- Email: [email protected]
Chloride diffusion in steel fibre reinforced concrete containing PFA
CEMENT and CONCRETE RESEARCH. Vol. 17, pp. 640-650, 1987. Printed in the USA. 0008-8846/87 $3.00+00. Copyright (c) 1987 Pergamon Journals, Ltd.
CHLORIDE
P.S.
DIFFUSION IN STEEL FIBRE REINFORCED CONCRETE CONTAINING PFA
Mangat and Krlbanandan Gurusamy D e p a r t m e n t of E n g i n e e r i n g U n i v e r s i t y of A b e r d e e n Marischal College Broad Street A b e r d e e n , U.K.
(Communicated by A.J. Majumdar) (Received March 24, 1987) ABSTRACT
The paper presents chloride diffusion characteristics of a s t e e l f i b r e reinforced 0PC-pfa concrete mix which was manufactured by replacing 26 p e r c e n t of o r d i n a r y Portland cement with pfa. Steel fibre reinforced marine mixes generally require h i g h c e m e n t c o n t e n t s of the o r d e r
of 590 k g / m 3 a n d u s e
of p f a r e s u l t s
in e q u i v -
valent practical mixes of a more reasonable cement content. A m i x of p r o p o r t i o n s b y w e i g h t of 0 . 2 6 (pfa) : 0 . 7 4 (0PC) : 1.51 : 0 . 8 4 w i t h a w a t e r / ( 0 P C + p f a ) ratio of 0.4 w a s r e i n f o r c e d w i t h t h r e e t y p e s of s t e e l fibres. Uncracked and pre-cracked prism specimens were cured under simulated splash zone e x p o s u r e in the l a b o r a t o r y a n d at A b e r d e e n beach, a f t e r i n i t i a l d r y c u r i n g in the laboratory. T h e r e s u l t s s h o w that the p e r i o d of i n i t i a l d r y c u r i n g has an insignificant effect on C1 d i f f u s i o n in c o n crete. C1 concentrations are h i g h e r in the 0 P C - p f a m i x in c o m p a r i s o n with the marine mix based only on OPC. Most of the C1 p e n e t r a t i o n o c c u r s w i t h i n 150 m a r i n e c y c l e s (110 days) of e x p o s u r e a n d Cl concentrations increase significantly in the v i c i n i t y of w i d e r cracks. Introduction
Steel fibre reinforced concrete mixes require a high "fines" c o n t e n t in o r d e r to allow efficient e m b e d m e n t of f i b r e s in the matrix without impairing workability. To m e e t the s t a n d a r d d u r a b i l i t y r e q u i r e m e n t of low water/cement r a t i o for m a r i n e c o n c r e t e (1, 2), s t e e l f i b r e r e i n f o r c e d m i x e s , t h e r e f o r e , t e n d to r e q u i r e a very high cement content (S). A r e c e n t m i x d e v e l g p e d b y the a u t h o r s r e s u l t e d in a cement content of 590 k g / m - (3). One 640
Vol. 17, No. 4
641
CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
convenient w a y of r e d u c i n g the cement content a n d at t h e s a m e time maintaining a low water/cementitious material ratio and a h i g h f i n e s c o n t e n t is to r e p l a c e a f r a c t i o n of the c e m e n t w i t h pfa. Such a mix for m a r i n e a p p l i c a t i o n s has been developed (4),
resulting
in a c e m e n t
content
of
430
kg/m 3 which
satisfies
the m i n i m u m c e m e n t r e q u i r e m e n t of m a r i n e m i x e s (5). T h e Cldiffusion characteristics of s u c h a n O P C - p f a m i x a r e r e p o r t e d in this paper and a comparison of d i f f u s i o n c h a r a c t e r i s t i c s is m a d e with the original marine mix of steel fibre concrete which was b a s e d o n o r d i n a r y P o r t l a n d c e m e n t a l o n e (OPC mix). Research in r e c e n t y e a r s h a s c o n c l u d e d t h a t p f a c o n c r e t e d o e s n o t d e c r e a s e the c o r r o s i o n p r o t e c t i o n to s t e e l r e i n f o r c e m e n t compared with normal concrete (6). In fact s o m e r e s e a r c h e r s report that corrosion protection is i n c r e a s e d b y the i n c l u s i o n of p f a d u e to greater resistance a g a i n s t Cl diffusion (7, 8, 9). These conclusions, however, are dependent on the source of p f a a n d a r e based on controlled laboratory curing conditions which are highly favourable for p o z z o l a n i c reaction.
Experimental Mixes
and
Materials
A steel fibre reinforced c o n c r e t e m i x for m a r i n e a p p l i c a t i o n s was d e v e l o p e d u s i n g p f a as a p a r t i a l replacement for O P C in a n e x i s ting marine mix which has been reported previously (3,10). The mix design and trial mixes for this OPC-pfa mix are reported elsewhere (4). The proportions b y w e i g h t of t h e m i x w e r e 0 . 2 6 :1.51 :0.84 with a water /(OPC+pfa) r a t i o of tent
of
this
mix
was
435
were manufactured with ment, d e t a i l s of w h i c h
k g / m 3.
Four
different are given TABLE
Mix B
Fibre details d v (mm) (~)
-
o
-
0
of
t y p e s of s t e e l in T a b l e 1.
: 0 . 7 4 (OPC) The OPC con-
these fibre
proportions reinforce-
I
D e t a i l s of mlxee,
1 (mm)
mixes
(pfa) 0.4.
fibres and curing
vf i/d F i b r e type
Curing " Conditions Sh , Sh~4 Bh14
0
BME
26.5
0.44
1.7
100
Melt e x t r a c t (ME}
BMS
28.2
0.48
1.7
100
Low c a r b o n steel, (MS)
Sh14
BCR
40
0.60
1.7
112
C o r r o s i o n reslstant, (CR)
Sh14
Sh 1, S h 1 4
- m a r i n e s h o w e r c u r e d after l a b o r a t o r y air c u r i n g
Bh14
- beach curing after curing
"
I or 14 d a y s
14 days l a b o r a t o r y air
642
Vo]. ]7, No. 4 P.S. Mangat and K. Gurusamy
O r d i n a r y P o r t l a n d c e m e n t (OPC), f i n e a g g r e g a t e c o n f o r m i n g to z o n e 2 of B S 8 8 2 a n d granite coarse aggregate of i0 m m n o m i n a l s i z e were used. The pfa was obtained from Longannet power station near Edinburgh. Typically the ash contained about 48~ silica, 38% alumina and 4.5~ iron oxide. T h r e e t y p e s of s t e e l f i b r e s were used namely, melt extract (ME), l o w c a r b o n s t e e l (MS) a n d corrosion resistant (CR). The latter two fibres had hooked ends. A maximum vfl/d ratio of 112 w a s u s e d , vf b e i n g f i b r e volume, Castinq,
1 the
length
Curing
and
and
d the
fibre
diameter.
Testing
i00 x i00 x 500 m m p r i s m s p e c i m e n s w e r e c a s t in t h r e e l a y e r s e a c h layer being compacted on a vibrating table. The fresh concrete was covered with polythene sheets a n d d e m o u l d e d a f t e r 24 h o u r s . T h e s p e c i m e n s w e r e t h e n l e f t to c u r e in t h e l a b o r a t o r y air, u n d e r uncontrolled humidity and temperature for a p e r i o d of b e t w e e n o n e and fourteendays as indicated in Table I. Subsequently the prism specimens were transferred either to a sea water spray c h a m b e r in t h e l a b o r a t o r y or to A b e r d e e n b e a c h . T h e s e a w a t e r s p r a y c h a m b e r in the l a b o r a t o r y w a s b u i l t to s i m u late marine splash and tidal zone conditions. It w a s a u t o m a t i c a l l y c o n t r o l l e d to p r o v i d e t w o w e t a n d two d r y c y c l e s in t w e n t y four hours. This cyclic exposure corresponded c l o s e l y to t h e t i d a l c y c l e s of t h e sea. The s p e c i m e n s at A b e r d e e n b e a c h w e r e a t t a c h e d to g r o y n e s w h e r e t h e y w e r e e x p o s e d to t i d a l c y c l e s . A l i m i t e d n u m b e r of p r i s m s p e c i m e n s w e r e l o a d e d in f l e x u r e a f t e r t h e i n i t i a l 14 d a y s of laboratory a i r c u r i n g in o r d e r to i n d u c e c r a c k s of w i d t h s r a n g i n g between 0.07 and 0.76 mm. The prec r a c k e d s p e c i m e n s w e r e , then, t r a n s f e r r e d to the s e a w a t e r s p r a y c h a m b e r in the l a b o r a t o r y . In t h e c a s e of i n i t i a l l y uncracked specimens, tests were conduct e d a f t e r 150, 300 a n d 1 2 0 0 cycles of w e t t i n g a n d d r y i n g in t h e marine spray chamber. These corresponded to the age of IiO, 185 a n d 620 days respectively. The beach cured specimens w e r e t e s t e d a f t e r 150, 300, a n d 1 2 0 0 tidal cycles which corresp o n d e d to i00, 160 a n d 640 d a y s respectively. The prism specimens with initially induced cracks w e r e t e s t e d a f t e r 650 m a r i n e s p r a y c y c l e s in t h e l a b o r a t o r y s p r a y c h a m b e r . In t h e c a s e of initially uncracked specimens, three prisms per m i x in T a b l e 1 w e r e tested in f l e x u r e a f t e r e a c h a g e of m a r i n e exposure. T h e f r a c t u r e d f a c e f r o m e a c h of t h e p r i s m s w a s u s e d to o b t a i n s a m p l e s for c h l o r i d e a n a l y s i s . A s i n d i c a t e d in Fig. i, a c o o r d i n a t e s y s t e m w i t h f a c e I b e i n g t h e x-axis and face 2 being the y-axis was selected, the top face d u r i n g c a s t i n g b e i n g F a c e 4. S a m p l e s w e r e t a k e n a l o n g x = 50 m m and at y = 8, 15, 20, 25, 35, 50, 65, 75, 80, 85, a n d 92 mm, depending on the duration of curing. The d r i l l i n g s at e a c h sample position, for t h e t h r e e p r i s m s p e c i m e n s , w e r e c o m b i n e d to g i v e a t e s t s a m p l e for c h l o r i d e a n a l y s i s .
Vol.
17, No. 4
643
CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA y-axis
Face 3
lOOmm gO
o?e,
80
70-
,6
60
l
.4-
'~50i
e,
o;
30-
i
20-
,e
10-
P
10 2'0 3'0 iO .~0 dO 7'0 gO 9'0 lOOrnm x-axis Face1 Fig.
1
Sampling
locations
for
chloride
analysis
In t h e c a s e of p r i s m s with initially induced cracks, the proced u r e for t a k i n g s a m p l e s for Cl analysis is g i v e n in d e t a i l in a p r e v i o u s p a p e r (10). Samples were t a k e n a d j a c e n t to a c r a c k at different depths from the extreme tension f a c e of t h e p r i s m s . Corresponding samples representing uncracked concrete were obtained f r o m a p o s i t i o n r e m o t e f r o m the c r a c k (I0). For chemical analysis, 1.5 to 2.5 g of p o w d e r e d c o n c r e t e w a s taken and chloride extracted by heating in d i l u t e n i t r i c acid. On cooling the neutralized solution was filtered and the Mohr titration (10, 11) c o n d u c t e d . The percentage chloride by weight of concrete was obtained from the following f o r m u l a (3, 4, 10) 35.453 vN Cl- i0 w w h e r e N is t h e n o r m a l i t y of A g N O 3, v is the v a l u e of A g N O 3, a n d w is t h e weight of powdered sample in grams. Since the mix proportions of c o n c r e t e from which chloride was extracted were k n o w n , t h e ~ Cl b y w e i g h t of c e m e n t c o u l d b e c a l c u l a t e d .
Results
and
Discussion
T h e i n f l u e n c e of fibre volume o n Cl diffusion characteristics w a s f o u n d to b e insignificant from the data presented in t h i s paper and also results reported elsewhere (3). Therefore, data at d i f f e r e n t v f I/d ratios have been combined where relevant "Best fit"" d i f f u s l o n curves were plotted through the Cl: penetration data by using a computer programme for the s o l u t i o n of F i c k s l a w of diffusion (12, 13), as d e s c r i b e d in g r e a t e r detail elsewhere (3, I0). The values of D c, the chloridediffusion
constant,
and
C° ,
the
equilibrium
chloride
Vol. 1 7 ,
644
No. 4
P.S. Mangat and K. Gurusamy
level
on
concrete
surface,
were
also
obtained
by
this
computation. The Cl- p e n e t r a t i o n r e s u l t s for l a b o r a t o r y s h o w e r c u r e d and b e a c h c u r e d s p e c i m e n s , after 150 and 300 c y c l e s of e x p o s u r e , are g i v e n in Figs. 2 a n d 3. It is c l e a r l y e v i d e n t that Cl levels are s i g n i f i c a n t l y h i g h e r in m a r i n e shower c u r e d specimens. This is e s s e n t i a l l y due to the higher Clcontent of sea w a t e r in the s h o w e r _ o w i n g to c o n t i n u o u s e v a p o r a t i o n (i0). In Figs. 2 and 3, the C1 p r o f i l e s of shower c u r e d s p e c i m e n s (MC) are r e p r e s e n t e d by two lines, shl and shl4, w h e r e 1 and 14 d e n o t e the d u r a t i o n in days of initial dry curing prior to marine exposure. It is e v i d e n t that the duration of this initial dry c u r i n g has an i n s i g n i f i c a n t i n f l u e n c e on CIconcentrations in concrete. In the f o r t h c o m i n g d i s c u s s i o n , therefore, results for shl and sh14 have b e e n combined. The Cl- p e n e t r a t i o n p r o f i l e s a t up 1200 c y c l e s of m a r i n e e x p o s u r e are p l o t t e d in Fig. 4. It is e v i d e n t that D c d e c r e a s e s w i t h duration cycles
of exposure, being
the v a l u e s
8.58 x 10 -8,
respectively.
In
corresponding
steel
150,
7.18 xlO -8
comparison,
mix of
after
the
fibre
and
average reinforced
300 and
1200 m a r i n e
1.35 xl0 -8 c m 2 / s e c values
of D c for a
c o n c r e t e w h i c h did
3.0 ~[ (
Hix proportions: 0.26:0-7~,:1.51:0.8&:0.~0 Fibre type:HE, HS, ER
2.8 ~ :,.6 -~
•~
vf
0.1 and 112
"~ 2.z,,-
.9 2"2g 2.0-
~ 2-8.~ 1-6! E
-e EH2/sec
._~
)-8CMZ/sec
~ 1.00.8-
0.6 04 0.2 0
Dc
~'o
~
20 '
z~
3b
3'5
~o
Depth of penetration into concrete (ram)
Flg.
2
Chloride penetration c y c l e s a n d 160 tidal
into c o n c r e t e a f t e r c y c l e s of e x p o s u r e
150 m a r i n e
Vol. 17, No. 4
645
CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
3-0-
Mix proportions:0.26:0-7/,: 1-51:(}S&: 0-6,0 Fibre fype:ME,MS, CR vf I/d: 0,100 and 112
2.8to
~
26
Oc=7.23x10"s CMZ/sec
22. \ Dc=7.12x10 -a
._o 2-2-
[MZ/sec
~ 2.0~ 1.8-
~01"62 1.4-
1.2~=1"0$ O.B~o O~O-&-
0.2- Dc=3.S9xI0-B
15
i~
25
z~
35
3~
40
Depth of penetration into concrete(ram) Fig.
3
Chloride or t i d a l
not
incorporate
2.81
xl0 -8 c m 2 / s e c
tively
(10).
The
penetration into concrete c y c l e s of e x p o s u r e
any
pfa
aZter
were
150,
reduction
300
6.13 and
of D c w i t h
x
10 -8,
2000 age
after
300 m a r i n e
3.90
marine
x 10 -8
cycles
is clear,
and
respec-
although
the
e f f e c t of p f a i n c l u s i o n is not r e a d i l y evident. The r e s u l t s in Fig. 4 a l s o s h o w that most of the C1 penetration had taken place a f t e r 150 MC (110 days) with s u b s e q u e n t i n c r e a s e s b e i n g small. T h i s o b s e r v a t i o n has a l s o b e e n r e p o r t e d e l s e w h e r e (10, 14). The C1 penetration profiles at up to 1200 c y c l e s of tidal exposure at A b e r d e e n b e a c h are p l o t t e d in Fig. 5. It is e v i d e n t that the v a l u e s of D c decrease with c u r i n g age, as n o t e d a b o v e for m a r i n e
spray
cured
specimens.
The v a l u e s
after
160,
300
and
1200 tidal cycles are 9.95 xlO -8, 3.59 xlO -8 and 1.60 x 10 -8 2 cm /sec r e s p e c t i v e l y . In comparison, the a v e r a g e v a l u e s of D for a c o r r e s p o n d i n g cm2/sec
after
mix
150 a n d
without
1200
tidal
pfa were cycles
7 . 5 6 x 1 0 -8 a n d
respectively
2 . 3 x 1 0 -~
(10).
The CI- c o n c e n t r a t i o n d a t a of the OPC b a s e d m i x a n d the O P C - p f a m i x at 150 a n d 300 m a r i n e c y c l e s of e x p o s u r e are p l o t t e d in Fig. 6. The g r a p h s s h o w that C1 levels are s i g n i f i c a n t l y h i g h e r in the O P C - p f a mixes, especially within the s u r f a c e zones. This i n d i c a t e s g r e a t e r p e r m e a b i l i t y of OPC-pfa concrete which results
646
Vol. 17, No. 4 P.S. Mangat and K. Gurusamy
3"8 3~3"&Mix proportions: 0.26: 0.7& :1.51: 0.8/+: 0./+0 Fibre type: ME, MS, ER. Vf~d: 0,100 and 112
3"2= ._m 3"0¢ L-
2.8 (
~2-6o z 2-&g ~ 2.2-
Oc = 1.35 ~ 10"s CM21sec
~6 2-OT: .-~ 1-8-
=>,
1-6-
1./,.-
_~ 1.2~I... 1.0o
0.8-
Oc=7.18x10 s [MZ/sec
0.604+-
Oc=8.S8xlC
0.2-
Depth of penetration into concrefe (ram)
Fig.
4
Chloride marine
penetration cycles
into
concrete
exposed
to
spray
in more r a p i d Cl diffusion characteristics. In recent years, it has generally been stated that OPC-pfa concretes are more i m p e r m e a b l e than OPC c o n c r e t e (15, 16, 17). For example, P a g e (17) has c o n c l u d e d that b l e n d e d c e m e n t s c o n t a i n i n g pfa limit Cl d i f f u s i o n into c o n c r e t e more effectively than P o r t l a n d cement. T h e s e c o n c l u s i o n s are c o n t r a r y to the o b s e r v a t i o n of Fig. 6 due to the d i f f e r e n c e in initial c u r i n g c o n d i t i o n s a d o p t e d in these v a r i o u s studies. W h e r e a s the s p e c i m e n s of the p r e s e n t i n v e s t i g a tion w e r e initially dry cured in the laboratory, the c u r i n g conditions adopted by others ensured prolonged moist c u r i n g (15, 16) or c u r i n g in C a ( O H ) 2 s o l u t i o n p r i o r to e x p o s u r e to salt s o l u t i o n s (17). It is k n o w n that the p o z z o l a n i c a c t i o n of pfa is considerably enhanced by initial curing conditions such as a d o p t e d by Page (17) and, therefore, the r e s u l t i n g i m p e r m e a b i l i t y of O P C - p f a concretes is understandable. However, such curing conditions are normally impractical on site. The i n i t i a l l y dry c u r i n g c o n d i t i o n s u s e d in this i n v e s t i g a t i o n represent site conditions to which structural c o n c r e t e s are o f t e n exposed. T h e s e c o n d i t i o n s w e r e c h o s e n to a l l o w m a x i m u m s h r i n k a g e and reduced hydration and consequently determine diffusion
Vol.
17, No. b,
G47 CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
~ 2'6 ~o 2-2- ~ ~ =1`60x10-eCMZlsec .#-
Z.08 1.8-
Oc = 3-59x 10e £HZ/sec
1.6-
~= •~ 1.~,-
\
.
~-
Htx proportions:0.26:0.%: 1-51:0-8/,:0.~,0 Fibre type:ME v,t,.:0 and 100
~., ~ \ \ ~ o, ~ 1.0-
~, ~.2o/
~> 0.86 0
0.60./, 0.25
Fig.
5
Chloride
10 15 20 25 30 Depth of penetration into concrete(mm)
penetration
into
concrete
35
~0
exposed
to
tidal
cycles
3"0-
2'8t
2"6-
==
2.~-
._o2.2 2.0
',',, ~t~
--
~,
Hix A (OPC'Vf[/d =0 and%7)
".... MixB (OPC-pfa,vf [/d =0and 100)
=E
1.8~= 1,61.~-
"~ •
~= 1"2-
~
",
300MCl304days)
1"0-
iilM£ 1110days)
~ o.e-
~ o.g
150HC M£(15/, (15~days) d a y s )~
~ " '~- . . " '~- . . . .". . . . _
..
0.2i
5 Fig.
6
i
1
i
i
i
----
i
10 15 20 25 30 35 Depth of penetration into concrete(ram)
Chloride penetration to laboratory marine
profiles into spray cycles
m"
concrete
~0 exposed
648
Vol. 17, No. 4 P.S. Mangat and K. Gurusamy
characteristics under more critical conditions w i t h r e s p e c t to construction practice. Under such conditions OPC-pfa concretes a r e l e s s r e s i s t a n t to Cl penetration. Cl penetration profiles in pre-cracked concrete, for the r a n g e of i n i t i a l c r a c k w i d t h s i n d u c e d , are plotted in Fig. 7. It is e v i d e n t t h a t C1 concentration increases with increasing crack w i d t h , the r a t e of i n c r e a s e in C1 being greater nearer the concrete surface. Depfh(mm)
8
20
30
50
Symbo{
o
~,
v
o
1'0"
0.9
o ° °
Bmm
o
0.8"6 0 7 T= cm •~ 0.63~
~05-
~, 0.3-
~
~o
m
20ram
o
a
30-50ram
02 "Co t_l
0.10
0'.1 o'2 0'.3 0'4 ols 0'.6 0!7 o'.s 019 1'-0 Avernge crock widfh (mm)
Fig.
7
E f f e c t of c r a c k w i d t h on c h l o r i d e p e n e t r a t i o n , 6 5 0 m a r i n e s p r a y c y c l e s of e x p o s u r e
after
Detailed profiles of CIdiffusion across the d e p t h of p r e c r a c k e d s p e c i m e n s a r e g i v e n in Fig. 8, in the v i c i n i t y of c r a c k s of w i d t h 0.2 m m and O.61 mm. The corresponding profiles for uncracked c o n c r e t e a r e a l s o shown. It is a p p a r e n t t h a t i n c r e a s e s in Cl concentrations r e l a t i v e to u n c r a c k e d c o n c r e t e a r e s m a l l in the v i c i n i t y of c r a c k s of w i d t h 0.2 m m w h e r e a s t h e y b e c o m e s i g n i f i c a n t for l a r g e r c r a c k s . Conclusions The following conclusions presented in t h i s p a p e r .
are
based
on
the
experimental
takes
results
i.
M o s t of t h e c h o r i d e penetration in concrete 150 c y c l e s (ii0 days) of m a r i n e e x p o s u r e .
place
by
2.
The has
3.
Partial replacement of ordinary P o r t l a n d c e m e n t w i t h pfa, in m a r i n e m i x e s of s t e e l fibre concrete, r e s u l t s in h i g h e r Cl
d u r a t i o n of i n i t i a l d r y _ c u r i n g , p r i o r to m a r i n e e x p o s u r e , l i m i t e d i n f l u e n c e o n Cl diffusion characteristics.
Vol. 17, No. 4
649 CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
100-
/ / ~ ' ~
%0%
\
/°?:
\
/
%A %% ~%
%
~
.
.
.A. vicinity of
"~ A , . crack uncracked " ~ - o "'----~
lo-
~-i o'.2 0:3 o'.~ 0% o'.6 o'.7 o'.8 0:9
% Chloride content by weight of concrete .
"~
Oet 8
m
801 -~7o
/ ~/,0" /c~30-
~, ",%.. vicinity of "~-. crack uncrocked "-'~=oP
o:1 0:2 o~3 o:~ o% o% ~7 ~8 ~.9
%Chloride content by weight of concrete
Fig.
8
Chloride penetration marine spray cycles
into c r a c k e d
d i f f u s i o n r a t e s w h e n the concrete tions p r i o r to m a r i n e e x p o s u r e . 4.
In c r a c k e d c o n c r e t e , cracks increase with
concrete
is c u r e d u n d e r
after
650
dry c o n d i -
Cl concentrations in the v i c i n i t y i n c r e a s i n g c r a c k width.
of
Acknowledgements The a u t h o r s g r a t e f u l l y a c k n o w l e d g e the f i n a n c i a l s u p p o r t from the SERC M a r i n e T e c h n o l o g y Directorate for the r e s e a r c h p r o j e c t on m a r i n e d u r a b i l i t y of steel fibre concrete. The a u t h o r s also g r a t e f u l l y a c k n o w l e d g e the advice and f a c i l i t i e s made a v a i l a b l e by P r o f e s s o r F.P. G l a s s e r of the C h e m i s t r y D e p a r t m e n t , A b e r d e e n University.
References
i •
2. 3. 4.
FIP, R e c o m m e n d a t i o n s for the design and c o n s t r u c t i o n of c o n c r e t e sea s t r u c t u r e s , 28 (1974). R.D. BROWNE, P.L. DOMONE and M.P. G E O G H E G A N , Proc. Instn. Civ. Engrs., part I 137 (1977). P.S. M A N G A T and K. GURUSAMY, Int. Conf. on b e h a v i o u r of o f f s h o r e s t r u c t u r e s , Delft, 867 (1985). P.S. M A N G A T and K. G U R U S A M Y , R i l e m symp. on d e v e l o p m e n t s in fibre feint, c e m e n t and concrete, Sheffield, 2 p a p e r 7.9 (1986).
650
Vol. 17, No. 4
P.S. Mangat and K. Gurusamy
5. 6. 7.
8. 9. i0.
11. 12. 13. 14.
B r i t i s h S t a n d a r d 8110, Part 1 (1985). S.S. REHSI, Information Circular IC8640, U.S. B u r e a u of Mines, W a s h i n g t o n DC, 231 (1973). T.J. L A R S E N a n d C.L. PAGE, Proceedings of the f o u r t h A s h U t i l i z a t i o n Symp., St. Louis, ERDA, M E R C / S P - 7 6 / 4 , US B u r e a u of mines, W a s h i n g t o n DC, 573 (1976). J.B. NEWMAN, P.J.E. S U L L I V A N and A.M. BELL, Concrete, 17, 9 (Dec. 1983). C.L. PAGE, N.R. SHORT and A.E.L. TARRAS, Cem. and Concr. Res., 11, 395, (1981). P.S. M A N G A T and K. GURUSAMY, " C h l o r i d e d i f f u s i o n in steel fibre r e i n f o r c e d marine concrete". Cem. and Conc. Res., under publication. I.A VOGEL, A T e x t b o o k of Q u a n t i t a t i v e I n o r g a n i c A n a l y s i s , p. 1216, L o n g m a n s , L o n d o n (1961). R.D. BROWNE, A.C.I., SP-65, 169 (1980). J. CRANK, The mathematics of diffusion, p. 414, O x f o r d press, London, (1975). J.A. S T I L L W E L L , C o n c r e t e in the o c e a n s Tech. Rep. No. 8, 59
(1983). 15. 16. 17.
D. M A N M O H A N a n d P.K. MEHTA, Cement, C o n c r e t e and A g g r e g a t e s , 3, 63 (Summer 1981). P.K. MEHTA, A.C.I., SP-79, !, 1, (1983). C.L. PAGE, N.R. S H O R T and A.EL TARRAS, Cem. a n d Conc. Res. 11, 395 (1981).
CHLORIDE
P.S.
DIFFUSION IN STEEL FIBRE REINFORCED CONCRETE CONTAINING PFA
Mangat and Krlbanandan Gurusamy D e p a r t m e n t of E n g i n e e r i n g U n i v e r s i t y of A b e r d e e n Marischal College Broad Street A b e r d e e n , U.K.
(Communicated by A.J. Majumdar) (Received March 24, 1987) ABSTRACT
The paper presents chloride diffusion characteristics of a s t e e l f i b r e reinforced 0PC-pfa concrete mix which was manufactured by replacing 26 p e r c e n t of o r d i n a r y Portland cement with pfa. Steel fibre reinforced marine mixes generally require h i g h c e m e n t c o n t e n t s of the o r d e r
of 590 k g / m 3 a n d u s e
of p f a r e s u l t s
in e q u i v -
valent practical mixes of a more reasonable cement content. A m i x of p r o p o r t i o n s b y w e i g h t of 0 . 2 6 (pfa) : 0 . 7 4 (0PC) : 1.51 : 0 . 8 4 w i t h a w a t e r / ( 0 P C + p f a ) ratio of 0.4 w a s r e i n f o r c e d w i t h t h r e e t y p e s of s t e e l fibres. Uncracked and pre-cracked prism specimens were cured under simulated splash zone e x p o s u r e in the l a b o r a t o r y a n d at A b e r d e e n beach, a f t e r i n i t i a l d r y c u r i n g in the laboratory. T h e r e s u l t s s h o w that the p e r i o d of i n i t i a l d r y c u r i n g has an insignificant effect on C1 d i f f u s i o n in c o n crete. C1 concentrations are h i g h e r in the 0 P C - p f a m i x in c o m p a r i s o n with the marine mix based only on OPC. Most of the C1 p e n e t r a t i o n o c c u r s w i t h i n 150 m a r i n e c y c l e s (110 days) of e x p o s u r e a n d Cl concentrations increase significantly in the v i c i n i t y of w i d e r cracks. Introduction
Steel fibre reinforced concrete mixes require a high "fines" c o n t e n t in o r d e r to allow efficient e m b e d m e n t of f i b r e s in the matrix without impairing workability. To m e e t the s t a n d a r d d u r a b i l i t y r e q u i r e m e n t of low water/cement r a t i o for m a r i n e c o n c r e t e (1, 2), s t e e l f i b r e r e i n f o r c e d m i x e s , t h e r e f o r e , t e n d to r e q u i r e a very high cement content (S). A r e c e n t m i x d e v e l g p e d b y the a u t h o r s r e s u l t e d in a cement content of 590 k g / m - (3). One 640
Vol. 17, No. 4
641
CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
convenient w a y of r e d u c i n g the cement content a n d at t h e s a m e time maintaining a low water/cementitious material ratio and a h i g h f i n e s c o n t e n t is to r e p l a c e a f r a c t i o n of the c e m e n t w i t h pfa. Such a mix for m a r i n e a p p l i c a t i o n s has been developed (4),
resulting
in a c e m e n t
content
of
430
kg/m 3 which
satisfies
the m i n i m u m c e m e n t r e q u i r e m e n t of m a r i n e m i x e s (5). T h e Cldiffusion characteristics of s u c h a n O P C - p f a m i x a r e r e p o r t e d in this paper and a comparison of d i f f u s i o n c h a r a c t e r i s t i c s is m a d e with the original marine mix of steel fibre concrete which was b a s e d o n o r d i n a r y P o r t l a n d c e m e n t a l o n e (OPC mix). Research in r e c e n t y e a r s h a s c o n c l u d e d t h a t p f a c o n c r e t e d o e s n o t d e c r e a s e the c o r r o s i o n p r o t e c t i o n to s t e e l r e i n f o r c e m e n t compared with normal concrete (6). In fact s o m e r e s e a r c h e r s report that corrosion protection is i n c r e a s e d b y the i n c l u s i o n of p f a d u e to greater resistance a g a i n s t Cl diffusion (7, 8, 9). These conclusions, however, are dependent on the source of p f a a n d a r e based on controlled laboratory curing conditions which are highly favourable for p o z z o l a n i c reaction.
Experimental Mixes
and
Materials
A steel fibre reinforced c o n c r e t e m i x for m a r i n e a p p l i c a t i o n s was d e v e l o p e d u s i n g p f a as a p a r t i a l replacement for O P C in a n e x i s ting marine mix which has been reported previously (3,10). The mix design and trial mixes for this OPC-pfa mix are reported elsewhere (4). The proportions b y w e i g h t of t h e m i x w e r e 0 . 2 6 :1.51 :0.84 with a water /(OPC+pfa) r a t i o of tent
of
this
mix
was
435
were manufactured with ment, d e t a i l s of w h i c h
k g / m 3.
Four
different are given TABLE
Mix B
Fibre details d v (mm) (~)
-
o
-
0
of
t y p e s of s t e e l in T a b l e 1.
: 0 . 7 4 (OPC) The OPC con-
these fibre
proportions reinforce-
I
D e t a i l s of mlxee,
1 (mm)
mixes
(pfa) 0.4.
fibres and curing
vf i/d F i b r e type
Curing " Conditions Sh , Sh~4 Bh14
0
BME
26.5
0.44
1.7
100
Melt e x t r a c t (ME}
BMS
28.2
0.48
1.7
100
Low c a r b o n steel, (MS)
Sh14
BCR
40
0.60
1.7
112
C o r r o s i o n reslstant, (CR)
Sh14
Sh 1, S h 1 4
- m a r i n e s h o w e r c u r e d after l a b o r a t o r y air c u r i n g
Bh14
- beach curing after curing
"
I or 14 d a y s
14 days l a b o r a t o r y air
642
Vo]. ]7, No. 4 P.S. Mangat and K. Gurusamy
O r d i n a r y P o r t l a n d c e m e n t (OPC), f i n e a g g r e g a t e c o n f o r m i n g to z o n e 2 of B S 8 8 2 a n d granite coarse aggregate of i0 m m n o m i n a l s i z e were used. The pfa was obtained from Longannet power station near Edinburgh. Typically the ash contained about 48~ silica, 38% alumina and 4.5~ iron oxide. T h r e e t y p e s of s t e e l f i b r e s were used namely, melt extract (ME), l o w c a r b o n s t e e l (MS) a n d corrosion resistant (CR). The latter two fibres had hooked ends. A maximum vfl/d ratio of 112 w a s u s e d , vf b e i n g f i b r e volume, Castinq,
1 the
length
Curing
and
and
d the
fibre
diameter.
Testing
i00 x i00 x 500 m m p r i s m s p e c i m e n s w e r e c a s t in t h r e e l a y e r s e a c h layer being compacted on a vibrating table. The fresh concrete was covered with polythene sheets a n d d e m o u l d e d a f t e r 24 h o u r s . T h e s p e c i m e n s w e r e t h e n l e f t to c u r e in t h e l a b o r a t o r y air, u n d e r uncontrolled humidity and temperature for a p e r i o d of b e t w e e n o n e and fourteendays as indicated in Table I. Subsequently the prism specimens were transferred either to a sea water spray c h a m b e r in t h e l a b o r a t o r y or to A b e r d e e n b e a c h . T h e s e a w a t e r s p r a y c h a m b e r in the l a b o r a t o r y w a s b u i l t to s i m u late marine splash and tidal zone conditions. It w a s a u t o m a t i c a l l y c o n t r o l l e d to p r o v i d e t w o w e t a n d two d r y c y c l e s in t w e n t y four hours. This cyclic exposure corresponded c l o s e l y to t h e t i d a l c y c l e s of t h e sea. The s p e c i m e n s at A b e r d e e n b e a c h w e r e a t t a c h e d to g r o y n e s w h e r e t h e y w e r e e x p o s e d to t i d a l c y c l e s . A l i m i t e d n u m b e r of p r i s m s p e c i m e n s w e r e l o a d e d in f l e x u r e a f t e r t h e i n i t i a l 14 d a y s of laboratory a i r c u r i n g in o r d e r to i n d u c e c r a c k s of w i d t h s r a n g i n g between 0.07 and 0.76 mm. The prec r a c k e d s p e c i m e n s w e r e , then, t r a n s f e r r e d to the s e a w a t e r s p r a y c h a m b e r in the l a b o r a t o r y . In t h e c a s e of i n i t i a l l y uncracked specimens, tests were conduct e d a f t e r 150, 300 a n d 1 2 0 0 cycles of w e t t i n g a n d d r y i n g in t h e marine spray chamber. These corresponded to the age of IiO, 185 a n d 620 days respectively. The beach cured specimens w e r e t e s t e d a f t e r 150, 300, a n d 1 2 0 0 tidal cycles which corresp o n d e d to i00, 160 a n d 640 d a y s respectively. The prism specimens with initially induced cracks w e r e t e s t e d a f t e r 650 m a r i n e s p r a y c y c l e s in t h e l a b o r a t o r y s p r a y c h a m b e r . In t h e c a s e of initially uncracked specimens, three prisms per m i x in T a b l e 1 w e r e tested in f l e x u r e a f t e r e a c h a g e of m a r i n e exposure. T h e f r a c t u r e d f a c e f r o m e a c h of t h e p r i s m s w a s u s e d to o b t a i n s a m p l e s for c h l o r i d e a n a l y s i s . A s i n d i c a t e d in Fig. i, a c o o r d i n a t e s y s t e m w i t h f a c e I b e i n g t h e x-axis and face 2 being the y-axis was selected, the top face d u r i n g c a s t i n g b e i n g F a c e 4. S a m p l e s w e r e t a k e n a l o n g x = 50 m m and at y = 8, 15, 20, 25, 35, 50, 65, 75, 80, 85, a n d 92 mm, depending on the duration of curing. The d r i l l i n g s at e a c h sample position, for t h e t h r e e p r i s m s p e c i m e n s , w e r e c o m b i n e d to g i v e a t e s t s a m p l e for c h l o r i d e a n a l y s i s .
Vol.
17, No. 4
643
CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA y-axis
Face 3
lOOmm gO
o?e,
80
70-
,6
60
l
.4-
'~50i
e,
o;
30-
i
20-
,e
10-
P
10 2'0 3'0 iO .~0 dO 7'0 gO 9'0 lOOrnm x-axis Face1 Fig.
1
Sampling
locations
for
chloride
analysis
In t h e c a s e of p r i s m s with initially induced cracks, the proced u r e for t a k i n g s a m p l e s for Cl analysis is g i v e n in d e t a i l in a p r e v i o u s p a p e r (10). Samples were t a k e n a d j a c e n t to a c r a c k at different depths from the extreme tension f a c e of t h e p r i s m s . Corresponding samples representing uncracked concrete were obtained f r o m a p o s i t i o n r e m o t e f r o m the c r a c k (I0). For chemical analysis, 1.5 to 2.5 g of p o w d e r e d c o n c r e t e w a s taken and chloride extracted by heating in d i l u t e n i t r i c acid. On cooling the neutralized solution was filtered and the Mohr titration (10, 11) c o n d u c t e d . The percentage chloride by weight of concrete was obtained from the following f o r m u l a (3, 4, 10) 35.453 vN Cl- i0 w w h e r e N is t h e n o r m a l i t y of A g N O 3, v is the v a l u e of A g N O 3, a n d w is t h e weight of powdered sample in grams. Since the mix proportions of c o n c r e t e from which chloride was extracted were k n o w n , t h e ~ Cl b y w e i g h t of c e m e n t c o u l d b e c a l c u l a t e d .
Results
and
Discussion
T h e i n f l u e n c e of fibre volume o n Cl diffusion characteristics w a s f o u n d to b e insignificant from the data presented in t h i s paper and also results reported elsewhere (3). Therefore, data at d i f f e r e n t v f I/d ratios have been combined where relevant "Best fit"" d i f f u s l o n curves were plotted through the Cl: penetration data by using a computer programme for the s o l u t i o n of F i c k s l a w of diffusion (12, 13), as d e s c r i b e d in g r e a t e r detail elsewhere (3, I0). The values of D c, the chloridediffusion
constant,
and
C° ,
the
equilibrium
chloride
Vol. 1 7 ,
644
No. 4
P.S. Mangat and K. Gurusamy
level
on
concrete
surface,
were
also
obtained
by
this
computation. The Cl- p e n e t r a t i o n r e s u l t s for l a b o r a t o r y s h o w e r c u r e d and b e a c h c u r e d s p e c i m e n s , after 150 and 300 c y c l e s of e x p o s u r e , are g i v e n in Figs. 2 a n d 3. It is c l e a r l y e v i d e n t that Cl levels are s i g n i f i c a n t l y h i g h e r in m a r i n e shower c u r e d specimens. This is e s s e n t i a l l y due to the higher Clcontent of sea w a t e r in the s h o w e r _ o w i n g to c o n t i n u o u s e v a p o r a t i o n (i0). In Figs. 2 and 3, the C1 p r o f i l e s of shower c u r e d s p e c i m e n s (MC) are r e p r e s e n t e d by two lines, shl and shl4, w h e r e 1 and 14 d e n o t e the d u r a t i o n in days of initial dry curing prior to marine exposure. It is e v i d e n t that the duration of this initial dry c u r i n g has an i n s i g n i f i c a n t i n f l u e n c e on CIconcentrations in concrete. In the f o r t h c o m i n g d i s c u s s i o n , therefore, results for shl and sh14 have b e e n combined. The Cl- p e n e t r a t i o n p r o f i l e s a t up 1200 c y c l e s of m a r i n e e x p o s u r e are p l o t t e d in Fig. 4. It is e v i d e n t that D c d e c r e a s e s w i t h duration cycles
of exposure, being
the v a l u e s
8.58 x 10 -8,
respectively.
In
corresponding
steel
150,
7.18 xlO -8
comparison,
mix of
after
the
fibre
and
average reinforced
300 and
1200 m a r i n e
1.35 xl0 -8 c m 2 / s e c values
of D c for a
c o n c r e t e w h i c h did
3.0 ~[ (
Hix proportions: 0.26:0-7~,:1.51:0.8&:0.~0 Fibre type:HE, HS, ER
2.8 ~ :,.6 -~
•~
vf
0.1 and 112
"~ 2.z,,-
.9 2"2g 2.0-
~ 2-8.~ 1-6! E
-e EH2/sec
._~
)-8CMZ/sec
~ 1.00.8-
0.6 04 0.2 0
Dc
~'o
~
20 '
z~
3b
3'5
~o
Depth of penetration into concrete (ram)
Flg.
2
Chloride penetration c y c l e s a n d 160 tidal
into c o n c r e t e a f t e r c y c l e s of e x p o s u r e
150 m a r i n e
Vol. 17, No. 4
645
CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
3-0-
Mix proportions:0.26:0-7/,: 1-51:(}S&: 0-6,0 Fibre fype:ME,MS, CR vf I/d: 0,100 and 112
2.8to
~
26
Oc=7.23x10"s CMZ/sec
22. \ Dc=7.12x10 -a
._o 2-2-
[MZ/sec
~ 2.0~ 1.8-
~01"62 1.4-
1.2~=1"0$ O.B~o O~O-&-
0.2- Dc=3.S9xI0-B
15
i~
25
z~
35
3~
40
Depth of penetration into concrete(ram) Fig.
3
Chloride or t i d a l
not
incorporate
2.81
xl0 -8 c m 2 / s e c
tively
(10).
The
penetration into concrete c y c l e s of e x p o s u r e
any
pfa
aZter
were
150,
reduction
300
6.13 and
of D c w i t h
x
10 -8,
2000 age
after
300 m a r i n e
3.90
marine
x 10 -8
cycles
is clear,
and
respec-
although
the
e f f e c t of p f a i n c l u s i o n is not r e a d i l y evident. The r e s u l t s in Fig. 4 a l s o s h o w that most of the C1 penetration had taken place a f t e r 150 MC (110 days) with s u b s e q u e n t i n c r e a s e s b e i n g small. T h i s o b s e r v a t i o n has a l s o b e e n r e p o r t e d e l s e w h e r e (10, 14). The C1 penetration profiles at up to 1200 c y c l e s of tidal exposure at A b e r d e e n b e a c h are p l o t t e d in Fig. 5. It is e v i d e n t that the v a l u e s of D c decrease with c u r i n g age, as n o t e d a b o v e for m a r i n e
spray
cured
specimens.
The v a l u e s
after
160,
300
and
1200 tidal cycles are 9.95 xlO -8, 3.59 xlO -8 and 1.60 x 10 -8 2 cm /sec r e s p e c t i v e l y . In comparison, the a v e r a g e v a l u e s of D for a c o r r e s p o n d i n g cm2/sec
after
mix
150 a n d
without
1200
tidal
pfa were cycles
7 . 5 6 x 1 0 -8 a n d
respectively
2 . 3 x 1 0 -~
(10).
The CI- c o n c e n t r a t i o n d a t a of the OPC b a s e d m i x a n d the O P C - p f a m i x at 150 a n d 300 m a r i n e c y c l e s of e x p o s u r e are p l o t t e d in Fig. 6. The g r a p h s s h o w that C1 levels are s i g n i f i c a n t l y h i g h e r in the O P C - p f a mixes, especially within the s u r f a c e zones. This i n d i c a t e s g r e a t e r p e r m e a b i l i t y of OPC-pfa concrete which results
646
Vol. 17, No. 4 P.S. Mangat and K. Gurusamy
3"8 3~3"&Mix proportions: 0.26: 0.7& :1.51: 0.8/+: 0./+0 Fibre type: ME, MS, ER. Vf~d: 0,100 and 112
3"2= ._m 3"0¢ L-
2.8 (
~2-6o z 2-&g ~ 2.2-
Oc = 1.35 ~ 10"s CM21sec
~6 2-OT: .-~ 1-8-
=>,
1-6-
1./,.-
_~ 1.2~I... 1.0o
0.8-
Oc=7.18x10 s [MZ/sec
0.604+-
Oc=8.S8xlC
0.2-
Depth of penetration into concrefe (ram)
Fig.
4
Chloride marine
penetration cycles
into
concrete
exposed
to
spray
in more r a p i d Cl diffusion characteristics. In recent years, it has generally been stated that OPC-pfa concretes are more i m p e r m e a b l e than OPC c o n c r e t e (15, 16, 17). For example, P a g e (17) has c o n c l u d e d that b l e n d e d c e m e n t s c o n t a i n i n g pfa limit Cl d i f f u s i o n into c o n c r e t e more effectively than P o r t l a n d cement. T h e s e c o n c l u s i o n s are c o n t r a r y to the o b s e r v a t i o n of Fig. 6 due to the d i f f e r e n c e in initial c u r i n g c o n d i t i o n s a d o p t e d in these v a r i o u s studies. W h e r e a s the s p e c i m e n s of the p r e s e n t i n v e s t i g a tion w e r e initially dry cured in the laboratory, the c u r i n g conditions adopted by others ensured prolonged moist c u r i n g (15, 16) or c u r i n g in C a ( O H ) 2 s o l u t i o n p r i o r to e x p o s u r e to salt s o l u t i o n s (17). It is k n o w n that the p o z z o l a n i c a c t i o n of pfa is considerably enhanced by initial curing conditions such as a d o p t e d by Page (17) and, therefore, the r e s u l t i n g i m p e r m e a b i l i t y of O P C - p f a concretes is understandable. However, such curing conditions are normally impractical on site. The i n i t i a l l y dry c u r i n g c o n d i t i o n s u s e d in this i n v e s t i g a t i o n represent site conditions to which structural c o n c r e t e s are o f t e n exposed. T h e s e c o n d i t i o n s w e r e c h o s e n to a l l o w m a x i m u m s h r i n k a g e and reduced hydration and consequently determine diffusion
Vol.
17, No. b,
G47 CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
~ 2'6 ~o 2-2- ~ ~ =1`60x10-eCMZlsec .#-
Z.08 1.8-
Oc = 3-59x 10e £HZ/sec
1.6-
~= •~ 1.~,-
\
.
~-
Htx proportions:0.26:0.%: 1-51:0-8/,:0.~,0 Fibre type:ME v,t,.:0 and 100
~., ~ \ \ ~ o, ~ 1.0-
~, ~.2o/
~> 0.86 0
0.60./, 0.25
Fig.
5
Chloride
10 15 20 25 30 Depth of penetration into concrete(mm)
penetration
into
concrete
35
~0
exposed
to
tidal
cycles
3"0-
2'8t
2"6-
==
2.~-
._o2.2 2.0
',',, ~t~
--
~,
Hix A (OPC'Vf[/d =0 and%7)
".... MixB (OPC-pfa,vf [/d =0and 100)
=E
1.8~= 1,61.~-
"~ •
~= 1"2-
~
",
300MCl304days)
1"0-
iilM£ 1110days)
~ o.e-
~ o.g
150HC M£(15/, (15~days) d a y s )~
~ " '~- . . " '~- . . . .". . . . _
..
0.2i
5 Fig.
6
i
1
i
i
i
----
i
10 15 20 25 30 35 Depth of penetration into concrete(ram)
Chloride penetration to laboratory marine
profiles into spray cycles
m"
concrete
~0 exposed
648
Vol. 17, No. 4 P.S. Mangat and K. Gurusamy
characteristics under more critical conditions w i t h r e s p e c t to construction practice. Under such conditions OPC-pfa concretes a r e l e s s r e s i s t a n t to Cl penetration. Cl penetration profiles in pre-cracked concrete, for the r a n g e of i n i t i a l c r a c k w i d t h s i n d u c e d , are plotted in Fig. 7. It is e v i d e n t t h a t C1 concentration increases with increasing crack w i d t h , the r a t e of i n c r e a s e in C1 being greater nearer the concrete surface. Depfh(mm)
8
20
30
50
Symbo{
o
~,
v
o
1'0"
0.9
o ° °
Bmm
o
0.8"6 0 7 T= cm •~ 0.63~
~05-
~, 0.3-
~
~o
m
20ram
o
a
30-50ram
02 "Co t_l
0.10
0'.1 o'2 0'.3 0'4 ols 0'.6 0!7 o'.s 019 1'-0 Avernge crock widfh (mm)
Fig.
7
E f f e c t of c r a c k w i d t h on c h l o r i d e p e n e t r a t i o n , 6 5 0 m a r i n e s p r a y c y c l e s of e x p o s u r e
after
Detailed profiles of CIdiffusion across the d e p t h of p r e c r a c k e d s p e c i m e n s a r e g i v e n in Fig. 8, in the v i c i n i t y of c r a c k s of w i d t h 0.2 m m and O.61 mm. The corresponding profiles for uncracked c o n c r e t e a r e a l s o shown. It is a p p a r e n t t h a t i n c r e a s e s in Cl concentrations r e l a t i v e to u n c r a c k e d c o n c r e t e a r e s m a l l in the v i c i n i t y of c r a c k s of w i d t h 0.2 m m w h e r e a s t h e y b e c o m e s i g n i f i c a n t for l a r g e r c r a c k s . Conclusions The following conclusions presented in t h i s p a p e r .
are
based
on
the
experimental
takes
results
i.
M o s t of t h e c h o r i d e penetration in concrete 150 c y c l e s (ii0 days) of m a r i n e e x p o s u r e .
place
by
2.
The has
3.
Partial replacement of ordinary P o r t l a n d c e m e n t w i t h pfa, in m a r i n e m i x e s of s t e e l fibre concrete, r e s u l t s in h i g h e r Cl
d u r a t i o n of i n i t i a l d r y _ c u r i n g , p r i o r to m a r i n e e x p o s u r e , l i m i t e d i n f l u e n c e o n Cl diffusion characteristics.
Vol. 17, No. 4
649 CHLORIDE DIFFUSION, STEEL FIBRE, CONCRETE, PFA
100-
/ / ~ ' ~
%0%
\
/°?:
\
/
%A %% ~%
%
~
.
.
.A. vicinity of
"~ A , . crack uncracked " ~ - o "'----~
lo-
~-i o'.2 0:3 o'.~ 0% o'.6 o'.7 o'.8 0:9
% Chloride content by weight of concrete .
"~
Oet 8
m
801 -~7o
/ ~/,0" /c~30-
~, ",%.. vicinity of "~-. crack uncrocked "-'~=oP
o:1 0:2 o~3 o:~ o% o% ~7 ~8 ~.9
%Chloride content by weight of concrete
Fig.
8
Chloride penetration marine spray cycles
into c r a c k e d
d i f f u s i o n r a t e s w h e n the concrete tions p r i o r to m a r i n e e x p o s u r e . 4.
In c r a c k e d c o n c r e t e , cracks increase with
concrete
is c u r e d u n d e r
after
650
dry c o n d i -
Cl concentrations in the v i c i n i t y i n c r e a s i n g c r a c k width.
of
Acknowledgements The a u t h o r s g r a t e f u l l y a c k n o w l e d g e the f i n a n c i a l s u p p o r t from the SERC M a r i n e T e c h n o l o g y Directorate for the r e s e a r c h p r o j e c t on m a r i n e d u r a b i l i t y of steel fibre concrete. The a u t h o r s also g r a t e f u l l y a c k n o w l e d g e the advice and f a c i l i t i e s made a v a i l a b l e by P r o f e s s o r F.P. G l a s s e r of the C h e m i s t r y D e p a r t m e n t , A b e r d e e n University.
References
i •
2. 3. 4.
FIP, R e c o m m e n d a t i o n s for the design and c o n s t r u c t i o n of c o n c r e t e sea s t r u c t u r e s , 28 (1974). R.D. BROWNE, P.L. DOMONE and M.P. G E O G H E G A N , Proc. Instn. Civ. Engrs., part I 137 (1977). P.S. M A N G A T and K. GURUSAMY, Int. Conf. on b e h a v i o u r of o f f s h o r e s t r u c t u r e s , Delft, 867 (1985). P.S. M A N G A T and K. G U R U S A M Y , R i l e m symp. on d e v e l o p m e n t s in fibre feint, c e m e n t and concrete, Sheffield, 2 p a p e r 7.9 (1986).
650
Vol. 17, No. 4
P.S. Mangat and K. Gurusamy
5. 6. 7.
8. 9. i0.
11. 12. 13. 14.
B r i t i s h S t a n d a r d 8110, Part 1 (1985). S.S. REHSI, Information Circular IC8640, U.S. B u r e a u of Mines, W a s h i n g t o n DC, 231 (1973). T.J. L A R S E N a n d C.L. PAGE, Proceedings of the f o u r t h A s h U t i l i z a t i o n Symp., St. Louis, ERDA, M E R C / S P - 7 6 / 4 , US B u r e a u of mines, W a s h i n g t o n DC, 573 (1976). J.B. NEWMAN, P.J.E. S U L L I V A N and A.M. BELL, Concrete, 17, 9 (Dec. 1983). C.L. PAGE, N.R. SHORT and A.E.L. TARRAS, Cem. and Concr. Res., 11, 395, (1981). P.S. M A N G A T and K. GURUSAMY, " C h l o r i d e d i f f u s i o n in steel fibre r e i n f o r c e d marine concrete". Cem. and Conc. Res., under publication. I.A VOGEL, A T e x t b o o k of Q u a n t i t a t i v e I n o r g a n i c A n a l y s i s , p. 1216, L o n g m a n s , L o n d o n (1961). R.D. BROWNE, A.C.I., SP-65, 169 (1980). J. CRANK, The mathematics of diffusion, p. 414, O x f o r d press, London, (1975). J.A. S T I L L W E L L , C o n c r e t e in the o c e a n s Tech. Rep. No. 8, 59
(1983). 15. 16. 17.
D. M A N M O H A N a n d P.K. MEHTA, Cement, C o n c r e t e and A g g r e g a t e s , 3, 63 (Summer 1981). P.K. MEHTA, A.C.I., SP-79, !, 1, (1983). C.L. PAGE, N.R. S H O R T and A.EL TARRAS, Cem. a n d Conc. Res. 11, 395 (1981).