UHPC (Ultra High Performance Concrete) based on steel fiber equivalent diameter method and particle accumulation model and preparation method

Abstract

The invention discloses a UHPC (Ultra High Performance Concrete) based on a steel fiber equivalent diameter method and a particle accumulation model and a preparation method, and belongs to the technical field of concrete. The method comprises the following steps: determining the mix proportion of UHPC according to target strength, toughness and durability, wherein the mix proportion comprises the use amounts of cement, silica fume, fine aggregate, water, a water reducing agent and steel fibers; an optimal grain composition curve is determined by adopting an improved Andersen model and an improved Andersen model, so that the stacking compactness of the grains is the highest; calculating the equivalent spherical diameter of the steel fiber according to the length, diameter and shape of the steel fiber, and taking the equivalent spherical diameter as spherical particles to be incorporated into a particle accumulation model; stirring the raw materials according to the mixing ratio to obtain UHPC slurry; uniformly dispersing steel fibers in the slurry and carrying out secondary stirring; pouring the slurry into a mold, vibrating and compacting; and after curing, demolding to obtain the UHPC component. The steel fiber distribution is optimized through an equivalent diameter method, and the compactness is improved in combination with a particle accumulation model, so that the UHPC has high strength, high toughness and excellent durability, and meanwhile, the shrinkage rate and the cost are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and in particular relates to an UHPC and a preparation method thereof based on a steel fiber equivalent diameter method and a particle stacking model. Background Art

[0002] Ultra-high performance concrete (UHPC) is a cement-based concrete material with superb mechanical properties, high toughness, ultra-high durability, and excellent pouring and molding properties. UHPC is made by selecting highly active fine materials and using the most compact and fiber-reinforced technology. Its compressive strength can reach over 150MPa, shear strength can reach over 25MPa, and toughness can reach 15kJ / m 2 The durability can reach more than 100 years. Generally, UHPC is prepared by increasing the fineness and activity of the components to minimize the defects (pores and microcracks) inside the material, thereby achieving ultra-high strength and high durability. The main ways to achieve this are as follows:

[0003] (1) Eliminate coarse aggregate and limit the maximum particle size of fine aggregate to no more than 5 mm to improve the uniformity of aggregate;

[0004] (2) Improve the density of the system by optimizing the gradation of fine aggregate and achieving dense packing as much as possible;

[0005] (3) Adding ultrafine active mineral admixtures such as silica fume and mineral powder to give it a good micro-powder filling effect, and reducing the pore size and porosity through chemical reaction, thereby optimizing the internal pore structure of the system;

[0006] (4) During the hardening process, CSH is converted into tobermorite and then into hard calcium silicate through pressurization and heat curing, which improves the mechanical properties of the material and minimizes chemical shrinkage;

[0007] (5) Improve the toughness of concrete by adding short and thin steel fibers or other types of high modulus fibers.

[0008] Although UHPC has many advantages, there are also some problems and challenges in its preparation process. One of the important issues is how to evenly disperse steel fibers in the UHPC slurry and form an optimal stacking state in space. As an important reinforcing material, steel fiber plays a key role in improving the tensile, shear, bending and impact resistance of UHPC. However, steel fibers are prone to agglomeration, entanglement and sedimentation during the mixing process, resulting in uneven distribution of steel fibers, affecting the performance and quality of UHPC. In addition, the shape, size and amount of steel fibers will also affect the fluidity, consistency and filling properties of UHPC, thereby affecting the casting and molding effects of UHPC.

[0009] Therefore, how to effectively incorporate steel fiber into the formulation design of UHPC so that it can form the best synergistic effect with other components is an urgent problem to be solved in UHPC research and application. Summary of the Invention

[0010] The purpose of the present invention is to provide an UHPC and preparation method based on the steel fiber equivalent diameter method and particle packing model. This method can effectively regard steel fibers as spherical particles with an equivalent spherical diameter, incorporate them into the particle packing model, and retain the influence of steel fibers on the packing density of the entire surrounding particles, thereby better designing and optimizing the mix ratio of UHPC and improving the performance and quality of UHPC.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0012] A UHPC preparation method based on a steel fiber equivalent diameter method and a particle packing model comprises the following steps:

[0013] (1) According to the target strength of not less than 150MPa and toughness of not less than 15kJ / m 2 and durability of not less than 100 years, determine the mix ratio of UHPC, including the amount of cement, silica fume, fine aggregate, water, water reducing agent and steel fiber;

[0014] (2) According to the improved Andreasen and Andersen (MAA) model, the optimal particle gradation curve is determined, and the gradation curve satisfies:

[0015]

[0016] Where D is the particle diameter, D max =5mm, q=0.37, particle diameter range is 0.01~5mm;

[0017] (3) Calculate the equivalent spherical diameter d based on the length L = 6 to 60 mm, diameter d = 0.1 to 1 mm, and shape of the steel fiber:

[0018]

[0019] Where A is the cross-sectional area of the steel fiber, and the steel fiber with equivalent spherical diameter is included in the particle packing model;

[0020] (4) Mixing cement, silica fume, fine aggregate, water, and water reducer according to the mix ratio of step (1) for 4-6 minutes to obtain a UHPC slurry with a fluidity of 250-300 mm;

[0021] (5) Disperse the steel fibers evenly in the slurry and stir for a second time for 2-4 minutes;

[0022] (6) Pour the slurry into the mold and vibrate and compact it. After curing at a temperature of 60-90°C and a humidity of ≥90% for 24-48 hours, demould the mold to obtain the desired UHPC component.

[0023] Preferably, the mixing ratio is:

[0024] Cement 800-1200kg / m 3 Silica fume 200-400kg / m 3 , fine aggregate 600-1000kg / m 3 , water 150-250kg / m 3 , water reducing agent 20-40kg / m 3 , Steel fiber 100-200kg / m 3 .

[0025] Preferably, the cement is 52.5 silicate cement or sulphoaluminate cement, the water reducer is polycarboxylate water reducer, the steel fiber is corrugated or straight, the silica fume is Grade I or Grade II silica fume, and the fine aggregate is quartz sand or basalt sand.

[0026] Preferably, the curing adopts steam curing or natural curing, the mold size is 100×100×400 mm, and the vibration frequency is 50 Hz.

[0027] Preferably, the steel fiber is dispersed by mechanical vibration or air jet, and the stirring speed is 80 revolutions per minute.

[0028] The present invention also provides a UHPC based on the steel fiber equivalent diameter method and the particle stacking model, comprising the following components and amounts:

[0029] Cement 800-1200kg / m 3 Silica fume 200-400kg / m 3 , fine aggregate 600-1000kg / m 3 , water 150-250kg / m 3 , water reducing agent 20-40kg / m 3 , Steel fiber 100-200kg / m 3 ;

[0030] The steel fiber has a length of 6-60 mm, a diameter of 0.1-1 mm, and a wavy or straight shape;

[0031] The compressive strength of the UHPC is ≥150MPa and the toughness is ≥15kJ / m 2 , durability ≥ 100 years, total shrinkage ≤ 0.027%.

[0032] Preferably, the drying shrinkage is ≤0.015%, and the autogenous shrinkage is ≤0.012%.

[0033] Preferably, the freeze-thaw resistance mass loss rate is ≤0.01%, the carbonization resistance depth is ≤0.5mm, and the chloride ion penetration charge flux is ≤100C.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) The steel fiber equivalent diameter method can effectively incorporate steel fibers into the particle packing model, retaining the effect of steel fibers on the packing density of the entire surrounding particles, thereby better designing and optimizing the mix ratio of UHPC;

[0036] (2) Through the particle packing model, the most compact packing of particles of different sizes, shapes and compositions can be achieved in space, so that UHPC has the lowest porosity and the highest density, thereby improving the strength, toughness and durability of UHPC;

[0037] (3) The preparation method provided by the present invention can produce high-performance, low-cost, and environmentally friendly UHPC components, which are suitable for various engineering application scenarios, such as bridges, tunnels, and buildings. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Example 1

[0040] (1) Based on the target strength of 150MPa and toughness of 15kJ / m 2 and durability of 100 years, according to the modified Andreasen and Andersen (MAA) model, the optimal particle gradation curve, including the amount of cement, silica fume, fine aggregate, water, water reducer and steel fiber, is determined as follows:

[0041] Cement: 1000kg / m 3 ;

[0042] Silica fume: 300kg / m 3 ;

[0043] Fine aggregate: 800kg / m 3 ;

[0044] Water: 200kg / m 3 ;

[0045] Water reducing agent: 30kg / m3 ;

[0046] Steel fiber: 150kg / m 3 .

[0047] (2) Based on the length, diameter and shape of the steel fiber, the equivalent spherical diameter of the steel fiber is calculated, and the steel fiber is regarded as a spherical particle with an equivalent spherical diameter and incorporated into the particle packing model, and the following conditions are met:

[0048] The length of steel fiber is 20 mm;

[0049] The diameter of the steel fiber is 0.5 mm;

[0050] The steel fiber is wavy in shape;

[0051] According to formula (1), the equivalent spherical diameter of the steel fiber is calculated to be 1.14 mm.

[0052] (3) According to the determined mix ratio, cement, silica fume, fine aggregate, water and water reducing agent are added to the mixer in sequence and stirred for 5 minutes at a stirring speed of 60 rpm to obtain a uniform UHPC slurry; the UHPC slurry has high fluidity and low viscosity, and the fluidity is 280 mm; the steel fiber is evenly added to the UHPC slurry by air jet to avoid aggregation or sedimentation of the steel fiber in the slurry, and a secondary stirring is performed with a stirring time of 3 minutes and a stirring speed of 80 rpm to make the steel fiber evenly distributed in the UHPC slurry; the molding is carried out with a curing temperature of 80 ° C, a curing humidity of 95%, a curing time of 36 hours, and a steam curing method to make the UHPC slurry fully hydrated and achieve the expected performance.

[0053] Example 2

[0054] (1) Based on the target strength of 160MPa and toughness of 18kJ / m 2 and durability of 110 years, according to the modified Andreasen and Andersen (MAA) model, the optimal particle gradation curve, including the amount of cement, silica fume, fine aggregate, water, water reducer and steel fiber, is determined as follows:

[0055] Cement: 1050kg / m 3 ;

[0056] Silica fume: 325kg / m 3 ;

[0057] Fine aggregate: 850kg / m 3 ;

[0058] Water: 190kg / m 3 ;

[0059] Water reducing agent: 32.5kg / m 3 ;

[0060] Steel fiber: 165kg / m 3 .

[0061] (2) Based on the length, diameter and shape of the steel fiber, the equivalent spherical diameter of the steel fiber is calculated, and the steel fiber is regarded as a spherical particle with an equivalent spherical diameter and incorporated into the particle packing model, and the following conditions are met:

[0062] The length of steel fiber is 25mm;

[0063] The diameter of the steel fiber is 0.55 mm;

[0064] The shape of steel fiber is straight;

[0065] According to formula (1), the equivalent spherical diameter of the steel fiber is calculated to be 1.23 mm.

[0066]

[0067] (3) According to the determined mix ratio, cement, silica fume, fine aggregate, water and water reducing agent are added to the mixer in sequence for stirring. The stirring time is 5.5 minutes and the stirring speed is 60 rpm to obtain a uniform UHPC slurry. The UHPC slurry has high fluidity and low viscosity, and the fluidity is 270 mm. The steel fiber is evenly added to the UHPC slurry by mechanical vibration to avoid aggregation or sedimentation of the steel fiber in the slurry, and a secondary stirring is performed. The stirring time is 3.5 minutes and the stirring speed is 80 rpm to make the steel fiber evenly distributed in the UHPC slurry. The molding is carried out with a curing temperature of 85 ° C, a curing humidity of 92%, a curing time of 42 hours, and a steam curing method to make the UHPC slurry fully hydrated and achieve the expected performance.

[0068] Example 3

[0069] (1) Based on the target strength of 180MPa and toughness of 20kJ / m 2 and durability of 120 years, according to the modified Andreasen and Andersen (MAA) model, the optimal particle gradation curve, including the amount of cement, silica fume, fine aggregate, water, water reducer and steel fiber, is determined as follows:

[0070] Cement: 1100kg / m 3 ;

[0071] Silica fume: 350kg / m 3 ;

[0072] Fine aggregate: 900kg / m3 ;

[0073] Water: 180kg / m 3 ;

[0074] Water reducing agent: 35kg / m 3 ;

[0075] Steel fiber: 180kg / m 3 .

[0076] (2) Based on the length, diameter and shape of the steel fiber, the equivalent spherical diameter of the steel fiber is calculated, and the steel fiber is regarded as a spherical particle with an equivalent spherical diameter and incorporated into the particle packing model, and the following conditions are met:

[0077] The length of steel fiber is 30mm;

[0078] The diameter of the steel fiber is 0.6 mm;

[0079] The shape of steel fiber is straight;

[0080] According to formula (1), the equivalent spherical diameter of the steel fiber is calculated to be 1.32 mm.

[0081] (3) According to the determined mix ratio, cement, silica fume, fine aggregate, water and water reducing agent are added to the mixer in sequence and stirred for 6 minutes at a stirring speed of 60 rpm to obtain a uniform UHPC slurry; the UHPC slurry has high fluidity and low viscosity, and the fluidity is 260 mm; the steel fiber is evenly dispersed in the UHPC slurry, and mechanical vibration is used to prevent the steel fiber from aggregating or settling in the slurry, and a secondary stirring is performed with a stirring time of 4 minutes and a stirring speed of 80 rpm to ensure that the steel fiber is evenly distributed in the UHPC slurry; the molding is carried out, the curing temperature is 80 ° C, the curing humidity is 90%, the curing time is 48 hours, and steam curing is used to ensure that the UHPC slurry is fully hydrated and achieves the expected performance.

[0082] Example 4

[0083] (1) Based on the target strength of 200 MPa and toughness of 25 kJ / m 2 and durability of 150 years, according to the modified Andreasen and Andersen (MAA) model, the optimal particle gradation curve, including the amount of cement, silica fume, fine aggregate, water, water reducer and steel fiber, is determined as follows:

[0084] Cement: 1200kg / m 3

[0085] Silica fume: 400kg / m 3

[0086] Fine aggregate: 1000kg / m 3

[0087] Water: 150kg / m 3

[0088] Water reducing agent: 40kg / m 3

[0089] Steel fiber: 200kg / m 3

[0090] (2) Based on the length, diameter and shape of the steel fiber, the equivalent spherical diameter of the steel fiber is calculated, and the steel fiber is regarded as a spherical particle with an equivalent spherical diameter and incorporated into the particle packing model, and the following conditions are met:

[0091] The length of steel fiber is 40mm;

[0092] The diameter of the steel fiber is 0.8 mm;

[0093] The steel fiber is wavy in shape;

[0094] According to formula (1), the equivalent spherical diameter of the steel fiber is calculated to be 1.54 mm.

[0095] (3) According to the determined mix ratio, cement, silica fume, fine aggregate, water and water reducing agent are added to the mixer in sequence and stirred for 4 minutes at a stirring speed of 60 rpm to obtain a uniform UHPC slurry; the UHPC slurry has high fluidity and low viscosity, and the fluidity is 300 mm; the steel fiber is evenly dispersed in the UHPC slurry, and mechanical vibration is used to prevent the steel fiber from aggregating or settling in the slurry, and a secondary stirring is performed with a stirring time of 2 minutes and a stirring speed of 80 rpm to ensure that the steel fiber is evenly distributed in the UHPC slurry; the molding is carried out, the curing temperature is 90 ° C, the curing humidity is 95%, the curing time is 24 hours, and steam curing is used to ensure that the UHPC slurry is fully hydrated and achieves the expected performance.

[0096] Performance Testing

[0097] The mechanical properties and shrinkage properties of the ultra-high performance concrete prepared in Examples 1-4 based on the steel fiber equivalent diameter method and the particle stacking model were tested; the mechanical properties test was carried out in accordance with the "GB / T 50081-2019 Standard for Test Methods for Physical and Mechanical Properties of Concrete". Durability testing was conducted according to the "GB / T 50082-2009 Standard for Test Methods for Long-term Properties and Durability of Concrete." Freeze-thaw resistance was tested using the rapid freeze-thaw method, subjecting UHPC specimens to cyclic freeze-thaw cycles between -20°C and 20°C for four hours each. The mass change and relative dynamic modulus of the specimens were measured every 50 cycles until failure or 300 cycles. Carbonation resistance was tested using the accelerated carbonization method, subjecting UHPC specimens to accelerated carbonization in an atmosphere containing 1% CO₂. The carbonation depth was measured every 28 days until carbonization reached the steel bar or 180 days. Chloride ion permeation resistance was tested using the rapid chloride ion permeation method, subjecting UHPC specimens to accelerated chloride ion permeation at 60V. The charge flux was measured every six hours until the specimens reached 96 hours. Tables 1-3 present the test results.

[0098] Table 1 Mechanical properties test results of ultra-high performance concrete

[0099]

[0100]

[0101] Table 2 Ultra-high performance concrete shrinkage performance test results

[0102] Example Drying shrinkage (%) Autogenous shrinkage (%) Total shrinkage (%) 1 0.015 0.012 0.027 2 0.013 0.011 0.024 3 0.011 0.009 0.020 4 0.009 0.007 0.016

[0103] Table 3 Durability test results of ultra-high performance concrete

[0104]

[0105] As can be seen from Tables 1 and 2, the ultra-high performance concrete based on the steel fiber equivalent diameter method and particle packing model has excellent mechanical properties and shrinkage properties. Its compressive strength, tensile strength, and fracture energy all meet or exceed the target requirements, and the mechanical properties improve with increasing steel fiber length, diameter, and curing temperature. Its drying shrinkage, autogenous shrinkage, and total shrinkage are all lower than those of ordinary concrete, and the shrinkage properties improve with increasing steel fiber length, diameter, and curing temperature. At the same time, the ultra-high performance concrete based on the steel fiber equivalent diameter method and particle packing model has excellent durability. Its freeze-thaw resistance, carbonation resistance, and chloride ion permeability resistance all meet or exceed the levels of ordinary concrete, and the durability improves with increasing steel fiber length, diameter, and curing temperature. These results show that the ultra-high performance concrete preparation method based on the steel fiber equivalent diameter method and particle packing model proposed in this invention is effective and feasible, and can provide a new idea and method for the design and application of UHPC.

[0106] In summary, the results of the embodiment show that the ultra-high performance concrete based on the steel fiber equivalent diameter method and particle packing model has the set superior mechanical properties and durability.

[0107] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A UHPC preparation method based on the steel fiber equivalent diameter method and particle stacking model, characterized in that: The following steps are involved: (1) According to the target strength of not less than 150MPa and toughness of not less than 15kJ / m 2 and durability of not less than 100 years, determine the mix ratio of UHPC, including the amount of cement, silica fume, fine aggregate, water, water reducing agent and steel fiber; (2) According to the improved Andreasen and Andersen (MAA) model, the optimal particle gradation curve is determined, and the gradation curve satisfies: Where D is the particle diameter, D max =5mm, q=0.37, particle diameter range is 0.01~5mm; (3) Calculate the equivalent spherical diameter d based on the length L = 6 to 60 mm, diameter d = 0.1 to 1 mm, and shape of the steel fiber: Where A is the cross-sectional area of the steel fiber, and the steel fiber with equivalent spherical diameter is included in the particle packing model; (4) Mixing cement, silica fume, fine aggregate, water, and water reducer according to the mix ratio of step (1) for 4-6 minutes to obtain a UHPC slurry with a fluidity of 250-300 mm; (5) Disperse the steel fibers evenly in the slurry and stir for a second time for 2-4 minutes; (6) Pour the slurry into the mold and vibrate and compact it. After curing at a temperature of 60-90°C and a humidity of ≥90% for 24-48 hours, demould the mold to obtain the desired UHPC component.

2. The method according to claim 1, characterized in that The mixing ratio is: Cement 800-1200kg / m 3 Silica fume 200-400kg / m 3 , fine aggregate 600-1000kg / m 3 , water 150-250kg / m 3 , water reducing agent 20-40kg / m 3 , Steel fiber 100-200kg / m 3 .

3. The method according to claim 1, characterized in that The cement is 52.5 silicate cement or sulphoaluminate cement, the water reducer is polycarboxylate water reducer, the steel fiber is corrugated or straight, the silica fume is grade I or grade II silica fume, and the fine aggregate is quartz sand or basalt sand.

4. The method according to claim 1, wherein The curing adopts steam curing or natural curing, the mold size is 100×100×400 mm, and the vibration frequency is 50 Hz.

5. The method according to any one of claims 1 to 4, characterized in that: The steel fiber is dispersed by mechanical vibration or air jet, and the stirring speed is 80 revolutions per minute.

6. A UHPC based on the steel fiber equivalent diameter method and particle packing model, characterized in that: Includes the following components and dosage: Cement 800-1200kg / m 3 Silica fume 200-400kg / m 3 , fine aggregate 600-1000kg / m 3 , water 150-250kg / m 3 , water reducing agent 20-40kg / m 3 , Steel fiber 100-200kg / m 3 ; The steel fiber has a length of 6-60 mm, a diameter of 0.1-1 mm, and a wavy or straight shape; The compressive strength of the UHPC is ≥150MPa and the toughness is ≥15kJ / m 2 , durability ≥ 100 years, total shrinkage ≤ 0.027%.

7. The UHPC according to claim 6, characterized in that Its drying shrinkage is ≤0.015% and its autogenous shrinkage is ≤0.012%.

8. The UHPC according to claim 6 or 7, characterized in that Its freeze-thaw resistance mass loss rate is ≤0.01%, its carbonization resistance depth is ≤0.5mm, and its chloride ion penetration charge flux is ≤100C.

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