AU2020457381B2

AU2020457381B2 - Concrete for 3d printing of coastal special-shaped structure, and processing method and application thereof

Info

Publication number: AU2020457381B2
Application number: AU2020457381A
Authority: AU
Inventors: Song Gao; Dongshuai HOU; Qiuyi LI; Jianlin Luo; Fei TENG; Jigang Zhang
Original assignee: Qingdao University of Technology
Current assignee: Qingdao University of Technology
Priority date: 2020-07-10
Filing date: 2020-07-30
Publication date: 2023-10-19
Anticipated expiration: 2040-07-30
Also published as: AU2020457381A1; CN113307597B; JP2022542640A; JP7362083B2; CN113307597A; WO2022007063A1; CN111848081A

Abstract

A coastal special-shaped structure 3D printing concrete, a processing technology and the use thereof. The raw materials thereof are compounded cement, regenerated sand, fly ash, polyvinyl alcohol, graphene oxide, steel fibers, organic fibers, a water reducing agent, a thickening time control agent, a mineral admixture and water. The 3D printing concrete has a good cohesive water retention and adjacent thin layer interface cohesiveness. The formation of a micro-capacitor by combining GO with a PVA electrolyte avoids the formation of a corrosion cell in a thin layer of concrete, and the concrete has a good marine durability.

Description

CONCRETE FOR 3D PRINTING OF COASTAL SPECIAL-SHAPED

STRUCTURE, AND PROCESSING METHOD AND APPLICATION THEREOF

TECHNICAL FIELD The present disclosure belongs to the field of 3D printing technology of coastal structures, and

in particular relates to a concrete for 3D printing of coastal special-shaped structure, a processing

method of the concrete for 3D printing of coastal special-shaped structure and an application in a

preparation of the coastal special-shaped structure.

BACKGROUND Information of the Related Art part is merely disclosed to increase the understanding of the

overall background of the present disclosure, but is not necessarily regarded as acknowledging or

suggesting, in any form, that the information constitutes the prior art known to a person of ordinary

skill in the art.

At present, a status of industrial upgrading of digitalization, industrialization and

intellectualization of the construction field requires the rapid manufacture of various concrete

special-shaped components for assembly buildings with different specifications and structural types,

such as shear walls, laminated floors, laminated beams, laminated columns, special-shaped stairs,

integral sanitary rooms, garbage tanks, etc. Meanwhile, the resource utilization of construction waste

effectively relieves the pressure of ecological protection and has witnessed rapid development in

cities and towns in recent years. Digital construction methods based on robotic 3D printing not only

accurately controls the construction accuracy of various types of concrete special-shaped structures,

but also manufactures various curved components of beautiful shape without the necessity of

manufacturing molds in advance, dealing with a large number of materials in the manufacturing

process, or going through complex forging technology, and ultimately achieves structural

optimization, material and energy reduction in production, and effectively realizes industrialization,

intelligentization, and resource conservation in special-shaped buildings with broad prospects.

At the same time, reinforced concrete structures are widely used in coastal structural engineering fields such as offshore buildings, bridges and tunnels, wind energy nuclear power plants, oil drilling platforms, docks and etc. Similarly, based on 3D printing technology, coastal special-shaped structures such as well cover, rainwater grate, underground pipe gallery, oval water tank, subway segment, honeycomb beam, composite beam/or composite plate and so on can be quickly manufactured, which has attracted wide attention.

It should not be overlooked that the reinforcement framework is generally not added to the 3D

printing concrete, but the requirements of high early-strength, well toughness deformation of the 3D

printing concrete are realized by doping short cut steel fibers with high strength and high modulus.

However, the successful 3D printing of complex concrete components also depends on the features

of corresponding concrete slurry such as fast in setting, good viscidity and water-keeping ability,

good plasticity, good interfacial bonding and thixotropy between layers. At the same time, the

concrete for coastal special-shaped structure are mostly multi-porous, multi-phase non-homogeneous

materials, seawater and oxygen will reach the surface of the steel fiber along the pores in the

concrete, resulting in corrosion free electrons. These electrons are sent to the cathode area through

the steel fiber, the negative ions in the solution are sent to the anode area through the pore solution,

and it is prone to form a large number of corrosion microcell, and results in premature failure.

However, when developing the 3D printing concrete materials for coastal special-shaped

structures, the inventors find the following problems:

(1) Coastal special-shaped structures are with complex curved surfaces and are mostly

thin-walled structures, the 3D printing concrete adopts layer by layer print mode, and are

correspondingly difficult to have sufficient thickness of concrete protective layer to protect the

randomly dispersed steel fibers from marine corrosion; at the same time, the surface is coated with

anti-corrosion layer, plus cathodic protection and other common marine anti-corrosion technology is

either not applicable, or is with poor results for the continued existence of printed interface layers of

coastal special-shaped structures.

(2) When using conventional 3D printing concrete material to print the coastal special-shaped

structure, there is difficult to ensure that it having good rheology, water retention cohesion,

mechanical toughness and volume stability, while having sufficient interlayer interface bonding and

thixotropy.

(3) When using conventional 3D printing concrete materials to print the coastal special-shaped structures, there is often difficult to achieve resource utilization of construction or industrial solid waste, reduce the pressure of urban ecological protection and energy conservation and emission reduction, and achieve green environmental benefits.

SUMMARY In view of the above problems recorded in the background, the present disclosure aims to

provide an optimized concrete for 3D printing of coastal special-shaped structures, and obtained

coastal special-shaped structure printed with the concrete has better marine anti-corrosion effects and

interface bonding and thixotropic properties.

Based on the above technical effects, the present disclosure provides the following technical

solutions.

A first aspect of the present disclosure, provided a concrete for 3D printing of coastal

special-shaped structure, the concrete for 3D printing of coastal special-shaped structure consists of

following raw materials with weight parts: 1 part of compound cement, 1 - 2 parts of reclaimed sand,

0.05 - 0.2 parts of fly ash (FA), 0.005 - 0.05 parts of polyvinyl alcohol (PVA), 0.0002 - 0.002 parts of

graphene oxide (GO), 0.01 - 0.05 parts of steel fiber, 0.005 - 0.02 parts of organic fiber, 0.005 - 0.01

parts of water-reducing agent, 0.005 - 0.01 parts of thickening time control agent, 0 - 0.05 parts of

mineral admixture and 0.3 - 0.5 parts of water; oxidant and catalyst are included in the PVA.

The concrete for 3D printing of coastal special-shaped structure prepared by the raw materials

and the ratios, can fit well with the printing requirements of existing printing arms and structural

model parameters, and print the coastal special-shaped concrete structure of different specifications.

In addition, the coastal special-shaped structure obtained by printing has good marine durability

performance.

The present disclosure obtained the raw materials and ratios of the 3D printing concrete by

continuously attempt, through the GO containing many functional groups such as hydroxyl, epoxy

and carboxyl groups and the PVA containing many hydroxyl groups, not only made the 3D printing

concrete has good adhesion and water retention, but also the adjacent thin layers of the 3D printing

concrete have good interface bonding; containing the GO-PVAH@FA can make a slurry material of

the 3D printing concrete has an effect of shearing and thinning, and realize that the slurry material

has a good thixotropy and a plasticity; meanwhile, a large number of GO-PVAH micro-capacitors formed by a stable combination of the GO containing hydrophilic groups and PVA electrolyte, and evenly dispersing in thin layers of the 3D printing concrete by an FA medium, can store a large number of electrolytes in pore solution of the thin layers of the 3D printing concrete and capture ions migrating from seawater medium, which avoids a formation of corrosion cells in steel fibers in the thin layers of the 3D printing concrete, effectively prevents an electrochemical corrosion of the steel fibers, and further significantly improves properties of against chloride ion penetration and seawater corrosion resistance of the integral coastal special-shaped structure.

Based on the above-mentioned effects, a second aspect of the present disclosure provided a

processing method of a concrete for 3D printing of coastal special-shaped structure, the processing

method comprising: printing a dry blend of the raw materials of the 3D printing concrete of the first

aspect of the present disclosure into a shape by the 3D printing technology.

A third aspect of the present disclosure provided an application of a concrete for 3D printing of

coastal special-shaped structure of the first aspect in a preparation of the coastal special-shaped

structure.

The beneficial effects of one or more of the above technical solutions are:

(1) adopting the concrete for 3D printing of coastal special-shaped structure and processing

method of the present disclosure, cannot only accelerates the manufacture of the coastal

special-shaped structure, but also effectively guarantees marine durability performance of the

concrete. The disclosure innovatively wraps the surface of FA medium with dispersed and stable

GO-PVAH to achieve its long-lasting even distribution in the subsequent nano-scaled regenerated

concrete system, which effectively counteracts the problem of substantially reducing the fluidity of

recycled concrete when the GO is directly mixed with recycled concrete, and brings good viscosity

and thixotropy to the corresponding nano-scaled regenerated concrete slurry; meanwhile, the

GO-PVA prepolymer containing hydrophilic groups is evenly distributed in recycled concrete to

effectively advance the segregation resistance and time rheology of nano-scaled regenerated concrete;

secondly, maintenance of recycled aggregate and the ball lubrication effect of FA will help to realize

the water-keeping function of the recycled concrete; thirdly, an adjust solidification effect of the

thickening time control agent and the fast setting feature of the compound cement will further

guarantee the printability and constructability of the layers of the nano-scaled regenerated concrete.

A realization mechanism of mechanical toughness and durability of a hardening body of the 3D printing concrete: on one hand, the GO's surface contains many hydroxyl, epoxy and carboxyl groups and other hydrophilic groups, which is conducive to the compatibility of the GO with concrete mortar system, while the GO can give full play to the nano-crystalline nuclei and template effect to improve a microscopic morphology of the corresponding recycled concrete hardening body; on the other hand, GO-PVAH hydrogel and recycled aggregate can act as internal maintenance components during the forming process of nano-regenerated concrete, and a subsequent slow release of water can effectively offset a heat shrinkage stress generated by rapid hydration of cement and achieve volume stabilization; on another hand, a toughening effect of doped short-cut steel fibers and organic fiber bridging effect will further ensure the mechanical toughness and cracking and seepage resistance of nano-scaled regenerated concrete.

(2) The concrete for 3D printing of coastal special-shaped structure of the present disclosure,

firstly, the GO containing many hydroxyl, epoxy and carboxyl functional groups and PVA containing

many hydroxyl groups not only make the 3D printing concrete have good viscidity and

water-keeping ability, but also make the adjacent thin layers of the 3D printing concrete have good

interfacial adhesion; secondly, containing the GO-PVAH@FA can make the slurry material of the 3D

printing concrete have the effect of shear and thinning, realize good thixotropy and plasticity; thirdly,

a stable combination of the GO containing hydrophilic groups and PVA electrolyte forms a large

number of GO-PVAH micro-capacitors, the GO-PVAH micro-capacitors dispersing evenly in thin

layers of the 3D printing concrete by the FA medium, can store a large number of electrolytes in pore

solution of the thin layers of the 3D printing concrete and capture the ions migrating from the

seawater medium, which avoids the formation of corrosion cells in the steel fibers of the thin layer of

the 3D printing concrete, effectively prevents electrochemical corrosion of the steel fibers, and

further significantly improves the properties of against chloride ion penetration and seawater

corrosion resistance of the coastal special-shaped structure.

In the nano-scaled regenerated concrete of the present disclosure, the GO-PVAH being

synthesized on a surface of FA to generate the GO-PVAH@FA, under a medium action of admixture

aqueous solution, a time of the GO-PVAH@FA integrating into the nano-scaled regenerated concrete

can be effectively delayed, and combined using a compound cement with low alkalinity and the FA

with reduced alkalinity and other extenders, which innovatively avoids a bottleneck problem that the

GO will deoxidize in a strong alkali environment. Through the surface of FA medium wrapped by the

GO-PVAH, a self-curing of regenerated aggregate and a ball lubrication effect of the FA, a thixotropy,

a time-dependent rheology and a water retention function of the slurry of the nano-scaled regenerated

concrete being realized; using a nano-scaled formwork of the GO, a fiber bridging and an effect of

quick-setting early-strength of the composite cement, to comprehensively realize functions of a

sustained early-strength and a crack resistance and toughening of the nano-scaled regenerated

concrete; through the GO-PVAH and the self-curing of the regenerated aggregate, and a micro

expansion of the compound cement and a reduction effect of the FA, a stability of interface volume

of the nano-scaled regenerated concrete being realized; by giving full play to an energy storage effect

of micro-capacitor of the GO-PVAH to avoid the formation of micro corrosion batteries in steel

fibers in the 3D printed coastal structure, realizing an effect of autoimmunity of reinforcement

corrosion, and innovatively and synchronously realizing a printability and constructability of the

nano-scaled regenerated concrete for 3D printing of the of coastal special-shaped structure, and a

stability of the early-strength volume, crack resistance and toughening, and the effect of the

autoimmunity of corrosion of a hardened body; simultaneously broadened a resource utilization of

solid waste.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings constituting a part of the present disclosure are used to provide a

further understanding of the present disclosure. The exemplary examples of the present disclosure

and descriptions thereof are used to explain the present disclosure, and do not constitute an improper

limitation of the present disclosure.

FIG. 1 is a schematic diagram of an intercalation polymerization of GO-PVA and a cladding

process of GO-PVAH@FA of Embodiment 3;

wherein: 1- FA particle, 2- GO-PVA hydrogel layer, 21- GO lamella, 22- PVA polymer, 23

hydrogel. The GO-PVA intercalation structure is to schematically reflect the intercalation structure

formed by GO lamella and PVA linear chain polymer, and the SEM microscopic morphology of FA

is to schematically reflect an FA spherical hollow structure and size specifications for better

understanding by those skilled in the art.

FIG. 2 is a flow chart of a processing method of the concrete for 3D printing of coastal

special-shaped structure of Embodiment 3.

DETAILED DESCRIPTION It should be pointed out that the following detailed descriptions are all illustrative and are

intended to provide further descriptions of the present disclosure. Unless otherwise specified, all

technical and scientific terms used in the present disclosure have the same meanings as those usually

understood by a person of ordinary skill in the art to which the present disclosure belongs.

It should be noted that the terms used herein are merely used for describing specific

implementations, and are not intended to limit exemplary implementations of the present disclosure.

As used herein, the singular form is also intended to include the plural form unless the context

clearly dictates otherwise. In addition, it should further be understood that, terms "comprise" and/or

"include" used in this specification indicate that there are features, steps, operations, devices,

components, and/or combinations thereof.

In view of the above-mentioned shortcomings of the prior art, the present disclosure provided a

concrete for 3D printing and a processing method thereof, and of which an application in the rapid

manufacturing of coastal special-shaped structures. A GO-PVAH being synthesized on a surface of

FA to generate a GO-PVAH@FA, under a medium action of admixture aqueous solution, a time of

the GO-PVAH@FA integrating into a nano-scaled regenerated concrete can be effectively delayed,

and combined using a compound cement with low alkalinity and the FA with reduced alkalinity and

other extenders, which innovatively avoids a bottleneck problem that the GO will deoxidize in a

strong alkali environment. Through the surface of FA medium wrapped by the GO-PVAH, a

self-curing of regenerated aggregate and a ball lubrication effect of the FA, a thixotropy, a

time-dependent rheology and a water retention function of the slurry of the nano-scaled regenerated

fibers in the 3D printed coastal structure, realizing an effect of autoimmunity of reinforcement corrosion, and innovatively and synchronously realizing a printability and constructability of the nano-scaled regenerated concrete for 3D printing of the of coastal special-shaped structure, and a stability of the early-strength volume, crack resistance and toughening, and the effect of the autoimmunity of corrosion of a hardened body; simultaneously broadened a resource utilization of solid waste, and finally containing huge economic and environmental benefits in the field of rapid manufacturing of coastal special-shaped structures.

special-shaped structure, the concrete for 3D printing of coastal special-shaped structure comprises

raw materials with following weight parts: 1 part of compound cement, 1 - 2 parts of reclaimed sand,

mineral admixture and 0.3 - 0.5 parts of water; the PVA further having an oxidant and a catalyst.

Preferably, the compound cement is blended with high-belite sulfoaluminate cement (HBSC),

portland cement, and gypsum with a parts ratio by weight of 1: (0.65 - 1.25) : (0 - 0.15).

The compound cement obtained by the formulation has a characteristic of quick-setting

early-strength, combined with a ball lubrication characteristic of the FA, there is helpful to realize

printability and constructability of a corresponding nano-scaled regenerated concrete.

Preferably, the reclaimed sand comprises coarse sand, medium sand, fine sand and ultra-fine

sand; wherein, a sand percentage of the medium sand is 27% - 33%.

Further preferably, the coarse sand is a coarse sand with a fineness modulus of 3.7 - 3.1 and an

average particle size of more than 0.5 mm.

Further preferably, the medium sand is a medium sand with the fineness modulus of 3.0 - 2.3

and the average particle size of 0.5 mm - 0.35 mm.

Further preferably, the fine sand is a fine sand with the fineness modulus of 2.2 - 1.6 and the

average particle size of 0.35 mm - 0.25 mm.

Further preferably, the ultra-fine sand is an ultra-fine sand with the fineness modulus of 1.5 - 0.7

and the average particle size of less than 0.25 mm.

Further preferably, the mass ratio of the coarse sand, the medium sand, the fine sand and the

ultra-fine sand is 1 : (1.1 - 2.0) : (1 - 1.5) : (1 - 1.5); after mixing the components under this ratio, there could achieve a good particle gradation curve.

No special limitation is made for specific types of the reclaimed sand in the present disclosure,

in some embodiments, the reclaimed sand is a kind of reclaimed sand made of demolished

construction waste or industrial waste residue after crushing and particle shaping, and meeting the

requirements of the JC/T2548-2019. The use of the reclaimed sand can effectively improve the

self-curing effect of the slurry of the nano-scaled regenerated concrete and synchronously broadened

the resource utilization of solid waste.

Preferably, the FA is a Grade I FA with a burn-off < 5% specified in the GB/T1596-2017, for

obtaining a superior ball lubrication effect.

Preferably, the PVA is a PVA aqueous solution with an average polymerization degree of 500 ~

600 and an alcoholysis degree of 88%; the GO is dispersed in the PVA aqueous solution to form a

stable prepolymer solution of GO-PVA.

Preferably, the PVA oxidizer is one of sodium periodate, potassium permanganate or potassium

chlorate mentioned in Chinese patent CN103450489, the PVA catalyst is one of concentrated

hydrochloric acid, dilute sulfuric acid, dilute nitric acid or boric acid mentioned in Chinese patent

CN105885064A, to intercalate PVA prepolymer in the GO lamellar structure by in situ

polymerization intercalation technology.

Preferably, the GO is a GO powder with monolayer ratio > 90% and oxygen content of 35 ~ 45 %, or an aqueous dispersion with concentration of 0.05 ~ 10 mg/mL; wherein, when the GO

aqueous dispersion is used, calculating a mass of the GO in the aqueous dispersion follow proportion

of concentration, and water in the corresponding aqueous dispersion is calculated into a total amount

of the water used for the 3D printing concrete.

No special limitation is made for the specific type of water-reducing agent in the present

disclosure, thus the products available in the market can meet the application requirements for

preparing the coastal special-shaped structures in the present disclosure. In some specific

embodiments, the water-reducing agent is one or an optimal combination of more of polycarboxylic

acid high efficiency water-reducing agent, early-strength polycarboxylic acid water-reducing agent,

naphthalene system sodium sulfonate high efficiency water-reducing agent or melamine resin high

efficiency water-reducing agent.

Preferably, the thickening time control agent is one of anhydrous sodium sulfate, triethanolamine or nano C-S-H nuclei.

The admixtures such as the thickening time control agent are conducive to the rapid setting of

the concrete for 3D printing of coastal special-shaped provided by the present disclosure, and

effectively ensure a realization of the rapid setting function of the nano-scaled regenerated concrete.

The present disclosure adopted a steel fiber, and of which the specific source is not specifically

limited. The material of the steel fiber is generally the production waste of the steel processing

industry. For the consideration of convenience of purchase and cost saving, in some embodiments of

the present disclosure, the steel fiber is one or combination of more of cut steel fiber, sheared steel

fiber, milled steel fiber, and melt drawn steel fiber.

Similarly, no limitation is made for the specific source of the organic fiber in the present

disclosure, in some embodiments, the organic fiber is one or combination of more of short-cut type

polyvinyl alcohol fiber, polypropylene fiber and high density polyethylene fiber.

Preferably, the mineral admixture is one or combination of more of recycled micronized powder,

ground slag, fly ash, volcanic ash and silica fume. No limitation is made for the source of the

above-mentioned raw materials such as recycled micronized powder.

Preferably, the water is one of but not limited to distilled water, demonized water, tap water or

electrolytic water, and technicians can make a choice according to the construction situation.

A second aspect of the present disclosure provided a processing method for a concrete for 3D

printing of coastal special-shaped structure, the processing method comprising: printing a dry blend

of the raw materials of the 3D printing concrete of the first aspect of the present disclosure into a

shape by the 3D printing technology.

Preferably, a preparation method of the dry blend of the concrete comprising specific steps of:

preparing a prepolymer liquid of GO-PVA from a PVA, a GO and an oxidant by an in-situ

polymerization intercalation; evenly mixing a FA, a water-reducing agent, a catalyst and the

prepolymer liquid of GO-PVAH to form the prepolymer liquid of the FA wrapped the GO-PVAH,

that is, formed a GO-PVAH@FA; dispersing the GO-PVAH@FA in a solution containing the

water-reducing agent and a thickening time control agent to form a suspension of GO-PVAH@FA;

mixing a compound cement, a reclaimed sand, a steel fiber, an organic fiber and a mineral

admixture mechanically in a feed bin to form a dry blend of nano-scaled regenerated concrete.

Further preferably, the suspension of GO-PVAH@FA and the dry blend of the nano-scaled regenerated concrete are rapidly mixed within a 3D printing head, and setting printing specifications

(speed, flow rate and layer thickness) of a 3D printing arm, and printing out thin layers of

nano-scaled regenerated concrete with different thicknesses layer by layer, thus obtaining the coastal

special-shaped structure.

The present disclosure provided a processing method of a concrete for 3D printing of coastal

special-shaped structure, in some embodiments with better effects, the processing method comprising

steps of:

Si: preparing the PVA aqueous solution by dissolving the PVA into a hot water; in a presence of

PVA oxidant, mixing the GO powder or the aqueous dispersion into the PVA aqueous solution, and

using in situ polymerization intercalation process to intercalate the PVA prepolymer in the lamellar

structure of the GO, obtaining the prepolymer solution of GO-PVA;

S2: adding the FA, part of the water-reducing agent, and the PVA catalyst into the prepolymer

solution of GO-PVA, further employing a thermal sonication technology to wrap a GO-PVA hydrogel

(GO-PVAH) on a surface of the FA particles, obtaining the GO-PVAH@FA and sealing standby;

S3: adding the GO-PVAH@FA to the admixture aqueous solution formed by the remaining

water-reducing agent and the thickening time control agent, being stirred evenly at a high speed,

obtaining a suspension of the GO-PVAH@FA; meanwhile, mixing the compound cement, the

reclaimed sand, the steel fiber, the organic fiber and the mineral admixture mechanically in a feed bin

to form a dry blend of the nano-scaled regenerated concrete;

S4: determining a model of coastal special-shaped structure with different specifications, sizes

and material parameters, determining printing specification requirements (speed, flow rate and layer

thickness) of the 3D printing arm, by using methods well known in the art, mixing the suspension of

GO-PVAH@FA with the dry blend of the nano-scaled regenerated concrete quickly at a 3D printing

head, layer by layer printing out the thin layers of the nano-scaled regenerated concrete with different

thickness, and finally the coastal special-shaped structure is quickly manufactured.

In the step S1, an intercalation efficiency of the PVA and a dispersion effect of the GO in the

prepolymer solution of GO-PVA are analyzed by combining an automatic titration, a rotational

viscometer, a UV-Vis spectrophotometry and a microscopic morphology.

In the step S2, an equilibrium swelling rate, a transmittance, a structural cross-linking, a

microscopic distribution and a density of the GO-PVAH are measured by combining a freeze-drying method, a UV-Vis spectrophotometry, a TG-DSC comprehensive thermal analysis and a microscopic morphology method respectively; an overall density, a water content and an organic content, an interfacial peel resistance and a coating thickness of the GO-PVAH@FA are measured by combining an ethanol drainage method, the TG-DSC comprehensive thermal analysis, a peel strength method and a film thickness meter method respectively.

In the step S4, the nano-scaled regenerated concrete may be prepared by a conventional

preparation method of the nano-scaled regenerated 3D printing concrete well known to those skilled

in the art, and the types and dosages of the corresponding water-reducing agent and thickening time

control agent are optimized through a nano-scaled regenerated concrete rheometer (viscosity

coefficient, shear stress, thixotropic ring, thixotropic area), and a fully automatic concrete setting

time and consistency tester (setting time, consistency, rheology over time), etc. A characterization of

each performance of the nano-scaled regenerated concrete can be carried out in combination with

large-scaled printability and marine durability (freeze-thaw resistance, chloride resistance, sulfate

corrosion resistance, etc.) test method of the nano-scaled regenerated concrete well known to those

skilled in the art. A characterization of the electrochemical parameters of the nano-scaled regenerated

concrete, such as steel fiber corrosion potential, polarization resistance, corrosion current density,

and electrochemical impedance spectra can be carried out in combination with characterization

methods of electrochemical properties of the nano-scaled regenerated concrete containing steel fibers

well known to those skilled in the art. The performance parameters such as interlayer bonding tensile

and interlayer shear forces of thin layers of nano-scaled regenerated concrete with different layer

thicknesses are characterized according to the printing specifications (speed, flow rate and layer

thickness) of the 3D printing arm by methods well known in the art. And the construction quality of

different layers of nano-scaled regenerated concrete and the deterioration of interlayer bond under

the effect of freeze-thaw cycles, ion erosion and sulfate corrosion are evaluated by methods such as

ultrasonic echo or radar wave nondestructive detection known to those skilled in the art.

coastal special-shaped structure of the first aspect for a preparation of the coastal special-shaped

structure.

Preferably, the coastal special-shaped structures comprising, but not limited to, well covers, rain

grates, underground pipe corridors, oval gutters, subway pipe sheets, honeycomb beams, laminated beams or laminated slabs, etc.

In order to enable a person skilled in the art to understand the technical solution of the present

disclosure more clearly, the technical solution will be described in detail below in combination with

the specific embodiments, and the raw materials mentioned in following embodiments are

commercially available products.

Example 1

In the present embodiment, provided a concrete for 3D printing of coastal special-shaped

structure, the concrete for 3D printing of coastal special-shaped structure, comprises components of:

a compound cement, a reclaimed sand, a fly ash (FA), a polyvinyl alcohol (PVA), a graphene oxide

(GO), a steel fiber, an organic fiber, a water-reducing agent, a thickening time control agent, a

mineral admixture and water; a mass ratio of each the components is 1 : 1 : 0.05 : 0.005 : 0.0002

0.01 : 0.005 : (0.005 - 0.01) : 0.005 : 0.01 : 0.3.

Wherein, the compound cement comprises components of: a high-belite sulfoaluminate cement

(HBSC), a portland cement, a gypsum, and the mass ratio of the components is 1 : 0.65 : 0.1; a

characteristic of fast setting and early-strength of the compound cement and a ball lubrication

characteristic of the FA are helpful to realize functions of printable and constructable of the

corresponding nano-scaled regenerated concrete.

In the reclaimed sand, a mass ratio of a coarse sand, a medium sand, a fine sand and a ultra-fine

sand is 1 : 1.1 : 1 : 1.

The FA is a class I FA with burn-off < 5% as specified in the standard GB/T 1596-2017.

The PVA is an aqueous PVA solution with an average polymerization degree of 500 ~ 600 and

an alcoholysis degree of 88%; the GO being dispersed in the aqueous PVA solution, formed a stable

prepolymer solution of GO-PVA.

The PVA oxidizer and PVA catalyst respectively are sodium periodate and a concentrated

hydrochloric acid.

The GO is a GO powder with monolayer rate of > 90% and oxygen content of 40%.

The water-reducing agent is polycarboxylic acid type high efficiency water-reducing agent.

The thickening time control agent is an anhydrous sodium sulfate.

The steel fiber is a cut steel fiber.

The organic fiber is a high-density polyethylene fiber.

The mineral admixture is recycled micronized powder, finely ground slag mixed in a mass ratio

of 1 : 1.

The water is tap water.

Example 2

mineral admixture and water; a mass ratio of each the components is 1: 2 : 0.2 : 0.05 : 0.002 : 0.05

0.02 : 0.01 : 0.01 : 0.05 : 0.5.

Wherein the compound cement comprises components of: a high-belite sulfoaluminate cement

(HBSC), a portland cement, gypsum, and a mass ratio of the components is 1 : 1.25 : 0.15.

sand is 1 : 2.0 : 1.5 : 1.5.

The FA isa class I FA with burn-off < 5% as specified in standard GB/T 1596-2017.

prepolymer solution of GO-PVA.

The PVA oxidizer and PVA catalyst respectively are a potassium permanganate and a dilute

sulfuric acid.

The GO is a GO powder with monolayer rate of > 90% and oxygen content of 35%.

The water-reducing agent is an early-strength polycarboxylic acid type water-reducing agent.

The thickening time control agent is a triethanolamine.

The steel fiber is a combination of sheared-type steel fiber and milled-type steel fiber mixed in a

mass ratio of 0.5 : 1.

The organic fiber is a polypropylene fiber.

The mineral admixture is a fly ash.

The water is demonized water.

Example 3

In the present embodiment, provide a processing method of a concrete for 3D printing of coastal special-shaped structure, specifically comprising steps of:

Si: preparing a PVA aqueous solution with a concentration of 5%, an average polymerization

degree of 500 ~ 600, and an alcoholysis degree of 88% by dissolving 0.25 kg of PVA in 5 L hot water

with a temperature of 70°C; under a condition of containing 0.02 kg of sodium periodate (PVA

oxidant), mixing 0.025 kg of GO powder into the PVA aqueous solution, and by adopting an in situ

polymerization intercalation technology, the GO lamellar structure being intercalated with PVA

prepolymer, obtaining a prepolymer solution of GO-PVA;

S2: adding 1.0 ekg of FA, 0.1 kg of polycarboxylic acid type high efficiency water-reducing

agent, 0.01 kg of concentrated hydrochloric acid (PVA catalyst) into the prepolymer solution of

GO-PVA, further by using thermal ultrasonic dispersion technology of oil bath pot (an oil

temperature is 100°C, a frequency is 10 kHz, a power is 50 W, an ultrasonic time is 30 min), the

surface of the FA particles being wrapped by GO-PVA hydrogel (GO-PVAH), obtaining a

GO-PVAH@FA and sealed standby;

S3: adding the GO-PVAH@FA into an admixture aqueous solution formed by the remaining

0.15 kg of PCA-I polycarboxylic high performance water-reducing agent (purchased from Jiangsu

Sobute New Materials Co., Ltd.) and 0.3 kg of anhydrous sodium sulfate (commercially available),

stirring evenly at high speed, obtaining a suspension of GO-PVAH@FA; meanwhile, adding 20 kg of

compound cement (consisting of 10 kg of a 525 HBSC, 9.5 kg of P.052.5 a portland cement and 0.5

kg of a gypsum), 40 kg of typeII granitic reclaimed sand (obtained from the local C40, 28-age

concrete structure demolition construction waste in Qingdao by crushing and particle shaping, with

an average apparent density of 2860 kg/m 3) (consisting of 8 kg of coarse sand, 12 kg of medium sand,

10 kg of fine sand and 10 kg of superfine sand) and 0.5 kg of finely ground slag powder (obtained

from a heavy slag of Bensteel blast furnace with an apparent density of 2930 kg/m3 after ball-milled),

and adding shear type steel fibers of 1.0 kg/m3 (length 3 - 15 mm, diameter 0.12 - 0.25 mm, tensile

strength > 2850 MPa, produced by Laiwu Jinhengtong Engineering Materials Co., Ltd), polyvinyl

alcohol fiber of 0.5 kg/m3 (linear density 1.9 g/cm 3 , dry fracture strength > 11.5 MPa, dry fracture

elongation > 4.0 - 9.0%, initial modulus > 280 MPa, length is 6 mm, equivalent diameter < 14 m,

produced by Shandong Changyuan New Material Technology Co., Ltd), into a feed bin of

HC-3DPRT concrete (mortar) 3D printing system (produced by Jianyanhuace (Hangzhou) Science

and Technology Co., Ltd.) to mechanically mixed evenly, forming a dry blend of the corresponding nano-scaled regenerated concrete;

S4: adding the suspension of GO-PVAH@FA and a remaining distilled water obtained by

calculation according a water cement ratio of 0.45 into the dry blend of the corresponding

nano-scaled regenerated 3D printing concrete, and mechanically mixing the components evenly in

the feed bin of the HC-3DPRT concrete (mortar) 3D printing system, preparing and obtaining a

slurry of the nano-scaled regenerated concrete for 3D printing.

Determining a specification (an equivalent diameter of nozzle is 2.5 cm) of print head of

concrete (mortar) 3D printing system, a plane printing speed is 5 cm/s, a vertical lifting speed is 1.5

cm/s, a layer thickness is 2 cm; combined with structure parameters (300 mm x 450 mm x 60 mm) of

a rainwater grate, layer by layer printing the prepared nano-scaled regenerated concrete mixtures out

into the structure of the coastal rainwater grate; the system evaluating the performances of rapid

fabrication, interlayer bonding and marine durability thereof.

prepolymer solution of GO-PVA are shown in FIG. 1. In the step S2, a swelling rate and a wrap

thickness of the GO-PVAH@FA respectively are 30% and 65 pm. In the step S4, the performances of

the rapid fabrication, interlayer bonding and marine durability of the nano-scaled regenerated

concrete for 3D printing of the rainwater grate structures are shown in Table 1.

FIG. 1 shows a schematic diagram of the polymeric interlayer of the GO-PVA and the wrap

structure of the GO-PVAH@FA, the GO-PVA hydrogel layer is wrapped on the surface of FA

particles, and the PVA polymer effectively interlaces the GO lamellar structure to form

positive-negative double-electric layers of a micro-capacitor, and effectively enhances the marine

corrosion resistance of nano-scaled regenerated concrete.

Example 4

Specific steps of a preparation method of nano-scaled regenerated concrete for 3D printing of

the present embodiment are as follows:

Sl: preparing a PVA aqueous solution with a concentration of 10%, an average polymerization

degree of 500 ~ 600, and an alcoholysis degree of 88% by dissolving 0.5 kg of PVA in 5 L hot water

with a temperature of 80°C; under a condition of containing 0.015 kg of potassium permanganate

(PVA oxidant), mixing 2 L aqueous dispersion of the GO with concentration of 10 mg/mL into the

PVA aqueous solution, and by adopting an in situ polymerization intercalation technology, the GO lamellar structure being intercalated with PVA prepolymer, obtaining a prepolymer solution of

GO-PVA;

S2: adding 1.5 kg of FA, 0.2 kg of SBT*-510 early-strength polycarboxylic acid type

water-reducing agent (purchased from Jiangsu Sobute New Materials Co., Ltd.), 0.01 kg of dilute

sulphuric acid (PVA catalyst) into the prepolymer solution of GO-PVA, further by using thermal

ultrasonic dispersion technology of oil bath pot (an oil temperature is 120°C, a frequency is 20 kHz,

a power is 50 W, an ultrasonic time is 45 min), the surface of the FA particles being wrapped by

GO-PVA hydrogel (GO-PVAH), obtaining a GO-PVAH@FA and sealed standby;

S3: adding the GO-PVAH@FA to an admixture aqueous solution formed by the remaining 0.1

kg of SBT*-510 early-strength polycarboxylic acid type water-reducing agent and 0.25 kg of citric

acid, stirring evenly at high speed, obtaining a suspension of GO-PVAH@FA; meanwhile, mixing 25

kg of compound cement (consisting of 12 kg of 525 HBSC, 12 kg of P.052.5 portland cement and 1

kg of gypsum), 35 kg of type II reclaimed sand (obtained from a tailing sand of slag of Bensteel with

an average apparent density of 3160 kg of/m3 , with a chemical constitution of CaO = 35 ~ 38%,

Fe203 = 20 ~ 24%, SiO 2 = 18 ~ 21%, A1203 = 5 ~ 8%, MgO = 5 ~ 7%) (consisting of 8 kg of coarse

sand, 12 kg of medium sand, 8 kg of fine sand and 7 kg of superfine sand) and 1 kg of fly ash (type I,

produced by Qingdao Sifang Power Plant), and adding shear type steel fibers of 1.0 kg of/m3 (a

length is 10 - 60 mm, a diameter is 0.2 - 0.6 mm, a tensile strength > 850 MPa, produced by Laiwu

Jinhengtong Engineering Materials Co., Ltd), polypropylene fibers of 0.6 kg of/m3 (a linear density

is 0.91 g/cm 3, a tensile strength > 450 MPa, a ultimate elongation > 10%, an elasticity modulus >

3500 MPa, a length is 12 mm, an equivalent diameter < 100 m, produced by Shandong Changyuan

New Material Technology Co., Ltd), then mechanically mixed evenly to form a dry blend of the

corresponding nano-scaled regenerated concrete;

calculation according a water cement ratio of 0.42 to the dry blend of the corresponding nano-scaled

regenerated 3D printing concrete, and mechanically mixing the components evenly in the feed bin of

the HC-3DPRT concrete (mortar) 3D printing system, preparing and obtaining a slurry of the

nano-scaled regenerated concrete for 3D printing.

Determining a specification (an equivalent diameter of nozzle is 3 cm) of print head of concrete

(mortar) 3D printing system, a plane printing speed is 6 cm/s, a vertical lifting speed is 2 cm/s, a layer thickness is 3 cm; combined with structure parameters (D600 mm x 50 mm) of a coastal well cover, layer by layer printing the prepared nano-scaled regenerated concrete mixtures out into the structure of the coastal well cover; the system evaluating the performances of rapid fabrication, interlayer bonding and marine durability thereof.

In the step S2, a swelling rate and a wrap thickness of the GO-PVAH@FA respectively are 40%

and 50 pm. In the step S4, the performances of the rapid fabrication, interlayer bonding and marine

durability of the nano-scaled regenerated concrete for 3D printing of the circular well cover structure

are shown in Table 1.

Example 5

the present embodiment are as follows:

SI: preparing a PVA aqueous solution with a concentration of 6%, an average polymerization

degree of 500 ~ 600, and an alcoholysis degree of 88% by dissolving 0.3 kg of PVA in 5 L hot water

with a temperature of 65°C; under a condition of containing 0.02 kg of potassium chlorate (PVA

oxidant), mixing 5 L aqueous dispersion of the GO with concentration of 4 mg/mL into the PVA

aqueous solution, and by adopting an in situ polymerization intercalation technology, the GO

lamellar structure being intercalated with PVA prepolymer, obtaining a prepolymer solution of

GO-PVA;

S2: adding 1.2 kg of FA, 0.15 kg of SBTJM-9 polycarboxylic acid type and melamine resin type

combined high efficiency water-reducing agent (purchased from Jiangsu Sobute New Materials Co.,

Ltd.), 0.01kg of boric acid (PVA catalyst) into the prepolymer solution of GO-PVA, further by using

thermal ultrasonic dispersion technology of oil bath pot (an oil temperature is 100°C, a frequency is

20 kHz, a power is 50 W, an ultrasonic time is 60 min), the surface of the FA particles being wrapped

by GO-PVA hydrogel (GO-PVAH), obtaining a GO-PVAH@FA and sealed standby;

0.15 kg of SBTJM-9 polycarboxylic and melamine resin type combined high performance

water-reducing agent and 0.3 kg of tartaric acid, stirring evenly at high speed, obtaining a suspension

of GO-PVAH@FA; meanwhile, adding 25 kg of compound cement (consisting of 12 kg of 625

HBSC, 12 kg of P.142.5 portland cement and 1 kg of gypsum), 40 kg of gold tailing sand type II

reclaimed sand (an average apparent density is 2670 kg/m , composed mainly of SiO 2 and A1 20 3 from gold tailing in Laizhou Mining Co., Ltd, obtained by crushing and particle shaping) (consisting of 10 kg of coarse sand, 10 kg of medium sand, 10 kg of fine sand and 10 kg of superfine sand), and

1 kg of volcanic ash (100 mesh, commercially available), and adding melt draw type steel fibers of

1.0 kg/m3 (length is 13 mm, diameter is 0.3 mm, a tensile strength > 850 MPa, elasticity modulus 2

210 GPa, produced by Baoding Xinhuo Steel Fiber Manufacturing Co., Ltd), and high density

polypropylene fibers of 0.5 kg/m3 (density is 0.97 g/cm 3, tensile strength = 2.8 - 4 N/tex, elasticity

modulus = 91 - 140 N/tex, elongation = 3.5 - 3.7, produced by Dongguan Sovetl Special Rope

& Webbing Co., Ltd), into a feed bin of HC-3DPRT concrete (mortar) 3D printing system (produced by

Jianyanhuace (Hangzhou) Science and Technology Co., Ltd.) to mechanically mixed evenly, forming

a dry blend of the corresponding nano-scaled regenerated concrete;

calculation according a water cement ratio of 0.35 to the dry blend of the corresponding nano-scaled

the HC-3DPRT industrial grade concrete (mortar) 3D printing system, preparing and obtaining a

slurry of the nano-scaled regenerated concrete for 3D printing.

Determining a specification (an equivalent diameter of nozzle is 5 cm) of print head of concrete

(mortar) 3D printing system, a plane printing speed is 4 cm/s, a vertical lifting speed is 1.2 cm/s, a

layer thickness is 1 cm; combined with structure parameters (1500 mm x 450 mm x 300 mm) of oval

gutter, layer by layer printing the prepared nano-scaled regenerated concrete mixtures out into the

structure of the oval gutter; the system evaluating the performances of rapid fabrication, interlayer

bonding and marine durability thereof.

durability of the nano-scaled regenerated concrete for 3D printing of the oval gutter structures are

shown in Table 1.

Example 6

The preparation method of the present embodiment is the same as the embodiment 3, with the

differences that, in the step S3, the 20 kg of compound cement is consisted of 10 kg of 525 type

HBSC and 10 kg of P.052.5 portland cement, without gypsum, and a dosage of corresponding

mineral admixture is 0 kg.

In the step S2, a swelling rate and a wrap thickness of the GO-PVAH@FA respectively are 30%

and 65 pm. In the step S4, the related performances of the nano-scaled regenerated concrete for 3D

printing are shown in Table 1

Table 1 Comparative Performance Test Results of Nano-scaled regenerated 3D printing

concrete in Embodiments 3 to 6

Test items Value of Each Performance Index

Conventional CN109020422B Embodiment Embodiment Embodiment Embodiment

3D printing 3D printing 3 4 5 6

concrete nano-concrete

Flow rate(mm) 215 205 200 190 205 195

Bleeding secretion - - 1.14 2.12 1.83 1.78

rate(%)

Thixotropic index - - 7.5 7.1 6.8 7.2

Setting Initial 28 27 25 22 13 19

ime(min) setting

Final 58 56 55 53 32 48

setting

Compressive Id 43.29 54.43 47.45 50.29 59.85 51.27

strength 3d 54.62 69.80 67.84 62.76 70.43 68.61 (MPa) 28d 128.9 139.6 137.1 140.9 139.3 141.6

Flexural Id 10.69 12.76 11.52 10.56 11.34 10.91

strength 3d 13.86 16.30 14.26 14.87 14.95 14.13 (MPa) 28d 22.62 28.52 25.43 24.65 26.31 25.54

Fracture toughness - - 2.35 2.28 2.41 1.96

(MPa.mi/2)

[nterlayer bond - - 0.43 0.53 0.55 1.46 strength (MPa)

56d Cl- diffusion - - -183 -177 -165 -181

coefficient

(10- 12m 2/s)

Steelpotential - - 0.48 0.56 0.66 0.49

(mV)

56d steel bar - 0.38 0.45 0.56 0.39 corrosion current

density ( A.cm 2 )

The foregoing descriptions are merely preferred embodiments of the present disclosure, but not

intended to limit the present disclosure. A person skilled in the art may make various alterations and

variations to the present disclosure. Any modification, equivalent replacement, or improvement made

within the spirit and principle of the present disclosure shall fall within the protection scope of the

present disclosure.

Claims

CLAIMS 1. A method of three-dimensional (3D) printing a coastal structure using concrete for the method of the 3D printing the coastal structure, comprising: mixing rapidly a GO-PVAH@FA suspension and a dry blend of the concrete for the method of the 3D printing the coastal structure in a printing head of a 3D printing machine, to form the concrete for the method of the 3D printing the coastal structure; setting printing specifications for a robotic arm of the 3D printing machine; printing out, layer by layer, thin layers of the concrete for the method of the 3D printing the coastal structure with different thicknesses, thus obtaining the coastal structure; wherein, preparing the GO-PVAH@FA suspension, comprising: preparing, by using an in-situ polymerization intercalation, a prepolymer liquid of a GO-PVA using a graphene oxide (GO), a polyvinyl alcohol (PVA) and a PVA oxidant; mixing the prepolymer liquid of the GO-PVA with a fly ash (FA), a water-reducing agent, and a PVA catalyst evenly to form a GO-PVAH@FA being the FA wrapped by hydrogel of the GO-PVA; dispersing the GO-PVAH@FA in a solution containing the water-reducing agent and a thickening time control agent, then obtaining the GO PVAH@FA suspension; and preparing the dry blend of the concrete for the method of the 3D printing the coastal structure, comprising: mechanically mixing a compound cement, a reclaimed sand, steel fibers, organic fibers, and a mineral admixture in a feed bin of the 3D printing machine, obtaining the dry blend of the concrete for the method of the 3D printing the coastal structure; wherein, the concrete for the method of the 3D printing the coastal structure, comprising raw materials by weight parts are as follows: 1 part of the compound cement, 1 - 2 parts of the reclaimed sand, 0.05 - 0.2 parts of the FA, 0.005 - 0.05 parts of the PVA, 0.0002 - 0.002 parts of the GO, 0.01 - 0.05 parts of the steel fibers, 0.005 - 0.02 parts of the organic fibers, 0.005 - 0.01 parts of the water-reducing agent, 0.005 0.01 parts of the thickening time control agent, 0 - 0.05 parts of the mineral admixture and 0.3 - 0.5 parts of water; the PVA oxidant and the PVA catalyst are further provided for the PVA; wherein, the concrete for the method of the 3D printing the coastal structure is a nano-scaled recycled concrete.
2. The method according to claim 1, wherein, the compound cement comprises a high-belite sulfoaluminate cement (HBSC), a portland cement, and a gypsum with a parts by weight ratio of 1: (0.65 - 1.25) : (0 - 0.15).
3. The method according to claim 1, wherein, the FA is a Grade I FA with burn-off < 5% as being specifiedin GB/T 1596-2017 National Standard of the People's Republic of China; or, the PVA is an aqueous solution of the PVA with an average polymerization degree of 500 600 and an alcoholysis degree of 88%; or, the PVA oxidant is any one of a sodium periodate, a potassium permanganate or a potassium chlorate, and the PVA catalyst is any one of a concentrated hydrochloric acid, a dilute sulfuric acid, a dilute nitric acid or a boric acid; or the GO is a powder of the GO with monolayer rate > 90% and oxygen content 35 - 45% oran aqueous dispersion with a concentration of 0.05 - 10 mg/mL.
4. The method according to claim 1, wherein, the water-reducing agent is any one or more of a polycarboxylic acid high efficiency water-reducing agent, an early-strength polycarboxylic acid water-reducing agent, a naphthalene system sodium sulfonate high efficiency water-reducing agent or a melamine resin high efficiency water-reducing agent; or, the thickening time control agent is any one of an anhydrous sodium sulfate, a triethanolamine,or a nano calcium-silicate-hydrate (C-S-H) nuclei.
5. The method according to claim 1, wherein, the steel fibers are any one or more of cut steel fibers, sheared steel fibers, milled steel fibers, or melt drawn steel fibers; or, the organic fibers are any one or more of short-cut type PVAfibers, polypropylene fibers, and high density polyethylene fibers.
6. The method according to claim 1, wherein, the mineral admixture is any one or more of a recycled micronized powder, a ground slag, a FA, a volcanic ash or a silica fume; or, the water is any one of but not limited to a distilled water, a deionized water, a tap water or an electrolytic water.