Mortar technology

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected].

Questions? Contact the NRC Publications Archive team at

[email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Mortar technology

Davison, J. I.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=04b0cf72-6009-431c-b336-ef073782b987 https://publications-cnrc.canada.ca/fra/voir/objet/?id=04b0cf72-6009-431c-b336-ef073782b987

National Research

Conseil national

*

Council Canada

de recherches Canada

MORTAR TECHNOLOGY

ANALYZED

by J.I. Davison

Reprinted, with permission, from

Proceedings, First Canadian Masonry Symposium held at the University of Calgary, Calgary, Alberta 7

-

10 June, 1976

p. 12 21

DBR Paper No. 692

La technologie nord-am6ricaine du mortier, qui a 6volu6e durant les dernisres cinquante annses, compte beaucoup sur la technologie du b6ton. Par exemple, la rssistance en compression, une exigence principale dans les spEcifications pour le mortier, est essentielle pour le bgton, un mat6riau structural, mais n'est seulement qu'une du nombre important des propri6t6s du mortier qui a peu de r6sis- tance 2 la traction ou 2 _{la flexion et beaucoup de r6sistance} 5 _la

compression. Les architectes et les ingsnieurs ont de la difficult6 I Etablir un rapport entre plusieurs essais courants sur le mortier et la pratique "in situ". Le besoin existe pour une technologie du mortier qui prendrait en considgration le r81e du mortier dans un mur de maqonnerie et son interaction avec les 616ments de maqon- nerie. La nouvelle technologie devrait aussi ctre suffisamment

flexible pour 6valuer les nouveaux matEriaux apparaissant sur le march6 et faire valoir une apprgciation des avantages de la maqon- nerie. La communication traite de certaines raisons du status quo actuel, comprenant les difficult6s 2 mesurer les propri6tGs du mortier et les alternatives qui en ressortent telles que la mise 5

l'essai par prisme e t les msthodes scandinaves conques pour assor- tir les 616ments de mortier et de maqonnerie compatibles.

MORTAR TECHNOLOGY

J . I . Davison

D i v i s i o n of B u i l d i n g R e s e a r c h

N a t i o n a l R e s e a r c h C o u n c i l , O t t a w a , O n t a r i o

A N A L Y Z E D

Many o f t h e t e s t methods used t o a s s e s s t h e p r o p e r t i e s o f masonry m o r t a r were

o r i g i n a l l y developed a s cement a n d c o n c r e t e t e s t s . They r e f l e c t c o n c r e t e technology t o such an e x t e n t t h a t i t i s n o t u n f a i r t o s u g g e s t t h a t t h e r e i s no r e a l m o r t a r t e c h n o l o g y i n North America. T h i s r e l i a n c e on c o n c r e t e technology i s c o n f u s i n g t o e n g i n e e r s a n d a r c h i t e c t s who do n o t a p p r e c i a t e t h e d i f f e r e n t f u n c t i o n s o f m o r t a r and c o n c r e t e a n d t h u s have d i f f i c u l t y i n r e l a t i n g c u r r e n t m o r t a r p r o c e d u r e s and r e s u l t s t o t h e p e r f o r - mance o f m o r t a r i n a masonry w a l l .

The importance o f a more meaningful m o r t a r technology

i s

becoming e v i d e n t i n t h e wake o f demands f o r a p e r f o r m a n c e - o r i e n t e d s p e c i f i c a t i o n . Such a s p e c i f i c a t i o n w i l l r e q u i r e t e s t p r o c e d u r e s t h a t c a n b e r e l a t e d t o f i e l d p r a c t i c e . The p u r p o s e of t h i s p a p e r i s t o examine t h e development o f t h e c u r r e n t technology and t o c o n s i d e r some a 1 t e r n a t i v e s

.

I

HISTORICAL

The u s e o f b r i c k s and m o r t a r d a t e s back t o t h e b e g i n n i n g o f c i v i l i z a t i o n . Through t h e c e n t u r i e s advances were by t r i a l and e r r o r and t h e " t r a d e " was p a s s e d from genera- t i o n t o g e n e r a t i o n . There was no r e a l technology p r i o r t o t h e s t a r t o f t h i s c e n t u r y .

E a r l y North American r e q u i r e m e n t s f o r m o r t a r s a p p e a r e d i n t h e 1924 Report o f t h e

,

B u i l d i n g Code Committee o f t h e U.S. Department o f Commerce. During t h e l a t e 1 9 3 0 ' s ASTM Committee C-12 s t a r t e d t o d e v e l o p a m o r t a r s p e c i f i c a t i o n , which was f i n a l l y

I p u b l i s h e d a s ~ 2 7 0 ( ' ) i n 1951. T h i s s p e c i f i c a t i o n c o n t a i n e d r e q u i r e m e n t s f o r t h e w a t e r

I

I r e t e n t i v i t y o f p l a s t i c m o r t a r and compressive s t r e n g t h o f h a r d e n e d m o r t a r ; t h e s e

I r e q u i r e m e n t s remain i n c u r r e n t ASTM and CSA s p e c i f i c a t i o n s . I n e a r l y a t t e m ts t o

p r e p a r e t h e s p e c i f i c a t i o n , t h e Committee i d e n t i f i e d n i n e m o r t a r p r o p e r t i e s

r2)

which

1

were t o b e t h e b a s i s o f a performance-type s p e c i f i c a t i o n . Most o f t h e t e s t methods

/

recommended t o a s s e s s t h e s e p r o p e r t i e s had been developed f o r p o r t l a n d cement. T h i s

/

i s n o t s u r p r i s i n g b e c a u s e t h e r e were no m o r t a r t e s t methods and t h e cement i n d u s t r y ,

'

_{c o m p a r a t i v e l y young and a g g r e s s i v e , was h e a v i l y committed t o r e s e a r c h and development}

work. One o f t h e p r o d u c t s emerging a t t h e time was t h e llnew" masonry cement. The

p e r f o r m a n c e - o r i e n t e d d r a f t was r e j e c t e d b e c a u s e a r c h i t e c t s and e n g i n e e r s c o u l d n o t

.

r e l a t e t h e t e s t methods and r e s u l t s t o masonry c o n s t r u c t i o n , and a d r a f t i n c l u d i n g a

- -

p r o p e r t y and a p r o p o r t i o n s p e c i f i c a t i o n was adopted. P r i o r t o p u b l i c a t i o n o f CSA

S p e c i f i c a t i o n A17g0) i n 1967 t h e N a t i o n a l B u i l d i n g Code o f Canada r e f e r e n c e d ASTM C270. The f i r s t e d i t i o n o f A179 was s i m i l a r i n c o n t e n t t o t h e American s p e c i f i c a t i o n . R e c e n t l y some f i e l d t e s t methods have been d e v e l o p e d and p u b l i s h e d a s ASTM T e s t Method C780, Some o f t h e s e t e s t s a r e i n c l u d e d i n t h e 197.5 r e v i s i o n o f t h e CSA s p e c i f i c a t i o n .

FUNCTION OF MORTAR

Any approach t o m o r t a r technology r e q u i r e s a n u n d e r s t a n d i n g o f t h e i n t e r a c t i o n o f m o r t a r and masonry u n i t s , and a knowledge o f t h e f u n c t i o n o f t h e m o r t a r i n t h e w a l l . When a m o r t a r bed i s s p r e a d on a l a y e r o f masonry u n i t s i t immediately s t a r t s t o l o s e w a t e r by s u c t i o n o f t h e a b s o r p t i v e u n i t s and by e v a p o r a t i o n t o t h e a i r from t h e s u r f a c e o f t h e j o i n t s . This c o n t r a s t s w i t h c o n c r e t e which i s p l a c e d i n nonabsorbent m e t a l o r wooden forms i n an e f f o r t t o e n s u r e t h a t a l l t h e w a t e r i s r e t a i n e d .

The f u n c t i o n o f t h e m o r t a r i s t w o - f o l d . F i r s t , i t must p r o v i d e a uniform b e d d i n g s u r f a c e f o r t h e u n i t s . This r e q u i r e s t h a t t h e p l a s t i c m o r t a r must have s a t i s f a c t o r y w o r k a b i l i t y s o t h a t i t w i l l s p r e a d e a s i l y u n d e r t h e i n f l u e n c e o f t h e t r o w e l and flow

i n t o a l l t h e c r e v i c e s o f t h e u n i t s , t h u s c o r r e c t i n g any dimensional i r r e g u l a r i t i e s . Second, t h e m o r t a r b i n d s t h e u n i t s i n t o a m o n o l i t h i c mass. The hardened m o r t a r must p o s s e s s s u f f i c i e n t s t r e n g t h t o h o l d t h e u n i t s t o g e t h e r and e n s u r e adequate d u r a b i l i t y t o r e s i s t t h e d e s t r u c t i v e f o r c e s o f t h e w e a t h e r . The s t r e n g t h t o s u s t a i n l o a d s i n a masonry w a l l i s p r o v i d e d by t h e u n i t s ; t h e m o r t a r i s merely t h e "glue" t h a t h o l d s them t o g e t h e r . T h i s t h e n i s t h e second c o n t r a s t w i t h c o n c r e t e , which i s a s t r u c t u r a l m a t e r i a l i n i t s e l f .

Thus t h e m o r t a r h o l d s t h e u n i t s a p a r t and, a t t h e same t i m e , b i n d s them t o g e t h e r . W o r k a b i l i t y i n p l a s t i c m o r t a r and s t r e n g t h i n h a r d e n e d m o r t a r a r e a s s e s s e d i n s p e c i f i - c a t i o n s on t h e b a s i s o f w a t e r r e t e n t i v i t y and c o m p r e s s i v e s t r e n g t h , n e i t h e r o f which g i v e s a t r u e i n d i c a t i o n o f t h e a b i l i t y o f t h e m o r t a r t o f u l f i l i t s d i v e r s e f u n c t i o n s . PLASTIC MORTAR W o r k a b i Z i ~ .

-

W o r k a b i l i t y i s t h e p r o p e r t y t h a t e n a b l e s a m o r t a r t o s p r e a d , when t r o w e l l e d , i n t o a l l c r a c k s and c r e v i c e s o f t h e u n i t s . T h i s i s n e c e s s a r y . f o r a complete " e x t e n t o f bond," e s s e n t i a l i f t h e w a l l i s t o p r o v i d e a s a t i s f a c t o r y b a r r i e r t o r a i n p e n e t r a t i o n . W o r k a b i l i t y i s a combination o f s e v e r a l p r o p e r t i e s i n c l u d i n g p l a s t i c i t y , c o n s i s t e n c y and c o h e s i o n . Although l a r g e l y d e t e r m i n e d by a g g r e g a t e g r a d i n g and

m a t e r i a l p r o p o r t i o n s , t h e u l t i m a t e w o r k a b i l i t y depends on w a t e r c o n t e n t . I t i s t h e r e s u l t o f t h e r o l l e r b e a r i n g e f f e c t o f t h e a g g r e g a t e p a r t i c l e s l u b r i c a t e d by t h e c e m e n t i t i o u s s l u r r y .

Many t e s t methods have been developed, b u t none a c c u r a t e l y measures workabi l i t y

.

The mason who a s s e s s e s w o r k a b i l i t y by t h e r e s p o n s e o f t h e m o r t a r t o t h e t r o w e l remains t h e b e s t i # g e . Among c u r r e n t t e s t s t h e ASTM flow t a b l e ( 4 ) and t h e S c a n d i n a v i a n

MO- m e t e r measure t h e s p r e a d o f a m o r t a r u n d e r t h e i n f l u e n c e o f a dropping i m p a c t . The cone p e n e t r o m e t e r ( 6 ) and t h e B r i t i s h d r o p p i n g b a l l ( 7 ) t e s t s measure c o n s i s t e n c y .

The flow t a b l e and t h e dropping b a l l t e s t s a r e l a b o r a t o r y p r o c e d u r e s ; t h e MO-meter and t h e cone p e n e t r o m e t e r can b e used i n t h e f i e l d . The flow t a b l e i s w i d e l y u s e d d e s p i t e much c r i t i c i s m . Some c o n f u s i o n r e s u l t s from t h e f a c t t h a t mortars t e s t e d u n d e r c u r r e n t s p e c i f i c a t i o n s a r e mixed t o flow v a l u e s t h a t a r e lower than t h e v a l u e s f o r m o r t a r s mixed on c o n s t r u c t i o n s i t e s . A c o n s i s t e n c y t e s t u s i n g t h e cone penetlometer

.-

i s f i n d i n g i n c r e a s i n g u s e i n m o r t a r t e s t i n g l a b o r a t o r i e s .

I n a s t u d y conducted a t t h e B r i t i s h B u i l d i n g Research S t a t i o n comparing t h e r e s u l t s o f t h e s e t e s t methods w i t h a mason's a s s e s s m e n t o f c o n s i s t e n c y , t h e b e s t

. c o r r e l a t i o n was o b t a i n e d w i t h t h e d r o p p i n g b a l l t e s t . I t was a l s o found t h a t flow v a l u e s f o r d i f f e r e n t m o r t a r s mixed t o t h e same c o n s i s t e n c y g i v e an i n d i c a t i o n o f

w o r k a b i l i t y . T h i s i s i l l u s t r a t e d i n F i g u r e 1 which shows lower flow v a l u e s f o r p l a s t i c

.

m o r t a r s w i t h h i g h lime c o n t e n t t h a n f o r h a r s h m o r t a r s w i t h h i g h cement c o n t e n t . T h i s a

r e l a t i o n can b e f u r t h e r r e f i n e d by a p p l y i n g a c o r r e c t i o n f a c t o r , f o r m o r t a r d e n s i t y a n d / o r a i r e n t r a i n m e n t , t o flow v a l u e s .

Thus, a l t h o u g h w o r k a b i l i t y c a n n o t b e measured by a s i n g l e t e s t method, i t can p o s s i b l y b e measured by a combination o f t e s t s . The c o m p l i c a t i o n o f doing two t e s t s t o d e t e r m i n e one p r o p e r t y e x p l a i n s r e l u c t a n c e t o a c c e p t t h i s approach and t h e s e a r c h

c o n t i n u e s f o r a s i n g l e t e s t method t o measure t h i s e l u s i v e p r o p e r t y .

Water R e t e n t i v i t y .

-

Water r e t e n t i v i t y i s t h e p r o p e r t y t h a t d e t e r m i n e s t h e a b i l i t y o f a m o r t a r t o r e t a i n i t s w o r k a b i l i t y . When m o r t a r i s p l a c e d on a b r i c k i t immediately s t a r t s t o l o s e w a t e r t o t h e b r i c k by s u c t i o n . I t i s i m p o r t a n t t h a t s u f f i c i e n t w a t e r b e r e t a i n e d i n t h e m o r t a r t o e n s u r e s a t i s f a c t o r y w o r k a b i l i t y t o a c h i e v e a good bond when t h e t o p b r i c k i s p l a c e d . Water r e t e n t i o n v a l u e s a r e i n c l u d e d i n m o r t a r s p e c i f i c a - t i o n s .

But good w a t e r r e t e n t i o n i s n o t always d e s i r a b l e . I t i s e s s e n t i a l when m o r t a r i s b e i n g u s e d w i t h h i g h - s u c t i o n b r i c k s o r i f t h e w e a t h e r i s h o t and d r y . I f i t is u s e d w i t h l o w - s u c t i o n b r i c k s d u r i n g c o l d w e a t h e r when f r e e z i n g may o c c u r , i t i s i m p o r t a n t t h a t s u f f i c i e n t w a t e r s h o u l d b e e x t r a c t e d from t h e m o r t a r b e f o r e f r e e z i n g t o minimize I

i t s d e s t r u c t i v e e f f e c t . I n summary, h i g h w a t e r r e t e n t i v i t y i s g e n e r a l l y d e s i r a b l e , b u t t h e r e a r e times when low r e t e n t i v i t y i s e q u a l l y d e s i r a b l e .

The l a b o r a t o r y t e s t

('I

used i n s p e c i f i c a t i o n s t o measure r e t e n t i v i t y was d e s i g n e d t o s i m u l a t e t h e a c t i o n o f b r i c k s u c t i o n e x t r a c t i n g w a t e r from m o r t a r . I t compares t h e f l o w v a l u e f o r a m o r t a r sample, s u b j e c t e d t o vacuum s u c t i o n , w i t h i t s o r i g i n a l v a l u e . During t h e procedure t h e m o r t a r i s moved from t h e flow t a b l e t o a f u n n e l and, a f t e r s u c t i o n , moved back t o t h e flow t a b l e . The e f f e c t on t h e flow v a l u e o f h a n d l i n g t h e m o r t a r i s q u e s t i o n e d . B r i t i s h t e s t m e t h o d s ( 7 ) i n c l u d e a r e t e n t i v i t y t e s t b a s e d on a comparison o f dropping b a l l p e n e t r a t i o n v a l u e s b e f o r e and a f t e r s u c t i o n i s a p p l i e d t o a m o r t a r sample. The s u c t i o n i s a p p l i e d by p l a c i n g e i g h t s h e e t s o f " e x t r a t h i c k w h i t e f i l t e r paper" on t h e sample f o r two minutes.

ASTM C270 d e s c r i b e s a c o n s i s t e n c y r e t e n t i o n t e s t u s i n g t h e cone p e n e t r o m e t e r . No w a t e r i s e x t r a c t e d from t h e sample i n t h i s t e s t ; i t i s s i m p l y a measure o f r e t e n t i v i t y . - a t d i f f e r e n t i n t e r v a l s a f t e r t h e m o r t a r h a s been mixed. I t i s a f i e l d t e s t u s i n g a

l a r g e r sample t h a n t h a t used i n t h e B r i t i s h t e s t . A combination o f t h e s e c o n s i s t e n c y r e t e n t i o n t e s t s would p r o v i d e a c r e d i b l e a l t e r n a t i v e t o t h e p r e s e n t t e s t .

I n a n o t h e r approach t o r e t e n t i v i t y , B r i t i s h and S c a n d i n a v i a n t e s t s measure t h e amount o f w a t e r e x t r a c t e d from m o r t a r samples by f i l t e r p a p e r and b r i c k s , r e s p e c t i v e l y . These t e s t s have p a r t i c u l a r v a l u e i n a s s e s s i n g t h e c o m p a t i b i l i t y o f d i f f e r e n t b r i c k - m o r t a r c o m b i n a t i o n s .

Time

of

S e t .

- The time r e q u i r e d f o r a masonry m o r t a r t o s e t i s i m p o r t a n t t o t h e masonry c o n t r a c t o r

-

h e h a s t o know i t s "working l i f e . ' ' The s e t t i n g c h a r a c t e r i s t i c s o f cements a r e w e l l known and t h e r e a r e t e s t s methods i n cement and masonry cement

s p e c i f i c a t i o n s . Lime c u r e s much more s l o w l y t h a n cement a n d t h e w o r k i n g l i f e o f c e m e n t - l i m e m o r t a r s i s t h e r e f o r e a compromise between t h e d i v e r s e p r o p e r t i e s o f t h e s e

two m a t e r i a l s . The p r o v i s i o n s f o r r e t e m p e r i n g i n m o r t a r s p e c i f i c a t i o n s a p p e a r a d e q u a t e t o c o n t r o l t h e s e t t i n g t i m e .

Air Entrainment.

-

The u s e o f a i r e n t r a i n m e n t i n m o r t a r s i s c o n t r o v e r s i a l . I n most p o r t l a n d cement-lime m o r t a r s a i r c o n t e n t l e v e l s a r e minimal a n d a r e n o t a m a t t e r o f

c o n c e r n , b u t some h y d r a t e d l i m e s a n d a l l masonry cements c o n t a i n a i r - e n t r a i n i n g a g e n t s . -

A i r e n t r a i n m e n t adds w o r k a b i l i t y t o h a r s h masonry c e m e n t s ; t h e s m a l l a i r b u b b l e s p r o v i d e t h e r o l l e r b e a r i n g e f f e c t t h a t lime a d d s t o c e m e n t - l i m e m o r t a r s . The improved d u r a b i l i t y o f c o n c r e t e c o n t a i n i n g e n t r a i n e d a i r i s w e l l known and t h e r e a r e o f t e n s u g g e s t i o n s t h a t a i r h a s t h e same b e n e f i c i a l e f f e c t on m o r t a r s . Although t h e improved d u r a b i l i t y o f m o r t a r w i t h m o d e r a t e a i r c o n t e n t s can r e a d i l y b e s u b s t a n t i a t e d , t h e e x c e l l e n t performance, t h r o u g h - t h e y e a r s , o f w e l l d e s i g n e d a n d c o n s t r u c t e d masonry s t r u c t u r e s i s e v i d e n c e o f t h e a d e q u a t e d u r a b i l i t y o f m o r t a r s w i t h n o e n t r a i n e d a i r . On t h e o t h e r h a n d , m o r t a r s t r e n g t h i s a d v e r s e l y a f f e c t e d by i n c r e a s i n g a i r c o n t e n t a s i s c o m p r e s s i v e s t r e n g t h ( F i g u r e 2 ) . Bond s t r e n g t h , t o o , i s r e d u c e d as a i r c o n t e n t s i n c r e a s e . I f t h e m o r t a r l a y e r i n t e r f a c i n g a masonry u n i t c o n t a i n s numerous t i n y a i r b u b b l e s t h e c o n t a c t b e t w e e n m o r t a r a n d u n i t w i l l b e less t h a n c o m p l e t e a n d t h e bond s t r e n g t h w i l l b e r e d u c e d a s t h e amount o f a i r i n t h e m o r t a r i s i n c r e a s e d . T h i s i s a m a t t e r o f r e a l c o n c e r n .

% e r e a r e a number o f good t e s t

method^(^,^)

f o r d e t e r m i n i n g a i r c o n t e n t b u t u n f o r t u n a t e l y t h e r e a r e no l i m i t s p r e s c r i b e d i n t h e

ASTM

a n d CSA s p e c i f i c a t i o n s , r e f l e c t i n g t h e l a c k o f a r e l i a b l e bond s t r e n g t h t e s t method t h a t c a n p r o d u c e d a t a n e e d e d t o e s t a b l i s h maximum t o l e r a b l e l i m i t s . Masonry cement s p e c i f i c a t i o n s c o n t a i n maximum and minimum l i m i t s , b u t t h e s e do n o t e n s u r e s a t i s f a c t o r y l e v e l s i n m o r t a r s where s u c h f a c t o r s a s a g g r e g a t e g r a d a t i o n , c o n t a m i n a n t s and e x c e s s i v e m i x i n g t i a l e c a n c a u s e e x c e s s i v e l y h i g h a i r c o n t e n t s . I t i s hoped t h a t bond s t r e n g t h t e s t methods r e c e n t l y d e v e l o p e d a n d / o r a i r c o n t e n t d a t a from t h e f i e l d w i l l s o o n r e s o l v e t h e p r o b l e m o f e s t a b l i s h i n g r e a l i s t i c maximum a i r c o n t e n t v a l u e s . HARDENED MORTAR Covpressive S t r e n g t h . - The u s e o f c o m p r e s s i v e s t r e n g t h v a l u e s a s t h e a c c e p t a n c e - - r e j e c t i o n c r i t e r i o n i n m o r t a r s p e c i f i c a t i o n s i s q u e s t i o n e d f o r r e a s o n s t h a t a r e w e l l documented. A s n o t e d p r e v i o u s l y t h e c o m p r e s s i v e s t r e n g t h o f a masonry w a l l i s d e r i v e d m a i n l y froin t h e masonry u n i t s ; t h e s t r e n g t h o f t h e m o r t a r i s o f l e s s i m p o r t a n c e . T h i s i s i l l u s t r a t e d i n F i g u r e 3 from t h e work o f Davey and Thomas(') a t t h e B r i t i s h Bui 1 d i n g Research S t a t i o n .

1 s b e r n e r ( ' ) s u g g e s t s t h a t c o m p r e s s i v e s t r e n g t h v a l u e s f o r 2 - i n . cubes do n o t a p p r o a c h t h e s t r e n g t h a c h i e v e d i n m o r t a r j o i n t s i n masonry w a l l s . S t r e n g t h v a l u e s v a r y w i t h m o r t a r c o m p o s i t i o n , t h e s h a p e o f t h e sample a n d t h e method o f c u r i n g , a s i l l u s t r a t e d i n F i g u r e 4 where v a l u e s f o r samples 2 i n . s q u a r e a n d 2, 1, 1 / 2 a n d 3 / 8 i n . t h i c k a r e shown f o r Types S a n d N m o r t a r s . The l a r g e i n c r e a s e i n s t r e n g t h f o r t h e t h i n samples s h o u l d b e n o t e d . The i n c r e a s e a s t h e t h i c k n e s s was r e d u c e d from 1 / 2 t o 3 / 8 i n . p r o b a b l y r e f l e c t s t h e d i f f e r e n c e i n c u r i n g more t h a n t h e r e d u c t i o n i n t h i c k n e s s The 3 / 8 - i n . sample was c u t from 3 m o r t a r bed c u r e d between b r i c k s , which r e d i ~ c c d t h e

w a t e r : c e m e r ~ t r a t i o a n d t h e r e b y i n c r e a s e d t h e c o m p r e s s i v e s t r e n g t h , c o n ~ p a r e d w i t h t h e l a r g e r samples molded i n m e t a l molds a n d c u r e d i n w a t e r o r m o i s t a i r .

I t h a s a l s o been shown t h a t t h e f a i l u r e o f masonry w a l l s , under compressive l o a d i n g , i s by v e r t i c a l t e n s i l e s p l i t t i n g ; t h i s i s i l l u s t r a t e d i n F i g u r e 5 from work done a t t h e Brick I n s t i t u t e o f ~ m e r i c a . ( " ) F i g u r e 6 i l l u s t r a t e s t h a t m o r t a r cubes f a i l i n a s i m i l a r manner u n d e r compressive l o a d i n g .

The u s e o f compressive s t r e n g t h i n s p e c i f i c a t i o n s r e f l e c t s t h e f a c t t h a t t h e t e s t i s s i m p l e and t h e v a l u e s c a n b e r e l a t e d t o o t h e r p r o p e r t i e s o f m o r t a r . But t h e t e s t

. method does n o t r e f l e c t masonry p r a c t i c e . The cubes a r e c a s t i n nonabsorbent metal

1

- molds and a r e c u r e d i n w a t e r o r m o i s t a i r ; i n p r a c t i c e m o r t a r s a r e c a s t between j a b s o r b e n t u n i t s and t h e y s t a r t t o l o s e w a t e r t o t h e u n i t s a s soon a s c o n t a c t i s made. I

I

B r i t i s h and S c a n d i n a v i a n t e s t methods a r e more r e a l i s t i c i n terms o f masonry p r a c t i c e . T e s t Prisms (25 by 25 by 100 mm) a r e c a s t i n molds and s u b j e c t e d t o s u c t i o n by p l a c i n g t h e molds o f p l a s t i c m o r t a r between l a y e r s o f f i l t e r o r b l o t t i n g p a p e r .

Bond

S t r e n g t h .

-

The s t r e n g t h and e x t e n t o f bond w i t h masonry u n i t s a r e t h e most i m p o r t a n t r o p e r t i e s o f m o r t a r a s t h e y d e t e r m i n e t h e u l t i m a t e d u r a b i l i t y o f masonry. Hogberg ( ' l P s u g g e s t s t h a t t h e f i n a l bond between m o r t a r and b r i c k i s determined t h e moment t h e y make c o n t a c t . The b e s t t e s t f o r e x t e n t o f bond i s t o remove a b r i c k from

t h e m o r t a r bed s h o r t l y a f t e r i t h a s been p l a c e d . The p a t t e r n o f f r e s h m o r t a r a d h e r i n g t o t h e b r i c k w i l l i n d i c a t e t h e e x t e n t of bond. (This i s n o t a v e r y s c i e n t i f i c t e s t -

b u t a very e f f e c t i v e one

-

performed a t a time when t h e w o r k a b i l i t y o f t h e m o r t a r can b e a 1 te r e d w i t h minimum d e l a y and c o s t . ) Many bond s t r e n g t h t e s t s have been developed b u t none h a s g a i n e d a c c e p t a n c e . The

ASTM

c r o s s e d b r i c k c o u p l e t t e s t ( ' * ) and

Kuenning's improved method f o r t e n s i l e bond t e s t i n g ( 3 , a r e r e c o g n i z e d methods b u t

t h e r e a r e problems i n o b t a i n i n g c o n s i s t e n t l y r e p r o d u c i b l e r e s u l t s . The S c a n d i n a v i a n s use t h e Hinderson method, ( 5 ) a d a p t e d from a t e s t t o measure p l a s t e r a d h e s i o n . B r i c k

c o u p l e t s a r e c a s t w i t h a l a y e r o f gauze between t h e t o p b r i c k and t h e m o r t a r bed. A f t e r t h e c u r i n g p e r i o d t h e t o p b r i c k i s e a s i l y removed, a d i s c - s h a p e d sample i s

i s o l a t e d from t h e m o r t a r b e d w i t h a c i r c u l a r d r i l l , a metal p l a t e i s f a s t e n e d t o t h e sample w i t h an epoxy and i t $s t h e n p u l l e d from t h e b r i c k w i t h a h y d r a u l i c pump. T h i s method r a t e s some c o n s i d e r a t i o n . T!le new ASTM ~ 5 1 8 ( " ) F l e x u r a l Bond S t r e n g t h T e s t i s a l s o p r o m i s i n g . I t d e s c r i b e s a t e s t on stack-bonded p r i s m s a t l e a s t 18 i n . h i g h w i t h e i t h e r 3 - p o i n t o r uniform l o a d i n g . The use o f t h e t e s t w i l l b e somewhat r e s t r i c t e d by t h e r e q u i r e m e n t f o r a l a r g e s i z e t e s t i n g machine, b u t i t i s hoped t h a t i t w i l l p r o v i d e some r e p r o d u c i b l e d a t a t h a t w i l l h e l p e s t a b l i s h limits f o r a i r c o n t e n t a s w e l l a s bond s t r e n g t h

.

FZexumZ S t r e n g t h .

-

F l e x u r a l s t r e n g t h , r e q u i r e d t o r e s i s t t h e l a t e r a l l o a d i n g of

--

masonry w a l l s , a l s o depends on t h e s t r e n g t h o f t h e bond between m o r t a r and u n i t s . Palmer and P a r s o n s ( 1 5 ) found t h a t t h e f l e x u r a l s t r e n g t h o f b r i c k beams was l e s s than t h a t o f e i t h e r m o r t a r o r t h e b r i c k s , i . e . , t h e i n f l u e n c e o f bond' s t r e n g t h was t h e :-predominant f a c t o r . B r i t i s h and S c a n d i n a v i a n methods p e r m i t compressive and f l e x u r a l

t e s t s on t h e same m o r t a r p r i s m .

' T e n s i l e S t r e n g t h .

-

T e n s i l e s t r e n g t h s a r e much lower t h a n compressive and f l e x u r a l s t r e n g t h s ( t h e y a r e o f t h e o r d e r o f one- t e n t h o f compressive v a l u e s , ) and, a s n o t e d p r e v i o u s l y , m o r t a r f a i l u r e s a r e u s u a l l y i n t e n s i o n . Thus s t r e s s e s and s t r a i n s t h a t develop i n t h e masonry can b e r e l i e v e d by c r a c k s i n t h e m o r t a r b e d s where t h e y a r e e a s i e s t t o r e p a i r . T h i s i s one o f t h e r e a s o n s f o r t h e s u c c e s s f u l performance of masonry s t r u c t u r e s t h r o u g h t h e y e a r s . The many minute c r a c k s t h a t developed i n t h e

low s t r e n g t h m o r t a r s were t o o s m a l l t o p e r m i t s e r i o u s r a i n p e n e t r a t i o n and t h e y were " s e l f - h e a l i n g " by a mechanism whereby lime, c a r r i e d i n s o l u t i o n by w a t e r permeating t h e masonry, e v e n t u a l l y f i l l e d t h e c r a c k s a s t h e w a t e r e v a p o r a t e d . The s t r o n g e r

niort;lrs, wi tll h i g h e r t c n s i l c s t r - c ~ ~ g t l i s , usccl i 11 cot1 tclapor;1ry ~ o ; l s o ~ i r y , a r c 11ot c ; I ~ ) : I ~ I I ('

o f a b s o r b i n g s t r e s s e s i n t h i s mnnrier a n d , a s :I rcsirl t , Itlrgc ~ t - a c k s C V C \ I I ~ L I : I I Iy oci-111.

and p r o v i d e open p a t h s f o r r a i n p e n e t r a t i o n . The p l a c e o f t e n s i l e s t r e n g t h i n m r t a r

t e c h n o l o g y s h o u l d n o t b e o v e r l o o k e d ; t h e use o f low t e n s i l e s t r e n g t h m o r t a r s i n t h e

r i g h t a p p l i c a t i o n h a s a d v a n t a g e s . There a r e s i m p l e t e s t methods f o r i t s d e t e r m i n a t i o n .

Other Properties.

- When t h e ASTM m o r t a r s p e c i f i c a t i o n was b e i n g d r a f t e d i t was d e c i d e d t h a t soundness was a f u n c t i o n o f t h e c o n s t i t u e n t m a t e r i a l s and t h a t t e s t methods s h o u l d

b e developed and i n c l u d e d i n t h e r e s p e c t i v e s p e c i f i c a t i o n s . A s i n t h e c a s e o f a i r

c o n t e n t t h i s i s no g u a r a n t e e t h a t m o r t a r s c o n t a i n i n g t h e s e materia1.s w i l l perform

s a t i s f a c t o r i l y . A s new m a t e r i a l s become a v a i l a b l e i t w i l l become more i m p o r t a n t t o

have a t e s t method t o measure s o u n d n e s s i f m o r t a r f a i l u r e s r e s u l t i n g from t h e u s e o f i n c o m p a t i b l e m a t e r i a l s a r e t o b e p r e v e n t e d .

Absorption v a l u e s f o r masonry m o r t a r s a r e o f v a l u e i n p r e d i c t i n g w a t e r p e n e t r a t i o n

t e n d e n c y and d u r a b i l i t y . A b s o r p t i o n can b e p r e d i c t e d from c o m p r e s s i v e s t r e n g t h v a l u e s -

u s u a l l y a s s t r e n g t h i n c r e a s e s t h e a b s o r p t i o n d e c r e a s e s . And t h e r e a r e a l s o s i m p l e t e s t

methods f o r measuring a b s o r p t i o n . P a r t i c l e s i z e and p o r e d i s t r i b u t i o n s t u d i e s c o u l d b e

used t o p r e d i c t a v a r i e t y o f p r o p e r t i e s , i n c l u d i n g a b s o r p t i o n , b u t t h e s e would i n v o l v e l a b o r a t o r y t e c h n i q u e s t h a t might b e d i f f i c u l t t o a d a p t f o r s p e c i f i c a t i o n p u r p o s e s .

Mortars may c o n t r i b u t e t o e f f l o r e s c e n c e on masonry w a l l s , b e c a u s e o f t h e a l k a l i i n t h e i r cement c o n t e n t . T h e i r e f f l o r e s c i n g tendency w i t h a s t a n d a r d c e r a m i c r e f e r e n c e o r

a p a r t i c u l a r b r i c k , c a n b e measured by a wick t e s t . ( 1 6 ) T h i s method i s n o t u s e d , how-

e v e r , a s r e s u l t s a r e a s s e s s e d by v i s u a l o b s e r v a t i o n and c a n t h u s l e a d t o d i f f e r e n c e s o f

o p i n i o n . I n a p o l l u t i o n - c o n s c i o u s world t h e i n c i d e n c e o f e f f l o r e s c e n c e w i l l p r o b a b l y

i n c r e a s e a s s t a c k e m i s s i o n s from cement p l a n t s a r e c u t back and more o f t h e c o n t a -

minants f i n d t h e i r way back i n t o t h e cement. I t i s t h e r e f o r e o f some i m p o r t a n c e t o

d e v e l o p an a c c e p t a b l e t e s t method t o measure t h e e f f l o r e s c i n g t e n d e n c i e s o f m o r t a r s .

PROBLEMS

There a r e many v a r i a b l e s i n m o r t a r r e s e a r c h . The c e m e n t i t i o u s m a t e r i a l s - lime

and cement

-

can have v a r i a b l e c o n t e n t s . The chemical and p h y s i c a l p r o p e r t i e s o f t h e

masonry u n i t s w i t h which m o r t a r s a r e t e s t e d , p a r t i c u l a r l y c l a y b r i c k s , can a l s o v a r y

c o n s i d e r a b l y . I t i s v e r y d i f f i c u l t t o o b t a i n r e p r o d u c i b l e r e s u l t s w i t h t h e s e m a t e r i a l s

under t h e most i d e a l c o n d i t i o n s .

The human v a r i a b l e s a r e many and d i f f i c u l t t o c o n t r o l . I n c l u d e d i n t h e s e a r e

d i f f e r e n c e s i n t h e i n t e r p r e t a t i o n o f t e s t methods and d i f f e r e n t l e v e l s i n t h e p e r f o r -

mance o f t e s t equipment. T h e r e a r e a l s o v a r i a t i o n s i n some t e s t methods; f o r example,

t h e w a t e r r e t e n t i v i t y t e s t d e s c r i b e d i n lime s p e c i f i c a t i o n s v a r i e s from t h e one d e s c r i b e d i n m o r t a r and cement s p e c i f i c a t i o n s .

Some o b s e r v e r s q u e s t i o n t h e c r e d i b i l i t y o f m o r t a r t e s t methods i n v o l v i n g

i n d i v i d u a l u n i t s o r s m a l l p r i s m s . Such methods- have a d e c i d e d economic a d v a n t a g e o v e r '

c o s t l y t e s t s u s i n g l a r g e p a n e l s . I n t h e f i n a l a n a l y s i s c o s t i s a major f a c t o r . There

i s a danger t h a t s o p h i s t i c a t e d t e s t methods may b e t o o e x p e n s i v e f o r t h e i n d u s t r y .

A performance o r i e n t e d m o r t a r s p e c i f i c a t i o n w i l l r e q u i r e c r i t e r i a and t e s t methods

T h e r e a r e no r e l i a b l e t e s t s t o measure t h e most i m p o r t a n t m o r t a r p r o p e r t i e s : t h e w o r k a b i l i t y o f p l a s t i c m o r t a r and t h e bond s t r e n g t h between h a r d e n e d m o r t a r and

masonry u n i t s ,

The w a t e r r e t e n t i v i t y t e s t is o f q u e s t i o n a b l e v a l u e . O t h e r methods f o r measuring

r e t e n t i o n o f c o n s i s t e n c y may b e more c r e d i b l e .

The u s e o f compressive s t r e n g t h as t h e a c c e p t a n c e - r e j e c t i o n c r i t e r i o n i n

s p e c i f i c a t i o n s i s q u e s t i o n a b l e . U n t i l a r e l i a b l e bond s t r e n g t h t e s t i s developed,

t h e compressive s t r e n g t h t e s t

i s

t h e b e s t a l t e r n a t i v e . The p r e s e n t t e s t method would

b e more a c c e p t a b l e i f i t i n c l u d e d p r o c e d u r e s r e l a t e d t o masonry p r a c t i c e .

R e s u l t s o f t e s t methods i n s p e c i f i c a t i o n s f o r c e m e n t i t i o u s m a t e r i a l s s h o u l d n o t b e r e l i e d upon t o p r e d i c t t h e performance o f m o r t a r s .

The economics o f masonry s h o u l d b e a major c o n s i d e r a t i o n i n m o r t a r r e s e a r c h . The aim s h o u l d b e t o develop s i m p l e t e s t p r o c e d u r e s t h a t w i l l p r o v i d e a c c e p t a b l e r e s u l t s .

APPENDIX

-

REFERENCES

( ') S t a n d a r d S p e c i f i c a t i o n f o r Mortar f o r U n i t Masonry, ASTM C270-51T.

( 2 ) A P r e l i m i n a r y C o n s i d e r a t i o n o f Some Proposed Methods o f Sampling and T e s t i n g Mortar f o r Unit Masonry, ASTM B u l l e t i n , October 1938, pp. 40-46.

( 3 ) Mortar and Grout f o r U n i t Masonrv. CSA S t a n d a r d A179-1967.

Masonry Cement, CSA S t a n d a r d A8- 1970.

( 5 ) "Winter Masonry," B u i l d i n g Technology and Community Development P u b l i c a t i o n 1,

The T e c h n i c a l Research C e n t e r o f F i n l a n d , H e l s i n k i , 19 72.

( 6 ) S t a n d a r d Method f o r P r e c o n s t r u c t i o n and C o n s t r u c t i o n E v a l u a t i o n of Mortars f o r

P l a i n and R e i n f o r c e d U n i t Masonry, ASTM C780-74.

(

'I Methods o f T e s t i n g M o r t a r s , B r i t i s h S t a n d a r d 4551 : 1970.

('I Davey, N . and Thomas, F.G. "The S t r u c t u r a l Uses o f Brickwork." S t r u c t u r a l and

~ u i l d i n ~ paper No. 24, I n s t i t u t i o n o f C i v i l E n g i n e e r s o f G r e a t ~ r i t a i n , London:

The I n s t i t u t i o n 1950.

-- _{I s b e r n e r , A l b e r t} W . " S p e c i f i c a t i o n s and S e l e c t i o n o f M a t e r i a l s f o r Elasonry

Mortars and Grouts," Research a n d Development B u l l e t i n RD024.01M, P o r t l a n d

Cement A s s o c i a t i o n , Skokie, I l l i n o i s .

( l o ) T e c h n i c a l Note 39A, J u l y / A u g u s t 1975, Brick I n s t i t u t e o f America, McLean, V i r g i n i a

(

'

l) HSgberg, E r i k . "Mortar Bond," Report 40: 1967, N a t i o n a l Swedish I n s t i t u t e f o r

B u i l d i n g Research, Stockholm.

( 12) S t a n d a r d Method o f T e s t f o r Bond S t r e n g t h of Mortar t o Masonry U n i t s .

(' 3 , Kuenning,

W.H.

"Improved Method o f T e s t i n g T e n s i l e Bond S t r e n g t h o f Masonry

Mortars." ASTM J o u r n a l o f M a t e r i a l s , Vol. 1, 1966, p . 180.

(I4) Standard Methods of T e s t f o r F l e x u r a l Bond S t r e n g t h o f Masonry, ASTM E518-74.

(I5) Palmer, L . A . and Parsons, D . A . "A Study o f P r o p e r t i e s o f Mortars and Bricks and -

T h e i r R e l a t i o n t o Bond." J o u r n a l o f ~ e s e a r c h , -N a t i o n a l Bureau o f S t a n d a r d s ,

Washington, Vol. 12, May 1934, pp. 609-644.

(I6) R i t c h i e , T. "Study of E f f l o r e s c e n c e Produced on Ceramic Wicks by Masonry Mortar." J o u r n a l American Ceramic S o c i e t y , Vol. 38, No. 10, 1955, pp. 362-366.

This paper i s a c o n t r i b u t i o n from t h e D i v i s i o n o f B u i l d i n g Research, National

Research Council of Canada and i s published w i t h t h e approval of t h e D i r e c t o r of

t h e D i v i s i o n .

80' I 1 I I I 1 I

Type M Type S TypeN Type 0 Type K Type L

2 0 % L 3 4 % L 50%L 66%L 75%L IOO%L

8O%C 6 6 % C 50%C 3 4 % C 25%C

PROPORTION OF CEMENT 8 LIME IN MORTAR

FIGURE I

FLOW VALUES FOR MORTARS M I X E D TO I O M M

CONSISTENCY

A I R CONTENT, %

FIGURE 2

EFFECT OF AIR CONTENT ON COMPRESSIVE

0 C 2 0 C 4 0 C 6 0 C 8 0 C 1 0 0 C 100 L 8 0 L 6 0 L 40 L 2 0 L 0 L

PROPORTION OF CEMENT [C): L I M E [ L ) IN MORTAR ( C t L ) :SAND= I:3 BY VOLUME

FIGURE 3

MORTAR COMPOSITION AND STRENGTH IN RELATION TO STRENGTH OF BRICKWORK

THICKNESS OF SAMPLE, IN.

FIGURE 4

EFFECT OF SPECIMEN THICKNESS ON COMPRESSIVE STRENGTH

F i g u r e 5 . S o l i d b r i c k compressive p r i s m - t e n s i l e s p l i t t i n g f a i l u r e . ( C o u r t e s y Brick I n s t i t u t e o f America)

F i g u r e 6 . T e n s i l e s p l i t t i n g f a i l u r e o f m o r t a r cube under compressive l o a d .