ORIGINAL ARTICLE

The effect of incorporation of steatite wasteson the mechanical properties of cementitious composites

K. Strecker • T. H. Panzera • A. L. R. Sabariz •

J. S. Miranda

Received: 17 November 2008 / Accepted: 14 October 2009 / Published online: 23 October 2009

� RILEM 2009

Abstract The recycling of mineral wastes is consid-

ered today an activity of utmost importance, contrib-

uting in the diversification of products, reduction of

final costs, besides promoting alternative raw materials

for some industrial sectors. This work focuses on the

incorporation of steatite wastes in cementitious com-

posites. A full design of experiment was carried out in

order to investigate the effect of the experimental

factors: fraction and particle size of steatite and

compaction pressures (10 and 30 MPa) on the mechan-

ical properties of the ceramic composites. The increase

of the steatite fraction provided an increase of the bulk

density and apparent porosity of the composites. Large

particles of steatite provided an increase of the

apparent porosity decreasing the mechanical strength.

The increase of the pressing compaction decreased the

apparent porosity, increasing the bulk density and the

mechanical strength of the composites.

Keywords Waste recycling � Cementitious

composites � Mechanical properties � Full design

of experiment

1 Introduction

The use of inorganic wastes in cementitious products

has been the focus of several researches in order to

produce a sustainable and environmental correct

material. The necessity to develop concrete from

non-conventional raw materials is indispensable for

the environment and also for the economic sector in

the reduction of costs [1, 2]. Amongst the main

wastes incorporated into cementitious matrix are:

rubber of tires [3]; debris from demolition of civil

constructions [4]; mineral rocks, such as granite,

basalt, etc. [5]; glasses [6], natural fibres, wood, etc.

[7] and rejects of the ceramic industry [8–10].

The mineral wastes proceeding from the mining

and the comminution process are being widely

investigated due to the great environmental impact

when indiscriminately discarded in the nature and

also because of their large potential as ceramic raw

materials [11].

The steatite mineral, commonly known as soap-

stone, is the name given to a metamorphic rock,

compacts, composed, mainly of talc, and many other

minerals such as magnesite and silica [12]. Talc is a

mineral composed of hydrated magnesium silicate

with the chemical formula Mg3Si4O10 (OH)2 [13].

The addition of the steatite as dispersed phase in

cementitious composites was investigated in this

work. A full design of experiment (DOE), was carried

out in order to identify the main and the interaction

effects of the experimental factors: fraction and

K. Strecker � T. H. Panzera (&) � A. L. R. Sabariz �J. S. Miranda

Mechanical Engineering Department (DEMEC),

University of Sao Joao del-Rei (UFSJ), Campus Sto

Antonio, Praca Frei Orlando 170, Sao Joao del-Rei,

MG 36.307-352, Brazil

e-mail: panzera@ufsj.edu.br; tuliopanzera@hotmail.com

Materials and Structures (2010) 43:923–932

DOI 10.1617/s11527-009-9556-1

particle size of the steatite and compaction pressure

on the variable responses, such as bulk density,

compressive and flexural strength and apparent

porosity of the composites. Optical microscope

images were taken to observe the material’s

microstructure.

2 Materials and methods

The ceramic particulated composites investigated in

this work were constituted of a cementitious matrix

phase (Portland cement) and a dispersive phase of

steatite particles.

2.1 Matrix phase: Portland cement

The physical and chemical analysis of the Portland

cement (CP-V ARI PLUS), shown in Table 1, are in

accordance with the Brazilian Standard requirements

(NBR 11578-ABNT) [14].

2.2 Dispersive phase: steatite mineral

The steatite waste was received from the city of

Congonhas, state of Minas Gerais, Brazil. The

particles were dried at 80�C for 24 h and later on

classified by sieving in two particle size classes: 16/40

and 100/200 US-Tyler, ASTM standard. Table 2

shows the chemical analysis of the steatite, carried

out by X-ray fluorescence spectroscopy, showing

high percentages of silicon oxide (44.73%) and

magnesium oxide (29.28%).

2.3 Full factorial design

The full factorial design of the type nk consists of

investigating all the possible combinations of the

experimental factors (k) and its respective levels (n).

The result of the factorial nk corresponds to the

number of the investigated experimental conditions

[15, 16].

The following properties responses were investi-

gated in this experiment: bulk density, compressive

strength, flexural strength and apparent porosity.

Three experimental factors were chosen: fraction of

the dispersive phase of steatite (5, 20 and 40%),

particle size range (16/40 and 100/200 US-Tyler) and

compaction pressure (10 and 30 MPa). The factors

kept constant in the experiment were: type of matrix

(Portland cement), water ratio (30%), time of mixture

and temperature of manufacture. Table 3 shows the

experimental factors and the levels investigated in

this work, establishing a factorial planning of type

312121, supplying 12 distinct experimental

combinations.

The statistical method of Design of Experiment

(DOE) and the Analysis of Variance (ANOVA) will

provide the significance of each experimental factor

on the responses. The statistical software Minitab

version 14 was used for the treatment of the data and

analysis of the results.

2.4 Specimen manufacturing

The manufacture and cure preparation of the ceramic

material for of the test samples followed the

Table 1 Physical and chemical analysis of the Portland

cement

Chemical compound Results

CO2 (%) 1.13

SO3 (%) 2.85

SiO2 (%) 19.45

Al2O3 (%) 4.75

Fe2O3 (%) 3.12

CaO (%) 64.14

MgO (%) 0.8

K2O (%) 0.66

Air permeability (Blaine) (cm2/g) 4,729

Table 2 Chemical analysis of steatite mineral

Chemical compound Results (%)

SiO2 44.73

Al2O3 3.70

Fe2O3 8.38

TiO2 \0.001

CaO 2.95

MgO 29.28

NaO2 \0.001

KO2 \0.001

MnO 0.13

P2O5 0.01

Loss of ignition 10.34

924 Materials and Structures (2010) 43:923–932

recommendations of British Standard EN12390-2

[17], in order to allow only a small variability in the

manufacturing process. The randomization procedure

was also adopted to manufacture the test samples and

performing the experimental tests, in order to avoid

that the effect of not-controlled factors affected the

responses [15, 16].

Prismatic (Fig. 1a) and cylindrical (Fig. 1b) steel

moulds have been used to compact the test samples.

The dimensions of the prismatic and the cylindrical

samples were: 20.5 9 70.6 9 8.5 mm and 45 9 /20.2 mm, respectively. The ceramic material was

poured and compacted under two pressure levels of 10

and 30 MPa, during 30 s, and being packed in plastic

bags to avoid any loss of moisture during the cure.

Six test samples have been manufactured for each

experimental condition. Two replicates and 12

experimental conditions provided 144 samples. The

replicate consists of the repetition of the experimental

condition, in order to provide the estimation of the

magnitude of the experimental error against which

the differences among treatments are judged. The

extension of this error is important to decide whether

significant effects exist or they may be attributed to

the action of the factors [15, 16]. The experimental

tests were performed at 28 days of curing.

3 Experimental results

Table 4 exhibits the P-values of Analysis of Variance

(ANOVA) for the mean of the responses. The P-

values (Table 4) indicate which of the effects in the

system are statistically significant, based on exami-

nation of the experimental data from replicate 1 and

replicate 2. If the P-value is less than or equal to 0.05

the effect is considered significant. A a-level of 0.05

is the level of significance which implies that there is

95% of probability of the effect being significant. The

results will be presented via ‘main effect’ and

‘interaction’ plots. These graphic plots cannot be

considered typical ‘scatter’ plots, but serve to illus-

trate the statistical analysis and provide the variation

on the significant effects. The main effect of a factor

must be interpreted individually only if there is no

evidence that one factor does not interact with other

factors. When one or more interaction effects of

superior order are significant, the factors that interact

must be considered jointly [15, 16].

The ‘main effects’ plot is most useful when you

have several factors such as particle size, weight

Table 3 Experimental planning matrix

Particle size range

(US-TYLER)

Fraction of

steatite (%)

Compaction

pressure (MPa)

C1 16–40 5 10

C2 16–40 5 30

C3 100–200 5 10

C4 100–200 5 30

C5 16–40 20 10

C6 16–40 20 30

C7 100–200 20 10

C8 100–200 20 30

C9 16–40 40 10

C10 16–40 40 30

C11 100–200 40 10

C12 100–200 40 30

Fig. 1 Prismatic (a) and

cylindrical (b) steel moulds

Materials and Structures (2010) 43:923–932 925

fraction and compacting pressure that influence the

composite properties. These plots are used to com-

pare the changes in the mean level to examine which

of the processing factors influence the response (e.g.

apparent density) the most. A ‘main effect’ is present

when different levels of a factor affect the response

differently.

An ‘interaction’ is present when the change in the

mean response of the composite (e.g. apparent

density) from a low to high level of a factor (e.g.

particle size) depends on the level of a second factor

(e.g. weight fraction) [15]. Interactions plots are used

to visualize the interaction effect of two or more

factors (e.g. size and geometry; size and pressure;

geometry and pressure; size, geometry and pressure)

on the response and to compare the relative strength

of the effects.

The value of ‘R2 adjust’ shown in the ANOVA

analysis indicates how well the model predicts

responses for new observations. Larger values of

adjusted R2 (adj) suggest models of greater predictive

ability [15, 16]. Table 4 shows the values of R2 (adj)

for the responses observing a variation from 85.70 to

95.10% showing that the quality of adjustment of the

models has been satisfactory.

The ‘residual plots’ can be useful for comparing

the plots to determine whether the model meets the

assumptions of the analysis. The normal probability

plot indicates whether the data are normally distrib-

uted, other variables are influencing the response, or

outliers exist in the data.

3.1 Bulk density

The bulk density data presented a percentual mean

variation of 5.5%. The P-values (0.006, 0.005 and

0.000) underlined in Table 4 show that only the main

effects ‘‘fraction of steatite, granulometria and com-

paction’’ are significant. The adjusted R2 value was

92.15%, indicating the adjustment quality of the

model. The normal probability plot shown in Fig. 2

validates the model of the ANOVA analysis. The

residuals are normally distributed following a straight

line.

Figures 3, 4 and 5 show the main effect plots for

the bulk density response. Figure 3 shows the effect

of the steatite fraction on the bulk density, presenting

a small percentual variation of 1.33% between the

steatite fractions of 5 and 40%. This behaviour can be

explained by the higher specific mass of the steatite

mineral in comparison to the Portland cement.

The increase of the bulk density as a function of

the increase of the steatite particle size is observed in

Fig. 4. The particle packing factor obtained by the

large particles of steatite with 16 the 40 US-Tyler, is

superior to the small particles of the mineral in the

100 the 200 US-Tyler range. For this reason, the

composites manufactured with large steatite particles

provided bulk density values superior to those with

small steatite particles.

The increase of the compacting pressure provides

the increase of the bulk density due to reduction of the

pore diameters, thus reaching cementitious products

Table 4 Analysis of

variance (P-values)Experimental factors Bulk

density

(g/cm3)

Compressive

strength

(MPa)

Flexural

strength

(MPa)

Apparent

porosity

(%)

Main effects

Fraction of steatite 0.006 0.000 0.205 0.018

Particle size 0.005 0.031 0.853 0.957

Compaction 0.000 0.000 0.003 0.000

Interaction effects

Fraction of steatite * Particle size 0.164 0.000 0.944 0.065

Fraction of steatite * Compaction 0.801 0.002 0.590 0.479

Particle size * Compaction 0.893 0.332 0.302 0.279

Fraction of steatite * Particle size *

Compaction

0.403 0.055 0.587 0.224

R2 (adjust) (%) 92.15 94.85 79.16 82.92

926 Materials and Structures (2010) 43:923–932

of high density and strength [9]. A percentual

variation of 2.82% was found between the pressure

levels of 10 and 30 MPa (Fig. 5).

3.2 Compressive strength

The compressive strength results varied from 43.89 to

83.95 MPa. The interaction effect ‘‘fraction of stea-

tite, granulometry and compacting’’ was significant

exhibiting a P-value of 0.055 (see Table 4). The

adjusted R2 value of 94.85% indicates that the model

has been adequately adjusted to the flexural strength

data. The normal probability plot shown in Fig. 6

Residual

Per

cen

t

0,030,020,010,00-0,01-0,02-0,03

99

95

90

80

7060504030

20

10

5

1

Fig. 2 Normal probability

plot of the residuals for bulk

density

Fraction of steatite (%)

Mea

n o

f B

ulk

den

sity

(g

/cm

^3)

40205

2,260

2,255

2,250

2,245

2,240

2,235

2,230

Fig. 3 Main effect plot for the bulk density, fraction of steatite

Particle size (US-Tyler)

Mea

n o

f B

ulk

den

sity

(g

/cm

^3)

10016

2,255

2,250

2,245

2,240

2,235

Fig. 4 Main effect plot for the bulk density, particle size

Compaction (MPa)

Mea

n o

f B

ulk

den

sity

(g

/cm

^3)

3010

2,28

2,27

2,26

2,25

2,24

2,23

2,22

2,21

2,82%

Fig. 5 Main effect plot for the bulk density, compacting

pressure

Materials and Structures (2010) 43:923–932 927

reveals that the data are in accordance to the

conditions of normality for validation of the ANOVA

analysis. Figure 7 shows the interaction effect plot

for the compressive strength response.

Figure 7a shows the interaction effect plot of

‘‘fraction and particle size of the steatite’’. An

increase of the compressive strength of the compos-

ites when manufactured with the steatite particle size

distribution of 100–200 US-Tyler can be observed,

except for the steatite fraction of 40%.

Figure 7b presents the interaction effect plot of

‘‘compacting pressure and fraction of steatite’’. The

increase of the compacting pressure from 10 to

30 MPa provides a percentual average increase of

33% of the compressive strength. This result confirms

the studies performed by Bajza [18], which states that

the addition of compacting pressure tends to increase

the density, diminishing the pore diameters, and

consequently providing high strength cementitious

products. The steatite fraction of 5% exhibited a

superior mechanical strength, demonstrating that the

addition of the steatite phase in the cementitious

matrix decreases the strength of the composites. This

can be attributed to the interphase conditions between

the steatite particles and the cementitious phase. A

similar behaviour is also observed between the

steatite fractions of 20 and 40%.

Figure 7c shows the interaction effect plot of

‘‘particle size and compacting pressure’’, indicating

that the increase of the compacting pressure provides

Residual

Per

cen

t

1050-5-10

99

95

90

80

7060504030

20

10

5

1

Fig. 6 Normal probability

plot of the residuals for

compressive strength

Fraction of steatite

Particle size

Compaction

10016 3010

80

60

40

80

60

40

5

20

40

steatite

of

Fraction

16

100

sizeParticle

(a) (b)

(c)

Fig. 7 Interaction effect

plot for compressive

strength, fraction of steatite,

particle size and

compaction

928 Materials and Structures (2010) 43:923–932

the increase of the compressive strength for both

particle size ranges used. It is observed that the

steatite particle size of 100–200 US-Tyler presents a

mechanical strength higher than those manufactured

with 16–40 US-Tyler under both compacting pressure

levels.

3.3 Flexural strength

The flexural strength data varied from 8.21 to

11.15 MPa. The main factor ‘‘compacting pressure’’

was significant exhibiting a P-value of 0.003 (see

Table 4). The adjusted R2 value of 79.16% shows that

the model postulated for the flexural strength mea-

surements fitted the data well (Fig. 8).

Figure 9 shows the effect of the compacting

pressure on the flexural strength, revealing that the

increase of the compacting pressure provides an

increase of the flexural strength. A percentual vari-

ation of 16.50% was identified between the compact-

ing pressure levels. The increase of the compaction

pressure provides high strength composites due to

reduction of the porosity.

3.4 Apparent porosity

The apparent porosity results varied from 7.83

13.24%. The main factors ‘‘fraction of steatite and

compaction’’ were significant showing P-values of

0.018 and 0.000, respectively (see Table 4). The

adjusted R2 of 82.92% indicates that the model

postulated for the flexural strength measurements fitted

the data well. Figure 10 shows the residual plot of

normal probability for the apparent porosity response,

which validates the adopted ANOVA model.

Figures 11 and 12 show the interaction effect plots

for the apparent porosity response. The increase of

the compacting pressure from 10 to 30 MPa

decreased the apparent porosity of the cementitious

composites in 26%. This behaviour can be attributed

due to the increase of the particle packing factor,

avoiding the formation of internal pores (Fig. 11).

Figure 12 shows the effect of the steatite fractions

on the apparent porosity. An increase of the porosity

as a function of the increase of the steatite fraction is

observed. This behaviour can be explained by the

Residual

Per

cen

t

210-1-2

99

95

90

80

7060504030

20

10

5

1

Fig. 8 Normal probability

plot of the residuals for

flexural strength

Compaction (MPa)

Mea

n o

f F

lexu

ral s

tren

gth

(M

Pa)

3010

11,0

10,5

10,0

9,5

16,50%

Fig. 9 Main effect plot for the flexural strength, compaction

Materials and Structures (2010) 43:923–932 929

increase of the amount of interphase regions, dispersed

phase (steatite) and matrix (cement), providing the

presence of a larger number of pores. A small

percentual variation of 3.33% achieved for apparent

porosity between the steatite fractions of 20 and 40%

demonstrates the formation of a similar microstructure

explaining the proximity of the mechanical behaviour

reached under these experimental conditions.

3.5 Microstructure

After 28 days of curing, the composites were cut

using a precision saw and a micrograph preparation

was standardized for all samples. Figures 13, 14 and

15 show optical microscope images of the composites

C9, C10 and C11. The composite C9 was manufac-

tured with 16–40 US Tyler steatite particle size, 40%

of steatite and 10 MPa of compaction pressure.

Figures 13 and 14 show the steatite geometry which

can be classified as non-spherical particles. Compar-

ing the composites C9 and C10 (Figs. 13, 14,

respectively), it is possible to observe a large amount

of pores around the steatite particles, manufactured

under the low level of pressure (10 MPa), which

demonstrates the effect of the compaction process on

the material’s microstructure. Pores can be observed

in the steatite particle (see Fig. 13). These optical

microscope images confirm the experimental results

of the apparent porosity and also the mechanical

properties achieved.

Residual

Per

cen

t

210-1-2

99

95

90

80

7060504030

20

10

5

1

Fig. 10 Normal probability

plot of the residuals for

apparent porosity

Compaction (MPa)

Mea

n o

f A

pp

aren

t p

oro

sity

(%

)

3010

12,5

12,0

11,5

11,0

10,5

10,0

9,5

26,09%

Fig. 11 Main effect plot for the apparent porosity, compaction

Fraction of steatite

Mea

n o

f A

pp

aren

t p

oro

sity

(%

)

40205

12,0

11,5

11,0

10,5

10,0

3,33%

15,63%

Fig. 12 Main effect plot for the apparent porosity, fraction of

steatite

930 Materials and Structures (2010) 43:923–932

Figure 15 exhibits the composite C11 which

manufactured with small steatite particles (100–200

US-Tyler), 40% of steatite fraction and 10 MPa of

pressure. The dark areas correspond to the porous

areas, gray areas are the cementitious matrix and the

bright areas are the steatite particles.

4 Conclusions

This study pointed out the effects of the factors:

steatite fraction, steatite particle size and compaction

pressure on the mechanical properties of cementitious

composites. The main conclusions of this paper are:

(i) The increase of the steatite fraction provided an

increase of the bulk density and the apparent

porosity of the composites, which demonstrates

an enlargement of pores in the interphase

region steatite-matrix. However, the steatite

addition provided a reduction of the compres-

sive strength of the composites, being attrib-

uted to the interphase condition.

(ii) The particle size reducing lowered the apparent

porosity and the increased of mechanical

compressive strength.

(iii) The compaction pressure significantly affects

the mechanical properties of the composites.

The increase of the compacting pressure from

10 to 30 MPa not only provides an increase of

the bulk density of the composites, but also

increases mechanical strength and decreases

apparent porosity.

The addition of steatite in cementitious composites

demonstrated to be promising in collaborating in the

recycling of these mineral wastes and glimpsing

possible applications in historical monument restora-

tions sculptured of soapstone.

Acknowledgments The author would like to thank

FAPEMIG for financial support under grant no. CEX 00221/

06 and an under graduation scholarship (PIBIC 2008).

References

1. Khaloo AR (1995) Crushed tile coarse aggregate concrete.

Cem Concr Aggreg 17:119–125. doi:10.1016/0958-9465

(94)00004-I

2. Modesto C, Bristot V, Menegali G, Brida M, Mazzuco M,

Mazon A, Borba G, Virtuoso J, Gastaldon M, Oliveira AP

Fig. 13 Optical microscope image, Composite C9

Fig. 14 Optical microscope image, Composite C10

Fig. 15 Optical microscope image, Composite C11

Materials and Structures (2010) 43:923–932 931

(2003) Obtencao e caracterizacao de materiais ceramicos a

partir de resıduos solidos industriais. Ceram Industr 8:14–

18

3. Monce N, Ashjaq K (2001) Cementitious composites

containing recycled tire rubber: an overview of engineering

properties and potential applications. Cem Concr Aggreg

23:3–10. doi:10.1016/S0958-9465(00)00051-2

4. Padmini AK, Ramamurthy K, Mathews MS (2001)

Behaviour of concrete with low strength bricks as light-

weight coarse aggregate. Mag Concr Res 53:367–375. doi:

10.1680/macr.53.6.367.40798

5. Binici H (2007) Effect of crushed ceramic and basaltic

pumice as fine aggregates on concrete mortars properties.

Constr Build Mater 21:1191–1197. doi:10.1016/j.conbuild

mat.2006.06.002

6. Sobolev K, Turker P, Soboleva S, Iscioglu G (2007) Uti-

lization of waste glass in ECO-cement: strength properties

and microstructural observations. Waste Manag 27:971–

976. doi:10.1016/j.wasman.2006.07.014

7. Rim KA, Ledhem A, Douzane O, Dheilly RM, Queneudec

M (1999) Influence of the proportion of wood on the

thermal and mechanical performances of clay-cement-

wood composites. Cem Concr Compos 21:269–276. doi:

10.1016/S0958-9465(99)00008-6

8. Pereira FR, Hotza D, Segadaes AM, Labrincha JA (2006)

Ceramic formulations prepared with industrial wastes and

natural sub-products. Ceram Int 32:173–179. doi:10.1016/

j.ceramint.2005.01.014

9. Malhotra SK, Dave NG (1999) Investigations into the

effect of addition of flyash and burnt clay pozzolana on

certain engineering properties of cement composites. Cem

Concr Compos 21:285–291. doi:10.1016/S0958-9465(99)

00006-2

10. Senthamarai RM, Manoharan PD (2005) Concrete with

ceramic waste aggregate. Cem Concr Compos 27:910–913.

doi:10.1016/j.cemconcomp.2005.04.003

11. Menezes RR, Neves GA, Ferreira HC (2002) O estado da

arte sobre o uso de resıduos como materias-pimas ceram-

icas alternativas. Rev Bras Engenharia Agricola Ambiental

6:303–313

12. Mielcarek W, Wozny DN, Prociow K (2004) Correlation

between mgsio3 phases and mechanical durability of ste-

atite ceramics. J Eur Ceram Soc 24:3817–3821. doi:

10.1016/j.jeurceramsoc.2003.12.030

13. White JS (1944) Particle-size distribution of steatite talc.

J Am Ceram Soc 27:320–323. doi:10.1111/j.1151-2916.19

44.tb14477.x

14. Associacao Brasileira de Normas Tecnicas. NBR 11578:

Cimento Portland Cimento Portland Composto, Rio de

Janeiro, 1991

15. Werkema MCC, Aguiar S (1996) Planejamento e analise

de experimentos: como identificar e avaliar as principais

variaveis influentes em um processo. Fundacao Christiano

Ottoni, Escola de Engenharia da UFMG, Belo Horizonte

16. Montgomery DC (1997) Introduction to statistical quality

control. Wiley, USA

17. British Standard (2000) BS EN 12390-2: Testing hardened

concrete. Making and curing specimens for strength tests

18. Bajza A (1983) Structure of compacted cement pastes.

Cem Concr Res 13:239–245. doi:10.1016/0008-8846(83)

90107-2

932 Materials and Structures (2010) 43:923–932