymer-modified phase change mortar on top of the thermal barrier insulation layer and control the surface elevation to form the slope i of the fireproof isolation and diversion component.

[0044] Step 5, Curing and Accessory Installation: Curing is carried out on the completed phase change heat absorption bearing layer. After the strength meets the standard, the temporary shielding of the groove is removed, and a heavy-duty liquid permeable cover plate is installed above the fireproof isolation and diversion component.

[0045] In step three, the fireproof isolation and diversion component is a prefabricated double-layer bottom fire-resistant channel with a rigid heat insulation pad. It sits directly on the base layer and is anchored to the base layer by mechanical anchors penetrating its bottom and the rigid heat insulation pad.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] 1. Significant Cooling and Protective Layer Effect: Comparative calculations based on transient heat conduction equations show that under extreme conditions of a constant 1000℃ fire source for 60 minutes, if a 50mm thick layer of ordinary C30 concrete is used as a protective layer, the theoretical temperature at a depth of 50mm reaches as high as 483℃, approaching the critical point (500℃) where the yield strength of the reinforcing steel drops sharply, posing an extremely high risk of structural failure. This invention, however, utilizes the latent heat absorption effect of phase change aggregates and the insulation effect of the thermal barrier layer to successfully control the interface temperature at approximately 150℃ at the same depth. This temperature is far below the softening point of the reinforcing steel and the severe cracking point of the concrete, providing ample safety margin for the existing structure at the bottom.

[0048] 2. The dual thermal protection mechanism of "phase change active heat absorption + bottom passive insulation": Unlike the traditional ground airport model that relies solely on external fire suppression, this invention is designed for the roof environment. It utilizes the huge latent heat absorbed by phase change aggregate during the phase change process to effectively "shave off" the extreme thermal shock in the early stages of a fire. Combined with the aerogel thermal barrier layer at the bottom, it ensures that even when the upper layer is thermally saturated, the heat transferred to the existing floor slab remains extremely low, ensuring that the base temperature is always below the concrete bursting threshold, thus fundamentally preventing structural collapse.

[0049] 3. A high-temperature chemical corrosion resistant active fire control system was constructed: Addressing the high temperatures and strong corrosive properties of hydrofluoric acid (HF) generated during the combustion of eVTOL battery electrolyte, a dedicated flow-guiding component with a stainless steel substrate and ceramicized lining was designed. Combined with a precisely designed floor slope, this system can rapidly drain leaked flammable liquid away from the shutdown position within 60 seconds, physically cutting off the fire's spread path and achieving the passive defense objective of "preventing fire spread."

[0050] 4. Achieved high-standard renovation of existing building roofs: This method utilizes lightweight porous ceramsite as a phase change carrier, combined with ultra-thin, high-efficiency aerogel insulation material, resulting in an overall surface density significantly lower than traditional thickened concrete solutions. Without increasing the cost of reinforcing the existing building's main structure, it provides a high level of fire resistance that meets airworthiness standards.

[0051] 5. Provides scientific engineering design basis: The quantitative design method based on the "thermal-mechanical-fluid" coupling theory transforms the complex lithium battery fire protection into quantifiable engineering parameters (thickness, slope, strength), avoiding safety hazards or material waste caused by construction based purely on experience, and providing technical support for the standardized construction of eVTOL infrastructure. Attached Figure Description

[0052] Figure 1 This is a plan view of the grid layout of the rooftop helipad and the flow path of the fire diversion as described in this invention.

[0053] Figure 2This is a schematic diagram of the longitudinal cross-sectional structure of the composite structure described in this invention.

[0054] Figure 3 This is a flowchart of the design calculation based on the thermo-mechanical-fluid coupling theory of the present invention.

[0055] Figure 4 This is a standardized construction process flow chart of the structure described in this invention.

[0056] The markings in the diagram are as follows: 1-Reinforced concrete floor slab base, 2-Thermal barrier insulation layer, 3-Phase change heat absorption bearing layer, 4-Fireproof isolation and diversion component, 41-Precast double-layer bottom fire-resistant trough, 41a-Air insulation cavity, 41b-Rigid insulation pad, 42-High temperature resistant and corrosion resistant lining, 43-Heavy liquid permeable cover plate, 44-Mechanical anchor. Detailed Implementation

[0057] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0058] This invention aims to address the following core deficiencies in existing technologies for dealing with lithium battery fires on building rooftops and elevated eVTOL helipads: Thermal vulnerability of existing structures: Existing building rooftops and the top floors of multi-story parking garages are typically constructed of ordinary reinforced concrete. The extreme thermal shock (center temperature >1000℃) generated by the thermal runaway of lithium-ion batteries can cause the reinforcing steel to soften rapidly above 500℃, easily leading to burn-through and collapse of the floor slab. Poor applicability of conventional materials: Asphalt-based materials are flammable and prone to static creep (rutting); ordinary thin-layer cement mortar is brittle and cannot withstand the impact and vibration of eVTOL heavy landings. Cascade damage from flowing fire: Existing technologies lack high-temperature and chemically resistant flow guidance systems, causing high-temperature electrolyte to spread uncontrollably. Lack of scientific design: Existing designs lack quantitative calculations regarding the energy of lithium battery fires and the structural fire resistance limits.

[0059] To achieve the above objectives, the present invention provides a polymer-modified phase change fireproof structure for rooftop eVTOL helipads and its design and construction method.

[0060] Construction system:

[0061] This structure is laid on the reinforced concrete floor slab base 1 of a building roof or elevated structure, and includes, from bottom to top:

[0062] Thermal barrier layer 2: Lay on the surface of the base layer as the last line of defense for thermal protection. It uses high-temperature resistant thermal insulation materials with extremely low thermal conductivity (<0.05W / (m·K)) (such as silica aerogel felt or nanoporous thermal insulation board) to completely cut off the conduction path of residual heat to the existing main structure after the surface layer is saturated with heat absorption.

[0063] Phase change heat-absorbing load-bearing layer 3: Cast on top of the thermal barrier insulation layer 2, serving as the main functional component directly bearing loads and thermal shocks. Its matrix is ​​a polymer-modified cementitious composite material, with lightweight porous aggregate encapsulated with phase change material (PCM) and toughening and crack-resistant fibers uniformly dispersed inside. This layer utilizes polymer modification technology to impart high toughness and strong adhesion to the cement matrix, and utilizes the latent heat of solid-liquid phase change of the phase change aggregate to absorb the extreme thermal energy in the initial stage of a fire.

[0064] Fireproof isolation and diversion component 4: Distributed in a grid pattern and penetrating through the two layers, it divides the apron surface into several independent fire-resistant zones. The main body of the component is a prefabricated double-layer bottom variable cross-section stainless steel tank, characterized by a horizontal outer bottom surface, a prefabricated drainage slope on the inner bottom surface, and an air insulation cavity 41a formed between the inner and outer bottom plates; the bottom of the prefabricated double-layer bottom fire-resistant tank 41 is prefabricated with a rigid heat insulation pad 41b (such as a high-density ceramic fiber board) and directly anchored to the reinforced concrete floor slab base 1; the inner wall is coated with a high-temperature resistant ceramic anti-corrosion coating, and the top is covered with a heavy-duty permeable cover plate that meets the eVTOL wheel pressure requirements for rapid collection and discharge of highly corrosive high-temperature electrolyte.

[0065] Design Methodology:

[0066] This invention establishes a quantitative design method based on the "thermal-mechanical-fluid" coupling theory, specifically including the following steps and formulas:

[0067] S1 performs local impact bearing capacity verification based on the impulse principle and mechanics of materials: First, the mechanical safety of the structural layer is determined. According to the formula... Calculate the impact pressure during the hard landing of the eVTOL. Where: is the impact pressure during a hard landing of the eVTOL (MPa); k is the impact coefficient (taking into account the requirements of MH / T 5013 standard and CCAR-23 / 27 airworthiness regulations regarding the landing gear limiting inertial load coefficient, taken as 1.5~3.0); M is the maximum takeoff weight of the aircraft (kg); g is the gravitational acceleration (taken as 9.8m / s²). Effective contact area; For the number of landing gear wheels; This represents the effective contact area (m²) of a single wheel. A strength check is then performed, and it must meet the following requirements. .in, [K] represents the measured compressive strength (MPa) of the phase change endothermic load-bearing layer material; [K] is the minimum safety margin factor (usually ≥2.0). This step aims to ensure that the structural layer does not experience brittle fracture or crushing failure under extreme landing conditions.

[0068] S2 determines the thickness (H1) of the phase change heat-absorbing support layer 3 based on the sensible heat-latent heat coupling mechanism: The calculation is performed using the "total enthalpy change capacity method" according to the first law of thermodynamics. This method explicitly decomposes the material's heat absorption capacity into two parts: "sensible heat absorption of the matrix" and "latent heat absorption of the PCM," as shown in the following formula:

[0069]

[0070] in, The net heat flux density during a fire is taken into account the strong radiative heat dissipation and convective heat loss generated by the high temperature of the floor surface under fire conditions. The actual net heat flux intruding into the structural layer is taken as 1 / 6 to 1 / 5 of the design fire heat flux (60~80kW / m²) (recommended value is 10,000~15,000W / m²). The duration of intense burning in the fire, The mixing density of the phase change heat absorption bearing layer 3 is given. The average specific heat capacity of phase change heat absorption bearing layer 3, The ultimate design temperature for the bottom of the phase change heat absorption support layer 3. The initial ambient temperature is φ, the mass content of the phase change aggregate is φ, and ΔH is the effective latent heat of phase change of the phase change aggregate.

[0071] The minimum design thickness H1 should be the larger of the above thermal calculation value and the "geometric matching requirement" (such as the minimum depth required for the prefabricated double-bottom fire-resistant groove 41, for example, 100 mm).

[0072] S3 determines the thickness (H2) of the thermal barrier insulation layer 2 based on the steady-state heat conduction formula: according to the formula

[0073] ,

[0074] in, The thermal conductivity of the insulation material is... The interface design temperature (taken as 300℃) is the temperature at which the phase change heat absorption support layer fails. The maximum safe temperature allowed for the base layer of reinforced concrete floor slabs (taken as 150℃). To allow for a design limit (W / m²) of residual heat flux density transferred to the base layer, and to prevent the base concrete from cracking due to heat buildup, this value should be set based on the thermal properties of the base material, typically ranging from 200 to 500 W / m². This step aims to prevent the reinforced concrete slab base concrete from cracking.

[0075] S4 determines the four parameters of the flow guide component based on the Manning formula in fluid dynamics (dual slope collaborative design): First, determine the slope (S) of the channel guide: according to the formula

[0076]

[0077] in, The drainage capacity of the trench is (m³ / s); A is the cross-sectional area of ​​the trench (m²); n is the Manning roughness coefficient of the inner wall of the trench (0.01~0.013 for stainless steel); R is the hydraulic radius (m, i.e., cross-sectional area / wetted perimeter); S is the drainage slope at the bottom of the trench. To ensure that viscous liquids (such as electrolytes) can be effectively discharged without sedimentation, the value of S is set to be 0.5%~1.0%. Total amount of battery electrolyte leakage (m³); The leakage duration (s) is defined. This step aims to ensure that the electrolyte does not overflow. Then, the surface layer guiding slope (i) is determined: to overcome the capillary retention effect on the phase change mortar surface and prevent flammable liquids from accumulating on the apron surface, the guiding slope i of the top surface of the phase change heat-absorbing bearing layer 3 towards the trench is set. Collaborative design principle: The surface layer guiding slope should be greater than the trench drainage slope (i>S), and i ≥ 1.5% (recommended value 1.5%~2.0%). This design aims to create a "fast collection and fast drainage" mechanism, meaning the surface layer confluence velocity is greater than or equal to the initial response of the trench drainage velocity, preventing the formation of dead zones at the trench edges.

[0078] Construction method:

[0079] This invention also provides a standardized construction method to ensure the achievement of structural performance, which mainly includes the following key steps:

[0080] Strengthening the base layer: Clean the surface of the new floor slab base layer, deeply mill and repair cracks in the existing floor slab base layer, and apply a penetrating polymer interface agent to ensure that the bonding strength between the new and old interfaces meets the impact resistance requirements.

[0081] Complete laying of thermal barrier layer: Thermal barrier insulation layer 2 is laid on the base layer to fully cover it, and the joints are sealed with high temperature resistant treatment to ensure the formation of a continuous and uninterrupted thermal insulation interface.

[0082] Embedded installation of components: Cut a groove in the laid thermal barrier layer 2 and thoroughly clean the bottom base layer; place the prefabricated double-layer bottom fire-resistant trough 41, with a prefabricated rigid heat insulation pad 41b at the bottom and a prefabricated drainage slope S inside, directly into the groove so that it rests directly on the concrete base layer; check the top elevation using a laser level (if necessary, place a thin sheet under the rigid heat insulation pad 41b for fine adjustment); use mechanical anchors 44 (such as expansion bolts) to penetrate the bottom plate of the prefabricated double-layer bottom fire-resistant trough 41 and the rigid heat insulation pad 41b for structural anchoring, and seal the anchoring points. After completing the spraying of the high-temperature resistant and anti-corrosion lining 42 on the inner wall of the prefabricated double-layer bottom fire-resistant trough 41, immediately implement temporary full-enclosure protection at the groove opening (such as covering with a temporary cover plate) to prevent mortar from splashing into and contaminating the lining during subsequent surface layer construction.

[0083] Integrated surface layer pouring and slope finding: polymer-modified phase change mortar is poured using formwork and precisely spread using a laser leveling machine, while simultaneously controlling the surface layer guide slope i to achieve synergy between rapid surface layer flow convergence and stable drainage in the trench.

[0084] Complete functional protection: After the surface layer has cured, perform surface anti-slip and wear-resistant treatment; remove the temporary shielding protective layer at the trench opening, install heavy-duty liquid-permeable cover plate, and complete the final delivery.

[0085] Example: Fireproofing renovation project of an existing commercial center's rooftop eVTOL helipad.

[0086] This embodiment demonstrates the entire process from high-performance material proportioning and parameter calculation based on coupling theory to standardized construction implementation.

[0087] Material proportioning design:

[0088] This embodiment uses a dedicated "high-performance polymer-modified phase change mortar (PMCC)" as the core functional layer, and its specific formulation is as follows:

[0089] Cemented matrix: P.O52.5R rapid-hardening silicate cement is selected, and 10% of ultrafine silica fume by weight of cementing material is added to improve the density and early strength of the matrix.

[0090] Polymer modifier: 8% water-based epoxy resin emulsion by weight of the cementitious material. This component forms a film during cement hydration, creating an interpenetrating polymer network (IPN) structure, significantly improving the material's impact resistance and adhesion to the existing substrate (measured bond strength > 2.5 MPa). Although it contains organic components, because the dosage is controlled within a safe range and it is encapsulated by an inorganic matrix, the material only undergoes trace carbonization at high temperatures, without producing a sustained open flame, meeting the A2 non-combustible standard of GB 8624-2012.

[0091] Phase change energy storage aggregate: High-strength porous ceramsite with a particle size of 4-8mm is selected, and composite paraffin wax with a phase change point of 58℃ is vacuum adsorbed. The surface is then encapsulated with a double layer of epoxy resin. The mass content is set at 35%.

[0092] Toughening and crack-resistant fiber: 1.2% by volume of short-cut basalt fiber is incorporated to suppress matrix cracking and microcrack propagation at high temperatures.

[0093] Theoretical design calculations of construction parameters:

[0094] To ensure the safety and economy of the structure, the key parameters of each functional layer are determined using the "thermal-mechanical-fluid" coupling model proposed in this invention:

[0095] Set the design conditions. Object parameters: eVTOL maximum takeoff weight M = 2500 kg, 4-wheel landing. Simulate landing with landing gear skids or high-pressure wheels, with the effective contact area of ​​a single wheel taken as... =0.005m² (i.e., 50cm²). Fire parameters: Design heat flux density for lithium battery fire q = 60kW / m², duration of intense combustion t = 3600s. Structural limits: Maximum permissible safe temperature of the base concrete. =150℃. Geometric grid: The helipad is divided into a standard independent grid of 15m × 15m.

[0096] Step 1: Local Impact Bearing Capacity Verification (Mechanical Dimension). Considering the impact of a "hard landing" under extreme conditions, and referring to the high standard stipulated in CCAR-23 Article 23.473(g) regarding the limitation of the inertial load factor of general aviation aircraft landing gear to not less than 2.67, the impact factor k=3.0 is taken. Calculate the impact pressure of a single wheel. , , =(3.0×2500×9.8) / (4×0.005)≈3.68MPa. Verification conclusion: 3.68MPa is much lower than the measured compressive strength of the PMCC material in this embodiment. =38MPa. This proves that the structural layer has sufficient load-bearing safety under extreme high-pressure landing conditions.

[0097] Step 2: Calculation of the thickness H1 of the phase change heat-absorbing load layer 3 (thermal-heat-absorbing dimension). Based on the first law of thermodynamics (enthalpy change increment method), the heat absorption capacity of the material is divided into two parts: "sensible heat absorption" and "latent heat absorption", and the minimum thickness required to meet the limit temperature rise control is calculated. (1) Parameter setting: net heat flux density Referring to the heat flux decay law in open spaces in GB / T31593.5, and combining relevant data on radiation and convection heat dissipation in lithium battery fires, 1 / 6 of the design heat flux is taken, i.e. =10kW / m². Duration t=3600s. Composite material density. =1800 kg / m³. Average specific heat capacity of composite materials. =1200 J / (kg·K). Phase change aggregate mass content φ=35%. Latent heat of phase change ΔH=160kJ / kg. Design allowable extreme temperature. =300℃ (meaning the material is allowed to fully utilize its sensible heat absorption potential until it approaches the upper limit of the bottom interface temperature). Initial ambient temperature =20℃. (2) Main calculation process: Total net heat input of the system = ×t = 10 × 3600 = 36,000 kJ / m² = 36 MJ / m². Sensible heat absorbed per unit volume. =1800×1.2×(300-20)=604,800kJ / m³=604.8MJ / m³. Latent heat absorbed per unit volume. =1800×0.35×160=100,800kJ / m³=100.8MJ / m³. Total heat absorption capacity =604.8 + 100.8 = 705.6 MJ / m³. Theoretical minimum thickness. ≥ =36 / 705.6≈0.051m=51mm. Initially, H1 is set to 60mm. (Considering geometric matching, H1 is ultimately set to 90mm, see step four for details)

[0098] Step 3: Calculation of the thickness H2 of the thermal barrier layer 2 (thermal-insulation dimension). Assume that under extreme conditions after phase change endothermic saturation, the interface temperature on the thermal barrier layer reaches... =300℃ (at which point the surface polymer will decompose), it is necessary to ensure that the temperature is conducted to the bottom. ≤150℃. Safety limit setting: Taking into account the thermal diffusivity of the base concrete, the maximum residual heat flux density allowed to be transferred to the base is set. =300W / m², the minimum required thermal resistance is calculated using the formula, and then the thickness of the thermal barrier layer 2 is determined to ensure the actual heat flux density. Calculate thickness: Select thermal conductivity For a silica aerogel felt with a strength of 0.02 W / (m·K), substituting into the formula in the text, we calculate: H2 ≥ [0.02 × (300 - 150)] / 300 = 0.01 m = 10 mm. Design decision: Considering the construction difficulty and safety margin, we take H2 = 20 mm. This thickness is sufficient to limit the residual heat flow transferred to the substrate within a safe range, effectively preventing the substrate from overheating and cracking.

[0099] Step 4: Design of the isolation and diversion assembly using 4 parameters (fluid dimension). The minimum drainage flow rate required to ensure complete leakage of 100L (0.1m³) electrolyte within 60 seconds. =1.7L / s. The “dual slope coordinated flow guidance” strategy is adopted for configuration. (1) Geometric structure matching: Precast double-bottom fire-resistant trough 41 selection: 304 stainless steel “inner slope and outer flat” double-bottom U-shaped trough is selected. The outer bottom surface is horizontal and the height of the whole section is constant at 105mm. Vertical matching: Total height of the trough = 105mm outer height of the precast double-bottom fire-resistant trough + 5mm of the bottom precast rigid heat insulation pad 41b = 110mm. According to the total elevation control, the thickness H1 of the phase change heat absorption bearing layer 3 is 110mm minus the thickness of H2 20mm, and the final value is 90mm. This combination ensures that the top surface of the precast double-bottom fire-resistant trough 41 is precisely flush with the finished surface of the phase change heat absorption bearing layer 3, realizing the direct laying of the whole dry method. Cover plate configuration: 30mm thick heavy stainless steel grating cover plate that meets the EN 1433 F900 level is selected to withstand the eVTOL wheel pressure and tractor load. (2) Slope setting (S=0.5%): Drainage strategy: V-shaped bidirectional slope is adopted, and the single-section drainage length L=7.5m. Set the slope of the prefabricated drainage guide inside the trench to S=0.5%. Internal depth change: According to S=0.5%, a height difference of 37.5mm is generated at 7.5m. Starting end (shallow point): effective net depth 30mm. End (deep point): effective net depth 67.5mm. Space verification: The physical space required at the end (including cover plate and double bottom plate) is about 103.5mm, which is less than the height limit of 105mm for the outer shell, so the structure is valid. (3) Vertical drainage guide node: For a large-area apron, relying on surface flow cannot meet the drainage time and will cause the prefabricated double bottom fireproof trough 41 at the end to be too deep. Therefore, a through-plate drain is set at the lowest point of the grid trench intersection. A Φ110mm stainless steel short pipe is used to vertically penetrate the floor slab and connect to the dedicated chemical wastewater collection network on the lower floor (leading to the emergency pool). Direct discharge into the rainwater system is strictly prohibited. A water-swellable sealing ring and a rigid waterproof sleeve are installed at the penetration point. (4) Drainage capacity verification: Calculated based on the shallowest section at the starting end (30mm×200mm). In the Manning formula, A=0.03m×0.2m=0.006m² (cross-sectional area of ​​the trench); n=0.01 (Manning roughness coefficient of the inner wall of 304 stainless steel); R=A / wet perimeter=0.006 / (2×0.03+0.2)=0.02308m (hydraulic radius); S=0.005 (drainage slope), thus obtaining =(0.006 / 0.01)×0.02308^(2 / 3)×0.005^(1 / 2)≈3.5L / s>1.7L / s. (5) Surface layer guiding design: Set the surface layer guiding slope i=2% to meet the synergistic requirements of i≥1.5% and i>S. This gradient difference design of "steep surface and gentle tank" ensures that the liquid preferentially converges to the prefabricated double-bottom flame-retardant tank 41 under the action of gravity, effectively overcomes the surface tension of high viscosity electrolyte, and realizes the active control goal of "zero residue on the surface layer and no backflow in the tank".

[0100] Construction process flow:

[0101] S1 Base Interface Reinforcement: Deep milling of existing roof slabs (complete removal of the original waterproof protective layer) and crack repair, followed by application of a penetrating polymer interface agent to ensure that the bonding strength between the new and old interfaces meets the impact resistance requirements for eVTOL heavy landing.

[0102] S2 Thermal Barrier Insulation Layer Full Coverage Installation: A 20mm aerogel fiberglass felt is laid on the prepared base layer for full coverage. During installation, staggered joints are used, and the joints are tightly sealed with high-temperature resistant aluminum foil tape to form a continuous, uninterrupted thermal insulation interface.

[0103] S3 Fireproof Isolation and Diversion Component Embedded Installation: Cut a groove in the laid thermal barrier layer 2 and thoroughly clean the base layer. Place the prefabricated double-layer bottom fire-resistant channel 41, with a 5mm prefabricated rigid heat insulation pad 41b at the bottom and an internal prefabricated drainage slope S (S=0.5%), directly into the groove, allowing it to rest on the floor slab base. Use a laser level to verify the top elevation (fine-tuning is allowed by placing a thin stainless steel sheet under the rigid heat insulation pad 41b). Then, use expansion bolts to penetrate the bottom plate of the prefabricated double-layer bottom fire-resistant channel 41 and the rigid heat insulation pad 41b for structural anchoring, and seal the anchoring points with high-temperature resistant seals. Connect the through-slab drainage pipe at the drain outlet. Clean the inner wall of the prefabricated double-layer bottom fire-resistant channel 41 and spray it with a 300μm ceramicized silicone rubber high-temperature resistant and corrosion-resistant lining 42 (to resist HF acid corrosion). After the lining has cured, a temporary protective cover is placed over the top opening of the precast double-bottom fire-resistant trough 41 to completely seal the opening and prevent cement mortar from splashing into and contaminating the lining during subsequent surface layer pouring.

[0104] S4 Integrated Surface Layer Casting: Polymer-modified phase change mortar is prepared on-site, and then spread using a laser screed after formwork is erected. During construction, the material's fluidity is strictly utilized to control the surface layer's guide slope of i=2% from the center of the machine stop position towards the surrounding trenches (meeting the design requirements of i>S and i≥1.5%), thus achieving integrated molding of the structural slope and functional layers.

[0105] S5 Functional Protection Complete: After the surface layer has initially set, apply corundum aggregate for anti-slip and wear-resistant treatment and cure for 7 days. Remove the temporary protective cover plate on the top of the prefabricated double-bottom fire-retardant tank 41, check the integrity of the lining, and finally install the 304 stainless steel heavy-duty liquid-permeable cover plate to complete the final delivery.

[0106] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0107] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A polymer-modified phase change fireproof structure for rooftop eVTOL helipads, laid on a reinforced concrete floor slab base (1) of a building roof or elevated structure, characterized in that, From bottom to top, they include: A thermal barrier insulation layer (2) is laid on the surface of the reinforced concrete floor slab base (1) to block heat conduction; The phase change heat-absorbing bearing layer (3) is cast on the thermal barrier insulation layer (2) and is a polymer-modified cement-based composite material containing aggregates encapsulated with phase change material PCM. The fireproof isolation and diversion component (4) is distributed in a grid pattern and penetrates the thermal barrier insulation layer (2) and the phase change heat absorption bearing layer (3), dividing the apron surface into several independent fire-resistant zones; The top surface of the phase change heat absorption bearing layer (3) is provided with a flow guiding slope i that slopes toward the fireproof isolation flow guiding component (4), and the flow guiding slope i ≥ 1.5%.

2. The polymer-modified phase change fireproof structure for rooftop eVTOL helipads according to claim 1, characterized in that, The matrix material of the phase change heat-absorbing bearing layer (3) is high-performance polymer-modified cement mortar, comprising: Special cementitious materials: rapid-hardening sulfoaluminate cement or high-grade silicate cement; Polymer modifier: The dosage is 3%-15% of the mass of the special cementitious material, and it is selected from one of water-based epoxy resin emulsion, acrylic emulsion or redispersible latex powder. Phase change energy storage aggregate: The dosage is 30%-50% of the mass of special cementitious materials. It is made by adsorbing phase change materials with porous lightweight aggregate and then encapsulating them on the surface. Toughening and crack-resistant fiber: The volumetric dosage is 0.5%-1.5% of the high-performance polymer-modified cement mortar, and it is selected from either polyvinyl alcohol fiber or basalt fiber.

3. The polymer-modified phase change fireproof structure for rooftop eVTOL helipads according to claim 1, characterized in that, The fireproof isolation and diversion assembly (4) includes: A prefabricated double-layer bottom fire-resistant groove (41) is embedded in the thermal barrier insulation layer (2) and the phase change heat absorption bearing layer (3). It has a horizontal outer bottom plate and an internal flow guiding bottom plate with an internal drainage slope S. An air insulation cavity (41a) is formed between the inner and outer bottom plates. A rigid heat insulation pad (41b) is prefabricated and integrated or laid below the outer bottom surface of the prefabricated double-layer bottom fire-resistant channel (41), and the prefabricated double-layer bottom fire-resistant channel (41) is directly placed on the reinforced concrete floor slab base (1) through the rigid heat insulation pad (41b). Mechanical anchors (44) penetrate vertically through the bottom of the prefabricated double-layer bottom fire-resistant groove (41) and the rigid heat insulation pad (41b) to anchor the fireproof isolation and diversion component (4) into the reinforced concrete floor slab base (1). A high-temperature resistant and corrosion-resistant inner lining (42) is coated on the inner wall of the prefabricated double-layer bottom fire-resistant tank (41); A heavy-duty liquid-permeable cover plate (43) is placed on top of the prefabricated double-layer bottom fire-resistant tank (41). Its load-bearing capacity meets the eVTOL wheel pressure requirements, and its opening ratio is not less than 30%. The top surface guiding slope i of the phase change heat absorption bearing layer (3) and the internal drainage slope S of the prefabricated double-layer bottom fire-resistant trough (41) satisfy the synergistic relationship of i > S.

4. The polymer-modified phase change fireproof structure for rooftop eVTOL helipads according to claim 3, characterized in that, The internal drainage slope S ranges from 0.5% to 1.0%.

5. The polymer-modified phase change fireproof structure for rooftop eVTOL helipads according to claim 1, characterized in that, The thermal barrier insulation layer (2) is made of a high-temperature resistant heat insulation material with a thermal conductivity of less than 0.05 W / (m·K), selected from one of silica aerogel felt, nanoporous heat insulation board or ceramic fiber board.

6. The design method for a polymer-modified phase change fireproof structure for a rooftop eVTOL helipad as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Local Impact Pressure Calculation: Based on the impulse principle, calculate the impact pressure during the eVTOL's hard landing. And check the compressive strength of the phase change heat absorption bearing layer (3) material. Does it meet safety requirements? S2. Determine the thickness H1 of the phase change heat-absorbing load layer (3): Based on the first law of thermodynamics, the thickness is calculated according to the balance relationship between the net heat flow input of the fire and the total enthalpy change capacity of the sensible heat and latent heat of the phase change heat-absorbing load layer (3) material, so as to ensure that the interface temperature at the bottom of the layer does not exceed the set value during the designed fire duration. S3. Determine the thickness H2 of the thermal barrier insulation layer (2): Based on the steady-state heat conduction formula, according to the maximum allowable safe temperature of the reinforced concrete floor slab base (1). Calculated; S4. Determine the parameters of the fireproof isolation and diversion component (4): Based on the Manning formula of fluid mechanics, calculate the minimum water passage section and internal drainage slope S of the fireproof isolation and diversion component (4) according to the total amount of battery electrolyte leakage and time, and determine the surface layer diversion slope i.

7. The design method for a polymer-modified phase change fireproof structure for a rooftop eVTOL helipad according to claim 6, characterized in that, In step S2, the thickness H1 of the phase change heat absorption bearing layer (3) is calculated according to the following formula: , in, Net heat flux density in a fire. The duration of intense burning in the fire, The mixing density of the phase change heat absorption support layer (3) is... The average specific heat capacity of the phase change heat absorption support layer (3) is, The ultimate design temperature is the bottom of the phase change heat absorption support layer (3). The initial ambient temperature is φ, the mass content of the phase change aggregate is φ, and ΔH is the effective latent heat of phase change of the phase change aggregate.

8. The design method for a polymer-modified phase change fireproof structure for a rooftop eVTOL helipad according to claim 6, characterized in that, In step S3, the thickness H2 of the thermal barrier insulation layer (2) is calculated according to the following formula: ， in, The thermal conductivity of the insulation material is... The interface design temperature is the temperature at which the phase change heat absorption support layer (3) fails. The maximum safe temperature allowed for the reinforced concrete floor slab base (1) Design limits for the residual heat flux density that can be transferred to the base layer.

9. The construction method of the polymer-modified phase change fireproof structure for rooftop eVTOL helipads as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1, Base treatment: Clean, level and apply interface agent to the reinforced concrete floor slab base (1); Step 2, laying the thermal barrier insulation layer: lay the thermal barrier insulation layer (2) on the prepared base layer (1) and seal its joints; Step 3: Installation of fireproof isolation diversion components: Cut grooves in the laid thermal barrier insulation layer (2), place the fireproof isolation diversion components (4) into the groove and place them on the base layer (1), fix them to the base layer (1) using mechanical anchors (44), then coat the inner wall of the groove with a high temperature resistant and corrosion resistant lining (42), and temporarily shield the groove opening for protection. Step 4: Pour and slope the phase change heat-absorbing load-bearing layer: Pour polymer-modified phase change mortar on the thermal barrier insulation layer (2) and control the surface elevation to form a flow-guiding slope i to the fireproof isolation flow-guiding component (4). Step 5, Curing and Accessory Installation: Curing is carried out on the completed phase change heat absorption bearing layer (3). After the strength reaches the standard, the temporary shielding of the groove is removed, and a heavy-duty liquid permeable cover plate (43) is installed above the fireproof isolation and diversion component (4).

10. The construction method of the polymer-modified phase change fireproof structure for rooftop eVTOL helipads according to claim 9, characterized in that, In step three, the fireproof isolation and diversion component (4) is a prefabricated double-layer bottom fire-resistant groove (41) with a prefabricated rigid heat insulation pad (41b). It sits directly on the base layer (1) and is anchored in the base layer (1) through the bottom of the mechanical anchor (44) and the rigid heat insulation pad (41b).

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