RU2739910C1 - Polymer-cement dry construction mixture for 3d printing - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: present invention relates to a polymer-cement dry construction mixture for 3D printing, comprising portland cement, polymer binder, sand, fiber glass and modifier, wherein polymer binder used is redispersible polymer powder of polyvinyl acetate or copolymers of polyvinyl acetate, sand is used with grain diameter up to 5 mm, fibrous fiber is used as fibrous fiber with dimensions l×d = 6 ÷ 12 × 0.005÷0.05 mm, modifier is a powdered floroglyucinfurfural modifier in the following ratio, wt% portland cement - 27.45-32.55, redispersible polymer powder - 1.63-2.75, sand - 65.10-68.60, fiber glass - 0.65-1.12, powder modifier - 0.07-0.15. Invention is developed in dependent claims.

EFFECT: providing high thixotropic properties, fast structure formation and high plastic strength at rest, high adhesion between layers, low loss of water from exposed surfaces of hardening material and low shrinkage deformations.

5 cl, 2 tbl

Description

The invention relates to building materials, in particular to dry building mixtures, and can be used for construction printing using additive technologies.

The classical compositions of sand concrete on a cement binder used in construction, according to GOST 31357-2007, when used in additive technologies, have a number of disadvantages: low plasticity, high viscosity for extrusion, low plastic strength for laying without formwork, large cracking during drying, insufficient adhesion between layers , low strength during storage in air-dry conditions, which are most often realized in construction printing of finished objects and structures. To overcome the disadvantages presented, it is necessary to chemize concrete with a number of chemical additives to obtain the rheotechnological and physical-mechanical properties required for printing. However, a complex of additives can have both a synergistic and antagonistic effect. In this case, an overdose of individual chemical components can lead to a drop in strength.

Known dry building mixture in the field of building materials with good adhesive properties [RU, 2540999 C1, publ. 11/07/2013] with the following ratio of the mixture components, wt. %: binder 30-45, ground fired ceramics 10-30, cellulose ether 0.1-0.5, redispersible powder 0.5-3.0, cellulose fibers 0.1-0.5, mineral filler (sand) - rest. The invention is used as a tile adhesive.

The disadvantage of this technical solution is the inconsistency of the rheotechnological properties of the building mixture with the requirements of additive technologies.

Known dry mortar for 3D printing [CN 106064911A, publ. 02.11.2016] containing the following components: cement 100 parts, 50-200 parts of sand, mineral active admixture 5-40 parts, powder superplasticizer 0.05-2 parts, viscosity modifier 0.01-0.5 parts, adhesive functional agent aggregates 0.5-10 parts, accelerator 1-10 parts, reinforcing fiber 0.5-20 parts.

The disadvantage of this technical solution is the low adhesion between the layers due to the use of polyvinyl alcohol as an adhesive. This choice is probably due to its good thixotropic properties.

An analogue of the claimed invention is a dry construction mixture for 3D printing [Poluektova VA, Kozhanova EP. Improvement of technology for the production of dry building mixtures for 3D printing / Additive manufacturing technologies. 2019.Vol. 1. # 1. S. 14-23.] Of the following composition: redispersible polymer powder
Re-polF-14B (10%) produced by "Kuban-Polymer" based on polyvinyl acetate with a specific surface area S _beats = 8336 cm ² / g; phloroglucinofurfural modifier (SB-FF 0.2%) with a density of 1210 kg / m ³ and M = 950 ± 10; Portland cement PC500-D0 produced by CJSC Oskolcement with a specific surface area of 2856 cm ² / g; finely dispersed chalk MTD-1 with a CaCO ₃ + MgCO ₃ content of 98% and a specific surface area S _beats = 8336 cm ² / g; sand has a fineness module Mk = 2.0 - 2.5; basalt reinforcing fiber - Izovol production waste with specific surface area S _beats = 4272 cm ² / g.

The disadvantage of the analogue technical solution is the low thixotropy of the mixture, firstly, due to the high specific surface area of the fillers: 1) chalk, which was used as a filler to impart decorative properties; 2) basalt reinforcing fiber, which, with such a high specific surface area, loses its micro-reinforcing properties and performs the function of a filler, which leads to a decrease in the strength of the material. Secondly, the modifier based on phloroglucinfurfural oligomers with a molecular weight of 950 ± 10 does not provide the required thixotropy, and its introduction in liquid form into a dry mixture causes difficulties in uniform distribution and leads to caking of the mixture over time.

Closest to the proposed invention, taken as a prototype, is a modified polymer-cement composite material for 3D printing [RU 2662838, publ. 07/31/2018], including in wt%: Portland cement (CEM I 42.5 N) 24.37-34.13; polymeric binder (in the form of a polyvinyl acetate dispersion) 2.44-2.56; sand (with a fineness modulus Мк = 2.0 ÷ 2.5) 50.74-61.38; sodium silicate (in the form of an aqueous solution (liquid glass)) 1.70-2.44; micro-reinforcing fiber (basalt with a length of 12 mm and a fiber diameter of 20 microns) 0.03-0.10; phloroglucinol furfural modifier 0.05-0.07; water is the rest.

The following set of prototype features coincides with the essential features of the invention: Portland cement, polymer binder, sand, fiberglass, modifier.

The disadvantage of the technical solution of the prototype is the limited viability of the mixture due to the fact that the building composite of the proposed composition includes a number of components (binder, modifier) in liquid form. This predetermines the need for dosing and receiving the solution directly at the construction site, which leads to errors in dosing of chemical components of low content and, as a result, to a possible decrease in the rheological and strength characteristics of the hardened material by 20-30%.

The claimed invention is aimed at expanding the arsenal of technical means by obtaining a polymer-cement dry construction mixture for 3D printing with the required rheological and technological properties: controlled structure formation, pronounced thixotropy, high plastic strength at rest, high adhesion between layers, low shrinkage deformations.

This is achieved by the fact that the polymer-cement dry construction mixture for 3D printing contains Portland cement, polymer binder, sand, fiberglass and a modifier , redispersible polymer powder of polyvinyl acetate or polyvinyl acetate copolymers is used as a polymer binder, sand is used with a grain diameter of up to 5 mm, as a fiber a fiberglass with dimensions l × d = 6 ÷ 12 × 0.005 ÷ 0.05 mm is used, as a modifier, a powder phloroglucinofurfural modifier is used in the following mass ratio,%: Portland cement - 27.45-32.55%; redispersible polymer powder - 1.63-2.75%; sand - 65.10-68.60%; fiberglass - 0.65-1.12%; powder modifier - 0.07-0.15%. Portland cement CEM II / A-Sh 32.5 or white Portland cement PCB 1-500-D0 can be used as Portland cement. A two-fraction composition can be used as sand, an additional fraction is a fraction of crushed mechanically activated sand with a specific surface area S _beats = 3000 cm ² / g. Basalt fiber filler in the form of crushed technogenic fibrous materials with a specific surface area of up to S _beats = 4000 cm ² / g can also be used as a fiberglass. Powder polycarboxylate superplasticizer Sika ViscoCrete or powdered naphthalene-formaldehyde superplasticizer Polyplast SP-1 VP (C-3) are additionally used as a powder modifier.

Comparative analysis with the prototype shows that the claimed polymer-cement dry mortar for 3D printing differs in that redispersible polymer powder of polyvinyl acetate or copolymers of polyvinyl acetate is used in the form of a polymer binder, sand is used with a grain diameter of up to 5 mm, as a fiber fiber with dimensions l × d = 6 ÷ 12 × 0.005 ÷ 0.05 mm, powder phloroglucinofurfural modifier is used as a modifier in the following mass ratio,%: Portland cement - 27.45-32.55%; redispersible polymer powder - 1.63-2.75%; sand - 65.10-68.60%; fiberglass - 0.65-1.12%; powder modifier - 0.07-0.15%. CEM II / A-Sh 32.5 or white Portland cement PCB 1-500-D0 are used as Portland cement. A two-fraction composition is used as sand, an additional fraction is a fraction of crushed mechanically activated sand with a specific surface area S _beats = 3000 cm ² / g. Basalt fiber filler in the form of crushed technogenic fibrous materials with a specific surface area of up to S _beats = 4000 cm ² / g is used as a fiber. Powdered polycarboxylate superplasticizer Sika ViscoCrete or powdered naphthalene formaldehyde superplasticizer Polyplast SP-1 VP (C-3) are additionally used as a powder modifier. Thus, the claimed solution meets the criterion of the invention "novelty".

Comparison of the proposed solution not only with the prototype, but also with other known technical solutions in this field of technology did not confirm the presence in the latter of features that coincide with its distinctive features, or features that affect the achievement of the specified technical result. This made it possible to conclude that the invention meets the criterion "inventive step"

Characteristics of the original components

Portland cement can be used as Portland cement according to GOST 31108-2003: CEM I 42.5N and Portland cement with mineral additives CEM II / A-Sh 32.5, as well as white Portland cement PCB 1-500-D0 according to GOST 965-89.

Natural sands according to GOST 8736-2014 with a grain size of up to 5 mm can be used as sand, as well as sands with an improved grain size composition and a lower content of dusty and clay particles obtained using special equipment, and a partial replacement of the main fine filler on mechanically activated (crushed sand), obtained by stepwise crushing-shear deformation of particles in a press roll grinder and subsequent grinding of silica material in the lower grinding chamber of the unit [RU 2692624 C1, publ. 06/25/2019].

The polymer binder is a redispersible polymer powder (RPP), which can be used as polymer powders of polyvinyl acetate and (or) its copolymers according to TU 20.52.10 - 021 - 51375167 - 2017 Redispersible polymer powders "Repol".

Fiber can be basalt, polypropylene with geometric characteristics of fibers up to l × d = 6 ÷ 12 × 0.005 ÷ 0.05 mm, as well as crushed technogenic fibrous materials (TVM), for example Izovol basalt waste (fiber filler). TVM previously cleaned from foreign objects and metal inclusions were crushed in the device [RU 2692624 C1, publ. 06/25/2019] up to S _beats = 4000 cm ² / g.

As a modifier used powder phloroglucinofurfural modifier, synthesized according to the method described in the patent [RU 2662838 C1, publ. 07/31/2018] in the form of a 20% aqueous solution with a molecular weight of 1000-1200 phloroglucinfurfural oligomers and dehydrated to a powder state, and additionally, a powder polycarboxylate superplasticizer Sika ViscoCrete 225 or naphthalene formaldehyde superplasticizer "Polyplast SP-1 VP" according to 5870-005-58042865-05 in the form of a powder, which is a complete analogue of the plasticizer "S-3". Drying of phloroglucinofurfural oligomers by the convective method was not effective due to the crosslinking of oligomers into polymer molecules; the modifier lost its plasticizing properties. During freeze-drying and vacuum drying, the oligomers do not cross-link, the water-reducing and plasticizing properties are retained. Sublimation dehydration is not economically profitable due to the energy consumption and duration of the process. Therefore, the most effective is the method of dehydration in vacuum at a temperature of 40 ° C.

The mortar mixture is prepared in accordance with the formula as follows: Portland cement, sand, RPP, modifier, fiberglass are dosed in the powder mass with automatic dispensers under strict control of the dosage of organic components (RPP and modifier) and mixed in a mixer for at least 5 minutes. To increase the uniformity of distribution of components, especially fibrous materials and, as a consequence, to increase the physical and mechanical characteristics of the hardened material, it is recommended to mix in devices like the invention [RU 2 624 306 C1, publ. 2017.07.03]. The rheological properties, thixotropy and restoration of the structure of the mixture are controlled using the forward and reverse motion of the "Reotest-2" rotary viscometer. The plastic strength of the solution is determined with a conical plastometer P.A. Rebinder. The adhesion between the layers is determined with an adhesion meter of the PSO - MG4 type. Determination of the physical and mechanical properties of the obtained material is carried out in accordance with GOST 10180-2012, GOST 24544-81, GOST 12730.3-78, GOST 31356-2007 on samples in the form of a cube with rib length 70 × 70 × 70 mm and in the form of square prisms 40 × 40 × 160 mm in accordance with GOST 10180-2012. The hardening conditions of the samples are air-dry, which is optimal for hardening polymer-cement materials and most suitable for hardening large-sized products obtained using three-dimensional printing.

Various compositions of polymer-cement dry mortar for 3D printing have been developed and studied. The compositions that showed the best research results on rheotechnological and physical and mechanical properties are presented in Table 1.

Table 1

Compositions of polymer-cement dry mortar for 3D printing

Developed formulations Components, wt% Portland cement Sand Polymer binder Fiberglass Modifier sand with d _grain up to 5 mm mechanically activated
sand cS _oud= 3000 cm²/ r PVAD RPP fiberglass
l × d = 6 ÷ 12 × 0.005 ÷ 0.05 mm fiber filler
up to S _beats = 4000 cm ² / g phloroglucinol furfural superplasticizer
powder 20% solution powder Example 1 32.55
CEM I 42.5N 65.10 - - 1.63 0.65 - - 0.07 - Example 2 29.67
CEM I 42.5N 33.38 33.38 - 2.23 0.30 0.89 - 0.06 0.09 C-3 Example 3 27.63
CEM II / A-Sh 34.54 34.54 - 2.07 0.28 0.83 - 0.06 0.05 Sika Example 4 27.45
CEM II / A-Sh 24,00 44.59 - 2.75 0.27 0.82 - 0.08 0.04 Sika Example 5 27.63
CEM I 42.5N 34.54 34.54 - 2.07 0.28 0.83 - 0.11 - Example 6 27.45
PCB
1-500-D0 68.60 - - 2.75 - 1.12 - 0.08 - Prototype 34.13
CEM I 42.5N 51.19 - 2.56 - 0.10 - 0.07 -

The physical and mechanical properties of the hardened material based on the developed compositions of polymer-cement dry construction mixture for 3D printing are presented in Table 2.

The phloroglucinofurfural modifier has a high plasticizing and water-reducing ability in polymer-mineral mixtures, which makes it possible to use a low W / C value = 0.3-0.33, which is typical for rigid mixtures, and to obtain the required plasticity and plastic strength of the solution for additive technologies. At the same time, it gives the mixture pronounced thixotropic properties, especially for CEM II / A-Sh. After removal of the mechanical effect, the system is rapidly structured in the presence of the phloroglucinofurfural modifier. The limiting dynamic shear stress τ ₀ , obtained with direct recording of the rheological curve in the absence of a modifier, is equal to 80 Pa, and with the introduction of 0.1% of the modifier -132 Pa, with 0.2% - 115 Pa and only more than 0.3% leads to reducing the rate of structure formation. It should be noted that under the mechanical action of the reverse stroke, τ ₀ tends to zero with an increase in the concentration of the modifier. The possibility of additional introduction of naphthalene or polycarboxylate superplasticizers will provide the required plasticity without reducing the thixotropic effect (which is possible with an increase in the phloroglucinfurfural modifier content to increase plasticity) when using coarse sand up to 5 mm or Portland cements with an activity below 42.5 MPa.

table 2

Physical and mechanical properties of samples based on
polymer-cement dry mortar for 3D printing

Structure W / T Plastic strength, kPa Water retention,% Shrinkage deformations
mm / m Strength
R _compressed , MPa Adhesion strength
(7 days), MPa 7 days 28days Example 1 0.12 1.15 91 0.8 8.1 19.9 1.8 Example 2 0.11 1.20 94 0.7 8.5 22.7 1.9 Example 3 0.12 1.32 93 0.5 9.4 25.5 1.9 Example 4 0.10 1.30 96 0,4 10.5 26.3 2.9 Example 5 0.11 1.25 94 0.5 11.3 29.3 2.0 Example 6 0.12 1.19 96 0.8 8.2 21.8 2.1 Prototype 0.12 - - 0.6 - 41.1 1.9

The molecules of the phloroglucinfurfural modifier, adsorbing on the surface of the dispersed phase particles, lead to an increase in the strength of the material due to the peptizing action, as a result of which the surface of the hydrated cement particles increases, which leads to the formation of a denser, fine-crystalline structure of the polymer-cement stone matrix.

The relatively fast hardening of the polymer binder on the open surface of the printed module with the formation of a polymer film due to dehydration (evaporation) and hydration of the cement solves the problem of clinker pool, shrinkage and crack resistance. After hydration and hardening of the cement matrix, the polymer film begins to fill the pore space and defective places, compacting and additionally joining the elements of the cement stone structure, which causes strengthening and the formation of a more elastic structure, which causes an increase in the material's flexural strength even after the normalized age.

Uncured polymer film on the surface of the layer during the extrusion of the material for a certain time has a great influence on the strength of the adhesive joint between the layers. The achieved positive effect is due to the intrinsic adhesion of the polymer in a thin layer, which significantly exceeds the adhesion of cement.

A decrease in the W / C ratio due to the water-reducing action of the phloroglucinfurfural modifier can significantly reduce the setting time, including leveling the negative effect of slowing down the setting time due to the action of phloroglucinfurfural modifier and polyvinyl alcohol, which is present in the polymer binder solution as a stabilizer and transforms into a redispersant when ... At the same time, polyvinyl alcohol also imparts thixotropic properties to the system and increases plastic strength.

Fiber fiber provides micro-reinforcement of the material, minimal shrinkage deformations, resistance to cracking, and also promotes the acceleration of hydration at the initial stage of hardening (internal loads are reduced), and provides a reduction in the time between the beginning and end of setting. As a result of the introduction of fiber in the specified amount, as well as its partial or complete replacement with a fiber filler made of TVG with a specific surface area of not more than 4000 cm ² / g, the strength of the material increases. Replacement with technogenic fibrous filler solves a number of environmental problems in the disposal of Izovol waste.

The technical result achieved in the implementation of the invention is that the components of the polymer-cement dry mortar for 3D printing, in the indicated amounts, together provide pronounced thixotropic properties, fast structure formation and high plastic strength at rest, high adhesion between layers , low water loss from exposed surfaces of the hardening material and low shrinkage deformations.

The proposed composition of a polymer-cement dry construction mixture for 3D printing makes it possible to obtain a mortar mixture of the required rheology and plasticity for extrusion and printing without formwork, and the hardened material has the required compressive and tensile strength in bending, high bond strength between layers, required setting times and high crack resistance. ...

Claims (6)

1. Polymer-cement dry building mixture for 3D printing, including Portland cement, polymer binder, sand, fiberglass and modifier, characterized in that a redispersible polymer powder of polyvinyl acetate or polyvinyl acetate copolymers is used in the form of a polymer binder, sand is used with a grain diameter of up to 5 mm, in As a fiber, a fiber with dimensions l × d = 6 ÷ 12 × 0.005 ÷ 0.05 mm is used, as a modifier, a powder phloroglucinofurfural modifier is used in the following mass ratio,%: Portland cement 27.45-32.55 redispersible polymer powder 1.63-2.75 sand 65.10-68.60 fiberglass 0.65-1.12 powder modifier 0.07-0.15 2. Polymer-cement dry mortar for 3D-printing according to claim 1, characterized in that CEM II / A-Sh 32.5 or white Portland cement PCB 1-500-D0 are used as Portland cement. 3. Polymer-cement dry mortar for 3D printing according to claim 1, characterized in that a two-fraction composition is used as sand, an additional fraction is a fraction of crushed mechanically activated sand with a specific surface area S _beats = 3000 cm ² / g. 4. Polymer-cement dry mortar for 3D printing according to claim 1, characterized in that as a fiber is used additionally (or) a basalt fiber filler in the form of crushed technogenic fibrous materials with a specific surface area of up to S _beats = 4000 cm ² / g. 5. Polymer-cement dry mortar for 3D printing according to claim 1, characterized in that powder polycarboxylate superplasticizer Sika ViscoCrete or powder naphthalene formaldehyde superplasticizer Polyplast SP-1 VP (C-3) is additionally used as a powder modifier.