A design method for a high elastic modulus CA-RPC system based on ductility grading index

Abstract

The present disclosure relates to the technical field of coarse aggregate reactive powder concrete (CA-RPC), and provides a design method for a high elastic modulus CA-RPC system based on ductility classification indexes. According to the target structural performance requirements and the proposed reinforcement state of the CA-RPC system, it is divided into a compression zone, a reinforced tension zone, and an unreinforced shear zone; a low ductility index is adopted for the compression zone, a medium ductility index is adopted for the reinforced tension zone, and a high ductility index is adopted for the unreinforced shear zone; for the low ductility index, low strain hardening CA-RPC is used; for the medium ductility index, medium strain hardening CA-RPC is used; for the high ductility index, high strain hardening CA-RPC is used. The present invention establishes a complete set of system design methods characterized by three major ductility indexes of low, medium, and high, which is beneficial to the further engineering promotion of CA-RPC.

Description

Technical Field

[0001] The invention belongs to the technical field of reactive powder concrete in the field of civil engineering, and specifically relates to a design method of a high elastic modulus CA-RPC system based on ductility grading indexes for structural application requirements. Background Technique

[0002] Reactive powder (RPC) has excellent crack resistance and strong microcrack self-healing ability, and is widely applicable to precast and assembled bridges. However, the high material price and the small increase in elastic modulus compared to strength seriously restrict the wide application of RPC materials. Domestic and foreign scholars have developed a low-cost coarse aggregate RPC system with low shrinkage and high elastic modulus by adding coarse aggregates, and reduced the consumption of coarse aggregate RPC materials by reducing the cross-section height, etc., laying a foundation for the application of coarse aggregate RPC materials in the composite girder cable-stayed bridge of the Fifth Nanjing Yangtze River Bridge, and successfully contributing to the performance leap and system innovation of bridge structures.

[0003] Through domestic and foreign research and engineering practice, it is found that there is an uneven distribution of phases perpendicular to the pouring direction during the pouring of the coarse aggregate RPC system, resulting in a weak area with far lower performance than that along the pouring direction, thus preventing the ultra-high performance of the coarse aggregate RPC material from being exerted and restricting the popularization and application of the coarse aggregate RPC material in structures. In addition, the lack of evaluation indexes for CA-RPC also seriously restricts the exertion of the ultra-high performance of the material and the rapid popularization and selection in actual projects. Summary of the Invention

[0004] To solve the above problems, the invention discloses a design method of a high elastic modulus CA-RPC system based on ductility grading indexes for structural function requirements. Starting from different structural function requirements, three major ductility indexes of low, medium and high for structural requirements are established; according to the determined high elastic modulus mix ratio of the basic CA-RPC, three technical means such as fiber hybrid mixing, aggregate-fiber coupling, and fiber grid migration and limitation are adopted to realize the corresponding ductility index requirements, and finally a complete set of design methods for the high elastic modulus CA-RPC system considering ductility grading indexes is formed.

[0005] To achieve the above object, the technical solution of the invention is as follows:

[0006] A design method of a high elastic modulus CA-RPC system based on ductility grading indexes,

[0007] According to the target structural performance requirements and the proposed reinforcement state of the CA-RPC system, it is divided into a compression zone, a reinforced tension zone and an unreinforced shear zone;

[0008] The low ductility index is adopted in the compression zone, the medium ductility index is adopted in the reinforced tension zone, and the high ductility index is adopted in the unreinforced shear zone;

[0009] For low ductility index, low strain-hardening CA-RPC is adopted;

[0010] For medium ductility index, medium strain-hardening CA-RPC is adopted;

[0011] For high ductility index, high strain-hardening CA-RPC is adopted.

[0012] Furthermore, for low ductility index, the fiber hybrid mixing technology is adopted to achieve strain hardening;

[0013] For medium ductility index, the fiber hybrid mixing technology combined with the fiber-aggregate coupling technology is adopted to achieve strain hardening;

[0014] For high ductility index, the fiber hybrid mixing technology combined with the continuous fiber grid migration and confinement technology is adopted to achieve strain hardening.

[0015] Furthermore, the fiber hybrid mixing is the hybrid mixing of 1% straight fiber and 1% hooked-end fiber by volume, achieving low strain hardening under tension, with the strain reaching 0.1%-0.2%.

[0016] Furthermore, the fiber-aggregate coupling technology is to mix epoxy resin with steel fibers to form an integrated effect of aggregate-fiber, achieving medium strain hardening under tension, with the strain reaching 0.2-0.3%.

[0017] Furthermore, the continuous fiber grid migration and confinement technology is to lay continuous carbon fiber / basalt fiber grids between layers. By preventing the sinking of aggregates and the floating migration of fibers through the fiber grids, a synergistic effect of continuous fiber grid-matrix-steel fiber is formed to achieve high strain hardening characteristics, with the strain reaching above 0.4%.

[0018] Furthermore, the straight steel fiber is 13 mm long and 0.2 mm in diameter; the hooked-end steel fiber is 20 mm long and 0.2 mm in diameter.

[0019] Furthermore, the mass ratio of high elastic modulus system CA-RPC powder and aggregate is: cement 0.8-1.2, silica fume 0.2-0.3, quartz sand 0.4-0.6, basalt 0.4-0.6, water 0.1-0.2, water reducer 0.03-0.05, and the volume fraction of steel fiber is 1%-2% of the total volume. Basalt aggregate with a diameter of 5-8 mm is adopted, and the aggregate mass substitution rate is 40%-60%.

[0020] Furthermore, the preparation of CA-RPC for high ductility index includes:

[0021] Wash and dry the basalt, and then soak it in adhesive and stick on the steel fibers;

[0022] Load the materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80-200 seconds;

[0023] Add the processed basalt coarse aggregate, stir for 120 - 160 seconds and then pour. During the pouring process, lay a layer of fiber grid every 1 - 2 cm until all pouring is completed, and complete the preparation of high-ductility system CA-RPC.

[0024] Furthermore, the preparation of CA-RPC with low ductility index includes:

[0025] Wash and dry the basalt for later use;

[0026] Load materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80 - 200 seconds;

[0027] Add basalt coarse aggregate, stir for 120 - 160 seconds and then add short straight steel fibers in proportion.

[0028] Furthermore, the preparation of CA-RPC with medium ductility index includes:

[0029] Wash and dry the basalt, soak it in glue and stick end-hooked steel fibers;

[0030] Load materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80 - 200 seconds;

[0031] Add the processed basalt coarse aggregate, stir for 120 - 160 seconds, then add short straight fibers and stir for another 120 - 160 seconds before pouring to complete the preparation of medium-ductility system CA-RPC. The system indexes are: compressive strength greater than 150 Mpa, elastic modulus greater than 55 Gpa, tensile strength greater than 9 Mpa, and having strain hardening characteristics.

[0032] The beneficial effects of the present invention are:

[0033] 1. The present invention provides a high elastic modulus basic formula of CA-RPC material according to functional requirements. The high elastic modulus characteristics can effectively reduce the structural cross-sectional area, reduce the material consumption, lower the cost, and are beneficial to the popularization and application of CA-RPC materials;

[0034] 2. The present invention provides a full system preparation method of CA-RPC with low, medium, and high ductility indexes. Among them, the aggregate fiber coupling technology can effectively solve the fiber-aggregate mutual exclusion effect and improve the material property stability of CA-RPC;

[0035] 3. The continuous fiber grid migration limiting technology in the present invention can effectively solve the problem of poor performance stability caused by complex phase migration and further improve the material property stability of CA-RPC;

[0036] 4. The invention finally forms a high-elasticity modulus CA-RPC system based on ductility classification indicators, which can be directly used for material selection in structural design and provides a calculation basis for practical engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the design method of the high-elasticity modulus CA-RPC system based on ductility classification indicators in the present invention;

[0038] Figure 2 shows the aggregate-fiber coupling and fiber mesh limiting effects under different ductility indicators in the present invention. EMBODIMENTS

[0039] The present invention will be further clarified below in conjunction with the drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The relevant descriptions are exemplary and are not intended to limit the scope of the present disclosure. In the detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is obvious that one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0040] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0041] Please refer to Figure 1 and Figure 2 , the present invention provides a design method for a high-elasticity modulus CA-RPC system based on ductility classification indicators.

[0042] According to the target structural performance requirements and the proposed reinforcement state of the CA-RPC system, it is divided into a compression zone, a reinforced tension zone, and an unreinforced shear zone;

[0043] A low ductility indicator is adopted in the compression zone, a medium ductility indicator is adopted in the reinforced tension zone, and a high ductility indicator is adopted in the unreinforced shear zone;

[0044] For the low ductility indicator, low-variable softening CA-RPC is adopted;

[0045] For the medium ductility indicator, medium strain hardening CA-RPC is adopted;

[0046] For the high ductility indicator, high strain hardening CA-RPC is adopted.

[0047] Furthermore, for the low ductility indicator, the fiber compound admixture technology is adopted to achieve strain hardening;

[0048] For the medium ductility index, the fiber hybrid technology is combined with the fiber-aggregate coupling technology to achieve strain hardening;

[0049] For the high ductility index, the fiber hybrid technology is combined with the fiber-fiber mesh confinement technology to achieve strain hardening.

[0050] Furthermore, the fiber hybrid mixing is the hybrid mixing with a volume ratio of 1% straight fibers and 1% hooked-end fibers, achieving low strain hardening under tension, with the strain reaching 0.1% - 0.2%.

[0051] By hybrid mixing 1% straight fibers and 1% hooked-end fibers, low strain hardening under tension can be achieved, improving the energy dissipation capacity.

[0052] Furthermore, the fiber-aggregate coupling technology is to form an integrated aggregate-fiber effect by mixing epoxy resin with steel fibers, achieving medium strain hardening under tension, with the strain reaching 0.2 - 0.3%.

[0053] The fiber-aggregate coupling technology, that is, after cleaning and drying, epoxy resin is mixed with steel fibers, finally forming a "hedgehog-shaped" integrated aggregate-fiber effect, solving the problem of fiber-aggregate distribution conflict to a certain extent, and can achieve medium strain hardening under tension.

[0054] Furthermore, the continuous fiber grid migration confinement technology is to lay continuous carbon fiber / basalt fiber grids between layers, prevent the aggregate from sinking and the fiber from floating and migrating through the fiber grid, form the synergistic effect of continuous fiber mesh - matrix - steel fiber, and achieve the high strain hardening characteristics, with the strain reaching more than 0.4%.

[0055] Furthermore, the straight steel fiber is 13 mm long and 0.2 mm in diameter; the hooked-end steel fiber is 20 mm long and 0.2 mm in diameter.

[0056] Furthermore, the mass ratio of the high elastic modulus system CA-RPC powder and aggregate is as follows: cement 0.8 - 1.2, silica fume 0.2 - 0.3, quartz sand 0.4 - 0.6, basalt 0.4 - 0.6, water 0.1 - 0.2, water reducer 0.03 - 0.05, and the volume fraction of steel fiber is 1% - 2% of the total volume. Basalt aggregate with a diameter of 5 - 8 mm is used, and the aggregate mass substitution rate is 40% - 60%.

[0057] The above-mentioned powder and aggregate mix ratio can achieve a high elastic modulus index with an elastic modulus not lower than 55 GPa.

[0058] In the above system, the volume ratio of the steel fiber is not accounted for, and the others are mass ratios.

[0059] Furthermore, the preparation of CA-RPC for low ductility index includes:

[0060] Wash and dry the basalt for later use;

[0061] Load materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80 - 200 seconds;

[0062] Add basalt coarse aggregate, stir for 120 - 160 seconds, then add short straight steel fibers and hooked - end steel fibers in proportion for fiber hybrid doping, continue to stir for 120 - 160 seconds and then pour to complete the preparation of CA - RPC for the low - ductility system. The system indexes are: compressive strength greater than 150 Mpa, elastic modulus greater than 55 Gpa, tensile strength greater than 7 Mpa, with slightly strain - hardening characteristics.

[0063] Furthermore, the preparation of CA - RPC for medium - ductility indexes includes:

[0064] Wash and dry the basalt, then soak it in adhesive and stick hooked - end steel fibers;

[0065] Load materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80 - 200 seconds;

[0066] Add the treated basalt coarse aggregate, stir for 120 - 160 seconds, then add short straight fibers again and stir for 120 - 160 seconds and then pour to complete the preparation of CA - RPC for the medium - ductility system. The system indexes are: compressive strength greater than 150 Mpa, elastic modulus greater than 55 Gpa, tensile strength greater than 9 Mpa, with strain - hardening characteristics.

[0067] Furthermore, the preparation of CA - RPC for high - ductility indexes includes:

[0068] Wash and dry the basalt, then soak it in adhesive and stick steel fibers;

[0069] Load materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80 - 200 seconds;

[0070] Add the treated basalt coarse aggregate, stir for 120 - 160 seconds and then pour. During the pouring process, lay a layer of fiber grid every 1 - 2 cm until all pouring is completed to complete the preparation of CA - RPC for the high - ductility system. The system indexes are: compressive strength greater than 150 Mpa, elastic modulus greater than 55 Gpa, tensile strength greater than 11 Mpa, with obvious strain - hardening characteristics.

[0071] The specific implementation process of the present invention is as follows:

[0072] Step S1: Determine the mix ratio of high elastic modulus system CA-RPC powder and aggregate. Through a large number of tests, the basic mix ratio of the high elastic modulus CA-RPC system is determined: cement (0.8 - 1.2), silica fume (0.2 - 0.3), quartz sand (0.4 - 0.6), basalt (0.4 - 0.6), water (0.1 - 0.2), water reducer (0.03 - 0.05), steel fiber (1% - 2%). Use basalt aggregate with a diameter of 5 - 8 mm, and the aggregate mass substitution rate is 40% - 60%;

[0073] Step S2: Determine the target structural performance requirements and analyze the material ductility indexes in different stress areas;

[0074] Step S2.1: For the compression zone, adopt a low strain hardening material system, and use the fiber hybrid technology to achieve strain hardening, with the strain exceeding 0.1%, and at the same time, the initial cracking strength should be greater than 9 MPa;

[0075] Step S2.2: For the reinforced tension zone, adopt a medium strain hardening material system, and use the fiber hybrid technology combined with the fiber-aggregate coupling technology to further achieve strain hardening, with the strain exceeding 0.2%, and at the same time, the initial cracking strength should be greater than 11 MPa;

[0076] Step S2.3: For the unreinforced shear zone, adopt a high strain hardening material system, and use the fiber hybrid technology combined with the fiber-fiber mesh confinement technology to further achieve strain hardening, with the strain exceeding 0.4%, and at the same time, the initial cracking strength should be greater than 11 MPa;

[0077] After completing the preparation of materials for the multi-ductility index system, the present disclosure example also tested the prepared CA-RPC for compressive strength, direct tensile strength, peak strain, and elastic modulus. The specific results are as follows:

[0078] Step S3: Select appropriate materials at different required parts of the structure, carry out large-scale mixing production, and finally form a high-efficiency structure that can fully exert the excellent performance of the materials, thus forming a design method of a high elastic modulus CA-RPC system based on ductility grading indexes for structural function requirements;

[0079] Specifically, this example realizes the "material-structure" integrated design method by establishing the ductility indexes of the CA-RPC high elastic modulus material system for structural requirements and combining the structural function requirements and the basic material design. At the same time, three technical means, namely fiber hybrid mixing, fiber-aggregate coupling, and fiber grid migration confinement, are used to meet the corresponding ductility index requirements, and finally a complete set of design methods for the high elastic modulus CA-RPC system considering ductility grading indexes is formed, which has significant technical and economic value.

[0080] Based on the different functional requirements of structural compression, tension, and shear, this invention establishes three major ductility indicators of low, medium, and high levels for structural requirements. Among them, low-ductility materials, namely low-strain-hardening CA-RPC, are used for the slab elements in the compression zone; medium-ductility, namely medium-strain-hardening CA-RPC, is used for the reinforced tensile slab elements; and high-ductility materials, namely high-strain-hardening CA-RPC, are used for the shear slab elements without web reinforcement. According to the determined high elastic modulus mix ratio of the basic CA-RPC, three technical means, namely fiber hybrid mixing (mixing short straight fibers and long-end hooked fibers), aggregate-fiber coupling (coarse aggregate impregnated with glue and bonded with steel fibers to form an "aggregate-fiber" integrated component), and fiber grid migration and limitation (laying continuous carbon fiber / basalt fiber grids between layers to limit the sinking of aggregates), are adopted to meet the corresponding ductility index requirements, and finally a complete set of design methods for the high elastic modulus CA-RPC system considering ductility grading indicators is formed.

[0081] The technical means disclosed in the solution of this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims

1. A design method for a high elastic modulus CA-RPC system based on ductility classification index, Characterized in that: According to the target structural performance requirements and the proposed reinforcement state of the CA-RPC system, it is divided into a compression zone, a reinforced tension zone, and an unreinforced shear zone; The low ductility index is adopted in the compression zone, the medium ductility index is adopted in the reinforced tension zone, and the high ductility index is adopted in the unreinforced shear zone; For the low ductility index, low strain-hardening CA-RPC is adopted; For the medium ductility index, medium strain-hardening CA-RPC is adopted; For the high ductility index, high strain-hardening CA-RPC is adopted; For the low ductility index, the fiber hybrid technology is adopted to achieve strain hardening; For the medium ductility index, the fiber hybrid technology combined with the fiber-aggregate coupling technology is adopted to achieve strain hardening; For the high ductility index, the fiber hybrid technology combined with the fiber-fiber mesh confinement technology is adopted to achieve strain hardening; The fiber hybrid mentioned above is the hybrid of 1% straight fiber and 1% hooked-end fiber by volume ratio, achieving low strain hardening under tension, with the strain reaching 0.1%-0.2%; The fiber-aggregate coupling technology mentioned above is to mix epoxy resin with steel fibers to form an integrated effect of aggregate-fiber, achieving medium strain hardening under tension, with the strain reaching 0.2-0.3%; The fiber-fiber mesh confinement technology mentioned above is to lay continuous carbon fiber / basalt fiber meshes between layers. By preventing the sinking of aggregates and the floating migration of fibers through the fiber meshes, a synergistic effect of continuous fiber mesh-matrix-steel fiber is formed to achieve high strain hardening characteristics, with the strain reaching more than 0.4%; The straight fiber is 13mm long and 0.2mm in diameter; The hooked-end fiber is 20mm long and 0.2mm in diameter.

2. A design method for a high elastic modulus CA-RPC system based on ductility classification index according to claim 1, Characterized in that: The mass ratio of the CA-RPC powder and aggregate in the high elastic modulus system is: cement 0.8-1.2, silica fume 0.2-0.3, quartz sand 0.4-0.6, basalt 0.4-0.6, water 0.1-0.2, water reducer 0.03-0.05, and the volume fraction of steel fibers is 1%-2% of the total volume. Basalt aggregates with a diameter of 5-8mm are used, and the aggregate mass substitution rate is 40%-60%.

3. A design method for a high elastic modulus CA-RPC system based on ductility classification index according to claim 1, Characterized in that: The preparation of CA-RPC for the high ductility index includes: Clean and dry the basalt, and then soak it in glue and stick on the steel fibers; Load the materials in the order of cement, silica fume, quartz sand, water, and water reducer, and stir for 80-200 seconds; Add the treated basalt coarse aggregates, stir for 120-160 seconds and then pour. During the pouring process, lay a layer of fiber mesh every 1-2 cm until all pouring is completed, and complete the preparation of CA-RPC for the high ductility system.

4. A design method for a high elastic modulus CA-RPC system based on ductility classification index according to claim 3, Characterized in that: The preparation of CA-RPC for the low ductility index includes: Clean and dry the basalt for later use; Charge materials in the order of cement, silica fume, quartz sand, water, and water reducer, and mix for 80 - 200 seconds; Add basalt coarse aggregate, after mixing for 120 - 160 seconds, add short straight steel fibers and end-hooked steel fibers in proportion to achieve fiber hybrid doping, continue to mix for 120 - 160 seconds and then pour, to complete the preparation of CA-RPC for the low ductility system.

5. A design method for a high elastic modulus CA-RPC system based on a ductility grading index according to claim 4, characterized in that: The preparation of CA-RPC for medium ductility index includes: Clean and dry the basalt, soak it in glue and stick end-hooked steel fibers; Charge materials in the order of cement, silica fume, quartz sand, water, and water reducer, and mix for 80 - 200 seconds; Add the treated basalt coarse aggregate, after mixing for 120 - 160 seconds, add short straight fibers again and mix for 120 - 160 seconds and then pour, to complete the preparation of CA-RPC for the medium ductility system.

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