Preparation method of high-performance recycled concrete

Abstract

The invention relates to the technical field of concrete, and discloses a preparation method of high-performance recycled concrete, which comprises the following steps: preparing modified hyperbranched polypropylene fibers from an intermediate 1 and an intermediate 2, and stirring the hyperbranched polypropylene fibers with fly ash, slag, cement, silica fume, sand, stone, recycled aggregate, water, a water reducer and steel fibers to obtain the high-performance recycled concrete. And synthesizing the high-performance recycled concrete. In the invention, the modified hyperbranched polypropylene fiber disperses stress through a three-dimensional network structure, the steel fiber provides macroscopic toughness, the hyperbranched polypropylene fiber delays the damage process through bridging cracks, and the steel fiber absorbs energy through pullout work to form a coarse-fine graded toughening system. An imidazoline functional group on the surface of the modified hyperbranched polypropylene fiber and the surface of the steel bar form a passive film, the steel bar is prevented from corroding the recycled aggregate concrete, the performance of the recycled aggregate concrete is close to that of common concrete, and natural aggregate exploitation and carbon emission are reduced by optimizing the utilization rate of the recycled aggregate.

Description

Technical Field

[0001] The present invention relates to the technical field of recycled concrete, and specifically provides a preparation method for high-performance recycled concrete. Background Art

[0002] In recent years, the technology of recycled concrete has become an important way to solve resource shortage and environmental pollution. However, the large-scale engineering application of traditional recycled concrete is restricted by the following technical bottlenecks: the mortar and impurities adhered to the surface of recycled aggregates result in significant defects in the interfacial transition zone between aggregates and paste, and the compressive strength is only 60%-70% of that of natural aggregate concrete. The splitting strength and flexural strength decrease more significantly. The brittleness of recycled concrete is significantly higher than that of ordinary concrete. It is easy to crack and the crack propagates rapidly under impact loads, making it difficult to meet the requirements of impact-resistant structures such as bridges and tunnels. The steel bars in recycled concrete are easily corroded, leading to the expansion of steel bar corrosion and shortening of the structural life. Due to the high porosity and strong water absorption of traditional recycled aggregates, the dosage in actual engineering is usually less than 30%, and the degree of resource utilization is insufficient.

[0003] At present, some properties have been improved by adding ordinary polypropylene fibers or steel fibers, but the bonding strength between ordinary fibers and recycled aggregates and the matrix is low, and they are prone to agglomeration, unable to fully play the role of strengthening and toughening, and lack long-term anti-corrosion measures. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] In view of the deficiencies of the prior art, the present invention provides a preparation method for high-performance recycled concrete. By using modified hyperbranched polypropylene fibers and recycled aggregates, the problems of "low strength, high brittleness, and poor corrosion resistance" of recycled concrete are solved, and it has engineering practicability, economy, and environmental friendliness.

[0006] (2) Technical Solutions

[0007] (1) Intermediate 1 and Intermediate 2 with a mass ratio of 1:(1 - 1.2) are added to a reaction vessel, 100 - 120 mL of ethanol is added, heated to 80 - 90 °C, and reacted for 18 - 24 h. After filtration, the precipitate is washed with ethanol to generate a modified hyperbranched polypropylene polymer. Then, the modified hyperbranched polypropylene is dried at 120 - 140 °C for 24 - 36 h, granulated and spun to obtain modified hyperbranched polypropylene fibers;

[0008] (2) Waste concrete is pretreated by grinding and screening to obtain recycled aggregates. Sand, stones, recycled aggregates, and water are mixed and stirred for 1 - 3 min, and then fly ash, cement, silica fume, slag, steel fiber modified hyperbranched polypropylene fibers, and water reducing agent are added and stirred for 30 - 60 min to obtain high-performance recycled concrete.

[0009] Furthermore, the mass ratio of fly ash, slag, cement, silica fume, sand, stone, recycled aggregate, water, water reducer, steel fiber, and hyperbranched polypropylene fiber is: (180 - 190):(45 - 47):(205 - 210):(23 - 24):(400 - 500):(700 - 730):(400 - 500):(200 - 250):(2.25 - 2.30):(18 - 22):10.

[0010] Furthermore, the preparation method of intermediate 1 is as follows:

[0011] (1) Add p-chlorobenzoic acid and β-hydroxyethyl ethylenediamine with a mass ratio of 1:(0.6 - 0.73) to a reaction vessel, then add 400 - 420 mL of xylene, stir, reflux at 150 - 170 °C for 7 - 10 h, cool, perform vacuum distillation, wash, and recrystallize to obtain an imidazoline compound;

[0012] (2) Add the imidazoline compound to a reaction vessel, add 100 - 110 mL of isopropanol and 100 - 110 mL of deionized water, then dropwise add 16.1 g of chloroethanol to the reaction vessel, heat in a water bath at 80 - 85 °C, stir, and react for 4 - 6 h. After the reaction, perform vacuum distillation and extraction to obtain an imidazoline quaternary ammonium salt;

[0013] (3) Add terminal carboxylated polypropylene and imidazoline quaternary ammonium salt with a mass ratio of 1:(1.5 - 1.8) to a reaction vessel, then add 200 - 220 mL of distilled water, heat to 75 - 85 °C, stir to dissolve, cool, add N,N-methylenebisacrylamide and ammonium persulfate, heat to 65 - 75 °C, react for 3 - 5 h. After the reaction, perform vacuum distillation, wash, and dry to obtain intermediate 1.

[0014] Furthermore, the mass ratio of the imidazoline compound to chloroethanol is (2.2 - 2.7):1.

[0015] Furthermore, the mass ratio of N,N-methylenebisacrylamide to ammonium persulfate is 1:(0.8 - 0.9).

[0016] Furthermore, the preparation method of intermediate 2 is as follows: Add toluene, trimethylolpropane, hydroxybutanedioic acid, and p-toluenesulfonic acid to a reaction vessel, heat to 85 - 95 °C, react for 12 - 16 h, perform vacuum concentration, wash with petroleum ether, and dry to obtain intermediate 2.

[0017] Furthermore, the mass ratio of trimethylolpropane, hydroxybutanedioic acid, and p-toluenesulfonic acid is 1:(1 - 1.1):(0.06 - 0.08).

[0018] (III) Beneficial technical effects

[0019] In the present invention, the synthesized imidazoline compound and chloroethanol are reacted to form an imidazoline quaternary ammonium salt. The terminal carboxyl groups of polypropylene are carboxylated to obtain carboxyl-terminated polypropylene. Then, the carboxyl-terminated polypropylene and the imidazoline quaternary ammonium salt are reacted to obtain Intermediate 1. Trimethylolpropane and hydroxybutanedioic acid are reacted under the catalysis of p-toluenesulfonic acid to form Intermediate 2. Based on Intermediate 1 and Intermediate 2, modified hyperbranched polypropylene fibers are obtained. The hyperbranched polypropylene fibers are stirred together with fly ash, slag, cement, silica fume, sand, stone, recycled aggregate, water, water reducer, and steel fibers to synthesize high-performance recycled concrete.

[0020] In the present invention, the modified hyperbranched polypropylene fibers disperse stress through a three-dimensional network structure, the steel fibers provide macroscopic toughness, the recycled aggregate is bonded to the matrix with enhanced adhesion after interface optimization, the hyperbranched fibers fill the defects in the interfacial transition zone between the recycled aggregate and the paste, and the pozzolanic reaction of fly ash / silica fume generates C-S-H gel to improve the density. The hyperbranched polypropylene fibers delay the failure process by bridging cracks, and the steel fibers absorb energy through the pull-out work, forming a "coarse-fine" hierarchical toughening system. The imidazoline functional groups on the surface of the modified hyperbranched polypropylene fibers form a passivation film with the surface of the steel bars to prevent steel bar corrosion. The hydrophobic polypropylene fibers reduce the capillary water absorption rate. Through grinding and screening, and the activation of the activity of fly ash / silica fume, the performance of the recycled aggregate concrete is close to that of ordinary concrete. By optimizing the utilization rate of recycled aggregates, the extraction of natural aggregates is reduced, and carbon emissions are lowered. Description of the Drawings

[0021] Figure 1 is the preparation process of the modified hyperbranched polypropylene fibers.

[0022] Figure 2 is the preparation process of Intermediate 1.

[0023] Figure 3 is the preparation process of Intermediate 2. Detailed Embodiments

[0024] Carboxyl-terminated polypropylene was prepared according to the method of the article "Preparation of Carboxyl-Terminated Polypropylene by Nitric Acid Oxidation Method" in the Journal of Zhongkai University of Agriculture and Engineering. The method is as follows: Polypropylene powder and nitric acid were added to a three-necked flask, stirred and reacted at 130 °C for 8 h, filtered after cooling, washed with water to remove nitric acid, and the product was dried in vacuo to obtain carboxyl-terminated polypropylene.

[0025] Example 1

[0026] (1) 30 g of p-chlorobenzoic acid and 18 g of β-hydroxyethyl ethylenediamine were added to a reaction vessel, and then 420 mL of xylene was added. After stirring, the mixture was refluxed at 150 °C for 10 h. After cooling, it was subjected to vacuum distillation, washing, and recrystallization to obtain the imidazoline compound;

[0027] (2) Add 35 g of imidazoline compound into a reaction vessel, then add 110 mL of isopropanol and 100 mL of deionized water. Dropwise add 16 g of chloroethanol into the reaction vessel, heat it in a water bath at 80 °C, stir, and react for 6 h. After the reaction is completed, perform vacuum distillation and extraction to obtain imidazoline quaternary ammonium salt;

[0028] (3) Add 6 g of terminal carboxylated polypropylene and 9 g of imidazoline quaternary ammonium salt into a reaction vessel, then add 200 mL of distilled water. Heat it to 75 °C, stir to dissolve, and after cooling, add 0.06 g of N,N - methylenebisacrylamide and 0.054 g of ammonium persulfate. Heat it to 75 °C and react for 5 h. After the reaction is completed, perform vacuum distillation, wash and dry to obtain Intermediate 1;

[0029] (4) Add 140 mL of toluene, 4 g of trimethylolpropane, 4.4 g of hydroxybutanedioic acid, and 0.32 g of p - toluenesulfonic acid into a reaction vessel. Heat it to 85 °C and react for 16 h. Perform vacuum concentration, wash and dry with petroleum ether to obtain Intermediate 2;

[0030] (5) Add 5 g of Intermediate 1 and 5 g of Intermediate 2 into a reaction vessel, add 100 mL of ethanol, heat it to 80 °C, react for 18 h, filter, wash the precipitate with ethanol to form a modified hyperbranched polypropylene polymer. Then dry the modified hyperbranched polypropylene at 140 °C for 24 h, perform granulation and spinning to obtain modified hyperbranched polypropylene fibers;

[0031] (6) Pretreat the waste concrete by grinding and screening to obtain recycled aggregates. Mix 400 g of sand, 700 g of stone, 500 g of recycled aggregates and 200 g of water and stir for 3 min. Then add 180 g of fly ash, 205 g of cement, 24 g of silica fume, 45 g of slag, 22 g of steel fibers, 10 g of modified hyperbranched polypropylene fibers, and 2.25 g of water - reducing agent, and stir for 60 min to obtain high - performance recycled concrete.

[0032] Example 2

[0033] (1) Add 30 g of p - chlorobenzoic acid and 22 g of β - hydroxyethyl ethylenediamine into a reaction vessel, and then add them into 400 mL of xylene. Stir and reflux at 170 °C for 7 h. After cooling, perform vacuum distillation, wash, and recrystallize to obtain imidazoline compound;

[0034] (2) Add 43 g of imidazoline compound into a reaction vessel, add 100 mL of isopropanol and 110 mL of deionized water. Dropwise add 16 g of chloroethanol into the reaction vessel, heat it in a water bath at 85 °C, stir, and react for 4 h. After the reaction is completed, perform vacuum distillation and extraction to obtain imidazoline quaternary ammonium salt;

[0035] (3) Add 6 g of end-carboxylated polypropylene and 10.8 g of imidazoline quaternary ammonium salt into a reaction vessel, then add 220 mL of distilled water, heat to 85 °C, stir to dissolve, after cooling, add 0.06 g of N,N-methylenebisacrylamide and 0.048 g of ammonium persulfate, heat to 65 °C, react for 3 h, after the reaction ends, carry out vacuum distillation, wash and dry to obtain intermediate 1;

[0036] (4) Add 120 mL of toluene, 4 g of trimethylolpropane, 4 g of hydroxybutanedioic acid, and 0.24 g of p-toluenesulfonic acid into a reaction vessel, heat to 95 °C, react for 12 h, carry out vacuum concentration, wash and dry with petroleum ether to obtain intermediate 2;

[0037] (5) Add 5 g of intermediate 1 and 6 g of intermediate 2 into a reaction vessel, add 120 mL of ethanol, heat to 90 °C, react for 24 h, filter, wash the precipitate with ethanol to generate a modified hyperbranched polypropylene polymer, then dry the modified hyperbranched polypropylene at 120 °C for 36 h, carry out granulation and spinning to obtain modified hyperbranched polypropylene fibers;

[0038] (6) Pretreat waste concrete by grinding and screening to obtain recycled aggregates, mix 500 g of sand, 730 g of stone, 400 g of recycled aggregates and 250 g of water and stir for 1 min, then add 190 g of fly ash, 210 g of cement, 23 g of silica fume, 47 g of slag, 22 g of steel fibers, 10 g of modified hyperbranched polypropylene fibers, and 2.30 g of water reducer, stir for 30 min to obtain high-performance recycled concrete.

[0039] Example 3

[0040] (1) Add 30 g of p-chlorobenzoic acid and 20 g of β-hydroxyethyl ethylenediamine into a reaction vessel, then add them into 410 mL of xylene, stir, reflux at 160 °C for 8 h, after cooling, carry out vacuum distillation, wash, and recrystallize to obtain an imidazoline compound;

[0041] (2) Add 40 g of the imidazoline compound into a reaction vessel, add 105 mL of isopropanol and 105 of deionized water, dropwise add 16 g of chloroethanol into the reaction vessel, heat in a water bath at 80 °C, stir, react for 5 h, after the reaction ends, carry out vacuum distillation, extract to obtain an imidazoline quaternary ammonium salt;

[0042] (3) Add 6 g of end-carboxylated polypropylene and 10 g of imidazoline quaternary ammonium salt into a reaction vessel, then add 210 mL of distilled water, heat to 80 °C, stir to dissolve, after cooling, add 0.06 g of N,N-methylenebisacrylamide and 0.05 g of ammonium persulfate, heat to 70 °C, react for 4 h, after the reaction ends, carry out vacuum distillation, wash and dry to obtain intermediate 1;

[0043] (4) Add 130 mL of toluene, 4 g of trimethylolpropane, 4.2 g of hydroxybutanedioic acid, and 0.3 g of p-toluenesulfonic acid to the reaction vessel, heat to 90 °C, react for 13 h, concentrate under reduced pressure, wash with petroleum ether and dry to obtain Intermediate 2;

[0044] (5) Add 5 g of Intermediate 1 and 5.5 g of Intermediate 2 to the reaction vessel, add 110 mL of ethanol, heat to 85 °C, react for 20 h, filter, wash the precipitate with ethanol to form a modified hyperbranched polypropylene polymer, and then dry the modified hyperbranched polypropylene at 130 °C for 30 h, granulate and spin to obtain modified hyperbranched polypropylene fibers;

[0045] (6) Pretreat the waste concrete by grinding and screening to obtain recycled aggregate. Mix 450 g of sand, 710 g of stone, 450 g of recycled aggregate and 220 g of water and stir for 2 min, then add 185 g of fly ash, 210 g of cement, 24 g of silica fume, 46 g of slag, 20 g of steel fiber, 10 g of modified hyperbranched polypropylene fiber, and 2.30 g of water reducing agent, and stir for 40 min to obtain high-performance recycled concrete.

[0046] Example 4

[0047] (1) Add 30 g of p-chlorobenzoic acid and 18 g of β-hydroxyethyl ethylenediamine to the reaction vessel, then add it to 400 mL of xylene, stir, reflux at 170 °C for 7 h, cool and then perform vacuum distillation, washing, and recrystallization to obtain an imidazoline compound;

[0048] (2) Add 40 g of the imidazoline compound to the reaction vessel, add 100 mL of isopropanol and 100 mL of deionized water, dropwise add 16 g of chloroethanol to the reaction vessel, heat in a water bath at 85 °C, stir, react for 6 h, after the reaction is completed, perform vacuum distillation and extraction to obtain an imidazoline quaternary ammonium salt;

[0049] (3) Add 6 g of end-carboxylated polypropylene and 9 g of the imidazoline quaternary ammonium salt to the reaction vessel, then add 200 mL of distilled water, heat to 75 °C, stir to dissolve, after cooling, add 0.06 g of N,N-methylenebisacrylamide and 0.054 g of ammonium persulfate, heat to 75 °C, react for 3 h, after the reaction is completed, perform vacuum distillation, wash and dry to obtain Intermediate 1;

[0050] (4) Add 140 mL of toluene, 4 g of trimethylolpropane, 4.4 g of hydroxybutanedioic acid, and 0.24 g of p-toluenesulfonic acid to the reaction vessel, heat to 85 °C, react for 12 h, concentrate under reduced pressure, wash with petroleum ether and dry to obtain Intermediate 2;

[0051] (5) Add 5 g of intermediate 1 and 6 g of intermediate 2 into a reaction vessel, add 100 mL of ethanol, heat to 90 °C, react for 24 h, filter, wash the precipitate with ethanol, generate a modified hyperbranched polypropylene polymer, and then dry the modified hyperbranched polypropylene at 120 °C for 24 h, followed by granulation and spinning to obtain modified hyperbranched polypropylene fibers;

[0052] (6) Pretreat waste concrete by grinding and screening to obtain recycled aggregates. Mix 400 g of sand, 730 g of stone, 500 g of recycled aggregates and 250 g of water and stir for 3 min. Then add 190 g of fly ash, 210 g of cement, 24 g of silica fume, 45 g of slag, 18 g of steel fibers, 10 g of modified hyperbranched polypropylene fibers, and 2.30 g of water reducer, and stir for 60 min to obtain high-performance recycled concrete.

[0053] Comparative Example 1

[0054] (1) Pretreat waste concrete by grinding and screening to obtain recycled aggregates. Mix 400 g of sand, 700 g of stone, 500 g of recycled aggregates and 200 g of water and stir for 3 min. Then add 180 g of fly ash, 205 g of cement, 24 g of silica fume, 45 g of slag, and 2.25 g of water reducer, and stir for 60 min to obtain high-performance recycled concrete.

[0055] Comparative Example 2

[0056] (1) Pretreat waste concrete by grinding and screening to obtain recycled aggregates. Mix 400 g of sand, 700 g of stone, 500 g of recycled aggregates and 200 g of water and stir for 3 min. Then add 180 g of fly ash, 205 g of cement, 24 g of silica fume, 45 g of slag, 22 g of steel fibers, 10 g of polypropylene fibers, and 2.25 g of water reducer, and stir for 60 min to obtain high-performance recycled concrete.

[0057] Comparative Example 3

[0058] (1) Add 140 mL of toluene, 4 g of trimethylolpropane, 6 g of end-carboxylated polypropylene, and 0.32 g of p-toluenesulfonic acid into a reaction vessel, heat to 85 °C, react for 16 h, concentrate under reduced pressure, wash and dry with petroleum ether to obtain hyperbranched polypropylene;

[0059] (2) Pretreat the waste concrete by grinding and screening to obtain recycled aggregates. Mix 400 g of sand, 700 g of stones, 500 g of recycled aggregates and 200 g of water and stir for 3 min. Then add 180 g of fly ash, 205 g of cement, 24 g of silica fume, 45 g of slag, 22 g of steel fibers, 10 g of hyperbranched polypropylene, and 2.25 g of water reducer, and stir for 60 min to obtain high-performance recycled concrete.

[0060] Control Example 4

[0061] (1) Add 30 g of p-chlorobenzoic acid and 18 g of β-hydroxyethyl ethylenediamine to a reaction vessel, and then add them to 420 mL of xylene. Stir and reflux at 150 °C for 10 h. After cooling, perform vacuum distillation, washing, and recrystallization to obtain an imidazoline compound.

[0062] (3) Add 6 g of end-carboxylated polypropylene and 7.2 g of imidazoline compound to a reaction vessel, then add 200 mL of distilled water, heat to 75 °C, stir to dissolve, cool, add 0.06 g of N,N-methylenebisacrylamide and 0.054 g of ammonium persulfate, heat to 75 °C, and react for 5 h. After the reaction is completed, perform vacuum distillation, washing, and drying to obtain a compound.

[0063] (4) Add 140 mL of toluene, 4 g of trimethylolpropane, 4.4 g of hydroxybutanedioic acid, and 0.32 g of p-toluenesulfonic acid to a reaction vessel, heat to 85 °C, react for 16 h, perform vacuum concentration, wash with petroleum ether, and dry to obtain Intermediate 2.

[0064] (5) Add 5 g of Compound 1 and 5 g of Intermediate 2 to a reaction vessel, add 100 mL of ethanol, heat to 80 °C, react for 18 h, filter, wash the precipitate with ethanol to generate modified hyperbranched polypropylene polymer 1. Then dry the modified hyperbranched polypropylene at 140 °C for 24 h, perform granulation and spinning to obtain modified hyperbranched polypropylene fiber 1.

[0065] (6) Pretreat the waste concrete by grinding and screening to obtain recycled aggregates. Mix 400 g of sand, 700 g of stones, 500 g of recycled aggregates and 200 g of water and stir for 3 min. Then add 180 g of fly ash, 205 g of cement, 24 g of silica fume, 45 g of slag, 22 g of steel fibers, 10 g of modified hyperbranched polypropylene fiber 1, and 2.25 g of water reducer, and stir for 60 min to obtain high-performance recycled concrete.

[0066] The concrete prepared in the examples and comparative examples was molded according to the "Test Regulations for Cement and Cement Concrete in Highway Engineering" and vibrated on a vibrating table for 30 s. After demolding for 1 d, it was cured by covering with a thin film for 7 d, and then air-cured until 28 d. The curing humidity was 50% - 70%, and the temperature was (20 ± 2)°C.

[0067] For the specimens obtained from the preparation and curing processes of the concrete in the comparative examples and examples, according to GB-T50081-2019, the compressive strength, splitting strength and flexural strength of the high-strength concrete specimens were tested.

[0068] According to CECS13—2009, the impact resistance of the fiber-reinforced recycled concrete was tested by the drop hammer impact method, and the impact resistance was the number of impacts of the recycled concrete.

[0069] According to GB 8076-2008, the steel bars were processed into cylindrical shapes of 7 mm × 35 mm from ordinary steel bars for construction. The surface was polished step by step with sandpaper to 1000#. One steel sample (working electrode) and one auxiliary electrode were buried parallelly in each test block. The cover thickness of the steel sample was 10 mm. The test block was mechanically vibrated for 2 minutes during molding, demolded about 24 hours after molding, cured in a curing room for 14 days, and the concrete test block was cured for 28 days. The salt spray was cyclically sprayed with a 3.5% NaCl solution in a salt spray chamber at a constant temperature of 45 ± 2°C for 15 minutes, with an interval of 45 minutes. After curing, it was first placed in an oven at 80°C for 4 days, taken out and cooled, and then put into an alternating immersion and drying in salt water with a cycle of 7 days; immersed in 5% NaCl solution for 6 hours, measured, and then put into an oven at 60°C and dried until 7 days. The Tafel constant B was determined.

[0070] Table 1 shows the compressive strength, splitting strength and flexural strength of the high-strength concrete specimens

[0071]

[0072] Table 2 shows the impact resistance of the high-strength concrete specimens and the corrosion resistance of the steel bars

[0073]

[0074] As shown in Table 1 and Table 2, the properties of recycled aggregate concrete are close to those of ordinary concrete. The modified hyperbranched polypropylene fiber improves the mechanical properties, impact resistance and corrosion resistance of steel bars. In the present invention, for the compressive strength, splitting strength, flexural strength and impact resistance, Examples 1-4 are superior to Comparative Example 1. This is because Intermediate 1 grafts imidazoline quaternary ammonium salt onto the surface of polypropylene fiber through the reaction of imidazoline compound with terminal carboxylated polypropylene. The nitrogen atom on the imidazoline ring can form a coordination bond with iron ions on the surface of the steel bar through electrostatic adsorption, and chelation occurs. At the same time, magnesium / aluminum hydroxide colloid is generated by hydrolysis in an alkaline environment to fill the pores of the concrete. The modified fiber improves the corrosion resistance of the steel bar by passivating the surface of the steel bar. The three-dimensional network structure of hyperbranched polypropylene can disperse the impact energy, reduce stress concentration, keep the fiber flexible at low temperature, adapt to the uneven deformation of recycled aggregate, improve toughness and increase impact resistance.

[0075] Compared with Example 1, the deficiency of Comparative Example 1 is that no fiber is added, lacking fiber reinforcement, the interface bonding between the recycled aggregate and the matrix is weak, stress cannot be effectively transmitted, fiber bridging cracks are not introduced, there is no impact resistance mechanism, and no imidazoline functional group is added, so the steel bar is prone to corrosion. Therefore, the performance of Example 1 is superior to that of Comparative Example 1.

[0076] Compared with Example 1, the deficiency of Comparative Example 2 is that only ordinary polypropylene fiber is added, and hyperbranched polypropylene fiber is not used. The rigidity of ordinary polypropylene fiber is insufficient and it cannot form synergistic toughening with steel fiber. The defects in the interfacial transition zone between the unmodified fiber and the recycled aggregate and the matrix are not repaired, the interfacial bonding is weak, and no imidazoline functional group is introduced, so the steel bar is still vulnerable to chloride ion erosion. Therefore, the performance of Example 1 is superior to that of Comparative Example 2.

[0077] Compared with Example 1, the deficiency of Comparative Example 3 is that unmodified hyperbranched polypropylene fiber is used. The hyperbranched fiber without grafted imidazoline functional group cannot form chemical bonding with the steel bar, and the improvement of corrosion resistance is limited. Therefore, the corrosion resistance of Example 1 to the steel bar is superior to that of Comparative Example 3.

[0078] Compared with Example 1, the deficiency of Comparative Example 4 is that the modified hyperbranched polypropylene fiber 1 generated by using polypropylene fiber grafted with imidazoline compound has no grafting of imidazoline functional group and quaternary ammonium salt. The passivation film on the surface of the steel bar is incomplete, the corrosion resistance decreases, the coordination bond density between imidazoline and iron ions decreases, and the inhibition effect of Cl- erosion is poor. Therefore, the corrosion resistance of Example 1 to the steel bar is superior to that of Comparative Example 4.

Claims

1. A method for preparing high-performance recycled concrete, characterized in that, The preparation method includes: (1) Add intermediate 1 and intermediate 2 into a reaction vessel, add 100 - 120 mL of ethanol, heat to 80 - 90 °C, react for 18 - 24 h, filter, wash the precipitate with ethanol to form a modified hyperbranched polypropylene polymer, and then dry the modified hyperbranched polypropylene at 120 - 140 °C for 24 - 36 h, followed by granulation and spinning to obtain modified hyperbranched polypropylene fibers; (2) Pretreat waste concrete by grinding and screening to obtain recycled aggregates. Mix sand, stones, recycled aggregates and water and stir for 1 - 3 min, then add fly ash, cement, silica fume, slag, steel fibers, modified hyperbranched polypropylene fibers, and water reducing agent, and stir for 30 - 60 min to obtain high-performance recycled concrete.

2. The method for preparing high-performance recycled concrete according to claim 1, characterized in that, In the step (1), the mass ratio of intermediate 1 to intermediate 2 is 1:(1 - 1.2).

3. The preparation method of the high-performance recycled concrete according to claim 1, wherein, In the step (2), the mass ratio of fly ash, slag, cement, silica fume, sand, stones, recycled aggregates, water, water reducing agent, steel fibers and hyperbranched polypropylene fibers is: (180 - 190):(45 - 47):(205 - 210):(23 - 24):(400 - 500):(700 - 730):(400 - 500):(200 - 250):(2.25 - 2.30):(18 - 22):

10.

4. The preparation method of the high-performance recycled concrete according to claim 1, characterized in that, The preparation method of the intermediate 1 is as follows: (1) Add p-chlorobenzoic acid and β-hydroxyethyl ethylenediamine into a reaction vessel, and then add them into 400 - 420 mL of xylene, stir, reflux at 150 - 170 °C for 7 - 10 h, cool and then carry out vacuum distillation, washing and recrystallization to obtain an imidazoline compound; (2) Add the imidazoline compound into a reaction vessel, add 100 - 110 mL of isopropanol and 100 - 110 mL of deionized water, then drop 16.1 g of chloroethanol into the reaction vessel, heat in a water bath at 80 - 85 °C, stir, react for 4 - 6 h, after the reaction is completed, carry out vacuum distillation and extraction to obtain an imidazoline quaternary ammonium salt; (3) Add terminal carboxylated polypropylene and imidazoline quaternary ammonium salt into a reaction vessel, then add 200 - 220 mL of distilled water, heat to 75 - 85 °C, stir to dissolve, after cooling, add N,N-methylenebisacrylamide and ammonium persulfate, heat to 65 - 75 °C, react for 3 - 5 h, after the reaction is completed, carry out vacuum distillation, washing and drying to obtain intermediate 1.

5. The preparation method of the high-performance recycled concrete according to claim 4, wherein, In the step (1), the mass ratio of p-chlorobenzoic acid to β-hydroxyethyl ethylenediamine is 1:(0.6 - 0.73).

6. The method for preparing the high-performance recycled concrete according to claim 4, characterized in that, In the step (2), the mass ratio of the imidazoline compound to chloroethanol is (2.2 - 2.7):

1.

7. The preparation method of high-performance recycled concrete according to claim 4, characterized in that In the step (3), the mass ratio of terminal carboxylated polypropylene to imidazoline quaternary ammonium salt is 1:(1.5 - 1.8).

8. The method for preparing high-performance recycled concrete according to claim 4, characterized in that, In the step (3), the mass ratio of N,N-methylenebisacrylamide to ammonium persulfate is 1:(0.8 - 0.9).

9. The preparation method of the high-performance recycled concrete according to claim 1, characterized in that The preparation method of the intermediate 2 is as follows: add toluene, trimethylolpropane, hydroxybutanedioic acid, and p-toluenesulfonic acid into a reaction vessel, heat to 85 - 95 °C, react for 12 - 16 h, concentrate under reduced pressure, wash with petroleum ether and dry to obtain the intermediate 2.

10. The preparation method of high-performance recycled concrete according to claim 9, characterized in that, The mass ratio of trimethylolpropane, hydroxybutanedioic acid, and p-toluenesulfonic acid is 1:(1 - 1.1):(0.06 - 0.08).

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