Preparation method of environment-friendly high-performance radiation shielding concrete and product thereof

Abstract

This invention discloses a method for preparing environmentally friendly, high-performance radiation-shielding concrete. The method involves ball milling waste cathode ray tube (CRT) glass into fine CRT glass powder aggregate; immersing the waste CRT glass powder aggregate in a chemical encapsulation solution for surface strengthening treatment; mixing the surface-strengthened waste CRT glass powder aggregate, river sand fine aggregate, crushed stone coarse aggregate, cementitious materials, graphene, water, and a high-efficiency water-reducing agent to obtain fresh-mixed radiation-shielding concrete; and after demolding, subjecting the fresh-mixed radiation-shielding concrete to surface densification treatment in a carbon dioxide environment to prepare environmentally friendly, high-performance CRT glass radiation-shielding concrete. This invention achieves the resource-based recycling and reuse of waste materials. The prepared radiation-shielding concrete exhibits better workability, mechanical properties, radiation shielding effect, and lower permeability than traditional radiation-shielding concrete, has a wide range of applications, and can generate significant technical, economic, social, and environmental benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of environment-friendly, high-performance radiation shielding concrete preparation method and its product, belong to industrial waste recycling and radiation shielding material preparation field. BACKGROUND

[0002] With the progress of world industrial civilization, the environmental problems caused by traditional energy such as coal and oil have become a problem of the world. In the global trend of low-carbon economy, nuclear power technology as a new, clean and efficient energy has been paid attention by the world since its inception. As of 2010, China's nuclear power units under construction reached 2540 million kilowatts, accounting for 40% of the world's total nuclear power, and has become the largest country in the world in terms of nuclear power construction. With the continuous strengthening of people's health awareness in modern society, the development of new medical technology and the continuous emergence of new treatment methods, nuclear technology has been more and more widely used in medical research field. Nuclear technology also plays a more important role in military, agriculture, exploration and other aspects.

[0003] While enjoying the huge economic and social benefits brought by nuclear technology, nuclear safety as a key factor restricting the development of nuclear technology has also attracted more attention. Nuclear facilities and nuclear equipment will produce radioactive rays during actual operation. Long-term exposure to radioactive radiation environment will cause skin burns, hair loss, white blood cell reduction, and even cause malignant tumors, thyroid dysfunction, infertility, miscarriage and birth defects. Under long-term radioactive radiation, the genes of crops will mutate and endanger crop growth. The negative effects of radioactive rays on crops have a long incubation period and cannot be known in a short time. Radiation sources in nuclear power and medical equipment will produce fission fragments and release high energy when fission and decay occur, which will cause the instrument material to heat and reduce the performance of the measuring instrument. How to effectively shield the radioactive radiation in nuclear facilities, reduce the impact of radiation on the surrounding environment and protect the health of workers has become the focus of attention of the world.

[0004] Currently, commonly used radiation shielding materials include lead plates, steel plates, water, and radiation-shielding concrete. While lead offers good shielding against radioactive rays, it has a "blind spot" for certain energy ranges. Lead is scarce, and its engineering applications are costly. Furthermore, lead exhibits significant creep, making it unsuitable for heavy-load or structurally demanding components. Steel plates offer good mechanical properties when used as radiation shielding materials, but suffer from poor workability and susceptibility to corrosion. Water effectively protects against neutron rays at a low cost, but requires significant thickness, making the shielding layer structure difficult to define and complex in terms of construction, maintenance, and management. Radiation-shielding concrete offers advantages such as low material cost, ease of construction, the ability to build structures of any size and shape, excellent protective performance, and the ability to serve as structural support. Considering technical, economic, and effectiveness factors, concrete is currently the most widely used radiation shielding material. Today, radiation-shielding concrete is used in the protection of nuclear reactor containment vessels, military nuclear facility shells, radiation source shells in educational, research, and medical institutions, and nuclear waste storage facilities, playing a crucial role in shielding radiation and ensuring the safe use of nuclear equipment.

[0005] Nuclear radiation includes many types of rays, among which alpha, beta, x-ray, gamma, and neutron rays are the most harmful to the human body. Alpha and beta rays have low penetrating energy and are easily absorbed; even a thin layer of shielding material can shield them. X-rays and gamma rays are high-frequency, high-energy electromagnetic waves. When X-rays and gamma rays pass through high-density concrete, they lose most of their energy due to the Compton scattering effect, reducing their intensity. When radiation-shielding concrete reaches a certain density and thickness, X-rays and gamma rays can be completely absorbed. Neutron rays are a stream of neutral particles, and their penetrating power is far stronger than that of X-rays and gamma rays. Neutron rays can be classified into fast, medium, and slow neutrons according to their radiation intensity, and the shielding mechanisms differ for each type. When fast neutrons collide with heavy atomic nuclei, they undergo elastic and inelastic scattering, losing energy and becoming slow neutrons, which can be absorbed or captured by relevant substances, achieving a shielding and deceleration effect. Shielding of medium and slow neutrons can be achieved by adding absorbents of light elements such as hydrogen, boron, lithium, and cadmium. In the preparation of radiation-shielding concrete, increasing the concrete's strength, apparent density, and compactness, and reducing its porosity can effectively improve its radiation shielding capabilities. Meanwhile, the content of heavy atomic nuclei, light elements, and water of crystallization (a cement hydration product) in the concrete directly affects its radiation shielding effect against neutron rays.

[0006] The composition of radiation-shielding concrete is similar to that of ordinary concrete, mainly consisting of cement, mineral admixtures, fine aggregates, coarse aggregates, water, and chemical additives mixed in specific proportions. Introducing boron- and lithium-containing light element compounds and water of crystallization is the most common method in the preparation of radiation-shielding concrete. Adding mineral admixtures can reduce the water-cement ratio of concrete, decrease shrinkage, and improve its crack resistance, density, and radiation shielding ability. Adding barite, limonite, hematite, magnetite, barite, serpentine, olivine rock, and steel grit as coarse and fine aggregates is crucial for preparing high-performance radiation-shielding concrete. However, currently, the mineral admixtures in radiation shielding concrete contain relatively few light elements such as hydrogen, boron, lithium, and cadmium. These light elements are mainly achieved through the addition of light element admixtures and fine aggregates. Mineral admixtures have limited effect on improving the shielding effect of radiation shielding concrete. While ferrous heavy aggregates and natural heavy aggregates can increase the apparent density and shielding effect of concrete, their low water content results in poor neutron protection. Under neutron influence, ferrous heavy aggregates can generate strong secondary gamma rays. Furthermore, the apparent density of ferrous and natural heavy aggregates is greater than that of cement paste, compromising the uniformity of freshly mixed radiation shielding concrete. Uneven shrinkage during hardening leads to cracking and reduced shielding performance. Using heavy aggregates in radiation shielding concrete also increases the building's weight, negatively impacting the seismic performance of nuclear buildings. Finally, heavy aggregates generally have lower strength, making radiation shielding concrete with heavy aggregates weaker than ordinary concrete, and therefore unsuitable for load-bearing components in nuclear facilities. Therefore, finding other widely available mineral admixtures with higher radiation shielding effects, replacing commonly used heavy aggregates with new lightweight aggregates, and preparing modern radiation shielding concrete with good workability, volume stability, high crystal water content in hardened concrete, good mechanical properties, and good radiation shielding effect are hot research topics in this field both domestically and internationally.

[0007] Currently, the comprehensive utilization rate of copper slag is low, and a large amount of copper slag waste is landfilled without treatment. Chemical analysis of copper slag shows that the weight percentages of SiO2, Fe2O3, CaO, MgO, and Al2O3 in copper slag are 8-23%, 15-26%, 30-60%, 4-11%, and 3-8%, respectively. Copper slag contains minerals such as tricalcium silicate, dicalcium silicate, calcium magnesium olivine, calcium magnesium rhodochrosite, dicalcium ferrite, free calcium oxide, and free magnesium oxide, with a vitreous content as high as 85%, exhibiting high pozzolanic activity. Finely ground copper slag powder can be used as a mineral admixture in the preparation of radiation-shielding concrete. Finely ground copper slag mineral admixture also contains copper, lead, zinc, arsenic metals, and water of crystallization, providing good shielding against radiation. The small particle size and highly dense structure of finely ground copper slag powder, when added to concrete, can optimize the particle size distribution of fine particles in the concrete, effectively fill the voids in the concrete, form a dense network structure, and improve the radiation-shielding mechanical properties of the concrete.

[0008] Previous studies have found that lightweight aggregates made from industrial waste can replace commonly used heavy iron aggregates and natural heavy aggregates in the preparation of radiation shielding concrete. Huang Xiulin (Research on the Preparation of Radiation Shielding Functional Aggregates and Concrete from Heavy Metal-Containing Sludge, Wuhan University of Technology, Doctoral Dissertation, 2011) used heavy metal-containing sludge aggregates to prepare radiation shielding concrete. He systematically studied the influence of the mineral composition, calcination temperature, and calcination time of the heavy metal sludge on the physical and mechanical properties, microstructure, and shielding performance of the sludge functional aggregates, establishing the relationship between concrete composition, pore structure, and radiation shielding performance. Using microscopic analysis methods such as XRD, SEM, microhardness, and MPI, he systematically studied the hardening mechanism, microstructure, and interface characteristics of radiation shielding concrete, elucidating the mechanism of its excellent physical and mechanical properties, crack resistance, durability, and shielding performance. However, heavy metal-containing sludge has a wide range of sources, complex mineral composition and structure, high water content, and fluctuating physical and mechanical properties and heavy metal content. When the proportion of functional aggregate containing heavy metal sludge replacing iron-based heavy aggregate and natural heavy aggregate is too large, the flowability and mechanical properties of radiation shielding concrete will be significantly reduced. In recent decades, with the increasing advancement of display technology, a large number of cathode ray tubes (CRTs) have entered the scrap stage, generating excessive CRT electronic waste. CRT glass is an important component of CRTs. CRT glass contains silicate glass and the heavy metal lead. Adding crushed waste CRT glass to replace traditional heavy aggregate in radiation shielding concrete, with its high PbO content, has a strong absorption and reflection effect on gamma rays and neutrons, effectively shielding radiation. This opens up a new direction for the preparation of high-performance radiation shielding concrete. Wang Can's research (Influence of CRT Waste Glass Micro-aggregate on the Performance of Barite Radiation Shielding Concrete, Nanhua University, Master's Thesis, 2020) shows that with the increase of the amount of waste CRT glass micro-aggregate, the slump, slump spread, and apparent density of self-compacting radiation shielding concrete increase, while the V-shaped funnel passage time and T500 expansion time decrease. Adding waste CRT glass as fine aggregate significantly improves the compressive strength, splitting tensile strength, axial compressive strength, and modulus of elasticity of self-compacting radiation-shielding concrete. CRT glass as fine aggregate can also effectively increase the gamma-ray absorption coefficient of radiation-shielding self-compacting concrete and reduce the gamma-ray half-life layer thickness and the ten-fold attenuation thickness. However, excessively increasing the amount of waste CRT glass as fine aggregate slightly reduces the mechanical properties and radiation shielding performance of radiation-shielding self-compacting concrete, with the reduction in gamma-ray half-life layer thickness and ten-fold attenuation thickness remaining between 0.03 and 0.08 cm. When waste CRT glass as fine aggregate is added to radiation-shielding concrete, the active silica in the CRT glass reacts with alkaline substances in the concrete to form alkali-silica gel. This alkali-silica gel absorbs water and expands in volume, leading to cracking, decreased volume stability, and long-term performance degradation of the radiation-shielding concrete.To improve the durability of radiation-shielding concrete, the amount of fine aggregate added from CRT glass generally needs to be controlled at around 30%. This affects the radiation shielding effect of the concrete and restricts its widespread application. While the lead, zinc, nickel, and cadmium heavy metals in the CRT glass aggregate have a shielding effect during the preparation of radiation-shielding concrete, these toxic heavy metals can permeate into the environment during the preparation and long-term use of the concrete, polluting the soil and water around nuclear facilities and impacting plant and animal growth and human health. Finding environmentally friendly methods for preparing radiation-shielding concrete from cathode ray tube glass has become a focus of research worldwide, offering a constructive approach to effectively address the environmental pollution caused by toxic heavy metals in CRT glass and improve the radiation resistance of concrete. Summary of the Invention

[0009] Objective of the Invention: This invention aims to enhance the contribution of mineral admixtures to the radiation shielding effect of radiation-shielding concrete, improve the compactness of CRT glass fine aggregate and cement paste, reduce the negative impact of alkali-silica reaction of CRT glass fine aggregate on the volume stability and mechanical properties of radiation-shielding concrete, and improve the environmental compatibility of CRT glass radiation shielding concrete. Using cement and finely ground copper slag powder as cementitious materials, graphene and surface-reinforced CRT glass fine aggregate are added to the radiation-shielding concrete. The surface of the radiation-shielding concrete is then subjected to densification curing treatment to prepare an environmentally friendly, high-performance waste CRT glass radiation shielding concrete.

[0010] Technical Solution: To achieve the above objectives, this invention provides a method for preparing environmentally friendly, high-performance radiation-shielding concrete, comprising the following steps:

[0011] (1) The waste CRT glass is crushed and ball-milled into waste CRT glass fine aggregate with a certain particle size distribution. The waste CRT glass fine aggregate is immersed in a chemical encapsulation solution for surface strengthening treatment. A layer of polymer film is covered on the surface of the waste CRT glass fine aggregate.

[0012] (2) Mix the surface-strengthened waste CRT glass powder fine aggregate, river sand fine aggregate, crushed stone coarse aggregate, cementitious materials, graphene, water, and high-efficiency water-reducing agent in proportion to obtain fresh radiation-proof concrete.

[0013] (3) After demolding the freshly mixed radiation-proof concrete, it is placed in a carbon dioxide environment for surface densification treatment to prepare environmentally friendly, high-performance CRT glass radiation-proof shielding concrete.

[0014] In step (1), sodium hexametaphosphate is used as a grinding aid, which accounts for 3% of the weight of the waste CRT glass powder fine aggregate. The grinding speed of the waste CRT glass powder fine aggregate is 800 rpm, and the grinding time is 5-10 minutes. The size of the waste CRT glass powder fine aggregate is controlled between 3.7-3.8 μm.

[0015] In step (1), the chemical encapsulation solution is a guanosine gum aqueous solution, the weight ratio of the waste CRT glass powder fine aggregate to the chemical encapsulation solution is 1:2.0-1:2.1, the strengthening temperature of the CRT glass powder fine aggregate is 35-40℃, and the strengthening time is 1.5-2 hours.

[0016] In step (2), the ratio of fine aggregate, coarse aggregate, cementitious material, and water is 4.31:6.74:2.86:1. The cementitious material includes cement and finely ground copper slag powder, with the finely ground copper slag powder accounting for 25-30% of the total cementitious material. Graphene accounts for 3% of the total cementitious material. The fine aggregate consists of surface-strengthened CRT glass powder fine aggregate and river sand fine aggregate, with a mass ratio of surface-strengthened CRT glass powder fine aggregate to river sand fine aggregate of 6:4. Polycarboxylate super-efficiency reducing agent accounts for 0.12% of the total cementitious material.

[0017] The freshly mixed radiation-proof concrete in step (2) is made according to the following components by weight: 320-325 parts cement, 135-140 parts finely ground copper slag powder, 13.5-14 parts graphene, 415-420 parts fine river sand aggregate, 275-280 parts fine aggregate of waste CRT glass powder after strengthening treatment, 1085-1090 parts coarse crushed stone aggregate, and 160-165 parts mixing water mixed with polycarboxylate superplasticizer.

[0018] Step (3) includes the following preparation steps: accelerate the mixing of fresh concrete slurry, pour fresh concrete into molds to prepare samples, cover the concrete molds with wet burlap sacks, place them in an indoor environment with a temperature of 25°C and a humidity of 55-65%, remove the molds after 24 hours, and transfer the concrete specimens to a standard carbonation environment for curing to the specified age.

[0019] The test molds include 100mm×100mm×100mm, 150mm×150mm×550mm, 100mm×100mm×300mm, and φ40mm×80mm.

[0020] The standard carbonization environment is defined as a CO2 concentration of 2±0.5%, a temperature of 20±5%, and a humidity of 70±5%.

[0021] The present invention also includes measuring the compressive strength, flexural strength, radiation shielding performance, and heavy metal leaching of the environmentally friendly, high-performance radiation shielding concrete prepared by the method at a specified age.

[0022] Reaction Mechanism: After strengthening discarded cathode ray tube (CRT) glass, finely ground copper slag powder, graphene, and fine aggregate from the strengthened CRT glass are used to prepare concrete. The concrete is then surface-densified to prepare CRT glass radiation-shielding concrete. Using this method to prepare radiation-shielding concrete, finely ground copper slag powder is used as an auxiliary cementitious material, reducing the amount of cement used in the concrete and the environmental impact of greenhouse gases such as CO2 and industrial dust emissions during cement production. The addition of finely ground copper slag powder as an auxiliary cementitious material also improves the contribution of mineral admixtures to the shielding effect of the radiation-shielding concrete. The addition of graphene improves the adhesion between fine aggregate and cement paste in the radiation-shielding concrete and reduces the concrete porosity. Using waste cathode ray tube (CRT) glass fine aggregate as a substitute for iron-based heavy aggregate and natural heavy aggregate in the preparation of radiation-shielding concrete consumes a large amount of CRT glass waste, avoiding the land occupation and severe environmental pollution problems associated with traditional landfill methods for solid CRT waste disposal. Surface strengthening treatment of the CRT glass fine aggregate reduces the leaching rate of toxic metals such as lead, zinc, nickel, and cadmium from the CRT glass powder into the concrete. Surface densification treatment of the concrete prevents contact between the active silica in the CRT glass fine aggregate and hydrated alkaline substances, reducing the possibility of alkali-silica reaction and improving the volume stability of the concrete. This method of preparing radiation-shielding concrete achieves the resource-based recycling of waste. The resulting radiation-shielding concrete has better workability, mechanical properties, radiation shielding effect, and lower permeability than traditional radiation-shielding concrete, has a wide range of applications, and can generate good technical, economic, social, and environmental benefits.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) Radiation shielding concrete is prepared using finely ground copper slag mineral admixture. The proportion of finely ground copper slag mineral admixture replacing cement reaches 30%. Compared with radiation shielding concrete using fly ash mineral admixture, the cost of mineral admixture can be saved up to 6.29 yuan per cubic meter of this type of radiation shielding concrete.

[0025] (2) Waste CRT glass powder fine aggregate can completely replace iron heavy aggregate and natural heavy aggregate, which can significantly improve the mechanical properties and radiation shielding performance of radiation shielding concrete. For every cubic meter of this radiation shielding concrete produced, an economic benefit of more than 3.12 yuan can be generated.

[0026] (3) Adding graphene to freshly mixed radiation shielding concrete improves the workability of cement paste, reduces the amount of concrete admixtures used, and increases the density of CRT glass fine aggregate radiation shielding concrete. For every cubic meter of this type of radiation shielding concrete produced, the cost of concrete admixtures can be reduced by 0.89 yuan.

[0027] (4) Carbon dioxide surface densification curing treatment is applied to radiation shielding concrete, which reduces the addition of alkali-silica reaction inhibitors in concrete materials. The prepared radiation shielding concrete has low alkali-silica reaction expansion and good volume stability. The cost of alkali-silica reaction inhibitors can be saved by RMB 1.54 per cubic meter of this type of radiation shielding concrete.

[0028] (5) Using solid waste to grind copper slag powder to prepare radiation shielding concrete reduces the environmental impact of CO2 greenhouse gas emissions and industrial dust emissions during cement production.

[0029] (6) Using waste CRT glass powder as fine aggregate consumes a large amount of waste cathode ray tube glass, avoiding the problems of occupying a large amount of land and causing serious pollution to the surrounding environment when using traditional landfill methods to dispose of waste cathode ray tube glass.

[0030] (7) Strengthening the fine aggregate of CRT glass powder reduces the leaching of toxic heavy metals in radiation shielding concrete, expands the application field and scope of waste cathode ray tube glass, and finds a new way out for the recycling of cathode ray tube glass waste.

[0031] Taking all factors into consideration, based on the preparation method of Example 1, and assuming an annual production of 100,000 cubic meters of this environmentally friendly, high-performance radiation shielding concrete, a total economic benefit of RMB 1.184 million can be generated. Attached Figure Description

[0032] Figure 1 A flowchart for preparing environmentally friendly, high-performance radiation-shielding concrete;

[0033] Figure 2 The initial slump flowability and slump flowability retention of three types of freshly mixed radiation shielding concrete were studied.

[0034] Figure 3 The bleeding rate of three types of freshly mixed radiation shielding concrete;

[0035] Figure 4 The wet density of three types of freshly mixed radiation shielding concrete;

[0036] Figure 5 The change in compressive strength of three types of radiation shielding concrete with curing time;

[0037] Figure 6The change in flexural strength of three types of radiation shielding concrete with curing time;

[0038] Figure 7 The radiation shielding performance of three types of radiation-shielding concrete;

[0039] Figure 8 The heavy metal leaching amounts are for three types of radiation shielding concrete. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0041] Example 1

[0042] Using this invention, one cubic meter of environmentally friendly, high-performance radiation shielding concrete was prepared. Under the same mix proportion, its performance was compared with that of radiation shielding concrete samples made with barite fine aggregate without graphene, barite fine aggregate without CO2 surface densification treatment, and CRT glass fine aggregate without surface strengthening.

[0043] 1. Preparation of fine aggregate from ground waste cathode ray tubes

[0044] 860 kg of waste cathode ray tube glass (from the Hong Kong Solid Waste Recycling Centre) was sorted, washed, dried, and then crushed. The crushed waste cathode ray tube glass was placed in a vibratory ball mill, and 25.5 kg of sodium hexametaphosphate (industrial grade, produced by Shandong Kemike New Material Co., Ltd.) grinding aid was added. The milling was carried out at 800 rpm for 5-10 minutes. The ball-milled waste cathode ray tube glass was then passed through a 0.60 mm round-hole sieve, retaining fine particles with a particle size smaller than 0.60 mm. After the finely ground cathode ray tube glass powder was sealed and left for 24 hours, 856.7 kg of fine aggregate of waste cathode ray tube glass powder was obtained. The average particle size of the fine aggregate of finely ground cathode ray tube glass powder was measured to be 3.783 μm using a laser particle size analyzer.

[0045] 2. Strengthening treatment of fine aggregate from ground waste cathode ray tubes

[0046] 850 kg of finely ground cathode ray tube glass powder aggregate was immersed in 1700 kg of a 0.1% (by weight) guanidine gum aqueous solution (industrial grade, produced by Shanghai Lihe Technology Co., Ltd.) for strengthening treatment. The strengthening solution temperature was 35℃, and the mixture was continuously stirred for 2 hours, resulting in a polymer film coating the surface of the waste CRT glass powder aggregate. The surface-strengthened finely ground cathode ray tube glass powder aggregate was then dried and further ball-milled in a vibratory ball mill for 5 minutes. After passing through a 0.6 mm round-hole sieve, the surface-strengthened finely ground cathode ray tube glass powder aggregate was obtained for later use.

[0047] 3. Preparation of radiation shielding concrete with fine aggregate of reinforced ground waste cathode ray tube glass powder

[0048] 3.1. Mix proportion of radiation shielding concrete

[0049] The goal was to prepare C50 radiation-shielding concrete with a 28-day strength of 50 MPa. Cement and finely ground copper slag powder were used as cementitious materials. The cement was 42.5 ordinary Portland cement produced by China Cement Corporation, and the finely ground copper slag powder was copper slag tailings from the copper slag flotation of Guixi Smelter in Jiangxi Province. The finely ground copper slag powder contained 94.80% particles smaller than 0.074 mm. It mainly included SiO2, f-CaO, MgO, as well as CaO·Fe2O3, MgO·3FeO, anorthite (CaAl2Si2O8), and andradite (Ca3Fe2(SiO4)3) minerals, and also contained 0.35% metallic copper, 0.21% metallic lead, and 1.69% metallic zinc. Graphene (industrial grade) was produced by Ningbo Moxi Technology Co., Ltd. The natural fine aggregate was river sand from the Waiqinhuai River in Nanjing, Jiangsu Province, with a particle size of less than 5 mm and a fineness modulus of 2.46. The surface-strengthened finely ground cathode ray tube glass powder prepared in step 2 was used as the fine aggregate for preparing radiation shielding concrete. Industrial-grade barite sand fine aggregate produced by Shandong Anqiu Linwu Barite Co., Ltd., and the un-surface-strengthened CRT glass powder prepared in step 1 were used as control fine aggregates. The fineness moduli of the three fine aggregates were 2.78, 1.24, and 1.56, respectively, and their oven-dry density was 3043.9 kg / m³. 3 4401.8kg / m 3 3064.1 kg / m 3 The fine aggregate for CRT glass prepared in step 1 contains 376.1 g / L lead oxide. The coarse aggregate is 5-25 mm continuously graded crushed stone from Hexian County, Anhui Province. The high-efficiency water-reducing agent is polycarboxylate superplasticizer (PCE) produced by Jiangsu Academy of Building Research, with a solid content of 20%. The mixing water is drinking water. The mix proportion of the radiation shielding concrete is: cementitious material (cement + finely ground copper slag powder): fine aggregate (river sand + barite sand; or river sand + unreinforced CRT glass powder; or river sand + surface-reinforced CRT glass powder): coarse aggregate: water = 1:1.51:2.36:0.35 (by weight). The total amount of cementitious material in one cubic meter of radiation shielding concrete is 460 kg / m³. 3Finely ground copper slag powder accounted for 30% of the total cementitious materials. Barite sand, unreinforced CRT glass powder, and fine aggregates of reinforced CRT glass powder replaced river sand fine aggregates in a 40% ratio. Graphene accounted for 3% of the total cementitious materials. Polycarboxylate superplasticizer accounted for 0.12% of the total cementitious materials. Radiation shielding concrete with added barite sand (BARITE-C50) and radiation shielding concrete with unreinforced CRT glass powder (NCRT-C50) were used as control samples. The mix proportions of the three C50 radiation shielding concrete groups are shown in Table 1.

[0050] Table 1. Mix proportions of C50 radiation shielding concrete for three groups

[0051]

[0052] 3.2. Preparation and Curing of Radiation-Shielding Concrete

[0053] 322 kg of cement, 138 kg of finely ground copper slag powder, and 13.8 kg of graphene were placed in a mixer and mixed at 30 rpm for 2 minutes. Then, 416.3 kg of river sand, 277.52 kg of reinforced waste CRT glass powder, and 1085.2 kg of crushed stone were added and mixed at 30 rpm for 2 minutes. Finally, 161 kg of mixing water mixed with polycarboxylate superplasticizer was added to the container, and the mixture was stirred at 30 rpm for 2 minutes. To prevent the fresh concrete paste from stratifying at the bottom of the container, the fresh concrete paste was manually stirred 1-2 times with a shovel. The fresh concrete paste was then accelerated by mixing at 60 rpm for 2 minutes. A small amount of the fresh CRT-C50 concrete was tested for initial fluidity, fluidity retention, workability, and wet density. Twenty-four specimens of freshly mixed CRT-C50 concrete were prepared by pouring a portion of the concrete into 100mm×100mm×100mm and 150mm×150mm×550mm molds, respectively, for testing the compressive and flexural strengths at 3, 7, 28, and 90 days. Three specimens of the remaining freshly mixed concrete slurry were prepared by pouring it into 100mm×100mm×300mm molds for testing the radiation shielding performance of the concrete after 28 days. The remaining freshly mixed CRT-C50 concrete slurry was poured into φ40mm×80mm molds for testing the heavy metal leaching content of the cured concrete after 28 days. Finally, the CRT-C50 concrete molds were covered with damp burlap sacks and placed indoors at 25℃ and 55-65% humidity. After 24 hours, the molds were removed, and the concrete specimens were transferred to a standard carbonation environment (CO2 concentration 2±0.5%, temperature 20±5%, humidity 70±5%) for curing to the specified age. The same number of BARITE-C50 and NCRT-C50 radiation shielding concrete samples were prepared for comparison and placed in a standard curing room with a temperature of 20℃ and a humidity of 90±5% to cure until the test age for comparative experiments.

[0054] 3.3. Test methods for radiation shielding concrete

[0055] 3.3.1. Initial fluidity and fluidity retention of freshly mixed concrete

[0056] Wipe the conical slump test cylinder clean with a damp cloth and place it on a horizontally positioned steel plate. Fill the slump test cylinder with fresh concrete in three layers, tamping it 25 times evenly from the edge to the center after each layer. After filling and compacting the cylinder, smooth the surface and gently lift the cylinder vertically. Once the fresh concrete stops flowing, measure the average value of the slump in two mutually perpendicular directions as the initial slump flowability. To determine the retention of concrete flowability, after the initial slump flowability test, place the concrete sample in an iron bucket and let it stand for 30, 60, 90, and 120 minutes, repeating the slump flowability test at the specified time intervals. The concrete sample must be re-stirred before each slump flowability test.

[0057] Figure 2 The figure shows the initial slump flowability and slump flowability retention of three types of freshly mixed radiation shielding concrete. From... Figure 2 As can be seen, the two types of CRT glass fine aggregate radiation shielding concrete have higher initial slump flowability than barite fine aggregate radiation shielding concrete. The addition of graphene slightly reduced the initial slump flowability of the freshly mixed surface-reinforced CRT glass fine aggregate radiation shielding concrete. Meanwhile, with increasing storage time, the slump flowability of all three types of freshly mixed radiation shielding concrete decreased. The two types of radiation shielding concrete with CRT glass fine aggregate exhibited a lower slump flowability loss rate than barite fine aggregate radiation shielding concrete, indicating that using CRT glass fine aggregate to prepare radiation shielding concrete results in better slump flowability retention.

[0058] 3.3.2. Workability of Freshly Mixed Concrete

[0059] The workability of fresh concrete can be evaluated using the bleeding rate index. Fresh concrete is poured into a container of a certain volume, and the container is placed on a vibrating table and vibrated for 20 seconds. The surface of the fresh concrete is then gently smoothed with a trowel. Starting from the time the surface is smoothed, for the first 60 minutes, the bleeding water on the concrete surface is suctioned out every 10 minutes, and then every 20 minutes thereafter, until no bleeding occurs for three consecutive times. The cumulative amount of bleeding water in the fresh concrete is measured. The bleeding rate of fresh concrete is the percentage of the cumulative bleeding water to the weight of the concrete mix water.

[0060] Figure 3 The bleeding rate of three types of freshly mixed radiation shielding concrete. From Figure 3 As can be seen, the two types of CRT glass fine aggregate radiation shielding concrete have a higher bleeding rate than barite fine aggregate radiation shielding concrete. The addition of graphene slightly reduced the bleeding rate of fresh surface-strengthened CRT glass fine aggregate concrete and improved the workability of fresh radiation shielding concrete.

[0061] 3.3.3. Wet density of freshly mixed concrete

[0062] Freshly mixed concrete was poured into a test container of a certain volume in three layers. After each layer of fresh concrete was poured, the container was vibrated and compacted 25 times. After the container was filled and compacted, the surface of the fresh concrete was smoothed and excess concrete was removed. The weight of the fresh concrete in the test container and the volume of the test container were weighed, and the weight of the fresh concrete per unit volume was defined as the wet density of the concrete.

[0063] Figure 4 The figures show the wet densities of three types of freshly mixed radiation shielding concrete. From... Figure 4 As can be seen, the two types of CRT glass fine aggregate radiation shielding concrete have a lower wet density than barite fine aggregate radiation shielding concrete. The addition of graphene slightly reduced the wet density of the freshly mixed surface-strengthened CRT glass fine aggregate radiation shielding concrete.

[0064] 3.3.4. Compressive strength of hardened concrete

[0065] The compressive strength of concrete was tested according to the national standard "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T50081-2002). The compressive strength of hardened concrete was tested using a YAW-3000 electro-hydraulic servo loading system at curing ages of 3, 7, 28, and 90 days, with a loading rate of 1.3 MPa / s during the test.

[0066] Figure 5 The figure shows the change in compressive strength of three types of radiation shielding concrete with curing time. From... Figure 5 As can be seen, the compressive strength of the three types of radiation shielding concrete continuously increases with the curing age. At the same curing age, the two types of radiation shielding concrete with CRT glass fine aggregate exhibit higher compressive strength than those with barite fine aggregate. Compared to traditional CRT glass fine aggregate radiation shielding concrete, the addition of graphene and carbon dioxide surface densification curing treatment increases the concrete's density and volume stability, while the CRT glass fine aggregate concrete with surface strengthening treatment exhibits higher compressive strength.

[0067] 3.3.5. Flexural strength of hardened concrete

[0068] The flexural strength of concrete was tested according to the three-point flexural method in the national standard "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T50081-2002). At the specified age, the prism-shaped concrete specimen was placed face up on a DYE-300 fully automatic flexural testing machine, and a loading rate of 40 N / s was applied to the side of the prism until the specimen broke.

[0069] Figure 6 The figure shows the change in flexural strength of three types of radiation shielding concrete with curing time. From...Figure 6 As can be seen, the flexural strength of the three types of radiation shielding concrete continuously increases with the curing age. At the same curing age, the two types of radiation shielding concrete with CRT glass fine aggregate exhibit higher flexural strength than those with barite fine aggregate. Compared to traditional CRT glass fine aggregate radiation shielding concrete, the addition of graphene and carbon dioxide surface densification curing treatment increases the concrete's density and volume stability, while the CRT glass fine aggregate concrete with surface strengthening treatment exhibits higher flexural strength.

[0070] 3.3.6. Radiation shielding performance of hardened concrete

[0071] After 28 days of water curing, a 6150AD-5 / H gamma-ray spectrometer manufactured by AUTOMEGG GmbH, Germany was used for the measurement. 137 Using Cs as the radiation source (energy 662 keV), the gamma-ray shielding performance of radiation-shielding concrete samples was tested. The gamma-ray spectrometer was placed 65 cm away from the radiation source, and the concrete sample was placed 5 cm away from the spectrometer. When a single-energy gamma ray passes through an object, some of the gamma rays are absorbed by the material, while the intensity of the remaining gamma rays passing through the concrete sample decreases to some extent. As the thickness of the sample increases, the intensity of the gamma rays decreases exponentially after passing through the sample. Based on the difference in the measured gamma-ray absorbed dose of the concrete, the linear attenuation coefficient (μ) of the radiation-shielding concrete was calculated using the Lambert-Beer method. The larger the μ, the stronger the radiation shielding performance of the concrete.

[0072] Figure 7 The image shows the radiation shielding performance of three types of radiation-shielding concrete. From... Figure 7 As can be seen, the two types of radiation-shielding concrete with CRT glass fine aggregate have higher linear attenuation coefficients and radiation shielding properties than those with barite fine aggregate. Compared with traditional CRT glass fine aggregate radiation-shielding concrete, the addition of graphene and carbon dioxide surface densification curing treatment increases the density of the concrete, and the CRT glass fine aggregate concrete with surface strengthening treatment has a higher linear attenuation coefficient and radiation shielding properties.

[0073] 3.3.7. Heavy metal leaching in hardened concrete

[0074] In this invention, the leaching amount of heavy metals from hardened concrete is determined according to the method specified in "Solid Waste Leaching Toxicity Leaching Method: Horizontal Oscillation Method, HJ 557-2010". Hardened concrete samples cured for 28 days are crushed, ground, and passed through a 10mm round-hole sieve. 5.0g of concrete powder sample is placed in an extraction bottle and mixed thoroughly with 100ml of extraction solution. The pH of the extraction solution is adjusted to 2-3 with concentrated nitric acid or concentrated hydrochloric acid. The extraction bottle is fixed on a rotary extraction apparatus, and extraction is carried out continuously with stirring at a speed of 30±2 revolutions per minute for 18 hours. After extraction, the liquid in the extraction bottle is poured into a quantitative bottle, and distilled water is used to measure the volume to 100ml. The leachate is filtered, and the leaching concentrations of zinc, copper, and lead in the hardened concrete are determined using a flame atomic absorption spectrometer.

[0075] Figure 8 The figure shows the heavy metal leaching rates of three types of radiation-shielding concrete. From... Figure 8 As can be seen, the two types of radiation-shielding concrete with CRT glass fine aggregate exhibit lower zinc and copper leaching concentrations and higher lead leaching concentrations compared to radiation-shielding concrete with barite fine aggregate. Compared to traditional CRT glass fine aggregate radiation-shielding concrete, surface strengthening treatment of the CRT glass fine aggregate further reduces the concentration of zinc, copper, and lead heavy metals leaching from the concrete.

Claims

1. A method for preparing an environmentally friendly, high-performance radiation-shielding concrete, characterized in that, Includes the following steps: (1) Waste CRT glass is crushed and ball-milled into waste CRT glass fine aggregate with a certain particle size distribution. The waste CRT glass fine aggregate is immersed in a chemical encapsulation solution for surface strengthening treatment. A layer of polymer film is coated on the surface of the waste CRT glass fine aggregate to obtain surface-strengthened waste CRT glass fine aggregate. The size of the waste CRT glass fine aggregate is controlled to be 3.7-3.8μm. (2) Freshly mixed radiation-proof concrete is prepared by mixing surface-strengthened waste CRT glass powder fine aggregate, river sand fine aggregate, crushed stone coarse aggregate, cementitious materials, graphene, water, and polycarboxylate superplasticizer. The cementitious material includes cement and finely ground copper slag powder, wherein the finely ground copper slag powder accounts for 25-30% of the total cementitious material. The weight ratio of the surface-strengthened waste CRT glass powder fine aggregate, river sand fine aggregate, crushed stone coarse aggregate, cementitious material, and water is 4.31:6.74:2.86:

1. The graphene accounts for 3% of the weight of the cementitious material. The mass ratio of the surface-strengthened waste CRT glass powder fine aggregate to the river sand fine aggregate is 4:

6. The polycarboxylate high-efficiency water-reducing agent accounts for 0.12% of the weight of the cementitious material. The freshly mixed radiation-proof concrete is made according to the following weight parts: 320-325 parts cement, 135-140 parts finely ground copper slag powder, 13.5-14.0 parts graphene, 415-420 parts river sand fine aggregate, 275-280 parts surface-strengthened waste CRT glass powder fine aggregate, 1085-1090 parts crushed stone coarse aggregate, and 160-165 parts mixing water mixed with polycarboxylate high-efficiency water-reducing agent. (3) After the freshly mixed radiation shielding concrete is demolded, it is placed in a carbon dioxide environment for surface densification treatment to prepare environmentally friendly, high-performance CRT glass radiation shielding concrete.

2. The method for preparing environmentally friendly, high-performance radiation-shielding concrete according to claim 1, characterized in that, The grinding aid used in step (1) during ball milling includes sodium hexametaphosphate, which is 3% of the weight of the waste CRT glass powder fine aggregate. The ball milling speed of the waste CRT glass powder fine aggregate in step (1) is 800 rpm, and the ball milling time is 5-10 minutes.

3. The method for preparing environmentally friendly, high-performance radiation-shielding concrete according to claim 1, characterized in that, The chemical encapsulation solution in step (1) is a guanosine gum aqueous solution. The weight ratio of the waste CRT glass powder fine aggregate to the chemical encapsulation solution is 1:2.0-1:2.

1. The strengthening temperature of the waste CRT glass powder fine aggregate in step (1) is 35-40°C, and the strengthening time is 1.5-2 hours.

4. The method for preparing environmentally friendly, high-performance radiation-shielding concrete according to claim 1, characterized in that, Step (3) includes the following preparation steps: accelerate the mixing of fresh concrete slurry, take a portion of fresh concrete and pour it into the mold to prepare the specimen, cover the concrete mold with a wet burlap sack, place it in an indoor environment with a temperature of 25°C and a humidity of 55-65%, remove the mold after 24 hours, and transfer the concrete specimen to a standard carbonation environment to cure for the specified age.

5. The method for preparing environmentally friendly, high-performance radiation-shielding concrete according to claim 4, characterized in that, The trial molds include 100 mm × 100 mm × 100 mm, 150 mm × 150 mm × 550 mm, 100 mm × 100 mm × 300 mm, and φ40 mm × 80 mm.

6. The method for preparing environmentally friendly, high-performance radiation-shielding concrete according to claim 4, characterized in that, The standard carbonization curing environment is a CO2 concentration of 2 ± 0.5%, a temperature of 20 ± 5%, and a humidity of 70 ± 5%.

7. The environmentally friendly, high-performance radiation shielding concrete prepared by the method according to any one of claims 1 to 6.

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