magnesium composites of porous combined structure€¦ · cellular structure of magnesium...

VOL. 12, NO. 24, DECEMBER 2017 ISSN 1819-6608

ARPN Journal of Engineering and Applied Sciences ©2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.

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MAGNESIUM COMPOSITES OF POROUS COMBINED STRUCTURE

Olga Aleksandrovna Miryuk

Rudny Industrial Institute, Oktyabrya Street, Rudny, Kostanay Region, Kazakhstan

E-Mail: [email protected]

ABSTRACT

In this paper have been studied composite materials based on caustic magnesite, technogenic fillers and porous

aggregates of various origin. During research work have been developed composites of a combined structure with the use

of wood sawdust, aluminosilicate microsphere and polystyrene granules. The possibility of creating a cellular combined

structure is established by combining various ways of forming pores and introducing porous granules.

Keywords: caustic magnesite, magnesium composites, foam concrete, porous granules.

1. INTRODUCTION

Modern construction engineering requires

efficient resource-saving materials. Concrete is the main

building material. The regulation of the molding mass

allows the creation of concretes for various purposes.

Porous concrete provides thermal protection and sound

insulation of building objects [1-4].

Optimization of structure is the most important

condition for improving the properties of porous concrete.

The formation of concrete structure essentially depends on

the quality of the binder [5-8]. For porous concrete

requires binder which ensure the formation of a structure

with high porosity and sufficient strength. Increasing

porosity and increasing the strength of concrete - conflict

areas.

The problem of increasing the strength of porous

concrete is very urgent [1, 4, 5, 9 - 11]. Prospects for the

development of the technology of porous concrete are

associated with the use of magnesium binders [12-15].

Development of magnesium concretes is aimed at

resource-saving manufacture and allows the use of a wide

range of methods for the formation of a porous structure.

Magnesium binders are distinguished by low energy

intensity of production, intensive hardening, high strength,

reliable adhesion to fillers of different origin [16-19].

Numerous scientific studies of recent years have been

devoted to the expansion of the raw material base and the

improvement of the technology of magnesium materials [12-

19]. The assortment of magnesia binders is expanded due to

composites based on caustic magnesite and mineral

technogenic fillers [17-19]. The development of porous

magnesium composite materials is not numerous and requires

development.

The purpose of this work is to study various ways of

forming the porous structure of magnesium materials.

2. RAW MATERIALS AND METHODS OF

RESEARCH

In the experiments was used a caustic magnesite

of PMK–75 brand with MgO content of 85–90%. Bonding

time for the binder test: beginning of 20 minutes; end is 2

hours and 40 minutes. Following technogenic materials:

iron ore dressing waste, metallurgical slag were added to

the composition of the magnesium composite binder.

Chemical composition of iron ore dressing waste, mass %:

SiO2 – 42; Al2O3 - 14; Fe2O3 - 16; CaO - 13; MgO - 6; SO3

- 4; R2O3 - 3; others - 2. Domain granulated slag has a

chemical composition, mass %: Si 2 - 45; А12 3 - 13;

Fe2O3 - 1; Са - 29; MgO - 12. Mineral basis of

technogenic materials are formed by calcium and

magnesium silicates, aluminosilicates.

As fillers of concrete were used following

materials of porous structure: aluminosilicate microsphere,

wood sawdust, polystyrene granules and specially

synthesized foam glass beads. The aluminosilicate

microsphere - the waste of heat power engineering is

represented by hollow particles with a diameter of 10-150

µm. The bulk density of the microsphere is 350 kg/m3.

Wood sawdust is formed due to sawing wood. Wood

sawdust with 0.14 - 5.0 mm in length was used in the

work. Bulk density of wood sawdust is 190 kg/m3.

Granules of expanded polystyrene with a diameter of 3 - 5

mm were obtained by the destruction of foam packagings.

The bulk density of polystyrene pellets is 20 kg/m3. Foam

glass granules with 3 - 5 mm in diameter are synthesized

in the laboratory. The bulk density of foam glass beads is

150 kg/m3.

An aqueous solution of magnesium chloride with

the density 1220-1260 kg/m3 was used to melt the

magnesia compositions.

Surface active substances were used to form the

cellular structure of magnesium materials: «Unipore» - a

foaming agent on a protein basis; «Fairy» is a foaming

agent on the synthetic basis. Hydrogen peroxide 2 2 was

used as a gas-forming additive.

The molding masses were prepared in the device

of a mixer type. The speed of rotation of the mixer was

adjusted taking into account the composition of the feed

mass. Samples of concrete with dimensions 40x40x160

mm and 40x40x40 mm were tested for strength on a

hydraulic press. The thermal conductivity of the materials

was measured on the instrument «ITP – MG4». The

microstructure of the composites was studied by electron

microscopy.

mailto:[email protected]




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3. MAGNETIC COMPOSITES OF FIBER-GRAINED

POROUS STRUCTURE

Magnesium binders are distinguished by high

adhesion strength with wood aggregate [15, 16].

Molding masses were prepared from binders (caustic

magnesite, magnesium composite binders with

technogenic fillers), sawdust and porous aggregates.

In the work were studied composites containing

20% of sawdust of various sizes (Table-1). It was found

that the use of short fibers contributes to the compaction of

the structure due to the compact arrangement of the

particles. The combination of different fractions of wood

particles allows regulating the structure of composites.

A comparative evaluation of composites

properties with different content of technogenic filler in

the binder indicates a high sensitivity of the strength of

fibrous structures to the composition of the binder. While

using composite binder are reduced by increasing density

and decreasing strength. This change is associated with a

decrease in the number of hydroxychlorides of

magnesium, predominance of amorphous hydrates based

on the technogenic component. The use of composite

binders provides an increase in the water resistance of the

material and the saving of caustic magnesite.

Table-1. Properties of composites with wood sawdust.

The content of

technogenic

component in the

binder,%

Fraction

of sawdust,

mm

Solution

of MgCl2,

%

Composite

density,

kg/m³

Coefficient

of water

resistance

Strength, MPa

(28 days)

in

bending

under

compression

0 0 38 2015 0.41 15 67

0 2.5 – 1.25 42 1390 0.38 17 50

0 1.25 – 0.63 43 1460 0.45 15 46

0 0.63 – 0.14 43 1585 0.43 13 46

30 5.0 – 2.5 29 1270 0.58 12 52

30 2.5 – 1.25 33 1415 0.57 16 48

30 1.25 – 0.63 30 1535 0.55 14 44

30 0.63 – 0.14 32 1595 0.63 15 45

30 0.63 – 0.14

2.5 – 1.25 31 1350 0.57 14 45

30 0.63 – 0.14

5.0 – 2.5 30 1300 0.60 13 48

50 2.5 – 1.25 27 1445 0.75 15 31

50 1.25 – 0.63 28 1590 0.72 13 30

50 0.63 – 0.14 27 1630 0.81 14 28

Adding 5 - 10% aluminosilicate microsphere

improves the homogenization of the molding mass,

increases the homogeneity of the structure (Table-2,

Figure-1). This is due to the spherical shape and smooth

surface of microsphere particles. The introduction of the

microsphere makes it possible to reduce the density of

composites by 60 - 125 kg/m³. The content of 10% of the

microsphere does not reduce the strength of the

composites.

The composites exhibit sensitivity to the

combination sequence of the components when the

molding material is mixed. The greatest strength is

provided by the method of preparation (Figure-2), which

provides for the primary contact of the binder with a

solution of magnesium chloride; adding incremental

fillers.

The proposed method of preparation molding

mixture provides an increase in strength by 15% in

comparison with other cooking options due to the strong

adhesion of the components in the mixture (Figure-3).

To increase the heat-protective properties of the

studied materials, polystyrene pellets were added to the

molding mass. Optimization of the aggregate composition

allows to obtain a combined structure with maximum pore

filling of various structures (Figure-4).




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Table-2. Influence of the microsphere on the properties of composites with wood sawdust.

Microsphere

content, %

Fraction of

sawdust, mm

Solution of

MgCl2, %

Density,

kg/m³

Strength during

compression, MPa

0 1.25 - 0.63 30 1535 44

5 1.25 - 0.63 29 1475 45

10 1.25 - 0.63 28 1410 42

10 2.5 - 1.25 31 1315 46

10 0.63 - 0.14 30 1470 43

Figure-1. Structure of composites with different ratio «wood sawdust: microsphere.

Figure-2. Scheme of preparation of molding material for a composite.

Caustic

magnesite Technogenic

component

Microsphere Wood

sawdust

Composite binder

Suspension

Mixture

Molding mass

A solution of magnesium

chloride

1 : 0 0 : 1 5 : 1




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Figure-3. Microstructure of the composite with wood sawdust and 10% of microsphere.

Figure-4. Microstructure of composite with wood sawdust, microsphere and polystyrene pellets.

Composites are characterized by a minimum

consumption of caustic magnesite, density of 350 - 650

kg/m3, compressive strength 1-7 MPa. The combination of

wood fibers with porous granules of various origin makes

it possible to reduce the coefficient of thermal

conductivity of composites from 0.19 W/(м∙0С) to 0.09

W/(м∙0С).

4. MAGNESIUM COMPOSITES OF THE

CELLULAR STRUCTURE Cellular concrete is widely used for energy-

efficient construction. The development of cellular

concrete technology is aimed at improving the methods of

cellular structure formation [20 - 25].

Salt solutions are used for the milling of

magnesium materials that exceed the density of water, the

traditional shutter of cement concretes. Information on the

nature of the porosity of magnesium cellular concrete is

not numerous.

Foam concrete is a kind of cellular concrete. The

pores in the foam concrete are formed mechanically by the

involved air. The results of the study showed (Table 3)

that compared to water; a solution of magnesium chloride

provides foam of reduced multiplicity and increased

density. During the study has been identified the

advantage of a protein foaming agent for salt solutions.

High ability to foaming solutions of magnesium chloride

confirms the feasibility of producing cellular materials

based on magnesium binders.

Due to the experiments was investigated the

effect of the density of the shutter on the stability of the

foam. A solution of MgCl2 with different densities

was mixed with the «Unipore» foaming agent (Table-4).

Concentration of the foaming agent in the solution is 2%.

It is determined that with increasing

concentration of the MgCl2 solution, foam of dense

structure is formed. This helped to reduce the flow of

liquid and increase the stability of the foam. Optimal

density of MgCl2 solution is 1200 - 1250 kg/m3.

The addition of a foaming agent has a dual effect

on the quality of the concrete. The surface activity of the

foaming agent contributes to the formation of the porous

structure of cellular concrete and provides a given density of

concrete. At the same time, the addition of a foaming agent

can slow down the hardening of the binder, and reduce the

strength of the concrete. It was found that an increase in the

concentration of a foaming agent in a working solution of

magnesium chloride of more than 3% is inadvisable due to a

decrease in the foaming effect.

The strength characteristics of cellular composites

have an increased sensitivity to changes in the composition

of the binder. The strength of composites decreases with the




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introduction of an anthropogenic component. This makes it

necessary to limit the content of metallurgical slags to 30%.

Fine grinding of composite binders helps increase the

strength of porous concretes.

Previously were investigated various variants of

preparation of magnesia molding masses, which are

accepted in the production of foam concrete [1, 6, 14].

Comparative characteristics of the structure, density and

strength indicators, technological process conditions make it

possible to note the one-stage method as promising and

requiring further development (Table-5).

Magnesium binders provide the possibility of

obtaining low-density foam concrete (Figure-5).

Magnesium foam concrete is characterized by strength,

which is 1.5 - 1.7 times higher than the strength of

Portland cement foam (density of foam concrete is 500

kg/m3).

High strength of magnesium cellular concrete is

provided by magnesium hydroxychloride crystals, which

form a reliable partition between the cells (Figure-6).

Aerated concrete is a type of cellular concrete.

Pores in aerated concrete are formed chemically by gas,

which is released through the transformation of special

components of the molding mass. We have studied

magnesium cellular aerocrete, in which hydrogen peroxide

was used in an amount of 3%.

When decomposing hydrogen peroxide in the

molding mass, oxygen is released. The structure of aerated

concrete differs from foam concrete with larger pores

(Figure-7).

Table-3. Properties of foam based on a solution of magnesium chloride.

Type of blowing agent

(Concentration in solution 3%)

Solution density,

kg/m3

Multiplicity

of foam

Foam density,

kg/m3

Protein «Unipore»

вода 9.4 54

1100 5.8 205

1150 5.7 235

1200 5.5 280

1250 4.9 285

1300 4.3 310

Synthetic «Fairy»

Вода 10.2 20

1100 1.02 1105

1150 1.01 1135

1200 1.00 1190

1250 1,00 1235

1300 1.00 1245

Table-4. Properties of foam based on a solution of magnesium chloride.

Density of solution MgCl2,

kg/m3

Multiplicity

of foam

Foam stability for 80 min

outflow of fluid, % sludge of foam, %

1100 5.8 40 12

1150 5.7 32 8

1200 5.5 23 4

1250 4.9 20 4




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Figure-5. Microstructure of magnesium foam concrete with a density of 500 kg/m3.

To obtain cellular low density concrete, have

been studied combined pore formation methods (Table-6).

The possibility of additional porosity was studied:

introduction of 5 - 20% of porous granules of various

types. The maximum effect of density reduction is

achieved with the introduction of polystyrene pellets: the

average density decreases 1.6 - 2.2 times. Porous

composites using foamed glass granules have the greatest

strength for materials with a density of 220 - 350 kg/m3.

The combination of various techniques allows the

development of composites of different structures (Figure-

8).

Table-5. Influence of preparation method of magnesium molding material on the properties of foam concrete.

Method

of making

foam

Diameter

of spreading

mass, mm

Multipli

city of

foam

Density of

foam concrete,

kg/m3

Compressive

strength, MPa

Structure

Three-stage 110 4.7 430 4.1

Two-stage 120 3.5 550 7.3

One-stage 150 3.1 570 7.5

Table-6. Methods for the formation of cellular porosity in magnesium composites.

Method of pores formation Density,

kg/m3

Thermal conductivity, W/(m∙0С)

Compressive

strength, MPa

No pore (viscous molding mass) 2050 0.93 50.0

No pores (flow molding mass) 1500 0.84 22.5

Foaming 525 0.07 4.0

Gas formation 650 0.09 4.6

Foam + gas formation 290 0.05 2.2

Foam + microsphere 435 0.08 3.6

Foam formation + foam glass granules 350 0.05 3.2

Foam + polystyrene pellets 315 0.05 1.0

Foaming + gassing + polystyrene

pellets 220 0.04 0.8




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Figure-6. The matrix of cellular concrete: magnesium (left) and portlandcement (right).

Figure-7. The structure of magnesium aerated concrete with a density of 650 kg/m3.

1- foaming + gas formation; 2- foaming + microsphere;

3 -foaming + foam glass granules; 4 - foaming + polystyrene pellets

Figure-8. Microstructure of magnesium composites combined cellular structure.

1 2

3 4




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High heat engineering properties of the developed

cellular composites are predominantly closed porosity,

strong adhesion to porous granules.

5. CONCLUSIONS

During investigation have been developed the

magnesium composite materials of the porous structure

with adjustable technical characteristics. Magnesium

composites are intended for the production of wall and

heat-insulating products.

The activating effect of caustic magnesite on silicate

materials makes it possible to use composite binders

with an anthropogenic component.

The pronounced adhesion to various surfaces

predetermines the possibility of creating composites of

a combined structure.

The increased density and chemical activity of the salt

remover of the magnesium compositions ensure the

stability of the foam masses and allow obtaining a

highly porous structure of cellular materials.

The possibility of producing low-density cellular

magnesium composites is shown through complex

porosity of the molding mass through various

mechanisms of swelling and subsequent

homogenization of porous granules.

The multicomponent composition of magnesium

composites favors the formation of multimodal cells.

Highly porous structure of composites promotes

increase of heat-shielding properties of products and

reduction of expenses for erection and operation of

buildings.

ACKNOWLEDGEMENTS

The work was implemented within the grant of

the Ministry of Education and Science of the Republic of

Kazakhstan on the topic 2112/GF4 «Development of

thermal insulation materials of a highly porous combined

structure based on low-energy-intensive compositions with

technogenic filler».

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