Study of Exposed Reinforced Concrete Facings

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PREFACE

P r e c a s t c o n c r e t e p a n e l s a r e e x t e n s i v e l y used i n Canadian construction^ Recommended p r a c t i c e s f o r t h e p r o d u c t i o n of t h i s t y p e o f e x t e r i o r w z l l c l a d d i n g I n European c o u n t r i e s a r e t h e r e f o r e of s p e c i a l I n t e r e s t t o t h e ~ I v i s i o n . The p a p e r o u t l i n e s t h e r e q u i r e m e n t s used i n France f o r c o n c r e t e m a t e r i a l s , p a n e , - forms,

p l a c i n g and c u r i n g t o p r o v i d e a d u r a b l e f a c i n g . V a r l o u s techniques a r e b r i e f l y d e s c r i b e d which e n a b l e a r a n g e o f s u r f a c e f i n i s h e s t o be o b t a i n e d . T h f s t r a n s l a t i o n w a s p r e p a r e d by M r . P.A. S l n c l a i r o f t h e T r a n s l a t i o n s S e c t i o n o f t h e N a t i o n a l Research C o u n c i l , t o whom t h e D i v i s i o n o f B u i l d i n g Research r e c o r d s i t s t h a n k s . O t t a w a November 1961 R . F . L e ~ e t D i r e c t o r

NATIONAL RESEARCH COUNCIL OF CANADA

T e c h n i c a l T r a n s l a t i o n 993

T i t l e : A s t u d y of exposed r e i n f o r c e d c o n c r e t e f a c i n g s (Etude s u r l e s parements de bgton arm6 a p p a r e n t )

Author : A . Adam

Reference: Annales d e 1 ' I n s t i t u t Technique du Bgtiment e t des. Travaux P u b l i c s , (159-160): 377-388, 1961

A STUDY O F EXPOSED REII\IFORCED CONCRETE FACINGS

The Chambre Syndicale d e s C o n s t r u c t e u r s en Ciment Arm6 ( t h e Reinforced Concrete Buil-ders' ~ s s o c i a t i o n ) w a s i n s t r u c t e d t o draw up, i n l i n e with t h e programme of t h e I n t e r n a t i o n a l B u i l d i n g Committee, a study on exposed r e i n f o r c e d c o n c r e t e f a c i n g s .

To t h i s end t h e widest p o s s i b l e c o n s u l t a t i o n w a s undertaken among b u i l d e r s h a v i n g a c q u i r e d e x p e r i e n c e t h a t could be c o n s i d e r e d a u t h o r i t a t i v e i n t h e f i e l d , and numerous t e s t s were made.

The e x t e n s i v e documentation t h u s accumulated has made i t p o s s i b l e t o d r a f t t h e p r e s e n t r e p o r t which d e a l s s u c c e s s i v e l y with g e n e r a l i t i e s as t o m a t e r i a l s

t o be used and t h e i r p l a c i n g , then with t h e v a r i o u s t y p e s of f a c i n g s most c u r r e n t l y used i n France,

t o g e t h e r with t h e m a t e r i a l s used, working methods, t h e advantages and t h e economic a s p e c t of t h e p r o c e s s e s of e x e c u t i o n , and f i n a l l y with a g i n g behaviour from t h e p o i n t of view of d e t e r i o r a t i o n , c r a c k i n g , impermeability,

Institut de Recherches Appliqu6es du ~ 6 t o n ~ r m 6 (IRABA) at Saint-Remy-les-Chevreuse

Tiles kept for laboratory facade facings Bottom: tiles for the subfoundation (see Fig. 12 and 13)

Centre: tiles for superstructures (Seine aggregates and white cement )

Top : tiles for office storey (Berchkres aggregates and white cement )

1. General C o n s i d e r a t i o n s on t h e Q u a l i t v of t h e M a t e r i a l s and on T h e i r Employment

1.1. Concrete

I n o r d e r t o o b t a i n a p r o p e r f a c i n g which does n o t r e q u i r e r e t o u c h i n g ; which i s always a p p a r e n t , i t i s n e c e s s a r y :

t o use c o n c r e t e s w i t h a g g r e g a t e s of very uniform g r a d i n g o b t a i n e d from a s i n g l e s o u r c e ;

t o use b i n d e r s of uniform c o l o u r , 1.e. coming from t h e same p l a n t and b e i n g o f t h e same c l a s s and type.

Idhen, f o r r e a s o n s o f economy, o n l y a s i n g l e s u r f a c e l a y e r a few crn t h i c k c o n s t i t u t e s t h e f a c i n g s p e c i a l c a r e h a s t o be t a k e n t o a v o i d any i n t e r f e r e n c e w i t h t h e mass c o n c r e t e , s i n c e t h i s can pro- duce an u n s i g h t l y e f f e c t ( F i g . 1).

Any c o n c r e t e t h a t i s t o remain v i s i b l e should be v i b r a t e d s o a s t o i n c r e a s e i t s d e n s i t y and t o e l i m i n a t e a i r bubbles. The b e s t method a p p e a r s t o be i n t e r n a l v i b r a t i o n , n o t c a r r i e d t o o f a r i n o r d e r t o a v o i d s e g r e g a t i o n . For t h i s purpose one may a l t e r n a t e l y p l a c e and v i b r a t e t h e c o n c r e t e uniformly by s u c c e s s i v e t h i n l a y e r s . I f t h e h e i g h t of t h e l i f t i s t o o g r e a t t h e a i r i s unable t o r i s e and escape ( p u n c t u r i n g s i m u l t a n e o u s l y a l o n g t h e formwork f a c i l i t a t e s t h e r e l e a s e of t h e b u b b l e s ) .

The use of admixtures and a i r e n t r a i n e r s i s d e l i c a t e because t h e mixture i s r a r e l y c o n s t a n t and c o l o u r v a r i a t i o n s of a more o r l e s s s e r i o u s n a t u r e may a r i s e , depending on t h e c o m p a t i b i l i t y of t h e admixtures w i t h c e r t s i n b i n d e r s o r a g g r e g a t e s , which i s n o t always a s s u r e d .

The t i n t i n g of t h e c o n c r e t e by means of dyes c o n t a i n e d i n t h e mixing w a t e r i s d i f f i c u l t t o keep c o n s t a n t . I t should t h e r e f o r e be a p p l i e d o n l y t o c e r t a i n s e p z r a t e u n i t s such as m u l l i o n s and

transoms. On brcad s u r f a c e s comparatively p u r e r a i n w a t e r may cause t h e lime t o s e p a r a t e o u t from t h e cement a f t e r a t i m e , l e a v i n g

d i s t i n c t t r a c e s .

The p r e c a u t i o n s t o be t a k e n a f t e r s e t t i n g must n o t be n e g l e c t e d ( d r y i n g o u t , f r e e z i n g , e t c . )

1.2. Formwork

Formwork must b e :

e a s y t o s t r i p ( smooth and vrel-1 p r o t e c t e d ) ;

impermeable and r i g i d . ; a n y p e r m e a b i l i t y w i l l r e s u l t i n i n h o m o g e n e i t i e s a t r i g h t a n g l e s t o t h e J o i n t s w i t h l e a k s o f l a i t a n c e . Absence of r i g i d i t y w l l l produce i r r e g u l a r i - t i e s o f s u r f a c e ( F i g . 2 ) . C o a t i n g s a p p l i e d t o t h e formwork f o r i t s p r o t e c t i o n o r t o f a c i l i t a t e s t r i p p i n g ( o i l s , v a r n i s h , p a i n t , e t c . ) must n o t a t t a c k t h e c o n c r e t e . 1.3. R e i n f o r c e m e n t s R e i n f o r c e m e n t s must be p r o t e c t e d by a t l e a s t : 3 crc of c o n c r e t e , a f t e r t r e a t m e n t , i n s h e l t e r e d z o n e s ; 5 t o 6 cm c c n c r e t e a f t e r t r e a t m e n t , i n exposed zones. I t i s very i m p o r t a n t f o r t h e r e i n f o r c e m e n t s n e a r f a c i n g s t o

form a f i n e , c l o s e network. T h i s i n c r e a s e s t h e number o f p o s s i b l e c r a c k s b u t r e d u c e s t h e i r u n i t w i d t h and t h u s Improves t h e r e s l s t a n c e t o c o r r o s i v e a g e n t s ,

2 . W J o u s Types o f 3acin.g i n C u r r e n t Use

2.1 H o u ~ h - c a s t f a c i n g s

( a ) Gu_ali&t of material_s_ and o f c o n c r e t e : Ag,gregates : s t a n d a r d ; uniform g r a d i n g ,

Maximum s i z e o f a g g r e g a t e s l l m i t e d t o e / 3 f o r f i n e u n i t s o f t h i c k n e s s e.

Avoid s a n d s t h a t . a r e t o o c o a r s e .

B i n d e r s : be c a r e f u l w i t h c e r t a i n contemporary s l a g cements which a r e n o t o f uniform sha.de,

Dosage and water-cement r a t i o : depends on t h e p l a c i n g p r o c e s s and t h e dintensions o f u n i t s .

I n g e n e r a l 270 t o 350 kg/m3 f o r s t a n d a r d u n i t s ; 350 kg/m3 or

Enough water t o e n s u r e a very p l a s t i c c o n c r e t e . ( b ) P l a c i n r ~ of t h e c o n c r e t e : I n p l z c i n g one must a v o l d : s e g r e g a t i o n s ; t h e forination of b l i s t e r s ; u n s i g h t l y c o n s t r u c t i o n j o i n t s ; f o r t h i s purpose a c a r e f u l s t u d y of t h e a r c h i t e c t u r e should e n a b l e t h e b u i l d e r t o make every c o n s t r u c t l o n j o i n t c o i n c i d e with a break i n t h e facade. This important p r l n c l p l e h a s been recommended and s u p p l i e d b y t h e great advocate of c o n c r e t e a r c h i t e c t u r e , Auguste P e r r e t ( F i g . 3).

I t i s p o s s i b l e t o avoid t h e s e d i s a d v a n t a g e s e i t h e r by i n t r o - d u c i n g t h e c o n c r e t e a t t h e bottom of t h e fornwork o r by d i s c h a r g i n g

i t a t as low a l e v e l as p o s s i b l e with t h e a i d of a c h u t e , and i n any c a s e by a p p l y i n g t h i n l a y e r s ( 2 5 t o 30 cm maximum).

There should be c a r e f u l v i b r a t i o n , e s p e c i a l l y c l o s e t o t h e forms, but n o t t o o prolonged and above a l l r e g u l a r .

I n p a r t i c u l a r , v i b r a t i o n by means of t h e forms, when e x c e s s i v e - l y prolonged, produces p a r t i a l , i r r e g u l a r s e g r e g a t i o n of t h e c o n c r e t e w i t h an e x c e s s of l a i t a n c e c l o s e t o t h e forms. T h i s i m p a r t s a

r a t h e r d l sagmeable marbled appearance t o t h e f a c i n g .

Remedy: Remove forms a f t e r s e t t i n g i s complete and u s e a c u r i n g t r e a t m e n t depending on t h e type of b i n d e r , e s p e c i a l l y where s l a g cements a r e involved,

( c ) ProductLon t e c h n l a u e s :

c.1. The formwork may be of m e t a l , c o n c r e t e , wood o r s p e c i a l u n i t s .

c . l . 1 . K e t a l : smooth appearance,

B l i s t e r i n g , sometimes of a s e v e r e c h a r a c t e r , i f t h e form- work i s of l i g h t - w e l & t s h e e t metal. C o n s t r u c t i o n j o i n t s and j o l n t s between p a n e l s v i s i b l e ( ~ i g . 4 ) .

c.1.2. Concrete: smooth appearance. Few b l i s t e r s .

Handsome f a c i n g s f o r l a r g e h o r i z o n t a l s u r f a c e s . c.1.3. Xood:

Formwork of planking: i m p r i n t of g r a i n .

of assembled planks s t i f f e n e d by p r o f i l e i r o n s w i t h f a s t e n i n g h o l e s ; t h i s e n a b l e s t h e p l a n k s t o be used over again s e v e r a l times* Panel formwork: c l e a n s u r f a c e s r e t a i n i n g t h e i m p r i n t Of t h e panels. B l i s t e r i n g i n v e r s e l y p r o p o r t i o n a l t o t h e t h i c k n e s s of t h e p a n e l s ( F i g . 5 and 6 ) , The c o n s t r u c t i o n J o i n t s a r e v i s i b l e , b u t t h e i r appearance can be improved by grooving with t h e a i d of a r a i l on t h e i n s i d e of t h e formwork.

The j o i n t s between p l a n k s o r p a n e l s must be f a i r l y t i g h t t o p r e v e n t l e a k s o r l a i t a n c e .

c.1.4. S p e c i a l d e v i c e s :

Forms f i t t e d w i t h backings t h a t l e a v e a d e s i r e d i m p r i n t on t h e c o n c r e t e .

Such backings may be of v a r i o u s form, e . g. :

l i n l n g s of t h e Formica t y p e : very handsome g l a z l n g , on which t h e s m a l l e s t b l i s t e r o r s u r f a c e i r r e g u l a r i t y i s n o t i c e a b l e .

s o f t f i n l n g s of t h e G e r f l e x type: l e s s g l a z i n g e f f e c t ; perrnlts l i n i n g of broad s u r f a c e s , b u t t e a r s e a s i l y . c.2. Forms a r e g e n e r a l l y coated with a g e n t s t o p r o t e c t them and f a c i l i t a t e stripping; t h e s e p r o d u c t s must a l s o :

n o t s t a i n t h e c o n c r e t e nor a t t a c k t h e q o u t i n g ( a s

c e r t a i n o i l s d o ) ;

promote w e t t i n g of t h e form-vrork by t h e c o n c r e t e (avoidance of b l i s t e r i n g ) ;

not adhere t o t h e c o n c r e t e a f t e r i t h a s s e t (some p a i n t s

do thls).

( d ) Various a d v a n t a m s :

d.1. Labour: apart from the c a r e f u l c o n t r o l of t h e fornwork, t h i s procedure i s t h e one whlch r e q u i r e s t h e l e a s t l a b o u r , because a f t e r s t r i p p i n g the c o n c r e t e w i l l need a t most o n l y a c u r i n g

Various t y p e s of forn~uork and t h e i r a p p l i c a t i o n s

-

; ; a t e r i a l s Metal

--

Concrete s!ood S p e c i a l u n i t s I Cost F a i r l j . h i g h H i & Moderate V a r i a b l e F a i r l y h i g h V a r i a b l e 21 H i @ 1 Ee-use 50 t o 100 o r

,

more 100 o r more to 2 0 15 t o 60 to 50 50 t o 200 5 t o 2 0 I A p p l i c a t i o n Concrete poured on s i t e Fre f a b r i c a - t i o n Pref a b r i c a - t i o n , bottom of mould Poured on s i t e A l l a p p l i c a t i o n s do. A l l Large complex s u r f a c e s

I

Type

~-

Li s h t assembled u n i t s Heavy m c n o l i t h i c u n i t s Heavy m o n o l i t h i c unl t s (bottom o f mould ) Assembled boards (II rl a G rd c4 Appearance V i s i b l e , some- times ugly j o i n t s Very good Very good Average

Soget imes poor

do. Grainy o r smooth Very n e a t , c a r e w i t h j o i n t s Avoidance of j o i n t s , f i n e appearance I Plywood F i b r e board R i g l a S o f t I a l i s t ~ r i n g Frequent b l i s t e r s Few Very few b l l s t s r s B l i s t e r s s c a r c s l y v i s i b l e S l i s t e r s u n l e s s r i g i d Few b l i s t e r s very v i s i b l e A few b l i s t e r s i P r e c a u t i o n s E a s i l y chipped Very l i t t l e n a i c t e n a n c e S t r a i g h t oil in^ 'Jeak edges r e q u i r i x g r e i n f o r c e - ment Zequire r i g 1 3 s u p p o r t s ; frequent o i l i n g Porn Simple ugl t s

--

Any form Can be s t r i p z e d ?le,glar s u r f a c e s F l a t possible de

-

f l e c t i o n s Breakable F r a g i l e , ' s u b j e c t t o t e a r i n g F l a t 3e7e lop- a b l e s u r f a c z s

I

d.2, Q u a l i t y and appearance:

With t h e s e methods t h e c o n c r e t e n o t only r e t a i n s i t s s k i n , b u t i s n o t s u b j e c t e d a t a r e l a t i v e l y young age t o v a r i o u s mechanical t r e a t m e n t s which may d i s r u p t i t on t h e s u r f a c e , f r e q u e n t l y s t a r t c r a c k s and d e s t r o y t h e zone of t h e c o n c r e t e which i s p a r t i c u l a r l y impermeable, namely t h e s k i n ,

The appearance depends on t h e kind of formwork used and v a r i e s g-reatly,

( e ) Aging

Aging i s g e n e r a l l y very uniform. I r r e g u l a r i t i e s of appearance a r e g e n e r a l l y due t o t h e l o c a l t r i c k l i n g of r a i n w a t e r down t h e

facade. T'nis i s p r i m a r i l y a n a r c l ? i t e c t u r a l problem.

However, rough-cas t f a c i n g s provide a c o n t i n u o u s veneer which may emphasize variations of hue o r s t a i n s , b u t which I s e a s y t o c l e a n .

Cracks can be l o c a l i z e d by t h e p r o v i s i o n of l i n e s o f l e a s t

r e s i s t a n c e and by l i m i t i n g t h e dlrnensions of t h e u n i t s , s i n c e c r a c k s on a f l a t f a c i n g a r e always u n s i g h t l y .

2 . 2 , Facin,ys of V i s i b l e A m r e ~ a t e

2.2.1. Slashin,? (Yig. 7 and 9 )

( a ) Q , u a l i t y of m a t e r i a l s and of c o n c r e t e :

A g p e g a t e s : d i a m e t e r l e s s t h a n 1 2 mm i n continuous -adingo Discontinuous g r a d i n g , edge 18/22 m m , f o r example.

P r e f e r a b l y rounded a g g r e g a t e s (crushed a g g r e g a t e s a r e unseated by t h e b r u s h i n g p r o c e s s ) ,

Choose t h e mixture and c o l o u r w i t h t a s t e , B i n d e r s : t r a n s p a r e n t b i n d e r s p r e f e r r e d .

Mixture: continuous @ading; moderate c o n c e n t r a t i o n ; d i s c o n - t i n u o u s p?adin$; high c o n c e ~ i t r a t i o n ,

P a s t y c o n s i s t e n c y y

( b ) Concret In:? PI-occ s s :

G e n c x l l y u s e d i n p r ~ f a b r i c a t i o n where o n l y a s i n g l e s u r f a c e l a y e r i s of c o n c r e t e s p e c i a l l y lnzde f o r t h i s purpose. I t i s bonded t o t h e r e s t of t h e s t r u c t u r e by v i b r a t i o n (which p e r m i t s a n

i n t e r p e n e t r a t i o n of t h e v a r i o u s l a y e r s ) . ( c ) Production t e c h n i q u e :

If t h e f a c e t o be washed i s a t t h e bottom of t h e mould t h e u n i t i s t u r n e d o v e r f o r t r e a t m e n t . I n t h e o p p o s i t e c a s e t h e u n i t i s s l i c h t l y i n c l i n e d .

The t r e a t m e n t i s c a r r i e d o u t a b o u t one hour a f t e r t h e u n i t s have been made, o r , i f a s e t t i n g r e t a r d e r h a s been used, 2 4 t o 36

h o u r s l a t e r .

The water i s f i r s t sprayed on g e n t l y , t h e n i n a j e t o v e r t h e f a c e , which i s i n c l i n e d 5% o r 2 0 % on t h e washing bench w h i l e a t t h e same time t h e u n i t i s worked o v e r w i t h a s o f t brush.

No puddles must remain a f t e r washing. These form milky f l l m s on d r y i n g whicl? a r e d i f f i c u l t t o c1ea.n o f f .

Cl.ea.ning t a k e s p l a c e one o r two days a f t e r w a r d s w i t h d i l u t e h y d r o c h l o r i c a c i d . T h i s i s follorved by r i n s i n g f r e e l y w i t h water.

( d ) Various advaIl,t_a~eg:

The p r o c e s s i s more popular I n p r e f a b r i c a t i o n because f a i r l y p r e c i s e time i n t e r v a l s have t o be observed i f i t i s t o be s u c c e s s f u l and t h e o p e r a t i o n must n o t be pushed too f a r f o r f e a r of d i s l o d g i n g t h e pebbles.

The c o n c r e t e c o n t i n u e s s e t t i n g a f t e r t h e treatment;. This does n o t a f f e c t t h e mass and t h e r e f o r e t h e l a t t e r r e t a i n s i t s impermea-

b i l i t y and mechanical s t r e n g t h p r o p e r t i e s .

The appearance, v:hich depends on t h e p e b b l e s , i s a g r e e a b l e , The c o s t of t h e shop o p e r a t i o n i s low, provided t h e p r o c e s s i s p r o p e r l y executed.

( e ) A,qiny, rnaiy1tena~ce :

The washes u r ~ i t s age w e l l and uniformly. T h e i r v s r l e g a t e d ap-pearunce c o u n t e r a c t s s t a i n i f i e and t h e s l i z h t mechanical a t t z c k of t h e s u r f a c e d u e t o t h e treatment f a c i l l t a t e s c l e a n i n g .

2 . 2 . I n ~ ~ ~ r r ~ e r 9 t e s

A klnd of nlosaic, t h e appearance of which depends e s s e n t i a l l y on t h e a r - t i s t i c t z l e n t of t h e a r c h i t e c t who s e l e c t s t h e g r a v e l s , p e b b l e s , p l e c e s of g l a s s , e t c . and on t h e a r t l s a n who a p p l i e s them.

(5.) Q u a l l t y of r n z t e r i a l s

-

c o n c r e t e s :

S t a n d a r d c o n c r e t e i s used. The i n l a i d e l e m e n t s a r e s e l e c t e d , ( b ) P l a c i ~ ~ q , t r e a t m e n t :

b.1, I n p r e f a . b r i c a t i o n : The s e l - e c t e d e l e m e n t s a r e p l a c e d a t t h e bottom of t h e b a r e mould, o r b e t t e r , on a l a y e r of sand. The c o n c r e t e i s t h e n poured on t o p . F i n a l l y , a f t e r s t r i p p i n g , t h e sand i s washed o r brushed o f f ( F i g . 8 , 9 and 1 6 ) -

h.2. F o r c o n c r e t e poured on t h e s i t e t h e s o - c a l l e d t r a n s f e r method c a n be used. The a g g r e g a t e s a r e f i r s t g l u e d t o t h e formwork p a n e l s w i t h s w a t e r - s c l ~ b l e g l u e and f i n e sand i s t h e n added, A f t e r

s t r i p p i n g t h e ?.??laid e l e m e n t s remain embedded i n t h e c o n c r e t e and c a n be b r c u g h t u? by b r u s h i n g .

( c ) Various a d T ~ i t . e r e s :

Does n o t r e d u c e t h e q u a l i t y of t h e c o n c r e t e ( i m p e r m e a b i l i t y , etc.), a p p e z r a n c e sometimes v e r y handsone,

Cost, v a r i e s g r e a t l y , ( d ) A g i n . ~ . maintenance :

Aging depends on t h e k i n d of e l e m e n t s i n l a i d . Washing i s g e n e r a i l y e a s y .

Some of t h e e l e m e n t s may become d i s l o d g e d and t h i s w i l l i m p a i r t h e a p p e a r a n c e o f t h e fa.c i n g g r e a t l y , 2.2.3. G r a n u l a t i n s ( F i g . 2 and 1 0 ) ( a ) Quality o f _ m a t e r i a l s znd. o f c o n c r e t e : A g g r e g a t e s : c o n c r e t e w i t h minimum sa-nd; c o n t i n u o u s g r a d i n g ; b e s t r e s u l t s r ; i t h p e b b l e s . Avoid m a t e r i a l s of e x c e s s i v e h a r d n e s s . S i n d e r s : t y p e s i n common u s e , X i x t u r e : s tar;d.ard. ( b ) P l a c ! . ~ . , ~ and t r e - e ~ t o f t h e c o n c r e t e : C o ~ i s t r u c t i o n jo i n t s t o be made w i t h e x t r e m e c a r e u s i n g a s l l g h t l y more p l a s t i c c o n c r e t e t h a n f o r t h e whole; v i b r a t e e n e r g e t - i c a l l y ( d o n o t courlt c n t h e r o u g h e n i n g t o d i s g u i s e s e g r e g a t i o n f a u l t s o r d i s c c n t i n u i t i e s a t t h e j o i n t s ) . R e i n f o r c e r e n t s s h o u l d be p l a c e d a t l e a s t 3 t o 5 cm from t h e f l n l s h e d f a c i n g .

( c ) Production t e c h n l a u e :

G r a n u l a t e over 5 m m , use 16-toothed o r 25-toothed hammer; f i n i s h wlth a 49-toothed o r 64-toothed hammer.

Do n o t granula.te u n t i l t h e c o n c r e t e i s thoroughly hardened. Do n o t g r a n u l a t e r i b s ; l e a v e a rough-cast l i s t e l ( i t i s n o t a d v i s a b l e t o c a r r y on t h e l i s t e l s with b u i l t up mortar

-

c h i p p i n g , f l a k i n g , e t c .

1.

( d ) Various a d v z n t a ~ e s a.nd disadva.nta@s:

Handsome appearance when t h e concrete i s very u n i form, Concrete s u b j e c t e d t o s e v e r e mechanical t r e a t m e n t which may s t a r t c r a c k s , cause p e r m e a b i l i t y and c o r r o s i o n of r e i n f o r c e m e n t s .

An expensive and somewhat slow p r o c e s s ( c o n c r e t e must be h a r d )

.

G e n e r a l l y a p p l i e d t o c o n c r e t e a l r e a d y i n s t a l l e d . Sometimes a subsequent s a n d - b l a s t i n g i s needed. ( e ) Apinp. maintenance :

A g e s w e l l

-

d i f f i c u l t t o wash

-

d e t e r i o r a . t i o n s due t o permea- b i l i t y r e s u l t i n g from r e p e a t e d hammer blows,

2.2.4, S a n d - b l a s t i n g ( ~ i g . 1 2 , 13 and photograph on page 4 )

( a ) Q u a l i t y o f m a t e r i a l s and of c o n c r e t e :

Cf. Sec. 2.2.3. ( a ) (pebbly o r crushed-stone a g g r e g a t e s ) . ( b ) Pourlnfi of c o n c r e t s , t r e a t m e n t :

Cf. Sec, 2.2.3. ( b ) f o r c o n c r e t e on s i t e . However, t h i s method i s more popular i n p r e f a b r i c a t i o n where t h e sand can be r e c y c l e d , I n t h i s c a s e t h e c o n c r e t e must be b l a s t e d very uniformly.

( c ) P r o d u c t i o n . t e c h n i ~ u e :

B l a s t i n g i s c a r r i e d o u t when t h e c o n c r e t e h a s b a r e l y hardened. Thus, i f i t i s poured i n t h e morning, i t w i l l be b l a s t e d t h a t everling. The b l a s t i n g i s done s o a s n o t t o s p o i l t h e p o l i s h o f t h e s t o n e s . I t should n o t be accomplished by washing, which might d i s l o d g e t h e s t o n e s ( F i g . 11).

Mechanical a t t a c k on t h e c o n c r e t e i s s l i g h t ,

A r a p i d shop o p e r a t i o n , b u t one r e q u i r i n g a c e r t a i n c a r e i n t h e observance of time i n t e r v a l s and t h e d u r a t i o n o f

Moderate c o s t by i n d u s t r i a l s t a n d a r d s . ( e ) A ~ i n e :

Good a g i n g , easy maintenance i f b l a s t i n g h a s n o t been overdone. 2.2.5. Pumicing ( F i e . 1 4 , 1 5 and 1 6 )

( a ) and ( b )

Cf. Sec. 2.2.3. end 2.2.4. ( a ) and ( b ) .

The a g g r e g a t e s must be chosen s o as t o g i v e a f i n e , p o l i s h e d s u r f a c e ( b a s a l t s , marbles, p o r p h y r i e s , L o i r e s t o n e , E c u e l l e s g r a v e l s , e t c . ).

( c ) Production technique:

F i r s t r e g u l a r g r a n u l a t i n g , t h e n smoothing w i t h t h e 100-toothed hammer, and f i n a l l y pumicing.

( d ) Various a d v a n t a m s and disadvantage$:

Very handsome f a c i n g when s u c c e s s f u l . Very c o s t l y p r o c e s s .

Cracks o c c u r e a s i l y ; i t i s t h e r e f o r e b e s t t o t r e a t o n l y r a t h e r s m a l l u n i t s which are s u b j e c t t o l i t t l e s t r e s s . ( e ) A ~ i n g , maintenance :

Aging depends on t h e a g g r e g a t e s chosen, b u t t h e l a t t e r can be p o l i s h e d w i t h pumice p e r i o d i c a l l y .

Very e a s y t o wash.

2.3 P r e f a b r i c a t e d t i l e f a c i n g s

P r e f a b r i c a t e d t i l e , i n t h e i r t u r n , can be used e i t h e r as forms i n c o r p o r a t e d i n a c o n c r e t e w a l l o r as f a c i n g s a p p l i e d t o a w a l l a l r e a d y c o n s t r u c t e d .

Obviously, any t y p e of p r e f a b r i c a t e d t i l e s can be used f o r t h i s purpose, e.g. c u t s t o n e o r r e c o n s t i t u t e d s t o n e ( e s p e c i a l l y of

r o c k d u s t ) o r p a n e l s of wood o r m e t a l , a l t h o u g h t h e l a t t e r do n o t come w i t h i n t h e scope of t h e p r e s e n t study., u n l e s s t h e c o n c r e t e i s v i s i b l e .

True c o n c r e t e t i l e s a r e g e n e r a l l y o f s m a l l s i z e t o p e r m i t e a s y h a n d l i n g and a r e s l i g h t l y r e i n f o r c e d t o prevent damage i n t r a n s i t .

The c h o i c e of ccmponent m a t e r i a l s snd m a n u f a c t u r i n g p r o c e s s e s o b v i o u s l y depends on t h e s u r f a c e t r e a t m e n t i n t e n d e d , as s e l e c t e d by

t h e a r c h i t e c t from t h e v a r i o u s p r o c e s s e s d e s c r i b e d above.

The s i d e o p p o s i t e t h e f a c i n g , which must hold t h e t i l e t o i t s s u p p o r t , i s o f t e n t h e s u b j e c t of s p e c i a l study by t h e b u i l d e r . A s

a consequence t h e r e are many more o r l e s s i n g e n i o u s methods and p a t e n t s i n e x i s t e n c e , r a n g i n g from simple grooving of t h e s u r f a c e

t o very complex a n c h o r i n g d e v i c e s , 2,3.1. P r e f a b r i c a t e d t i l e s i n i n c o r p o r a t e d forms (photograph on page 4) ( a , b and c ) Q u a l i t y of m a t e r i a l s , t r e a t m e n t , p r o d u c t i o n Cf. above t h e s e c t i o n s c o r r e s p o n d i n g t o t h e t e c h n i q u e s employed. ( b ) P l a c i n ~ of t i l e s : T h i s i s a. d e l i c a t e o p e r a t i o n b u t must be c a r r i e d o u t i n a very s t e a d y , p e r f e c t l y r e g u l a t e d manner, s i n c e t h e s e t i l e s w i l l appear on t h e facade e x a c t l y a s t h e y a r e a f t e r t h e c o n c r e t e pla.ced on t h e s i t e h a s s e t , It i s wise t o p r o v i d e f i b r e s on t h e r e a r f a c e which w i l l be immersed i n t h e c o n c r e t e placed a t t h e s i t e and t o roughen t h i s f a c e s o as t o o b t a i n a good c o n c r e t e j o i n t , Since t h e j o i n t s between t h e t i l e s a r e n o t by themselves t i g h t i t i s a d v i s a b l e e i t h e r t o p l a c e t h e t i l e s on a mortar b a t h o r t o wash t h e i r s u r f a c e s as soon as t h e s u p p o r t s a r e withdrawn,

( d ) Various c h a r a c t e r i s t i c s :

F a c i n g of h i g h q u a l i t y and uniform appearance.

Cracks o c c u r r i n g i n t h e s k e l e t o n o f t h e b u i l d i n g r a r e l y break through t h e t i l e s , They may, however, t w i s t them, owing t o t h e comparatively s m a l l dimensions of t h e t i l e s . F r a g i i i t y ( d a n g e r of c h i p p i n g a t t h e edges d u r i n g i n s t a l l a - t i o n ) . Danger of displacement d u r i n g v i b r a t i o n of t h e c o n c r e t e p l a c e d a t t h e s i t e . T h i s i s i m p o s s i b l e t o c o r r e c t s u b s e q u e n t l y , High c o s t , b u t of i n t e r e s t n e v e r t h e l e s s , h a v i n g r e g a r d t o t h e s u r f a c e t r e a t m e n t employed by r e a s o n of t h e f a c t of shop production. ( e ) Agiw:, maintenance:

Depends on t h e t y p e o f f a c i n g chosen, Appearance a l m o s t always remains s a t i s f a c t o r y and uniform over t h e y e a r s owing t o t h e g r e a t e r

c o n s t a n c y o f s h o p - p r o c e s s e d f a c i n g s . 2.3.2, P r e f a b r i c a t e d t i l e s a p p l i e d

t o

t h e build in^ c o n c r e t e ( a , b and c ) Cf. a b o v e , Sec. 2.3.1. (b' ) I n s t a l l a t i o n o f t i l e s : I n s t a l l a t i o n i s s i m p l e ; i t i s m e r e l y n e c e s s a r y t o l e a v e h o l e s i n t h e w a l l f o r a d h e s i v e s o r a n c h o r i n g d e v i c e s . ( d ) V a r i o u s c h a r a c t e r i s t i c s : F a c i n g s o f h i g h qua11 t y a n d c o n s t a n t a p p e a r a n c e . The e f f e c t i v e n e s s o f c o n t r o l o v e r t h e i n s t a l l a t i o n o n a f i n i s h e d w a l l w i l l g e n e r a l l y depend o n t h e e x t e n t t o which t h e mass work i s c o m p l e t e d and a l l t h e s e t t l e m e n t and

c r a c k i n g h a s become s t a b i l i z e d . F r a g i l i t y i s o f t e n greater t h a n i n 2.3.1. owing t o a b s e n c e o f monol.ithism w i t h the w a l l . Cost n o t e x c e s s i v e f o r v e r y f i n e f a c i n g s , ( e ) A ~ l n a , m a i n t e n a n c e : C f - Sec. 2.3.1. ( e ) .

The c o n c r e t e may be c o a t e d by: s t u c c o ;

t i l i n g , t e r r a c o t t a , f r e e s t o n e , mosaic ;

p l a s t i c c o a t i n g s : a p p l i e d by b r u s h i n g o r s p r a y i n g ; p a i n t s , v a r n i s h e s .

Ide are n o t c o n c e r n e d w i t h t h e s e t y p e s o f c o a t i n g here b e c a u s e t h e y d o n o t come w i t h i n t h e s c o p e o f t h i s s t u d y , which i s l i m i t e d s t r i c t l y t o f a c i n g s o f v i s i b l e c o n c r e t e . 3. G e n e r a l C o n s i d e r a t i o n s o n Aging A b i l i t y 3.1. D e t e r i o r a t i o n D e t e r i o r a . t i o n o f t h e c o n c r e t e ( a p a r t f r c m cases of a b n o r m a l u s e o f t h e s t r u c t u r e ) i s g e n e r a l l y due t o : p o o r c o m p a c t i o n , r e s u l t i n g i n 2 p o r o u s c o n c r e t e ; r e i n f o r c e m e n t s b e i n g i n more o r l e s s d i r e c t c o n t a c t w i t h t h e a t m o s p h e r e ;

e x c e s s i v e c r a c k i n g due t o s h r i n k a g e ( u n i t s t o o l a r g e o r e x c e s s i v e dosage).

F i n a l l y , any m e c h ~ n i c a l tr e a t m e n t of t h e f a c i n g w i l l r e s u l t i n

a p r e d i s p o s i t i o n t o c r a c k i n g ( g r a n u l a t i n g , s a n d - b l a s t i n g , e t c . ) . 3.2. S t a i n s

These a r e due b a s i c a l l y t o r a i n i n a contaminated atmosphere, e s p e c i a l l y where t r i c k l i n ~ i s l o c a l i z e d a l o n g a facade.

On smooth f a c i n g s (rough-cast o r pumiced) s t a i n s show up more c l e a r l y , b u t a r e e a s i e r t o wash o f f .

The rugged f a c i n g s , e s p e c i a l l y t h e sand-blasted and washed ones, seem t o d i s p e r s e t h e d i r t and t o m i t i g a t e i t s u n s i g h t l i n e s s by reason of t h e v a r i e g a t e d background of s t o n e s .

Thus, c o n s i d e r i n g only t h e appearance i n a s s e s s i n g t h e a g i n g a b i l i t y of a c o n c r e t e , t h e b e s t f a c i n g s appear t o be t h e rough-cast f o r a l l ' c a s e s , and washed o r sand-blasted ones f o r u n i t s of small dimensions.

Fig.

1

Gable tiles, prefabricated flat

First a few centimetres of white cement facing concrete are placed

at the bottom of the mould, Reinforcements are then put in posi-

tion and the tiles are built

up

to full thickness by placing ordinary

concrete, Carelessness in execution

of the rigfit centre tile

Fig. 2

F a c i n g of g r a n u l a t e d c o n c r e t e placed i n forms c o n s i s t i n g of planks l a i d s i d e by s i d e . The c o n c r e t e h a s l o s t i t s f i n e c o n s t i t u e n t s

a t r i g h t a n g l e s t o t h e J o i n t s between p l a n k s , whence t h e l i n e s which g r a n u l a t i n g could n o t e r a s e

Fig. 3

C o n s t r u c t i o n j o i n t d e f e c t i n a g r a n u l a t e d c o n c r e t e

T h i s f a u l t w i l l always remain v i s i b l e no m a t t e r what p r o c e s s

i s

used. Thus, c o n c r e t e c o n s t r u c t i o n j o i n t s should always be made t o c o i n c i d e

w i t h a s u r f a c e d i s c o n t i n u i t y o f t h e s t r u c t u r e

Fig. 4

C i r c u l a r column placed i n 2 mm s h e e t m e t a l formwork

T h i s kind of formwork always b r l n g s o u t j o i n t s and b l i s t e r s a s w e l l a s f a u l t s of alignment between forms

Fig. 5

Wood f i b r e formwork, g r i l l s u r f a c e

D e t a i l : Note t h e e x c e l l e n t q u a l i t y of the concrete a t ri&t angles t o t h e j o i n t , t h e complete absence of b l i s t e r s and t h e marks l e f t

by t h e f a s t e n i n g p o i n t s of t h e panels which, i n t h i s c a s e , were n o t glued t o t h e i r support

Fig. 6

C y l i n d r i c a l fibre-board forrnwork with a r a d i u s of 1 m; smooth surface

Note t h e e x c e l l e n t appearance of t h e j o i n t a t r i g h t angles t o which the q u a l i t y of t h e concrete i s f u l l y maintained

Fig. 7

Facing of washed t i l e , pebbly aggregate of t h e P a r i s region c a l l e d n r i c e g r a i n s n ( p r e f a b r i c a t e d )

Fig. 8

IBABA.

Study f o r f a c a d e f a c i n g

Facing of s a n d - b l a s t e d c o n c r e t e w i t h c o a r s e Seine a g g r e g a t e s (40-50) arranged i n i t i a l l y a t t h e bottom of t h e mould ( b u i l t up a g g r e g a t e s )

Fig. 9

T i l e s i n a f a c i n g of b u i l t up a g g r e g a t e s ,

p ~ o s m o y p~ oq 91 saqa.xauoa uo B u y q s q q - p m s

ap=a=j T T B ~ ayq JOJ saTrq p a q e a ~ ~ q = j a ~ d

-vav81

11 -%d

s a q e . 8 a ~ 8 2 ~ auras

Fig. 1 2

IRABA. Cornice around t h e t e r r a c e reserved f o r t h e production of l a r g e u n i t s

Upper p a r t : sand-blasted topping c o n c r e t e produced on s i t e . Lower p a r t : p r e f a b r i c a t e d

t i l e ,

sand-blasted and used

i n

l o s t form

IRABA. D e t a i l o f a p r e f a b r i c a t e d f a c a i e t i l e

S e i n e a g g r e g a t e s 10-40 and P o r t l a n d cement 210-325. Very c a r e f u l g r a d i n g , s l o p e d a s i n t h e moulds and sancl-blasted t h e day a f t e r

p l a c i n g

I R A ~ A . Study f o r i n t e r i o r f a c i n g o f v i s i t o r s ' e n t r a n c e Pumicing o f p r e f a b r i c a t e d t i l e s

IRABA. Pumiced t i l e made from s i l e x g r a v e l 1 0

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20 E c u e l l e s sand and white cement

Fig. 1 6

IRABA. P r e f a b r i c a t e d pumiced t i l e w i t h s i l e x g r a v e l 20

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40 p l a c e d a t the bottom o f t h e mould and E c u e l l e s m o r t a r sand