SELF-COMPACTING FIBRE REINFORCED CONCRETE APPLIED IN THIN
PLATES
S t e f f e n G r ü n e w a l c l * S Riyosuke S h i o n a g a ^ Joost C. W a l r a v e n ^
1 Section of Concrete structures, Delft University of Technology, THE NETHERLANDS. 2IHI Corporation, Research Laboratory, JAPAN.
*: corresponding author. S.Grunewaldfatudelft.nl
A B S T R A C T
Floor panels produced with traditionally vibrated concrete are relatively thicl< due to the need to reinforce concrete and consequently, heavy. Without the need to place rebars in panels and by applying self-compacting fibre reinforced concrete (SCFRC) the production process becomes more efficient. Fibres improve the performance of concrete by counteracting the crack-growth during loading. Their efficiency also depends on how they are distributed and oriented in a cementitious matrix.
This paper describes a study on the application of thin plates with self-compacting concrete with and without fibres for floors; other materials like steel or wood often are applied for this application. Six concrete panels (dimensions: 600-600-15 mm j were tested in this study; no rebars were placed in the elements. Self-compacting concrete was applied and the dosage of steel fibres was varied (0; 0,99 and 1,97 Vot.-%). The plates were tested by point-loading; the failure pattern depended on the fibre dosage.
K e y w o r d s : s e l f - c o m p a c t i n g c o n c r e t e ; thin p l a t e s ; f i b r e s ; fibre o r i e n t a t i o n
I N T R O D U C T I O N
s h e e t piles [1] o r f a c a d e e l e m e n t s [2]) can be d e s i g n e d , r e d u c e d c o n s t r u c t i o n h e i g h t s a n d e l i m i n a t i o n o f s u p p o r t s , n e w s t r u c t u r a l a n d d e s i g n p o s s i b i l i t i e s [ 3 ] , d e c r e a s e o f t r a n s p o r t , s t o r a g e a n d p l a c e m e n t c o s t s , i m p r o v e d d u r a b i l i t y a n d / o r d e c r e a s e d m a i n t e n a n c e c o s t s . W i t h o u t t h e n e e d t o v i b r a t e c o n c r e t e t h e w o r k i n g c i r c u m s t a n c e s a r e i m p r o v e d a n d c o n c r e t e is m o r e h o m o g e n o u s , w h i c h e n h a n c e s t h e q u a l i t y a n d t h e p e r f o r m a n c e . C o m p a r e d t o o t h e r b u i l d i n g m a t e r i a l s , c o n c r e t e is i n f l a m m a b l e a n d can b e c o m p o s e d t o resist e x t r e m e f i r e - l o a d i n g s . In t h i s p a p e r , t h e a p p l i c a t i o n o f SCFRC f o r t h e a p p l i c a t i o n o f p l a t e s in a d o u b l e - f l o o r s y s t e m is d i s c u s s e d . Reasons t o a p p l y SCFRC f o r t h i n p l a t e s are a n i m p r o v e d p r o d u c t i o n e f f i c i e n c y , a t h i n n e r a n d l i g h t e r s t r u c t u r e ( p l a t e , s u p p o r t a n d f o u n d a t i o n ) a n d h i g h c o n c e n t r a t e d f o r c e s c a n b e t r a n s f e r r e d w i t h a h i g h c o m p r e s s i v e s t r e n g t h m a t e r i a l . T h e p e r f o r m a n c e o f t h e p l a t e s w a s c o m p a r e d t o c a t e g o r i e s d e f i n e d by EN 1 2 8 2 5 [ 4 ] , w h i c h d e p e n d o n t h e m a x i m u m d e s i g n l o a d , t h e c h o s e n s a f e t y f a c t o r a n d t h e a l l o w a b l e d e f o r m a t i o n o f t h e p l a t e s . In case o f s t a t i c l o a d i n g o f f l o o r p l a t e s , EN 1 2 8 2 5 d e f i n e s six c a t e g o r i e s d e p e n d e n t o n t h e l o a d c a p a c i t y (Table 1). Static l o a d i n g a n d w h e n n e c e s s a r y , o t h e r l o a d cases have t o b e t a k e n i n t o a c c o u n t f o r t h e d e s i g n (i.e. d y n a m i c l o a d i n g , f i r e r e s i s t a n c e , n o i s e r e d u c t i o n , e l e c t r i c a l c o n d u c t i v i t y a n d / o r i s o l a t i o n c a p a c i t y ) . In t h i s f e a s i b i l i t y - s t u d y , o n l y q u a s i - s t a t i c l o a d i n g is c o n s i d e r e d .
Table 1. Element class depending on the load capacity
Class Max. load [KN]
1 >4 2 >6 3 >8 4 >9 5 >10 6 >12 T h e m a x i m u m d e s i g n l o a d also d e p e n d s o n t h e s a f e t y f a c t o r (EN 1 2 8 2 5 : 2,0 o r 3,0). A n a d d i t i o n a l r e q u i r e m e n t f o r p l a t e s is t h e m a x i m u m v e r t i c a l d e f l e c t i o n . T h r e e d e f l e c t i o n c a t e g o r i e s are d e f i n e d ( C a t e g o r y A b e i n g t h e class w i t h t h e l o w e s t a l l o w e d d e f l e c t i o n o f 2,5 m m ; Class B: 3,0 m m / C l a s s C: 4 , 0 m m ) . A f t e r a l o a d i n g p e r i o d o f 3 0 m i n u t e s at t h e m a x i m u m l o a d a n d a 5 m i n u t e s p e r i o d o f d e - l o a d i n g , t h e m a x i m u m a l l o w e d v e r t i c a l d e f l e c t i o n is 0,5 m m . A t h i n p l a t e s u p p o r t e d o n f o u r p o i n t s at its e d g e s can fail a t d i f f e r e n t l o c a t i o n s w h e n l o a d e d by a c o n c e n t r a t e d f o r c e . T h e d i m e n s i o n i n g o f t h e s u p p o r t s is c r i t i c a l f o r t h e d e s i g n o f l o a d - b e a r i n g f l o o r s t r u c t u r e s . A c c o r d i n g t o EN 1 2 8 2 5 , t h e p l a t e s h a v e t o be l o a d e d by a t e s t i n g m a c h i n e w i t h a s t e e l p r i s m h a v i n g a r e l a t i v e l y s m a l l c o n t a c t area (25-25 m m ^ ) . Failure can i n i t i a t e in t h e m i d d l e o f t h e w e a k e s t p l a t e - s i d e , in t h e m i d d l e o f t h e p l a t e , in o n e o f t h e d i a g o n a l s o r at e v e r y o t h e r p o i n t o f a m a t e r i a l t h a t has w e a k s p o t s .
E X P E R I M E N T A L S E T - U P T h e t h i c k n e s s o f t h e plates in t h i s s t u d y w a s f i x e d t o 15 m m . W i t h a p l a t e t h i c k n e s s o f 15 m m a n d r e b a r s h a v i n g a d i a m e t e r o f 4-5 m m o n l y a t h i n c o n c r e t e c o v e r ( + / - 5 m m ) can be r e a l i z e d . A d u r a b l e b u t m o r e e x p e n s i v e o p t i o n w o u l d be t o a p p l y c o a t e d o r s t a i n l e s s s t e e l r e b a r s . S e l f - c o m p a c t i n g c o n c r e t e w i t h a n d w i t h o u t s t e e l f i b r e s w a s a p p l i e d ; t h e f i b r e s c o n t r i b u t e t o a high f l e x u r a l c a p a c i t y w i t h o u t t h e n e e d t o place r e b a r s . Six t h i n p l a t e s ( d i m e n s i o n s : 6 0 0 - 6 0 0 - 1 5 m m ^ ) w e r e p r o d u c e d a n d w e r e t e s t e d in t h e S t e v i n - L a b o r a t o r y o f D e l f t U n i v e r s i t y o f T e c h n o l o g y . T h e d o s a g e o f s t e e l f i b r e s ( s t r a i g h t , Lf=13 m m , d f = 0 , 2 0 m m ) w a s v a r i e d ( 0 ; 0,99 a n d 1,97 V o l . - % ) ; t w o p l a t e s w e r e p r o d u c e d w i t h e a c h m i x t u r e . T a b l e 2 s h o w s t h e m i x t u r e c o m p o s i t i o n o f M i x t u r e s 1-3. S e l f - c o m p a c t i n g c o n c r e t e ( v o l u m e : 60 litres) w a s p r e p a r e d w i t h a f o r c e d - p a n t y p e m i x e r ( p r o d u c e r : Zyklos, m a x i m u m m i x i n g c a p a c i t y : 1 2 0 l i t r e s ) .
Table 2. Mixture composition of self-compacting concrete with and without steel fibres for thin plates
Component Producer Mix Mix2 Mix 3 [kg/mM [kg/m^] [kg/m^] CEM 152.5 R CEM Ill/A 52.5 Silica f u m e Sand (0.125-0.5) Sand (0.5-1.0)
Steel fibres (OL13/0.20) Superplasticizer, Glenium 5 1 Total w a t e r (incl. superplasticizer) w a t e r / c e m e n t - r a t i o Figure I ' s h o w s t h e s e t - u p o f t h e t e s t i n g m a c h i n e . A w e l d e d f r a m e w i t h f o u r a d j u s t a b l e c o l u m n s (area o f p l a t e s u p p o r t : 3 0 ' 3 0 m m ^ ) w a s a r r a n g e d in a q u a d r a t i c l a y o u t ( 6 0 0 ' 6 0 0 m m ^ ) . T h e f r a m e w a s s u f f i c i e n t l y s t i f f i n o r d e r t o p r e v e n t d e f o r m a t i o n s a n d t h e d i s p l a c e m e n t o f t h e s u p p o r t s . T h e t o p o f each c o l u m n c o n s i s t e d o f a s t e e l p l a t e ( 4 0 ' 4 0 - 1 5 m m ^ ) w e l d e d o n a M 2 4 - b o l t in o r d e r t o be a b l e t o a d j u s t t h e h e i g h t o f t h e s u p p o r t s . T h e s t e e l c o l u m n s s u p p o r t e d t h e c o n c r e t e p l a t e s o n f o u r e d g e s . T h e c o n t a c t area o f t h e l o a d i n g h e a d o f t h e t e s t i n g m a c h i n e a n d t h e p l a t e s h a d t h e d i m e n s i o n s o f 2 5 - 2 5 m m ^ T h e t e s t s w e r e c a r r i e d o u t l o a d - c o n t r o l l e d . A c c o r d i n g t o EN 1 2 8 2 5 , t h e l o a d - c o n t r o l l e d t e s t s o n p l a t e s h a v e t o b e c a r r i e d o u t a t a r a t e o f 1 2 0 N/s + / - 10 % u n t i l f a i l u r e o f a n y p a r t o f t h e p l a t e is o b s e r v e d . In t h i s f e a s i b i l i t y - s t u d y , t h e load w a s m a n u a l l y i n c r e a s e d in s t e p s w i t h a p n e u m a t i c p u m p ; t h e l o a d a n d t h e d e f l e c t i o n o f t h e p l a t e ( a t t h e l o a d i n g h e a d ) w a s c o n t i n u o u s l y r e c o r d e d d u r i n g t e s t i n g . ENCI 358 358 358 ENCI 555 555 555 BASF 6 1 6 1 6 1 river, round 574 562 549 river, round 574 562 549 Dramix 0 77,5 155 BASF 21,0 21,0 21,0 226 226 226 0.25 0.25 0.25
Figure 1. Ttie testing macliine with a thin plate placed on four supports; the loading head is placed between two supports at the edge of the plate
T h e c a s t i n g m e t h o d w a s c h o s e n t o o p t i m i z e t h e p e r f o r m a n c e o f t h e f i b r e s by a l i g n i n g t h e m in t h e d i r e c t i o n o f p r i n c i p a l stresses. T h e m o s t c r i t i c a l l o a d i n g p o i n t o f t h e p l a t e w a s a s s u m e d t o b e a t t h e e d g e in t h e m i d d l e o f t h e s p a n b e t w e e n t h e s u p p o r t s ; f i b r e s a l i g n e d p a r a l l e l t o t h e w a l l s o f t h e f o r m w o r k i m p r o v e t h e l o a d - b e a r i n g c a p a c i t y in t h i s l o a d i n g case. S e l f - l e v e l l i n g c o n c r e t e w a s f i l l e d in a b u c k e t a n d t h e f o r m w o r k w a s f i l l e d a c c o r d i n g t o t h e p r o c e d u r e i n d i c a t e d b y Figure 2. T h e f i b r e s o r i e n t e d d u e t o t h e f l o w t h r o u g h t h e b u c k e t a n d d u e t o t h e f r e e f l o w in t h e m o u l d p a r a l l e l t o t h e w a l l s o f t h e f o r m w o r k . T h e s l u m p f l o w w a s 7 9 9 m m ( w i t h o u t f i b r e s ) , 7 5 2 m m ( V p 7 7 , 5 k g / m ^ ) a n d 6 8 8 m m (Vf=155 k g / m ^ ) .
R E S U L T S A N D D I S C U S S I O N
T h e p l a t e s w e r e t e s t e d 5 6 d a y s a f t e r c a s t i n g . T a b l e 3 s h o w s t h e r e s u l t s o f c o m p r e s s i o n a n d s p l i t t i n g t e n s i l e t e s t s e x e c u t e d a t d i f f e r e n t c o n c r e t e ages; t h e r e s u l t s are single t e s t s o b t a i n e d w i t h c u b e s o f 1 0 0 m m .
Table 3. Compressive and spiitting tensiie strengtiis at different concrete ages and witfi different fibre contents
Fibre dosage 0 77,5 155
Concrete age [days] [l<g/mM [kg/mM [kg/m^]
Compressive strengtti [MPa] [iVIPa] [MPa]
14 days 129,1 140,1
28 days -
-
150,356 days 148,1 144,7 164,2
Spiittinq tensile strength [IVlPa] [MPa] [MPa]
56 days 12,6 16,4 17,4 T h e i n c r e a s e in c o m p r e s s i v e s t r e n g t h d u e t o t h e a d d i t i o n o f 1 5 5 k g / m ^ s t e e l f i b r e s 5 6 days a f t e r c a s t i n g w a s 1 6 , 1 M P a (10,9 %) c o m p a r e d t o t h e r e f e r e n c e m i x t u r e w i t h o u t f i b r e s ( 1 4 d a y s : 1 5 , 7 M P a ) . A t t h e h i g h e s t f i b r e d o s a g e t h e s p l i t t i n g t e n s i l e s t r e n g t h 5 6 d a y s a f t e r c a s t i n g w a s 1 7 , 4 M P a , w h i c h is a s t r e n g t h i n c r e a s e o f 3 8 % c o m p a r e d t o t h e r e f e r e n c e m i x t u r e w i t h o u t f i b r e s . Figure 3 p r e s e n t s t h e l o a d - d e f l e c t i o n r e s u l t s o f t h e six p l a t e s .
Figure 3. Load-deflection diagram: concentrated loading of thin plates
3,5
3,0
2,5
Ou-1,0
0,0
11 _
V u—iz-iTG= T e s t 1 (No fibres)
Ik
— T e s t 2 (No fibres)
1
' 7 1 • •/
i i —* '10 15 20 25
30
t w o r e s u l t s ) w a s 3 9 3 % r e l a t i v e t o t h e m a x i m u m l o a d o b t a i n e d w i t h t h e r e f e r e n c e p l a t e s ( w i t h o u t f i b r e s ) w i t h 5 0 % o f t h e m a x i m u m f i b r e d o s a g e a n d 5 0 7 % w i t h 1 0 0 % o f t h e m a x i m u m f i b r e d o s a g e , r e s p e c t i v e l y . T h e i m p r o v e m e n t o f t h e m a x i m u m f l e x u r a l s t r e n g t h w i t h 7 7 , 5 k g / m ^ e x t r a f i b r e s w a s o n l y 2 9 % ( f i b r e c o n t e n t 1,97 V o l . - % c o m p a r e d t o 0,99 V o l . - % ) . T a b l e 4 s u m m a r i s e s r e s u l t s c o n c e r n i n g t h e m a x i m u m l o a d a n d t h e v e r t i c a l d e f o r m a t i o n at t h e m a x i m u m f l e x u r a l l o a d .
Table 4. Maximum load and vertical deformation at the maximum load
Plate Fibre Force Average Def. at
Nr. dosage [kN] max. max.
[Vol.-%] load load
[kN] [mm] 1 0 0,69 0,60 1,46 2 0 0,52 1,55 3 0,99 2,23 2,36 12,26 4 0,99 2,49 14,57 5 1,97 2,83 3,05 14,31 6 1,97 3,26 12,14 T h e h i g h e s t l o a d w a s o b t a i n e d in Test Nr. 6 ( 3 , 2 6 KN). T h e l o w e s t s t r e n g t h class a c c o r d i n g t o EN 1 2 8 2 5 (Table 1 : Class 1) r e q u i r e s a m i n i m u m l o a d o f 4 KN, w h i c h also i n c l u d e s a r e d u c t i o n o f t h e c h a r a c t e r i s t i c e x p e r i m e n t a l s t r e n g t h by a s a f e t y f a c t o r (2,0 o r 3,0 d e p e n d e n t o n t h e a p p l i c a t i o n ) . F u r t h e r m o r e , t h e m a x i m u m d e f l e c t i o n at th'e m a x i m u m l o a d is l i m i t e d . T h e m a x i m u m d e f l e c t i o n is a c r i t i c a l d e s i g n p a r a m e t e r f o r t h i n p l a t e s . T h e f l e x u r a l b e h a v i o u r o f Plates 5-6 is a l m o s t l i n e a r u p t o a v e r t i c a l d e f l e c t i o n o f 4 m m . A t a d e f l e c t i o n o f 4 m m (Class C), t h e e x p e r i m e n t a l l o a d o f Plate 6 w a s 2 , 0 3 KN ( o n l y 5 0 , 8 % o f t h e s t r e n g t h r e q u i r e d f o r Class 1 , T a b l e 1) w i t h o u t c o n s i d e r i n g s t a t i s t i c a l v a r i a t i o n a n d s a f e t y f a c t o r s (Table 5 ) . In s p i t e o f an i m p o r t a n t c o n t r i b u t i o n o f t h e s t e e l f i b r e s t o t h e f l e x u r a l p e r f o r m a n c e , t h e r e s u l t s i n d i c a t e t h a t t h i n p l a t e s r e q u i r e a h i g h e r s t r e n g t h a n d a s t i f f e r f l e x u r a l b e h a v i o u r in o r d e r t o f u l f i l t h e c r i t e r i a a c c o r d i n g t o EN 1 2 8 2 5 .
Table 5. Load of the 6 plates at a vertical deformation of 2,5, 3 and 4 mm, respectively
Deflection class A B C Load [KN] 2,5 mm 3 mm 4 mm Plate 1 0,49 - _ Plate 2 - - -Plate 3 1,29 1,48 1,72 Plate 4 1,42 1,63 1,90 Plate 5 1,06 1,29 1,63 Plate 6 1,25 1,52 2,03 T h e t h i c k n e s s o f t h e p l a t e s has t o b e i n c r e a s e d in o r d e r t o m e e t t h e r e q u i r e m e n t s -s t i f f n e -s -s . T h e -s t r e n g t h level can be i n c r e a -s e d by a d d i n g a d d i t i o n a l f i b r e -s a n d / o r r e b a
C o a t e d o r s t a i n l e s s s t e e l r e b a r s c o u l d b e a p p l i e d in case o f i n s u f f i c i e n t c o n c r e t e c o v e r a n d / o r t o o h i g h p r o d u c t i o n t o l e r a n c e s . Plates 1-2 f a i l e d b r i t t l e in b e n d i n g w i t h a single crack r u n n i n g t h r o u g h t h e m i d d l e o f t h e p l a t e b e t w e e n t h e s u p p o r t s (Figure 4 : Plate 1). T h e m a x i m u m l o a d o f Plate 2 w a s o n l y 0 , 5 2 K N .
Figure 4. Faiiure pattern of Piate 1 after tiie execution of the test
IT'
A"
I n \
Plates 3-6 l o c a l l y f a i l e d in t h e v i c i n i t y o f t h e l o a d i n g h e a d (Figure 5: Plate 3 (Vf=77,5 k g / m ^ ) ; Figure 6: Plate 6 V f = 1 5 5 k g / m ^ ) ) . In e a c h case, a s m a l l p a r t o f t h e p l a t e w a s p u s h e d d o w n by t h e l o a d i n g h e a d .
Figure 5. Horizontal view on Plate 3 Figure 6. Horizontal view on Plate 6 after the execution of the test after the execution of the test
T h e f a i l u r e p a t t e r n s o f Plates 4-5 w e r e s i m i l a r w i t h t h e f a i l u r e p a t t e r n s h o w n by Figure 5 (Plate 3 ) . T h e f a i l u r e p a t t e r n o f Plate 6 d i f f e r e d f r o m Tests 3 - 5 : a n a d d i t i o n a l c r a c k a p p e a r e d in t h e p u l l e d - o u t c o n c r e t e p a r t o f Plate 6 b e l o w t h e l o a d i n g p r i s m . T h e
m a x i m u m l o a d is t h e s u m o f t h e e l a s t i c d e f o r m a t i o n o f t h e p l a t e a n d a local d e f o r m a t i o n (by o p e n i n g o f cracks) c l o s e t o t h e l o a d i n g h e a d . C O N C L U S I O N S This p a p e r d e s c r i b e s t h e t e s t i n g o f t h i n p l a t e s p r o d u c e d w i t h s e l f - c o m p a c t i n g c o n c r e t e w i t h a n d w i t h o u t f i b r e s f o r t h e a p p l i c a t i o n ' p l a t e s in a d o u b l e - f l o o r s y s t e m ' . Based o n t h e e x p e r i m e n t a l s t u d y t h e f o l l o w i n g c o n c l u s i o n s can b e d r a w n : T h e f l e x u r a l p e r f o r m a n c e o f t h i n p l a t e s w a s s i g n i f i c a n t l y e n h a n c e d d u e t o t h e a d d i t i o n o f s t e e l f i b r e s . T h e m a x i m u m l o a d i n c r e a s e d by 3 9 3 % (Vf=77,5 k g / m ^ j c o m p a r e d t o p l a t e s t h a t c o n t a i n e d n o f i b r e s . By d o u b l i n g t h e f i b r e d o s a g e t h e m a x i m u m f l e x u r a l s t r e n g t h w a s i n c r e a s e d by a m o d e r a t e 2 9 % r e l a t i v e t o p l a t e s c o n t a i n i n g h a l f t h e f i b r e d o s a g e . T h e f a i l u r e p a t t e r n d e p e n d e d o n t h e c o n t e n t a n d t h e d i s t r i b u t i o n o f t h e f i b r e s . In o r d e r t o b e a p p l i e d as f l o o r p a n e l s a c c o r d i n g t o EN 1 2 8 2 5 t h e f l e x u r a l s t r e n g t h a n d f l e x u r a l s t i f f n e s s o f t h e p a n e l s h a v e t o be i n c r e a s e d . I n c r e a s i n g t h e t h i c k n e s s o f t h e p l a t e s ( a l t e r n a t i v e l y : r i b s c o u l d b e c o n s i d e r e d ) is n e c e s s a r y t o f u l f i l t h e c r i t e r i o n o n t h e m a x i m u m d e f l e c t i o n at t h e m a x i m u m l o a d . A C K N O W L E D G E M E N T S T h e s t u d y o n t h i n p l a t e s w i t h s e l f - c o m p a c t i n g f i b r e r e i n f o r c e d c o n c r e t e w a s c a r r i e d o u t in c o r p o r a t i o n w i t h F l o o r i n g BV (The N e t h e r l a n d s ) a n d B e k a e r t ( B e l g i u m ) . LIST O F R E F E R E N C E S
1. Grünewald, S., Performance-based design of self-compacting fibre reinforced concrete. PhD-thesis, Delft University of Technology, Department of Structural and Building Engineering, Delft University Press, 2004, ISBN: 9040724873.
2. Pereira, E.N.B., Barros, J.A.O. and Camoes, A., Steel fiber reinforced self-compacting concrete: Experimental research and numerical simulation, ASCE Journal of Structural Engineering, 134, 2008, pp. 1310-1321.
3. Maten, R. ter, Grünewald, S., Walraven, J.C: UHPFRC in large span shell structures, RILEM-fib-AFGC Int. Symposium on UHPFRC, UHPFRC 2013, Marseille, 2013 (to be published, October 2013).
