Concrete doped with solid waste fibers and preparation method thereof

Abstract

The invention discloses a solid waste fiber doped concrete and a preparation method thereof, the solid waste fiber doped concrete comprises the following preparation raw materials by mass: 320-520 parts of cement, 480-1000 parts of fly ash, 100-400 parts of quartz sand, 2200-2400 parts of water, 10-30 parts of PVA fiber, 5-15 parts of a water reducer, 5-15 parts of a thickener, and 100-400 parts of a carbonized solid waste material; the carbonized solid waste material is obtained by carbonizing 50-150 parts of recycled concrete micro powder, 50-100 parts of ferronickel slag and 1-5 parts of an ether compound. The recycled concrete micro powder is carbonized, the ratio of calcite to aragonite whiskers is controlled by adjusting the ratio of recycled aggregate to ferronickel slag and the concentration of methyl ether or diethyl ether, quartz sand and PVA fibers are replaced, the surface performance of the recycled concrete micro powder is improved, and the adopted fine aggregate has the effects of protecting the environment and improving the strength of the concrete. And the method is of great significance in reducing resource waste.

Description

Technical Field

[0001] The present invention belongs to the field of concrete materials, and particularly relates to a concrete doped with solid waste fibers and a preparation method thereof. Background Art

[0002] Engineered Cementitious Composites (ECC) is a fiber-reinforced composite material based on the design principle of meso-mechanics, with cement, quartz sand, etc. as the matrix. Compared with ordinary concrete, it has high strength, high toughness, high crack resistance and high damage tolerance. The cost of PVA fibers and quartz sand in ECC concrete is relatively high. If solid waste can be used to prepare fibers to replace PVA and quartz sand, the cost can be reduced, and it is low-carbon and environmentally friendly.

[0003] Recycled concrete aggregate is processed from concrete, mortar, stones, bricks and tiles in construction (structure) waste, and is a particle used to prepare concrete, abbreviated as recycled aggregate. Among them, the part with a particle size less than 600μm is recycled concrete powder, which mainly contains cement hydration products. The use of recycled concrete powder fully meets the three meanings of "green": (1) saving resources and energy; (2) environmental friendliness; (3) sustainable development, which can not only meet the needs of contemporary people, but also not harm the ability of future generations to meet their needs. Among them, the content of old cement paste in recycled concrete powder is higher, and its water absorption is relatively stronger than that of recycled coarse aggregate. Therefore, directly applying it to concrete will have an adverse impact on the performance, so the utilization rate of recycled concrete powder is relatively low.

[0004] CN117819893A discloses a green hybrid fiber toughened iron tailing sand concrete material and a preparation method thereof. The mix ratio design of each component is by mass fraction: water: 170 parts, cement: 358 parts, fly ash: 89 parts, iron tailing sand: 624 parts, crushed stone: 1159 parts, water reducing agent: 3.6 parts, recycled tire steel fiber: 39 parts, coconut shell fiber: 2.3 parts; First, the equipment investment is large. Special treatment equipment is required for recycling steel fibers and coconut shell fibers, which increases the difficulty of the preparation process and the production cost; Secondly, the preparation process is complex. For example, the steel fibers in waste tires are tightly combined with materials such as rubber and nylon, and need to go through multiple processes such as cutting, crushing, and magnetic separation to be completely separated; In addition, the raw material supply is limited. For example, coconut shells contain more impurities such as lignin and hemicellulose, and need to be pretreated with alkali, which may cause certain pollution to the environment and increase the production cost.

[0005] With the rapid development of my country's industry, nickel production has remained at a high level, with an annual output of more than 200,000 tons. Every ton of nickel produced emits about 6-16 tons of nickel-iron slag. Because nickel-iron slag is an industrial waste, direct landfilling will cause great pressure on the environment. The main components of nickel-iron slag are silicon oxide, magnesium oxide, calcium oxide, iron oxide and aluminum oxide. Its composition is similar to that of cement, so if it can be used in concrete, the recycling of solid waste can be achieved. Summary of the invention

[0006] The present invention provides a concrete doped with solid waste fibers, wherein recycled concrete powder and nickel-iron slag are carbonized to synthesize fibers, which are applied to ECC to partially replace quartz sand and PVA fibers, thereby achieving low-carbon and environmental protection, reducing costs, and producing concrete with high ductility.

[0007] The present invention provides a concrete doped with solid waste fibers, which mainly uses carbonization to treat recycled concrete powder and nickel-iron slag to generate calcite and fibrous aragonite, which replace quartz sand and PVA fiber respectively, thereby reducing the production cost of materials, recycling solid waste, and absorbing carbon dioxide. By adding methyl ether or ethyl ether, the ratio of calcite and aragonite is controlled, thereby adjusting the mechanical properties of concrete.

[0008] The technical solution adopted by the present invention is as follows: A concrete doped with solid waste fibers, wherein the raw materials for preparation include, by weight: 320-520 parts of cement, 480-1000 parts of fly ash, 100-400 parts of quartz sand, 2200-2400 parts of water, 10-30 parts of PVA fiber, 5-15 parts of water reducer, 5-15 parts of thickener, and 100-400 parts of carbonized solid waste material; the carbonized solid waste material is obtained by carbonizing 50-150 parts of recycled concrete powder, 50-100 parts of nickel-iron slag, and 1-5 parts of ether compound.

[0009] The carbonized solid waste material is composed of calcite and aragonite whiskers, and the mass ratio of the two is (5-10):1. The concrete prepared when the ratio is 6.2~7:1 has the highest toughness. The more preferred calcite and aragonite whiskers have a ratio of 6.2:1.

[0010] The total amount of carbonized solid waste material and quartz sand in concrete is 100-400 parts, the mass ratio of carbonized solid waste material to quartz sand is 1-3:1-3, and preferably the mass ratio of carbonized solid waste material to quartz sand is 1:1.

[0011] The ether compound is at least one of methyl ether, ethyl ether, dimethyl ether or ethylene oxide.

[0012] Methyl ether or ethyl ether is preferred.

[0013] The cement is ordinary Portland cement P.O42.5; The fly ash is class I fly ash with calcium oxide content less than 10%; The particle size range of the quartz sand is 10 - 600 μm, and the average particle size is 100 - 140 μm; The PVA fiber has a length of 9 - 15 mm, a diameter of 30 - 40 μm, and a density of 1.2 - 1.4 g / cm 3 ; The water - reducing agent is a polycarboxylate - based water - reducing agent with a water - reducing efficiency of more than 20%; The thickening agent is hydroxypropyl methylcellulose; The diameter of the recycled concrete powder is less than 600 μm, and the particle size of the nickel - iron slag is 0.5 - 200 μm.

[0014] The present invention also provides a preparation method of concrete doped with solid - waste fibers, comprising the following steps: 1) Carbonization treatment of solid - waste materials: Place the solid - waste materials in water, introduce carbon dioxide, add an ether compound, stir the mixture, heat and maintain it at 60 - 90 °C, after the reaction lasts for 1 - 4 h, centrifuge the solution, take out the solid product, and dry it for standby; the solid - waste materials are recycled concrete powder and nickel - iron slag; 2) Preparation of fiber - reinforced concrete: Put the fly ash and cement into a mixer, stir them evenly at a low speed, then add water and the water - reducing agent, stir them evenly at a high speed, then add the quartz sand and carbonized solid - waste materials, stir them evenly at a low speed, then add the PVA fibers, stir at a high speed, finally add the thickening agent, stir at a high speed, finally pour into a mold, cure and demold at room temperature, and then cure in a curing room with a humidity of 95% ± 2% and a temperature of 20 °C ± 2 °C for 28 d.

[0015] In step 1), the solid - liquid ratio of the solid - waste materials to water is 50 - 100 g / L, and the mass ratio of the recycled concrete powder to the nickel - iron slag in the solid - waste materials is (1 - 3):1.

[0016] In step 1), the concentration of the ether compound is 10 - 30 mmol / L.

[0017] In step 1), the carbon dioxide ventilation volume is 0.1 - 0.3 L / min / 100 mL.

[0018] In step 2), the low - speed stirring speed is 100 - 150 revolutions per minute, and the high - speed stirring speed is 200 - 300 revolutions per minute.

[0019] More specifically, Carbonization treatment of solid waste materials: Put recycled concrete powder and nickel iron slag in water, introduce carbon dioxide, and add methyl ether or ethyl ether (concentration 10 - 30 mmol / L); stir the mixture (stirring speed 400 - 600 r / min), heat and maintain at 80 °C. After the reaction lasts for 1 - 4 h, centrifuge the solution, take out the solid product, and dry it for standby.

[0020] In the present invention, the solid waste materials generate cubic calcite and aragonite whiskers after carbonization treatment. Calcite replaces quartz sand, and aragonite replaces PVA fiber. By adjusting the ratio of recycled concrete powder to nickel iron slag and the concentration of methyl ether or ethyl ether, the ratio of the two can be controlled. The mass ratio of recycled concrete powder to nickel iron slag is (1 - 3):1; preferably, the mass ratio of recycled concrete powder to nickel iron slag is 1:1.

[0021] When the ratio of recycled concrete fine powder to nickel iron slag increases, the ratio of calcite to aragonite generated increases, and the aragonite content decreases. Therefore, the axial tensile strength and axial tensile strain decrease. Therefore, the ratio of recycled concrete fine powder to nickel iron slag is selected as 1.

[0022] During the carbonization process, adding methyl ether will affect the morphology of the generated calcium carbonate and promote the formation of aragonite. However, the higher the content of methyl ether, the more aragonite is not generated. When the methyl ether content is 10 mmol / L, the most aragonite is generated, and the axial tensile strength and strain of the prepared concrete are the highest. Therefore, the methyl ether content of 10 mmol / L is selected.

[0023] Preparation of fiber-reinforced concrete: Put fly ash and cement into a mixer, stir at a low speed (100 - 150 revolutions per minute) for 2 minutes, then add water and water reducer, stir at a high speed (200 - 300 revolutions per minute) for about two minutes, then add quartz sand and carbonized solid waste materials, stir at a low speed (100 - 150 revolutions per minute) for 2 minutes, add PVA fiber, stir at a high speed for five minutes, finally add a thickening agent, stir at a high speed (200 - 300 revolutions per minute) for five minutes, finally pour into a mold, cure at room temperature for 24 hours and then demold, and then cure in a curing room at a humidity of 95% ± 2% and a temperature of 20 °C ± 2 °C for 28 d.

[0024] Using solid waste materials such as recycled concrete powder and nickel iron slag, cubic calcite and aragonite whiskers are generated after carbonization treatment and added to ECC concrete. Calcite replaces quartz sand, and aragonite replaces PVA fiber, thereby reducing the production cost of ECC and recycling solid waste at the same time. At the same time, carbon dioxide is applied during the carbonization of solid waste materials, which can achieve the purpose of carbon reduction.

[0025] The carbonization process of recycled concrete powder and nickel-iron slag is carried out in water at 80 °C, and aragonite whiskers can be stably and continuously generated. The aragonite whiskers can replace PVA fibers. In addition, granular calcite is generated, which can replace quartz sand.

[0026] The hydration products (calcium hydroxide and C-S-H gel) in the recycled concrete powder react with carbon dioxide to form calcite calcium carbonate.

[0027]

[0028] After adding nickel-iron slag, the nickel-iron slag dissolves in water to generate magnesium ions. Under the influence of magnesium ions, the generated calcium carbonate takes the form of fibrous aragonite. Because there are two kinds of calcium carbonate in the solution, calcite replaces quartz sand and aragonite whiskers replace PVA fibers. By controlling the ratio of nickel-iron slag to recycled concrete powder and adding methyl ether and ethyl ether, the ratio of aragonite and calcite is adjusted to control the performance of concrete.

[0029] Changing the ratio of the carbonized solid product replacing quartz sand and fiber will affect the axial tensile strength and axial tensile ultimate strain of concrete. Too much or too little content of the carbonized solid product has an adverse effect on the toughness of concrete, and the axial tensile strength and axial tensile ultimate strain reach the highest when the content is 50%.

[0030] Preferably, for a kind of concrete doped with waste solid fibers, calculated by mass parts, the preparation raw materials include: 420 parts of cement, 630 parts of fly ash, 190 parts of quartz sand, 2200 - 2400 parts of water, 10 parts of PVA fiber, 10 parts of water reducing agent, 10 parts of thickening agent, 190 parts of carbonized waste material; the carbonized waste material is obtained by carbonizing 50 parts of recycled concrete powder and 50 parts of nickel-iron slag with methyl ether, and the mass ratio of calcite and aragonite whiskers in the carbonized waste material is 6.2:1.

[0031] Beneficial effects

[0032] (1) In the present invention, the recycled concrete powder is carbonized. By adjusting the ratio of recycled aggregate to nickel-iron slag and controlling the concentration of methyl ether or ethyl ether, the ratio of calcite and aragonite whiskers is controlled to replace quartz sand and PVA fibers, improving the surface performance of the recycled concrete powder and not reducing the strength of the concrete when added to the concrete. Therefore, the fine aggregate adopted in the present invention has relatively important significance for environmental protection and reducing resource waste.

[0033] (2) Low cost. The recycled concrete powder and nickel-iron slag are solid wastes, and the products generated after carbonization can replace quartz sand and PVA fibers, greatly reducing the cost while ensuring the original high toughness characteristics of ECC.

[0034] (3) During the carbonization process of solid waste, the present invention absorbs gaseous carbon dioxide to form solid products, reduces the carbon dioxide content in the atmosphere, stabilizes carbon in solid materials, and reduces the carbon emissions of concrete. Specific Embodiments

[0035] The present invention provides a concrete doped with solid waste fibers, mainly using carbonization treatment of recycled concrete powder and nickel-iron slag to generate fibrous aragonite to replace PVA fibers and generate calcite to replace quartz sand, thereby reducing the production cost of materials, recycling solid waste, and absorbing carbon dioxide at the same time.

[0036] Sources of raw materials used in the following examples: The cement is ordinary Portland cement P.O42.5 from Hunan Pingtang Southern Cement Co., Ltd. The fly ash is grade I fly ash with a calcium oxide content of less than 10% from Shandong Jining Thermal Power Plant. The particle size range of the quartz sand is 10 - 600 μm, and the average particle size is 100 - 140 μm. The PVA fiber is REC15 type PVA fiber produced by Kuraray Co., Ltd. of Japan, with a length of 9 - 15 mm, a diameter of 30 - 40 μm, and a density of 1.2 - 1.4 g / cm 3 ; The water reducing agent is Nanjing Supote SBTJM series polycarboxylate water reducing agent with a water reducing efficiency of more than 20%. The thickening agent is hydroxypropyl methyl cellulose. The recycled concrete powder is prepared by crushing and screening laboratory waste concrete; the nickel-iron slag comes from a nickel-iron smelting enterprise in Fujian Province.

[0037] Example 1 (control group) Put 630 parts of fly ash and 420 parts of cement into a mixer and stir at a low speed (120 revolutions per minute) for 2 minutes. Then add 315 parts of water and 10 parts of water reducing agent and stir at a high speed (250 revolutions per minute) for about two minutes. Then add 380 parts of quartz sand and stir at a low speed (120 revolutions per minute) for 2 minutes. Then add 20 parts of PVA fiber and stir at a high speed for five minutes. Finally, add 10 parts of thickening agent and stir at a high speed (250 revolutions per minute) for five minutes. Finally, pour into a mold, cure at room temperature for 24 hours and then demold, and then cure in a curing room with a humidity of 95% ± 2% and a temperature of 20°C ± 2°C for 28 days.

[0038] Example 2

[0039] (1)Carbonization process: Put 50 parts of recycled concrete powder and 50 parts of nickel iron slag into 2000 g of water, and introduce carbon dioxide (ventilation rate 0.2 L / min / 100 mL). Stir the mixture (stirring speed 600 r / min), heat and maintain at 80 °C. After the reaction lasts for 2 h, centrifuge the solution, take out the solid product, and dry it for standby.

[0040] The concrete preparation process includes the following steps: (2)Put 630 parts of fly ash and 420 parts of cement into a mixer, stir at a low speed (120 revolutions per minute) for 2 minutes, then add 315 parts of water and 10 parts of water reducer, stir at a high speed (250 revolutions per minute) for about two minutes, then add 190 parts of quartz sand and 190 parts of the carbonized solid product prepared in (1), stir at a low speed (120 revolutions per minute) for 2 minutes, then add 10 parts of PVA fiber, stir at a high speed for five minutes, finally add 10 parts of thickener, stir at a high speed (250 revolutions per minute) for five minutes, finally pour into a mold, cure at room temperature for 24 hours and then demold, and then cure in a curing room with a humidity of 95% ± 2% and a temperature of 20 °C ± 2 °C for 28 d.

[0041] Example 3

[0042] The carbonization process and concrete preparation process of this example are similar to those of Example 2, except that the dosages of recycled concrete powder and nickel iron slag are 66.7 parts and 33.3 parts respectively.

[0043] Example 4

[0044] The carbonization process and concrete preparation process of this example are similar to those of Example 2, except that the dosages of recycled concrete powder and nickel iron slag are 75 parts and 25 parts respectively.

[0045] Example 5

[0046] The carbonization process and concrete preparation process of this example are similar to those of Example 2, except that 10 mmol / L of methyl ether is added during the carbonization process.

[0047] Carbonization process: Put 50 parts of recycled concrete powder and 50 parts of nickel iron slag into 2000 g of water, introduce carbon dioxide (ventilation rate 0.2 L / min / 100 mL), and add methyl ether (concentration 10 mmol / L, and the methyl ether is added until the methyl ether concentration in the solution is 10 mmol / L). Stir the mixture (stirring speed 600 r / min), heat and maintain at 80 °C. After the reaction lasts for 2 h, centrifuge the solution, take out the solid product, and dry it for standby.

[0048] Example 6

[0049] The carbonization process and concrete preparation process of this example are similar to those of Example 5, except that 20 mmol / L of methyl ether is added during the carbonization process.

[0050] Example 7

[0051] The carbonization process and the concrete preparation process in this example are similar to those in Example 5, except that 30 mmol / L of methyl ether is added during the carbonization process.

[0052] Example 8

[0053] The carbonization process and the concrete preparation process in this example are similar to those in Example 5, except that 10 mmol / L of ethyl ether is added during the carbonization process.

[0054] Example 9

[0055] The carbonization process and the concrete preparation process in this example are similar to those in Example 5, except that 20 mmol / L of ethyl ether is added during the carbonization process.

[0056] Example 10

[0057] The carbonization process and the concrete preparation process in this example are similar to those in Example 5, except that 30 mmol / L of ethyl ether is added during the carbonization process.

[0058] Example 11

[0059] The carbonization process and the concrete preparation process in this example are similar to those in Example 5, except that 285 parts of quartz sand, 15 parts of PVA fiber, and 95 parts of carbonized solid product are added during the concrete preparation process.

[0060] The concrete preparation process includes the following steps: Put 630 parts of fly ash and 420 parts of cement into a mixer and stir at a low speed (120 revolutions per minute) for 2 minutes. Then add 315 parts of water and 10 parts of water reducer and stir at a high speed (250 revolutions per minute) for about two minutes. Then add 285 parts of quartz sand and 95 parts of carbonized solid product and stir at a low speed (120 revolutions per minute) for 2 minutes. Then add 15 parts of PVA fiber and stir at a high speed for five minutes. Finally, add 10 parts of thickener and stir at a high speed (250 revolutions per minute) for five minutes. Finally, pour into a mold, cure at room temperature for 24 hours and then demold, and then cure in a curing room with a humidity of 95% ± 2% and a temperature of 20°C ± 2°C for 28 days.

[0061] Example 12

[0062] The carbonization process and the concrete preparation process in this example are similar to those in Example 5, except that 95 parts of quartz sand, 5 parts of PVA fiber, and 285 parts of carbonized solid product are added during the concrete preparation process.

[0063] The content and proportion of calcite and aragonite in the carbonized solid waste products were tested by an X-ray diffractometer. According to the standard "Standard Test Methods for Physical and Mechanical Properties of Concrete" GB / T 50081-2019, the performance of the concrete materials prepared in the above examples was tested, including indexes such as axial tensile strength and axial tensile ultimate strain. The results are shown in Table 1.

[0064] Table 1

[0065] It can be seen from Examples 1, 2, 3, 4, and 5 that when the carbonized solid waste materials are used to replace quartz sand and PVA fibers, the cost is greatly reduced. When the ratio of recycled concrete fine powder to nickel iron slag increases, the ratio of calcite to aragonite generated increases, and the content of aragonite decreases. Therefore, the axial tensile strength and axial tensile strain decrease. Therefore, the ratio of recycled concrete fine powder to nickel iron slag is selected as 1.

[0066] It can be seen from Examples 2, 5, 6, and 7 that during the carbonization process, adding methyl ether will affect the morphology of the generated calcium carbonate and promote the formation of aragonite. However, the higher the content of methyl ether is not, the more aragonite is generated. When the content of methyl ether is 10 mmol / L, the most aragonite is generated, and the axial tensile strength and strain of the prepared concrete are the highest. Therefore, the methyl ether content of 10 mmol / L is selected.

[0067] It can be seen from Examples 5, 11, and 12 that changing the ratio of the carbonized solid product replacing quartz sand and fibers will affect the axial tensile strength and axial tensile ultimate strain of the concrete. Too much or too little content of the carbonized solid product has an adverse effect on the toughness of the concrete. When the content is 50%, the axial tensile strength and axial tensile ultimate strain reach the highest. Therefore, Example 5 is recommended as the optimal mix ratio.

[0068] It can be seen from Examples 5-10 that methyl ether and ethyl ether have different effects on the formation ratio and aspect ratio of calcite and aragonite. Comparatively speaking, methyl ether is more conducive to the formation of calcite, while ethyl ether is more conducive to the formation of aragonite. However, at the same time, the content of methyl ether and ethyl ether has a greater impact on the aspect ratio of aragonite. Too much or too little incorporation results in a smaller aspect ratio of the generated aragonite. This is why the ratio of calcite to aragonite in Examples 7 and 9 is the same, but the toughness of the concrete is different.

Claims

1. A concrete doped with solid waste fibers, characterized in that: Included by mass: 320-520 parts of cement, 480-1000 parts of fly ash, 100-400 parts of quartz sand, 2200-2400 parts of water, 10-30 parts of PVA fiber, 5-15 parts of water reducer, 5-15 parts of thickener, and 100-400 parts of carbonized solid waste material; the carbonized solid waste material is a mixture of calcite and aragonite whiskers obtained by carbonizing 50-150 parts of recycled concrete powder, 50-100 parts of nickel-iron slag, and 1-5 parts of ether compounds.

2. The concrete doped with solid waste fibers according to claim 1, characterized in that: The mass ratio of calcite to aragonite whiskers in the carbonized solid waste material is (5-10):

1.

3. The concrete doped with solid waste fibers according to claim 1, characterized in that: The ether compound is at least one of methyl ether, ethyl ether, dimethyl ether or ethylene oxide.

4. The concrete doped with solid waste fibers according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid water reducing agent, and the thickener is hydroxypropyl methylcellulose.

5. The concrete doped with solid waste fibers according to claim 1, characterized in that: The diameter of the recycled concrete powder is less than 600 μm, and the particle size of the nickel-iron slag is 0.5-200 μm.

6. The method for preparing concrete doped with solid waste fibers according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Carbonization treatment of solid waste materials: put the solid waste materials in water, introduce carbon dioxide, add ether compounds, stir the mixed solution, heat and maintain it at 60-90°C, continue the reaction for 1-4 hours, centrifuge the solution, take out the solid product, and dry it to obtain carbonized solid waste materials; the solid waste materials are recycled concrete powder and nickel-iron slag; 2) Preparation of fiber reinforced concrete: Put fly ash and cement into a mixer, stir at low speed to mix, then add water and water reducing agent, stir at high speed to mix, then add quartz sand and carbonized solid waste materials, stir at low speed to mix, then add PVA fiber, stir at high speed, add thickener, stir at high speed, finally cast in mold, solidify, demold and maintain at room temperature.

7. The method for preparing concrete doped with solid waste fibers according to claim 6, characterized in that: In step 1), the solid-liquid ratio of the solid waste material to water is 50-100 g / L, and the mass ratio of the recycled concrete powder to the nickel-iron slag in the solid waste material is (1-3):

1.

8. The method for preparing concrete doped with solid waste fibers according to claim 6, characterized in that: In step 1), the concentration of the ether compound is 10-30 mmol / L.

9. The method for preparing concrete doped with solid waste fibers according to claim 6, characterized in that: In step 1), the carbon dioxide ventilation volume is 0.1-0.3 L / min / 100 mL.

10. The method for preparing concrete doped with solid waste fibers according to claim 6, characterized in that: Step 2) The low-speed stirring speed is 100-150 rpm, and the high-speed stirring speed is 200-300 rpm.

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