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Sealing of joints in construction
Walter, A. H.; National Research Council of Canada. Division of Building
Research
P R E F A C E
T h e development of industrialized building s y s t e m s in Europe
h a s g r e a t l y i n c r e a s e d the u s e of prefabricated wall e l e m e n t s . This
development h a s not been without i t s p r o b l e m s and one that h a s r e -
sulted in extensive investigation i s the sealing of the joints between
l a r g e wall components. Traditional m a t e r i a l s w e r e not able t o
withstand t h e s t r e s s e s imposed by dimensional changes in t h e panels
after prolonged exposure t o the weather.
T o overcome t h i s problem a number of s e a l a n t s of different
types have been introduced
toprovide the r e q u i r e d s e r v i c e life and
much attention h a s been given t o the design of the joint and t h e b e s t
configuration of the sealant.
This t r a n s l a t i o n d e s c r i b e s the various s e a l a n t s that a r e now
available in Sweden and the way in which they should be u s e d for
maximum s e r v i c e life. S e v e r a l c a s e h i s t o r i e s a r e included t o i l l u s -
t r a t e t h e r e s u l t s of i m p r o p e r joint design.
With the introduction of new building s y s t e m s in Canada,
many of which u s e l a r g e p r e c a s t c o n c r e t e e l e m e n t s , t h e Division of
Building R e s e a r c h h a s a keen i n t e r e s t in s t a t e - o f - t h e - a r t r e p o r t s
s u c h a s t h i s paper by Alexander H. Walter of Malm6, Sweden.
T h e Division wishes t o thank M r . D. A. S i n c l a i r , National
Science L i b r a r y , National R e s e a r c h Council of Canada, for t r a n s l a t i n g
t h i s paper and M r .
G. H.
Kuester of this Division who checked t h e
t r a n s l a t i o n .
Ottawa
M a r c h 1970
N. B. Hutcheon
D i r e c t o r .
NATIONAL RESEARCH COUNCIL OF C A N A D A T e c h n i c a 1 T r a n s l a t i o n
1 4
10 T i t l e : S e a l i n g o f j o i n t s i n c o n s t r u c t i o n ( V e r s i e g e l u n g von Fugen am B a u ) A u t h o r : A l e x a n d e r H . W a l t e r R e f e r e n c e : B a u w e l t , 60 ( 2 ) : 6 0 - 6 5 , 1969 T r a n s a l t o r : D . A . S i n c l a i r , T r a n s l a t i o n s S e c t i o n , N a t i o n a l S c i e n c e L i b r a r ySElALING O F JOINTS IN CONSTRUCTION
T h e sealing of expansion joints h a s become m o r e and m o r e important in p r e c a s t construction i n r e c e n t y e a r s . At t h e begin- ning of t h e 50's t h e s e p r o b l e m s w e r e given l e s s attention and b u i l d e r s w e r e s a t i s f i e d with t h e application of t r a d i t i o n a l jointing p l a s t e r , o r pos,sibly p l a s t i c jointing s u b s t a n c e s . About 1955 a change began t o t a k e p l a c e in t h e qualitative choice of s e a l i n g m a t e r i a l s , a s a consequence of n u m e r o u s f a i l u r e s .
1. F o r e w o r d
A s a r e s u l t of e x p e r i e n c e in t h e a i r c r a f t and shipbuilding i n d u s t r i e s , w h e r e the s e a l i n g of joints had become a m a t t e r of vital i m p o r t a n c e , s e a l i n g m a t e r i a l s with s o - c a l l e d e l a s t i c p r o p e r t i e s , despite t h e i r c o m p a r a t i v e l y high p r i c e , began t o b e u s e d m o r e and m o r e . Although t h i s m a d e p o s s i b l e g r e a t e r s a f e t y in the s e a l i n g of joints, it was n e v e r t h e l e s s found t h a t t h e attainment of t h i s goal depends not only on t h e a p p l i c a - tion of a n excellent s e a l i n g m a t e r i a l , but a l s o on o t h e r i m p o r t a n t f a c t o r s .
T h e specific p r o p e r t i e s of t h e s e a l i n g m a t e r i a l , t h e design and moving function of t h e joint unit, t h e s u r f a c e quality of t h e edges of t h e joints, the n a t u r e and m a n n e r of application and a knowledge of the s t r e s s e s t o which t h e s e a l i n g m a t e r i a l is s u b j e c t e d in t h e joint, constitute a single complex within which a s a t i s f a c t o r y solution t o each s e p a r a t e p r o b l e m m u s t be found.
In what follows, a s u r v e y of t h e e n t i r e question will be made. We s h a l l devote o u r s e l v e s m a i n l y t o a d e s c r i p t i o n of solutions which h a v e led t o s a t i s f a c t o r y p r a c t i c a l r e s u l t s . T h i s does not m e a n , however, t h a t other solutions might not lead t o equally good o r even b e t t e r r e s u l t s . T h e l i m i t e d m e a s u r a b i l i t y of t h e quality of a joint s i m p l y does not p e r m i t t h e value o r t h e quality t o be e x p r e s s e d in definite f i g u r e s ; one m u s t build on e x p e r i e n c e and r e l y on s a f e solutions.
F r o m t h e author's point of view, of c o u r s e , t h e p r o p e r t i e s of t h e s e a l i n g m a t e - r i a l s constitute t h e c e n t r a l p r o b l e m . I m u s t point out, however, that t h e b e s t of m a t e - r i a l s will f a i l if t h e joint itself i s badly designed and t h e r e q u i r e m e n t s of good w o r k - manship a r e neglected. H e r e , a s in m o s t advanced technological f i e l d s , i t is n e c e s s a r y f o r d e s i g n e r s , c h e m i s t s and j o i n t e r s t o c o o p e r a t e in a logical m a n n e r .
T h e r e i s a n o t h e r d i s c o v e r y t h a t s e e m s t o b e i m p o r t a n t , n a m e l y t h a t i n t h e c h e m i c a l d e s c r i p t i o n of p r o d u c t s it is g e n e r a l l y n e c e s s a r y t o d i v i d e t h e n ] i n t o d i f f e r e n t c l a s s e s a c c o r d i n g t o t y p e . F o r e x a m p l e , we t a l k of p o l y s u l p h i d e , a c r y l a t e , s i l i c o n a n d butyl m a t e r i a l s , o r t h e s e a l i n g m a t e r i a l s a r e d i v i d e d i n t o p r o d u c t s with e l a s t i c o r p l a s
-
t i c p r o p e r t i e s . T h i s c l a s s i f i c a t i o n , e s p e c i a l l y w h e n i t c o n t r i b u t e s t o a q u a l i t a t i v e i d e n t i f i c a t i o n , m a y e a s i l y l e a d t o e r r o n e o u s r e s u l t s . Within e a c h c l a s s t h e r e a r e p r o - d u c t s w i t h q u a l i t a t i v e l y d i f f e r e n t p r o p e r t i e s and t h e s e a r e t h e n u s e d , g e n e r a l l y s p e a k i n g , f o r d i f f e r e n t a p p l i c a t i o n s , o r t h e r e a r e d i f f e r e n c e s f r o m t h e s t a n d p o i n t of e c o n o m y . J u s t a s t h e r e a r e p o l y s u l p h i d e m a t e r i a l s which c a n n o t b e r e c o n ~ n ~ e n d e d f o r t h e s e a l i n g of j o i n t s in p r e c a s t c o n s t r u c t i o n , s o t h e r e a r e butyl m a t e r i a l s w h i c h i n c e r t a i n c a s e s I n a y g i v e v e r y s a t i s f a c t o r y r e s u l t s . T h e u n a v o i d a b l e c l a s s i f i c a t i o n [ n u s t t h e r e - f o r e b e r e f e r r e d t o t h e a c t u a l f i e l d of a p p l i c a t i o n . T h e r e f o r e , when I m e n t i o n t h e u s e f u l n e s s o r t h e l i n ~ i t e d a p p l i c a b i l i t y of c e r t a i n c l a s s e s , t h i s a p p l i e s s o l e l y t o t h e s e a l i n g of e x p a n s i o n j o i n t s in ~ ) l . t ~ c . , ~ s t c o n s t r c ~ c t ion and it i s a s s u m e d , m o r e o v e r , t h a t t h e s p e c i f i c p r o d u c t of t h i s c l a s s which i s m e n t i o n e d i s s u i t e d t o t h e s p e c l a 1 r e q u i r e n ~ e n t s of t h i s a p p l i c a t i o n . T h e s t a t e m e n t s m a d e i n t h i s c o n n e c t i o n a r e b a s e d on t h e k n o w l e d g e t h a t h a s b e e n d e r i v e d p r i m a r i l y f r o n ~ p r a c t i c a l e x p e r i e n c e . 2. T h e d e s i g n of t h e joint F i g u r e 1 s h o w s t h e c o r r e c t d e s i g n of a n e x p a n s i o n joint. A c c o r d i n g l y , i t c o m p r i s e s t w o s t r u c t u r a l c:lenlents a d j a c e n t t o o n e a n o t h e r . T h e s p a n b e t w e e n t h e s t r u c t u r a l u n i t s i s c a l l e d t h e a n ~ p l i t u c l e ( o r width) of t h e joint. T h e joint i s p a r t i a l l y f i l l e d by t h e s e a l i n g m a t e r i a l .2. 1 S p a n of t h e joint
T h e ~ n a x i r i i u n ~ s p a n is t o b e c h o s e n on t h e b a s i s of two e s s e n t i a l p o i n t s of view: on t h e o n e h a n d t h e jolnt I T I L L S ~ be w i d e enough t o g i v e t h e a d j a c e n t building corr>l>onents
s u f f i c i e n t r o o m s o a s t o be ; ~ b l e t o f r e e l y a b s o r b a n y c h a n g e s of s i z e t h a t n l a y r e s u l t f r o m t h e r m a 1, clitmatic o r a g i n g c o n d i t i o n s . T h i s i n v o l v e s n o t o n l y c o n t r a c t i v e a n d e x p a n s i v e m o t i o n s , but a l s o s h e a r i n g m o t i o n s . T h e l a t t e r o c c u r e s p e c i a l l y when t h e a d j a c e n t p r e c a s t p a r t s ( 2 ) a r e of d i f f e r e n t m a t e r i a l s ( e . g. , c o n c r e t e and s t e e l ) . T h e a n ~ p l i t u d e of t h e m o t i o n s d e p e n d s l a r g e l y on t h e s i z e of t h e building e l e m e n t ; ~ n d t h e t 6 1 r i p e r a t u l - ~ : graclient, and v a r i e s I,etween
+
2. 5 r r i r r ) .Another f a c t o r d e t e r m i n i n g the s p a n of t h e joint i s d e r i v e d f r o m t h e conditions of application and t h e subsequent functioning of the s e a l i n g m a t e r i a l . P r a c t i c e h a s shown t h a t placing i s difficult w h e r e s p a n s a r e l e s s than 10 m m and u n s a t i s f a c t o r y if t h e y a r e
l e s s than 5 m m . T h e r e a s o n s for t h i s will be t a k e n up l a t e r ( 3 ) .
Finally, s t u d i e s of placing technique show t h a t t h e o u t e r edge of t h e joint ought t o be r e c e s s e d in the f a c a d e plane, b e c a u s e in t h i s way t h e jointing o p e r a t i o n gives a r e l i a b l e r e s u l t .
2. 2 T h e c h a r a c t e r of t h e edge of the joint
Another i m p o r t a n t condition i s the c h a r a c t e r of the edge of t h e joint, which s e r v e s a s an a d h e r i n g s u r f a c e for t h e s e a l i n g m a t e r i a l . Not only m u s t i t be d r y , dust f r e e and c l e a n , but t h e r e should be no m a j o r i r r e g u l a r i t i e s due t o b a l l a s t m a t e r i a l , d a m a g e o r porosity. Not only i s t h i s d e t r i m e n t a l t o adhesion, but l e a d s d i r e c t l y t o l e a k s (4).
We r e c e n t l y o b s e r v e d in v a r i o u s c a s e s that t h e b a l l a s t m a t e r i a l w a s exposed even a t t h e edges of t h e joint. Such joint edges a r e t o t a l l y u n s a t i s f a c t o r y . T h e y m u s t f i r s t b e smoothed by grinding, o r a t l e a s t levelled off with a high quality p l a s t i c t r o w e l b e f o r e t h e s e a l i n g o p e r a t i o n s a r e begun. We s h a l l h a v e m o r e t o s a y about t h i s in
connection with i n s t a n c e s of damage.
3. P l a s t i c o r e l a s t i c s e a l i n g m a t e r i a l s
Whether an e l a s t i c o r p l a s t i c s e a l i n g m a t e r i a l should be c h o s e n h a s been a m a t t e r of dispute for y e a r s . Any final a n s w e r t o t h i s question i s p r o b a b l y i m p o s s i b l e , b e c a u s e t h e multiplicity and non-uniformity of t h e influences acting on t h e joint a r e n e i t h e r physically nor technologically controllable. T h i s applies p a r t i c u l a r l y t o the p e r i o d i c motions of t h e joints and t h e c l i m a t i c s t r e s s e s , and a l s o t o t h e c o m p l e x i t y of the p r o p e r t i e s of t h e s e a l i n g m a t e r i a l , i. e.
,
mixed p l a s t i c i t y and e l a s t i c i t y , h a r d n e s s , p r o f i l e of t h e joint m a t e r i a l o r deformability.Once one h a s b e c o m e f a i r l y well acquainted with t h e b a s i c r u l e s by m u c h r e f l e c t i o n and experimenting, it i s then b e t t e r to m a k e u s e of one's e x p e r i e n c e and choose a s e a l i n g m a t e r i a l f o r the m o s t p a r t accordingly. In t h e c o u r s e of t h i s , one will h a v e l e a r n e d that s e a l i n g m a t e r i a l s with q u a s i - e l a s t i c t e r m i n a l p r o p e r t i e s h a v e d e f i - nitely given by f a r the b e t t e r r e s u l t . T h e p r i n c i p a l r e a s o n s for t h i s would s e e m to be t h e r e v e r s i b i l i t y of s t r a i n of t h e e l a s t i c m a t e r i a l in t h e p r e s e n c e of a l t e r n a t i n g s t r e s s e s .
3. 1 Functional differences between p l a s t i c i t y and e l a s t i c i t y
The scope of t h e p r e s e n t paper does not p e r m i t a detailed exposition of t h e s e important questions, although it would contribute g r e a t l y t o an understanding of t h e problem of joints. However, I should like t o m a k e one o r two brief s t a t e m e n t s on t h e
subject of e l a s t i c i t y v e r s u s plasticity:
a) P l a s t i c m a t e r i a l s , owing to the i r r e v e r s i b i l i t y of t h e i r s t r a i n p r o p e r t i e s tend to form wrinkles a s a consequence of joint motion, and i n the hollows of t h e s e wrinkles incipient f r a c t u r e s m a y appear a s a r e s u l t of f u r t h e r alternating s t r e s s (5).
b) Ln p l a s t i c m a t e r i a l s s t r a i n phenomena a r e concentrated a t t h e n a r r o w e s t point in the joint profile, t h i s can a l s o lead locally t o incipient f r a c t u r e s
( 6 ) .
c) The deformability of p l a s t i c m a t e r i a l s in m o s t c a s e s depends strongly on t h e t e m p e r a t u r e , i. e.
,
t h e m a t e r i a l s become m o r e rigid at low t e m p e r a t u r e s (7).d) Ln p l a s t i c m a t e r i a l s , slow deformation lead to a relaxation of t h e physi- cally bound molecular entanglements. T h i s , too, l e a d s t o l o c a l f r a c t u r e phenomena.
e) Mixed p l a s t i c - e l a s t i c m a t e r i a l s , owing to the e l a s t i c components exhibit an i n t e r n a l s t a t e of s t r e s s a s a r e s u l t of t h e deformation, which in t h e c o u r s e of t i m e i s t r a n s m i t t e d to the plastic component in t h e f o r m of local expansions. Within a c r i t i c a l region t h e quantity of the plastic component i s too s m a l l t o a b s o r b t h e expan- sions; f r a c t u r e phenomena a r e t h e r e s u l t (8).
4. E l a s t i c sealinn m a t e r i a l s
Among t h e e l a s t i c sealing m a t e r i a l s available on the m a r k e t t h o s e employing a so-called polysulphide b a s e
-
often a l s o known by t h e t r a d e n a m e "Thiokol"-
hold a dominant position. Polysulphides a r e thickly liquid, organic sulphur compounds which have t h e p r o p e r t y of r e a c t i n g at r o o m t e m p e r a t u r e with s o - c a l l e d peroxide-
e.
g.,
lead dioxide
-
to f o r m solid, r u b b e r -like end products. However, t h e d e g r e e of e l a s t i c i t y cannot b e c o m p a r e d with that of vulcanized r u b b e r . On t h e c o n t r a r y , such m a t e r i a l s have a comparatively high p l a s t i c component, which under long t e r m s t r e s s e s r e s u l t s in t h e "cold flow" phenomenon.4. 1 Various types of sealing m a t e r i a l s
Ln
addition to polysulphide m a t e r i a l s we m a y mention sealing m a t e r i a l s uging a bonding agent b a s e of silicon r u b b e r and urethane r u b b e r and a l s o a b a s e ofa c r y l a t e r e s i n . At p r e s e n t , a p p l i c a t i o n s of t h e s e t y p e s a r e s t i l l s e v e r e l y l i m i t e d f o r t e c h n i c a l r e a s o n s , and t o s o m e extent f o r economlc r e a s o n s a s well; t h i s i s not t o s a y t h a t t h e y cannot gain a g r e a t e r s h a r e of t h e m a r k e t a f t e r s u i t a b l e modification.
Silicon m a t e r i a l s c o n s i s t of a thickly liquid p a s t e which r e a c t s with t h e a i r t o give a highly e l a s t i c m a t e r i a l . T h e m a t e r i a l t h u s h a s only one component. Depending on t h e r e a c t i o n m e c h a n i s m , i t m u s t a l w a y s b e well s e a l e d in i t s packing in o r d e r t o b e c o n s e r v e d f o r u s e .
I t s adhesion p r o p e r t i e s , even in t h e p r e s e n c e of m o i s t u r e and w a t e r , and i t s s t a b i l i t y with r e s p e c t t o t i m e , t e m p e r a t u r e and c h e m i c a l r e a c t i v i t y a r e e x c e l l e n t . T h e h a r d e n i n g t i m e i s not only long and u n r e s p o n s i v e t o t r e a t m e n t , but a l s o depends on t h e t h i c k n e s s of t h e m a t e r i a l applied. T h e m a i n r e a s o n f o r t h e l i m i t e d application of s i - licon m a t e r i a l s c o n s i s t s , however, in t h e i r high p r i c e , which a t p r e s e n t i s m o r e t h a n
50% g r e a t e r than t h a t of t h e polysulphide m a t e r i a l s , which a r e a l r e a d y v e r y expensive. F o r n a r r o w joints which c o n s u m e l i t t l e m a t e r i a l , e. g. , t h e s e a l i n g of i n s u - lating g l a s s windows o r s a n i t a r y equipment, however, t h e s e m a t e r i a l s a r e finding e v e r i n c r e a s i n g application.
T h e u r e t h a n e m a t e r i a l s , l i k e t h e polysulphide m a t e r i a l s , c o n s i s t of two components which m u s t b e mixed in a p r e d e t e r m i n e d r a t i o p r i o r t o application. Not only do t h e y h a v e advantageous t e r m i n a l p r o p e r t i e s , but t h e y a r e a l s o c h e a p e r t h a n t h e polysulphide m a t e r i a l s . T h e i r l i m i t e d application i s due t o t h e f a c t t h a t d u r i n g r e a c t i o n of t h e c o m p o n e n t s they a r e e x t r e m e l y s e n s i t i v e t o v e r y s m a l l q u a n t i t i e s of m o i s t u r e and t e n d t o bubble s e v e r e l y ( 9 ) . D e s p i t e e x t e n s i v e r e s e a r c h and development work, which h a s been going on m o r e than a decade, t h e s e difficulties h a v e not yet been o v e r c o m e , s o that t h e few p r o d u c t s a v a i l a b l e on t h e m a r k e t h a v e not yet been a b l e t o c a p t u r e a significant p a r t of it.
F i n a l l y , t h e r e a r e t h e a c r y l a t e m a t e r i a l s . T h e s e a r e a c t u a l l y of a p l a s t i c n a t u r e , but h a v e an a p p r e c i a b l e e l a s t i c component. T h e y c o n s i s t of a m i x t u r e of
a c r y l a t e r e s i n s , p l a s t i c i z e r s , s o l v e n t s and f i l l e r s . S i n c e t h e m a t e r i a l s , which c o m e in a s i n g l e component, h a v e a c o n s i s t e n c y a t r o o m t e m p e r a t u r e which i s too stiff f o r p l a c i n g with a caulking gun, t h e y m u s t b e h e a t e d b e f o r e application t o about 60°C.
In t h e i r t e r m i n a l p r o p e r t i e s t h e y show good adhesion (in m o s t c a s e s without t h e u s e of a p r i m e r , ) and good c l i m a t i c aging s t a b i l i t y . A f t e r evaporation of the
6
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8% content of s o l v e n t , they s t i f f e n t o s o m e extent a f t e r a t i m e . However, t h e y a r e s e n s i t i v e t o m o i s t u r e and w a t e r , e s p e c i a l l y t h e l a t t e r when i t i s alkaline. M o r e o v e rin place the m a t e r i a l s a r e unstable with r e s p e c t t o t e m p e r a t u r e , i. e.
,
at low t e m p e r a - t u r e they become very hard. F o r this r e a s o n the Laboratory of t h e Swedish Lightweight Concrete Industry has advised against t h e u s e of a c r y l a t e m a t e r i a l s in conjunction with p a r t s c a s t in a e r a t e d concrete. The basis for t h i s recommendation i s the alternating s t r e s s t e s t whose r e s u l t s a r e shown in F i g u r e 10; it i s found that the a c r y l a t e m a t e r i a l s have excellent p r o p e r t i e s at t e m p e r a t u r e s of 20°C, but fail completely at lower t e m p e r a - t u r e s .I should not like t o close t h e s e r e m a r k s on t h e different types of sealing m a t e - r i a l s without mentioning again the limited classifiability of chemical industrial products and emphasizing that their development is s t i l l in mid-course.
4. 2 Sealing with rubber o r plastic profiles
The sealing of joints in p r e c a s t construction with sealing m a t e r i a l s that m u s t be placed by hand i s diametrically opposed t o t h e basic idea of this method of c o n s t r u c - tion. Hence, the u s e of profiled sealing s t r i p s which can be i n s e r t e d into the joints
appears obvious. We can d i s c e r n t h r e e different f o r m s of technical solutions h e r e (1 1):
a) A subsequently i n s e r t e d sealing profile equivalent in its effect t o a sealing m a t e r i a l ;
b) A sealing s t r i p that prevents most of the m o i s t u r e f r o m penetrating into the joint, but r e q u i r e s additional sealing behind it;
c ) Sealing profiles which can be poured directly into the edges of the joint during casting of t h e p a r t s and a r e then coupled together during a s s e m b l y of the s t r u c t u r a l units.
None of t h e s e units have a s yet been fully applied. The main r e a s o n for t h i s would appear t o be the fact that t h e requirements with r e s p e c t t o dimensional t o l e r a n c e and accuracy execution of t h e edges of the joint a r e s o high that they a r e no longer
feasible. However, anyone who has studied the publication i s s u e d f r o m the CIB Congress in Oslo in September 1967 will understand that developments of p r a c t i c a l importance in this direction may be expected.
4. 3 The polysulphide or Thiokol m a t e r i a l s
The polysulphide m a t e r i a l s , in most c a s e s , consist of two components, one of which c o m p r i s e s a mixture of polysulphide, r e s i n , p l a s t i c i z e r s and pigments, while the other contains additional p l a s t i c i z e r s a s well a s t h e peroxide. The latter compo- nent is called the h a r d e n e r .
T h e r e a c t i o n r a t e c a n be c o n t r o l l e d within c e r t a i n l i m i t s by t h e u s e of a c c e l e r
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ating o r r e t a r d i n g a d d i t i v e s . A f t e r c a r e f u l m i x i n g of t h e c o m p o n e n t s a r e a c t i o n s e t s in and i t i s t h e n n e c e s s a r y t o d i s t i n g u i s h between t h e pot l i f e , within which t h e m a t e r i a l m u s t b e applied, and t h e c u r i n g t i m e , which t e r m i n a t e s with t h e s o l i d i f i c a t i o n of t h e m a t e r i a l . P o t life and c u r i n g t i m e a r e p r o p o r t i o n a l . T h e c u r i n g t i m e i s about 40-
50 t i m e s a s long a s t h e pot life. T a b l e I s h o w s t h e m e a s u r e d v a l u e s f r o m v a r i o u s c o m m e r-
cia1 p r o d u c t s .T h e d e g r e e of e l a s t i c s t r e n g t h o r r e s i s t a n c e t o d e f o r m a t i o n i s m e a s u r e d by d e t e r m i n i n g t h e h a r d n e s s i n S h o r e A - d e g r e e s . S u i t a b l e v a l u e s f o r polysulphide m a t e r i a l s in p r e c a s t c o n s t r u c t i o n a r e 10
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25 S h o r e A at 2 0 ° C .T h e h a r d n e s s depends on t e m p e r a t u r e and i n c r e a s e s with d e c r e a s i n g t e m p e r a - t u r e . T h e r e s i s t a n c e t o d e f o r m a t i o n i n c r e a s e s s i m u l t a n e o u s l y . T h i s i s an i m p o r t a n t point, s i n c e t h e g r e a t e s t s t r e s s e s in t h e joint m a y b e expected t o o c c u r at low t e m p e r a - t u r e s . F o r l a r g e expansion v a l u e s in t h e joint, t h e r e f o r e , t h e a p p l i c a t i o n of a m a t e r i a l with a low S h o r e A v a l u e i s r e c o m m e n d e d . Of c o u r s e , g e n e r a l l y s p e a k i n g , t h e p l a s t i c component i n c r e a s e s a c c o r d i n g l y (12). T h e r e s i s t a n c e t o d e f o r m a t i o n b e a r s a n i m p o r t a n t r e l a t i o n s h i p t o t h e a d h e s i o n , i. e . , t h e d e f o r m a t i o n f o r c e f o r m a x i m u m expansion m u s t a l w a y s b e l e s s t h a n t h e a d h e - s i v e f o r c e . O t h e r w i s e , a definite l o s s of a d h e s i o n w i l l o c c u r . F o r r e a s o n s of s a f e t y , t h e r e f o r e , it i s always a d v i s a b l e t o apply a n a d h e s i o n - i m p r o v i n g b a s e c o a t ( o r s o - c a l l e d p r i m e r ) t o t h e e d g e s of t h e joint b e f o r e u n d e r t a k i n g t o s e a l it. At t h e s a m e t i m e , d u s t i s r e m o v e d and i n s u l a t i o n a g a i n s t m o i s t u r e and a l k a l i n e a c t i o n i s a t t a i n e d . Excellent a d h e s i v e c o a t s , s u i t a b l e f o r v a r i o u s jointing m a t e r i a l s , a r e f u r n i s h e d by t h e r e s p e c t i v e m a n u f a c t u r e r s .
5. T h e c o r r e c t p r o f i l e of t h e s e a l i n g m a t e r i a l i n t h e joints
R e l i a b l e functioning of a s e a l depends not only on t h e p r o p e r t i e s of t h e s e a l i n g m a t e r i a l s . T h e p r o f i l e of t h e joint i s a l s o of d e c i s i v e i m p o r t a n c e . T h e a i m h e r e i s t o get a m i n i m u m d e f o r m i n g f o r c e with a m a x i m u m expansion, and m a x i m u m a d h e r i n g s u r f a c e .
On t h e b a s i s of p r a c t i c a l e x p e r i e n c e and e x p e r i m e n t a l i n v e s t i g a t i o n s t h e c o n - c l u s i o n h a s b e e n r e a c h e d t h a t t h e m o s t f a v o u r a b l e r e s u l t s a r e obtained f r o m a double- c o n c a v e p r o f i l e . T h e depth a t t h e e d g e of t h e joint should b e about h a l f t h e s p a n and i n t h e c e n t r e t h e joint p r o f i l e should be r e d u c e d to about 2 / 3 of t h e depth ( 1 3 ) . I n t h e S w e d i s h Building S p e c i f i c a t i o n Bygg
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AMA 1965 t h i s w a s e x p r e s s e d in t h e f o r m u l a( t K = depth of t h e edge of t h e joint; b = span), and f o r p r a c t i c a l r e a s o n s , a s well, i t
w a s s t a t e d a s a l i m i t i n g condition t h a t t h e depth i n t h e c e n t r e should not b e l e s s t h a n 4 m m . In p r a c t i c e t h i s r e q u i r e m e n t i s m e t by injecting a round b a s e filling
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c o n s i s t i n g for example, of a s t r i p of c e l l u l a r r u b b e r with c l o s e d p o r e s b e f o r e placing the s e a l i n g m a t e r i a l . In t h i s way a round p r o f i l e i s obtained at t h e b a c k of t h e s e a l i n g m a t e r i a l . T h e o u t s i d e f a c e i s molded into t h e p r o p e r f o r m b e f o r e h a r d e n i n g with t h e aid of a s u i t a b l y s h a p e d t r o w e l .So that t h e s e a l i n g m a t e r i a l c a n p e n e t r a t e deeply into t h e a n g u l a r s p a c e between t h e joint e d g e s and t h e round b a s e filling, in o r d e r t o a c h i e v e t h e r e q u i r e d wetting and
adhesion, it i s a d v i s a b l e t o i n s e r t t h e mouth p i e c e of t h e caulking gun deeply into t h e joint s o t h a t t h e l a t t e r i s f i l l e d with m a t e r i a l t o s o m e extent f r o m below.
6 .
Execution of iointingP r o p e r jointing i s t h u s c a r r i e d out a s follows:
a ) Cleaning of joint e d g e s . T h e s e m u s t b e f r e e of m o i s t u r e , g r e a s e , o i l and dust;
b) TrowelLingoff of i r r e g u l a r i t i e s , i n j u r i e s o r p o r e s a t t h e e d g e s of t h e joint with a n epoxy t r o w e l ;
c ) P l a c i n g of t h e b a s e f i l l i n g , taking c a r e t o m a i n t a i n a u n i f o r m depth; d) Application of a d h e s i v e ground coat. M a t e r i a l c h o s e n a c c o r d i n g t o r e c o m m e n d a t i o n of t h e s e a l i n g m a t e r i a l s u p p l i e r ;
e) Application of s e a l i n g m a t e r i a l .
f) Smoothing and p r o f i l i n g of t h e s u r f a c e of t h e u n h a r d e n e d m a t e r i a l u s i n g a s p e c i a l t r o w e l m o i s t e n e d with s o a p y w a t e r .
In what follows we s h a l l d e a l with two o t h e r i m p o r t a n t a u x i l i a r y p r o b l e m s of s e a l i n g technique, t h e c o n s i d e r a t i o n of which i s of g r e a t i m p o r t a n c e f o r t h e a c h i e v e m e n t of a s a t i s f a c t o r y f i n a l r e s u l t . Both p r o b l e m s a r e e x t r e m e l y complex: s e v e r a l p r o p e r t i e s and r e q u i r e m e n t s a r e c l o s e l y linked and i t i s n e c e s s a r y t o s t u d y t h e s e q u e s t i o n s i n o r d e r t o get an a c c u r a t e p i c t u r e of t h e conditions.
7. 1 Adhesion of the sealing m a t e r i a l t o the edge of the ioint
7. 1. 1 Conditions for s e c u r i n g an adhesion
T h e s e c u r i n g and t h e d e g r e e of m e c h a n i c a l adhesion obtained between two solid m a t e r i a l s a s s u m e s not only that t h e m a t e r i a l s have "adhesion affinity" t o each o t h e r , but that a) a t l e a s t one of t h e s u b s t a n c e s c o m e s i n liquid f o r m and b) t h e liquid substance (i. e , t h e sealing m a t e r i a l at the t i m e of application) is capable of wetting t h e solid s u p p o r t (i. e, t h e edge of t h e joint).
Thus adhesion a s s u m e s a wetting p r o c e s s . F o r t h i s t h e following fundamental r u l e s hold:
a) Highly viscous, i. e . , thickly liquid s u b s t a n c e s , h a v e p o o r e r wetting p r o p e r t i e s than thinly liquid s u b s t a n c e s of a s i m i l a r n a t u r e .
b) T h e d e g r e e of wetting depends on the p h y s i c a l c h a r a c t e r of t h e s u r f a c e of t h e solid m a t e r i a l . C o a r s e s u r f a c e s a r e m o r e difficult t o wet.
c ) T h e extent of wetting depends on t h e t i m e , i. e.
,
t h e wetting is i m p r o v e d i f t h e r e i s a long r e a c t i o n t i m e .7. 1. 2. T h e influence of t h e v i s c o s i t y of t h e s e a l i n g m a t e r i a l on wetting and adhesion
T h e p r o p e r adjustment of t h e v i s c o s i t y ( o r consistency) of a s e a l i n g m a t e r i a l i s d e t e r m i n e d by t h r e e mutually counteracting f a c t o r s :
a) A high wetting capacity r e q u i r e s a low viscosity.
b) In o r d e r t o p r e v e n t running down i n the joint a f t e r placing, t h e v i s c o s i t y m u s t be high.
c) Finally, application with t h e caulking gun r e q u i r e s a not too stiff consistency. T h e r e f o r e , in establishing t h e c o n s i s t e n c y of a s e a l i n g m a t e r i a l one i s f o r c e d t o a c o m p r o m i s e between t h e s e different r e q u i r e m e n t s . S a t i s f a c t o r y solutions t o t h i s p r o b l e m have been found in p r a c t i c e .
T h e v i s c o s i t y of a l l o r g a n i c s u b s t a n c e s depends on t h e t e m p e r a t u r e , i. e.
,
t h e m a t e r i a l stiffens p r o g r e s s i v e l y with d e c r e a s i n g t e m p e r a t u r e . At the s a m e t i m e ,however, t h e conditions for wetting and adhesion a r e i m p a i r e d . F o r t h i s r e a s o n i t is n e c e s s a r y t o b e v e r y c a r e f u l in placing s e a l i n g m a t e r i a l s a t low t e m p e r a t u r e s and it m u s t b e b o r n e in mind that heating the m a t e r i a l will not help g r e a t l y b e c a u s e on contact
with t h e edge of t h e joint it i s cooled in,nlediately. T h i s e f f e c t i s p a r t i c u l a r l y c l e a r in t h e c a s e of t h e a c r y l a t e m a t e r i a l s which have t o be applied w a r m , b e c a u s e r a p i d cooling r e s u l t s in s o s t r o n g a stiffening that t h e wetting e f f e c t i s quite c o n s i d e r a b l y i m p a i r e d .
Sealing o p e r a t i o n s have been c a r r i e d out in Sweden a t an o u t s i d e t e m p e r a t u r e of - 3 0 ° C with good r e s u l t s . In doing s o , however, t h e joint edges and t h e i r i m m e d i a t e vicinity w e r e s o s t r o n g l y h e a t e d t h a t t h e conditions of a n o r m a l jointing o p e r a t i o n w e r e s a t i s f i e d . In m y view, and t h a t of m o s t of t h e s p e c i a l i s t s , s e a l i n g o p e r a t i o n s ought not t o b e c a r r i e d out a t t e m p e r a t u r e s below t 5 " C u n l e s s it i s p o s s i b l e t o u n d e r t a k e p r o p e r heating of t h e joint units.
During r e a c t i o n of t h e components t h e v i s c o s i t y i n c r e a s e s s t e a d i l y . T h i s i s of no i m p o r t a n c e w h e r e a caulking gun i s used manually, b e c a u s e t h e a v a i l a b l e f o r c e f i x e s a n a t u r a l l i m i t t o t h e applicability. Where c o m p r e s s e d a i r i n j e c t o r s a r e used, however, c o n s i d e r a b l e caution m u s t b e e x e r c i s e d .
T h e wetting p r o c e s s t a k e s a c e r t a i n t i m e . Where n o r m a l pot l i f e of a few h o u r s i s involved, t h i s i s of no i m p o r t a n c e . H o w e v e r , if v e r y r a p i d l y h a r d e n i n g
polysulphide m a t e r i a l s a r e employed, t h e wetting p r o p e r t i e s at t h e joint edges m u s t b e sufficiently favour a b l e s o that t h e wetting p r o c e s s i s concluded b e f o r e t h e c r i t i c a l stiffening of t h e m a t e r i a l s e t s in.
C a r e f u l o b s e r v a n c e of t h e s e p o i n t s , e s p e c i a l l y a t t h e building s i t e , a p p e a r s e x t r e m e l y n e c e s s a r y if s e t - b a c k s a r e t o b e avoided.
7. 1. 3. T h e effect of t h e c h a r a c t e r of t h e joint e d g e s on t h e a d h e s i o n
Wetting a c t u a l l y m e a n s , of c o u r s e , that a liquid s u b s t a n c e i s a b l e t o s p r e a d out o v e r a s o l i d s u p p o r t and in doing s o p e n e t r a t e s into a l l t h e i r r e g u l a r i t i e s . T h e wetting s u r f a c e i s then equal t o t h e a d h e s i v e s u r f a c e and h e n c e p r o p o r t i o n a l t o t h e a d h e s i v e f o r c e .
If t h e s u r f a c e s a r e s m o o t h then t h e m o s t f a v o u r a b l e conditions a r e p r e s e n t f o r good adhesion. I r r e g u l a r i t i e s at t h e joint e d g e s , h o w e v e r , c a n i n t e r f e r e with t h e wetting t o s u c h a n extent that a s a t i s f a c t o r y adhesion i s just not p o s s i b l e even though t h e m a t e r i a l of t h e joint edge and t h e s e a l i n g m a t e r i a l would l e a d u s t o expect f a v o u r a b l e conditions.
Such s i t u a t i o n s a r e s u b s t a n t i a l l y enhanced, of c o u r s e , by t h e low t e m p e r a t u r e e f f e c t s on t h e v i s c o s i t y a l r e a d y mentioned. I s h a l l r e t u r n t o t h e s e points in t h e d i s - c u s s i o n of i n s t a n c e s of d a m a g e .
7 . 2 O c c u r r e n c e of c o n d e n s a t i o n behind t h e joint
By s e a l i n g t h e joints t h e a i m i s t o p r o t e c t t h e joint in e v e r y r e s p e c t f r o m m o i s t u r e p e n e t r a t i n g f r o m t h e o u t s i d e . At t h e s a m e t i m e , h o w e v e r , t h e joint i s s e a l e d f r o m t h e i n s i d e . If t h e r e a r e no e f f e c t i v e v a p o u r b a r r i e r s on t h e i n s i d e w a l l t h e m o i s - t u r e a r i s i n g i n t h e i n t e r i o r s p a c e s m i g r a t e s in t h e d i r e c t i o n of t h e c o l d s i d e , i. e . ,
outward, and in t h e event of an u n f a v o u r a b l e t e m p e r a t u r e g r a d i e n t in t h e e x t e r n a l w a l l w i l l p r e c i p i t a t e in t h e f o r m of c o n d e n s a t i o n . F o r t h i s c o n d e n s a t i o n , t h e i n t e r i o r s i d e of t h e joint i s e s p e c i a l l y c r i t i c a l , b e c a u s e h e r e t h e t e m p e r a t u r e in g e n e r a l i s c o n s i d e r - a b l y l o w e r t h a n t h e t e m p e r a t u r e a t t h e i n s i d e of t h e e x t e r n a l w a l l . T h i s i s shown in p r i n c i p l e in F i g u r e 14. When joints h a v e l a t e r b e e n opened up, it h a s often b e e n found t h a t t h e f i l l i n g m a t e r i a l behind t h e m , e. g.
,
f o a m p l a s t i c , i s s o a k e d with w a t e r , a n d i t i s often concluded p r e m a t u r e l y t h a t t h e joint h e r e w a s not s e a l e d . I s h o u l d l i k e t o s u g g e s t e m p h a t i c a l l y t h a t in m o s t c a s e s c o n d e n s a t i o n of i n t e r n a l m o i s t u r e i s a c t u a l l y r e s p o n s i b l e .T h e d a n g e r f r o m t h i s phenomenon i s not s o m u c h t h e i m p a i r m e n t of t h e s e a l i n g f r o m t h e o u t s i d e , s i n c e a c o r r e c t l y e x e c u t e d s e a l with a polysulphide m a t e r i a l should not b e d a m a g e d by c o n d e n s e d m o i s t u r e . T h i s d o e s not apply, h o w e v e r , t o a c r y l a t e m a t e r i a l s , s i n c e t h e s e a r e known t o b e s e n s i t i v e t o m o i s t u r e . T h e d a m a g e i s done r a t h e r t o t h e i n t e r i o r wall, s i n c e with r i s i n g t e m p e r a t u r e t h e c o n d e n s e d m o i s t u r e a g a i n m i g r a t e s i n w a r d and c a n then a c t in c o n c e n t r a t e d f o r m on t h e i n t e r n a l wall.
T h i s s i t u a t i o n c a n b e c o n s i d e r a b l y i m p r o v e d by u s i n g a b a s e f i l l i n g with c l o s e d p o r e s
-
e. g . , c e l l u l a r r u b b e r o r polyethylene f o a m . S i n c e s u c h m a t e r i a l s do not a b s o r b m o i s t u r e , t h e i r good i n s u l a t i o n p r o p e r t i e s a r e r e t a i n e d , s o t h a t t h e t e m - p e r a t u r e g r a d i e n t in t h e joint b e c o m e s m o r e f a v o u r a b l e . In addition, h o w e v e r , c e r t a i n s t r u c t u r a l m e a s u r e s in t h e f o r m of m o i s t u r e b a r r i e r s o r ventilation of t h e i n t e r n a l c a v i t y behind t h e e x t e r n a l f a c a d e should b e applied.7. 3 T h e e f f e c t s of bubbles in t h e h a r d e n e d s e a l i n g m a t e r i a l
During m a n u f a c t u r i n g o r packaging, and i n t h e c o u r s e of c a r e l e s s m i x i n g of s e a l i n g m a t e r i a l s , t h e a p p e a r a n c e of bubbles i n t h e joint c a n often be o b s e r v e d , and t h e q u e s t i o n i s r a i s e d a g a i n and a g a i n w h e t h e r t h e s e b u b b l e s a r e d e t r i m e n t a l t o t h e
functioning of t h e joint a s a whole.
In o r d e r t o get a n a n s w e r t o t h i s q u e s t i o n , m o d e l s w e r e p r o d u c e d with a r t i f i c i a l bubbling. Bubbles w e r e exposed and l o c a l d e f o r m a t i o n d u r i n g expansion of
t h e t e s t body was m e a s u r e d under t h e m i c r o s c o p e . T h e s i z e , f o r m and position of t h e bubble (in r e l a t i o n t o t h e d i r e c t i o n of expansion) w e r e taken into account. T h e r e s u l t s of t h e s e investigations a r e shown in p r i n c i p l e in F i g u r e 15. T h e following i m p o r t a n t conclusions for p r a c t i c a l application m a y b e drawn:
a) Elongated bubbles p a r a l l e l t o t h e d i r e c t i o n of expansion show g r e a t l y i n c r e a s e d expansion at t h e peaks (point B) at which d i r e c t f r a c t u r e phenomena can b e observed.
b) Round bubbles and bubbles that a r e elongated a t right angles t o the direction of expansion exhibit t h i s p r o p e r t y much l e s s strongly.
c ) L a r g e bubbles a r e c o n s i d e r a b l y m o r e c r i t i c a l than s m a l l ones.
d) Mixed p l a s t i c - e l a s t i c m a t e r i a l s ( a c c o r d i n g t o 3. 1 e) show an e s p e c i a l l y s t r o n g tendency t o w a r d s the a p p e a r a n c e of incipient f r a c t u r e s at p l a c e s of e x c e s s i v e s t r e s s .
e) In p l a s t i c m a t e r i a l the joining up of bubbles (and h e n c e e n l a r g e m e n t of t h e bubbles) c a n b e observed.
8. Methods of t e s t i n e s e a l i n e m a t e r i a l
T h e choice of a suitable s e a l i n g m a t e r i a l would b e c o n s i d e r a b l y facilitated by t e s t i n g and by a method of investigation that would r e p r o d u c e t h e p r a c t i c a l conditions. However, t h i s p r o b l e m i s c o n s i d e r a b l y m o r e difficult than one might imagine. T h e m a i n r e a s o n s a r e :
a ) T h e s t r e s s e s in the joint v a r y not only f r o m one s t r u c t u r e t o another, but v a r y in a n e n t i r e l y uncontrollable m a n n e r with t h e c l i m a t i c conditions. In t h e t e s t i n g of p a i n t s , for example, the m e c h a n i s m of which is b a s i c a l l y much s i m p l e r than t h a t of t h e s e a l i n g m a t e r i a l s , i t h a s b e e n found that t h e s a m e paint m a t e r i a l applied exactly under the s a m e conditions m a y give not only completely opposite r e s u l t s when t h e y a r e investigated on w e a t h e r t e s t i n g installations in different geographical situations, but that even on a single t e s t i n g stand t h e y yield a bewildering p a t t e r n a t different t i m e s of t h e y e a r , and
b) T h e p r o f i l e of t h e joint and t h e conditions of t h e placing p r o c e s s c a n v a r y s o g r e a t l y that it a p p e a r s i m p o s s i b l e t o develop a u n i f o r m s t a r t i n g point in t h i s r e s p e c t for a t e s t i n g method t h a t might b e g e n e r a l l y applicable.
A testing method m a k e s s e n s e , of c o u r s e , only i f i t i s possible either t o r e - produce the p r a c t i c a l conditions o r t o c r e a t e conditions allowing for a r e a l i s t i c c o m p a r i - son with reality.
S t r e s s e s in joints, in p r a c t i c e , a r e c h a r a c t e r i z e d by t h e fact that they generally involve slow alternating motions which come about under varying t e m p e r a t u r e conditions.
It can perhaps be r e g a r d e d a s a typical sign of the t i m e s that we know a g r e a t deal about f a s t motions, but v e r y little about slow ones, b e c a u s e we have forgotten how t o wait for the slow ones t o r u n their c o u r s e . Now, i f it i s t r u e that slow, continuous s t r e s s e s constitute the c r i t e r i a for the quality of sealing m a t e r i a l s , we find o u r s e l v e s on t h e h o r n s of a dilemma, because slow motions cannot be accelerated. Existing methods of investigations in t h e U. S. A.
,
England, Germany, Denmark, Sweden and other countries r e f l e c t t h e s e difficulties. The v e r y aging of t h e t e s t body i s s o poor that it in no way c o r r e s p o n d s t o r e a l i s t i c conditions. Table I1 shows the t e s t conditions for expansion, and i t i s evident that a l l conditions differ s h a r p l y f r o m each other and hardly ever correspond even approximately t o reality. Only t h e U. S. specification r e q u i r e s an expansion t e s t at low t e m p e r a t u r e s and t h e r a t e of expansion at 3 mm/h i s t h e lowest.All testing methods m u s t be r e g a r d e d a s s e r i o u s a t t e m p t s to solve a v e r y
difficult problem. In my view, however, p r a c t i c a l experience i n t h e choice of a suitable sealing m a t e r i a l must be p r e f e r r e d t o any of the inadequate t e s t i n g methods h i t h e r t o employed. Otherwise, t h e r e i s a danger not only of rejecting altogether suitable m a t e - r i a l s , but a l s o of using m a t e r i a l s that m a y have p a s s e d t h e t e s t , but will give u n s a t i s - f a c t o r y r e s u l t s in practice.
9. Discussion of instances of damage
In closing I should like t o deal with a number of difficult c a s e s of damage and look into their c a u s e s .
9.
1 Inadequate depth of jointsIn a v e r y l a r g e building in ~ z l m o t h e joints between p r e c a s t c o n c r e t e p a r t s of room s i z e w e r e sealed with a polysulphide m a t e r i a l which, in m y opinion, was of high quality. T h e climatic and constructional conditions w e r e favourable. After about half a y e a r t h e f i r s t c r a c k s appeared in t h e c e n t r e of the joint p r o f i l e and two y e a r s l a t e r t h e damage had become extensive.
An o n - s i t e investigation showed t h a t in t h e c e n t r e t h e joint p r o f i l e had a depth of only 1
-
2 m m . It c a n t h e r e f o r e b e p r e s u m e d t h a t t h e p r o f i l e was d e f o r m e d in t h e c e n t r e by continuous a l t e r n a t i n g s t r e s s e s and t h a t t h e d e f o r m a t i o n b e c a m e m o r e and m o r e i r r e v e r s i b l e a s a c o n s e q u e n c e of t h e p l a s t i c component, s o t h a t f r a c t u r i n g g r a d u - ally s e t in. E l s e w h e r e , t h e jointing m a t e r i a l showed no fatigue phenomena o r i m p a i r-
m e n t of e l a s t i c i t y . Where t h e p r o f i l e was d e e p e r ( t h i s was evident f r o m undamaged p a r t s of t h e d e f o r m a t i o n ) no d a m a g e o c c u r r e d .9. 2 Inadequate joint width
T h e joints between m a r b l e p a n e l s and 2 m long aluminium window
f r a m e s in a h i g h - r i s e building i n Stockholm w e r e s e a l e d with a polysulphide m a t e r i a l . T h e joint width a v e r a g e d 8 m m .
After two y e a r s e x t e n s i v e d a m a g e a p p e a r e d in t h e upper c o r n e r s of t h e joints. T h i s d a m a g e was c o n c e n t r a t e d on t h e south and w e s t s i d e s being insignificant on t h e north. It was concluded t h a t t h e m a i n c a u s e of t h e d a m a g e w a s t h e g r e a t d i f f e r e n c e between t h e coefficients of t h e r m a l expansion of t h e building m a t e r i a l s . In addition t h e r e was t h e f a c t that t h e joint widths, which on checking a p p e a r e d often t o b e a s l i t t l e a s 4 m m , w e r e m u c h t o o s m a l l .
T h e jointing had b e e n c a r r i e d out i n s p r i n g a t t e m p e r a t u r e s of 5
-
1 0 ° C . T h e c a l c u l a t e d joint d i s p l a c e m e n t s w e r e up t o 3 m m , and w e r e c o n c e n t r a t e d in t h e upper c o r n e r s , b e c a u s e at t h e lower edges t h e position of t h e window w a s s t a b i l i z e d . T h e p e r c e n t a g e o f expansion in t h e joints w a s s o g r e a t that it could not be a b s o r b e d b y t h e jointing m a t e r i a l , s o t h a t u l t i m a t e l y f r a c t u r i n g s e t in. T h i s effect was s m a l l e r on t h e n o r t h s i d e of t h e building.9. 3. Unfavourable joint edges and i n c o r r e c t choice of m a t e r i a l
In a l a r g e hfi??pital in s o u t h e r n Sweden t h e joints between rough s u r f a c e d c o n c r e t e (Waschbetong) in a l a t e r a l wing w e r e f i l l e d with an a c r y l a t e m a t e r i a l . T h e rough s u r f a c e d c o n c r e t e (Waschbetong) p e n e t r a t e d deeply into t h e e d g e s of t h e joint. T h e work had been c a r r i e d out in s p r i n g at a p p r o x i m a t e l y 1 0 ° C . ABter a s h o r t t i m e
s e v e r e m o i s t u r e d a m a g e a p p e a r e d i n t h e joints and on the i n t e r i o r of t h e w a l l s . It was found that t h e s e a l i n g m a t e r i a l had n e v e r a t t a i n e d adequate adhesion. T h i s w a s due p a r t l y t o t h e v e r y rough s u r f a c e and p a r t l y t o t h e f a c t t h a t t h e m a t e r i a l , which had been h e a t e d t o 6 0 ° C f o r application, b e c a m e s o s t i f f a t t h e t e m p e r a t u r e of t h e
joint edge t h a t no a d e q u a t e wetting could b e achieved. M o r e o v e r , t h e m a t e r i a l w a s p a r t l y softened by t h e action of a l k a l i n e m o i s t u r e . T h i s i s a c a s e in which t h e c a u s e s of d a m a g e l a y both in t h e d e s i g n , t h e m a t e r i a l p r o p e r t i e s and t h e m a n n e r of application.
F i n a l l y , t h e m a n n e r i n which t h e s e joints w e r e r e p a i r e d i s i n t e r e s t i n g and i n s t r u c t i v e . After r e m o v i n g t h e old jointing m a t e r i a l t h e e d g e s of t h e joint w e r e ground s m o o t h with a high-speed grinding disk, t h e p o r e s and d a m a g e d p l a c e s w e r e s e a l e d with an epoxy t r o w e l , a p r i m e r w a s applied, and f i n a l l y t h e joint was s e a l e d with a polysulphide m a t e r i a l . T h e i n i t i a l jointing had c o s t about 8 c r o w n s p e r m e t r e , while t h e r e j o i n t i n g o p e r a t i o n c a m e t o not l e s s than 80 c r o w n s / m e t r e , i. e . , 10 t i m e s t h e o r i g i n a l p r i c e .
I hope that I h a v e a d e q u a t e l y d e m o n s t r a t e d t h a t t h e s a t i s f a c t o r y solution of t h e jointing p r o b l e m i s s u b s t a n t i a l l y a question of c o o p e r a t i o n between d e s i g n e r s , c h e m i s t s and t h o s e who e x e c u t e t h e joints.
R e f e r e n c e s
1. Norwcglrcllcr Ilauforrchu~~gsinslitul, Rapporl 51 A - C , O r l o (1967 ulld 1968)
2 . A . V a l n u s ~ r . I2ci11hcrld I'ublirl~inl: Corp., NFW York, lYb7
3 . A . Wollcr, A d l l ; ~ s i o ~ ~ . U l l r l c i ~ ~ - V c r l o p 1967 ( I l c l l 9 ) ulld lYb8 ( l l c l l 4)
T a b l e I C u r i n g t i m e (in days) of v a r i o u s c o m m e r c i a l l y obtained polysulphide m a t e r i a l s Type 100% 9 0 % ' ~ ) 8070 (1) R e m a r k s c u r i n g curing c u r i n g A 12-15
6
-7 5 pot life :6
h r . B 8-10 4-5 2 - 3 pot l i f e : 50 min. C 106
-7 4-
5 pot life :6
h r . D-
-
-
not c u r e d a f t e r 28 days E 1 3 - 1 4 8 4 p o t l i f e : 3 . 5 h r . (1) T i m e a f t e r which 80% o r 90% of t e r m i n a l h a r d n e s s was r e a c h e dT a b l e I1 C o m p a r i s o n of t e s t i n g i n s t r u c t i o n s f o r s e a l i n g m a t e r i a l s i n d i f f e r e n t c o u n t r i e s ( e x p a n s i o n t e s t s ) . C o u n t r y I s s u e r Date S t o r a g e t i m e b e f o r e t e s t S i z e of s p e c i m e n R a t e of expansion Expansion t e s t ( d r Y) Expansion t e s t (wet) Expansion t e s t ( a f t e r aging) A p p r a i s a l U. S. A. US - F e d e r a t i o n S p e c i a l T T -S-227b J u n e 1965 10 d. a t 23" C t 4 d a y s i n w a t e r 9 x 2 4 x 4 8 m m 0 , 0 5 m m / m i n 3 c y c l e s 2 4 . /70°C 7h. /water 8h. /-17°C e x p a n s i o n 15070 - 1 7 ° C
-
m a x . 2 s q . in. l o s s of a d h e s i o n D e n m a r k A s s . of D a n i s h s u p p l i e r s of E l a s t i c jointing m a t e r i a l s J u n e 1966 3 d a y s at 5 0 " C t 16 h. at 25°C 2 0 x l 0 x 5 0 m m 5 m m / m i n 3 c y c l e s 4h/-15°C 200% exp./
16 h. 4h/25"C r e l a x a t i o n 16 h. /25"C 4d. /water exp. 250%/ 20°C 500 c y c l e s 102 m i n / 6 0 " ~ A t l a s 18 min/2O0 C exp. ZOO%/ 20" C m a x . 2 . 5 m m f r a c t u r e in joint Sweden Bygg-AMA 1965 7 d a y s at 25" C l 0 x l 0 x 5 0 m m 10 m m / m i n 2 5 0 7 0 / 2 5 " ~ 4d. /water exp. ZOO%/ 25°C 4d/70°C exp. Z O O % / 25°C 2 of 3 s p e c i m e n s f l a w l e s s G e r m a n y D e u t s c h e r Betoll- v e r e i n e . V. J u n e 1967 1 4 d a y s a t 20" C 1 5 x l 5 x 5 0 m m 5 m m / m i n 2O0~o/2O0 C 12 c y c l e s 16 h. /water 3 h/-20°C 2 h / t 2 0 " ~ 3 h/-20°C 6 4 h / w a t e r 20070/20" c a s a b o v e + 3 c y c l e s 250%/-20" C -5070/50" c o r v i b r a t i o n f r o m 8 0 - 1 2 0 ~ / 2 0 " ~ 1000 t i m e s / 2 h . max. 5 m m depth of c r a c k s England F e d e r a t i o n of B r i t i s h R u b b e r and Allied M a n u f a c t o r y F e b r u a r y 1964 7 d a y s at 25°C 12, 5 x 1 2 , 5 x 4 8 m m 0, 25 m m / m i n 250%/25"C 4d. /water 250%/24 h. a) 96h/70°C 4 / 2 5 " C 2 0 0 7 0 / 2 5 " ~ b ) 20070/-15°C 4h/25" c C o m p r e s s i o n : 50 yo 16h/25"C s a m e a s Sweden and D e n m a r ks p a n
W
u e v e l l e c l j o i n t f a c e . o u t s i d e e d g e s F i g . 1 C o r r e c t d e s i g n o f a j o i n t ; F i g .3
D i m e n s i o n i n g o f j o i n t s p a n e x p a n s i o n o r c o n t r a c t i o n j o i n t w i t h s h e a r i n g m o t i o n F i g . 2 J o i l - ~ t s f u n c t i o n i n g i n t i i f f e r e n t ways I n c o r r e c t'r
F i g .4
C o r r e c t a n d i n c o r r e c t s u r f a c e q u a l i t y o f j o i n t e d g e se l a s t i c p l a s t i c c o m p ~ . e s s i o n e x p a n s i o n c o m p r e s s i o n I / e x p a n s i o n a n d
mq?
p o s s i b l e f r a c - n u l l L c o n t r a c t i o n p o s i t i o n o f p r o f i l e e x p a n s i o n i n c i p i e n t f r a c t u r e t u r e F i g .5
F i g .6
S t a r t o f c r a c k i n g i n p l a s t i c S t a r t o f f r a c t u r e i n p l a s t i c m a t e r i a l m a t e r i a l d u e t o a l t e r n a t i n g s t r e s s d u e t o c o n t r a c t i o n o f p r o f i l e E l a s t i c m a t e r i a l w i t h s m a l l p l a s t i c c o m p o n e n t s s h o r e h a r d n e s s A-
A c r y l a t e m a t e r i a l ( p l a s t i c ) B-
S i l i c o n m a t e r i a l ( e l a s t i c ) C-
T h i o k o l m a t e r i a l H ( e l a s t i c ) D-
T h i o k o l m a t e r i a l W ( e l a s t i c ) E-
B u t y l m a t e r i a l ( p l a s t i c ) F i g .7
H a r d n e s s e s o f p l a s t i c a n d e l a s t i c s e a l i n g m a t e r i a l s a s a f u n c t i o n o f t h e t e m p e r a t u r e e x p a n s i o n o/. r e l a x a t i o n o f e l a s t i c component i n c i p i e n t A f r a c t u r ef
Z
t
ime A-
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