Ramamurthy Flyash Mortar Paper

Workability and strength of masonry mortars with high volume Class-C fly ash

Dr.K.Ramamurthy, FBMS, and R.Manikandan Professor Research Scholar Building Technology and Construction Management Division Department of Civil Engineering, Indian Institute of Technology Madras, Chennai-600 036, India Abstract:

This study is focused on the use of fly ash in mortar as an addition and replacement of cement by

equivalent volume. For each mix, the water content required for achieving a flow value of 135%,

was first determined. The water requirement for each mix increases as addition and replacement

level of fly ash increases. Based on this water content, the 7, 28 and 90-day compressive strengths

were determined. Irrespective of age for each mix, compressive strength decreases as the addition

level of fly ash increase for mix 1:3 and 1:4 and almost remains constant for 1:5. Increase in

strength is observed up to 100% addition level for mix 1:6 and 1:7. Replacement of cement causes

reduction in compressive strength at all age. For a given cement content, addition of fly ash results

in reduction in compressive strength for 1:3 mix and increase in strength for 1:4 and 1:5 mix.

Compressive strength obtained at all addition and replacement level of fly ash satisfies code

specified minimum compressive strength.

INTRODUCTION

Masonry mortar should possess good workability for better spreadability and filling of joints,

higher water retention capacity for hydration of cement and good adhesion capacity for better

bonding of masonry units [8]. Generally three types of masonry mortars namely, cement-lime-

sand, lime mortar and cement-sand mortar are being widely adopted in practice. Lime mortar,

which is being used since ancient times is known to possess high water retention, plasticity and

increase in workability but has low early age strength development. However, Portland cement-

sand mortar has higher early age strength gain properties but possesses lower water retentivity and

lead to higher shrinkage cracks. The deficiency in both the above mentioned masonry mortars are

overcome by cement-lime-sand mortar [8, 14]. BS 5628 and ASTM C 270 classify the most

practically used cement-lime-sand masonry mortar into four categories as shown in Table-1.

Table-1 Classification of masonry mortar [1,2]

Designation and Mix proportion by volume BS 5628 ASTM C 270

Minimum 28 days compressive strength, MPa

Des

igna

tion

Cement: Lime: Sand

Des

igna

tion

Cement: Lime: Sand

BS 5628

ASTM C 270

i 1:0 to 0.25:3 M 1:0.25: (S>2.25<3) 16 17.2 ii 1:0.5:4 to 4.5 S 1:0.25 to 0.5: (S>2.25<3) 6.5 12.4 iii 1:1:5 to 6 N 1:0.5 to 1.25: (S>2.25<3) 3.6 5.4 iv 1:2:8 to 9 O 1:1.25 to 2.5: (S>2.25<3) 1.5 2.4

Most standards prescribe the use of masonry mortar relatively weaker than the masonry units

[1,2]. Even though the above codes prescribe the use of lime in masonry mortar for better fresh

mortar characteristics such as workability, water retentivity and cohesiveness of mix, non-

availability of good quality of lime hinders its wider use in countries like India, wherein the lime

is mostly manufactured through small-scale cottage industry without strict quality control as in the

case of cement production. This has led to the use of high strength Ordinary Portland cements (28-

day compressive strength of cement tested using mortar cubes exceeding 43 MPa) in masonry

mortar, which results in higher strength, lower workability, occurrence of bleeding and

segregation.

Under such circumstances, masonry mortar with desirable workability can be achieved by the use

of high volume fly ash utilization. Table-2 summarises a review of available literature on use of

fly ash in mortar, in general. All these studies have attempted to replace a certain percentage by

weight of cement with fly ash. Though the codes [1-3] recommend mix proportion by volume

ratio, most researchers have used mixes by weight ratio, which result in higher paste content.

Considering all these aspects, a systematic study was undertaken on the fresh and hardened

properties of mortar with cement-sand mixes for the influence of high volume of fly ash as an

addition and replacement levels of cement by volume proportion.

Table-2 Review of literature on use of fly ash in masonry mortar

Parameters studied Authors, year Mix proportion (Cement:

Lime:Sand) Ty

pe o

f fly

ash

C

lass

as p

er A

STM

C61

8

Fly

ash

repl

acem

ent l

evel

(%)

Wor

kabi

lity

Com

pres

sive

stre

ngth

Flex

ural

stre

ngth

Bon

d st

reng

th

Wat

er re

tent

ion

Salient observations

Paya et al, 1995 1:0:3 F 15,30, 45,60

√ √ √ - - Increase in workability – increase in strength for 15 and 30% fly ash replacement and no improvement on the increase curing temperature

Malhotra & Dave, 1999

1:0:6, 1:1:6, 1:2:9, 1:3:12

F 50, 100, 150

- √ - √ √ Replacement of lime with fly ash shows poor performance but better than cement-sand mortar

Wong Y L et al, 1999

1:0:1.5 0.3 (w/c)

F 15,25, 45, 55

- √ √ √ - Replacement of fly ash increases interfacial bond strength and fracture toughness at 15% and decreases at 45% and 55% but enhanced with age

Kiattikomol et al, 2001

1:0:2.75 F 20 - √ - - - Strength increased with increase in fineness of fly ash and age, but decrease at early age

Reda Taha &Shrive, 2001

1:1:6 F & C

40 - - - √ - Significant improvement in bond strength by replacement of cement and lime with Class-C and F. Mix with Class-C shows limited enhancement compared to Class-F.

Ramazan Demirbog, 2003

1:0:2 0.5 (w/c)

C 10,20, 30

- √ - - - Replacement of fly ash reduced early age strength at all level of fly ash and increase with age

Cengiz Duran Atis et al, 2004

1:2 0.4(w/c)

C 10, 20, 30, 40

- √ √ - - 28 day Strengths are comparable with PC mortar for 10% and 20 % replacement level and shows decrease in for 30% and 40%

Chindaprasirt et al, 2005

1:0:3 F 20, 40 √ √ √ - Reduces water demand, enhances water retention and compressive strength

Gengying li & Xiaozhang, 2005

1:1:6 F 30, 50 √ √ - √ - Replacement of cement and lime enhances fluidity, bond strength and compressive and reduction in size of fly ash increases overall performance

Tangpagasit et al, 2005

1:2.75 0.485 (w/c)

F 20 - √ - - - Fly ash with median particle size of 2.7 m and 160 m improves the strength activity index at early ages due to packing effect and pozzolanic action at later ages

EXPERIMENTAL PROGRAMME

Materials used

Ordinary Portland cement with specific gravity and Blaine’s fineness values of 3.15 and 320

m2/kg respectively and having a 28-day compressive strength (tested using mortar cubes) of 53

MPa was used. River sand passing 4.75 mm with a specific gravity of 2.61 as fine aggregate, and

Fly ash conforming to class C as per ASTM C 618 [5] with specific gravity and Blaine’s fineness

values of 2.64 and 414 m2/kg respectively, and having a chemical composition as shown in

Table-3 were used.

Table-3 Chemical composition of fly ash

Properties of fly ash used and specifications Properties Fly ash used IS 3812-2003 [4] ASTM C 618 (Class-C) [5]SiO2 (%) 31.62 25 (min) -

SiO2 + Al2O3 + Fe2O3 (%) 70.67 50 (min) 50 (min) MgO (%) 3.71 5 (max) - SO3 (%) 5.72 3 (max) 5 (max) CaO (%) 17.17 >10 >10

Loss of ignition (%) 4.68 5(max) 6 (max)

Mix proportion

For the study of mortar mixes in which fly ash was included as addition, the basic five cement-

sand mortar mixes (i.e., 1:3, 1:4, 1:5, 1:6 and 1:7) by volume were considered. To each of these

mixes, fly ash was added by volume in the ratios of 0.5, 0.75, 1.0, 1.5 and 2. For mixes in which

fly ash was replaced with equivalent volume of cement (conventional method), three basic

cement-sand mortar mixes (i.e., 1:3, 1:4 and 1:5) with fly ash replacement ratio of 0.25, 0.4, 0.5

and 0.6 were considered. Mixes 1:6 and 1:7 were not included in the study on replacement of

cement with fly ash as the cement content in these mixes is already low. The fly ash addition and

replacement into the mix was done by equivalent volume of cement and shown in Table 4. The

fluidity (i.e., workability) of mortar was measured by the flow table test for the fixed flow value of

135%, an appropriate value prescribed for masonry mortar [6]. The water content required for

achieving a workability of 135% was determined on a trial and error basis for each of the above

mixes. For each mix, the results are based on the mean value of two trials. For the determined

water content, 7, 28 and 90 days compressive strength for each mix was determined using three

cubes each of size 70.7 mm.

Table 4 Mix proportions for addition and replacement of fly ash (by volume)

Addition of fly ash in mixes (Cement: Fly ash: Sand)

Replacement of fly ash

Con

trol

Mix

es

(Cem

ent:

Sand

)

C: F: S C: F: S C: F: S C: F: S C: F: S C: F: S C: F: S C: F: S C: F: S

1:3 1:0.5:3 1:0.75:3 1:1:3 1:1.5:3 1:2:3 0.75:0.25:3 0.6:0.4:3 0.5:0.5:3 0.4:0.6:3 1:4 1:0.5:4 1:0.75:4 1:1:4 1:1.5:4 1:2:4 0.75:0.25:4 0.6:0.4:4 0.5:0.5:4 0.4:0.6:4 1:5 1:0.5:5 1:0.75:5 1:1:5 1:1.5:5 1:2:5 0.75:0.25:5 0.6:0.4:5 0.5:0.5:5 0.4:0.6:5 1:6 1:0.5:6 1:0.75:6 1:1:6 1:1.5:6 1:2:6 - - - - 1:7 1:0.5:7 1:0.75:7 1:1:7 1:1.5:7 1:2:7 - - - -

DISCUSSION OF RESULTS

Properties of fresh mortar mixes: Addition of fly ash

Fig.1 shows the relationship between water content required to achieve the desired flow value of

135% for various mixes at different levels of addition of high volume fly ash. For a given

workability of control mix, the water requirement increases marginally with an increase in

aggregate-cement ratio. For a given percentage of fly ash addition, richer mixes (1:3 1:4 and 1:5)

demand higher water content. This is due to higher fineness and amount of fines in the mix, which

requires more water to coat the fly ash particles for achieving the desired workability. For example

at 75% fly ash addition level, the total fines content for 1:3 and 1:4 mixes are 774 and 665 Kg/m3

respectively and for 1:7 mix the total fines content is 448 kg/m3. However, for mix 1:6, the water

requirement remains constant up to 75% and than increases with addition of fly ash. But for 1:7

mix, the water content decreases up to 75% of fly ash addition and than increases. Initially, for the

control mix of 1:7, the water requirement is higher where segregation and bleeding occurred due

to increase in aggregate-cement ratio. When fly ash was added to the mix, bleeding and

segregation were eliminated as the mix becomes rich in fines. The bleed water was utilised by the

fly ash added which enhanced the cohesiveness and workability of the mix. This resulted in a

reduction of water content up to 75% of fly ash addition for a given workability. As the percentage

addition of fly ash is increased, the difference in water content between the mixes to achieve a

constant workability increases.

Fig.1 Water content required to produce a constant workability with addition of fly ash

Properties of fresh mortar mixes: Replacement of cement with fly ash

The water content required for various levels of replacement of cement with fly ash by volume is

shown in Fig.2. For a given workability, the water requirement in each mix increases as the

replacement level of fly ash increases. For a given replacement level of fly ash, the water content

requirement is significantly higher for mix 1:3 as compared to mix 1:4 and 1:5. This behaviour is

attributed to higher fineness value of fly ash as compared to that of cement. Similar graphs for the

type of fly ash proposed to be used would help in arriving at the approximate water content.

0 50 100 150 200

225

250

275

300

325

350

375

Wat

er c

onte

nt, k

g/m

3

% of fly ash addition by volume of cement

1:3 1:4 1:5 1:6 1:7

Fig.2 Water content required to produce a constant workability with replacement of fly ash

Properties of hardened mortar mixes: Addition of fly ash

The 7, 28 and 90-day compressive strength of each mortar mixes with high volume fly ash

addition are presented in Figs.3 to 5. For a given percentage addition of fly ash, the 7, 28 and 90-

day compressive strengths decrease with an increase in aggregate-cement ratio, which is attributed

to the reduction in cement content of the mix. Irrespective of the age, the compressive strength

decreases as the percentage of fly ash addition increases for mix 1:3 and 1:4. This behaviour is due

higher water demand to achieve the desired workability and a reduction in cement content. Since

the mix proportions are made by volume, an increase in percentage addition of fly ash reduces the

cement content in the mix. For the mix 1:5, the variation of compressive strength at all ages

remains almost constant for the various addition level of fly ash. However for mix 1:6 and 1:7, the

compressive strength increases up to 100% addition level and beyond this level it remains

constant. This initial increase in strength is attributed to the reduction in bleeding and segregation

achieved by fly ash addition. The percentage of increase in compressive strength with age is

0 10 20 30 40 50 60225

230

235

240

245

250

255

1:3 1:4 1:5

Wat

er C

onte

nt, K

g/m

3

% of fly ash replacement by volume of cement

marginally higher for all addition level of fly ash as compared to control mix. This is attributed to

the pozzolanic action of fly ash. All these mixes fall under different designations of mortar as

prescribed by ASTM and BS [1,2].

Fig.3 7-day Compressive strength for addition of fly ash


0 50 100 150 2000

5

10

15

20

25 1:3 1:4 1:5 1:6 1:7

7 da

y co

mpr

essi

ve s

treng

th, M

Pa

% of fly ash addition

0 50 100 150 2005

10

15

20

25

30

35

1:3 1:4 1:5 1:6 1:7

28 d

ay c

ompr

essi

ve s

treng

th, M

Pa



The 28-day compressive strengths of each of the mortar mixes obtained from tests are compared

with the minimum compressive strengths prescribed by BS 5628 and ASTM C270 and the

corresponding mix designation are presented in Table-5. It seen that, addition of fly ash up to

200% adopted in this study has resulted in mixes conforming to the code specified strength, and

there is scope for further increasing the level of addition.

Table-5 Classification of mixes as per BS and ASTM for addition of fly ash [1, 2]

Mix designation of mortar mixes based on minimum compressive strength as per ASTM C 270 and BS 5628 1:3 1:4 1:5 1:6 1:7

% o

f fly

ash

add

ition

Act

ual c

omp.

st

reng

th (M

Pa)

Des

igna

tion

as p

er

BS

5628

Des

igna

tion

as p

er

AST

M C

270

Act

ual c

omp.

st

ren g

th (M

Pa)

Des

igna

tion

as p

er

BS

5628

Des

igna

tion

as p

er

AST

M C

270

Act

ual c

omp.

st

reng

th (M

Pa)

Des

igna

tion

as p

er

BS

5628

Des

igna

tion

as p

er

AST

M C

270

Act

ual c

omp.

st

reng

th (M

Pa)

Des

igna

tion

as p

er

BS

5628

Des

igna

tion

as p

er

AST

M C

270

Act

ual c

omp.

st

reng

th (M

Pa)

Des

igna

tion

as p

er

BS

5628

Des

igna

tion

as p

er

AST

M C

270

0 32.3 i M 24.9 i M 16.4 i S 9.6 ii N 5.9 ii N 50 22.3 i M 21.5 i M 17.9 i M 15.7 ii S 11.5 ii N 75 24.2 i M 21.6 i M 21.7 i M 16.7 i S 14.4 ii S 100 24.1 i M 20.7 i M 19.4 i M 17.5 i M 13.7 ii S 150 21.5 i M 18.7 i M 16.3 i S 14.3 ii S 10.6 ii N 200 17.8 i M 18.7 i M 16.8 i S 14.9 ii S 13.2 ii S

0 50 100 150 2005

10

15

20

25

30

35 1:3 1:4 1:5 1:6 1:7

90 d

ay c

ompr

essi

ve s

treng

th, M

Pa


Properties of hardened mortar mixes: Replacement of cement with fly ash

Figs. 6 to 8 show the variation of compressive strength for various replacement level of cement

with fly ash at 7, 28 and 90-days respectively. Irrespective of the age of each mix, the compressive

strength decreases steeply as the replacement level increases. This is attributed to the combined

effect of increase in water content and reduction in cement content. An increase in compressive

strength with age is observed, which is attributed to the pozzolanic action of fly ash.

Fig.6 7-day compressive strength of mixes with replacement of fly ash with cement

The 28-day compressive strengths of each of the mortar mixes obtained from tests are compared

with the minimum compressive strengths prescribed by BS 5628 and ASTM C270 and the

corresponding mix designation are presented in Table-6. Replacement of cement up to 60% used

in this study, has resulted in mixes conforming to the code specified mix designations.

0 10 20 30 40 50 60

2

3

4

5

6

7

8

9

10

11

12

1:3 1:4 1:5

7 da

y co

mpr

essi

ve s

treng

th, M

Pa

% of fly ash replacement

Fig.7 28-day compressive strength for replacement of fly ash.

Fig.8 90-day compressive strength for replacement of fly ash.

0 10 20 30 40 50 605

10

15

20

25

30

35 1:3 1:4 1:5

28 d

ay c

ompr

essi

ve s

treng

th, M

Pa


0 10 20 30 40 50 605

10

15

20

25

30

35 1:3 1:4 1:5

90 d

ay c

ompr

essi

ve s

treng

th, M

Pa


Table-6 Classification of mixes as per BS and ASTM for addition of fly ash [1,2]

Comparison between Addition of fly ash to the mix and Replacement of cement with fly ash In the cases of addition of fly ash and replacement of cement with fly ash in different mixes, as the

mixes are made in volume proportions, the cement content in each of the mixes would be

different. Hence a comparison between these two methods of inclusion of fly ash into the mortar

mixes is compared on the basis of cement content in the mixes in Figs.9-11.

Fig.9 Comparison of methods of inclusion of fly ash (Addition vs. Replacement) for 1:3 Mix

Mix designation of mortar mixes based on minimum compressive strength as per ASTM C 270 and BS 5628

1:3 1:4 1:5

Rep

lace

men

t lev

el o

f ce

men

t with

fly

ash

Act

ual c

omp.

st

reng

th

(MPa

)

Des

igna

tion

as p

er B

S 56

28

Des

igna

tion

as p

er A

STM

C

270

Act

ual c

omp.

st

reng

th

(MPa

)

Des

igna

tion

as p

er B

S 56

28

Des

igna

tion

as p

er A

STM

C

270

Act

ual c

omp.

st

reng

th

(MPa

)

Des

igna

tion

as p

er B

S 56

28

Des

igna

tion

as p

er A

STM

C

270

0 32.3 i M 24.9 i M 16.4 i S 25 23.8 i M 17.8 i M 13.6 ii S 40 21.2 i M 15.1 ii S 11.5 ii N 50 20.5 i M 12.8 ii S 8.7 ii N 60 11.9 ii N 9.4 ii N 8.1 ii N

200 250 300 350 400 450 500 550

12

14

16

18

20

22

24

28-d

ays

com

pres

sive

stre

ngth

, MP

a

Cement content, kg/m3

1:3 mix Addition Replacement Addition Replacement



150 200 250 300 350 400 4508

10

12

14

16

18

20

22

28-d

ays

com

pres

sive

stre

ngth

, MPa



100 150 200 250 300 350 400

8

10

12

14

16

18

20

22

28-d

ays

com

pres

sive

stre

ngth

, MP

a



For the mix 1:3, within comparable range, for a given cement content, the mixes with addition of

fly ash results in relatively lower compressive strength as compared to the mixes with cement

replaced with fly ash. As the strength range under consideration is well within the standard high

strength masonry mortar, this reduction in strength is beneficial for richer mixes like 1:3, and

hence addition of fly ash is preferable for 1:3 mix, which facilitates higher fly ash utilization. In

the case of mixes 1:4 and 1:5 (Figs.10 and 11), to achieve a particular strength, the mixes in which

fly ash is added requires relatively lower cement content as compared to mixes with replacement

of cement with fly ash (conventional method adopted by researchers). Further, the reduction in

compressive strength with a reduction in cement content is steeper for mixes in which cement is

replaced with fly ash.

CONCLUSION

The following conclusions are applicable for the range of parameters considered and the materials

used in this study.

1. For a given workability, an increase in fly ash addition to the mortar mix, increases water

content, which is more pronounced for mixes 1:3, 1:4 and 1:5, Addition of fly ash reduced

bleeding and segregation in the mix 1:7. For a given replacement level of fly ash, the water

content requirement is significantly higher for mix 1:3 as compared to mixes 1:4 and 1:5,

to achieve the desired workability. This behaviour is attributed to higher fineness of fly

ash.

2. Increase in compressive strength with age is observed for both addition and replacement of

fly ash to each mix, which is attributed to the pozzolanic action of fly ash.

3. Within the comparable range, for a given cement content, addition of fly ash in the mix 1:3

results in relatively lower compressive strength as compared to replacement. However, the

obtained reduced strength is well within the standard high strength masonry mortar, which

facilitates higher fly ash utilization.

4. In the case of mixes 1:4 and 1:5, to achieve a particular strength, addition of fly ash

requires relatively lower cement content as compared to replacement of cement with fly

ash.

REFERENCES

1. American Society for Testing and Materials, Standard Specification for Mortar for Unit Masonry, ASTM C 270, 1989, Philadelphia

2. British Standards Institution, Code of Practice for Structural Use of Masonry, BS 5628 (Part I), 1978, London

3. Bureau of Indian Standards, Code of Practice for Preparation and Use of Masonry Mortars, IS 2250, 1981, India

4. Bureau of Indian Standards, Pulverized fuel ash – Specification – Part 1: For use as Pozzolana in Cement, Cement Mortar and Concrete, IS 3812 (Part 1), 2003, India

5. American Society for Testing and Materials, Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete, ASTM C 618, 1991, Philadelphia

6. Bureau of Indian Standards, Specification for Flow Table for Use in tests of Hydraulic Cements and Pozzolanic Materials, IS 5512, 1969, India.

7. Paya J, Monzob J, Peris-Mora E, Borrachero M V, Tercero R and Pinillos C, Early-strength development of Portland cement mortars containing air classified fly ashes, Cement and Concrete Research, Vol.25, No.2, 1995, pp.449-456.

8. Malhotra S K and Dave N G, Investigations into the effect of addition of fly ash and burnt clay pozzolana on certain engineering properties of cement composites, Cement and Concrete Composites, Vol.21, 1999, pp.285-291.

9. Wong Y L, Lam L, Poon C S and Zhou F P, Properties of fly ash-modified cement mortar-aggregate interfaces, Cement and Concrete Research, Vol.29,1999, pp.1905-1913.

10. Kraiwood kiattikomol, Chai Jaturapitakkul, Smith Songpiriyakij and Seksun Chutubtim, A study of ground coarse fly ashes with different finenesses from various sources as pozzolanic materials, Vol.23, 2001, pp.335-343.

11. Reda Taha M M and Shrive N G, The use of Pozzolans to improve bond and bond strength, 9th Canadian masonry symposium, June 2001.

12. Ramazan Demirbog, Influence of mineral admixtures on thermal conductivity and compressive strength of mortar, Energy and Buildings, Vol.35, 2003, pp.189-192.

13. Cengiz Duran Atis, Alaettin kilic and Umur Korkut Sevium, Strength and shrinkage properties of mortar containing a nonstandard high-calcium fly ash, Cement and Concrete Research, Vol.34, 2004, pp.99-102.

14. Gengying Li and Xiaozhong Wu, Influence of fly ash and its mean particle size on certain engineering properties of cement composite mortars, Cement and Concrete Research, Vol.35, 2005, pp.1128-1134.

15. Jatuphon Tangpagasit, Raungrut Cheerarot, Chat Jaturapitakkula and Kraiwood Kiattikomol, Packing effect and pozzolanic reaction of fly ash in mortar, Cement and Concrete Research, Vol.35, 2005, pp.1145-1151.

16. Chindaprasirt P, Buapa N and Cao H T, Mixed cement containing fly ash for masonry and plastering work, Construction and Building Materials, Vol.19, 2005, pp. 612-618.

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