Preparation method of adjustable-plasticity super-early-strength sulphoaluminate-based sprayed concrete

Abstract

The invention discloses an adjustable-plasticity super-early-strength sulphoaluminate-based sprayed concrete preparation method, which comprises: (1) adding sulphoaluminate cement, machine-made sand and stone into a stirring machine, and stirring for 30-90 s to ensure the uniformity; (2) uniformly adding an accelerator and a retarder into the stirrer, and stirring for 15-30 seconds; and (3) jointly adding the polycarboxylic acid water reducer and water into a stirrer, quickly stirring for 90-240 seconds, and adding the polycarboxylic acid water reducer and water at a constant speed within the first 15-30 seconds of the stirring process to finally obtain the sulphoaluminate-based sprayed concrete. Compared with existing Portland cement-based shotcrete, the prepared sulphoaluminate-based shotcrete has the advantages that the setting time of the sulphoaluminate-based shotcrete can be flexibly regulated and controlled by adjusting the mixing amount ratio of the retarder and the accelerator in the preparation process, and the requirements of stirring the type of shotcrete and performing long-distance construction in an existing premixed commercial concrete station are met; by adjusting the use amount of the accelerator, the 3h and 1d strength of the accelerator far exceeds the national standard requirements, and the accelerator is suitable for highway and railway tunnel engineering.

Description

Technical Field

[0001] The invention relates to the field of tunnel building materials, in particular to a method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete. Background Art

[0002] Shotcrete is a type of concrete created by using a spraying machine, compressed air or other power sources, to mix a mixture of raw materials—cement, sand, stone, admixtures, additives, and water—in a specific proportion. This mixture is then transported through pipes and sprayed at high speed onto the surface where it solidifies. A unique feature of shotcrete is that it doesn't rely on vibration to compact the concrete. Instead, during high-speed spraying, the concrete is compacted through repeated, continuous impact between the cement and the aggregate. Compared to conventional concrete, its construction is simpler and easier, eliminating the steps of formwork, pouring, and demolding. Instead, the concrete transportation, pouring, and compaction steps are combined into a single process, saving manpower and shortening construction time. Shotcrete also boasts a high density, excellent strength, and impermeability, conserving concrete. Furthermore, the delivery hose allows for construction in high-rise buildings or confined workspaces, making it easy to operate, flexible, and highly adaptable.

[0003] Shotcrete also has some disadvantages. The extensive use of accelerators makes the uniformity of the hydration products of shotcrete relatively poor. The erosion resistance of shotcrete is lower than that of cast concrete, resulting in poor durability of shotcrete structures and shortened structural life.

[0004] The low-cost admixture for shotcrete disclosed in the patent with announcement number CN202411305805 includes the following components in weight percentage: 40%~50% silica fume, 5%~10% fast-hardening sulphoaluminate cement, 35%~45% reinforcing agent, 2%~4% dispersant, 1%~2% shrinkage reducer, and 0.5%~1% regulator; however, the amount of silica fume used in this patent is relatively large, and a certain effect can only be achieved at a higher dosage.

[0005] The patent with announcement number CN115536302B: A silicon manganese slag-based ultra-early strength shotcrete admixture and shotcrete, discloses that it includes 40-60 parts of silicon manganese slag powder, 25-35 parts of silica fume, 15-25 parts of aluminate cement, 0.09-0.11 parts of sodium nitrite, 0.9-1.1 parts of water reducer, 0.009-0.011 parts of cellulose, 0.15-0.25 parts of triisopropanolamine, 0.15-0.25 parts of diethanol monoisopropanolamine and 0.45-0.55 parts of magnesium fluorosilicate. The sprayed concrete comprises, by weight, 300-400 parts of cement, 90-120 parts of fly ash, 700-1000 parts of sand, 700-1000 parts of small stones, 150-210 parts of water, 4-6 parts of water reducer, 25-40 parts of alkali-free accelerator, and 50-80 parts of admixtures. The sprayed concrete in this patent requires the addition of large amounts of fly ash and admixtures.

[0006] Patent CN 110128079A discloses a technical solution based on P·O 42.5R early-strength ordinary Portland cement. Leveraging the advantages of an alkali-free accelerator and nano-admixture to enhance and accelerate setting, the three-dimensional structure of the cement setting process is improved, resulting in a one-day strength of shotcrete exceeding 5.0 MPa. To improve the early strength of shotcrete, early-strength admixtures and accelerators have also been extensively researched and applied. Patent CN 112521070A discloses an early-high-strength shotcrete. The admixtures include 30% to 60% microsilica, 20% to 40% mineral powder, 10% to 20% sodium sulfate, 1% to 10% magnesium sulfate, and 0.2% to 0.8% sodium gluconate. Using P·O 42.5 ordinary Portland cement and an alkali-free accelerator, the shotcrete achieves a 3-hour strength of at least 1.8 MPa, an 8-hour strength of at least 5 MPa, a 1-day strength of at least 18 MPa, and a 28-day strength that meets C35 grade. However, the early strength growth rate of this silicate shotcrete is slow, and it cannot truly play its role of timeliness, sealing and bonding.

[0007] Currently, most shotcrete is made from Portland cement. To achieve rapid setting, an external accelerator must be added during the spraying process. This requires a high dosage of accelerator, making it difficult to maintain uniformity within the concrete. Furthermore, because tunnels often operate in environments characterized by high humidity, low temperatures, and complex chemical conditions, their durability is easily affected by surrounding salt solutions. Portland cement exhibits weak corrosion resistance, and after rapid spraying, it only hardens, resulting in low strength after 3 hours or 1 day. This can easily lead to expansion, cracking, and crystallization, leading to later strength reduction or collapse. Furthermore, existing Portland cement is not well-suited to temperature differences between internal and external surfaces, lacking the characteristic of high early strength, and is prone to cracking. This defect is particularly pronounced in geologically unstable terrain, high-temperature geothermal conditions, or water-rich environments, significantly impacting construction.

[0008] Compared to traditional Portland cement, sulphoaluminate cement features a lower calcination temperature and requires less limestone, significantly reducing energy consumption and CO2 emissions. It has become a key cement type attracting international attention in recent years. Sulphoaluminate cement offers excellent properties such as early strength, high strength, frost resistance, impermeability, minimal expansion, corrosion resistance, and low alkalinity, making it suitable for a variety of specialized projects.

[0009] Therefore, there is an urgent need to develop a method for preparing ultra-early strength sulphoaluminate-based shotcrete with adjustable plasticity. Summary of the Invention

[0010] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0011] A method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete comprises the following steps:

[0012] (1) Add sulphoaluminate cement, machine-made sand and stone into a mixer and mix for 30-90 seconds to ensure homogeneity;

[0013] (2) Add the accelerator and retarder evenly into the mixer and stir for 15-30 seconds;

[0014] (3) Add the polycarboxylate water reducer and water into the mixer and stir rapidly for 90 to 240 seconds. The polycarboxylate water reducer and water are added at a uniform speed within 15 to 30 seconds during the stirring process to finally obtain sulphoaluminate-based shotcrete.

[0015] Preferably, the accelerating agent is a lithium compound.

[0016] Preferably, the quick-setting agent is one or more of lithium hydroxide, lithium carbonate, and lithium sulfate.

[0017] Preferably, the retarder is a borate compound.

[0018] Preferably, the retarder is one or more of borax, boric acid, and calcium borate.

[0019] Preferably, the amount of sulphoaluminate cement in step (1) is 380-420 kg / m 3 The sand ratio (machine-made sand / machine-made sand + stone) is 0.53~0.57, the water-binder ratio is 0.43~0.47, and the total amount of machine-made sand and stone is 1750~1800kg / m 3 .

[0020] Preferably, in step (2), the amount of the accelerator is 0.03-0.06% of the mass of the sulphoaluminate cement, and the amount of the retarder is 0.4-0.5% of the mass of the cement.

[0021] Preferably, the amount of water reducer in step (3) is 0.15-0.3% of the mass of sulphoaluminate cement, and the overall density of shotcrete is 2320-2370 kg / m 3 .

[0022] Preferably, the stone size is 4.75~9.5mm; the machine-made sand size is less than 4.75mm, and the fineness modulus is 2.3~3.7; the sulphoaluminate cement needs to be sieved through a 100-mesh sieve (0.15mm) before use, and the stirring speed is 6-50 rpm.

[0023] Due to the adoption of the above technical solution, the present invention has the following technical advancements compared to the prior art:

[0024] 1. The sulphoaluminate-based shotcrete prepared by the present invention can control its setting time by adjusting the dosage ratio of the retarder and the accelerator during the preparation process, thereby achieving adjustable plasticity of the shotcrete; by adjusting the dosage of the accelerator, the ultra-early strength of the sulphoaluminate-based shotcrete can also be controlled, and its strength far exceeds the national standard.

[0025] Second, this method uses low-alkali sulphoaluminate cement materials to replace ordinary Portland cement for tunnel construction of roads and railways, etc., which expands the selection of cement materials for shotcrete. DETAILED DESCRIPTION

[0026] The following examples may help those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0027] Example

[0028] A method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete comprises the following steps:

[0029] (1) Add sulphoaluminate cement, machine-made sand and stone into a mixer and mix for 30-90 seconds to ensure homogeneity;

[0030] (2) Add the accelerator and retarder evenly into the mixer and stir for 15-30 seconds;

[0031] (3) Add the polycarboxylate water reducer and water into the mixer and stir rapidly for 90 to 240 seconds. The polycarboxylate water reducer and water are added at a uniform speed within 15 to 30 seconds during the stirring process to finally obtain sulphoaluminate-based shotcrete.

[0032] Furthermore, the quick-setting agent is a lithium compound.

[0033] Furthermore, the quick-setting agent is one or more of lithium hydroxide, lithium carbonate, and lithium sulfate.

[0034] Furthermore, the retarder is a borate compound.

[0035] Furthermore, the retarder is one or more of borax, boric acid, and calcium borate.

[0036] Furthermore, the amount of sulphoaluminate cement used in step (1) is 380~420kg / m 3 The sand ratio (machine-made sand / machine-made sand + stone) is 0.53~0.57, and the water-cement ratio is 0.43~0.47.

[0037] Furthermore, in step (2), the amount of the accelerating setting agent is 0.03-0.06% of the mass of the sulphoaluminate cement, and the amount of the retarding agent is 0.4-0.5% of the mass of the cement.

[0038] Furthermore, the water reducing agent dosage in step (3) is 0.15-0.3% of the mass of sulphoaluminate cement, and the overall density of the shotcrete is 2320-2370 kg / m 3 .

[0039] Furthermore, the stone size is 4.75~9.5mm; the machine-made sand size is below 4.75mm, and the fineness modulus is 2.3~3.7; and the sulphoaluminate cement needs to pass through a 100 mesh sieve (0.15mm) before use.

[0040] Reaction principle:

[0041] The hydration mechanism of low-alkali sulphoaluminate cement is mainly through formula (1)

[0042] 3(CaO·Al2O3)·CaSO4+2CaSO4·2H2O+34H2O=3CaO·Al2O3·3CaSO4·32H2O(AFt)+2AH3 (1)

[0043] Ca 2+ B4O7 2- = CaB4O7(2)

[0044] At the beginning of hydration, the alkalinity of the accelerator promotes the dissolution of cement particles. However, since the dosage of borate retarder is much larger than that of lithium-based accelerator, the borate retarder will dissociate into B4O7. 2- With Ca 2+ The calcium borate membrane is formed, as shown in formula (2), which wraps the particles to prevent the contact between cement and water, slowing down the early hydration process and achieving a retarding effect. + It will subsequently promote the dissolution of aluminum phase in cement particles, and make gypsum generate AFt seed crystals, accelerate the crystallization growth of AFt, break through the membrane that wraps the cement particles after a certain period of time, and begin to consume 3(CaO·Al2O3)·CaSO4 and CaSO4·2H2O, promote secondary hydration, and generate a large number of fine AFt that intertwine with each other to form a basic structure, generating an AH3 gel-filled structure with high mechanical properties.

[0045] The function of polycarboxylate water reducer: It forms an adsorption layer on the surface of cement particles to prevent the aggregation and coagulation of particles, reduce the cohesion and internal friction of concrete, and the adsorption film forms a stable solvated water film with water molecules, reducing the sliding resistance between cement particles and increasing fluidity.

[0046] The whole reaction begins with the water reducer improving the fluidity of concrete during the mixing stage, followed by the retarder supplementing or replacing part of the membrane to achieve the retarding effect, and finally the early strength agent acts to make AFt grow rapidly.

[0047] Example 1

[0048] A method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete comprises the following steps:

[0049] (1) Add sulphoaluminate cement, machine-made sand and stone into a mixer and mix for 30 seconds to ensure homogeneity;

[0050] (2) Add the accelerator and retarder evenly into the mixer and stir for 15 seconds;

[0051] (3) The polycarboxylate water reducer and water were added into the mixer and stirred rapidly for 120 seconds. The polycarboxylate water reducer and water were added at a uniform speed within 15 seconds during the stirring process to finally obtain sulphoaluminate-based shotcrete.

[0052] Furthermore, the quick-setting agent is a lithium compound.

[0053] Furthermore, the quick-setting agent is one or more of lithium hydroxide, lithium carbonate, and lithium sulfate.

[0054] Furthermore, the retarder is a borate compound.

[0055] Furthermore, the retarder is one or more of borax, boric acid, and calcium borate.

[0056] Furthermore, the amount of sulphoaluminate cement used in step (1) is 400 kg / m 3 The sand ratio (machine-made sand / machine-made sand + stone) is 0.57, and the water-cement ratio is 0.46.

[0057] Furthermore, in step (2), the amount of the accelerating setting agent is 0.04% by mass of the sulphoaluminate cement, and the amount of the retarding agent is 0.4% by mass of the cement.

[0058] Furthermore, the water reducing agent dosage in step (3) is 0.15% of the mass of sulphoaluminate cement, and the overall density of the shotcrete is 2320 kg / m 3 .

[0059] Furthermore, the stone size is 4.75 mm; the machine-made sand size is less than 4.75 mm, and the fineness modulus is 2.3; and the sulphoaluminate cement needs to be sieved through a 100-mesh sieve (0.15 mm) before use.

[0060] According to GB / T 50080-2016, the slump of sulphoaluminate-based shotcrete was tested to be 187 mm at 1 hour, 80 mm at 1.25 hours, and 0 mm at 1.5 hours. This indicates that the sulphoaluminate-based shotcrete prepared by this method is suitable for shotcreting within 0.5 to 1 hour.

[0061] The compressive strength of sulphoaluminate-based shotcrete tested according to GB / T 50081-2019 showed a 3-hour compressive strength of 9 MPa, a 1-day compressive strength of 23.5 MPa, and a 28-day compressive strength of 33 MPa. This shows that the sulphoaluminate-based shotcrete prepared by this method has the advantage of high early strength.

[0062] Example 2

[0063] A method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete comprises the following steps:

[0064] (1) Add sulphoaluminate cement, machine-made sand and stone into a mixer and mix for 60 seconds to ensure homogeneity;

[0065] (2) Add the accelerator and retarder evenly into the mixer and stir for 15 seconds;

[0066] (3) The polycarboxylate water reducer and water were added into the mixer and stirred rapidly for 90 seconds. The polycarboxylate water reducer and water were added at a uniform speed within 20 seconds during the stirring process to finally obtain sulphoaluminate-based shotcrete.

[0067] Furthermore, the quick-setting agent is a lithium compound.

[0068] Furthermore, the quick-setting agent is one or more of lithium hydroxide, lithium carbonate, and lithium sulfate.

[0069] Furthermore, the retarder is a borate compound.

[0070] Furthermore, the retarder is one or more of borax, boric acid, and calcium borate.

[0071] Furthermore, the amount of sulphoaluminate cement used in step (1) is 390 kg / m 3 The sand ratio (machine-made sand / machine-made sand + stone) is 0.55, and the water-cement ratio is 0.44.

[0072] Furthermore, in step (2), the amount of the accelerating setting agent is 0.03% of the mass of the sulphoaluminate cement, and the amount of the retarding agent is 0.4% of the mass of the cement.

[0073] Furthermore, the water reducing agent dosage in step (3) is 0.25% of the mass of sulphoaluminate cement, and the overall density of the shotcrete is 2350 kg / m 3 .

[0074] Furthermore, the stone size is 6 mm; the machine-made sand size is less than 4.75 mm, and the fineness modulus is 3; and the sulphoaluminate cement needs to be sieved through a 100-mesh sieve (0.15 mm) before use.

[0075] The slump of sulphoaluminate-based shotcrete tested according to GB / T 50080-2016 showed a slump of 175 mm at 1 hour, 93 mm at 1.25 hours, and 0 mm at 1.5 hours. This indicates that the sulphoaluminate-based shotcrete prepared by this method is suitable for shotcreting within a 0.5-1 hour timeframe.

[0076] According to GB / T 50081-2019, the compressive strength of sulphoaluminate-based shotcrete was tested, with a 3-hour compressive strength of 5 MPa, a 1-day compressive strength of 19 MPa, and a 28-day compressive strength of 30 MPa. This shows that the sulphoaluminate-based shotcrete prepared by this method has the advantage of high early strength.

[0077] Example 3

[0078] A method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete comprises the following steps:

[0079] (1) Add sulphoaluminate cement, machine-made sand and stone into a mixer and mix for 60 seconds to ensure homogeneity;

[0080] (2) Add the accelerator and retarder evenly into the mixer and stir for 15 seconds;

[0081] (3) The polycarboxylate water reducer and water were added into the mixer and stirred rapidly for 180 seconds. The polycarboxylate water reducer and water were added at a uniform speed within 30 seconds during the stirring process to finally obtain sulphoaluminate-based shotcrete.

[0082] Furthermore, the quick-setting agent is a lithium compound.

[0083] Furthermore, the quick-setting agent is one or more of lithium hydroxide, lithium carbonate, and lithium sulfate.

[0084] Furthermore, the retarder is a borate compound.

[0085] Furthermore, the retarder is one or more of borax, boric acid, and calcium borate.

[0086] Furthermore, the amount of sulphoaluminate cement used in step (1) is 400 kg / m 3, the sand ratio (machine-made sand / machine-made sand + stone) is 56, and the water-cement ratio is 0.45.

[0087] Furthermore, in step (2), the amount of the accelerating setting agent is 0.05% of the mass of the sulphoaluminate cement, and the amount of the retarding agent is 0.4% of the mass of the cement.

[0088] Furthermore, the water reducing agent dosage in step (3) is 0.2% of the mass of sulphoaluminate cement, and the overall density of the shotcrete is 2370kg / m 3 .

[0089] Furthermore, the stone size is 9.5mm; the machine-made sand size is less than 4.75mm, and the fineness modulus is 3.7; and the sulphoaluminate cement needs to pass through a 100-mesh sieve (0.15mm) before use.

[0090] According to GB / T 50080-2016, the concrete slump was 195 mm at 0.5 h, 55 mm at 0.75 h, and 0 mm at 1 h. This shows that the sulphoaluminate-based shotcrete prepared by this method is suitable for shotcrete construction within 0.5 to 1 h.

[0091] According to GB / T 50081-2019, the compressive strength of concrete was tested to be 16 MPa after 3 hours, 23.6 MPa after 1 day, and 35.5 MPa after 28 days. This shows that the sulphoaluminate-based shotcrete prepared by this method has the advantage of high early strength.

[0092] While the present invention has been generally described above, modifications and improvements are readily apparent to those skilled in the art. Therefore, modifications and improvements that do not depart from the spirit of the present invention are intended to be within the scope of the present invention.

Claims

1. A method for preparing adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete, characterized by: The following steps are involved: (1) Add sulphoaluminate cement, machine-made sand and stone into a mixer and mix for 30-90 seconds to ensure homogeneity; (2) Add the accelerator and retarder evenly into the mixer and stir for 15-30 seconds; (3) Add the polycarboxylate water reducer and water into the mixer and stir rapidly for 90 to 240 seconds. The polycarboxylate water reducer and water are added at a uniform speed within the first 15 to 30 seconds of the stirring process. After the stirring is completed, the sulfoaluminate-based shotcrete is obtained.

2. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 1, wherein: The amount of sulphoaluminate cement used in step (1) is 380~420kg / m 3 The total amount of machine-made sand and stone is 1750~1800kg / m 3 , the sand rate is 0.53~0.

57.

3. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 1, wherein: In step (2), the amount of the accelerating setting agent is 0.03-0.06% of the mass of the sulphoaluminate cement, and the amount of the retarding agent is 0.4-0.5% of the mass of the sulphoaluminate cement.

4. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 1, wherein: In step (3), the water-reducing agent dosage is 0.15-0.3% of the mass of sulphoaluminate cement, the water-binder ratio is 0.43-0.47, and the overall density of the shotcrete is 2320-2370 kg / m 3 .

5. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 1, wherein: The sulphoaluminate cement used must pass through a 100-mesh sieve, the stone size is 4.75~9.5mm; the machine-made sand size is below 4.75mm, the fineness modulus is 2.3~3.7, and the stirring speed is 6-50 rpm.

6. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 1, wherein: The accelerator is a lithium compound and the retarder is a borate compound.

7. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 6, wherein: The retarder is one or more of borax, boric acid and calcium borate.

8. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 6, wherein: The quick-setting agent is one or more of lithium hydroxide, lithium carbonate and lithium sulfate.

9. The method for preparing the adjustable plasticity ultra-early strength sulphoaluminate-based shotcrete according to claim 1, wherein: The sulphoaluminate-based shotcrete is used for wall filling and repairing work in tunnel engineering.