Expressway fly ash recycled concrete for construction as well as preparation method and application of expressway fly ash recycled concrete

Abstract

The invention provides expressway fly ash recycled concrete for construction as well as a preparation method and application thereof, and belongs to the technical field of building materials. The expressway fly ash recycled concrete for construction comprises the following raw material components in parts by weight: 28-36 parts of cement; 3-6 parts of fly ash; 38 to 58 parts of recycled coarse aggregate; 12 to 16 parts of recycled fine aggregate; 2 to 5 parts of metakaolin; 0.5 to 1.1 parts of a water reducing agent; 0.8 to 1.4 parts of shrinkage reducing agent; 1.5 to 2.4 parts of low viscosity cellulose ether; 4-6 parts of starch ether; 1-2 parts of shell powder; 1.1 to 1.5 parts of chitin nano crystal whisker; 0.1 to 0.3 part of pentaerythritol distearate; 5 to 8 parts of polypropylene oxide glycol; 1 to 2 parts of dicyclohexylmethane diisocyanate; and 15-20 parts of water. The performance of the recycled concrete for the road, which is obtained by compounding the raw materials, is remarkably improved, the mechanical property is excellent, the later strength is stable, and the freeze-thaw resistance is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials for road construction, and particularly relates to fly ash recycled concrete for expressway construction, and a preparation method and application thereof. Background Art

[0002] In recent years, the output of construction waste has increased year by year, while the recycling and reuse rate of construction waste in my country is less than 10%. Among them, the reuse rate of waste concrete directly used for roads is even lower. Most of it is mainly used directly for backfilling of road base and surface layers. How to reuse it with high quality and improve the construction progress of expressways for construction is an urgent engineering problem.

[0003] With rapid economic and social development, urbanization is accelerating. The global urbanization rate is projected to reach 68% by 2050, and the urban population is expected to reach 70% of the total population by 2050. This has led to the rapid development of civil engineering-related industries. Earlier models of housing and road construction are no longer sufficient to meet current demand, and highway construction is becoming increasingly important. In particular, the high-quality, green, and low-carbon construction of national ultra-high voltage transmission and transformation projects is becoming increasingly prominent as a model for key national projects. Concrete, as one of the most widely used building materials, is widely used in the construction and maintenance of buildings and roads. Its production and manufacturing process consumes large quantities of sand, gravel, aggregate, and cementitious materials. Furthermore, the cement production process generates greenhouse gases, further harming the natural environment. It is estimated that the global concrete industry consumes billions of tons of natural aggregate annually.

[0004] With the continuous exploitation of sand and gravel resources, natural aggregates are becoming increasingly scarce. The difficulty of securing high-quality aggregate supplies is increasing year by year, and the current supply of raw materials for concrete sand and gravel is extremely tight. Furthermore, large amounts of waste sand and gravel aggregate and concrete construction waste are generated annually due to mountain expressway construction, highway expansion and reconstruction, building demolition, and other construction projects involved in high-voltage power transmission and transformation projects. This production has been increasing annually with the advancement of the national energy strategy, and the resulting environmental problems are becoming increasingly serious in the construction of green and low-carbon expressways. A large amount of waste concrete from existing roads is often directly dumped in landfills or simply used as roadbed backfill, failing to be efficiently utilized. This not only incurs significant waste removal and land acquisition costs, but also generates large amounts of dust, ash, and sand, which pollute the environment. This not only wastes resources but also damages the ecological environment, contradicting the path of sustainable development. The use of green and low-carbon building materials has become a major trend in global economic and social sustainable development, and accelerating the development of recycled green building materials has become a common choice for countries around the world.

[0005] Fly ash is a major solid waste generated by thermal power plants. If left untreated, it not only occupies significant land but also creates dust pollution, polluting the air and water. Crushing and screening waste road concrete to produce recycled aggregate, a natural aggregate substitute, and using fly ash as a binder to partially replace cement in the production of fly ash recycled road concrete, can conserve resources and reduce carbon emissions.

[0006] To address the challenges of handling construction waste and industrial solid waste from various construction activities, actively reducing construction waste and recycling solid waste has become a priority. The vast majority of solid waste from construction waste is recyclable. After a series of processes, such as crushing and screening, it can be used as aggregate to replace natural aggregate in recycled concrete, or used to make building materials such as recycled bricks and blocks. Furthermore, waste concrete can be combined with fly ash to produce fly ash recycled concrete, further mitigating the negative environmental impact of disorderly solid waste storage and land occupation. Furthermore, fly ash can be used as a substitute for cement, and recycled aggregate as a substitute for natural aggregate to produce high-performance concrete. This not only reduces over-exploitation of natural sand and gravel resources, enabling construction using local materials, but also protects natural resources and the ecological environment. It also addresses issues such as solid waste storage and land occupation. This has significant social and environmental benefits, effectively addressing the coordinated development of resources and the environment, and promoting the green and low-carbon nature of construction activities. It holds significant engineering application prospects and practical significance.

[0007] Currently, numerous researchers at home and abroad have conducted extensive research on the performance and use of fly ash recycled concrete, achieving considerable success. However, the recycled aggregate used is mostly derived from construction waste concrete, while relatively little research has been conducted on road waste concrete. Currently, most road waste concrete is directly used for backfilling of road bases and cushion layers after crushing, and is not rationally used in new road construction, especially in the construction of expressways. Southwest my country, especially the high-altitude areas of Tibet, has hot and dry summers and severe cold and frigid winters, with large temperature differences between day and night. These climatic and environmental conditions have a significant impact on the performance and service life of concrete. These factors require special attention in the design and use of concrete materials, especially the durability and freeze-thaw resistance of recycled concrete in these areas. Furthermore, the use of fly ash recycled concrete to prepare recycled concrete for expressways not only alleviates the environmental problems caused by solid waste, enables local sourcing of construction materials, but also reduces greenhouse gas emissions during the production of transmission tower base concrete materials in the country's key energy industry, thus possessing significant engineering significance and application prospects.

[0008] However, how to increase the amount of fly ash in fly ash recycled concrete for high-altitude roads, and improve the mechanical properties and freeze-thaw resistance of recycled concrete prepared with fly ash to better meet the use requirements of rapid pavement projects in Tibet, has become a technical problem that needs to be solved urgently. Summary of the Invention

[0009] The present invention aims to address the aforementioned technical issues, providing fly ash recycled concrete for expressways, its preparation method, and its application. The technical objectives of the present invention are, on the one hand, to address the low fly ash usage and recycling rate in existing recycled concrete; and, on the other hand, to address the poor late-stage strength stability of existing recycled concrete, the need for improved cement performance, and its inability to fully meet the needs of high-altitude expressway repair projects.

[0010] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0011] The present invention first provides a fly ash recycled concrete for expressway construction, which comprises the following raw material components in parts by weight:

[0012] 26-36 parts of cement;

[0013] 3-8 parts fly ash;

[0014] 38-58 parts of recycled coarse aggregate;

[0015] 12-16 parts of recycled fine aggregate;

[0016] 2-5 parts of metakaolin;

[0017] 0.5-1.1 parts of water reducing agent;

[0018] 0.8-1.4 parts of shrinkage reducing agent;

[0019] 1.5-2.4 parts of low-viscosity cellulose ether;

[0020] 4-6 parts of starch ether;

[0021] 1-2 parts shell powder;

[0022] 1.1-1.5 parts of chitin nanowhiskers;

[0023] Pentaerythritol distearate 0.1-0.3 parts;

[0024] 5-8 parts of polypropylene oxide glycol;

[0025] 1-2 parts of dicyclohexylmethane diisocyanate;

[0026] 15-20 parts water.

[0027] The recycled concrete provided by the present invention successfully produces a rare-earth-activated, modified sulphoaluminate cement recycled cement material, resulting from the compounding of various materials. The inventors have discovered that the recycled concrete obtained through this compounding of raw materials exhibits significantly improved performance, including excellent mechanical properties, stable late-stage strength, and, in particular, significantly enhanced freeze-thaw resistance, making it well-suited for the repair of high-altitude expressways.

[0028] The compositions of the present invention can synergize with each other to fully activate the hydration activity of the recycled materials, thereby providing sufficient early hydration strength and maintaining the stability of the later strength under the premise of adding a large amount of fly ash and recycled aggregate. It can also improve the microstructure of the recycled concrete and inhibit the shrinkage of the later strength.

[0029] However, as shown in the comparative examples of the present invention, when the raw material compounding of the present invention is destroyed, the performance of the obtained recycled concrete will be significantly reduced; especially when a large amount of fly ash is added, it cannot meet the use requirements of pavement materials.

[0030] Furthermore, the particle size of the recycled coarse aggregate is 4.75-31.5 mm.

[0031] Furthermore, the particle size of the recycled fine aggregate is less than 4.75 mm.

[0032] Furthermore, the cement is ordinary Portland cement.

[0033] Furthermore, the water reducer is a polycarboxylate water reducer.

[0034] Furthermore, the fly ash is Class F II fly ash, and its density is 2.62-2.73 g / cm 3 , specific surface area 3600~4300cm 2 / g.

[0035] Furthermore, the shrinkage reducing agent is composed of polyethylene glycol monomethyl ether and methacrylic acid in a weight ratio of 2:1.

[0036] Furthermore, the starch ether includes hydroxyalkyl starch, carboxymethyl starch or cationic starch.

[0037] A second object of the present invention is to provide a method for preparing the above-mentioned road fly ash recycled concrete, comprising the following steps:

[0038] (1) Weigh the raw materials by weight and add them into the blender in the order of proportion, stirring for 2-3 minutes after each addition;

[0039] (2) Place the concrete mixture into the mold and vibrate on a vibration table until there are no obvious large bubbles on the surface and the concrete surface is slightly higher than the mold surface by 1-3 mm;

[0040] (3) After forming and plastering, let it stand for 24 hours, sprinkle water until the surface is moist, and apply a film on the surface to maintain humidity and isolate dust, and then carry out maintenance.

[0041] A third object of the present invention is to provide the application of the above-mentioned road fly ash recycled concrete in road construction projects.

[0042] The beneficial effects of the present invention are as follows:

[0043] (1) The present invention provides a sulphoaluminate cement that can fully utilize rare earth excitation modification, which is mainly composed of a composite combination of sulphoaluminate cement and a modifier. Through the dual excitation modification of the rare earth oxide and polyurethane prepolymer system of the present invention, the comprehensive properties of the sulphoaluminate cement are greatly improved, such as compressive strength and freeze-thaw resistance.

[0044] (2) The present invention achieves excellent early hydration strength of the recycled concrete prepared by adding a large amount of fly ash through a specific combination of raw materials, and well maintains the stability of the later strength, thereby suppressing the shrinkage of the later strength;

[0045] (3) The recycled concrete provided by the present invention can effectively realize the recycling of waste raw materials and can be well applied to rapid road construction and repair projects, and its application prospects are extremely broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Actual photo (a) and microscopic morphology (b) of fly ash selected for the present invention.

[0047] Figure 2 Actual pictures of the recycled coarse aggregate (left) and natural coarse aggregate (right) selected for the present invention.

[0048] Figure 3 Actual pictures of the recycled fine aggregate (left) and natural fine aggregate (right) selected for the present invention.

[0049] Figure 4 Schematic diagram of the static compressive elastic modulus loading method.

[0050] Figure 5 The number of freeze-thaw cycles of concrete. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in detail below with reference to the following embodiments. It is necessary to point out that the following embodiments are only used to explain and illustrate the present invention and are not intended to limit the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content still fall within the scope of protection of the present invention.

[0052] Example 1

[0053] 1. Experimental raw materials

[0054] (1) Fly ash and cement

[0055] The F-type II fly ash provided by Henan Zhengyuan Mineral Products Co., Ltd. is used, and its density is 2.62-2.73 g / cm 3 , specific surface area 3600~4300cm 2 / g. Ordinary Portland cement (OPC) is P·O 42.5 composite Portland cement produced by Lafarge Cement Co., Ltd., Dujiangyan, Chengdu, Sichuan Province. The chemical composition of fly ash and cement was analyzed by X-ray fluorescence spectrometry (XRF). The results are shown in Table 1. The physical and microscopic morphology photos are shown in Figure 1 .

[0056] Table 1 Main chemical components (wt / %)

[0057] CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[SO3]]> MgO <![CDATA[Na2O]]> LOI cement 52.77 23.4 6.82 4.44 4.06 2.46 1.14 2.28 fly ash 5.63 52.99 21.08 5.33 1.13 1.66 1.27 6.8

[0058] (2) Recycled aggregate

[0059] The recycled aggregate, sourced from a highway expansion and reconstruction project in the Tibet Autonomous Region, was crushed and screened in a laboratory. The recycled aggregate preparation process is as follows: Recycled waste concrete pavement is crushed into large blocks, and lightweight debris such as plastics are removed. The large blocks are then crushed a second time using a crusher. The resulting aggregate is then screened, rinsed, dusted, and air-dried, ultimately yielding recycled coarse aggregate with a particle size of 4.75 to 31.5 mm and recycled fine aggregate with a particle size of less than 4.75 mm. Because the coarse aggregate used in road construction is discontinuously graded, to improve the performance of the recycled concrete, the recycled coarse aggregate undergoes a second manual screening process to adjust it to a continuous particle size that meets regulatory requirements.

[0060] The material properties of recycled coarse aggregate are determined in accordance with "Recycled Coarse Aggregate for Concrete" (GB / T25177-2010), and the material properties of natural coarse aggregate are determined in accordance with "Pebbles and Crushed Stones for Construction" (GB / T14685-2022). The particle size distribution of recycled coarse aggregate is artificially adjusted to meet the requirements of Class II materials in the specification. The properties of recycled coarse aggregate are shown in Table 2. Figure 2 Left) and natural coarse aggregate ( Figure 2 (right) See the actual picture Figure 2 .

[0061] Table 2 Performance indexes of recycled coarse aggregate

[0062]

[0063] The material properties of recycled fine aggregate are determined in accordance with "Recycled Fine Aggregate for Concrete and Mortar" (GB / T25176-2010), and the material properties of natural fine aggregate are determined in accordance with "Construction Sand" (GB / T14684-2022). The experimental results show that the performance of recycled fine aggregate meets the requirements of Class I materials in the specification and can be put into use. The properties of recycled fine aggregate are shown in Table 3. Recycled fine aggregate ( Figure 3 Left) and natural fine aggregate ( Figure 3 Right) Figure 3 .

[0064] Table 3 Performance indexes of recycled fine aggregate

[0065]

[0066] (3) Water reducers and shrinkage reducers

[0067] Polycarboxylate high-performance water reducer: A solid polycarboxylate high-performance water reducer with a water reduction rate of ≥25%. Mixing water is tap water. The shrinkage reducer is composed of polyethylene glycol monomethyl ether and methacrylic acid in a weight ratio of 2:1.

[0068] (4) The low-viscosity cellulose ether is hydroxypropyl methylcellulose (400 viscosity) or hydroxyethyl cellulose; the starch ether is hydroxyalkyl starch or carboxymethyl starch, and the other raw materials are all commercially available conventional raw materials.

[0069] 2. Composition of recycled concrete raw materials

[0070] (1) The fly ash recycled concrete for roads provided in this embodiment comprises the following raw material components in parts by weight:

[0071] 28 parts of cement;

[0072] 5 parts of fly ash;

[0073] 45 parts of recycled coarse aggregate;

[0074] 14 parts of recycled fine aggregate;

[0075] 3 parts of metakaolin;

[0076] 1 part of water reducing agent;

[0077] 1.1 parts of shrinkage reducing agent;

[0078] 1.8 parts of low-viscosity cellulose ether;

[0079] 5 parts of starch ether;

[0080] 1 part shell powder;

[0081] 1.2 parts of chitin nanowhiskers;

[0082] 0.2 parts of pentaerythritol distearate;

[0083] 6 parts of polyoxypropylene glycol;

[0084] 1 part of dicyclohexylmethane diisocyanate;

[0085] 18 parts water.

[0086] 3. Performance test of recycled concrete specimens

[0087] 1. Preparation of recycled concrete specimens

[0088] The mix proportions for recycled fly ash concrete for roads were designed in accordance with the relevant requirements of the "Technical Specification for the Application of Recycled Aggregates" (JGJ / T 240-2011) and the "Specification for Mix Design of Ordinary Concrete" (JGJ 55-2011). Concrete specimens were prepared in accordance with the relevant requirements of the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T 50081-2019) and the "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009). The test equipment used was a single-shaft forced concrete mixer produced by the China Academy of Building Research. The specimen specifications and quantity and corresponding test contents are shown in Table 4.

[0089] Table 4 Specimen parameters

[0090] Specimen size (mm) Curing age (days) Number of test pieces (pieces) Test content 100×100×100 7、14、28、56 132 Cube compressive strength 100×100×300 7、14、28、56 132 Axial compressive strength 100×100×300 7、14、28、56 132 Static compressive elastic modulus 100×100×100 28 220 Anti-carbonization performance 100×100×400 28 33 Freeze-thaw resistance φ100, h50 28、56 66 Chloride ion corrosion resistance

[0091] The specific preparation steps are as follows: (1) Wipe the mold clean, apply a layer of oil evenly on all the internal surfaces and cover the small holes at the bottom with paper for later use; (2) Add the above raw materials into the mixer in accordance with the mix ratio, and stir for 2-3 minutes after each addition; (3) Put the concrete mixture into the mold prepared in advance, and vibrate it on the vibration table until there are no obvious large bubbles on the surface and the concrete surface is slightly higher than the mold surface by 1-3 mm; (4) After forming and plastering, let it stand for 24 hours, sprinkle water until the surface is moist, and cover the surface with film to maintain humidity and dustproof, and affix a numbered label on the surface of the plastic wrap.

[0092] 2. Specimen maintenance

[0093] The curing of concrete specimens was carried out in accordance with the relevant requirements of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019) and the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009). The curing location was the standard curing room of the Heavy Equipment Laboratory of Xinjiang University. The specific steps were as follows: (1) 24 hours after the specimens were cast, they were demoulded with an air pump, numbered, and placed in a standard curing room for curing. The temperature was controlled at (20±2)℃ and the humidity was maintained above 95%; (2) The specimens were placed on the bracket inside the standard curing room, with a spacing of (10-20)mm between adjacent specimens; (3) According to the requirements of different test contents, the specimens were taken out for testing after reaching the corresponding age.

[0094] 3. Cube compressive strength test

[0095] The compressive strength test of recycled concrete was conducted in accordance with the relevant requirements of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019). The test was conducted using an HCT306A microcomputer-controlled electro-hydraulic servo pressure testing machine produced by WanCe Testing Equipment Co., Ltd. The test specimens were non-standard cubic specimens measuring 100 mm × 100 mm × 100 mm. The size conversion factor was 0.95, and three specimens were used per group.

[0096] The specific test steps are as follows: (1) When the curing reaches the corresponding age, take out the specimen from the curing room, check its size and shape, wipe off the surface moisture, and immediately conduct the test; (2) Wipe clean the upper and lower pressure plates of the testing machine, use the side of the specimen when it is formed as the pressure surface, place the specimen on the pressure plate of the testing machine, and align the center of the specimen with the center of the pressure plate; (3) Turn on the testing machine, lower the upper pressure plate of the testing machine to close to the top of the cube specimen, leaving a certain gap, set the loading speed to 0.6MPa / s, and clear the press reading before each test; (4) Click to start the test, observe the development of the cracks in the specimen until the specimen is destroyed, and record the failure load. The compressive strength of the concrete cube is calculated according to formula (2.1):

[0097]

[0098] f cu ——Concrete cube compressive strength (MPa), calculated to the nearest 0.1MPa;

[0099] F——specimen failure load (N); A——specimen pressure bearing area (mm 2 ); 0.95—conversion factor for compressive strength of non-standard specimens.

[0100] 4. Axial compressive strength test

[0101] The compressive strength test of recycled concrete was conducted in accordance with the relevant requirements of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019). The test equipment was the same as that for the cube compressive strength test. The test specimens were prisms with a side length of 100mm×100mm×300mm. They were non-standard specimens with a size conversion factor of 0.95, and three specimens were used in each group. The test steps were the same as those for the cube compressive strength test. The axial compressive strength of concrete was calculated according to formula (2.2):

[0102]

[0103] f cp ——Axial compressive strength of concrete (MPa), calculated to the nearest 0.1MPa;

[0104] F——specimen failure load (N);

[0105] A——Test piece pressure bearing area (mm 2 );

[0106] 0.95——Conversion factor for compressive strength of non-standard specimens.

[0107] 5. Static compressive elastic modulus test

[0108] The static compressive elastic modulus test of recycled concrete was carried out in accordance with the relevant requirements of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019). The test used the HCT306A microcomputer-controlled electro-hydraulic servo pressure testing machine produced by WanCe Testing Equipment Co., Ltd., the DH3816 portable dynamic signal test and analysis system produced by Jiangsu Donghua Testing Technology Co., Ltd., and the resistance strain gauge produced by Chengdu DianCe Sensing Technology Co., Ltd. The specimen was a prismatic specimen with a side length of 100mm×100mm×300mm. It is a non-standard specimen with a size conversion coefficient of 0.95, and there are 3 pieces in each group. See the schematic diagram of the static compressive elastic modulus loading method for Figure 4 .

[0109] The specific test steps are as follows: (1) When the curing reaches the corresponding age, take out the specimen from the curing room, check its size and shape, wipe off the surface moisture, and clean the two opposite sides and the upper and lower surfaces with sandpaper; (2) Mark the side center axis with a marker, stick the strain gauge on the center axis with 502 glue, and the midpoint of the strain gauge coincides with the midpoint of the center axis; (3) Connect the strain gauge to the dynamic signal test and analysis system, wipe the upper and lower pressure plates of the testing machine clean, place the specimen on the testing machine pad, and align the center of the specimen with the center of the pad; (3) Lower the upper pressure plate of the testing machine to close to the top of the prismatic specimen, leaving a certain gap, and follow the Figure 3The loading mode is set as shown, and the press reading is cleared before each test; (4) Click to start the testing machine loading and dynamic signal test and analysis system acquisition at the same time, and record the corresponding load and strain during the loading process; (5) The specimen deforms rapidly and large cracks appear until it is destroyed, and the failure load is recorded, and the dynamic signal test and analysis system dot data is derived; (6) The average value of the left and right strain gauge data is taken as the strain, and then the stress is calculated according to the load and the force area of the specimen, and then a linear fit is performed with the strain data to obtain the stress-strain curve, and the slope is the static compressive elastic modulus.

[0110] 6. Rapid freeze-thaw test

[0111] The rapid freeze-thaw test of recycled concrete was carried out in accordance with the relevant requirements of the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009). The test instrument used was the HC-HDK9 / Y concrete rapid freeze-thaw tester produced by Jianyan Huace Technology Co., Ltd. The test specimens were prism specimens with a side length of 100mm×100mm×400mm, with 3 specimens per group. The results of the number of freeze-thaw cycles are shown in Figure 5 (Take Example 1 as an example).

[0112] The specific test steps are as follows: (1) When the curing age reaches 24 days, the specimen is taken out of the standard curing room and immersed in water for 4 days. The water temperature is maintained at (20±2)℃ and the water level is maintained at (20-30) mm above the top surface of the specimen; (2) When the curing age reaches 28 days, the specimen is taken out to wipe off the surface moisture, and the appearance dimensions of the specimen are measured. The specimens are numbered, and the initial mass W0i and the initial value of the transverse fundamental frequency f0i of the specimen are measured and recorded; (3) The specimen is placed in the specimen box and a solution is added to cover the top surface of the specimen. 5mm of clean water, wipe the surface of the specimen box clean and place it on the specimen rack inside the freeze-thaw machine; (4) During the freezing and thawing process, control the minimum temperature of the specimen center at (-18±2)℃ and the maximum temperature at (5±2)℃. Measure and record the transverse fundamental frequency fni of the specimen every 25 cycles, check the external damage of the specimen and weigh the mass Wni of the specimen; (5) Stop the test when the mass loss rate of the specimen reaches 5%, the relative dynamic elastic modulus drops to 60%, or the number of cycles is reached.

[0113] The relative dynamic elastic modulus of a single specimen is calculated according to formula (2.3):

[0114]

[0115] P i ——Relative dynamic elastic modulus of the i-th specimen after N freeze-thaw cycles (%);

[0116] f oi ——Initial value of the transverse fundamental frequency of the i-th specimen before the freeze-thaw cycle test (Hz);

[0117] f ni ——The transverse fundamental frequency (Hz) of the i-th specimen after N freeze-thaw cycles.

[0118] The relative dynamic elastic modulus of a group of specimens is calculated according to formula (2.4):

[0119]

[0120] P is the average relative dynamic elastic modulus (%) of a group of specimens after N freeze-thaw cycles.

[0121] The mass loss rate of a single specimen is calculated according to formula (2.5):

[0122]

[0123] ΔW ni ——Mass loss rate of the i-th specimen after N freeze-thaw cycles (%);

[0124] W 0i ——The mass of the i-th specimen before the freeze-thaw cycle test (g);

[0125] W ni ——The mass of the i-th specimen after N freeze-thaw cycles (g).

[0126] The mass loss rate of a group of specimens is calculated according to formula (2.6):

[0127]

[0128] ΔW n ——The average mass loss rate (%) of a group of specimens after N freeze-thaw cycles. When the test result is negative, it is taken as 0 and the average value is calculated.

[0129] The symbol F is used to represent the frost resistance grade of concrete, which is determined by the maximum number of freeze-thaw cycles when the mass loss rate does not exceed 5% or the relative dynamic elastic modulus drops to 60%.

[0130] Example 2

[0131] According to the method of Example 1, a fly ash recycled concrete for roads comprises the following raw material components in parts by weight:

[0132] 28 parts of cement;

[0133] 3 parts fly ash;

[0134] 38 parts of recycled coarse aggregate;

[0135] 12 parts of recycled fine aggregate;

[0136] 2 parts of metakaolin;

[0137] 0.5 parts of water reducing agent;

[0138] 0.8 parts of shrinkage reducing agent;

[0139] 1.5 parts of low viscosity cellulose ether;

[0140] 4 parts of starch ether;

[0141] 1 part shell powder;

[0142] 1.1 parts of chitin nanowhiskers;

[0143] 0.1 part of pentaerythritol distearate;

[0144] 5 parts of polypropylene oxide glycol;

[0145] 1 part of dicyclohexylmethane diisocyanate;

[0146] 15 parts water.

[0147] Example 3

[0148] According to the method of Example 1, a fly ash recycled concrete for roads comprises the following raw material components in parts by weight:

[0149] 36 parts of cement;

[0150] 6 parts of fly ash;

[0151] 58 parts of recycled coarse aggregate;

[0152] 16 parts of recycled fine aggregate;

[0153] 5 parts of metakaolin;

[0154] 1.1 parts of water reducer;

[0155] 1.4 parts of shrinkage reducing agent;

[0156] 2.4 parts of low viscosity cellulose ether;

[0157] 6 parts of starch ether;

[0158] 2 parts shell powder;

[0159] 1.5 parts of chitin nanowhiskers;

[0160] 0.3 parts of pentaerythritol distearate;

[0161] 8 parts of polypropylene oxide glycol;

[0162] 2 parts of dicyclohexylmethane diisocyanate;

[0163] 20 parts water.

[0164] Comparative Example 1

[0165] Road fly ash recycled concrete was prepared according to the method of Example 1, except that the starch ether and shell powder in the raw materials were deleted.

[0166] Comparative Example 2

[0167] Road fly ash recycled concrete was prepared according to the method of Example 1, except that the chitosan nano whiskers and pentaerythritol distearate were deleted from the raw materials.

[0168] Comparative Example 3

[0169] According to the method of Example 1, a fly ash recycled concrete for roads comprises the following raw material components in parts by weight:

[0170] 30 parts of cement;

[0171] 10 parts of fly ash;

[0172] 40 parts of recycled coarse aggregate;

[0173] 15 parts of recycled fine aggregate;

[0174] 3 parts of metakaolin;

[0175] 1.5 parts of water reducer;

[0176] 0.8 parts of shrinkage reducing agent;

[0177] 3 parts of low viscosity cellulose ether;

[0178] 1 part starch ether;

[0179] 5 parts shell powder;

[0180] 1 part of chitin nanowhiskers;

[0181] 0.1 part of pentaerythritol distearate;

[0182] 2 parts of polypropylene oxide glycol;

[0183] 3 parts of dicyclohexylmethane diisocyanate;

[0184] 30 parts water.

[0185] Experimental Example 1

[0186] The performance test of the recycled concrete specimens prepared in the embodiment and the comparative example was carried out. Two groups of specimens were calculated, each group of 10 specimens, and the average value was taken. The results of the measured cube compressive strength are shown in Table 5 below.

[0187] Table 5 Cube compressive strength

[0188]

[0189] The axial compressive strength is shown in Table 6:

[0190] Table 6 Axial compressive strength

[0191]

[0192] The test results of static compressive elastic modulus are shown in Table 7 below:

[0193] Table 7 Static compressive elastic modulus

[0194]

[0195] Freeze-thaw resistance performance is shown in Table 8 below:

[0196] Table 8 Freeze-thaw resistance

[0197]

[0198] From the above test results, it can be seen that the performance of the recycled concrete obtained under the embodiment of the present invention is significantly better than that of the comparative example, which proves that the combination of raw materials of the recycled concrete in the present invention synergistically promotes each other and jointly improves the performance of the recycled concrete.

Claims

1. A fly ash recycled concrete for expressway construction, characterized in that: Calculated by weight, it includes the following raw material components: 26-36 parts of cement; 3-8 parts fly ash; 38-58 parts of recycled coarse aggregate; 12-16 parts of recycled fine aggregate; 2-5 parts of metakaolin; 0.5-1.1 parts of water reducing agent; 0.8-1.4 parts of shrinkage reducing agent; 1.5-2.4 parts of low-viscosity cellulose ether; 4-6 parts of starch ether; 1-2 parts shell powder; 1.1-1.5 parts of chitin nanowhiskers; Pentaerythritol distearate 0.1-0.3 parts; 5-8 parts of polypropylene oxide glycol; 1-2 parts of dicyclohexylmethane diisocyanate; 15-20 parts water.

2. The fly ash recycled concrete for expressway construction according to claim 1, characterized in that: The particle size of the recycled coarse aggregate is 4.75-31.5 mm.

3. The fly ash recycled concrete for roads according to claim 1, characterized in that: The particle size of the recycled fine aggregate is less than 4.75 mm.

4. The fly ash recycled concrete for roads according to claim 1, characterized in that: The cement is ordinary Portland cement.

5. The fly ash recycled concrete for expressway construction according to claim 1, characterized in that: The water reducer is a polycarboxylate water reducer.

6. The fly ash recycled concrete for roads according to claim 1, characterized in that: The fly ash is Class F II fly ash, and its density is 2.62-2.73 g / cm 3 , specific surface area 3600~4300cm 2 / g.

7. The fly ash recycled concrete for expressway construction according to claim 1, characterized in that: The shrinkage reducing agent is composed of polyethylene glycol monomethyl ether and methacrylic acid in a weight ratio of 2:

1.

8. The fly ash recycled concrete for expressway construction according to claim 1, characterized in that: The starch ethers include hydroxyalkyl starch, carboxymethyl starch or cationic starch.

9. The method for preparing fly ash recycled concrete for expressway construction according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) Weigh the raw materials by weight and add them into the blender in the order of proportion, stirring for 2-3 minutes after each addition; (2) Place the concrete mixture into the mold and vibrate on a vibration table until there are no obvious large bubbles on the surface and the concrete surface is slightly higher than the mold surface by 1-3 mm; (3) After forming and plastering, let it stand for 24 hours, sprinkle water until the surface is moist, and apply a film on the surface to maintain humidity and isolate dust, and then carry out maintenance.

10. Use of the fly ash recycled concrete for expressway construction according to any one of claims 1 to 8 or the fly ash recycled concrete for expressway construction of various power transmission and transformation projects prepared by the method according to claim 9 in expressway construction projects.

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