Preparation method of seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars

Abstract

The present invention relates to a preparation method for seawater and sea sand recycled concrete beams reinforced with FRP bars cured with CO2. The specific process comprises: (1) mixing recycled aggregate, sea sand, artificial simulated seawater, water reducing agent and cement to prepare seawater and sea sand recycled concrete; (2) installing a bottom formwork; (3) laying FRP bars and erecting a sleeve for forming a duct; (4) installing a side formwork; (5) injecting the stirred seawater and sea sand recycled concrete into a mold, and forming a test block after the concrete pouring is completed. The test block is then sent to a curing room for standard curing; (6) after the expected standard curing time is reached, the erected sleeve is pulled out from the test block to expose the duct required for concrete carbonization near the FRP bars. The invention is beneficial to improving the durability of concrete and solving the problem that the high pH value of concrete easily leads to long-term performance degradation of FRP steel bars.

Description

Technical field:

[0001] The present invention relates to the technical field of curing of prefabricated concrete components, and in particular to a method for preparing seawater and sea sand recycled concrete beams by curing FRP bars using CO2. Background technology:

[0002] Concrete structures are the most important structures in civil engineering. They emit large amounts of CO2 during the production, transportation, and concrete preparation of their raw materials. CO2 is one of the main greenhouse gases. It is of great significance to find an effective method for producing concrete structures that saves energy and reduces emissions.

[0003] Carbon dioxide curing of concrete is one of the promising methods and is of great help in achieving carbon neutrality. However, there are certain limitations in the research on carbon dioxide in cementitious materials. The application experiments of carbon dioxide curing concrete are mostly concentrated on small-sized specimens such as blocks, and there is a lack of experiments on large-sized specimens, especially research on the carbonization curing process of large precast concrete.

[0004] The large-scale growth of the construction industry has generated a large amount of construction and demolition waste. Recycling waste concrete as a renewable resource and using it in new projects is an effective way to improve the resource utilization of construction solid waste. Due to the accumulation of internal damage in the waste concrete during the crushing process, the aggregates accumulate under the action of external forces, resulting in many microcracks and serious loss of particle size and strength. In addition, the loose and porous hardened cement mortar attached to the surface of the recycled aggregate makes the quality of the recycled aggregate lower than that of natural aggregate.

[0005] Current research progress shows that the carbonation depth of carbonization-enhanced concrete is generally low, which affects the improvement of the durability of fiber-reinforced composite (FRP) reinforced concrete structures. Summary of the invention:

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for preparing seawater-sand recycled concrete beams reinforced with FRP bars using CO2 curing. This method for preparing seawater-sand recycled concrete beams reinforced with FRP bars using CO2 curing is beneficial for solving the defect that the carbonization value of concrete is low and the steel bars are easily corroded.

[0007] The present invention provides a method for preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars, which is characterized by the following steps:

[0008] (1) Mix recycled aggregate, sea sand, artificial simulated sea water, water reducing agent and cement to make seawater and sea sand recycled concrete;

[0009] (2) Install the bottom template;

[0010] (3) Lay FRP bars and install casing for forming the hole;

[0011] (4) Install side formwork;

[0012] (5) Pour the stirred seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a test block, and then send the test block to the curing room for standard curing;

[0013] (6) After the expected standard curing time is reached, the casing is pulled out from the test block to expose the pores required for concrete carbonization near the FRP bars;

[0014] (7) The test block is then sent to a carbon dioxide curing box for curing. In a confined space, pressurized air pumps are set up on both sides of the reserved channel to introduce industrial waste carbon dioxide gas into the reserved channel for carbonization curing;

[0015] (8) When the curing time reaches the expected carbonization depth, remove the test piece;

[0016] (9) Finally, grouting is performed to fill the reserved channels.

[0017] The present invention provides a method for preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars, which is characterized by the following steps:

[0018] (1) Mix recycled aggregate, sea sand, artificial simulated sea water, water reducing agent and cement to make seawater and sea sand recycled concrete;

[0019] (2) Install the bottom template;

[0020] (3) Lay FRP bars and set up rectangular prefabricated molds;

[0021] (4) Install side formwork;

[0022] (5) Pour the stirred seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a test block, and send the test block to the curing room for standard curing;

[0023] (6) After the expected standard curing time is reached, the prefabricated cube mold is pulled out to expose the area near the steel bars required for concrete carbonization;

[0024] (7) The test piece is then sent to a carbon dioxide curing box for curing, and industrial waste carbon dioxide gas is introduced into the closed space for carbonization curing;

[0025] (8) When the curing time reaches the expected carbonization depth, remove the test piece;

[0026] (9) Finally, grouting is performed to fill the reserved area.

[0027] Preferably, the FRP bars include one or more of basalt fiber reinforced composite bars (BFRP), glass fiber reinforced composite bars (GFRP), and carbon fiber reinforced composite bars (CFRP).

[0028] Preferably, the water is artificial simulated seawater.

[0029] Preferably, the above-mentioned sea sand can be replaced by one or more of regenerated sand, river sand and shell sand.

[0030] Preferably, the mixed recycled aggregate includes construction waste recycled from crushed buildings and industrial carbon dioxide waste gas.

[0031] The carbon dioxide-cured concrete prepared in the present invention not only stores and fixes carbon dioxide gas but also possesses a very dense microstructure, resulting in excellent durability (corrosion resistance, impermeability, and freeze-thaw cycle resistance) not found in conventional concrete. Fiber-reinforced plastic (FRP) boasts high strength, light weight, and excellent corrosion resistance, and can be directly applied to seawater and sea sand concrete, rather than steel as a reinforcement. The combination of these two materials perfectly addresses the corrosion-prone steel reinforcement associated with seawater and sea sand. Furthermore, the high porosity of recycled aggregate improves the efficiency of carbon dioxide curing and significantly enhances the compressive strength of recycled concrete.

[0032] This method reserves carbonization channels in advance when manufacturing beams, creating conditions for rapid carbonization of the concrete around the steel bars. During the carbonization process, the concrete near the steel bars is fully exposed to carbon dioxide, allowing the concrete near the FRP bars to be quickly carbonized. This not only improves the early strength of precast concrete beams and shortens the curing age, but also effectively combines FRP bars with seawater and sea sand recycled concrete, solving the problem of chloride ion erosion in seawater and sea sand recycled concrete and the long-term performance degradation of FRP bars caused by high concrete pH values. Description of the drawings:

[0033] Figure 1 1 is a schematic diagram of the cross-section of a beam manufactured by the first method of the present invention;

[0034] In the figure, 1 refers to the hole, 2 refers to the FRP bar, 3 refers to the distance between the hole and the FRP bar, and 4 refers to the concrete area;

[0035] Figure 2 1 is a schematic diagram of the cross-section of a beam manufactured by the second method of the present invention;

[0036] In the figure, 1 refers to the opening area, 2 refers to the concrete area, 3 refers to the FRP reinforcement, and 4 refers to the longitudinal distance of the square hole;

[0037] Figure 31 is a schematic diagram of the cross-section of a beam according to a first embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the carbonization degree of concrete around the steel bars after curing is completed in the first embodiment;

[0039] Figure 5 1 is a schematic diagram of the cross-section of a beam according to a second embodiment of the present invention;

[0040] Figure 6 is a schematic diagram of the height of the compression zone;

[0041] Figure 7 1 is a schematic diagram of the specific dimensions of the cross section of the beam of the second embodiment of the present invention;

[0042] Figure 8 This is a schematic diagram of the carbonization degree of concrete around the steel bars after curing is completed in the second embodiment. Specific implementation method:

[0043] The first method of preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars is characterized by the following steps:

[0044] (1) Mix recycled aggregate, sea sand, artificial simulated sea water, water reducing agent and cement to make seawater and sea sand recycled concrete;

[0045] (2) Install the bottom template;

[0046] (3) Lay FRP bars and install casing for forming the hole;

[0047] (4) Install side formwork;

[0048] (5) Pour the stirred seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a test block, and then send the test block to the curing room for standard curing;

[0049] (6) After the expected standard curing time is reached, the casing is pulled out from the test block to expose the pores required for concrete carbonization near the FRP bars;

[0050] (7) The test block is then sent to a carbon dioxide curing box for curing. In a confined space, pressurized air pumps are set up on both sides of the reserved channel to introduce industrial waste carbon dioxide gas into the reserved channel for carbonization curing;

[0051] (8) When the curing time reaches the expected carbonization depth, remove the test piece;

[0052] (9) Finally, grouting is performed to fill the reserved channels.

[0053] The second method of the present invention for preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars is characterized in that the specific process includes:

[0054] (1) Mix recycled aggregate, sea sand, artificial simulated sea water, water reducing agent and cement to make seawater and sea sand recycled concrete;

[0055] (2) Install the bottom template;

[0056] (3) Lay FRP bars and set up cube prefabricated molds;

[0057] (4) Install side formwork;

[0058] (5) Pour the stirred seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a test block, and send the test block to the curing room for standard curing;

[0059] (6) After the expected standard curing time is reached, the prefabricated cube mold is pulled out to expose the area near the steel bars required for concrete carbonization;

[0060] (7) The test piece is then sent to a carbon dioxide curing box for curing, and industrial waste carbon dioxide gas is introduced into the closed space for carbonization curing;

[0061] (8) When the curing time reaches the expected carbonization depth, remove the test piece;

[0062] (9) Finally, grouting is performed to fill the reserved area.

[0063] The above-mentioned FRP bars include one or more of basalt fiber reinforced composite bars (BFRP), glass fiber reinforced composite bars (GFRP), and carbon fiber reinforced composite bars (CFRP); the above-mentioned water is artificial simulated seawater; the above-mentioned sea sand can be replaced by one or more of recycled sand, river sand, and shell sand; the above-mentioned mixed recycled aggregate includes construction waste recycled from crushed buildings and industrial carbon dioxide waste gas.

[0064] The carbon dioxide-cured concrete prepared in the present invention not only stores and fixes carbon dioxide gas but also possesses a very dense microstructure, resulting in excellent durability (corrosion resistance, impermeability, and freeze-thaw cycle resistance) not found in conventional concrete. Fiber-reinforced plastic (FRP) boasts high strength, light weight, and excellent corrosion resistance, and can be directly applied to seawater and sea sand concrete, rather than steel as a reinforcement. The combination of these two materials perfectly addresses the corrosion-prone steel reinforcement associated with seawater and sea sand. Furthermore, the high porosity of recycled aggregate improves the efficiency of carbon dioxide curing and significantly enhances the compressive strength of recycled concrete.

[0065] This method reserves carbonization channels in advance when manufacturing beams, creating conditions for rapid carbonization of the concrete around the steel bars. During the carbonization process, the concrete near the steel bars is fully exposed to carbon dioxide, allowing the concrete near the FRP bars to be quickly carbonized. This not only improves the early strength of precast concrete beams and shortens the curing age, but also effectively combines FRP bars with seawater and sea sand recycled concrete, solving the problem of chloride ion erosion in seawater and sea sand recycled concrete and the long-term performance degradation of FRP bars caused by high concrete pH values.

[0066] Embodiment of the first method of the present invention:

[0067] The materials used are 42.5 grade ordinary Portland cement, artificial simulated seawater, sea sand and other raw materials, with a water-cement ratio of 0.47 and the environmental category is Class I.

[0068] SSRAC concrete mix ratio

[0069]

[0070] Concrete is prepared according to the mix ratio of concrete in the table and mixed by dry mixing method. First, dry mix the cement, aggregate and fine aggregate for 90 seconds to ensure uniform mixing. Then add 90% mixing water into the mixer and stir for about 90 seconds. Then add 10% mixing water and water reducer and stir for 90 seconds before pouring into the mold.

[0071] According to the principle of concrete cover thickness, the minimum distance between the channel and the FRP reinforcement is limited to ensure the bonding between the concrete and the reinforcement. According to the specification, under normal indoor conditions, the minimum concrete cover thickness of the beam is 20mm, and 20mm is set as the minimum distance between the channel and the FRP reinforcement.

[0072] In the Chinese building standard "Code for Design of Ordinary Concrete Structures" (GB 50010-2010), it is stipulated that the minimum diameter of embedded pipes in concrete structures should be no less than 20mm, and the channel diameter is taken as 20mm.

[0073] The beam size is 200mm×300mm. The steel bar is GFRP bar with a diameter of 14mm. d is greater than 20mm

[0074] The main forms such as Figure 3 As shown in the figure, 3D20@40 is three holes with a diameter of 20mm and a spacing of 40mm; 4G14@40 is four GFRP bars with a diameter of 14mm.

[0075] The carbonation depth model is used to calculate the carbonation depth of seawater and sea sand recycled concrete. The carbonation depth is analyzed using the verified seawater and sea sand recycled concrete carbonization model to obtain the influence coefficient of this variable.

[0076] The specific model is as follows:

[0077]

[0078] Where: k W / C —Water-cement ratio influence coefficient; k SS —Influence coefficient of fine aggregate type; m—Constant reflecting other factors; T—Temperature; C0—Carbon dioxide concentration; RH—Humidity; W / C—Water-cement ratio; t—Carbonization time (d); t c —Standard curing time (d); f cu —Standard compressive strength; it is known that the standard compressive strength after standard curing is 34.302Mpa.

[0079] Basic parameters

[0080] Set the curing temperature (T) to 20 degrees; humidity (RH) to 70%; carbon dioxide concentration (C0) to 50%; sea sand water absorption rate to 4.69%; water-binder ratio to 0.47; after 7 days of standard curing, carbonization curing is performed for 21 days. Substitute the above parameters into the calculation

[0081]

[0082] The carbonization depth can reach 36mm. At this carbonization depth, the concrete around the FRP bars can be completely carbonized. After the curing is completed, the carbonization degree of the concrete around the steel bars is about Figure 4 As shown, the gray area is the carbonization completion area; this method is more efficient than the ordinary carbonization curing method; it can complete the carbonization of concrete near the steel bars in a shorter standard curing plus carbonization curing time.

[0083] The second method embodiment of the present invention:

[0084] The materials used are 42.5 grade ordinary Portland cement, artificial simulated seawater, sea sand and other raw materials, with a water-cement ratio of 0.47. The environmental category is Class I.

[0085] SSRAC concrete mix ratio

[0086] Concrete is prepared according to the mix ratio of concrete in the table and mixed by dry mixing method. First, dry mix the cement, aggregate and fine aggregate for 90 seconds to ensure uniform mixing. Then add 90% mixing water into the mixer and stir for about 90 seconds. Then add 10% mixing water and water reducer and stir for 90 seconds before pouring into the mold.

[0087] According to the principle of concrete beam cover thickness, the minimum distance between the hole and the FRP bar is limited to ensure the bonding between the concrete and the steel bar. According to the specification, under normal indoor environment, the minimum concrete cover thickness of the beam is 20mm, and 20mm is set as the minimum distance between the hole and the steel bar.

[0088] The concrete height of the compression zone of the concrete beam in bending is determined according to the limit D1. The size of the beam is 200mm×300mm. The steel bar is GFRP bar with a diameter of 14mm. The main forms are as follows: Figure 5 shown.

[0089] (1) Consider D1 size

[0090] The purpose of this calculation is to measure the height x of the compressed area. c (like Figure 6 shown)

[0091] According to the Code of Principles of Concrete Design:

[0092] α1f c bx=f y A s

[0093] x=2(1-0.6)x c =0.8x c

[0094] β1=2(1-k2)

[0095] Where: below C50, α1 is 1.0, and β1 is 0.8. c -Design value of concrete axial compressive strength, f y - Design value of steel bar tensile strength, A s -Area of ​​longitudinal reinforcement. b -Width of beam cross section 200mm. x -Height of compression zone of equivalent rectangular stress diagram, x c - Actual height of the compression zone. The compressive strength of the seawater sand recycled concrete cube cast in this experiment is 34.302Mpa, which belongs to the C30 strength grade concrete. c Take 14.3N / mm 2 The selected reinforcement is 14mm GFRP reinforcement, f y Take 400N / mm 2 , b is 200mm;

[0096] Substitute β1 = 0.8 to obtain

[0097] k2=1-0.4=0.6

[0098] x=2(1-0.6)x c =0.8x c

[0099] Substitute f c 、f y , b, α1, A s

[0100] α1f c bx=f y A s

[0101] 1.0×14.3×200×x=400×4×π×7 2

[0102] x=86.12mm

[0103] x c =86.12 / 0.8=107.65mm

[0104] Note: The distance from the top of the opening to the top of the concrete beam is limited to 107.65mm.

[0105] The figure shows the size limit of D1. The upper limit is 107.65≈108mm, the lower limit is 25mm for the protective layer thickness plus the steel bar diameter 14mm plus the hole to the steel bar limit thickness 20mm, which is 59mm. The specific size is as follows Figure 7 shown.

[0106] (2) Consider carbonization depth

[0107] 1. Set the curing temperature (T) to 20 degrees;

[0108] 2. Humidity (RH) 70%;

[0109] 3. Carbon dioxide concentration (C0) 50%;

[0110] 4. The water absorption rate of sea sand is 4.69%;

[0111] 5. Water-cement ratio 0.47;

[0112] 6. After 7 days of standard curing, send it to carbonization curing for 21 days;

[0113] The above parameters are brought into the calculation

[0114]

[0115] The carbonization depth can reach 36mm. The carbonization effect is shown in the figure below. The gray area is the carbonization completion area.

[0116] like Figure 8 shown.

[0117] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing seawater and sea sand recycled concrete beams using CO2-cured FRP bars, characterized by: The specific process includes: (1) Mix recycled aggregate, sea sand, artificial simulated sea water, water reducing agent and cement to make sea water and sea sand recycled concrete; (2) Install the bottom template; (3) Lay FRP bars and install casing for forming the channel; (4) Install side formwork; (5) Pour the mixed seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a test block, and then send the test block to the curing room for standard curing; (6) After the expected standard curing time is reached, the casing is pulled out from the test block to expose the pores required for carbonization of the concrete near the FRP bars; (7) The test block is then sent to a carbon dioxide curing box for curing. In a confined space, pressurized air pumps are set up on both sides of the reserved channel to introduce industrial waste carbon dioxide gas into the reserved channel for carbonization curing; (8) When the curing time reaches the expected carbonization depth, remove the test piece; (9) Finally, grouting is performed to fill the reserved channels.

2. A method for preparing seawater and sea sand recycled concrete beams using CO2-cured FRP bars, characterized by: The specific process includes: (1) Mix recycled aggregate, sea sand, artificial simulated sea water, water reducing agent and cement to make sea water and sea sand recycled concrete; (2) Install the bottom template; (3) Lay FRP bars and set up rectangular prefabricated molds; (4) Install side formwork; (5) Pour the mixed seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a test block, and then send the test block to the curing room for standard curing; (6) After the expected standard curing time is reached, the prefabricated rectangular mold is pulled out to expose the area required for concrete carbonization near the steel bars; (7) The test block is then sent to a carbon dioxide curing box for curing, where industrial waste carbon dioxide gas is introduced into the closed space for carbonization curing; (8) When the curing time reaches the expected carbonization depth, remove the test piece; (9) Finally, grouting is performed to fill the reserved area.

3. The method for preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars according to claim 1 or 2, characterized in that: The FRP bars include one or more of basalt fiber reinforced composite bars (BFRP), glass fiber reinforced composite bars (GFRP), and carbon fiber reinforced composite bars (CFRP).

4. The method for preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars according to claim 1 or 2, characterized in that: The sea sand is replaced by one or more of regenerated sand, river sand and shell sand.

5. The method for preparing seawater and sea sand recycled concrete beams reinforced with CO2-cured FRP bars according to claim 1 or 2, characterized in that: The mixed recycled aggregate includes construction waste that is crushed and recycled from buildings.

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