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Laboratory and industrial investigations on hybrid of acrylic and glass short fibers

as an alternative for substituting asbestos in Hatschek process

M. Jamshidi a,*, A.A. Ramezanianpour b

a Department of Polymer, Building and Housing Research Center (BHRC), Tehran, Iranb Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran

a r t i c l e i n f o

Article history:

Received 5 January 2008

Received in revised form 24 April 2010

Accepted 7 June 2010

Available online 3 July 2010

Keywords:

Hatschek process

Fibercement sheet

Reinforcement

Asbestos

Acrylic fiber

Glass fiber

a b s t r a c t

Asbestos fibers have been used in cement based materials to improve tensile strength and controlling

crack formation and propagation. Asbestoscement sheets are produced by the Hatschek technique in

a number of developing countries.

Due to the health and safety issues in the asbestos products, attempts have been made to substitute

other fibers using the Hatschek system for cement sheets. The quality and homogeneity of the products

depend on the type of fibers and varies substantially in the Hatschek system during production.

In this investigation acrylic and glass fibers in separate and hybrid forms were used for manufacture of

flat and corrugated sheets. Higher strength and ductility were obtained for the sheets containing glass

fibers. Performance was even better when hybrid system of acrylic and glass fibers was used. The hybrid

system was used for production of fibercement sheets in factory. This system is proposed as an appro-

priate alternative for substituting asbestos in the Hatschek process.

2010 Elsevier Ltd. All rights reserved.

1. Introduction

The use of fibers to reinforce cement based materials which are

much weaker in tension than in compression has been investigated

in some research works[1,2]. They can be used as;

Primary reinforcement; reinforcement materials which are

used to improve tensile and flexural strengths of cement base

materials such as steel bars in concrete and high volume con-

centrations of fibers in thin sheet cement materials.

Secondary reinforcement; fibers in low volume concentra-

tions are used in cement based materials to inhibit crack for-

mation or crack propagation.

Therefore, using fibers will lead to inhibition of crack growth

and transformation a rapid, brittle type of failure into a slow, stable

fracture with ductility and increased energy absorption capacity

prior to failure[3].

The most widely used manufactured composite in modern time

was asbestos cement, which was developed in the early 20th cen-

tury with the invention of the Hatschek process. The main use of

this process was in production of corrugated and flat sheets for

cladding of various buildings and water and wastewater pipes

[1,4].

Asbestoscement sheets are made in the Hatschek process bydewatering of dilute suspension of cementfiber mixture. Asbestos

had many applications in different industries before, but their

usages were limited due to health and safety problems. Attempts

have been made to replace asbestos in different applications for

the last 30 years[5].

The Hatschek system is a sensitive process and especial require-

ments must be met in its applications. One of the most important

requirements is fiber characteristics. Fibers which are used in the

Hatschek process must be similar to asbestos in physical/mechan-

ical properties. Thus, these requirements limit the application of

many fibers such as steel ones.

There have been several investigations on other processes to

substitute the Hatschek process[68], however because of excel-

lent homogeneity and high quality of cement sheets produced by

the Hatschek process; it is still being used as a major system for

production of fibercement sheets in many countries.

Many synthetic and natural fibers have already been investi-

gated as asbestos substitutes but only a few some of them exhib-

ited satisfactory performance[924].

In this work chopped glass and acrylic fibers were used sepa-

rately as asbestos replacements in laboratory experiments for pro-

duction of cement sheets. In addition, they were used together as

hybrid system for cement sheets manufacturing in different mix

designs. The performance of sheets was examined by three point

flexural strength test method.

Finally optimized and proposed mix design was used to produce

sheets in an industrial scale in a factory by the Hatschek machine.

0950-0618/$ - see front matter 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.conbuildmat.2010.06.026

* Corresponding author. Tel.: +98 21 88255942; fax: +98 21 88255941.

E-mail address:[email protected](M. Jamshidi).

Construction and Building Materials 25 (2011) 298302

Contents lists available at ScienceDirect

Construction and Building Materials

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o n b u i l d m a t
http://dx.doi.org/10.1016/j.conbuildmat.2010.06.026mailto:[email protected]://dx.doi.org/10.1016/j.conbuildmat.2010.06.026http://www.sciencedirect.com/science/journal/09500618http://www.elsevier.com/locate/conbuildmathttp://www.elsevier.com/locate/conbuildmathttp://www.sciencedirect.com/science/journal/09500618http://dx.doi.org/10.1016/j.conbuildmat.2010.06.026mailto:[email protected]://dx.doi.org/10.1016/j.conbuildmat.2010.06.026


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Flexural strength of specimens was measured and compared with

those made with asbestos cement composites.

2. Experimental program

2.1. Materials

2.1.1. CementASTM type II Portland cement was used in this investigation.

The chemical composition and physical properties of cement are

shown inTable 1.

2.1.2. Acrylic fiber(Ac)

This type of fibers was poly-acrylonitrile (PAN). They were tex-

tile grade with denier of 4(per filament). Apart from other fibers,

the acrylic fiber was in bean shape. The dimension of the fibers

was 14 24 lm. They were cut in 34 mm length using a blade

in laboratory. Fig. 1 shows the longitudinal and cross section

images of the fibers. The bean shape of the acrylic fibers is evident

in the cross section image.

Table 2shows the strength and elastic modulus of the fibers.

2.1.3. Glass fiber(GF)

These fibers were ER type and were cut in 6 mm especially for

concrete application (seeFig. 2). The strength and elastic modulus

of the fibers can be seen in Table 2.

2.2. Test apparatus

2.2.1. Flexural strength tester

Flexural strength of the fibercement sheets was evaluated

using a HOUNSFIELD H5KS apparatus with a three point bearing

clamp. A schematic image of flexural strength test apparatus is

shown inFig. 3. The flexural force (N) was measured continuously

at different deflections (mm) and forcedeflection curve was auto-

matically plotted.

Table 1

Chemical analysis of used cement.

Chemical composition Results (%)

SiO2 19.72

Al2O3 3.65

Fe2O3 4.2

MgO 3.4

CaO 60.48

Loss on ignition 4.76

Non-soluble residue 0.46

C3S 59.71

C2S 11.49

C3A 2.57

C4AF + 2C3A or C4A F + C2A 17.91

Na2O + 0.0658 K2O 0.75

(a) (b)

63x40x

Fig. 1. Optical microscope image of acrylic fiber (a) longitudinal view and (b) cross section.

Table 2

Strength and elastic modulus of fibers.

Fiber type Strength (cN/dtex) Elastic modulus (cN/dtex)

Acrylic 2.88 50.45

Glass 6.49 288.45

Fig. 2. An image of used glass fiber.

Fig. 3. Schematic image of flexural strength test apparatus by three point bearing

method.

M. Jamshidi, A.A. Ramezanianpour / Construction and Building Materials 25 (2011) 298302 299


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2.2.2. Specimen preparation apparatus

This is a well-known apparatus for sample preparation in asbes-

tos cement sheet manufacturers. It works on the basis of dewater-

ing from a dilute suspension of fibercement mix and then

pressing before removing sheet from die. Produced specimens

had dimensions of about 200 1006(to 10) mm.

Curing regime was moist curing for 1 day followed by 13 days

in ambient condition before testing.

2.3. Sample preparation

Different mix designs were prepared with constant water/ce-

ment ratio and various amounts of fibers. Therefore volume per-

centage of the fibers varied in different mix designs. The used

mix design is shown in Table 3.

To prepare specimens, water was first added to a laboratory

mixer having 1 kg capacity with three mixing speeds. Then cement

was added to it during a slow mixing speed and mixing continued

for 10 min. Finally, the fibers were added to cement paste and mix-

ing continued for another 15 min. The composite slurry was

poured into the sample preparation unit and dewatering started

after 30 s using a vacuum pump. At the end of the dewatering pro-cess a 10 kg weight was placed on the dewatered paste to remove

additional water and air pores from specimens. Finally, specimens

having thickness of 56 mm were removed from die and cured for

14 days. Three specimens were prepared and tested for each mix

design.

3. Results and discussion

3.1. Flexural strength test results

3.1.1. Acrylic fibercement sheets

Acrylic fibercement sheets were prepared at fiber volume frac-

tion of 1.5%. Results (average curves) are shown inFig. 4. The con-

trol specimens (without fiber) showed a brittle behavior. Theydepicted lower load bearing values in comparison with the speci-

mens containing acrylic fiber.

Although the acrylic containing cement sheets showed higher

load values but it is evident that the fracture occurs at maximum

load of 100 N. They still sustain lower load values (about 40 N)

after fracture. The mode of failure for these specimens was fiber

pullout.

3.1.2. Glass fibercement sheets

Glass fibercement sheets were prepared at fiber volume frac-

tion of 5%. The average curve of loaddeflection for this sheet is

shown inFig. 5. An improved load bearing, flexural strength andductility were observed in these specimens. Glass fiber is an inor-

ganic fiber with high tenacity similar to asbestos fibers having high

strength, high load bearing capacity and good adhesion to cement

matrix.

The failure mode for these specimens was fiber rupture.

3.1.3. Hybrid of glass and acrylic fibers

In order to investigate the effect of the hybrid fibers (glass and

acrylic) on the flexural strength of cement sheets, the hybrid fibers

sheets were prepared. Results as average curves are shown in

Fig. 6.

It is evident that the hybrid fibers showed synergistic effect and

better performance than that of each fiber separately. In fact, there

is not any fiber to perform exactly similar to asbestos. Thus, it was

decided to use hybrid of two fibers with higher modulus to resist

higher loads and low or medium modulus to enhance ductility.

To compare effect of fibers on flexural strength of cement com-

posites, modulus of rupture (MOR) was calculated for all samples

as follows:

MOR 3FL=2bh2 1

where,MOR,F, L,b andh are modulus of rupture (MPa) (the maxi-

mum flexural stress which sheets undergo before fracture), the

maximum borne flexural force, the distance between the supports

Table 3

Mix design of all laboratory produced sheets.

Components Weights(g)

Cement 180 g

Water 720 cc

Fiber Variable in each mix

-20

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1

Load

(N)

Acrylic Control

Deflection (mm)

Fig. 4. Flexural forcedeflection curve of Acrylic fiber reinforced cement compos-ites (AFRCC) at fiber volume content of 1.5%.

0

20

40

60

80

100

120

140

0 0.5 1 1.5 2

Load(N)

Deflection (mm)

Fig. 5. Flexural forcedeflection curve of Glass fiber reinforced cement composites

(GFRCC) at fiber volume content of 5%.

0

20

40

60

80

100

120

140

160

0 0.5 1 1.5 2

Load(N)

GF(Vf=5%)+Acrylic(Vf=1.5%) GF(Vf=5%) Acrylic(Vf=1.5%)

Deflection (mm)

Fig. 6. Flexural forcedeflection curve of cement composites reinforced with Glassand Acrylic hybrid fibers (HFRCC).

300 M. Jamshidi, A.A. Ramezanianpour / Construction and Building Materials 25 (2011) 298302


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in flexural fixture, the width and the thickness of sheets (test

specimens).

Results are shown inFig. 7.

3.1.4. Factory made specimens

Based on satisfactory performance of before mentioned the hy-

brid fibers in the laboratory made cement sheets, they were used in

a factory which produces flat and corrugated asbestos sheets usingHatschek method to manufacture non-asbestos flat sheets. Some of

the efforts which performed in the factory are shown in Figs. 811.

Fig. 8shows the milling stage of glass fiber. The acrylic fibers

were added to the cement at the final stage (see Fig. 9). As seen

in Fig. 10 the suspended fibers and cement in water applied to

the felt and then dewatered by a suction pump. Finally, authors

were able to produce 8 mm thickness sheets with hybrid fibers

(seeFig. 11).

Some specimens were cut from produced sheets and tested for

flexural strength similar to laboratory made specimens. Flexural

strength of asbestos cement (traditional factory production) and

glassacrylic hybrid fibercement sheets were measured and com-

pared. Average curves of loaddeflection of the both specimens are

compared in Fig. 12. Results of MOR for different specimens can beseen inFig. 13. It is evident that factory made asbestos and hybrid

0

2

4

6

8

10

12

Control AFRCC GFRCC HFRCC

Composite type

Modulusofrupture(MPa)

Fig. 7. Modulus of rupture (MOR) of laboratory made fiber reinforced cement

composites.

Fig. 8. Milling stage of glass fibers in Iranit Co.

Fig. 9. Mixing stage of fibers with cement in continuous mixer.

Fig. 10. Application stage and dewatering of fiber cement suspension on felt.

Fig. 11. Factory made sheet prepared of hybrid fiber reinforced cement composite.

0

50

100

150

200

250

300

350

0 0.5 1 1.5 2 2.5 3

Force(N)

Asbestos Hybrid(GF+Acrylic)

Deflection (mm)

Fig. 12. Flexural loaddeflection curve of specimens made in factory.

0

5

10

15

20

25

Asbetos cement

composite

Factory made HFRCC Laboratory made

HFRCC

Composite type

Modulusofruptu

re(MPa)

Fig. 13. Comparative modulus of rupture of laboratory and factory made cement

specimens.

M. Jamshidi, A.A. Ramezanianpour / Construction and Building Materials 25 (2011) 298302 301


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fiber reinforced cement sheets (F-HFRCC) have higher MOR than

laboratory made hybrid fiber reinforced cement sheets (L-HFRCC).

Toughness of all prepared specimens was calculated which results

presented inFig. 14. The MOR and toughness are lower for com-

posites containing the hybrid fibers than asbestos compositeshowever it is acceptable for construction applications.

4. Conclusion

Flexural performance of cementitious composites reinforced by

acrylic fiber, glass fiber and hybrid of these fibers was investigated

using a three point bearing flexural strength test method. The fol-

lowing conclusions can be drawn from the test results;

(1) Composites containing chopped glass fiber showed better

flexural performance and higher modulus of rupture

(MOR) than acrylic fiber reinforced composites.

(2) Composites containing hybrid of glass fiber (5%) and acrylic

fiber (1.5%) resulted in better flexural behavior and higherMOR. A synergistic effect was observed in application of high

modulus glass fibers and low modulus acrylic fibers. This

was attributed to matrix strengthening by glass fibers and

control of crack creation and propagation by acrylic fibers.

Also, it can be attributed to hybrid mode of failure of fiber

pullout and fiber rupture in composites containing hybrid

fibers.

(3) The laboratory mix design was applied in a pilot scale for

factory production line. Better flexural performance and

higher MOR was obtained when compared with laboratory

made specimens.

(4) Comparing the results of Hybrid fiber and asbestos rein-

forced cement composites showed that although the asbes-

tos composites shows higher flexural strength but due to itshealth and environmental problems, the hybrid fiber can be

replaced with asbestoscement sheets.

Finally, authors propose the hybrid fiber system to be replaced

with asbestos fiber in the production of flat and corrugated sheets

in the Hatschek process.

Acknowledgment

We appreciate Tehran Iranit Co. for their helps and cooperation

and assistance in production of non-asbestos cement sheets in

their factory.

References

[1] Bentur A, Mindess S. Fiber reinforced cementitious composites. London

(NY): Elsevier; 1990.

[2] Baroonian A, Keer JG, Hannant DJ, Mullord P. Theoretical and experimental

performance of asbestos cement and polypropylene network reinforced

cement corrugated sheeting, In: Developments in fibre reinforced cement

and concrete, RILEM symposium, Sheffield; 1986, paper 48.

[3] Xu G, Magnani S, Mesturini G. Hybrid polypropyleneglass/cement corrugated

sheets. Compos; Part A 1996;27A:45966.

[4] Krenchel H. Synthetic fibers for tough and durable concrete. In: Development

in fiber reinforced cement and concrete, RILEM symposium; 1986, p. 3338.

[5] Pye AM. A review of asbestos substitute materials in industrial applications. J

Hazard Mater 1997;3:12547.

[6] Xu G, Hannant DJ. Synergistic interaction between fibrillated polypropylene

networks and glass fibers in a cement based composite. J Cem Concr Compos

1991;13:95106.

[7] Baroonian A, Keer JG, Hannant DJ, Mullord P. Theoretical and experimental

performance of asbestos cement and polypropylene network reinforced

cement corrugated sheeting. Technical report of construction materials

research group at University of Surrey; 1983.[8] Takashima H, Miyagai K, Hashida T, Li VC. A design for the mechanical

properties of polypropylene discontinuous fiber reinforced cementitious

composites by extrusion molding. J Eng Fract Mech 2003;70:85370.

[9] Song PS, Hwang S, Sheu BC. Strength properties of nylon and polypropylene

fiber reinforced concretes. J Cem Conc Res 2005;35:154650.

[10] Hannant DJ. Durability of polypropylene fibers in Portland cement based

composites: 18 years of data. J Cem Conc Res 1998;28(12):180917.

[11] Yi CK, Ostertag CP. Strengthening and toughening mechanisms in microfiber

reinforced cementitious composites. J Mater Sci 2001;36:151322.

[12] Ouyang C, Shah SP. Toughening of high cementitious matrix reinforced by

discontinuous short fibers. J Cem Conc Res 1992;22:120115.

[13] Paled A, Bentur A. Fabric structure and its reinforcing efficiency in textile

reinforced cement composites. J Compos Part A: Appl Sci Manuf

2003;34:10718.

[14] Zollo RF. Fiber-reinforced concrete: an overview after 30years of

development. J Cem Conc Compos 1997;19:10722.

[15] Naaman AE, Reinhardt HW. High performance fiber reinforced cement

composites HPFRCC-4: international workshop. J Cem Conc Compos

2004;26:7579.[16] Bentur A, Peled A, Yankelevsky D. Enhanced bonding of low modulus polymer

fiberscement matrix by means of crimped geometry. Cem Conc Res

1997;27(7):1099111.

[17] Krenches H, Jensen HW. Organic reinforcing fibers for cementand concrete. In:

Fibrous concrete proceeding symposium. UK: The Concrete Society, The

Construction Press; 1980. p. 8798.

[18] Krenchel H, Shah SP. Application of polypropylene fibers in Scandinavia. Conc

Int Des Construct 1985;7:3240.

[19] Dave NJ, Ellis DG. Polypropylene fiber reinforced cement. Int J Cem Conc

1979;1:1928.

[20] Amat T, Blanco MT, Palomo A. Acrylic fibers as reinforcement for cement

pastes. J Cem Conc Compos 1994;16:317.

[21] Danirl JI, Anderson ED. Acrylic fiber reinforced cement composites. Technical

report by Hoechst fiber Industries and Portland Cement Association (PCA),

USA; 2006.

[22] Jamshidi M, Karimi M, Ramezanianpour AA, Parhizgar T, Prediction of fiber

reinforced cementitious composite using dynamic mechanical analysis (DMA).

In: Proceeding of advanced cement based materials international conference(ACI-ACBM), Lahore, Pakistan; 1417 December 2007.

[23] Jamshidi M, KarimiM. Study on theperformance of Iranian polymeric fibers as

asbestos substitutes in fiber reinforced cement sheets. In: Proceeding of

advanced cement based materials international conference (ACI-ACBM),

Lahore, Pakistan; 1417 December 2007.

[24] Jamshidi M, Karimi M. Characterization of polymeric fibers as reinforcements

of cement-based composites. J Appl Polym Sci 2010;115(5):277985.

0

5

10

15

20

25

30

35

Control

AFRC

C

GFR

CC

L-HF

RCC

F-HF

RCC

Asbe

stos

com

posite

Composite type

Toughness*10-3(

Joule/m3)

Fig. 14. Comparative toughness of different cement composites.

302 M. Jamshidi, A.A. Ramezanianpour / Construction and Building Materials 25 (2011) 298302

asbestos sheet

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