Early-strength, quick-setting concrete for emergency repair and construction of island and reef projects and its preparation method

Abstract

The invention discloses an early-strength, quick-setting concrete for emergency repair and construction of island and reef projects and a preparation method thereof. The method comprises weighing artificial seawater, sulphoaluminate cement, fly ash, silica fume, coral sand, regenerated coral coarse aggregate, a water reducer, a liquid alkali-free quick-setting agent and stainless steel fiber, uniformly mixing the sulphoaluminate cement, silica fume and fly ash to obtain a cementitious material, reserving a portion of artificial seawater, dry-stirring the cementitious material, then adding the remaining artificial seawater and the water reducer and stirring, then respectively adding coral sand, regenerated coral coarse aggregate and stainless steel fiber and stirring, adding the liquid alkali-free quick-setting agent and the reserved artificial seawater to the resulting mixture to obtain a concrete mixture in a gel state, placing the mixture into a mold for vibration, standing, demoulding and curing to obtain early-strength, quick-setting concrete. The early-strength, quick-setting concrete of the present invention has the advantages of short setting time, good early strength, high mechanical strength and stable chemical properties, and has good economic and environmental effects.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and relates to an early-strength, quick-setting concrete for emergency repair and construction of island and reef projects and a preparation method thereof, and specifically relates to a stainless steel reinforced recycled coral aggregate concrete for emergency repair and construction of island and reef projects and a preparation method thereof. Background Art

[0002] Coral concrete is commonly used in island construction projects. However, island buildings are vulnerable to threats such as earthquakes, tsunamis, and seawater erosion. Under these circumstances, damage is inevitable. Given the difficulty in predicting the frequency of these threats, rapid repairs to protect personnel and maintain the normal operation of island buildings are crucial. However, the large-scale use of coral concrete not only damages the original coral ecosystem but also generates a significant amount of solid waste. Reusing this solid waste as concrete aggregate in the production of recycled coral concrete would not only protect the island coral ecosystem but also conserve resources by reusing existing construction waste. However, the recycled coral concrete currently available on the market suffers from a long setting time (average initial setting time of 1-3 hours, final setting time of 5-8 hours) and is not resistant to seawater corrosion, making it unsuitable for rapid repairs in emergency situations. Traditional quick-setting concrete has very poor fluidity and is generally used as sprayed concrete. Sprayed concrete is used in two ways: one is dry spraying, which has the following disadvantages: (a) the water-cement ratio cannot be accurately controlled, which affects the uniformity of the concrete; (b) due to the fast material flow rate, the mixing time of the dry material and water is short, so the hydration of the cement is not sufficient, which affects the strength of the concrete; (c) there is a lot of dust during operation and the rebound is large; (d) the friction between the dry material and the feed pipe will generate static electricity, which affects the operation; the other is wet spraying, which has the disadvantages that the wet spraying process equipment is relatively complex and the transportation distance is relatively short. When the island is unable to communicate with the outside world due to extreme natural disasters, it is inconvenient to transport materials, and the air consumption is large. At the same time, it is not suitable for water seepage. Island and reef projects face the environment of seawater infiltration, so it is not suitable for island and reef projects. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide an early-strength, fast-setting concrete for emergency repair and construction of island and reef projects, which has short setting time, early strength, high strength, stable chemical properties, and excellent economic and environmental effects, and a preparation method thereof.

[0004] In order to solve the above technical problems, the present invention proposes the following solutions.

[0005] A method for preparing early-strength, quick-setting concrete for emergency repair and construction of island and reef projects, characterized by comprising the following steps:

[0006] (1) Weigh the following raw materials in parts by mass: 218.7 to 219 parts of artificial seawater, 710 to 712 parts of sulphoaluminate cement, 55 to 56 parts of fly ash, 45 to 47 parts of silica fume, 700 to 705 parts of coral sand, 500 to 505 parts of recycled coral coarse aggregate, 2.5 to 3 parts of water reducer, 40.5 to 41 parts of liquid alkali-free quick-setting agent, and 119.7 to 120 parts of stainless steel fiber;

[0007] (2) The sulphoaluminate cement, silica fume and fly ash weighed in step (1) are mixed evenly to obtain a cementitious material; a portion of the artificial seawater is reserved, and the reserved artificial seawater is recorded as ,but Satisfies the following formula (I):

[0008] Formula (I)

[0009] Where: is the reserved artificial seawater, unit is kg / m³, C is the amount of sulphoaluminate cement, unit is kg / m³, S is the amount of coral sand, unit is kg / m³, F is the amount of stainless steel fiber, unit is kg / m³, A is the amount of liquid alkali-free accelerator, unit is kg / m³, m³ refers to the volume of concrete, which can also be written as kg / m³ concrete;

[0010] The cementitious material is dry-mixed, and then the remaining artificial seawater and all the water reducers are added and stirred once, where the remaining artificial seawater is the total artificial seawater minus the reserved artificial seawater, to obtain a mixture, coral sand is added to the mixture and stirred twice, and then recycled coral coarse aggregate is added and stirred three times, and then stainless steel fiber is added and stirred four times to obtain a stainless steel fiber concrete mixture;

[0011] (3) adding a liquid alkali-free quick-setting agent and the reserved artificial seawater to the stainless steel fiber concrete mixture, and stirring for 15 seconds to 30 seconds to allow the resulting concrete mixture to form a uniform gel state;

[0012] (4) The gel-state concrete mixture obtained in step (3) is placed into a mold and vibrated. After standing, demoulding, and curing, an early-strength and fast-setting concrete for emergency repair and construction of island and reef projects is obtained.

[0013] In the method for preparing the early-strength, fast-setting concrete for the emergency repair and construction of island and reef projects, preferably, in step (1), the recycled coral coarse aggregate is obtained by crushing, screening, washing, and drying discarded coral concrete, and the discarded coral concrete is characterized by a mechanical property of achieving a compressive strength of 50 MPa or more at 28 days, more preferably 50 MPa to 60 MPa. The discarded coral concrete preferably comprises, by weight, 600 to 605 parts of ordinary Portland cement, 120 to 121 parts of slag powder, 480 to 485 parts of fly ash, 1320 to 1325 parts of coral sand, 12 to 13 parts of nano-silicon dioxide, 312 to 313 parts of artificial seawater, and a water-cement ratio of 0.26.

[0014] In the above-mentioned method for preparing the early-strength, fast-setting concrete for emergency repair and construction of island and reef projects, preferably, in step (1), the coral sand has the following characteristics: 0 < particle size ≤ 2.36 mm, fineness modulus is 2.1, and is fine sand.

[0015] In the above-mentioned method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects, preferably, in step (1), the stainless steel fiber is 316L stainless steel fiber, the diameter of the stainless steel fiber is 0.2 mm to 0.22 mm, the length of the stainless steel fiber is 13 mm to 13.2 mm, and the tensile strength of the stainless steel fiber is 1950 MPa to 1970 MPa.

[0016] In the above-mentioned method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects, preferably, in step (1), the liquid alkali-free quick-setting agent is an FSA-AF type liquid alkali-free quick-setting agent.

[0017] In the above-mentioned method for preparing the early-strength, fast-setting concrete for emergency repair and construction of island and reef projects, preferably, in step (1), the artificial seawater is composed of water and the following components at the following concentrations: sodium chloride 24 g·L -1 ~26 g·L -1 , magnesium chloride 4 g·L -1 ~5.5 g·L -1 , sodium sulfate 4 g·L -1 ~5 g·L -1 , potassium chloride 1.1 g·L -1 ~1.5 g·L -1 , sodium bicarbonate 0.1g·L -1 ~0.5 g·L -1 , magnesium bromide 0.1 g·L -1 ~0.5 g·L -1 .

[0018] In the above-mentioned method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects, preferably, in step (1): the sulphoaluminate cement is 62.5 sulphoaluminate cement;

[0019] The fly ash has the following characteristics: it is first-class fly ash, in the form of spherical particles, with a specific surface area of ​​1290m 2 / kg~1310m 2 / kg, water requirement is 96% to 98%;

[0020] The silica fume has the following characteristics: a specific surface area of ​​19400m 2 / kg~19500m 2 / kg, SiO2 content is 95% to 96.75%, water requirement ratio is 125%, moisture content is 0.4% to 0.5%, and burning vector is 3.5% to 3.7%;

[0021] The water reducer is a polycarboxylic acid water reducer, which is white powdery particles with a solid content of 99% and a water reduction rate of 25% to 29%.

[0022] In the method for preparing the early-strength, quick-setting concrete for emergency repair and construction of the above-mentioned island and reef engineering, preferably, in step (2), the cementitious material is added to the HJW-60 type mixing equipment for dry mixing, the dry mixing time is 3 min to 4 min, the first mixing time is 3 min to 4 min, the second mixing time is 2 min to 3 min, the third mixing time is 1 min to 2 min, and the fourth mixing time is 2 min to 3 min.

[0023] In the above-mentioned method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects, preferably, in step (4), the vibration time is 30s to 45s, the standing time is 24h to 25h, and the curing time is 1 day to 28 days.

[0024] As a general technical concept, the present invention also provides the early-strength and fast-setting concrete for emergency repair and construction of island and reef projects prepared by the method for preparing the above-mentioned early-strength and fast-setting concrete for emergency repair and construction of island and reef projects.

[0025] In the present invention, the regenerated coral coarse aggregate can be prepared by, but is not limited to, manually screening discarded coral concrete to remove impurities such as needle-like flakes, wood chips, cement mortar blocks, and other components, selecting high-quality solid blocks, crushing them into regenerated coral coarse aggregate of different particle sizes using a jaw crusher, sieving the aggregates using standard square-hole sieves of different particle sizes, repeatedly washing the aggregates to remove surface dust, impurities, and other surface attachments, and then airing and drying them to obtain the regenerated coral coarse aggregate.

[0026] In the preparation method of the present invention, the first stirring, the second stirring, the third stirring, and the fourth stirring refer to the first stirring, the second stirring, the third stirring, and the fourth stirring, respectively.

[0027] Glossary:

[0028] Sand ratio: mass percentage of coral sand / (coral sand + recycled coral coarse aggregate).

[0029] Early strength: The strength of concrete after preparation is a gradual increase process. It usually takes 28 days for the strength to reach the maximum. If the strength of concrete can be increased to the maximum or close to the maximum strength in a shorter time, it is called early strength, which is the characteristic of reaching the maximum strength early.

[0030] Slump: Used to measure the fluidity and workability of a mix, and supplemented by intuitive experience to assess cohesion and water retention. Slump is a quantitative indicator that measures the workability of concrete and is used to determine whether construction can proceed normally.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) The early-strength, quick-setting concrete for island and reef engineering emergency repair and construction of the present invention significantly reduces the setting time compared to existing concrete and has significant early strength. It is much stronger than existing regenerated coral concrete. The early-strength, quick-setting concrete of the present invention has an initial setting time of less than 25 minutes, a final setting time of less than 45 minutes, and a 3-day strength that can reach more than 90% of the 28-day strength. The 3-day compressive strength can reach an average of 85.0 MPa, and the 28-day compressive strength can reach 91.4 MPa, making it more suitable for the requirements of rapid emergency repair and construction of damaged buildings required for island and reef engineering construction. The early-strength, quick-setting concrete of the present invention is different from the C50-C60 strength of existing low-strength coral concrete. The maximum strength can reach more than 96 MPa. While having early strength, it also has excellent high strength and a particularly short setting time.

[0033] (2) In the preparation method of the present invention, since the main component of coral aggregate is calcium carbonate (CaCO3), it has the characteristics of porous surface, high brittleness, high water absorption rate and easy breakage, and the concrete prepared therefrom is usually of low strength. The morphology of the regenerated coral coarse aggregate particles used in the present invention is a porous structure with a rough surface. By uniformly mixing with cement, silica fume and fly ash in the preparation process of the present invention, the cementitious material (cement, fly ash, silica fume) particles can be effectively filled into the rough surface and pores of the regenerated coral coarse aggregate. The subsequent addition of seawater can enable the hydration products (calcium aluminate, calcium hydroxide, calcium silicate) formed by the cementitious material to effectively fill the regenerated coral coarse aggregate, so that the cement matrix and the regenerated coral coarse aggregate are tightly combined, the strength is significantly improved, and better mechanical properties are obtained. In the preparation process of the present invention, after the cementitious material and the aggregate are completely mixed, a liquid alkali-free quick-setting agent is added and the reserved artificial seawater W is added. res Due to the presence of liquid alkali-free accelerating setting agent and stainless steel fiber, the fluidity of concrete is greatly reduced. If the general concrete preparation process (all water is added) is followed, its fluidity will be too low to meet the use standard. The present invention reserves artificial seawater to The fluidity that was originally sharply reduced due to the addition of the quick-setting agent is restored to a level that can be poured.

[0034] The preparation method of the present invention uses highly corrosion-resistant sulphoaluminate cement and stainless steel fibers that prevent seawater corrosion. The two work together to make the concrete of the present invention have stable chemical properties. It can be used to construct buildings near the sea on the coast. It can effectively resist marine disasters such as coastal erosion and seawater erosion, and has strong resistance to marine disasters.

[0035] The reason for the deterioration of cement concrete performance in marine environment is often due to the poor durability of cement concrete, which leads to reduced strength. In the process of construction and use, the original Portland cement (OPC)-based concrete for marine engineering construction has two main hydration products, calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (CSH) gel. These hydration products are easily dissolved or corroded in seawater, resulting in reduced durability of concrete buildings. The main clinker mineral components of sulphoaluminate cement are calcium sulphoaluminate and dicalcium silicate. In the presence of CaSO4·2H2O When present in sufficient amounts, calcium sulfoaluminate rapidly hydrates upon contact with water to form needle-shaped trisulfur calcium sulfoaluminate hydrated crystals (AFt) and aluminum hydroxide (Al(OH)3) gel. The Al(OH)3 gel and ettringite crystals intertwine to form the dense skeleton structure of sulfoaluminate cement. The Ca(OH)2 formed by hydration of dicalcium silicate reacts with Al(OH)3 and CaSO4·2H2O to form ettringite (AFt). When the CaSO4·2H2O content is insufficient, calcium sulfoaluminate reacts to form monosulfur calcium sulfoaluminate hydrate (AFm). Sulphoaluminate cement exhibits excellent corrosion resistance against seawater, chlorides (NaCl, MgCl2), sulfates (Na2SO4, MgSO4, (NH4)2SO4), and especially their complex salts (MgSO4-NaCl).

[0036] The present invention has a shorter setting time, making it more suitable for emergency repair and construction projects. With an initial setting time of less than 25 minutes and a final setting time of less than 45 minutes, it can quickly repair buildings damaged by disasters. Furthermore, the special sulfoaluminate cement used in the present invention offers better corrosion resistance than commercially available products, making it more suitable for marine engineering. The early-strength, rapid-setting concrete of the present invention boasts a higher strength than existing recycled coral concrete materials used in island and reef projects, and exhibits superior resistance to dynamic impact damage, thus better protecting island and reef structures and personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is an SEM image of the early-strength, quick-setting concrete prepared in Example 1 of the present invention for emergency repair and construction of island and reef projects. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby. The materials and instruments used in the following examples are all commercially available.

[0039] Example 1

[0040] A method for preparing early-strength, quick-setting concrete for emergency repair and construction of island and reef projects of the present invention comprises the following steps:

[0041] (1) Weigh the following raw materials in parts by mass: 218.7 parts of artificial seawater, 710 parts of sulfoaluminate cement, 55 parts of fly ash, 45 parts of silica fume, 700 parts of coral sand, 500 parts of recycled coral coarse aggregate, 2.5 parts of water reducer, 40.5 parts of liquid alkali-free quick-setting agent, and 119.7 parts of stainless steel fiber; 1 part by mass is 1 kg, and 1 m³ of concrete is obtained;

[0042] (2) The sulphoaluminate cement, silica fume and fly ash weighed in step (1) are mixed evenly to obtain a cementitious material; a portion of the artificial seawater is reserved, and the reserved artificial seawater is recorded as ,but Satisfies the following formula (I):

[0043] Formula (I)

[0044] Where: is the reserved artificial seawater, unit is kg / m³, C is the amount of sulfoaluminate cement, unit is kg / m³, S is the amount of coral sand, unit is kg / m³, F is the amount of stainless steel fiber, unit is kg / m³, A is the amount of liquid alkali-free accelerator, unit is kg / m³, m³ refers to the volume of concrete; the reserved artificial seawater is 30.8kg / m³, i.e. 30.8 parts.

[0045] Add the cementitious material into the HJW-60 mixing equipment and dry-mix for 3 minutes, then add the remaining artificial seawater and all the water reducers and mix for 3 minutes. The remaining artificial seawater is the total artificial seawater minus the reserved artificial seawater to obtain a mixture. Add coral sand to the mixture and mix for 3 minutes. Then add recycled coral coarse aggregate and mix for 2 minutes. Then add stainless steel fiber and mix for 3 minutes to obtain a stainless steel fiber concrete mixture.

[0046] (3) Add liquid alkali-free accelerating agent and reserved artificial seawater to the stainless steel fiber concrete mixture and stir for 30 seconds to make the resulting concrete mixture form a uniform gel state;

[0047] (4) The gel-state concrete mixture obtained in step (3) was placed into a 100mm×100mm×100mm cubic mold, vibrated for 35s, left to stand for 24h, demoulded, and placed in a standard curing box for curing to obtain recycled coral aggregate concrete for island and reef engineering. The microscopic morphology is as follows: Figure 1 As shown. Figure 1It can be seen that the slender stainless steel fibers are evenly embedded in the cement matrix, the interface between the fibers and the matrix is ​​well bonded, there is no obvious debonding on the surface, the interface transition zone performs well, and the transition zone between the stainless steel fibers and the surrounding cement slurry is relatively tight, showing good bonding performance. This is because the artificial seawater reserved by the present invention can effectively improve the workability of concrete, control the hydration process of the cement matrix, thereby improving the fluidity and workability of concrete, and improving the density and fineness of the matrix. Therefore, it can be seen that the stainless steel fibers are well bonded to the cement matrix and no debonding occurs. In the figure, it can also be observed that some fibers "bridge" small microcracks, indicating that they have the effect of inhibiting crack expansion, enhancing the crack resistance and compressive strength of concrete, and improving its mechanical properties.

[0048] In step (1) of this embodiment:

[0049] Recycled coral coarse aggregate is made from discarded coral concrete through crushing, screening, washing, and drying. The discarded coral concrete exhibits mechanical properties, including a 28-day compressive strength of 50 MPa. The ingredients, by mass, include 600 parts of ordinary Portland cement, 120 parts of slag powder, 480 parts of fly ash, 1,320 parts of coral sand, 12 parts of nano-silica, and 312 parts of artificial seawater, with a water-to-binder ratio of 0.26.

[0050] Coral sand (fine aggregate) has the following characteristics: 0<particle size≤2.36mm, fineness modulus is 2.1, it is fine sand, and the sand ratio is 58.3%.

[0051] The stainless steel fiber is 316L stainless steel fiber with a diameter of 0.2 mm and a length of 13 mm. The tensile strength of the stainless steel fiber is 1950 MPa.

[0052] The liquid alkali-free quick-setting agent is FSA-AF type liquid alkali-free quick-setting agent.

[0053] Artificial seawater is composed of water and the following components at the following concentrations: sodium chloride 25.43 g·L -1 , magnesium chloride 5.2 g·L -1 , sodium sulfate 4.1 g·L -1 , potassium chloride 1.2 g·L -1 , sodium bicarbonate 0.2 g·L -1 , magnesium bromide 0.1 g·L -1 .

[0054] Sulphoaluminate cement is 62.5 sulphoaluminate cement;

[0055] Fly ash has the following characteristics: it is a first-class fly ash, in the form of spherical particles (fly ash microbeads), with a specific surface area of ​​1290m 2 / kg, water requirement is 98%, and sphere density is 2.25g / cm 3 The content of spherical particles is 90%, the fineness is 12%, the loss on ignition is 2.34%, and the strength activity index is 86%.

[0056] Silica fume has the following characteristics: Specific surface area is 19430m 2 / kg, SiO2 content is 96.2%, water requirement ratio is 125%, moisture content is 0.42%, and burning vector is 3.5%;

[0057] The water reducer is polycarboxylic acid water reducer, which is a white powdery granule with a solid content of 99% and a water reduction rate of 25% to 28%.

[0058] In step (4) of this embodiment, a portion of the specimens were taken for compressive strength tests at 1 day and 3 days of curing, and a compressive strength test was performed at the standard curing age of 28 days. The performance test results are shown in Table 1.

[0059] Comparative Example 1

[0060] A method for preparing quick-setting concrete, the preparation process is substantially the same as that of Example 1, except that the mass fraction of stainless steel fiber is 0 and the amount of reserved artificial seawater is 0. The performance test of the concrete is shown in Table 1.

[0061] Comparative Example 2

[0062] A method for preparing quick-setting concrete was described. The preparation process was essentially the same as in Example 1, except that the amount of reserved artificial seawater was zero. Performance tests of the concrete are shown in Table 1. Its slump was reduced by 43 mm to 75 mm, and its fluidity was significantly reduced by 36.4%.

[0063] Comparative Example 3

[0064] A method for preparing quick-setting concrete was described. The preparation process was essentially the same as in Example 1, except that the reserved artificial seawater volume was reduced to 43.74 parts, one-fifth of the total artificial seawater. Performance tests of the concrete are shown in Table 1. Its slump was reduced by 24 mm to 94 mm, and its fluidity was reduced to a certain extent, by 20.3%.

[0065]

[0066] As shown in Table 1, the 3-day strength of the early-strength, quick-setting concrete for the island and reef engineering emergency repair and construction of the present invention is significantly higher than that of comparative examples 1-3. Compared with comparative example 1, the strength is increased by 64.7%, and the 3-day strength can reach 93.0% of the 28-day strength, showing obvious early strength, while the early strength of conventional ordinary concrete is less obvious. The 28-day strength of the early-strength, quick-setting concrete of the present invention can reach C90, and its 3-day strength and 28-day strength are much higher than those of ordinary recycled coral concrete. The setting time of the present invention is also much lower than that of ordinary recycled coral concrete, with an initial setting time of less than 25 minutes and a final setting time of less than 45 minutes, which is much shorter than the setting time of conventional recycled coral concrete. It can quickly set when rapid rescue is needed, and can be used to build and repair relevant important facilities. The reserved water formula adopted by the present invention solves the defect of low fluidity caused by the addition of a quick-setting agent, and is suitable for construction. In summary, the early-strength quick-setting concrete for emergency repair and construction of island and reef projects of the present invention has excellent early strength and higher strength, and a short setting time. Combined with the actual situation of island and reef projects, it can be applied to emergency repair and construction of island and reef projects.

[0067] The above description is only a preferred embodiment of the present invention and does not constitute any formal limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing early-strength, quick-setting concrete for emergency repair and construction of island and reef projects, characterized in that: The following steps are involved: (1) Weigh the following raw materials in parts by mass: 218.7 to 219 parts of artificial seawater, 710 to 712 parts of sulphoaluminate cement, 55 to 56 parts of fly ash, 45 to 47 parts of silica fume, 700 to 705 parts of coral sand, 500 to 505 parts of recycled coral coarse aggregate, 2.5 to 3 parts of water reducer, 40.5 to 41 parts of liquid alkali-free quick-setting agent, and 119.7 to 120 parts of stainless steel fiber; (2) The sulphoaluminate cement, silica fume and fly ash weighed in step (1) are mixed evenly to obtain a cementitious material; a portion of the artificial seawater is reserved, and the reserved artificial seawater is recorded as ,but Satisfies the following formula (I): Formula (I) Where: is the reserved artificial seawater, in kg / m³ concrete, C is the amount of sulphoaluminate cement, in kg / m³ concrete, S is the amount of coral sand, in kg / m³ concrete, F is the amount of stainless steel fiber, in kg / m³ concrete, A is the amount of liquid alkali-free accelerator, in kg / m³ concrete; The cementitious material is dry-mixed, and then the remaining artificial seawater and all the water reducers are added and stirred once, where the remaining artificial seawater is the total artificial seawater minus the reserved artificial seawater, to obtain a mixture, coral sand is added to the mixture and stirred twice, and then recycled coral coarse aggregate is added and stirred three times, and then stainless steel fiber is added and stirred four times to obtain a stainless steel fiber concrete mixture; (3) adding a liquid alkali-free quick-setting agent and the reserved artificial seawater to the stainless steel fiber concrete mixture, and stirring for 15 seconds to 30 seconds to allow the resulting concrete mixture to form a uniform gel state; (4) The gel-state concrete mixture obtained in step (3) is placed into a mold and vibrated, and after standing, demoulding, and curing, an early-strength and fast-setting concrete for emergency repair and construction of island and reef projects is obtained; The sulphoaluminate cement is 62.5 sulphoaluminate cement; The coral sand has the following characteristics: 0 < particle size ≤ 2.36 mm, fineness modulus is 2.1, and it is fine sand; The stainless steel fiber is 316L stainless steel fiber, the diameter of the stainless steel fiber is 0.2 mm to 0.22 mm, the length of the stainless steel fiber is 13 mm to 13.2 mm, and the tensile strength of the stainless steel fiber is 1950 MPa to 1970 MPa; The liquid alkali-free quick-setting agent is an FSA-AF type liquid alkali-free quick-setting agent.

2. The method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects according to claim 1, characterized in that: In step (1), the regenerated coral coarse aggregate is obtained by crushing, screening, washing and drying discarded coral concrete, and the discarded coral concrete is characterized by a mechanical property of achieving a compressive strength value of 50 MPa or more at 28 days of age.

3. The method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects according to claim 1 or 2, characterized in that: In step (1), the artificial seawater is composed of water and the following components at the following concentrations: sodium chloride 24 g·L -1 ~26 g·L -1 , magnesium chloride 4 g·L -1 ~5.5 g·L -1 , sodium sulfate 4 g·L -1 ~5 g·L -1 , potassium chloride 1.1 g·L -1 ~1.5 g·L -1 , sodium bicarbonate 0.1 g·L -1 ~0.5 g·L -1 , magnesium bromide 0.1 g·L -1 ~0.5 g·L -1 .

4. The method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects according to claim 1 or 2, characterized in that: In step (1): the fly ash has the following characteristics: it is Class I fly ash, in the form of spherical particles, with a specific surface area of ​​1290m 2 / kg~1310m 2 / kg, water requirement is 96% to 98%; The silica fume has the following characteristics: a specific surface area of ​​19400m 2 / kg~19500m 2 / kg, SiO2 content is 95% to 96.75%, water requirement ratio is 125%, moisture content is 0.4% to 0.5%, and loss on ignition is 3.5% to 3.7%; The water reducer is a polycarboxylic acid water reducer, which is white powdery particles with a solid content of 99% and a water reduction rate of 25% to 29%.

5. The method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects according to claim 1 or 2, characterized in that: In step (2), the gelling material is added to the HJW-60 type stirring equipment for dry stirring, the dry stirring time is 3 minutes to 4 minutes, the first stirring time is 3 minutes to 4 minutes, the second stirring time is 2 minutes to 3 minutes, the third stirring time is 1 minute to 2 minutes, and the fourth stirring time is 2 minutes to 3 minutes.

6. The method for preparing the early-strength, quick-setting concrete for emergency repair and construction of island and reef projects according to claim 1 or 2, characterized in that: In step (4), the vibration time is 30s to 45s, the standing time is 24h to 25h, and the curing time is 1 day to 28 days.

7. An early-strength and fast-setting concrete for emergency repair and construction of island and reef projects, prepared by the method for preparing the early-strength and fast-setting concrete for emergency repair and construction of island and reef projects as claimed in any one of claims 1 to 6.

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