Strength and elastic properties of powdered and aqueous polymer-modified mortars

The effectiveness of powdered emulsions (powdered cement modifiers) and aqueous polymer dispersions (aqueous cement modifiers) on improvements in strength and elastic properties of mortars is investigated in this paper. Polymer-modified mortars using various powdered and aqueous cement modifiers were prepared with variation in polymer-cement ratio, and tested for flexural strength, compressive strength, tensile strength, deflection, extreme tensile fiber strain and tensile strain. It is concluded from the test results that powdered cement modifiers affect the properties of mortars similarly as the aqueous cement modifiers and the powdered polymer-modified mortars can be used in the same manner as the aqueous polymer-modified mortars for practical applications.

Pergamon

Cement and Concrete Research, VoL 24, No 7, pp 1199-1213 1994 i!ilili! iiiiiiiiill

Copyright © 1994 Elsevier Science Ltd iiiiiiili~ii

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0008-8846(94) 00064-6

S T R E N G T H A N D E L A S T I C P R O P E R T I E S O F P O W D E R E D

A N D A Q U E O U S P O L Y M E R - M O D I F I E D M O R T A R S

Musarrat Ullah Khan Afridi and Zia Ullah Chaudhary

Cement Research and Development Institute, State Cement Corporation,

Near Lahore Race Club, Kot Lakhpat, Lahore, Pakistan

Yoshihiko Ohama and Katsunori Demura

Department of Architecture, College of Engineering, Nihon University,

Koriyama, Fukushima-ken, 963 Japan

Muhammad Zafar Iqbal

Institute of Chemistry, University of the Punjab, Lahore, Pakistan

(Communicated by M Daimon) (Received October 29, 1993; in final form February 9, 1994)

A B S T R A C T

The effectiveness of powdered emulsions (powdered cement modifiers) and aqueous polymer dispersions (aqueous cement modifiers) on improvements in strength and elastic properties of mortars is investigated in this paper Polymer-modified mortars using various powdered and aqueous cement modifiers were prepared with variation in polymer-cement ratio, and tested for flexural strength, compressive strength, tensile strength, deflection, extreme tensile fiber strain and tensile strain It is concluded from the test results that powdered cement modifiers affect the properties of mortars similarly as the aqueous cement modifiers and the powdered polymer-modified mortars can be used in the same manner as the aqueous polymer-modified mortars for practical applications

I n t r o d u c t i o n

Polymer-modified mortars using aqueous cement modifiers are widely used as high

performance, low-cost construction materials particularly for finishing and repairing works

because of their excellent performance and durability A recent advance for the preparation

of polymer-modified mortars is the invention of powdered cement modifiers with improved qualities Much interest is focussed nowadays for the usage of mortars modified by such

powdered cement modifiers in U.S.A., U.K., Germany, Japan and elsewhere in the advance

countries of the world But sufficient data are not available on the performance of powdered cement modifiers or on the properties of mortars modified by them

The purpose of this paper is to evaluate and compare the performance of powdered

and aqueous cement modifiers in improving the strength and elastic properties of mortars

or to evaluate and compare the strength and elastic properties of powdered and aqueous

polymer-modified mortars In this paper, polymer-modified mortars using four types of commercially available powdered cement modifiers and two types of commercially available

aqueous cement modifiers were prepared with various polymer-cement ratios and tested

for flexural strength, compressive strength, tensile strength, deflection, extreme tensile

fiber strain and tensile strain

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1199

1200 M.U.IC Afridi et al Vol 24, No 7

M a t e r i a l s

C e m e n t a n d F i n e A g g r e g a t e

Ordinary portland c e m e n t and Toyoura standard sand as specified in J I S (Japanese Industrial Standard) were used in all mixes

C e m e n t M o d i f i e r s

Commercially available, four powdered and two aqueous c e m e n t modifiers were used T h e powdered c e m e n t modifiers used included one brand of poly (vinyl acetate-vinyl carboxylate) (VA/VeoVa) type and t h r e e brands of poly (ethylene-vinyl acetate), (EVA) type T h e aqueous c e m e n t modifiers used were one brand of EVA emulsion and one brand

of styrene-butadiene r u b b e r (SBR) latex type T h e i r typical properties are given in Table 1 Before mixing, a silicone emulsion type antifoamer containing 30% silicone solids was added to t h e c e m e n t modifiers in a ratio of 0.7% of t h e silicone solids in t h e antifoamer to

t h e total solids in t h e powdered and aqueous c e m e n t modifiers

T a b l e 1 T y p i c a l P r o p e r t i e s o f C e m e n t Modifiers

Coarse Particles

1.100

Coarse Particles

1.180

Coarse Particles

1.120

Coarse Parliclcs

1.180

Dispersion

Dispersion

Vol 24, No 7 STRENGTH, ELASTIC PROPERTIES, AQUEOUS POLYMERS, MORTARS 1201

T e s t i n g P r o c e d u r e s

P r e p a r a t i o n o f M o r t a r s

P o w d e r e d and a q u e o u s p o l y m e r - m o d i f i e d m o r t a r s w e r e m i x e d according to J I S A

1171 ( M e t h o d of M a k i n g T e s t S a m p l e of P o l y m e r - M o d i f i e d M o r t a r in Laboratory) as

follows: c e m e n t : s t a n d a r d sand = 1:3 (by weight), p o l y m e r - c e m e n t ratios, P / C (calculated

on t h e basis of t o t a l solids in p o w d e r e d and aqueous c e m e n t modifiers) of 0,5,10,15 and 20%

a n d t h e i r flows were a d j u s t e d to be c o n s t a n t a t 170 + 5 The mix p r o p o r t i o n s of polymer-

m o d i f i e d m o r t a r s are given in Table 2

Table 2 Mix Proportions of Polymer - Modified Mortars

rype of

Mortar

Unmodified

Powdered

VA/VeoVa-

Modified

Powdered

EVA-I-

Modified

Powdered

EVA-2-

Modified

Powdered

EVA-3-

Modified

EVA-

Modified

SBR-

Modified

Cement:Sand (by weight) 1:3

1:3

1:3

1:3

1:3

1:3

1:3

Polymer - Cement

Ratio (%)

5

10

15

20

5

10

15

20

5

10

15

20

5

10

15

20

5

10

15

20

5

10

15

20

Water-Cement

Ratio (%) 77.5 72.2 75.5 76.2 75.0 73.8 75.2 73.0 73.8 76.2 76.5 76.2 76.2 76.2 76.5 77.5 77.5 72.5 66.8 63.0 59.8 74.2 70.6 62.8 57.7

Flow

165

172

172

173

168

170

173

170

172

167

168

172

168

168

170

168

169 I70

167

167

168

172

168

168

168

F l e x u r a l a n d C o m p r e s s i v e S t r e n g t h T e s t s

B e a m type m o r t a r s p e c i m e n s 40x40x160 m m were m o u l d e d , and subjected to a 2- day-20°C-80% r.h.-moist, 5-day-20°C-water, and 21-day-20°C-50% r.h.-dry cure T h e cured

s p e c i m e n s w e r e t h e n t e s t e d for flexural and compressive s t r e n g t h s according to J I S A 1172 ( M e t h o d of T e s t for S t r e n g t h of P o l y m e r - M o d i f i e d M o r t a r ) using I n s t r o n - a n d A m s l e r - t y p e

u n i v e r s a l t e s t i n g machines

1202 M.U.K Afridi et al Vol 24, No 7

Tensile Strength Test

Briquet mortar specimens were moulded, and given a 2-day-20°C-80% r.h.-moist, 5- day-20°C-water and 21-day-20°C-50% r.h.-dry cure The cured specimens were then tested for tensile strength according to ASTM C 190 (Standard Test Method for Tensile Strength

of Hydraulic Cement Mortar) using an Amsler-type universal testing machine

D e f l e c t i o n and E x t r e m e Tensile Fiber Strain Measurements

During the flexural strength test as mentioned above, deflection and extreme tensile fiber strain (the fiber strain on the tension side of the specimens) were also measured The deflection was measured by attaching glass plates to the specimens and with the help of non-indicating displacement transducers Whereas, the extreme tensile fiber strain was measured by means of wire strain gauges attached to the center of the specimens The data so obtained were recorded on automatic recorders

Tensile Strain

During the tensile strength test as mentioned above, tensile strain was also measured by attaching wire strain gauges to the center of the specimens where the tensile stress occurs along the longitudinal direction The data so obtained were recorded on a automatic recorder

1~o

IOO

i

50

h

I

o

Modified Modified Modified Modified

Polymer - C~meflt Ratio ( % )

Figure 1 Polymer-Cement Ratio vs Flexural Strength of Powdered and Aqueous Polymer-

Modified Mortars

Vol 24, No 7 STRENGTH, ELASTIC PROPERTIES, A Q ~ U S POLYMERS, MORTARS 1203

T e s t R e s u l t s a n d D i s c u s s i o n

Figure 1 shows the polymer-cement ratio vs flexural strength of powdered and aqueous polymer-modified mortars Figure 2 depicts the polymer-cement ratio vs compressive strength of powdered and aqueous polymer-modified mortars Figure 3 represents the polymer-cement ratio vs tensile strength of powdered and aqueous polymer-modified mortars It is apparent from the above figures that except for powdered VA/VeoVa-modified mortar with a P/C of 5%, the addition of both powdered and aqueous cement modifiers to mortars generally increases their flexural, compressive and t e n s i l e strengths The powdered and aqueous polymer-modified mortars (PAAPMMs) show an improvement in flexural and tensile strengths mainly due to an improved bond between aggregate and matrix(i) or due to an improvement in sand-matrix adhesion level or due to

an overall improvement in cement-hydrate-aggregate bond because of a decrease in water- cement ratio and higher flexural and tensile strengths of polymer films present in PAAPMMs(2,3,4,5) Whereas, the increase in compressive strength of PAAPMMs is attributed mainly due to a reduction in water-cement ratio(6,7) which ultimately affects the gel - space ratio thereby causing a reduction in the capillary porosity of the system(6,8) and helping the pore maxima of pore size distribution range to shift towards the pores of the finer porosity(9) Polymer films present in such PAAPMMs may also contribute towards the compressive strength hike but to a lesser extent(10AD On the other hand, the slight reduction in compressive strength of powdered VA/VeoVa-modified mortar with

a P/C of 5% is associated with its highest air content i.e 13.1% (9)

The results reveal higher and pronounced gains in flexural and tensile strengths of PAAPMMs as compared to those in their compressive strength However, the magnitude to which the flexural, compressive and tensile strengths of PAAPMMs are improved, depends

V A / V e o V a - EVA I - EVA - 2 - EVA -5 Modified Modified

4O0

c

_.*,

i

O

t J

tO0

0 5 IO 1520 0 5 IO 15 20 0 5 '0 15. '43 0 5 IO 1520 0 5 I0 15 20 0 5 101520

Figure 2

P o l y m e r - Cement Rotio (%)

Polymer-Cement R a t i o vs Compressive Strength o f Powdered and A q u e o u s P o l y m e r -

M o d i f i e d Mortars

6C

5O

to

V A I V s o V c t - E V A - I - E V A - 2 - EVA - - - o Modified Mo dlfied

/j;;X

5 iOI5 0 ~0 1520 0 IO 20 5 I0 0 0 5 IO 1520 0 5 I 0 t 5 2 0

Polymer - Cement R ~ i o (0/.)

Figure 3, Polymer-Cement Ratio vs Tensile Strength of Powdered and Aqueous Polymer-

Modified Mom~"s

o

_.J

x

EL

50C

4 0 C

30C

2 0 (

iCK

Pdymer- Cement Ratio (%)

2 0

0.5 Def lection (X lO-Imm)

!

Figure 4 Flexural Load-Deflection Curves for Powdered VA/VeoVa-Modified Mortars

on the type of cement modifier used, polymer-cement ratio or both Generally, a rise in polymer-cement ratio also raises the flexural and tensile strengths of all PAAPMMs while, such a consistent relationship between polymer-cement ratio and compressive strength is present only in powdered EVA-2-modified, EVA-modified and SBR-modified mortars The

t

40{

50,

o

20(

o

" IOC

Figure 5

/

15

¢ I

0.5

Deflection ( X lO'tmm)

Polymer- Cement Relic (°/:,)

20

I

Flexural Load-Deflection Curves for Powdered EVA- 1-Modified Mortars

8

J

It

5 0 0

4 0 0

500

200

bOO

I

0 5

Deflection

//

IO

/

2O

Polymer- Cement

Ratio

(%)

15

!

(X IO-Imm)

Figure 6 Flexural Load-Deflection Curves for Powdered EVA-2-Modified Mortars

rest of the powdered polymer-modified mortars show an optimum level of P/C on which compressive strength is maximum

The results show that generally the performance of powdered cement modifiers in improving the flexural and compressive strengths of mortars is almost comparable to those

of aqueous cement modifiers However, powdered cement modifiers seem less effective than those of aqueous cement modifiers in improving the tensile strength of mortars

v

v

O

J

u_

Figure 7

500

4 0 0

3 0 0

2 0 0

I00

Deflection (X IO-Imm)

f

J

P o l y m e r -

Cemenl R~tio (%}

2o

I.O

Flexural Load-Deflection Curves for Powdered EVA-3-Modified Mortars

C"

0

.J

"6

e

h

5O0

4 0 0

500

2 0 0

I 0 0

Polymer- Cement Ratio

(%)

O,5

Deflection (X IO-Imm)

I

Figure 8 Flexural Load-Deflection Curves for EVA-Modified Mortars

Vol 24, No 7 STRENGTH, ELASTIC PROPERTIES, AQUEOUS POLYMERS, MORTARS 1207

probably because [i] the powdered c e m e n t modifiers are less effective in reducing the water-cement ratio of the mix(9), [ii] the powdered c e m e n t modifiers form inferior quality polymer films having lesser sand-matrix adhesion level or lesser overall improvement in cement-hydrate-aggregate bond(9)

Figures 4-9 show the flexural load deflection curves of various PAAPMMs Figures 10-15 depict the flexural stress - e x t r e m e tensile fiber strain curves of various PAAPMMs Figures 16-21 r e p r e s e n t the tensile stress - tensile strain curves of various PAAPMMs It is

A

' v '

0

J

X

I t

I

4 0 0

3 0 0

200

IO0

/

I0

15

Polymer - Cement Ratio (%)

20

I

Deflection (XlO-Imrn)

Figure 9 Flexural Load-Deflection Curves for SBR-Modified Mortars

N

E

I/)

t O

Lt

30

20

I0

zo

Polymer - Cement

/11 Ij/

• , I I I

Extreme Tensile Fiber Slroin (XlO -~)

| I

Figure 10 Flexural Stress-Extreme Tensile Fiber Strain Curves of Powdered

VA/Veo-Va-Modified Mortars

1208 M.U.K Afridi et at Vol 24, No 7

a p p a r e n t from t h e above figures t h a t the addition of both powdered and aqueous c e m e n t modifiers to m o r t a r s markedly improves their deflection (flexural deformation behaviour),

e x t r e m e tensile fiber strain and tensile strain Such properties of PAAPMMs are improved because of t h e i r modified structure due to the presence of r u b b e r y regions or polymer films which t h e m s e l v e s are highly ductile as compared to t h a t of c e m e n t hydrate(12) and are capable to a r r e s t the advancing cracks It is significant to note t h a t PAAPMMs are more extensible t h a n t h e unmodified m o r t a r not at the cost of strength Moreover, PAAPMMs also show improved toughness over the unmodified m o r t a r in conformity to the earlier results(13)

o0 E

i n

G)

.I=

8

i"7

30

2O

I0

P o l y m e r - Cemenf

F~tio (°Io)

I

Extreme Tensile Fiber Strain (XIO -6)

j S z °

I

1200

Figure 11 Flexural Stress-Extreme Tensile Fiber Strain Curves of Powdered

EVA- 1-Modified Mortars

E

(/l

03

o

It

50

20

I0

P o l y m e r - C e m e n t

Rotio (%)

ZO

o ~ j / > ~ ~ - t

20O

Extreme Tensile Fiber Strain (x I0 -6 )

Figure 12 Flexural Stress-Extreme Tensile Fiber Strain Curves of Powdered

EVA-2-Modified Mortars