Lightweight fibre-reinforced ferrocement in tension

Cement &Concrete Composites 13 ( 1991 ) 37 -48

Lightweight Fibre-Reinforced Ferrocement in Tension Prakash Desayi Department of Civil Engineering, Indian Institute of Science, Bangalore 560 012, India

& Said A. EI-Kholy Department of Civil Engineering, AI-Azhar University, Cairo, Egypt (Received 19 June 1990; accepted 26 November 1990)

Abstract

In this paper, results of tests on the strength and deformation of lightweight fibre reinforced ferrocement subjected to uniaxial tension are presented. Three values of direct sand replacement by foamed blast furnace slag, four values of fibre volume fraction and four values of mesh wire volume fraction in terms of the number of wire mesh layers per specimen have been used. Different combinations of these parameters resulted in 48 different specimens. Streamlined specimens were tested using friction grips working on lazytongs principle. An attempt is made to predict strength at first crack, strain at first crack, ultimate strength and strain at 90% of ultimate stress. A trilinear plot is proposed to represent the stress-strain characteristics of lightweight fibre reinforced ferrocement in tension. Also, the influence of the different constituent materials on the stress-strain characteristics is reported. Keywords: Ferrocement, tensile tests, steel fibres, wire mesh, ultimate tensile strength, stress strain diagrams, tensile properties, lightweight aggregate concrete, stresses, strains.

NOTATION A d fcu

Tu V, Vs

Ultimate tensile strength of single wire First crack strength of specimen Ultimate tensile strength of specimen Total number of mesh wires in the loading direction First crack load of specimen Ultimate load of specimen Volume fraction of fibres Volume fraction of mesh wires

~er E90

Strain at first crack Strain at 90% ultimate stress

fsu

Gross section area of the specimen's stem Average mesh wire diameter Cube compressive strength of mortar

f~r f~ n

cr

Subscripts cal Calculated exp Experimental

INTRODUCTION The application of ferrocement to low cost housing is receiving considerable attention. Since ferrocement units are thin, ranging from 20 to 40 mm, thermal comfort is one of the aspects to be borne in mind while designing or adopting ferrocement for housing construction. Replacement of sand by lightweight aggregate (LWA) would improve the thermal comfort inside buildings with such elements. A number of investigators have made experimental and analytical studies on normal ferrocement subjected to tension. 1-5 These studies mainly attempt to determine the first crack strength, ultimate strength, modulus of

37 Cement & Concrete Composites 0958-9465/91/$3.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain

38

P. Desayi, S. A. El-Kholy

elasticity, spacing and width of cracks and the influence of mesh wires on some of these properties. One study on lightweight ferrocement subjected to tension in which sand is replaced partially or fully by foamed blast furnace slag has been reported. 6 Short steel fibres when added to ferrocement or lightweight ferrocement improve its cracking behaviour and its stress-strain characteristics. Thus, lightweight fibre reinforced ferrocement appears to have considerable potential as a useful construction material for building construction. Literature on testing lightweight fibre reinforced ferrocement in tension is sparse. This paper presents the results of an experimental investigation on the stress-strain characteristics of lightweight fibre reinforced ferrocement in tension. Also, the effects of the constituent materials on the stress-strain characteristics are studied on the basis of a proposed stress-strain model. The results are expected to lead to a better understanding of the behaviour of lightweight fibre reinforced ferrocement specimens subjected to uniaxial tension.

SiO 2 = 30-35%, A 1 2 0 3 = 14-15% CaO = 22-25%, MgO = 5-15% S = traces, others = 3-5% Tests conducted earlier on the same aggregate6 showed that, up to 2.36 mm size, loose density was 4790 N/m 3, the compact density 7810 N/m 3 and moisture absorption was 37% by weight. (d) Galvanized woven square wire meshes of 4 x 20 gauge size (0.78 mm average wire diameter at 6.35 mm nominal spacing).

EXPERIMENTAL WORK Materials used In this study, the following materials have been used:

(a) Ordinary Portland cement passing Indian Standard (IS) 300/~m mesh. (b) River sand passing IS No. 4.75 mm (BS No. 3/16 inch) and having a fineness modulus of 3.76. (c) Crushed foamed blast furnace slag passing IS No. 4.75 mm and having a fineness modulus of 3"85. Table 1 gives the results of sieve analysis of sand and LWA. The chemical composition of LWA as given by the supplier is as follows:

Table 1. Sieve analysis of sand and LWA

Sample no. 1 2 3 4 5 6

BS sieve

3/16 inch No. 7 No. 14 No. 25 No. 52 No. 100

Equivalent Indian standard sieve 4-75 mm 2"36 m m 1.18 mm 600/~m 300/~m 150/tm

Percent passing Sand

L WA

100"00 48"00 42.30 23.55 9-00 1"00

100'00 42.00 29.80 20.80 14.40 7"80

Fig. 1. Crack pattern in specimens with 35% sand replacement. (a) Fibre content = 0"0%, (b) fibre content = 1.0%.

P. Desayi, S. A. El-Kholy

40

35% sand replacement by LWA. It is seen that the inclusion of fibres has reduced the total number of cracks in ferrocement specimens for all percentages of sand replacement used in the study. Also, specimens incorporating fibres have developed a single major crack leading to failure (see specimens C35-4 and C35_6, Fig. 1) which leads to the conclusion that with fibre inclusion the material has probably become more homogeneous. Experimental stress-strain diagrams and the proposed model

Typical experimental stress-strain diagrams are shown in Fig. 2. From Fig. 2 it is seen that there is a linear relationship between stress and strain up to the first crack. After cracking, the slope of the curve becomes smaller than its value before cracking. This could be considered as a 'transition stage' during which the load is being transferred from the matrix to the reinforcing mesh wires. With further loading, the curve starts rising indicating a 'strain hardening' effect. Both the additional load that the specimen can take beyond the 'transition zone' and the slope of the curve in the 'strain hardening' zone depend on an increase with the number of wire mesh layers and fibre content. The curve starts becoming flat before failure. Similar curve for ordinary ferrocement in tension has been reported in the ACI guide for the design and repair of ferrocement. 8 Since it was difficult to control the rate of deformation of specimens during testing, the descending portion

of the curve could not be obtained in this investigation. Hence, it is felt that idealizing the ascending portion of the stress-strain diagram to a trilinear plot as shown in Fig. 3 may give satisfactory agreement with the experimental curves. For the trilinear plot, points corresponding to cracking load and to 90% of ultimate load, i.e. points 13 and C respectively of Fig. 3, were selected to be used. Statistical analysis of the experimental data has been done to quantify the influence of the different parameters on the coordinates of the points B and C. In this analysis, it is assumed that the effect of sand replacement by LWA can be accounted through introducing ~/(fcu) of the plain mortar cubes. Values of fcu from tests are 50.4, 29.0 and 17"8 MPa for specimens with 0.0, 35 and 70% replacement respectively. These values indicate a reduction in the plain mortar cube strength with increase in the percentage of sand replacement. This is due to the smaller value of the crushing strength of the LWA compared to that of river sand used. The effects of the other parameters, namely volume fraction of fibres and volume fraction of mesh wires are evaluated as described below. First c r a c k s t r e n g t h

To study the effect of volume fraction of mesh wires on the tensile strength at the appearance of first visible crack f~r, data of plain specimens (three numbers) and of specimens reinforced only with wire meshes (nine numbers) have been used.

8 - 0 _B3s_4 • -D3s-4 A - D70-6 .... O.

Experimental Calculated

/

~"~.~"

6

~E *-4 u) GI Ul

2

i ....

[2 x 1(~1~1 Fig. 2.

HJ

I

i ILl Ii i

Strain

Experimental and calculated stress-strain curves of lightweight fibre reb'fforced fcrrocement.

Lightweight fibre-reinforced ferrocement in tension

0.9(

C

~ f~

41

0.21; the latter is on the high side. This is mainly because the determination of the load at which the first crack occurs is difficult in spite of using a magnifying glass to detect the appearance of the first crack.

D

-

Strain at first crack

A

I W

Ecr

%0

Strain

b

Fig. 3. Idealized tfilinear stress-strain plot for lightweight fibre reinforcement ferrocement in tension.

Using the data of plain specimens and of specimens reinforced only with wire meshes (a total of 12 specimens), variation of e,/,](f~u) with volume fraction of wire meshes has been examined. The equation of the line of best fit for this set of data is ec---x-r=0"0367 Vs+(0"383 x 10 -4)

A plot of fTr/,](fcu) versus volume fraction of mesh wires (V~) was made. The equation for the line of best fit is f~r/,/(Lu)= 40"11 Vs +0"234

(1)

and the correlation coefficient, 0.884. Similarly the relationship between fTr/x[(fcu) and fibre volume fraction (Vf) was plotted using the data of plain specimens and of specimens reinforced only with fibres (a total of 12 specimens). The following equation has been obtained for the line of best fit: fT~/,/(f~u)= 8.73 Vf+ 0.234

(2)

and the correlation coefficient, 0-49. The constant term (0.234) in both eqns (1) and (2) is the contribution of mortar to the ratio f~r/ ,](fcu). It is to be noted that eqns (1) and (2) are only for specimens reinforced with either wire meshes or with fibres. An equation which includes the effect of Vs and Ve could be obtained by adding the two equations, noting that the contribution of mortar is to be considered once only. The resulting equation is f~r/,/(fcu)=(40"ll Vs+8"73 Vf+0"234)

J(fcu)

(5)

and the correlation coefficient, 0.801. Also, variation of ecrA/(fcu) with Vf has been examined using the data of plain specimens and of specimens reinforced only with fibres (a total of 12 specimens). An equation for the line of best fit for this group is found to be ~cr

x/(fcu)=0"0079 Vf+(0"383 x 10 -4)

(6)

and the correlation coefficient, 0.323. The constant term (0.383 x 10 -4) in eqns (5) and (6) is the average of the three plain specimens (A0-0, A35-0 and A70_0) and is the contribution of plain mortar to the ratio eJ,/(f~u). To obtain an equation which includes the effect of both mesh wires and fibres, eqns (5) and (6) have been added

127

Average line

10

~65/='o

(3)

o

//o

z

or

T,=A,/(f~,).[40.11 Vs+8.73 Ve+0.234]

(4)

It may be noted that eqns (3) and (4) are obtained from the experimental data of 21 specimens out of 48 tested specimens. To examine the adequacy of eqn (4), all the 48 tested specimens have been used and calculated values of first crack load Tcr(cal ) as obtained from eqn (4) are compared with the experimental values in Fig. 4. In Fig. 4, it is seen that the average line is very close to the 45 ° equality line. The ratios T~r(c~)/Tcr(exp) have a mean value of 1.036 and a coefficient of variation of

o °oO- o

-~

.°

2 f o 0

0

I 2

..

I 4

,

I. , I 6 8 Tcr (exp) (KN)

I , I 10 12

Fig. 4. Experimental cracking load versus calculated cracking load.

42

P. Desayi, S. A. EI-Kholy

taking the contribution of mortar once only. The resulting equation is ec~=,~(fc,)(0.0367 I/, +0.0079 Vf +(0.383 × 10-4)) (7) It must be mentioned that eqn (7) is obtained using 21 specimens out of 48 tested ones. To examine the adequacy of this equation, the results of all tested specimens have been used and calculated values Gr(ca~las obtained from eqn (7) are compared with the experimental values in Fig. 5. The average value of the ratio ecr(cal)/ecr(exp) is found to be 1.39 and the coefficient of variation is 0.574. In Fig. 5, it is seen that there is more scatter of the results. This is because, (a) the determination of the stage at which the first crack occurs is difficult, (b) the surface strains measured are sensitive to the condition of the surface of the specimen over the gauge length, and (c) the strains being small, their accurate measurement is difficult. Ultimate

strength

It is known that mortar has no contribution to the ultimate strength of ferrocement or lightweight ferrocement subjected to uniaxial tension. Hence, ultimate load of such elements is equal to the ultimate tensile load of mesh wires in the loading direction. Ultimate tensile strength of ferrocement element can thus be calculated from n~d 2

f~-

4A

Lu

(8)

To study the effect of fibre inclusion on the ultimate tensile strength of lightweight fibre reinforced ferrocement, data of plain specimens and of specimens reinforced only with fibres (a total of 12 specimens) have been used. Variation of .fp/ ~(fcu) with V~ for these specimens has been examined. The equation of the line of best fit for this set of data is f t =,/(fcu) (14"15 Vf+ 0"234)

and the correlation coefficient, 0.67. An equation which includes the effect of both V~and Vf on ultimate strength can be obtained by adding eqns (8) and (9). Thus n~d 2

f~=,/(fcu)(14.15 V f + 0 . 0 2 3 4 ) + - fsu (10) 4A or n~d 2

Tu= A,/(f~u) (14.15 Vf+ 0 . 2 3 4 ) + - 4

Equations (10) and (11) have been obtained using 21 specimens only out of 48 tested specimens. Calculated values as obtained from eqn ( 11 ) for all the 48 specimens are compared with the experimental values in Fig. 6. In Fig. 6, it is seen that the average line is very close to the 45 ° equality line. Ratios Tu(caJTu(exp) have an average value of 1.023 and a coefficient of variation of 0-198. These values could be considered satisfactory taking into consideration that they are obtained after

12

Av.r...

line 10

/

~',o

_

/to

I

1

I

2

,

oo ~ O " % o

8

6

o ?joo

oof

/(°

4

0

o

.

o

o

O°o o

o 09607,//

0

Z

/

o

U

o

O

o/ / / & "

•

f,u (11)

14

:E 3

(9)

2 I

,

3

I

4

,

I

1

5

6

0

,

I

2

,

Ecr (exp) x 103

Fig. 5. Experimental cracking strain versus calculated cracking strain.

I

4

Fig. 6. Experimental ultimate load.

° ,

I

,

I

6 8 Tu (exp) (KN)

ultimate

load

,

I

10

versus

i

12

I

14

calculated

Lightweight fibre-reinforced ferrocement in tension including the data of 27 specimens which were not used initially while arriving at the best fit equations.

43

resulting equation is e90 = ~/(fc,) [0-111 Vs +0.0067 Vf +(0.383 x 10-4)] (14)

Strain at 90% ultimate stress

During testing it was possible to measure strain only up to one stage prior to the ultimate load. Hence, strain values at 90% ultimate stress, e90, have been selected to be used in plotting the stress-strain model (point C in Fig. 3). To study the effect of content of mesh wires on e90, data of plain specimens and of specimens reinforced only with wire meshes have been used. Variation of ego/~(fc,) with V~ has been examined and the equation of the line of best fit for this set of data is e90 =0.111 Vs+(0-383 x 10 -4)

J(f u)

(12)

and the correlation coefficient, 0"946. Similarly to study the effect of fibre volume fraction on e90, data of plain specimens and of specimens reinforced only with fibres have been used. The equation of the line of best fit for the variation of e90/x/(~u)with Veis found to be E90

J(Ic.) =0.0067

Vf+(0-383x 10 -4)

(13)

and the correlation coefficient, 0-537. The constant term in eqns (12) and (13) is the contribution of plain mortar to %o/,/(fcu). To obtain an equation which includes the effect of Vs and Vf, eqns (12) and (13) have been combined taking the contribution of mortar once only. The

It must be mentioned that eqn (14) has been obtained using the experimental data of 21 specimens out of 48 tested specimens. Values of e90(cal) as calculated from eqn (14) are compared with the experimental values in Fig. 7 for all tested specimens. The ratios g90(cal)/g90(exp) have an average value of 1.205 and a coefficient of variation of 0-377. The scatter of test results in Fig. 7 is less than the scatter observed in case of strain at first crack shown in Fig. 5. The results obtained could be considered satisfactory taking into consideration (a) the fairly large number of test data used for calculating the coefficient of variation, (b) the considerable number of variables in the study, viz. the percentage of sand replacement, V~ and Vf, and (c) the strains changing more sensitively (than stresses) due to small variations occurring in casting and testing. Comparison of experimental and proposed stress-strain curves

Using the lines of best fit equations determined in the previous sections, the coordinates of points B and C (in Fig. 3) have been calculated and the proposed stress-strain curves have been superimposed on the corresponding experimental curves for comparison. A typical sample of those plots is shown in Fig. 2. From these plots, the agreement between the experimental and proposed curves could be considered satisfactory.

12 Average line 10

oo

ff

,,~'4S*

8

o:/o/

X

=

: ~

/

S

°o

/

/oo/ o

-o//o /*

o~/'//°

o o

° o

0

2 I I , I , I 4 ' 6 8 10 ' 1~ EgO (exp) x 103 Experimental strain at 0-9 T. versus calculated

O0

J l ' 2

Fig. 7. strain at 0.9 Tu.

EFFECT OF CONSTITUENT MATERIALS ON STRESS-STRAIN CHARACTERISTICS After arriving at the lines of best fit equations (eqns 3, 7, 10 and 14), it is felt desirable to use these equations to quantitatively estimate the influence of Vf, Vs and sand replacement on the stress-strain characteristics of lightweight fibre reinforced ferrocement in tension. This has been done using ~u values of 50.4, 29.0 and 17.8 MPa respectively for specimens with 0.0, 35 and 70% sand replacement (obtained from tests) and the results are described below.

"

Effect on first crack strength

Figure 8 shows the effect of fibres, mesh wires and percentages of sand replacement on the first crack

f'. Desayi, S. A. El-Kholy

44

--

0 0% fibres

---0.5%

-

,,

-1.0%

fibres

' .... 1.5%

"-6 6

D_ v

2l.

~

)

6 mesh tayers

2

-. . . . --='-'=~2~:a-' } z,~o .. i

t

35 %

Fig. 8. Effect of different strength.

70

i

re pl

parameters

on first crack

strength as calculated from eqn (3). From Fig. 8, the following are noted: (a) Fibre inclusion has increased the first crack strength for all percentages of sand replacement used. (b) For specimens reinforced only with fibres, it is found that for a given fibre content, the increase in first crack strength is the same for all percentages of sand replacement including zero replacement. This increase is found to be about 18.6, 37.3 and 56"0% for specimens with 0.5, 1.0 and 1.5% fibre volume fraction respectively, compared to plain specimens. (c) First crack strength increases with increasing number of wire mesh layers in the specimen for all percentages of sand replacement and all fibre contents used. (d) For specimens reinforced with mesh wires only, it is noticed that for a given mesh wire content the increase in first crack strength is the same for all percentages of sand replacement. This increase is found to be about 67.2, 134.4 and 201.6% for specimens reinforced with 2, 4 and 6 layers respectively, compared to plain specimens. (e) Direct replacement of sand by LWA reduced the compressive strength and consequently the first crack strength is reduced. This reduction increases with increase in the percentage of sand replacement. (f) Comparing (b) and (d) above and noting that V~ is 0.382, 0.764 and 1-147 respectively, for 2, 4 and 6 layers, it could be seen that mesh wires are more effective than fibres in enhancing the first crack strength.

Effect on strain at first crack

The effect of the different constituent materials on strain at first crack is very similar to its effect on first crack strength shown in Fig. 8. The following points are noted: (a) Strain at first crack (ecr) increases with increasing fibre volume fraction for all percentages of sand replacement. (b) For specimens reinforced only with fibres, it is found that for a given fibre content, the percentage increase in ecr is the same for all percentages of sand replacement. This increase is found to be about 103,206 and 309% for specimens with 0-5, 1.0 and 1.5% fibre volume fraction respectively compared to plain specimens. (C) Ecr generally increases with increasing mesh wire content for all percentages of sand replacement and all fibre contents considered. (d) For specimens reinforced only with mesh wires, it is seen that, for a given mesh wire content the percentage increase in e~, is the same for all percentages of sand replacement used. This increase is found to be about 375, 750 and 1126% for specimens with 2, 4 and 6 layers respectively, compared to plain specimens. (e) Direct replacement of sand by LWA reduced compressive strength and hence the stress and strain at first crack. This reduction increases with increase in the percentage of replacement. (f) Comparing notes (b) and (d) and noting that volume fraction of mesh wire is 0.382, 0.764 and 1-147% respectively for 2, 4 and 6 layers, it could be seen that mesh wires are more effective than fibres in increasing ~cr"

Effect on ultimate strength

Making use of eqn (10), values of ultimate tensile strength (f~) have been calculated. In these calculations, it is assumed that the number of longitudinal wires in one mesh layer is 6, ultimate tensile strength of single wire is 480"0 N/mm: and the average diameter of mesh wires is 0.78 mm, Based on these calculated values, Fig. 9 has been plotted. From Fig. 9, the following points are noted: (a) Ultimate strength (f~') generally increases with increasing fibre volume fraction for all

Lightweight fibre-reinforced ferrocement in tension 10 6 mesh layers Z ~ : ....................

O-5"1o fibers - - - - 1.0*1ofibers ......... 1.5*/o f i b e r s , I

n

I

I

I

I. . . . . . . . .

4 mesh layers

03 E L 3

i

i

i

a) t-

5 -~.~.~..~....~

..........

t~

2~:'"'

--q. . . .

...............

2 mesh layers

£L-_2_-__._-~._-_

E

--.._.....__.

2

0

0 mesh layers

• .........

~---_____ 35

70 Repl. C*/.)

Fig. 9.

(b)

(c)

(d)

(e)

(f)

Effect of different parameters on ultimate strength.

percentages of replacement and all numbers of mesh layers used. For specimens reinforced only with fibres, it is seen that, for a given fibre content the percentage increase in f~ is the same for all percentages of sand replacement. This increase is about 30, 60 and 91% for specimens with 0-5, 1.0 and 1.5% fibre volume fraction respectively. Values of f~ increase with an increase in the volume fraction of mesh wires for all percentages of sand replacement and all fibre contents used. For plain specimens and specimens reinforced only with fibres (the lower part of Fig. 9), f~' reduces due to direct replacement of sand by LWA. This reduction increases with an increase in the percentage of sand replacement. For specimens containing mesh wires only (no fibres), sand replacement does not affect the ultimate strength value because mortar which has already cracked does not contribute to the strength at ultimate. Compared to plain specimens and considering the notes (d) and (e) above, it is

45

seen that, the percentage of increase in f[' due to the incorporation of 2, 4 and 6 layers respectively are, (i) 10.2, 121.1 and 231.3% for 0"0% replacement, (ii) 45.2, 191-3 and 336-5% for 35% replacement, and (iii) 215.2, 270.7 and 455"6% for specimens with 70% sand replacement. Effect on strain at 90% ultimate stress

The effect of the different constituent materials on strain at 90% ultimate stress (e90) has been found to be very similar to its effect on first crack strength shown in Fig. 8. The following points are noted: (a) Values of E90 increase with increasing fibre volume fraction for all percentages of replacement and all mesh wires contents considered. (b) For specimens reinforced only with fibres, for a given fibre content, the percentage increase in e90 is the same for all percentages of replacement. This increase is about 87, 174 and 262% for specimens with 0.5, 1.0 and 1.5% fibre volume fractions respectively, compared to plain specimens. (c) Values of E90 increase with increasing number of mesh layers in the specimen for all percentages of sand replacement and all mesh wire contents used. (d) For a given volume fraction of reinforcement, mesh wires are more effective than fibres in enhancing the strain at 90% of ultimate stress. (e) For specimens reinforced only with mesh wires, it is noticed that, for a given mesh wire content the increase in £90 is the same for all percentages of sand replacement. (f) Direct replacement of sand by LWA reduces e90. However, the reduction is less in case of plain specimens and specimens reinforced only with fibres compared to specimens incorporating mesh layers. This reduction increases with an increase in the percentage of sand replacement. Proposed stress-strain diagrams

In order to appreciate the effect of constituent materials on the stress-strain characteristics, it is felt desirable to suitably group and present the different stress-strain plots. For this purpose, Figs 10, 11 and 12 have been plotted. It must be mentioned that, these figures were plotted assuming that, (a) number of mesh wires is 6 per layer,

P. Desayi, S. A. El-Kholy

46

8

Vf = 0"0 *10

Vf =0.5"1. 0.0"/. repl.

0 ' 0 01. repl.

Z

4

l

5

2 Oi

//

/

2x10-31

Strain

3

/

1 Vs : 0 ' 0 '2 Vs = 3'B2 x l O -3 3 V s = 7"64X10 -3

6

3

4

n ~E 4 - -

11

=2

/' [2x10 ~

Vf = 1.0 *1. 0"001* repl.

4

_4 v= : 11.47x10-3~.

:E ~4

/

/

3

J

f

f------2

/

J

i

r

Strain

i:-

Vf --0'5010 35010 repl.

i

13

i

2

''2

Strain

2x10"31

i

8 6 ~E

Vs=O'O Vs = 3"82 x l O -3 Vs = 7.64 x l O -3 Vs =11.47x10 -3 y

i

j,/ /

i1 I

Strain

2x10-~

4

4

f

/ / / 1 2 3 4

1

Effect of V, on stress-strain characteristics for a given Vf and 0.0% replacement.

f

w~

f

[2x10" I

i

~E 4

3

1

/

Vf =0.0"/. 3 5 *1, r e p I.

n

4

4 - - L ~

f

o

6

j-

J

6

Strain

Fig. 10.

Y

2

//

ZxlO-31

Vf : 1.5 *1, 0"0"1, repl.

-

/

Strain

21

Vf = 1.0"/, 35"1, repl. 4

8

t

6

Vf= 1-5"1, 35"1, repl.

i

/

F "-"

/

-3

~4 2

4

/

I

!

,

4 L

i3

/

" 2

/ 2x10-31

Fig. 11.

St ra in

o 12,~1o41

Strain

Effect of V~on stress-strain characteristics for a given Vf and 35% replacement.

(b) values of fcu are 50.4, 29.0 a n d 17.8 M P a respectively for s p e c i m e n s with 0.0, 35 and 7 0 % sand replacement, (c) fsu of wire is 4 8 0 MPa, and (d) values of Vs are 3.82 x 10 -3, 7.64 x 10 -3 and 11.47 x 10 -3 ( c o r r e s p o n d i n g to s p e c i m e n s with 2, 4 a n d 6 m e s h layers).

CONCLUSIONS T h e following conclusions can be d r a w n f r o m this investigation: (1) Idealizing the rising p o r t i o n of the stress-strain curve of lightweight fibre re-

47

Lightweight fibre-reinforced ferrocement in tension 81

Vf : 0.0"/, 70"/, repl.

Vf =0-5% 7 0 % repl.

6

4

IE

,,r

7I"

/

:/

/

/

4 /

/

3

/

/

/

/ /

2

Strain

12x10" I

i

4

/

2 tI

Strain Vf =1.0=1o 70% repl.

Vs = 0 . o

8

2 Vs=3"82xlO -3 :3 Vs =7-64x 10"3~ m 6 _4 Vs : 1 1 4 7 x 1 ~ IE

3

4

Vf= 1.5 °1o 8 - 70°1° repl. E

,,.

/ _

~.4

/

/

/

/

'2'

/

0

Fig. 12.

Strain

/

oJ2xlo-~J

Strain

/'

Effect of ~ on stress-strain characteristics for a given I/f and 70% replacement.

inforced ferrocement in tension to a trilinear diagram as given a satisfactory agreement with the experimental curves. (2) The inclusion of fibres has reduced the total number of cracks forming on the ferrocement specimens with all percentages of sand replacement used. Also, due to fibre inclusion, the failure of fibre reinforced specimens (groups B, C and D) was due to a single major crack that formed in the specimen. From this, it is felt that a fibre reinforced ferrocement tension member shows the behaviour of a member made of more 'homogeneous' material than a ferrocement element only. (3) Additional studies on the transition zone at cracking and subsequent 'strain-hardening' leading to an S-shaped curve in the rising portion and controlled testing to determine the descending portion of the stress-strain diagram are required to fully understand and define the behaviour of lightweight fibre reinforced ferrocement in tension. (4) On average, first crack strength for specimens without mesh layers has increased by 18"6, 37.3 and 56.0% due to the inclusion of 0"5, 1.0 and 1.5% fibre volume fractions respectively, for all percentages of sand replacement used in the study.

(5) On average, first crack strength of specimens without fibres increased by 67.2, 134.4 and 201.6% due to incorporating 2, 4 and 6 mesh layers respectively for all percentages of sand replacement considered. (6) For the same volume fraction of mesh wires or of fibres, mesh wires are found to be more effective than fibres in enhancing the first crack strength, strain at first crack, ultimate tensile strength and strain at 90% of ultimate load of lightweight fibre reinforced ferrocement specimens subjected to uniaxial tension. (7) Strength and strain capacity increase due to the inclusion of fibres or mesh wires separately or together. (8) Stresses and strains at first crack and at 90% of ultimate load reduce due to direct replacement of sand by LWA because of a reduction in the compressive strength. The reduction increases with the increase of the percentage of replacement. ACKNOWLEDGEMENTS

The second author would like to thank the Egyptian Ministry of Education and the Indian Ministry of Human Resources Development for

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P. Desayi, S. A. EI-Kholy

sponsoring him under the INDO-ARE cultural exchange programme to do research at the Indian Institute of Science, Bangalore, during 1987-90. REFERENCES 1. Desayi, P. & Jacob, K. A., Strength and behaviour of ferrocement in tension and flexure. In Proceedings of Symposium, Modern Trends in Civil Engineering, Nauchandi Grounds, Meerut, India, 11-13 November 1972, pp. 274-9. 2. Huq, S. & Pama, R. E, Ferrocement in tension: analysis and design. Z Ferrocement, 8 (3)(1978) 143-67. 3. Johnston, C. D. & Mattar, S. G., Ferrocement -- behaviour in tension and compression. J. Struc. Division, ASCE, 102 (ST5)(1976) 875-89.

4. Naaman, A. E. & Shah, S. P., Tensile tests of ferrocement. ACIJ., 68 (9)(1971) 693-8. 5. Somayaji, S. & Naaman, A. E., Stress-strain response and cracking of ferrocement in tension. J. Ferrocement, 11 (2) (1981) 127-42. 6. Desayi, P. & Reddy, V., Strength and behaviour of lightweight ferrocement in tension. Proceedings, Second buernational Symposium on Ferrocement, International Ferrocement Information Centre, Asian Institute of Technology, Bangkok, Thailand, Jan. 1985, pp. 61-73. 7. Ward, M. A. & Cook, D. J., The development of uniaxial tension test for concrete and similar brittle materials. Materials Research and Standards, 9 (5) (1969) 16-20. 8. ACI Committee 549 report. Guide for the design, construction and repair of ferrocement. AC1 Struc. J., ACI Committee 549, 85 (3)(1988) 325-51.