An improved river bottom suction and a method for preparing roadbed material thereof

Abstract

The application discloses an improved river bottom sucking mud and a method for preparing roadbed materials therefrom, and belongs to the technical field of road material preparation. According to percentages, the river bottom sucking mud comprises the following raw materials: 28.6-31.4% of the river bottom sucking mud, 9.6-12.3% of water, 53.2-56.8% of construction waste and 13.03-16.99% of a curing agent. The curing agent is composed of 8.7-10.2% of blast furnace slag, 1.95-3.9% of coal ash, 2.1-2.55% of an alkali activator and 0.28-0.34% of an activator. The activator is composed of sodium acetate and sodium lignosulfonate in a mass ratio of 1:1. The raw material ratio of the application aims at improving the performance of the river bottom sucking mud. After the curing agent, the river bottom sucking mud and the construction waste are mixed, water is added, the alkali activator promotes the recombination of the mineral structures of the blast furnace slag and the coal ash, the generated hydration products form stable structures, and with the increase of the curing time, the structures are further developed, so that the mechanical strength is improved.

Description

Technical Field

[0001] This invention belongs to the field of road material preparation technology, specifically relating to an improved riverbed sludge suction method and a method for preparing roadbed materials. Background Technology

[0002] Currently, several attempts have been made both domestically and internationally to treat riverbed sludge with high water content. Regarding traditional solidification and stabilization technologies, scholars such as Sun Yuhang have conducted solidification research using materials like sodium aluminate, synthesizing various road filling materials. Duc Trong Nguyen et al. studied the changes in the macroscopic physical properties of solidified riverbed sludge under different cement dosages and environmental temperatures, finding that the strength and permeability of the solidified sludge basically meet the requirements for use as roadbed filler and landfill lining material. To address these issues, methods for solidifying sludge have been modified to improve its durability. Scholars such as Wang Chaohui introduced organic bentonite and sodium silicate into traditional solidification methods, finding that this further improved the compressive strength of the solidified body; they also studied its engineering mechanical properties under wet-dry and freeze-thaw cycles, achieving good experimental results.

[0003] Existing research indicates that the solidification materials used in special mud slurries from riverbed sludge suction generally suffer from unavoidable problems such as high cost, high energy consumption, and environmental unfriendliness. Therefore, there is an urgent need to develop an environmentally friendly and energy-saving material for the harmless treatment and resource utilization of this special mud. Furthermore, current research on this type of mud primarily focuses on its physical properties, with insufficient research on its pore structure, mineral composition, elemental binding energy, and other cementation mechanisms. Research into the basic characteristics of riverbed sludge suction and methods for its stabilization and resource utilization is urgently needed. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an improved riverbed silt suction device.

[0005] To achieve the above objectives, the present invention provides the following technical solution: comprising the following raw materials: riverbed sludge: 28.6%–31.4%, water: 9.6%–12.3%, construction waste: 53.2%–56.8%, and curing agent: 13.03%–16.99%; the curing agent is composed of 8.7%–10.2% blast furnace slag, 1.95%–3.9% coal ash, 2.1%–2.55% alkali activator, and 0.28%–0.34% activator; the activator is composed of sodium acetate and sodium lignosulfonate in a mass ratio of 1:1.

[0006] Furthermore, it also includes a modified method for preparing roadbed materials by sludge suction from riverbeds, comprising the following steps:

[0007] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0008] S2. Add the riverbed sludge, construction waste, solidifying agent, and water to the mixer in sequence and mix thoroughly to obtain a mixture. Control the moisture content of the mixture to 12% by adding water externally. Continue to increase the mixing speed to obtain the roadbed material.

[0009] Furthermore, the roadbed material is sealed and stored for 24-48 hours to allow moisture to be evenly dispersed in the mixture.

[0010] Furthermore, in step S2, the mixture is first stirred at 55-65 r / min for 10-15 minutes; after adding external water, the speed is increased to 110-130 r / min and stirred for 1-3 minutes.

[0011] Furthermore, the roadbed material is subjected to high-pressure molding at a molding pressure of 160kN and a pressing rate of 5-7kN, and is left to stand for 1-5 minutes to reduce the possibility of springback of the solidified body.

[0012] Furthermore, after the roadbed material is pressed and formed, it is cured for 25-30 days using a normal temperature and natural moisture-retaining curing process, with curing conditions of 18-22 degrees Celsius and relative humidity greater than 90%.

[0013] Furthermore, the roadbed material is used to improve the unconfined compressive strength of the riverbed silt suction.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. The curing agent of the present invention is used to improve the performance of sludge suction at the bottom of the river. It uses blast furnace slag and coal ash as the main raw materials. By adjusting the ratio of alkali activator and activator, the blast furnace slag and coal ash are fully mixed with the alkali activator, and the activator accelerates the decomposition of minerals.

[0016] 2. The sodium acetate in the activator of this invention is the sodium salt of acetic acid, which is normally soluble in water. It can form a mixed solution with sodium lignosulfonate in water. When mixed within a certain mass range, the two can interact, altering their solubility and surface tension in the solution. Simultaneously, sodium acetate also acts as a pH adjuster, adjusting the acidity or alkalinity of the road subbase material, helping to reduce its swelling and improve the stability of the base mixture.

[0017] 3. The sodium lignosulfonate in the activator of this invention has a dispersing effect after dissolving in water, forming a colloidal structure between the base layer mixture materials and improving the uniformity of the base layer. Furthermore, sodium lignosulfonate also helps improve the adhesion between particles of the base layer mixture materials, reducing the adhesion of moisture to the base layer mixture materials.

[0018] 4. The raw material ratio of the present invention aims to improve the performance of river bottom sludge suction. After mixing the solidifying agent, river bottom sludge suction and construction waste, water is added. The alkali activator promotes the reorganization of the mineral structure of slag and coal ash. The resulting hydration products form a stable structure, and the structure further develops with the increase of curing time, thereby improving mechanical strength.

[0019] 5. The preparation method of the roadbed material of the present invention significantly improves the solidification strength performance of riverbed sludge, meeting the application requirements of roadbed materials in actual engineering. In addition, the improved method of the present invention can not only improve the unconfined compressive strength of riverbed sludge, but also improve the engineering applicability of riverbed sludge. Moreover, the improved method of the present invention uses raw materials with wide availability and low cost, which not only improves the comprehensive utilization rate of industrial solid waste, but also solves the problem of silt accumulation in urban bridge construction projects, achieving the goal of "treating waste with waste".

[0020] Other advantages, objectives, and features of the invention will be set forth in the following description and will be apparent to those skilled in the art in some respects, or may be learned by practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0021] To make the purpose, technical solution, and beneficial effects of the invention clearer, the following figures are provided for illustration:

[0022] Figure 1 Drawings of the finished product of the road material consolidation structure;

[0023] Figure 2 To develop the mineral structure composition of the base material for deep riverbed silt suction road construction;

[0024] Figure 3 The adsorption-desorption isotherm of the subgrade material for deep riverbed silt suction road construction.

[0025] Figure 4 Pore ​​volume-pore size distribution curve of subbase material for deep riverbed silt suction road construction;

[0026] Figure 5 The bonding energy of deep riverbed silt suction road base materials. Detailed Implementation

[0027] An improved method for sludge suction from riverbeds and its preparation of roadbed materials:

[0028] In all embodiments of this invention, an NRJ-411A cement mortar mixer (Wuxi Jianyi Instrument Machinery Co., Ltd.) was used for mixing. After the roadbed material was prepared, it was placed in a cylindrical mold with Φ=100mm and H=60mm, and constant pressure was applied using a YAW-2000 microcomputer-controlled electro-hydraulic servo pressure testing machine (Jinan Zhongluchang Testing Machine Manufacturing Co., Ltd.). The loading rate during pressure application was 5kN / s, and the compaction degree was 2.0g / cm3. Before mixing, the raw materials were first dried to constant weight in a 105℃ forced-air constant-temperature drying oven, and then placed in a planetary ball mill and ball-milled for 5 minutes at 150r / min. The construction waste used in this application includes slag, bricks, asphalt blocks, gypsum, mortar, and waste concrete.

[0029] Example 1

[0030] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0031] S2. Add 30% of the riverbed mud, 55% of the construction waste, 15% of the solidifying agent and 11% of the water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

[0032] In this embodiment, slag accounts for 68% of the weight of the curing agent, coal ash accounts for 16% of the weight of the curing agent, alkali activator accounts for 14% of the weight of the curing agent, and activator accounts for 2% of the weight of the curing agent.

[0033] Example 2

[0034] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0035] S2. Add 30% of the riverbed mud, 55% of the construction waste, 15% of the solidifying agent and 11% of the water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

[0036] In this embodiment, slag accounts for 63% of the weight of the curing agent, coal ash accounts for 21% of the weight of the curing agent, alkali activator accounts for 14% of the weight of the curing agent, and activator accounts for 2% of the weight of the curing agent.

[0037] Example 3

[0038] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0039] S2. Add 30% of the riverbed mud, 55% of the construction waste, 15% of the solidifying agent and 11% of the water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

[0040] In this embodiment, slag accounts for 58% of the weight of the curing agent, coal ash accounts for 26% of the weight of the curing agent, alkali activator accounts for 14% of the weight of the curing agent, and activator accounts for 2% of the weight of the curing agent.

[0041] Example 4

[0042] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0043] S2. Add 30% of the riverbed mud, 55% of the construction waste, 15% of the solidifying agent and 11% of the water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

[0044] In this embodiment, slag accounts for 68% of the weight of the curing agent, coal ash accounts for 13% of the weight of the curing agent, alkali activator accounts for 17% of the weight of the curing agent, and activator accounts for 2% of the weight of the curing agent.

[0045] Example 5

[0046] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0047] S2. Add 30% of the riverbed mud, 55% of the construction waste, 15% of the solidifying agent and 11% of the water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

[0048] In this embodiment, slag accounts for 63% of the weight of the curing agent, coal ash accounts for 18% of the weight of the curing agent, alkali activator accounts for 17% of the weight of the curing agent, and activator accounts for 2% of the weight of the curing agent.

[0049] Example 6

[0050] S1. Dry the mud at the bottom of the river and let it air dry naturally until the moisture content is less than 15%;

[0051] S2. Add 30% of the riverbed mud, 55% of the construction waste, 15% of the solidifying agent and 11% of the water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

[0052] In this embodiment, slag accounts for 58% of the weight of the curing agent, coal ash accounts for 23% of the weight of the curing agent, alkali activator accounts for 17% of the weight of the curing agent, and activator accounts for 2% of the weight of the curing agent.

[0053] The mixing ratio of curing agent materials is shown in Table 1:

[0054] Slag (%) Coal fly ash (%) Alkali activator (%) Activator (%) Example 1 68 16 14 2 Example 2 63 21 14 2 Example 3 58 26 14 2 Example 4 68 13 17 2 Example 5 63 18 17 2 Example 6 58 23 17 2

[0055] The subgrade materials of Examples 1-6 were tested according to the mortar strength test procedure in "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021). The unconfined compressive strength of the specimens was tested on the 7th and 28th day after molding. The results are shown in Table 2:

[0056] Table 2 Compressive Strength Test Table for Examples 1-6

[0057] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 7 day 1.1 MPa 2.1 MPa 1.7 MPa 1.7 MPa 1.8 MPa 0.86 MPa 28 day 1.66 MPa 4 MPa 3.05 MPa 2.52 MPa 2.77 MPa 1.08 MPa

[0058] As shown in Table 1, the compressive strength of the subgrade materials in Examples 1-6 increased with the progress of curing during the maintenance period. The 28-day compressive strength of all samples reached above 1.0 MPa, with samples L2, L3, L4, and L5 reaching above 1.5 MPa. This meets the minimum strength limit requirement (greater than 1.5 MPa) for road subbase materials in the "Code for Construction and Quality Acceptance of Urban Road Engineering" (CJJ1-2008) and can be used as road subbase filler.

[0059] Comparing the compressive strength of the finished samples prepared with different proportions of curing agent, it can be seen that the strength of the sample in Example 2 is significantly higher than that of the other examples, and the later compressive strength is also higher. The compressive strength reaches 2.1 MPa at 7 days and further increases by 90.5% to 4.0 MPa at 28 days, exhibiting better mechanical properties. Comparing the addition amounts of slag and alkali activator, the compressive strength of Examples 2 and 5, with 63% slag addition, is higher than that of Examples 5, while the compressive strength of Example 2, with 14% alkali activator addition, is higher than that of Example 5, with 17% alkali activator addition. In addition, the strength development of the examples with higher 28-day compressive strength is mainly in the later stages, such as Examples 2 and 3, where the strength at 7 days is only 52.5% and 55.7% of that at 28 days, respectively.

[0060] In this application, construction waste serves as a stabilized substance after reaction, acting as a skeletal structure in the road subbase material. The slag in the curing agent, as the active component of the calcium agent, enhances chemical activity under the action of the alkali activator, achieving stable encapsulation of the riverbed sludge particles and thus increasing strength. The main chemical components of coal ash are Si and Al elements, which, under the action of the alkali activator, can supplement the material structure. As shown in Example 2, when the dosage of the alkali activator is sufficient to promote a full chemical reaction between the slag and coal ash, the compressive strength reaches its maximum value, and its structural stability is strongest.

[0061] In this application, to study the mix proportions and strength test results of road subbase materials, three groups—Example 6 (cured for 28 days), Example 2 (cured for 28 days), and Example 2 (cured for 7 days)—were selected. XRD analysis was performed on these three groups of consolidated bodies with significant differences in mix proportions and strength. The results are as follows: Figure 2 As shown. The sample was dried at 105℃, crushed into powder, and passed through a 350-mesh sieve. The experiment used a Rigaku SmartLab SEX X-ray diffractometer from Japan. The test target was a Cu target, the working voltage was 40.0kV, the current was 40.0mA, the emission wavelength was 0.15406nm, the scanning speed was 5° / min (2θ), and the scanning range was 10°~80° (2θ).

[0062] analyze Figure 2 It was found that the main phase components in the solidified sample included quartz, orthorhombic calcium zeolite, calcite, and nacreous mica. The presence of orthorhombic calcium zeolite indicates the formation of hydration products; it is a monoclinic mineral with a robust framework structure composed of Si, Al, and O, and also possesses porous "nodules" that support the material's framework. The slag in the curing agent provided a source of calcium for recombination, while the coal ash provided a sufficient source of silicon and aluminum. Under the influence of large-scale ion exchange, Ca... 2+ Entering the crystal lattice system promotes the formation of new mineral phases. Furthermore, a slight bulge in the diffraction curve between 20° and 40° indicates the production of CSH-like gel-like amorphous substances during the reaction, further enhancing the material's structural strength.

[0063] Comparing the diffraction curves of road subbase material samples at different curing ages reveals that the peak intensities of all mineral phases significantly decreased with increasing curing time. Mineral diffraction peaks with diffraction angles greater than 45° gradually disappeared. This indicates that as the reaction proceeds, the mineral structure is involved with amorphous substances and undergoes autolysis, participating in the hydration reaction. Furthermore, the peak intensities of all diffraction peaks in the sample cured for 28 days in Example 2 were slightly lower than those in Example 6, indicating that the reaction in the sample of Example 2 was more complete. This is consistent with the test results of the unconfined compressive strength.

[0064] In addition, to study the specific surface area and pore properties of the consolidated road subbase material, N2-isothermal adsorption-desorption tests were conducted on the dried and ground deep riverbed sludge samples and the consolidated road subbase material samples after compressive strength tests (the samples with significant differences in strength and composition were selected from Example 6 (cured for 28 days), Example 2 (cured for 28 days), and Example 2 (cured for 7 days). The adsorption-desorption isotherms of the deep riverbed sludge road subbase material are shown below. Figure 3As shown in Table 3, the pore structure parameters are as follows. The experiment used a Micromeritics ASAP 2460 multi-station fully automated specific surface area and pore size analyzer (USA). The specific surface area analysis range was above 0.01 m² / g, the pore size distribution analysis range was 0.4 nm-200 nm, and the degassing temperature was 50℃-350℃.

[0065] Table 3 Pore structure parameters of road subbase materials

[0066]

[0067]

[0068] Through analysis Figure 3 According to the isotherm classification published by the International Union of Pure and Applied Chemistry (IUPAC), both the original riverbed sludge sample and the solidified material belong to Type IV isotherms. At low relative pressures (P / P0), the adsorption and desorption curves coincide. When the relative pressure reaches 0.4, they separate, with the desorption process significantly lagging behind the adsorption process until the adsorption capacity reaches its peak. This indicates that both the riverbed sludge and the solidified material undergo multilayer adsorption processes. The adsorption process generates significant interaction forces, and near adsorption saturation, capillary aggregation occurs, resulting in a significant and sharp increase in adsorption capacity at higher relative pressures.

[0069] Pore ​​volume-pore size distribution curves before and after curing are as follows: Figure 4 As shown, the maximum pore diameter of the riverbed sludge is around 50 nm. However, after incorporating construction waste and cementing materials, the maximum pore diameter increases to over 100 nm, which is consistent with the isotherm analysis. When the cementing materials react with the riverbed sludge, the particle lattice and mineral structure change significantly, and the pore blockage becomes increasingly apparent, resulting in an overall increase in the number of pores. Due to the heat of the chemical reaction, the hydration curing process releases some gas, thereby expanding the pore volume and leading to an overall increase in pore volume. Furthermore, the degree of hydration reaction also determines the pore development. The pore structure distribution of the sample in Example 6 is significantly different from that in Example 2, with a lower proportion of mesopores and a higher proportion of micropores, which is due to incomplete reaction.

[0070] In Example 2, the average porosity and total pore volume after 28 days of curing increased by 33.34% and 96.12% respectively compared to the riverbed sludge, showing a significant upward trend as the curing reaction progressed, resulting in a more rational and optimized pore structure distribution. Furthermore, the specific surface area also increased with the progress of the curing reaction. This is because the surface of the riverbed sludge is relatively smooth, which is one of the reasons for its lower compressive strength. The curing process generates amorphous materials that fill the pores. In addition, the high roughness of the construction waste particles and pore surfaces promotes the increase in specific surface area. The increase in curing age also leads to an increase in specific surface area; the specific surface area of ​​the Example 2 sample after 28 days increased by 16.19% compared to after 7 days.

[0071] To further determine the hydration reaction products and clarify the formation of new minerals during the reaction process, photoelectron spectroscopy was performed on the samples from Example 2 that had been cured for 28 days. The mineral phase formation was analyzed based on key elements Si, Al, and Ca. The results are as follows: Figure 5 As shown. In the experiment, the Axis Ultra DLD Kratos AXIS SUPRA instrument from the UK was used to analyze the relationship between the relative pulse intensity and the photoelectron kinetic energy of the sample. The experimental results were used to determine the binding energy variation by peak segmentation using Thermo Avantage software. The elements detected in the experiment were Si 2p and Al 2p.

[0072] analyze Figure 5 It can be seen that the photoelectron spectrum curves fluctuate significantly under different binding energy conditions, with Si and Al showing more pronounced fluctuations. This is because the solidified material is a multiphase material, and the influence of different chemical bond structures causes fluctuations in peak intensity. However, after fitting and peak separation, the characteristic peak values ​​can still be clearly seen.

[0073] After the solidification reaction, the individual SiO2 and Al2O3 structures in the riverbed silt underwent significant changes, with structural reorganization of the Si-Al-Ca-O bonds following physicochemical reactions. A new substance, SiO2(Al2O3)2.1, was generated at a Si 2p binding energy of 102.50 eV. This was essentially due to the breaking and reorganization of silicon-oxygen bonds with the green sample, forming a new stable Si-Al-O structural system. Similarly, SiO2(Al2O3)0.55 was generated at an Al 2p binding energy of 74.50 eV. Its structure is similar to Si 2p, both representing new substances formed by the combination of silicon-oxygen and aluminum-oxygen structures in different proportions.

[0074] Davidovits' analysis shows that in the alkaline environment provided by the cementing material, the structural chemical bonds break and the coordination number of silicon and aluminum changes. Silicon-oxygen and aluminum-oxygen structures can typically form tetrahedra, existing in the system as SiO2(Al2O3)x. At this point, the binding energy range of Si 2p is 102.00–102.60 eV, and the binding energy range of Al 2p is 74.10–74.60 eV, both consistent with the results obtained in this experiment. This indicates that after solidification, the riverbed sludge forms a more stable amorphous three-dimensional network structure. The Ca 2p results also show that CaSiO3 and CaCO3 are generated at binding energies of 347.04 eV and 347.70 eV, respectively. This is consistent with the formation of calcium-based zeolites in the mineral structure, confirming that in addition to stabilizing the silicon-aluminum system, CSH gel substances also exist in the material, further strengthening the structure and improving the overall stability of the material.

[0075] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A roadbed material prepared by improved riverbed silt suction, characterized in that: The raw materials, by percentage, include: riverbed sludge: 28.6%~31.4%, water: 9.6%~12.3%, construction waste: 53.2%~56.8%, and curing agent: 13.03-16.99%; the curing agent is composed of 8.7%~10.2% blast furnace slag, 1.95%~3.9% coal ash, 2.1%~2.55% alkali activator, and 0.28%-0.34% activator; the activator is composed of sodium acetate and sodium lignosulfonate in a mass ratio of 1:

1. The mud suction from the riverbed refers to the mud suction generated during the air suction construction process of sinking caissons in bridge construction. The method for preparing the roadbed material. Includes the following steps, S1. Dry the mud sucked from the riverbed and let it air dry naturally until the moisture content is below 15%; S2. Add the riverbed sludge, construction waste, solidifying agent and water to the mixer in sequence and mix evenly to obtain the mixture. Control the moisture content of the mixture to 12% by adding water externally, and continue to speed up the mixing to obtain the roadbed material.

2. The roadbed material prepared by improved riverbed siltation as described in claim 1, characterized in that: The roadbed material is sealed and stored for 24-48 hours to allow moisture to be evenly dispersed in the mixture.

3. The roadbed material prepared by improved riverbed sludge suction as described in claim 2, characterized in that: In step S2, the mixture is first stirred at 55-65 r / min for 10-15 minutes; after adding external water, the speed is increased to 110-130 r / min and stirred for 1-3 minutes.

4. The roadbed material prepared by improved riverbed sludge suction as described in claim 3, characterized in that: The roadbed material is formed under high pressure with a molding pressure of 160kN and a pressing rate of 5-7kN, and then left to stand for 1-5 minutes to reduce the possibility of springback of the solidified body.

5. The roadbed material prepared by improved riverbed siltation as described in claim 4, characterized in that: After the roadbed material is pressed into shape, it is cured for 25-30 days using a normal temperature and natural moisture-retaining curing process. The curing conditions are 18-22 degrees Celsius and relative humidity greater than 90%.

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