Lightweight composite material of wind driven generator blade and preparation method of lightweight composite material

Abstract

The invention relates to the technical field of wind turbine blade materials, in particular to a light composite material of a wind turbine blade and a preparation method of the light composite material, and the light composite material comprises light concrete, epoxy resin and first-grade carbon fiber cloth; the lightweight concrete is prepared from the following components in parts by weight: 90 parts of ordinary Portland cement, 10 parts of silica fume, 5 to 40 parts of ceramic hollow microspheres, 0.3 to 2 parts of polyvinyl alcohol fiber, 0.05 to 1 part of polycarboxylic acid water reducing agent, 0 to 0.2 part of hydroxypropyl methyl cellulose and 25 to 100 parts of water. The lightweight composite material for the wind driven generator blade prepared by the invention has excellent fracture resistance and tensile property, high regulation degree and good durability, and the wind driven generator blade prepared from the lightweight composite material has excellent performance and low cost and can be widely applied to vertical axis type wind driven generator blades.

Description

Technical Field

[0001] The invention relates to the technical field of wind power generation blade materials, and in particular to a lightweight composite material for wind power generator blades and a preparation method thereof. Background Art

[0002] As global energy demand continues to rise, wind energy, as a renewable energy source, is seen as a highly promising way to generate electricity. The use of larger blades with longer chord lengths has become a development trend in the field of wind power generation. In order to cope with complex and changing force and load challenges, the blade design of wind turbines must take into account lightweight, high rigidity, high strength and excellent durability. At present, composite materials are not only light in weight, but also have high strength, high rigidity and good durability, which is crucial for resisting aerodynamic, gravity and centrifugal loads, and controlling the resulting deformation. Therefore, in the process of selecting composite materials, the coordinated optimization of performance, materials, shape and process has become a core consideration.

[0003] At present, polymer resin-based composite materials, especially glass fiber composite materials, are commonly used in the manufacture of wind turbine blades. However, these glass fiber composite materials require complex molding processes and a large amount of manual operations, which increases the overall production cost of wind turbine blades. During the service life of wind turbine blades, glass fiber composites will experience harsh environments such as strong ultraviolet rays, high humidity, and high temperatures, which will cause cracks, deformation or aging on the surface of the glass fiber composites, further leading to degradation of mechanical properties and increasing the maintenance cost of wind turbine blades during use. In addition, it is difficult to recycle and reuse wind turbine blade materials after they have been put into service, and the recycling cost is relatively high.

[0004] As a low-cost building material, traditional cement-based materials have a history of practical engineering application for hundreds of years. Previous studies have shown that the stable chemical composition of cement-based materials allows it to have a long service life and maintain its stability in extreme environments, and is not easily affected by corrosion or aging. Using lightweight cement-based materials as the matrix of wind turbine blades can make the matrix material of wind turbine blades have excellent durability, thereby effectively solving the problems of poor durability of wind turbine blades and the need for long-term maintenance. However, the density of existing cement-based materials is usually about 2000Kg / m 3 Compared with the density of traditional wind turbine blade materials of 1200Kg / m 3 Compared with the traditional wind turbine blades, it is still heavier; its tensile strength is low, usually less than 20MPa; and its poor flexural strength cannot meet the practical application requirements of lightweight wind turbine blade materials that mainly withstand tensile stress.

[0005] Therefore, it is necessary to develop a lightweight concrete composite wind turbine blade material with better comprehensive performance. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a lightweight composite material for wind turbine blades and blades prepared therefrom. The lightweight concrete composite wind turbine blade material itself has low volume density, high tensile strength, good flexural strength, low cost, and is energy-saving and environmentally friendly.

[0007] The purpose of the present invention is achieved by adopting the following technical solutions:

[0008] In a first aspect, the present invention provides a lightweight composite material for a wind turbine blade, comprising lightweight concrete, epoxy resin and primary carbon fiber cloth; wherein the lightweight concrete is composed of the following components calculated by weight:

[0009] Ordinary Portland cement: 90 parts; silica fume: 10 parts; ceramic hollow microspheres: 5-40 parts; polyvinyl alcohol fiber: 0.3-2 parts; polycarboxylic acid water reducer: 0.05-1 parts; hydroxypropyl methylcellulose: 0-0.2 parts; water: 25-100 parts.

[0010] Preferably, the ordinary Portland cement type is 52.5 model, the cement particle size distribution is 1-30 μm, the calcium oxide content is between 50%-65%, the silicon oxide content is between 15%-25%, the iron oxide content is between 1%-6%, the sulfur trioxide content should not be greater than 3.5%, the magnesium oxide content is not greater than 5%, the chloride ion content is not greater than 0.1%, and the 28-day compressive strength should not be less than 52.5 MPa.

[0011] Preferably, the SiO2 content in the silica fume is greater than 90%, and the particle size of the silica fume ranges from 0.5 to 110 μm.

[0012] Preferably, the mass ratio of the oxides SiO2, Al2O3, MgO, Na2O and CaO in the ceramic hollow microspheres is 60-90:0-2:0-2:2-10:5-20, and the X-ray diffraction test results show a hump at 15-25 degrees, indicating that the material is an amorphous material, and the Fourier transform infrared spectrometer test results show a hump at 1250-1000cm -1 There is a hump in the range, the particle size range is mainly distributed in 1-100 μm, and the true density is 0.1-0.3 g / cm 3 , bulk density is 0.05-0.2g / cm 3 , the compressive strength is 2-8MPa.

[0013] Preferably, the polyvinyl alcohol fiber has a fiber length of 6-9 mm and a fiber diameter of 15 μm.

[0014] Preferably, the viscosity of the hydroxypropyl methylcellulose is 200,000, the pH range is 5.0-7.5, and the fineness is greater than 80 mesh.

[0015] Preferably, the primary carbon fiber cloth has a thickness of 0.16-0.17 mm, a tensile strength of about 1600 MPa, an elongation of ≥1.7%, and a weight of about 200-300 g / m 2 .

[0016] Preferably, the amount of the epoxy resin used depends on the area of ​​the lightweight concrete substrate to be bonded and the number of fiber cloth layers, and the specific amount used is 500-1000 g / m2.

[0017] Preferably, the amount of the primary carbon fiber cloth used depends on the area of ​​the lightweight concrete substrate to be bonded, and the specific amount used is 200-300 g / m2.

[0018] Preferably, the epoxy resin complies with GB50367-2013 standard, is divided into Class A glue and Class B glue components, has a tensile strength ≥30MPa, an elongation ≥1.5%, a flexural strength ≥40MPa, a compressive strength ≥70MPa, and a tensile elastic modulus ≥1.5GPa.

[0019] Preferably, the chemical composition of the polycarboxylate water reducer is mainly modified polycarboxylic acid, and the density is 0.4-0.6 g / cm 3 , PH range 9-12, total chloride ion content ≤0.1%, alkali content ≤3%.

[0020] In a second aspect, the present invention provides a method for preparing a lightweight composite material for a wind turbine blade, comprising the following steps:

[0021] (1) drying ordinary Portland cement, silica fume, ceramic hollow microspheres, hydroxypropyl methylcellulose, and polycarboxylate water reducer, and then mixing to obtain a dry powder mixture;

[0022] (2) adding half of the amount of water to the dry powder mixture and stirring thoroughly for 30 seconds, then adding the remaining amount of water and polyvinyl alcohol fiber to the mixture and mixing thoroughly to obtain a wet material;

[0023] (3) pouring the wet material into the corresponding mold to obtain an embryo;

[0024] (4) Curing, polishing, and cleaning the dust on the surface of the embryo, and then leveling the surface of the embryo with epoxy resin;

[0025] (5) Apply a base layer of epoxy resin on the surface of the leveled embryo, then press the first-level carbon fiber cloth on the surface, continue to apply a layer of epoxy resin surface on the surface of the embryo, and scrape off the bubbles in the first-level carbon fiber cloth until a uniform surface composite is obtained, and then maintain.

[0026] Preferably, in step (4), the curing conditions include: curing for 28-30 days at a temperature of 15-25°C and a humidity of 95%RH-100%RH.

[0027] Preferably, in step (5), the thickness of the epoxy resin bottom layer is 0.1-0.5 mm, and the thickness of the epoxy resin surface layer is 0.2-1.5 mm.

[0028] Preferably, in step (5), the re-curing conditions include: curing for 6-8 days at a temperature of 15-25°C and a humidity of 95%RH-100%RH.

[0029] The beneficial effects of the present invention are:

[0030] 1. The lightweight composite material of the wind turbine blade prepared by the present invention has excellent flexural and tensile properties, a high degree of controllability, and good durability. The wind turbine blade prepared by the composite material has excellent performance and low cost, and can be widely used in vertical axis wind turbine blades.

[0031] 2. Ceramic hollow microspheres are added to the lightweight composite material of the wind turbine blade of the present invention. The ceramic hollow microspheres contain components such as silicon dioxide, calcium oxide, sodium oxide, aluminum oxide, and the mass ratio of the oxides SiO2, Al2O3, MgO, Na2O and CaO is 60-90:0-2:0-2:2-10:5-20. The ceramic hollow microspheres have an obvious hump at 15-25 degrees in the X-ray diffraction test results. They are mainly an amorphous material and can act as an excellent inert aggregate in the composite matrix of cement and silica fume. This allows the lightweight concrete matrix itself to have a stable chemical composition, good stress-bearing properties, and is not easily affected by corrosion or aging during service, which may affect the mechanical properties of the material.

[0032] 3. The lightweight composite material of the present invention is composited with primary carbon fiber cloth, epoxy resin and lightweight concrete. The primary carbon fiber cloth not only improves the mechanical properties of the composite such as tensile strength and flexural strength, but its stable chemical structure can also significantly improve the stability of the wind turbine blade material in maintaining its own physical and chemical properties, and enhance the corrosion resistance of the blade material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention is further described using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention. A person skilled in the art can obtain other drawings based on the following drawings without creative work.

[0034] Figure 1 A schematic diagram of the lightweight composite material for wind turbine blades and the steps of the preparation method thereof of the present invention;

[0035] Figure 2 A schematic diagram of a wind turbine blade made of a lightweight concrete composite material according to the present invention;

[0036] Figure 3 for Figure 2 A schematic front view of a lightweight composite material;

[0037] Figure 4 for Figure 2 Schematic top view of lightweight composite materials;

[0038] Figure 5 for Figure 2 Physical schematic diagram of lightweight composite materials;

[0039] Figure 6 for Figure 3 Schematic diagram of lightweight composite materials. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0041] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0042] The present invention will be further described below in conjunction with the following examples.

[0043] Example 1

[0044] A lightweight composite material for a wind turbine blade is prepared by weighing the following raw materials in parts by weight: 90 parts of ordinary Portland cement 52.5, 10 parts of silica fume, 7 parts of ceramic hollow microspheres, 0.6 parts of polyvinyl alcohol fiber, 0.3 parts of polycarboxylic acid water reducer, 30 parts of water, 1000 g / m2 of epoxy resin, and 300 g / m2 of primary carbon fiber cloth.

[0045] Then follow these steps to prepare lightweight composite materials for wind turbine blades:

[0046] 1) drying ordinary Portland cement, silica fume, ceramic hollow microspheres and hydroxypropyl methylcellulose, and then mixing to obtain a dry powder mixture;

[0047] 2) Add half of the water to the dry powder mixture and stir thoroughly for 30 seconds, then add the remaining amount of water, polyvinyl alcohol fiber and polycarboxylate water reducer to the mixture and mix thoroughly to obtain a wet material;

[0048] 3) pouring the wet material into the corresponding mold to obtain an embryo;

[0049] 4) Place the body in a standard curing box and cure it at 20°C and 95% RH for 28 days. When the body reaches the curing age, use an angle grinder to grind the surface of the body, use a blower to clean the dust on the polished surface, and then use leveling epoxy resin to level the surface of the body and wait for 24 hours;

[0050] 5) Apply a base layer of epoxy resin on the leveled surface of the embryo, and then stick the primary carbon fiber cloth on the surface, and then continue to apply a layer of epoxy resin on the surface of the primary carbon fiber cloth, and scrape off the bubbles in the primary carbon fiber cloth until a composite with a uniform surface is obtained, and then place it in a standard curing box and continue to cure for 8 days at 20°C and 95% RH.

[0051] The obtained lightweight composite material of the wind turbine blade was tested, and the test method is as follows:

[0052] The size of the obtained lightweight composite material for the wind turbine blade is measured and the material volume V is calculated. Then, the mass of the material is measured, the material weight m is measured and the volume density of the obtained material is calculated. The lightweight composite material of the wind turbine blade cured for 28 days was tested for compressive strength. The test block was 20cm high and 10cm in diameter. The test block was not attached with carbon fiber cloth and was directly tested for compressive strength using a universal material testing machine with a range of 300 tons. The pressure loading rate was 2.5Kn / s. The size of the flexural test piece was 35cm long, 10cm wide, and 2cm thick. The three-point flexural test was performed on the carbon fiber cloth-attached test piece. The test machine loading pressure rate was 0.15mm / min. The method that met the JCES test block tensile strength specification was used to directly test the carbon fiber cloth-attached test piece. The test machine loading rate was 0.15mm / min. All data were transmitted to a computer equipped with special acquisition software.

[0053] The compressive strength, flexural strength and tensile strength of the tested products are shown in the following table:

[0054]

[0055] Example 2

[0056] A lightweight composite material for a wind turbine blade is prepared by weighing the following raw materials in parts by weight: 90 parts of ordinary Portland cement, 10 parts of silica fume, 12 parts of ceramic hollow microspheres, 0.8 parts of polyvinyl alcohol fiber, 0.3 parts of polycarboxylic acid water reducer, 33 parts of water, 1000 g / m2 of epoxy resin, and 300 g / m2 of primary carbon fiber cloth.

[0057] Then follow these steps to prepare lightweight composite materials for wind turbine blades:

[0058] 1) drying 52.5% of ordinary Portland cement, silica fume, ceramic hollow microspheres and hydroxypropyl methylcellulose, and then mixing to obtain a dry powder mixture;

[0059] 2) Add half of the water to the dry powder mixture and stir thoroughly for 30 seconds, then add the remaining amount of water, polyvinyl alcohol fiber and polycarboxylate water reducer to the mixture and mix thoroughly to obtain a wet material;

[0060] 3) pouring the wet material into the corresponding mold to obtain an embryo;

[0061] 4) Place the body in a standard curing box and cure it at 20°C and 95% RH for 28 days. When the body reaches the curing age, use an angle grinder to grind the surface of the body, use a blower to clean the dust on the polished surface, and then use leveling epoxy resin to level the surface of the body and wait for 24 hours;

[0062] 5) Apply a base layer of epoxy resin on the leveled surface of the embryo, and then stick the primary carbon fiber cloth on the surface, and then continue to apply a layer of epoxy resin on the surface of the primary carbon fiber cloth, and scrape off the bubbles in the primary carbon fiber cloth until a composite with a uniform surface is obtained, and then place it in a standard curing box and continue to cure for 8 days at 20°C and 95% RH.

[0063] The obtained lightweight composite material for wind turbine blades was tested using the same testing method as in Example 1. The results are shown in the following table:

[0064]

[0065] Example 3

[0066] A lightweight composite material for a wind turbine blade is prepared by weighing the following raw materials in parts by weight: 90 parts of ordinary Portland cement 52.5, 10 parts of silica fume, 30 parts of ceramic hollow microspheres, 2 parts of polyvinyl alcohol fiber, 0.8 parts of polycarboxylic acid water reducer, 80 parts of water, 0.2 parts of hydroxypropyl methylcellulose, 1000 g / m2 of epoxy resin, and 300 g / m2 of primary carbon fiber cloth.

[0067] Then follow these steps to prepare lightweight composite materials for wind turbine blades:

[0068] 1) drying 52.5% of ordinary Portland cement, silica fume, ceramic hollow microspheres and hydroxypropyl methylcellulose, and then mixing to obtain a dry powder mixture;

[0069] 2) Add half of the water to the dry powder mixture and stir thoroughly for 30 seconds, then add the remaining amount of water, polyvinyl alcohol fiber and polycarboxylate water reducer to the mixture and mix thoroughly to obtain a wet material;

[0070] 3) pouring the wet material into the corresponding mold to obtain an embryo;

[0071] 4) Place the body in a standard curing box and cure it at 20°C and 95% RH for 28 days. When the body reaches the curing age, use an angle grinder to grind the surface of the body, use a blower to clean the dust on the polished surface, and then use leveling epoxy resin to level the surface of the body and wait for 24 hours;

[0072] 5) Apply a base layer of epoxy resin on the leveled surface of the embryo, and then stick the primary carbon fiber cloth on the surface, and then continue to apply a layer of epoxy resin on the surface of the primary carbon fiber cloth, and scrape off the bubbles in the primary carbon fiber cloth until a composite with a uniform surface is obtained, and then place it in a standard curing box and continue to cure for 8 days at 20°C and 95% RH.

[0073] The obtained lightweight composite material for wind turbine blades was tested using the same testing method as in Example 1. The results are shown in the following table:

[0074]

[0075] Comparative Example

[0076] Weigh the following raw materials by weight: 90 parts of ordinary Portland cement 52.5, 10 parts of silica fume, 2 parts of polyvinyl alcohol fiber, 0.2 parts of polycarboxylic acid water reducer, 30 parts of water, 1000 g / m2 of epoxy resin, 300 g / m2 of primary carbon fiber cloth. Then prepare the composite wind turbine blade material according to the following steps:

[0077] 1) Drying 52.5% of ordinary Portland cement and silica fume, and then mixing them to obtain a dry powder mixture;

[0078] 2) Add half of the water to the dry powder mixture and stir thoroughly for 30 seconds, then add the remaining amount of water, polyvinyl alcohol fiber and polycarboxylate water reducer to the mixture and mix thoroughly to obtain a wet material;

[0079] 3) pouring the wet material into the corresponding mold to obtain an embryo;

[0080] 4) Place the body in a standard curing box and cure it at 20°C and 95% RH for 28 days. When the body reaches the curing age, use an angle grinder to grind the surface of the body, use a blower to clean the dust on the polished surface, and then use leveling epoxy resin to level the surface of the body and wait for 24 hours;

[0081] 5) Apply a base layer of epoxy resin on the leveled surface of the embryo, and then stick the primary carbon fiber cloth on the surface, and then continue to apply a layer of epoxy resin on the surface of the primary carbon fiber cloth, and scrape off the bubbles in the primary carbon fiber cloth until a composite with a uniform surface is obtained, and then place it in a standard curing box and continue to cure for 8 days at 20°C and 95% RH.

[0082] The obtained lightweight concrete composite wind turbine blade material was tested using the same testing method as in Example 1.

[0083]

[0084] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0085] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A lightweight composite material for a wind turbine blade, characterized in that: It includes lightweight concrete, epoxy resin and first-grade carbon fiber cloth; wherein the lightweight concrete is composed of the following components calculated by weight: Ordinary Portland cement: 90 parts; silica fume: 10 parts; ceramic hollow microspheres: 5-40 parts; polyvinyl alcohol fiber: 0.3-2 parts; polycarboxylic acid water reducer: 0.2-1 parts; hydroxypropyl methylcellulose: 0-0.2 parts; water: 25-100 parts.

2. The lightweight composite material for wind turbine blades according to claim 1, characterized in that: The ordinary Portland cement type is 52.5 model, the cement particle size distribution is 1-30 μm, the calcium oxide content is between 50%-65%, the silicon oxide content is between 15%-25%, the iron oxide content is between 1%-6%, the sulfur trioxide content should not be greater than 3.5%, the magnesium oxide content is not greater than 5%, the chloride ion content is not greater than 0.1%, and the 28-day compressive strength should not be less than 52.5 MPa.

3. The lightweight composite material for wind turbine blades according to claim 1, characterized in that: The SiO2 content in the silica fume is greater than 90%, and the particle size of the silica fume ranges from 0.5 to 110 μm.

4. The lightweight composite material for wind turbine blades according to claim 1, characterized in that: The mass ratio of the oxides SiO2, Al2O3, MgO, Na2O and CaO in the ceramic hollow microspheres is 60-90:0-2:0-2:2-10:5-20. In the X-ray diffraction test results, there is an obvious hump at 15-25 degrees, indicating that the ceramic hollow microspheres are an amorphous material. In the Fourier transform infrared spectrometer test results, there is an obvious hump at 1250-1000cm -1 There is a hump in the range, the particle size range is mainly distributed in 1-100 μm, and the true density is 0.1-0.3 g / cm 3 , bulk density is 0.05-0.2g / cm 3 , the compressive strength is 2-8MPa.

5. The lightweight composite material for wind turbine blades according to claim 1, characterized in that: The fiber length of the polyvinyl alcohol fiber is 6-9 mm, and the fiber diameter is 15 μm; the viscosity of the hydroxypropyl methylcellulose is 200,000, the pH range is 5.0-7.5, and the fineness is greater than 80 meshes.

6. The lightweight composite material for wind turbine blades according to claim 1, characterized in that: The primary carbon fiber cloth has a thickness of 0.16-0.17 mm, a tensile strength of about 1600 MPa, an elongation of ≥1.7%, and a weight of about 200-300 g / m 2 .

7. The lightweight composite material for wind turbine blades according to claim 1, characterized in that: The amount of the epoxy resin used depends on the area of ​​the lightweight concrete substrate to be pasted, and the specific amount used is 500-1000 grams per square meter; the amount of the primary carbon fiber cloth used depends on the area of ​​the lightweight concrete substrate to be pasted, and the specific amount used is 200-300 grams per square meter.

8. A method for preparing the lightweight composite material for wind turbine blades according to claim 1, characterized in that: The following steps are involved: (1) drying ordinary Portland cement, silica fume, ceramic hollow microspheres, hydroxypropyl methylcellulose, and polycarboxylate water reducer, and then mixing to obtain a dry powder mixture; (2) adding half of the amount of water to the dry powder mixture and stirring thoroughly for 30 seconds, then adding the remaining amount of water and polyvinyl alcohol fiber to the mixture and mixing thoroughly to obtain a wet material; (3) pouring the wet material into the corresponding mold to obtain an embryo; (4) Curing, polishing, and cleaning the dust on the surface of the embryo, and then leveling the surface of the embryo with epoxy resin; (5) Apply a base layer of epoxy resin on the surface of the leveled embryo, then press the first-level carbon fiber cloth on the surface, continue to apply a layer of epoxy resin surface on the surface of the embryo, and scrape off the bubbles in the first-level carbon fiber cloth until a uniform surface composite is obtained, and then maintain.

9. The method for preparing a lightweight composite material for a wind turbine blade according to claim 7, characterized in that: In step (4), the curing conditions include: curing for 28-30 days at a temperature of 15-25°C and a humidity of 95%RH-100%RH.

10. The method for preparing a lightweight composite material for a wind turbine blade according to claim 7, characterized in that: In step (5), the re-curing conditions include: curing for 6-8 days at a temperature of 15-25°C and a humidity of 95%RH-100%RH.

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