Dust-suppressing low-rebound sprayed ultra-high performance concrete and its preparation method and construction method

Abstract

The present invention provides a dust-suppressed, low-rebound sprayed ultra-high performance concrete, and a preparation method and construction method thereof. The raw materials include silicate cement, fly ash beads, nano-mineral additives, quartz sand, functional porous lightweight aggregate, conductive aggregate, steel fiber, water reducer and mixing water. The purpose of using sodium alginate solution to pre-wet the porous lightweight aggregate is to adjust the rheological properties of the freshly mixed ultra-high performance concrete and reduce the rebound rate; through the selection and proportioning of raw materials, the later strength and flexural toughness of the sprayed concrete can be improved, the rebound rate can be reduced, and the dust concentration in the working environment can be reduced. The purpose of applying voltage at both ends of the working surface during the spraying construction process is to charge the sprayed ultra-high performance concrete, produce an adsorption effect on dust, and reduce the dust concentration in the working environment. The present invention can solve the current problems of low late strength, relatively poor toughness, poor durability, high rebound rate during construction, and harsh working environment of sprayed concrete.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and in particular relates to a preparation and construction method of dust-suppressing low-rebound sprayed ultra-high performance concrete. Background Art

[0002] Shotcrete is often used in construction environments such as mines, underground, tunnels, and structural reinforcement due to its advantages such as short setting time, high early strength, simple processing, and flexible operation methods. In recent years, with the large-scale planning and construction of highway tunnels, urban rail transit, and underground space projects, as well as the periodic maintenance of many buildings, shotcrete has been more widely used as a common support and reinforcement material, which has also led to more stringent requirements for its performance.

[0003] However, current shotcrete construction suffers from low post-production strength and relatively poor toughness, limiting its use to temporary support. Furthermore, conventional shotcrete has a high rebound rate, resulting in significant material waste, while the large amount of dust generated during construction can be harmful to the health of operators. Summary of the Invention

[0004] The purpose of the present invention is to provide a dust-suppressed, low-rebound sprayed ultra-high performance concrete and its preparation method and construction method. Through raw material design, the later strength and flexural toughness of the sprayed concrete can be greatly improved, the rebound rate can be reduced, and the dust concentration in the working environment can be reduced.

[0005] The specific technical solutions of the present invention are as follows:

[0006] The invention discloses a dust-suppressing and low-rebound sprayed ultra-high performance concrete, the raw materials of which include silicate cement, fly ash floating beads, nano mineral additives, quartz sand, functional porous lightweight aggregate, conductive aggregate, steel fiber, water reducer and mixing water.

[0007] The dust-suppressing, low-rebound sprayed ultra-high performance concrete comprises the following raw materials in parts by weight: 600-800 parts of Portland cement, 150-250 parts of fly ash beads, 20-50 parts of nano-mineral additives, 400-600 parts of quartz sand, 100-200 parts of functional porous lightweight aggregate, 80-150 parts of conductive aggregate, 80-120 parts of steel fiber, 15-25 parts of water reducer, and 100-150 parts of mixing water.

[0008] The silicate cement is silicate cement with a strength grade of not less than 42.5 and a specific surface area of ​​350-400m 2 / kg, spherical cement, the sphericity coefficient of cement particles is greater than 80%;

[0009] The average particle size of the fly ash beads is 1-5 μm, and the specific surface area is greater than 2000 m 2 / kg;

[0010] The nano mineral additive is a mixture of one or both of nano SiO2 and nano CaCO3, wherein the total content of nano SiO2 and nano CaCO3 is greater than 95%, and the average particle size is not greater than 100 nm;

[0011] The quartz sand has a particle size ranging from 0.75 mm to 2.36 mm.

[0012] The method for preparing the functional porous lightweight aggregate comprises: immersing the porous lightweight aggregate in a viscosity modifying liquid, and then taking it out and draining it.

[0013] The soaking time is 24-48h;

[0014] The viscosity modifying liquid is a sodium alginate solution with a mass concentration of 6% to 10%, wherein the sodium alginate is a light yellow powder, chemically pure, and has an average molecular weight of 2780.

[0015] The porous lightweight aggregate comprises the following raw materials in parts by weight:

[0016] 80-120 parts of dehydrated red mud, 5-20 parts of silica fume, and 10-15 parts of starch.

[0017] The raw materials of the porous lightweight aggregate include: the red mud is Bayer red mud, and the Al2O3 content is not less than 20%; the particle size of the dehydrated red mud is less than 75 μm; the specific surface area of ​​the silica fume is not less than 20,000 m 2 / kg, SiO2 content not less than 97%;

[0018] The preparation method of the porous lightweight aggregate comprises the following steps: uniformly mixing a formulated amount of dehydrated red mud, silica fume and starch, adding water which accounts for 15 to 30% of the total mass of the dehydrated red mud, silica fume and starch to prepare raw material balls with a particle size of 2 to 5 mm; placing the raw material balls in a cool and ventilated place to air-dry for 12 to 24 hours, and then sintering them at high temperature; and grinding the raw material balls after sintering.

[0019] In the preparation method of porous lightweight aggregate, the sintering process is as follows: heating to 600-700°C at a rate of 8-15°C / min, holding at that temperature for 10-30 minutes, then heating to 1000-1200°C at a further rate of 8-15°C / min, holding at that temperature for 10-20 minutes, and naturally cooling. The grinding process is performed to a particle size of 0.75mm-2.36mm, a saturated water absorption rate of 8%-15%, and a pore size range of 2-50μm.

[0020] The conductive aggregate is a mixture of one or both of iron sand and steel sand, with a particle size of 0.75 mm to 2.36 mm;

[0021] The steel fiber is a microfilament steel fiber with an aspect ratio of 50-70 and a diameter of 0.08-0.20 mm;

[0022] The water reducing agent is a commercially available polycarboxylic acid-based high-performance water reducing agent with a water reduction rate of not less than 38%;

[0023] The mixing water is magnetized water, that is, municipal tap water treated by a magnetizer under the conditions of a magnetization intensity of 180 to 220 mT and a water flow rate of 1 to 2 m / s.

[0024] The dust suppression low rebound sprayed ultra-high performance concrete meets the requirements of 28d compressive strength ≥115Mpa, 28d flexural strength ≥15Mpa, flexural toughness index I5 ≥3.5, I 10 ≥9, I 10 ≥21, rebound rate ≤9%, dust concentration in the working environment ≤9.5%.

[0025] The present invention provides a method for preparing dust-suppressed low-rebound sprayed ultra-high performance concrete, comprising the following steps:

[0026] 1) Fully mixing the formulated amount of Portland cement, fly ash beads, nano mineral additives, quartz sand, and conductive aggregate to obtain a mixed material;

[0027] 2) placing the functional porous lightweight aggregate and the mixed material prepared in step 1) in a blender and mixing them;

[0028] 3) adding the formulated amount of water reducer and magnetized water to the material mixed in step 2) and mixing;

[0029] 4) adding steel fibers to the mixed material in step 2) and continuing to stir to obtain dust-suppressed low-rebound sprayed ultra-high performance concrete.

[0030] The mixing time in step 2) is 1-2 minutes;

[0031] The mixing time in step 3) is 3 to 5 minutes;

[0032] The mixing time in step 4) is 2 to 4 minutes.

[0033] The present invention provides a construction method for dust-suppressed, low-rebound sprayed ultra-high performance concrete, specifically comprising:

[0034] The spraying construction is carried out by dense flow method, and a safety voltage of 36V is applied to both ends of the spraying working surface during construction.

[0035] Conventional shotcrete is usually mixed with accelerators to reduce rebound during construction. However, accelerators can significantly reduce the concrete's later strength and long-term durability. The dust-suppressing, low-rebound, ultra-high-performance shotcrete of the present invention does not require accelerators during construction. Instead, rebound is reduced by adjusting the material's own properties. The specific design concept is as follows:

[0036] The specific surface area is 350-400m 2 The purpose of spherical cement is to reduce the hydration rate by 100g / kg. A too small specific surface area reduces the hydration rate, while a large specific surface area increases the heat of hydration and the risk of cracking. The good spherical coefficient of cement particles further reduces the water requirement and increases the later strength of concrete.

[0037] The purpose of using nano-mineral additives is to: Nano-SiO2 and nano-CaCO3 can act as nucleating agents to accelerate cement hydration and improve the early strength of shotcrete. Nanomaterials can also fill the tiny gaps between particles in the ultra-high performance concrete cementitious material system, releasing more free water, thereby further reducing the water-binder ratio and improving the concrete's later strength. The "ball effect" of nanomaterials can also reduce the dynamic viscosity of the mixture during pumping and spraying, increasing the pumpability of ultra-high performance concrete.

[0038] The purpose of using porous lightweight aggregate is: by limiting its particle size range, it can ensure that the final particle gradation meets the most compact particle packing model; by limiting its water absorption rate, it can ensure that the porous lightweight aggregate will not affect the strength and fluidity of ultra-high performance concrete due to excessive water absorption; by limiting its pore size range, it can ensure that after pre-wetting, it can play the role of a "water reservoir" in the hydration process of ultra-high performance concrete. When the internal humidity of ultra-high performance concrete drops to a critical value, the water stored in the porous lightweight aggregate can be released to play a role of humidity compensation, maintain the hydration rate, and reduce volume deformation.

[0039] The purpose of using a viscosity modifier to pre-wet the porous lightweight aggregate is that sodium alginate has strong flocculating and thickening properties, which can adjust the rheological properties of fresh ultra-high performance concrete, increase the static yield stress of the mixture without affecting its dynamic viscosity, and improve the adhesion of the sprayed ultra-high performance concrete to the work surface, thereby reducing rebound and increasing the thickness of the sprayed concrete in one shot. The introduction of sodium alginate into the porous lightweight aggregate allows for a more uniform dispersion of the sodium alginate in the mixture system, facilitating the precise control of the rheological properties of fresh ultra-high performance concrete. In addition, the porous aggregate is rich in silica and alumina, which can undergo a pozzolanic reaction, thereby strengthening the interfacial transition zone without weakening the mechanical properties of the ultra-high performance concrete.

[0040] Using steel grit and iron sand of the same particle size as conductive aggregate to replace some of the quartz sand is intended to enhance the conductivity of ultra-high performance concrete without affecting the compactness of the particles. This is because, although a considerable amount of steel fiber is incorporated into ultra-high performance concrete to increase its strength and toughness, it is still a poor conductor of electricity.

[0041] The purpose of using magnetized water is to significantly increase its activity after magnetization, accelerating the cement hydration reaction and making the hydrated structure more uniform and dense, ultimately improving the mechanical properties and durability of concrete. Magnetized water also enhances the interfacial bond strength between cement paste and aggregate, compensating for the loss of concrete mechanical properties caused by the numerous interfacial weak zones created by the incorporation of porous lightweight aggregate.

[0042] The purpose of applying voltage across the work surface during spraying is to charge the ultra-high performance concrete. This charge, along with the steel fibers and conductive aggregates within the ultra-high performance concrete, absorbs dust generated during spraying, reducing dust concentration in the working environment.

[0043] The dust-suppressed, low-rebound ultra-high-performance sprayed concrete provided by this invention can improve the late-stage strength and flexural toughness of shotcrete, reduce rebound rate, and lower dust concentration in the working environment. This addresses the current problems of shotcrete, such as low late-stage strength, relatively poor toughness, poor durability, high rebound rate during construction, and harsh working environments. It meets the high-performance requirements of support materials for large-scale underground engineering construction and optimizes the working environment. DETAILED DESCRIPTION

[0044] Example 1-Example 4

[0045] A dust-suppressing, low-rebound sprayed ultra-high performance concrete comprises the following raw materials in parts by weight: 600-800 parts of Portland cement, 150-250 parts of fly ash beads, 20-50 parts of nano-mineral additives, 400-600 parts of quartz sand, 100-200 parts of functional porous lightweight aggregate, 80-150 parts of conductive aggregate, 80-120 parts of steel fiber, 15-25 parts of water reducer, and 100-150 parts of mixing water.

[0046] The silicate cement is silicate cement with a strength grade of not less than 42.5 and a specific surface area of ​​350-400m 2 / kg, spherical cement, the sphericity coefficient of cement particles is greater than 80%;

[0047] The average particle size of the fly ash beads is 1-5 μm, and the specific surface area is greater than 2000 m 2 / kg;

[0048] The nano mineral additive is a mixture of one or both of nano SiO2 and nano CaCO3, wherein the total content of nano SiO2 and nano CaCO3 is greater than 95%, and the average particle size is not greater than 100 nm;

[0049] The quartz sand has a particle size ranging from 0.75 mm to 2.36 mm.

[0050] The preparation method of the functional porous lightweight aggregate is as follows: immersing the porous lightweight aggregate in a 6% to 10% sodium alginate solution for 24-48 hours, taking it out and draining it; wherein the sodium alginate is a light yellow powder, chemically pure, and has an average molecular weight of 2780.

[0051] The porous lightweight aggregate comprises the following raw materials in parts by weight:

[0052] 80-120 parts of dehydrated red mud, 5-20 parts of silica fume, and 10-15 parts of starch.

[0053] The preparation method of the porous lightweight aggregate is as follows: after uniformly mixing the formulated amount of dehydrated red mud, silica fume and starch, 15-30% of water is added to form raw material balls with a particle size of 2-5 mm; the raw material balls are placed in a cool and ventilated place to air dry for 12-24 hours, and then sintered at high temperature, heating to 600-700°C at a rate of 8-15°C / min, keeping warm for 10-30 minutes, and continuing to heat to 1000-1200°C at a rate of 8-15°C / min, keeping warm for 10-20 minutes, and cooling naturally; after sintering, grind to a particle size of 0.75mm-2.36mm, its saturated water absorption rate should be 8%-15%, and the pore size range should be 2-50μm. The red mud is Bayer red mud with an Al2O3 content of not less than 20%; the particle size of the dehydrated red mud is less than 75μm; the specific surface area of ​​the silica fume is not less than 20,000m 2 / kg, SiO2 content not less than 97%;

[0054] The conductive aggregate is a mixture of one or both of iron sand and steel sand, with a particle size of 0.75 mm to 2.36 mm;

[0055] The steel fiber is a microfilament steel fiber with an aspect ratio of 50-70 and a diameter of 0.08-0.20 mm;

[0056] The water reducing agent is a commercially available polycarboxylic acid-based high-performance water reducing agent with a water reduction rate of not less than 38%;

[0057] The mixing water is magnetized water, that is, municipal tap water treated by a magnetizer under the conditions of a magnetization intensity of 180 to 220 mT and a water flow rate of 1 to 2 m / s.

[0058] The preparation method of the dust-suppressed low-rebound sprayed ultra-high performance concrete in each embodiment comprises the following steps:

[0059] 1) Fully mixing the formulated amount of Portland cement, fly ash beads, nano mineral additives, quartz sand, and conductive aggregate to obtain a mixed material;

[0060] 2) placing the functional porous lightweight aggregate and the mixed material prepared in step 1) in a blender and mixing for 2 minutes;

[0061] 3) Add the formulated amount of water reducer and magnetized water to the mixed material in step 2) and mix for 5 minutes;

[0062] 4) Add steel fiber to the mixed material in step 2) and continue stirring for 3 minutes to obtain dust-suppressed low-rebound sprayed ultra-high performance concrete.

[0063] The specific raw material weight parts of each example are shown in Table 1 below.

[0064] Table 1 Dust suppression low rebound spraying ultra-high performance concrete mix ratio (kg / m 3 )

[0065]

[0066] The obtained ultra-high performance concrete was sprayed using the dense flow method. During construction, a safety voltage of 36V was applied to both ends of the spraying working surface. The performance is shown in Table 2 below.

[0067] Table 2 Performance of dust suppression low rebound sprayed ultra high performance concrete in each embodiment

[0068]

[0069] The present invention improves the later strength and flexural toughness of shotcrete, reduces the rebound rate, and reduces the dust concentration in the working environment.

Claims

1. A dust suppression low rebound sprayed ultra-high performance concrete, characterized in that: The dust suppression low-rebound sprayed ultra-high performance concrete comprises the following raw materials in parts by weight: 600-800 parts of Portland cement, 150-250 parts of fly ash beads, 20-50 parts of nano-mineral additives, 400-600 parts of quartz sand, 100-200 parts of functional porous lightweight aggregate, 80-150 parts of conductive aggregate, 80-120 parts of steel fiber, 15-25 parts of water reducer, and 100-150 parts of mixing water; The nano mineral additive is a mixture of one or both of nano SiO2 and nano CaCO3, wherein the total content of nano SiO2 and nano CaCO3 is greater than 95%, and the average particle size is not greater than 100 nm; The method for preparing the functional porous lightweight aggregate comprises: immersing the porous lightweight aggregate in a viscosity modifying liquid, taking it out and draining it; The porous lightweight aggregate comprises the following raw materials in parts by weight: 80-120 parts of dehydrated red mud, 5-20 parts of silica fume, 10-15 parts of starch; The viscosity modifying liquid is a 6% to 10% sodium alginate solution.

2. The dust suppression low-rebound sprayed ultra-high performance concrete according to claim 1, characterized in that: The silicate cement is silicate cement with a strength grade of not less than 42.5 and a specific surface area of ​​350-400m 2 / kg, is spherical cement, and the sphericity coefficient of cement particles is greater than 80%.

3. The dust suppression low-rebound sprayed ultra-high performance concrete according to claim 1, characterized in that: The preparation method of the porous lightweight aggregate comprises: uniformly mixing a prescribed amount of dehydrated red mud, silica fume and starch, adding 15-30% of water to prepare raw material balls with a particle size of 2-5 mm; placing the raw material balls in a cool and ventilated place to air-dry for 12-24 hours, and then sintering them at high temperature; and grinding them after sintering.

4. The dust suppression low-rebound sprayed ultra-high performance concrete according to claim 3, characterized in that: The sintering is specifically as follows: heating to 600-700°C at a rate of 8-15°C / min, keeping the temperature for 10-30 minutes, continuing to heat to 1000-1200°C at a rate of 8-15°C / min, keeping the temperature for 10-20 minutes, and cooling naturally; The grinding means grinding to a particle size of 0.75 mm to 2.36 mm, with a saturated water absorption rate of 8% to 15% and a pore size range of 2 to 50 μm.

5. A method for preparing the dust-suppressing low-rebound sprayed ultra-high performance concrete according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: 1) Fully mixing the formulated amount of Portland cement, fly ash beads, nano mineral additives, quartz sand, and conductive aggregate to obtain a mixed material; 2) placing the functional porous lightweight aggregate and the mixed material prepared in step 1) in a blender and mixing them; 3) adding the formulated amount of water reducer and magnetized water to the material mixed in step 2) and mixing; 4) adding steel fibers to the mixed material in step 2) and continuing to stir to obtain dust-suppressed low-rebound sprayed ultra-high performance concrete.

6. A construction method for the dust-suppressing, low-rebound sprayed ultra-high performance concrete according to any one of claims 1 to 4, comprising: The spraying construction is carried out by dense flow method, and a safety voltage of 36V is applied to both ends of the spraying working surface during construction.

Images