62 Vth International Brick Masonry Conference

11-6. Design for Mix Proportion of Joint Mortar and Bond Strength Akio Baba

Building Research Institute Ministry ofConsl'Tuction

Katsuro Kamimura B uilding Research lnstitute

Minislly o[ Constnlclion

So Kato Kunishiro Company Ltd.

ABSTRACT

The design for miJe proportion of joint mortar has been decided by setting the ratio of binder (cement and lime) and fine aggregates apreori and then unit water content is determined to get proper jluidity. By this method, the strength of joint mortar is largely effected by particle size distributions of fine aggregates, which makes dif.Jicult to contrai the strength of joint mortar and the brick masonry -the composite of bricks and joint mortar conse-quently.

For development of new construction methods, actively performed recently, ming bricks of high strength, the way of miJe design which can contrai the strength ofjoint mortar and the bond strength between bricks and joint mortar is required.

Therefore it is proposed lhat miJe design of joint mortar should be based on the waler-cement ratio and requisites of miJe design to determine workability ofjoint mortar has been examined experimentally.

Besides, performances of joint mortar ming variom particle size distributions of fine aggregates were examined experimentally and the range of proper pariicle size distributions was proposed.

A Iso efJects of joint mortar materiais and miJe proportion on the bond strength between bricks and joint mortar were examined experimentally ming variom mortar.

SCOPE

joint mortar is an indispensable element of brick masonry and its quality largely influences on the structural perfor-mance of brick masonry. The other hand, development of various construction methods using high-strength bricks have been advanced in j a pan, and it is necessary to use high-bond mortar suitable for high-strength brick.

The first purpose of this paper is to examine the tra-ditional design for mix proportion of joint mortar which is decided by setting the ratio of cement and fine aggre-gate apreori, and then to propose the new design for mix proportion which insures masonry strength.

The second purpose is to propose the range of proper particle size distribution of fine aggregates for masonry mortar that largely influences the performance of joint mortar.

As cunclusions, the relation between mix proportion or bond-strength of joint mortar and masonry strength is examined and importance of mix proportion of joint mor-tar is reconfirmed.

DESIGN FOR MIX PROPORTION OF MASONRY MORTA R

Fundamental Idea of Design of Mix Proportion

Up to present, the mix proportion of joint mortar has been decided by the way of setting the ratio of cement and fine aggregates apreori and then unit water content will be determined to get the proper fluidity. This method

prevents drying shrinkage or cracks of joint mortar by insuring the quantity of fine aggregates and improves the waterproof performance and durability. The other hand , it is based on the idea that the necessary strength is rather small and generally insured in any condition of mix pro-portion .

In cases of using high-strength masonry units, joint mortar is required to have the bond-strength of definite standard, and design of mix proportion should be based on water/cement ratio.

Fig. 1 shows the flow for determination of mix propor-tion of joint mortar. The degree of independence of mix proportion of joint mortar is 2, and it is proposed that, after setting water/cement ratio to determine strength, the quantity of fine aggregates determine workability (fluid-ity).

Determination of FIow

The flow of cement mortar varies by various factors of mix proportion. In the experiment using normal Portland cement and fine aggregates of various particle size distri-bution, the relation between the unit water content and flow is shown as the unique curve (Fig. 2 & Fig. 3). There-fore, mix proportion can be designed by determination of the unit water content to correspond the flow. Fig. 4 and Fig. 5 show an example of relation between flow or slump of joint mortar and mix proportion. This relation is the result of the experiment of No. 4 fine aggregate in the Table 3 (Values of the upper limit of the permissible range

Session lI, Paper 6, Design for Mix PTOportion of joint Mortar and Bond Strength 63

of particle size distribution of fine aggregate for masonry mortar in BS, the permissible finest aggregates.) In case of using fine aggregates of different particle size distri-uution, amendment is required.

Amendment of Mix Proportion by Particle Size Distribution of Fine Aggregates

Accord ing to Fig. 2 and Fig. 3, the flow (FL) 01' slump (SL) of joint mortar is expressed as follows:

FL - I 00 = O' (W - f3) SL = 0'* (W - {3*)

0', 0'* , {3, {3* are the experimental constant, and W is the unit water content. Having the experimental constant 0', {3 with various particle size distribution of fine aggregates, o' is a lmost same in the range of practical particle size distribution of fine aggregates and it is expressed as fo l-lows :

o' = 0'* = 1.5 mm/(kg/m3 )

The Table 4 shows values of {3, {3* with various particle size distribution of fine aggregates. From these values , the flow of joint mortar with the chosen particle size distri-bution of fin e aggregates can be determined.

PARTICLE SIZE DISTRIBUTION OF FINE AGGREGATES FOR MASONRY MORT AR

Method of Experiment

T he mechanical properties of masonry mortar are large ly influenced by the particle size distribution of fine aggregates used , but the quantitative study on this influ-ence is rare . T his paper reports the experimental exami-nation of influence of particle size distribution of fine aggregates on the various performances of cement mortar and shows the permissible range of the particle size dis-tribution of fine aggregates for cement mortar in masonry construction . Fig. 6 shows the particle size distribution of fine aggregates used in the experiment. Subjects of the experiment were strength of mortar, dimensional stability, workability and economical aspects. Table 3 shows frac-tional volume of solid phase unit weight, F. M. a nd specific surface of each particle size distribution of fine aggregates. The ratio of cement and fine aggregates in the cement mortar with same water-cement ratio, 0.50 and same flow, 210 mm ± 10 mm was examined. Compressive strength , flexual strength and drying sh rinkage after aged at 28 days in water curing at 20°C ± 1°C, dry curing at 20°C ± 1°C and 60%RH ± 5%RH was measured. Worka-bi li ty of cement morta r of flow 210 mm ± 10 mm was also examined empirically by specia l experts.

Experimental Results

Table 5 and Fig. 7- 12 show the experimental resu lts. The particle size distribution was estimated using grades shown in Table 3. Considering the larger fine aggregates / cement ratio means more economical, the result was that

ones with larger F. M. are generally more economical (Fig. 7). On the contrary, ones with small F. M. show larger flexual strength and compressive strength, and ones with particle size distribution show better results. This tendency is more remarkable in flexual strength (Fig. 8-11 ). As to drying shrinkage, ones with larger F. M. contain larger quantity of fine aggregates and show less contraction (Fig. 12). Table 7 shows single size distribution has worse work-abi lity, and 6 and 10 is superior. In overall valuation, adopting the lowest value of each performance, 4, 6, 9, and 10 are superior as a whole. These are within the range of the permissible particle size distribution of fine aggre-gates for masonry in B. S. and ali other particle size dis-tribu tions are o ut of this range.

INFLUENCE OF jOINT MORTAR ON STRENGTH OF BRICK MASONRY

Uniaxial Compressive Strength l - 4

Fig. 13 shows the experimental results of uniaxial com-p.·essive strength of masonry. This figure shows the ten-dency that masonry strength against brick strength becomes small when strength of joint mortar is extremely small compared with bricks. Therefore, it is important to use joint mortar of proper strength in order to utilize the compressive strength of high-strength bricks.

Flexual Strength

Fig. 14 shows flexual strength of brick masonry using high-bond cement mortar with various water/ce ment ratio. Wate r/cement ratio of about 0.40 gives the largest flexual strength. The same results will be obtained about tensile strength and shea.' strength.

REFERENCES

I . Portland Cement Association , Special Concretes, Mortars and Products. 2. Walter C. Voss, Exterior Masom) Construction, National Lime Association . 3. Fatiai , S.C.; Cattaneo, L.E., S/ruc/ural Performance of Masonry Wall Under Compression and Flexure, NBS Building Science Series 73. 4. Kirtschig , K., Kasten, D., Statische Auswer/ung von Mauerwerks-versuchen, Ziegel Industrie, 1976.

64

requirements of strength

for masonry

(compressive. flexual.

shear strength. etc.)

several types of bond strength

particle ~ze distribution

of fine aggregate

proportion required

bond strength

(amount of additive.

water- cement ratio)

workability

type of addltlve

durability

water-cement ratio

mix proportion of joint mortar

Figure 1. Flow for determ ination of mix proportion of joint mortal'

Ê E

o LO N

o ~ O .2 N -

o

Vth International Brick Masonry Conference

I I

/W/ C=0.6

/ / ",W/ C= 0 .5

, " / /" W/ C= 0 .4

, I

// • I

!/ ,/

lJ I '

F.M .= 1.89

300 350 unit water con t ent(kg ; mJ )

Figure 2 - 1. Experimental re lation between flow and unit water con tent of j oint morta r

Ê E

O O

0.0 E. LO ::J

ü)

I I

W/ C= 0 .6 / / /

) A'

I' I

. / l' /1

,W/ C = 0.5

F.M .= 1.89

o 2~0 300 350 unit water content (kg ; mJ )

Figure 2 - 2. Experimental re lation between slump and unit water conlent of join t mortal'

Session Il, Paper 6, Design for Mix Proportion of j oint Mortar and Bond Strength 65

0,--------------------------------, O M

S / C=2.0 I

I .-I .-'-

O ·In

_N

1'.-/ W / C=0.5 /'

;~' W / C=0.4 E E

; .

3 .2 -O

O N

o

/ /

/

200

HIGHBOND cement morfar

(a / c=0.20)

F.M.=2.22

250 300 unif water content (kg/m')

Figure 3. Experimental relation between fl ow and unit water content of high bond mortar

-r---~----------~--------------~ E water-cement ratio E w/c =

0.60 w/c = 0.50 I -w c-

unit water content

8 N

0.40 kg/m 3

--w = 330 -- w - 320

---w-310

' ..... w - 290

300 500 700 900 1100 unit cement contant (kg/m 3 )

Figure 4. Experimental relation between flow and mix proportion

""'r-------------------------------~ E water-cement ratio ~ w/c= 0.60 w/c =

o ....

Il)

--Q.

E _ .... :::l Clt

0.50 unit water content

kg/m 3

--'w = 330

w:a 320 -'w:= 310

w:a 300 "'W os 290

300 500 700 900 unit cement content

Figure 5. Experimental relatio n between slump and mix proportion

Or--------,----~------------------~ _ .In "

~ *, I , ..... O "- of' )I' o ~ ")' ,. __ ~~__ /

,,, 1 '\ / -c a) O E M a) "-u .!: O

N

1 '< ,y 10 ' I" ... )I' \ -.,. ', , 1 , \; \

I 1- , "--/.,,,~ , 8 ' ,~~, 9~'-'~-~~~

7 " )I' '" "'~, 1 / "- \,""'

1 / ,,\' ,

61

/ ,,""' )I' "-

5/ " " O~~--~----~----~----~----~

0 . 15 0 .3 0 .6 1.2 2.5 5.0

~ OI :l O

O "-~ ~ -"C a)

O VI VI N l1:l a. -~ OI ai 3 size of square openlng of sieve (mm)

Figtl1'e 6. Particle size distribution of fine aggregate

66

o

-Q)-E :c j Cl

g ~ --00 oLn C")N

o LnO NO

N

... ~g ... N O ; Ln E Q)

'tO !Ln «I-a»

r-------------------------~

.14.6 12.7 .24.9

21.3023.5

ti o + 32.5 29.6

S - 49.8 cm 2 /g

~, O ~o O w/c = 0.50 «10 - flaw - 210 ± 10mm

~ -T 11--_-'--2_0_0 c_--,-__ ~ 50 60 70

fractional volume'of solid phase of sand ( o Ivol)

Figure 7. Fine aggregate content under constant water-cement ratio and flow

O O Ln

O _Ln to v E ~ Cl

.:,t.

.cO "'0 ~~ Q) '-... cn Q) > ~O Q)1t)

a. M

Vth International Brick Masonry Conference

+

*

g 20° C, 28 days (J

2 4 finess modulus (F.M.l

Figure 8 . Experimental relation between compressive strength and F. M. (cured in water)

Session I!, Paper 6, Design for Mix Proporti01~ of joint Mortm' and Bond Strength 67

O O'

Á

• C Â V

O LO

_M ... E (,J -O) ~ -~O ..... 0 O)M C (1) ... ..... '" (1) > "'o ~LO êi N E O (,J

+ *

20°C,60%AH 28 days

2 4 finess modulus (F.MJ

Figure 9. Experimental relation between compressive strength and F. M. (cured in drying condition)

O O)

*

20° C, 28 days

2 4 finess modulus (F.M.l

Figu.re 10. Experimental relation between flexual strength and F. M. (cured in water)

.... E

O

68

8

~E U ...... CD ~

.L: -CD C O GI ... 1t) -CIl 'U C o ~

"ii :l )(

~ -o

red brick

Vth International Brick Masonry Conference

co c:i o

o

o

o o

~ .:.. °m ó. o ;-:; ~ o o E ~ o o 0 ° o

.:Jl . ~ -tl o o o u..c .- °0 'Ô :õõ tl°o·:O~~°cAg Oo o~ A ~ ~ O.;§~i • Â O O ~ () õ,C",," 6. ~ 6. t c~cif-() ~ O O •

o o

o

o

o o

"o

strength of brick

o

8 o o

Q.J - _. ~ CI O· Z In ~O 6. ;; .~ -1?ffl;:

. ~ ~ ···l .... () o 0- 100 kg/cm' 0100-200

(t

a; a.

Session lI, PapeT 6, DesignfoT Mix PTop01"lion of j oint MOTtar and Bond StTength

o

: '. av o value of __________ L ______________ brown brick

---~;-----;----------.--- red brick ---.!'--- --- .. -------------- white brick ". .

• hig~ bond-cement mortar

(w/c=O.40. s/c=3.00. a/c=0.2(0) 28 days

5 l/O

lO

(span of bending test/hight of beam)

.co ã,1ll C ai ... -UI

red brick high bond -cement mortar

w/c=O.40. s/c=3.00. a/c=0.20

.. ________________________ avo value of

:. 28days 't:J III ---;!-----.-----------·----7days c: N • • O A. ~

.Q

cu ~ )(

!R -O .---õ-----..... ------------ 3days

o -• • ~

l/O lO

FiguTe 16-1 . Experimental results of flexual bond strength of brick masonry prism

FiguTe 16-2. Experimental resu lts of flexual bond strength of brick masonry prism

o white brick Á brown brick - red brick

T ABLE l-Properties of Portland Cement

normal portland cement 3.010 250 68.3 400

o 3 days Á 7 days - 28 days

TABLE 2-Properties of Fine Aggregates

soma silica sand

90 I

95

3 0 .15 0.3 I 2 .62 1.87 59.2

6 0 . 7

TABLE 3-Effect on the Properties of Joint Mortar by Particle Size Distribution of Fine Aggregate

;:s ~~

: ~ \e ;:s "'~ ,$- .,:.0 ~~ ... "" ~e .;;' ~ v' +"''Õ ",,~0 o~ ",,'Õ ~v \! ~e {y ~ ~v~ ~... ~v~ é.~ ~'I>~ ~ v~ ~... ~ v~ ... 0 .... ~ ~ '1>.... 'S' ... '1> .... ... ~~~ ~'I> ~~ 'Õ~ .,,~ 'Õ~ ç'l>~'" .~ .~ ., I 'I> .~ ~O) .~ \.,+0) ~'I> I 'I> ~ ~ .:r.'I>~ 1 2. 15 2 .02 517 396 0 .77 89.4 60.4 0 .68 14.8 6 .6 2 2 .21 2 .09 397 359 0 .91 71 .1 49.9 0 .70 10.1 5 .0 3 2 .22 2 .26 395 326 0 .82 68.7 49.1 0 .71 9 .3 5.3 4 2. 14 2 . 17 409 81 .2 57.5 0 .71 10.2 5. 1 5 2.20 2.27 483 397 0.82 75.0 59.0 0 .79 9.9 5 .1 6 2. 15 2 .22 399 76.1 56.9 0 .75 9 . 1 4 .8 7 2 .16 2.13 442 404 0 .91 75.0 63.2 0 .84 11.0 5.5 8 2. 16 2 .21 397 74.7 63 .3 0.85 10.5 4 .7

9 2.21 2 .28 390 370 0 .95 85.0 60.0 0 .71 9.0 7.6 10 2. 18 2 .20 409 369 0 .90 78.3 63.1 0 .81 9.7 5. 1

69

70

T ABLE 4-Properties and Particle Size Distribution of Fine Aggregate U sed in

Experiment

01;-' ~0 01;-' ~0 ii- v "".;:) ii- "".;:) '1> á- c,ç \.v « . I .

1 1.40 53.4 46.6 130.4 1.00 2 1.53 58.4 41.6 66.7 3.00

3 1.55 59.4 40.6 33.3 4.00

4 1.55 59.2 40.8 85 .3 1.87

5 1.67 63.9 36.1 38.3 3.13

6 1.59 60.9 39.1 55.8 2.49

7 1.51 57.7 42.3 72.7 2.00

8 1.64 62.8 37 .2 61 .7 2.50

9 1.62 61.8 38.2 65 .2 2.60

10 1.69 64.5 35 .5 77.6 2.22 note: specifoc gravity; 2.62. watar absorption

O.oo/ wt

Vth International Brick Masonry Conference

TABLE 5-Experimental Relation Between {3, {3* and F. M. of Fine Aggregate

No. F.M. p(kg ·m') po(kgm')

1 1.00 323 341

2 3.00 246 252

3 4.00 235 239

4 1.87 256 258

5 3.13 238 244

6 2.49 253 262

7 2.00 282 283

8 2.50 247 259

9 2.67 238 247

10 2.22 240 254

note : = 1.5mm/ (kg/ m') 0 0 = 1.5mmj (kg/ cm3 )

T ABLE 6-Grading for Performance Evaluation of Joint Mortar

~ ~0 ~Oj ~'1>

. ~ ~ \e ~,~ .. '" 9' i:>~' .,C; v~ ~ *'1> o