Modified counterweight steel aggregate as well as preparation method and application thereof

Abstract

The invention belongs to the field of building materials, and particularly relates to a modified counterweight steel aggregate and a preparation method and application thereof.The modified counterweight steel aggregate comprises a steel shot serving as a core medium and a modified layer arranged outside the steel shot, the modified layer is prepared by rolling and coating the outer side of the steel shot with a powder material, and the thickness of the modified layer is 1-2 mm. According to the invention, the surface roughness of the aggregate is increased by bonding the powder particles with different sizes on the surfaces of the steel shots, so that the compatibility and bonding effect of the counterweight steel aggregate and a concrete interface can be effectively improved, the adhesion of a gel product is facilitated, and the blocking force of aggregate sinking is increased; the sinking problem of the steel aggregate in newly poured concrete is effectively inhibited, the workability of a concrete mixture is improved, and the segregation risk is reduced. The characteristics that the surfaces of the steel shots are smooth and do not absorb water are improved, and the situation that due to the existence of the steel shots in a system, more water is used for hydration or serves as free water, an interface transition area is fragile, and the strength of prepared concrete is reduced is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly to a modified weighted steel aggregate, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of nuclear power concrete engineering, in order to enable concrete to have strong shielding ability against γ-rays, X-rays, and neutron radiation, improving the apparent density of concrete to absorb and attenuate these rays is an important means to enhance the radiation protection performance. Therefore, the high apparent density and other technical requirements of radiation protection concrete result in certain differences in raw material selection compared with ordinary concrete.

[0003] Since the density of steel materials is much greater than that of natural mineral materials, using spherical steel shots (apparent density of 7200 - 8000 kg / m 3 ) as a weighting material is an important technical means to increase the apparent density of radiation protection concrete. It has a very significant effect on improving the density of radiation protection concrete and also has a high cost performance. On the other hand, due to its spherical particle shape, steel shots can play a rolling effect in the system, and the workability of high apparent density concrete mixtures can also be improved to a certain extent. Therefore, if it is necessary to ensure that radiation protection concrete has a sufficiently high density and excellent workability and even meets the requirements of self-compacting, adding a certain amount of steel shots as fine aggregate has a significant effect. The patent "A Premixed Pumpable Heavy Concrete with High Apparent Density and Its Preparation Method" introduces the preparation of heavy concrete using steel shots with different gradations, and overweight concrete with a density of 4400 kg / m 3 can be prepared, and the density is highly designable.

[0004] Steel shots can significantly increase the apparent density of concrete, but there are also certain problems: First, the interface of steel shots is smoother and does not absorb water compared with natural aggregates. Under the premise of the same water-binder ratio, more water can be free water, and concrete is more likely to have risks of segregation and bleeding. This will also lead to insufficient interfacial bonding force between it and cement mortar, weakening the interfacial transition zone of concrete, and thus affecting the overall mechanical properties of concrete; at the same time, under the action of its own gravity, smooth steel shots will increase the settlement risk during the concrete pouring process, and density unevenness will occur after the concrete hardens and forms. Based on the above problems, it is of great significance to develop a modified steel shot. This material can not only keep the high apparent density of concrete but also avoid problems of stratification and segregation caused by too large a density difference between steel materials and other materials.

[0005] The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The first object of the present invention is to provide a modified weighted steel aggregate. After modification, the aggregate can greatly improve its interfacial bonding force with the cement mortar layer, effectively improve the workability of the concrete mixture, and reduce the segregation and bleeding risks caused by the excessive density difference between various materials. The involved preparation method is simple and convenient to operate, and is suitable for popularization.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A modified weighted steel aggregate includes steel shots as the core medium and a modified layer provided outside the steel shots. The modified layer is obtained by rolling and coating powder materials on the outside of the steel shots, and the thickness of the modified layer is 1 - 2 mm.

[0009] The reason for using the modified layer to wrap the steel shots to form a core - shell structure is mainly aimed at the interface problem and settlement problem of ordinary steel shots: (1) Through the interface modifier and hydration reaction, the bonding force between the cement - based shell layer and the steel shots is enhanced, and at the same time, the adhesiveness between the steel shots and the surrounding mortar and hydration product gel is improved; (2) By the surface roughness and interfacial affinity of the modified layer, the frictional resistance with the slurry is increased, and combined with the high - density core of the steel shots, a more uniform density gradient is formed, thereby slowing down the sinking trend.

[0010] The steel shots themselves do not have radiation - proof performance. Their main purpose in the system is to provide weight. Although the density of the modified weighted steel aggregate formed after wrapping the modified layer will decrease, the degree of decrease is small. At the same time, a certain degree of decrease can make the overall density of the concrete more uniform, form a better density gradient, and avoid excessive density difference between various materials, resulting in concrete stratification.

[0011] In the present invention, the wrapping of the modified layer will improve the interfacial bonding problem between the modified weighted steel aggregate and the concrete slurry compared with ordinary steel shots. The modified layer is formed by coating with cement - based powder materials, which can undergo hydration reactions during the hardening process of the concrete and form a strong interfacial bond with the surrounding cement slurry; it increases the mechanical biting force and chemical bonding force between the modified weighted steel aggregate and the concrete matrix. Compared with the untreated steel shots, the spherical particle size of the modified weighted steel aggregate in the present invention is uniform, improving the characteristics of the smooth and non - water - absorbing surface of the steel shots, solving the problem that more water in the system is used for hydration or acts as free water due to the presence of the steel shots, resulting in more Ca(OH) 2 formed at the interface between the steel shots and the cement stone, and widening the interfacial transition zone, resulting in the weakness of the interfacial transition zone and the decrease in the strength of the prepared concrete. At the same time, after the concrete hardens, the modified weighted steel aggregate is firmly embedded in the matrix, reducing micro - defects and improving the overall mechanical properties and durability of the concrete.

[0012] The second object of the present invention is to provide a preparation method of the modified weighted steel aggregate, which has the same technical effects.

[0013] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0014] A preparation method of modified weight steel aggregate, comprising the following operating steps:

[0015] S01 Place steel shots with a diameter range of 0.5 - 5 mm into a polishing device for precision polishing pretreatment; then clean the polished steel spheres, specifically using ultrasonic cleaning or rinsing with deionized water and drying for standby;

[0016] During the polishing process of the steel shots, through dynamic contact with the workpiece surface, the surface roughness is reduced and the specific surface area is increased, thereby optimizing the surface characteristics of the material.

[0017] Preferably, a drum - type polishing machine or a vibratory polishing machine is selected, abrasives with a particle size of 60 - 400 mesh are used, the ratio of steel shots to abrasives is 1:2 - 3, and deionized water or a water - based polishing liquid is added. The surface roughness (Ra) of the steel shots is polished to reach 0.2 - 0.5 μm, ensuring that the interface modifier can adhere to the surface and the surface is not too smooth to cause a decrease in bonding force.

[0018] Specifically, in the rough grinding stage, abrasives with a larger particle size (such as 60 - 120 mesh) are used. Utilizing the stronger cutting force of the abrasives, surface defects and impurities are quickly removed, and the time is controlled within 20 - 30 min to remove large surface unevenness and impurities. In the fine grinding stage, abrasives with a finer particle size (such as 200 - 400 mesh) are used to further improve the surface flatness through a smaller cutting effect, and the time is controlled within 30 - 60 min to make the surface roughness reach the micron level.

[0019] Preferably, the abrasive is one or more of alumina powder, silicon carbide powder, or ceramic microparticles. Alumina powder and ceramic microparticles have moderate hardness, little impact on the microscopic morphology of the steel shots, and will not cause excessive cutting; silicon carbide powder has a higher hardness but has good self - sharpening properties, can maintain grinding sharpness, and reduce secondary damage of the abrasives to the steel shots; by controlling the particle size range of the abrasives (60 - 400 mesh), surface treatment from rough grinding to fine grinding can be gradually achieved, ensuring both surface flatness and smoothness of the steel shots.

[0020] S02 Modify the pretreated steel shots with an interface modifier, and wait for uniform dispersion before standby; among them, the interface modifier is a silane coupling agent, which can form active groups on the surface of the steel shots and enhance the interfacial bonding force between the steel shots and inorganic powders.

[0021] Preferably, the modification includes the following steps:

[0022] (1) Preparation of interface modifier solution: Add silane coupling agent (such as KH-550, KH-570) to deionized water or ethanol solution at a mass fraction of 0.5% to 2%, and stir to form a transparent solution; adjust the pH value of the solution to 4 to 5 to facilitate the hydrolysis of the coupling agent and the formation of active groups, and add surfactant to enhance uniformity; the dosage of surfactant is 0.1% to 0.3%, which can further reduce the surface tension and help the solution to adhere evenly to the surface of the steel shot;

[0023] (2) Interface modification of steel shot: The steel shot after polishing pretreatment is completely immersed in the interface modifier solution, and the immersion time is controlled to be 10 to 20 minutes to ensure that the modifier is evenly attached to the surface of the steel shot; the steel shot treated with the modifier is taken out of the solution and dried: the temperature is controlled at 60 to 80 ° C; the time is 30 to 60 minutes to ensure that the modifier is fully solidified on the surface of the steel shot and forms a stable coating. The surface of the steel shot after drying is uniform and slightly rough, which is conducive to the subsequent combination of powder materials.

[0024] During the process, the silane coupling agent is hydrolyzed under weakly acidic conditions to generate active groups, silanol groups (Si-OH), which undergo condensation reactions with hydroxyl groups (-OH) on the surface of the polished steel shots to form chemical bonds (Si-O-Si), allowing the modifier to adhere evenly and exist stably. At the drying temperature, the modifier is further cured to eventually form a dense, uniform, slightly rough and stable coating.

[0025] S03 mixes the powder materials evenly according to the proportion, and then puts them into the ball forming machine together with the interface modified steel shot. The ball forming machine makes the powder materials evenly adhere and coat the surface of the steel shot layer by layer through rolling, friction and impact, and rolls into balls. During this period, water is sprayed to provide the necessary wettability and adhesion to ensure that the powder is gradually formed during the rolling process.

[0026] Preferably, in step S03, the powder material includes 40-60 parts of cement, 20-35 parts of fly ash, 10-31 parts of silica fume and 0-5 parts of gypsum by weight. The above powder material is placed in a mixer and stirred for 5-10 minutes until the material is evenly distributed and there is no obvious agglomeration. A small amount of dispersant or water reducer can also be added to improve the fluidity of the powder. After mixing evenly, it is placed in a ball forming machine together with steel shots. The powder material and the surface of the steel shot after interface modification undergo mechanical bite and physical adhesion; the water activates the cement-based material in the powder during the rolling process to form a preliminary bonding layer; the presence of the interface modifier further enhances the bonding force between the powder and the steel shot to prevent the coating from falling off.

[0027] Preferably, in step S03, the mass ratio of the powder material to the steel shot is 1-2:1. The water is evenly sprayed using a micro-atomizing nozzle, and the water content is controlled at 5%-10% of the mass of the powder material to avoid the influence of excessive moisture on the ball forming strength.

[0028] Preferably, the rotation speed of the ball forming machine is 15-25 revolutions per minute, and the ball forming time is 10-20 minutes. The prepared modified weighted steel aggregate has uniform appearance dimensions and no obvious deviation of being too large or too small; the powder coating layer is dense and stable, improving the apparent density and compressive performance of the aggregate.

[0029] S04 Place the formed weighted steel aggregate in a concrete curing room and cure it for 7-14 days under standard conditions (20±2°C, humidity≥95%) to obtain the modified weighted steel aggregate.

[0030] Preferably, in step S04, the balled aggregate is placed in a ventilated environment and naturally cured for 2-4 hours, and then transported to the concrete curing room for curing for 7 days.

[0031] The third object of the present invention is to provide an application method of the modified weighted steel aggregate, which is used for weighting in self-compacting concrete, significantly improving the apparent density of the self-compacting concrete.

[0032] In order to achieve the above object, the technical solution adopted by the present invention is:

[0033] Prepare self-compacting concrete with the modified weighted steel aggregate prepared by the above method. By mass, the self-compacting concrete includes 270-300 parts of cement, 60-80 parts of Class I fly ash, 80-100 parts of S95 slag powder, 1100-1300 parts of fine sand, 1100-1300 parts of crushed stone, 450-550 parts of modified weighted steel aggregate, 160-180 parts of water, and 3-5 parts of admixture.

[0034] Preferably, ordinary Portland cement (such as P.O 42.5, P.O 52.5) is selected as the cement to provide gelling properties and strength; fine sand is used as fine aggregate, preferably medium-fine sand, specifically with a fineness modulus of 2.3-2.6 and an apparent density of 4600-4800 kg / m 3 of iron ore to ensure the workability of the concrete; crushed stone is used as coarse aggregate, with a particle size of 5-20 mm, good gradation, and an apparent density of 4600-4800 kg / m 3 of iron ore to play a role in skeleton support; the admixture is preferably a high-performance water reducer (such as polycarboxylate water reducer) to improve the fluidity and strength performance of the concrete.

[0035] The preparation method of the self-compacting concrete is:

[0036] Put cement, fine aggregate, coarse aggregate and modified heavyweight steel aggregate into a mixer in proportion and stir at a low speed for 0.5 - 1 min to preliminarily mix all solid materials evenly.

[0037] On the basis of uniform dry mixing, gradually add water and admixtures; increase the stirring speed and continue to stir for 2.5 - 4 min to make the concrete mixture reach a uniform state;

[0038] Pour the concrete mixture and use a vibrator to vibrate it to remove the air bubbles in the concrete and ensure its compactness;

[0039] Cover the surface of the poured concrete with a wet cloth or plastic film and cure it for 7 - 14 days under standard conditions (20 ± 2°C, humidity ≥ 95%) to make the concrete reach the design strength requirements.

[0040] Beneficial effects

[0041] (1) The modified materials are substances with strong activity such as cement and fly ash. By coating the steel shot aggregate with a core - shell structure, it not only makes it present a more uniform and regular spherical particle shape, improves the performance of the concrete mixture, but also significantly increases the interfacial bonding force with cement mortar and hydration product gel. At the same time, the modification treatment reduces the apparent density of the steel shot, effectively alleviating the segregation and bleeding problems caused by the too high density of heavy concrete. This preparation method is simple and easy to operate, and has good popularization and application value.

[0042] (2) During the modification process, the smaller - sized steel shot aggregate can effectively adhere to the raw material particles in different hydration states through continuous rolling, forming an apparently dense modified layer. This structure is not only beneficial to the attachment of C - S - H gel, but also improves the microscopic structure of the concrete interfacial transition zone, thus significantly enhancing the overall strength of the concrete.

[0043] (3) In the present invention, powder particles of different sizes are bonded to the surface of the steel shot, effectively increasing the roughness of the aggregate surface. This design can significantly increase the resistance to the sinking of the aggregate, thereby reducing the risk of the steel aggregate sinking in the fresh concrete. Specific embodiments

[0044] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, for a modified heavyweight steel aggregate and its preparation method and application provided according to the present invention, its specific embodiments, features and effects are described in detail as follows.

[0045] Sources of raw materials used in the examples:

[0046] Table 1

[0047] Components Commercial sources steel shot Wuhan Shanganyuan Building System Engineering Co., Ltd. Silane coupling agent Nanjing Shuguang Chemical Group Co., Ltd. Ethanol Nanyang Tianguan Group Co., Ltd. Surfactants Jianyan Building Materials Co., Ltd. PO 42.5 cement Beijing BBMG Group Co., Ltd. Fly ash Wuhan Yuanjin Building Materials Technology Co., Ltd. Mineral powder Wuhan Yuanjin Building Materials Technology Co., Ltd. Iron ore aggregate Lingshou County Huida Mineral Products Processing Factory Polycarboxylate water reducer Jiangsu Subote New Materials Co., Ltd.

[0048] Example 1

[0049] A modified counterweight steel aggregate includes steel shots as the core medium and a modified layer provided outside the steel shots. The modified layer is obtained by rolling and coating powder materials on the outside of the steel shots, and the thickness of the modified layer is 1 - 2 mm.

[0050] A preparation method of a modified counterweight steel aggregate includes the following operating steps:

[0051] S01 Place steel shots with a diameter range of 0.5 - 5 mm into a vibratory polishing machine for precision polishing pretreatment; use alumina powder abrasive with a particle size of 100 mesh, and the ratio of steel shots to abrasive is 1:3, and add deionized water or a water-based polishing liquid, polish until the surface roughness (Ra) of the steel shots reaches 0.2 μm, then clean the polished steel spheres, using ultrasonic cleaning or rinsing with deionized water, and dry for standby;

[0052] S02 Add KH-550 to an ethanol solution at a mass fraction of 0.5%, stir evenly to form a transparent solution; adjust the pH value of the solution to 4 - 5, add 0.1% surfactant to enhance uniformity; then completely immerse the polished and pretreated steel shots in the interfacial modifier solution, control the soaking time to 15 min to ensure uniform attachment of the modifier on the surface of the steel shots; take out the steel shots treated with the modifier from the solution and dry: control the temperature at 60°C; the time is 60 min to ensure that the modifier is fully cured on the surface of the steel shots and forms a stable coating;

[0053] S03 Weigh 45 parts of cement, 30 parts of fly ash, 20 parts of silica fume, and 5 parts of gypsum by mass, place them in a mixer and stir for 10 min until the materials are evenly distributed and there is no obvious agglomeration phenomenon, then put them into a pelletizer together with the steel shots modified by the interface at a mass ratio of 1 - 2:1, use a microatomizing nozzle to spray water evenly, and control the water content to 5% of the mass of the powder materials. Through the rolling, friction, and impact of the pelletizer, the powder materials are evenly attached and gradually coated on the surface of the steel shots to form balls by rolling. The rotation speed of the pelletizer is 25 revolutions / min, and the ball-forming time is 20 min.

[0054] S04 Place the ball-formed aggregate in a ventilated environment for natural curing for 12 hours, then move it to a concrete curing chamber and cure it for 7 days under standard conditions (20 ± 2°C, humidity ≥ 95%) to obtain the modified counterweight steel aggregate A.

[0055] Example 2

[0056] A modified counterweight steel aggregate includes steel shots as the core medium and a modified layer provided outside the steel shots. The modified layer is obtained by rolling and coating powder materials on the outside of the steel shots, and the thickness of the modified layer is 1 - 2 mm.

[0057] A preparation method of modified counterweight steel aggregate, comprising the following operating steps:

[0058] S01 Place steel shots with a diameter range of 0.5 - 5 mm into a vibratory polishing machine for precision polishing pretreatment; use alumina powder abrasive with a particle size of 200 mesh, with a ratio of steel shots to abrasive of 1:3, and add deionized water or water-based polishing liquid, polish until the surface roughness (Ra) of the steel shots reaches 0.5 μm, then clean the polished steel spheres, using ultrasonic cleaning or rinsing with deionized water, and dry for standby;

[0059] S02 Add KH-550 to an ethanol solution at a ratio of 1% by mass fraction, stir evenly to form a transparent solution; adjust the pH value of the solution to 4 - 5, add 0.3% surfactant to enhance uniformity; then completely immerse the polished and pretreated steel shots in the interfacial modifier solution, control the soaking time to 20 min to ensure uniform attachment of the modifier on the surface of the steel shots; take out the steel shots treated with the modifier from the solution and dry: control the temperature at 60 °C; the time is 60 min to ensure full curing of the modifier on the surface of the steel shots and form a stable coating;

[0060] S03 Weigh 50 parts of cement, 25 parts of fly ash, 20 parts of silica fume, and 5 parts of gypsum by mass, place them in a mixer and stir for 10 min until the materials are evenly distributed and there is no obvious agglomeration phenomenon, then put them into a pelletizer together with the steel shots after interfacial modification according to a mass ratio of 1 - 2:1, use a micro-atomizing nozzle to spray water evenly, control the water content to 5% of the mass of the powder material, and through the rolling, friction and impact of the pelletizer, make the powder material evenly adhere and coat layer by layer on the surface of the steel shots, and roll into balls. The rotation speed of the pelletizer is 25 revolutions / min, and the ball-forming time is 20 min.

[0061] S04 Place the ball-formed aggregate in a ventilated environment for natural curing for 12 hours, then transport it to a concrete curing room and cure it for 7 days under standard conditions (20 ± 2 °C, humidity ≥ 95%) to obtain modified counterweight steel aggregate B.

[0062] Example 3

[0063] A modified counterweight steel aggregate, comprising steel shots as the core medium and a modified layer provided outside the steel shots. The modified layer is obtained by rolling and coating powder materials on the outside of the steel shots, and the thickness of the modified layer is 1 - 2 mm.

[0064] A preparation method of modified counterweight steel aggregate, comprising the following operating steps:

[0065] S01 Place steel shots with a diameter range of 0.5 - 5 mm into a vibratory polishing machine for precision polishing pretreatment; use alumina powder abrasive with a particle size of 100 mesh, with a ratio of steel shots to abrasive of 1:3, and add deionized water or water-based polishing liquid, polish until the surface roughness (Ra) of the steel shots reaches 0.2 μm, then clean the polished steel spheres, using ultrasonic cleaning or rinsing with deionized water, and dry for standby;

[0066] S02 Add KH-550 to an ethanol solution at a mass fraction of 2%, stir evenly to form a transparent solution; adjust the pH value of the solution to 4 - 5, add 0.1% surfactant to enhance uniformity; then completely immerse the steel shots after polishing pretreatment in the interface modifier solution, control the soaking time to 15 min to ensure uniform adhesion of the modifier on the surface of the steel shots; take out the steel shots treated with the modifier from the solution and dry: control the temperature at 60 °C; the time is 60 min to ensure that the modifier is fully cured on the surface of the steel shots and forms a stable coating;

[0067] S03 Weigh 55 parts of cement, 20 parts of fly ash, 30 parts of silica fume and 5 parts of gypsum by mass, place them in a mixer and stir for 10 min until the materials are evenly distributed and there is no obvious agglomeration phenomenon, then put them into a pelletizer together with the steel shots after interface modification according to a mass ratio of 1 - 2:1, use a micro-atomizing nozzle to spray water evenly, and control the water content to 5% of the mass of the powder material. Through the rolling, friction and impact of the pelletizer, the powder material is evenly attached and gradually coated on the surface of the steel shots to form balls by rolling. The rotation speed of the pelletizer is 25 revolutions / min, and the ball-forming time is 20 min.

[0068] S04 Place the ball-formed aggregate in a ventilated environment for natural curing for 12 hours, then transport it to a concrete curing room and cure it for 7 days under standard conditions (20 ± 2 °C, humidity ≥ 95%) to obtain the modified weighted steel aggregate C.

[0069] Example 4

[0070] A modified weighted steel aggregate, comprising steel shots as the core medium, and a modified layer provided outside the steel shots. The modified layer is obtained by rolling and coating powder materials on the outside of the steel shots, and the thickness of the modified layer is 1 - 2 mm.

[0071] A preparation method of a modified weighted steel aggregate, comprising the following operation steps:

[0072] S01 Place steel shots with a diameter range of 0.5 - 5 mm into a vibratory polishing machine for precision polishing pretreatment; use alumina powder abrasive with a particle size of 60 mesh, with a ratio of steel shots to abrasive of 1:3, and add deionized water or water-based polishing liquid. Polish until the surface roughness (Ra) of the steel shots reaches 0.2 μm, then clean the polished steel spheres, using ultrasonic cleaning or rinsing with deionized water, and dry for standby;

[0073] S02 Add KH-570 to an ethanol solution at a mass fraction of 2%, stir evenly to form a transparent solution; adjust the pH value of the solution to 4 - 5, and add 0.1% surfactant to enhance uniformity; then completely immerse the polished and pretreated steel shots in the interfacial modifier solution, control the soaking time to 45 min to ensure uniform attachment of the modifier on the surface of the steel shots; take out the steel shots treated with the modifier from the solution for drying: control the temperature at 60 °C; the time is 60 min to ensure that the modifier is fully cured on the surface of the steel shots and forms a stable coating;

[0074] S03 Weigh 60 parts of cement, 20 parts of fly ash, 15 parts of silica fume, and 5 parts of gypsum by mass, place them in a mixer and stir for 10 min until the materials are evenly distributed and there is no obvious agglomeration phenomenon, then put them into a pelletizer together with the steel shots after interfacial modification according to a mass ratio of 1 - 2:1. Use a micro-atomizing nozzle to spray water evenly, with the water content controlled at 5% of the mass of the powder material. Through the rolling, friction, and impact of the pelletizer, the powder material is evenly attached and gradually coated on the surface of the steel shots to form balls by rolling. The rotation speed of the pelletizer is 25 revolutions / min, and the ball-forming time is 20 min.

[0075] S04 Place the ball-formed aggregate in a ventilated environment for natural curing for 12 hours, then move it to a concrete curing room and cure it for 7 days under standard conditions (20 ± 2 °C, humidity ≥ 95%) to obtain the modified weight steel aggregate D.

[0076] Comparative Example 1

[0077] In this comparative example, weight steel aggregate E is prepared using steel shots with a diameter of 0.5 - 5 mm without any treatment, and the remaining steps are the same as those in Example 1, which will not be elaborated here.

[0078] Comparative Example 2

[0079] In this comparative example, the difference from Example 1 is that the S02 modification treatment is not carried out, that is, after the steel shots are polished, they are directly mixed with the powder material to obtain weight steel aggregate F, and the remaining steps are the same as those in Example 1, which will not be elaborated here.

[0080] Performance Test

[0081] The C30 concrete is prepared with the modified counterweight steel aggregate prepared by the above method. The concrete includes 280 parts of P.O 42.5 cement, 70 parts of Class I fly ash, 90 parts of S95 blast furnace slag powder, 1100 parts of fine sand, 1010 parts of crushed stone, 550 parts of modified counterweight steel aggregate, 170 parts of water and 5 - 8 parts of polycarboxylate water reducer. Among them, both the fine sand and the crushed stone have an apparent density of 4600 - 4800 kg / m 3 iron ore aggregate.

[0082] Put the cement, fly ash, blast furnace slag powder, fine aggregate, coarse aggregate and modified counterweight steel aggregate into a mixer in proportion and stir at low speed for 1 - 2 min to preliminarily mix all solid materials evenly; on the basis of uniform dry mixing, gradually add water and admixtures; increase the stirring speed and continue to stir for 3 - 5 min to make the concrete mixture reach a uniform state; pour the concrete mixture into a mold and vibrate it with a vibrating table for 10 s to remove the air bubbles in the concrete and ensure compactness; cover the surface of the poured concrete with a plastic film and move it into a standard curing room (20 ± 2°C, humidity ≥ 95%) for curing for 28 days, and then test its compressive strength.

[0083] Compressive strength: Refer to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" to detect the 28-day compressive strength of the C30 radiation-proof heavy concrete in Examples 1 - 4 and Comparative Examples 1 - 2, and record the results in Table 2.

[0084] Fluidity: Refer to JGJ / T 283-2012 "Technical Specification for Application of Self-Compacting Concrete" to detect the slump flow and spread time of the C30 radiation-proof heavy concrete in Examples 1 - 4 and Comparative Examples 1 - 2, and record the results in Table 2. Segregation resistance: Refer to JGJ / T 283-2012 "Technical Specification for Application of Self-Compacting Concrete" to detect the segregation rate of the C30 radiation-proof heavy concrete mixture in Examples 1 - 4 and Comparative Examples 1 - 2, and record the results in Table 2.

[0085] Table 2

[0086]

[0087] The results of the above examples and comparative examples show that the decrease in the apparent density of the modified heavyweight steel aggregate obtained by the present invention is not significant when formulating self-compacting concrete, and the concrete can maintain a relatively high compressive strength at the age of 28 days. This is due to the powder material attached to the surface of the modified heavyweight steel aggregate. Firstly, the surface of the aggregate is rougher than that of the unmodified steel shot, which is beneficial to the attachment and encapsulation of the cement stone and hydration products such as C-S-H gel. In addition, the active powder materials (such as cement and fly ash) on the surface will also undergo a secondary hydration reaction during the concrete curing process, generating a small amount of calcium silicate hydrate (C-S-H) gel and calcium aluminosilicate hydrate (C-A-S-H) gel, which are cemented and nested with the original cement hydration products, forming a more stable interfacial transition zone, thus greatly improving the strength.

[0088] The apparent density of the comparative example concrete is slightly higher than that of the example. In comparative example 1, unmodified steel shot is used. Due to the overly smooth surface of the steel shot and under the action of its own gravity, the flow spread of the concrete mixture is small and segregation occurs, and the self-compacting effect cannot be achieved. The use of the modified heavyweight steel aggregate can effectively improve the segregation resistance and enhance the mechanical properties of the concrete.

[0089] In comparative example 2, since no interfacial modification treatment is carried out, there is no good attachment of active powder materials on the surface of the steel shot. Its compressive strength is only slightly stronger than that of comparative example 1, but the adhesion between the steel shot and the cement stone, hydration gel products, etc. is still poor, forming more fragile interfacial transition zones of the concrete, and the compressive strength of the concrete is low.

[0090] Those skilled in the art of this industry should understand that the present invention is not limited by the above examples. What is described in the above examples and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A modified counterweight steel aggregate, characterized in that: It comprises a steel shot as a core medium and a modified layer arranged outside the steel shot, wherein the modified layer is made by rolling and coating a powder material on the outer side of the steel shot, and the thickness of the modified layer is 1-2 mm.

2. The method for preparing a modified counterweight steel aggregate according to claim 1, characterized in that: The steps are as follows: S01 Place steel shots with a diameter range of 0.5 to 5 mm into a polishing device for polishing pretreatment; S02 uses an interface modifier to modify the pre-treated steel shot and prepare it for use after it is evenly dispersed; S03: Mix the powder materials evenly according to the proportion, and then put them into the ball forming machine together with the interface modified steel shot to roll into balls, and spray water during the process to increase the adhesion between the powder materials; S04: curing the formed counterweight steel aggregate to obtain modified counterweight steel aggregate.

3. The method for preparing a modified counterweight steel aggregate according to claim 2, characterized in that: In step S01, an abrasive with a particle size of 60-400 mesh is used, the ratio of the steel shot to the abrasive is 1:2-3, and deionized water or a water-based polishing liquid is added to polish until the surface roughness of the steel shot is Ra=0.2-0.5 μm.

4. The method for preparing a modified counterweight steel aggregate according to claim 3, characterized in that: The abrasive is one or more of aluminum oxide powder, silicon carbide powder or ceramic particles.

5. The method for preparing a modified counterweight steel aggregate according to claim 2, characterized in that: Step S01 also includes: cleaning the polished steel sphere and drying it for standby use.

6. The method for preparing a modified counterweight steel aggregate according to claim 2, characterized in that: In step S02, the modification includes the following steps: (1) Add silane coupling agent in a ratio of 0.5% to 2% by mass to deionized water or ethanol solution, stir evenly to form a transparent solution; adjust the pH value of the solution to 4 to 5, and add a surfactant to obtain an interface modifier solution; (2) Immerse the steel shot after polishing pretreatment in the interface modifier solution for 10 to 20 minutes, take out the steel shot treated with the modifier from the solution and dry it at a temperature of 60 to 80 ° C for 30 to 60 minutes to ensure that the modifier is fully cured on the surface of the steel shot and forms a stable coating.

7. The method for preparing a modified counterweight steel aggregate according to claim 2, characterized in that: In step S03, the powder material includes 40-50 parts of cement, 20-30 parts of fly ash, 10-15 parts of silica fume and 0-5 parts of gypsum in terms of mass fractions.

8. The method for preparing a modified counterweight steel aggregate according to claim 7, characterized in that: In step S03, the mass ratio of the powder material to the steel shot is 1-2:1, and water is sprayed evenly using a micro-atomizing nozzle. The moisture content is controlled to be 5%-10% of the mass of the powder material. The rotation speed of the ball forming machine is 15-25 rpm, and the ball forming time is 10-20 min.

9. The method for preparing a modified counterweight steel aggregate according to claim 2, characterized in that: In step S04, the balled aggregate is placed in a ventilated environment for natural curing for 2 to 4 hours, and then placed in a concrete curing room for curing for 7 to 14 days.

10. A method for preparing self-compacting concrete using the modified counterweight steel aggregate prepared by the method according to any one of claims 2 to 9, characterized in that: Calculated by weight, the concrete includes 270-300 parts of cement, 60-80 parts of Class I fly ash, 80-100 parts of S95 mineral powder, 1100-1300 parts of fine sand, 1100-1300 parts of crushed stone, 450-550 parts of modified counterweight steel aggregate, 160-180 parts of water, and 3-5 parts of admixture.

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