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M a t e r i a ls a n d S t r u c t u r e s / M a t ~ r ia u x e t C o n s t r u c t i o n s
Vol. 31 . October 1998 pp 568-574
w a t e r s o r p t iv it y t e st f o r m o r t a r a n d c o n c r e t e
B . B . Sabi r , S . W i l d and M . O F a r re l l
S c h o o l o f t h e B u i lt E n v i r o n m e n t , U n i v e r s it y o f G la m o rg , n , P o n t y p r i d d , M i d . G l a m o r g a n , U K , C F 3 7 1 D L
P aper r ece i ved: Ju ly 8 , 1997; P aper accep ted : N ovem ber 21 , I 99 7
A B S T R A C T
Th is p ap er d esc r ib es a t e s t r ig to m easu r e th e u n i - d i r ec -
t i o n a l w a t e r a b s o r p t i o n o f m o r t a r a n d c o n c r e t e . T h e t e s t
d a ta acq u is i t io n i s co n t r o l led b y p u r p o s e w r i t t en so ftw are
in s ta l led o n a PC an d th e r esu l t s a r e u t i l i s ed d i r ec t ly to
o b t a i n t h e s o r p t i v i t y m e a s u r e d i n g / m m 2 / m i n l / 2 . A s a n
ex am p le th e ap p ara tu s w as u sed to o b ta in th e so r p t iv ity o f
m o r t a r i n w h i c h t h e o r d i n a r y P o r tl a n d c e m e n t w a s p a r-
t ia l ly r ep laced b y g r o u n d w as te b r ick o b ta in e d f r o m d i f f e r-
en t so u r ces . T h e r esu l ts p r esen te d d em o n s t r a te th e v a l id i ty
o f th e t e s t , a n d t h e a p p a r a t u s a n d t h e m e t h o d o l o g y ar e
sh o w n to b e o f su f f ic ien t s en si tiv ity in d e tec t in g th e d i f f e r -
e n c e s b e t w e e n t h e s o r p t i v it i e s o f th e v a r i o u s m o r t a r s
t e s te d . T h e v a r i a t io n i n t h e s o r p ti v i ty w i t h c u r i n g t i m e a n d
m i x t u r e c o m p o s i t i o n w a s d e t e r m i n e d . T h e p a p e r a ls o g iv e s
th e r esu lt s o f to ta l w a te r ab so r p t io n te st s co n d u c te d o n th e
s o r p t i v it y t e s t s p e c i m e n s , a f te r b e i n g r e c o n d i t i o n e d , a n d
th e r esu l ts o f co m p r ess iv e s t r en g th te s t s f o r al l th e m o r ta r s
investigated.
R ~ S U M ~
C et ar t i c l e d r i t uu appar e i l d 'e s s a i po ur m es ur er l 'abs or p-
t ion u n id iw c t ionne l l e de l ' eau par l e mor t i er e t l e bd ton . Les don-
n s r u l t a n t d e s e s s a i s s o n t c o n tr 3 1 s a u m o y e n d ' u n l o g ic i e l
s p ia l emen t con fu ins ta l ld s ur P C , e t ces r u l ta t s s on t d i r ec te -
m e n t u t i l i s p o u r o b t e n i r la s o r p t i v it d m e s u r e n
g / m m 2 / m i n J / 2 . A t it r e d ' e x e m p l e , o n a u t il is d l 'a p p a r e i l p o u r
d d t e r m i n e r l a s o r p t i v i td d ' u n m o r t i e r d a n s l e q u e l le c i m e n t
P or t land or d ina i r e ava i t d td par t ia l em en t r emplacd pa r l e s br iques
de r up a t ion par t ia l em en t concas s s . Le s r u l ta t s pr e ' s en t i c i
dd m ou tw nt l a va l id i td de l 'e s s a i , e t le f a i t que l ' appar e i l e t la
mdthodo log ie on t u ne s ens ib i l it d s u f f i s an te pou r dd tec t er l e s d i f fd -
f e n c e s e n t r e l e s s o r p t i v i t d e s d i f f e n t s m o r t ie r s d t u d i . L e s
v a r i a ti o n s d e l a so r p t iv i td e n f o n c t i o n d u t e m p s d e c u w e t d e la
com pos i t i on du m glange on t d td dd ter min s . L ' ar t ic l e pr ds en te
@ le m en t l e s r u l ta t s d ' es s a i s d ' abs or p t ion to ta l e de l ' eau mene ' s
s ur le s @ ou ve t t e s u t ih ' s s po ur l es es s a i s de s or p t i v i td , ap t l eur
r econd i t i or mem ent , a ins i que l es r u l ta t s d ' es s a i s de r i s tance a
la com pr es s ion po ur tous l e s mor t i er s d tud ie ' s.
1 . IN T R O D U C T I O N
Th e d u r ab i l i ty o f co n cr e te l ar g ely d ep en d s o n th e ease
w i t h w h i c h f l u id s e n t e r a n d m o v e t h r o u g h t h e m a t r ix . F o r
e x a m p l e , d e t e r i o ra t i o n d u e t o c h l o r i d e i o n s f r o m d e - i c i n g
sa lt s o r s eaw ate r is cau sed b y th e t r an sp o r t o f a ch lo r id e
s o l u t i o n i n t o t h e m a t e r i a l . A l t h o u g h , i n g e n e r a l , p e r m e -
a b i l it y is t a k e n a s a n i n d i c a t o r o f a c o n c r e t e ' s a b i l i ty t o
t r an sp o r t w a te r ( o r o x y g en an d ca r b o n d io x id e ) , mo r e p r e -
c i se ly th e r e a r e tw o me ch an ism s co n t r o l l in g th e u p tak e an d
t r an sp o r t o f w a te r . P er meab i l i t y , w h i c h i s a m e a s u r e o f t h e
f l o w o f w a t e r u n d e r p r e s su r e i n a s a t u ra t e d p o r o u s
m e d i u m , a nd sorpt ivi ty , w h ich ch ar ac te r i s es th e mate r ia l ' s
ab i li ty to ab sor b a n d t r an smi t w a te r th r o u g h i t b y cap il la r y
s u c t io n . W h i l s t p e r m e a b i l i ty i s a n i m p o r t a n t p a r a m e t e r f o r
w a t e r r e t a i n i n g s tr u c tu r e s , a m o r e i m p o r t a n t p a r a m e t e r
( w h ich i s d i r ec t ly r e la ted to d u r ab i l i ty ) f o r ab o v e g r o u n d
s t r u c tu r es is so rp t iv i ty . Th e p r in c ip a l fea tu r e o f th e m at r ix
s t r u c tu r e o f co n cr e te th a t r e lates to th e t r an sp o r t o f w a te r i s
t h e p o r e s y s t e m o f t h e c e m e n t p a s t e , p a r t ic u l a r ly i n t h e
v i c i n i t y o f t h e a g g r e g a t e -p a s t e i n t e r f a c e . A g g r e g a t e s c a n
a lso a f f ec t th e t r an sp o r t p r o p er t ie s b u t th ese , in g en er a l ,
c o n t a i n p o r e s w h i c h a r e d i s c o n t i n u o u s a n d d o n o t a l l o w
w a t e r m o v e m e n t b y c a pi ll ar it y, a n d h e n c e d o n o t c o n -
t r ib u te to so rp t iv i ty . H o w e v er , d esp i te th e h ig h e r p o r o s i ty
a t t h e i n t e r r a c i a l z o n e , i t i s g e n e r a l l y f o u n d t h a t w a t e r
m o v e m e n t i n c o n c r e t e i s p r e d o m i n a n t l y c o n t r o l l e d b y t h e
b u l k o f th e h a r d e n e d O P C p a st e, w h i c h i s t h e o n l y c o n t i n -
u o u s p h a s e i n c o n c r e t e [ 1 1 . S o r p t i v i t y i s al so r e l a t e d t o
a b s o r p t io n , w i t h t h e l a t te r b e i n g s o m e t i m e s u s e d a s a n
in d ica to r o f th e v o lu m e o f th e cap i ll a ry p o r e sp ace o r o p en
p o r o s it y , t h o u g h o p e n p o r o s i t y i s m o r e e f f e ct i v e ly m e a -
s u r e d b y m e r c u r y i n t r u si o n .
S o m e o f t h e e ar li er w o r k o n t h e m e a s u r e m e n t o f s o r p -
t i v it y o f m o r t a r a n d c o n c r e t e w a s c a rr i e d o u t b y H o a n d
Lew is [ 2 -4 ] an d H a l l [ 5 -6 ] . A m o r e r ecen t r ev iew b y H a l l
[7] g ives the theore t ical backgro ur id and pract ical aspects of
as ses sin g th e so r p t iv i ty o f mo r ta r s a n d co n cr e te in th e lab o -
r a to r y. Th e se w o r k s an d o th e r s [ 8] h av e d em o n s t r a ted th a t
u s e f u l i n f o r m a t i o n f o r m o r t a r a n d c o n c r e t e c a n be
o b t a i n e d u s i n g s i m p l e t e s t in g a r r a n g e m e n t s . F u r t h e r m o r e ,
i t i s f o u n d th a t th e te s t s y ie ld r ep r o d u c ib le r e su l t s w h ich
1359-5997/98 9 RILEM 5 6 8
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Sabir,Wild,O Farrell
describe the material s behaviour, w ith regard to variations
in composition and curing conditions, in a rational and
meaningful way.
The work described in this paper originates from a
major project funded by the European Commission under
the Copernicus programme. T he research programme,
which is now in its final stage, exam ined the potential of
recycling waste brick as a partial pozzolan replacement of
OP C in concrete and mortar [9, 10]. Th e paper introduces
an autom ated testing system for the m easurem ent of sorp-
tivity in mortar and concrete. The test is validated by car-
rying out sorptivity measurements on mortar samples in
which the OPC is par t ia l ly replaced by ground br ick
obtained from Britain, Denmark, Lithuania and Poland.
Th e sensitivity o f the testing system was verified by detec t-
ing the difference in behaviours of mortars with different
compositions and curin g times.
2. CAPILLARY SUCTION AND SORPTIVITY
It is frequently found that ira mortar or concrete sur-
face is exposed to wetting by water then the cumulative
water absorpt ion i is propor t ional , dur ing the in i t ia l
absorption period, to the square root of elapsed wetting
time t:
i: S~ 7
S is the sorptivity measured in g per m m 2 (of wetted
area) per mini/2. It is easily determ ined f rom the slope of
the linear part of the i versus ~t curve. Some materials
with extremely coarse pore structure experience little cap-
illary suction and ma y show significant deviation from lin-
earity after prolo nged wetting. Capillary suction can only
be m easured in partially dry m ortar or concrete. Sorption
does no t take place in saturated materials, and in totally dry
materials substantial ab sorption o f water by the gel will dis-
tort the results. T he sorptivity will depen d on the initial
water conte nt and its uniformity throu ghou t the specimen
unde r test. It is important, therefore, to keep this in mi nd
both when relat ing laboratory measurements to f ie ld
behaviour and also in ensuring a consistent and standard-
ised drying procedu re for all specimens. Furtherm ore, as
water abso rption and capillary suction depe nd on porosity,
any non-uniformities in the latter could lead to different
sorptivities in samples obtained from what is supposed to
be th e sam e material. It is, therefore , essential that materials
unde r test be consistent and hom ogene ous. In practice the
poi nt o f origin, and frequent ly the very early readings, are
omit ted when determ ining the slope of the graph. This is
because there is an increase in the mass of the specimen
caused by the fill ing of the ope n surface pores on the
inflow face and the sides of the specimen when it is sub-
merged. In order to reduce these effects to a min imu m, it
is essential that the spec imen be subme rged in water to no
more than 2-5 mm [1l] .
3. TEST APPARATUS
Hall [7] described three possible test configurations to
measure the rate of uni-directional water absorption in a
porous medium: horizontal in-flow in which there are no
gravitational effects bu t abs orpt ion is affected by hyd rosta -
tic forces; infiltration where absorption is partly due to
capillary su ction and partly to gravitational forces; and the
capillary rise case wh ere the effects of capillarity an d gravity
forces are op posed. F or m ost buil ding materials, the forces
due to capillary action are domi nan t in all these config ura-
tions, and due to simplicity and ease of operation, th e cap-
illary rise met ho d is chosen in th e presen t study. The appa-
ratus, which is shown in Fig. 1, consists of a suspension
frame constructed of rigid copper wire, whic h is attached
to the sensor of an electronic balance. Th e other e nd o f the
frame is rigidly attached to a light alumini um tray contain-
ing a central hole, 45 mm in diameter. The specimen is
placed centrally on the alum inium tray with the hole facili-
tating exposure to water of the test surface. Th e balance
(Sartorius L C 3201D) is placed on a rigid table and is con-
trolled by pu rpose wri tten software, whic h is installed on a
PC . Th e balance has a sensitivity o f 0.001 g and a response
time o f less than ls. Th e readings are shown o n a digital
display. Th e test specimen on its suspension mec han ism is
positi oned centrally over a reservoir containin g water. Th e
weight gain by the test specimen is automatically recorded
at specified intervals. The se readings are recor ded in th e
computer system and can be retrieved, after the test is
completed, in bo th numerical and graphical forms.
Fig. 1 Test Apparatus .
4. SPECIMEN PREPARATION AND TESTING
PROCEDURE
Th e specimen used in the present study consisted of 52
mm diameter and 15 mm thick discs cut (wet) from the
central portion of cylindrical cores obtained from 100 mm
mortar cubes. Four specimens were retrieved from each
core and the re maining outer portions were discarded. T he
mortar discs were d ried to constant weights in a tempe ra-
ture controlled drying cabinet containing silica gel. The
temperature in the cabinet was kept constant at 40~ and
the sihca gel was renewed every 2 days. The time required
569
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M a t e r i a l s a n d S t r u c t u r e s / M a t 6 r ia u x e t
C o n s t r u c t i o n s V o l. 3 1 , O c t o b e r 1 9 9 8
t o a c h i e v e c o n s t a n t w e i g h t v a r i e d
b e t w e e n 2 2 a n d 2 6 d a y s . I t w a s f o u n d
tha t , i r r e spec t ive of the in it ia l m ois tur e
c o n t e n t o f th e s p e c i m e n s , a p p r o x i -
m a t e l y 8 0 o f t h e w e i g h t l o ss o c c u r r e d
w i th in 5 days .
T h e t o t a l d r y i n g t i m e s o f t h e v a r i -
o u s s p e c im e n s v a r ie d w i t h t h e c o m p o -
s i ti o n o f t h e m o r t a r a n d c u r i n g h i s to r y .
T h e t e m p e r a t e r e g i m e o f d r y i n g
a d o p t e d i n t h e p r e s e n t s t u d y w a s p r e -
f e r re d t o t h e s t a n d a rd o v e n d r y i n g a t
105~ used in to ta l absor p t ion te st s , in
o r d e r t o a v o i d a n y m o d i f i c a t i o n t o t h e
c a pi ll ar y p o r e s t r u c t u re t h a t w o u l d b e c a u s e d b y t h e h i g h e r
d r y i n g t e m p e r a t u r e . A n i d ea l a rr a n g e m e n t w o u l d h a v e
b e e n t o d r y t h e s am p l es a t a m b i e n t t e m p e r a t u r e , b u t t h is
w o u l d h a v e ta k e n t o o l o n g a n d w o u l d h a v e e x t e n d e d t h e
d r y i n g t i m e s i n a n u n c o n t r o l l a b l e m a n n e r . A n a lt er na ti ve
w o u l d h a v e b e e n t o c h e m i c a l l y d r y t h e s p e c i m e n s , b u t t h i s
w as r e jec ted as i t in t r oduc es ano the r f ac tor to th e sys tem.
A f t e r d r y i n g , t h e s p e c i m e n u n d e r t e s t w a s p l a c e d c e n -
t r a l l y o n t h e h o r i z o n t a l l y a l i g n e d a l u m i n i u m h o l d e r o v e r
the water reservoir . The suspension system is self - levell ing
a n d t h e t e st s p e c i m e n a l w a ys r es t e d i n a h o r i z o n t a l c o n f i g -
u r a t i o n . W a t e r , a t r o o m t e m p e r a t u r e , w a s t h e n a d d e d t o
the r ese r voi r un t i l th e f r ee sur face r eached a l eve l appr oxi -
m a t e l y 5 m m b e l o w t h e t e s t s u r fa c e . A t t h i s p o i n t t h e
w e i g h t d e t e c t i n g s y s t e m w a s a c ti v a t e d , a n d w a t e r w a s
Tab l e 2 - C h e m i c a l c o m p o s i t io n s o f t h e g r o u n d b r i c k s
Oxide (%) 810-B30 D10-D30 LIO - L30 P IO - P30
SiO2
TiO2
AI203
Fe203
MnO
M g O
CaO
Na20
K20
BaO
P205
Cr203
SrO
SO3
L.O.I.
54.83
0.97
19.05
6.00
0.06
1.77
9.39
0 . 50
3.15
0.04
0.20
.03
.05
2.90
1 . 4 8
69.99
0.55
10.62
4.02
0 . 0 8
1.39
8.86
1.02
2.61
0.05
0.11
0.01
0.03
0.04
0.25
68.79
0.85
9 15.23
6.28
0.07
2.02
1.79
0.26
3.71
0 . 0 4
0.07
0.02
0.01
0.13
0.19
T a b l e 1 - G e n e r a l d a t a f o r t h e b r i c k m a t e r i a l s
Mix Des ig n at io n s Co u n tr y f O r ig in Descr ip tio n Raw Mater ia ls F i r in g em p er a tur e
B 10, B20 and B30 Britain Red, F l e t t o n L o w e rOxford clay 1025~
facing br ick
DIO, D20 and D30 Denmark Yel low, 60% yel low 1050~ for 6 h
v a c u u m b u r n i n g l ay , 20%
extruded red burn ing clay
a n d 2 0 % s a n d
LIO, L20 and L30 L i th u a n ia Red ex t r ud ed UK m er g e c lay 975 - 1025~ *
m ester
petr ing with
perforations
PIO, P20 and P30 Poland Red Clay, sand, 980 - 1045~
basal t , bass PFA
9 De te rmined on the basis o f Fe 20 3 and C aO conten ts and co~our.
72.75
0.84
15.89
4.97
0.02
1.20
0.87
0.27
2.17
0.05
0.10
0.02
0.01
0.07
0 . 36
Tab l e 3 - M i n e r a l c o m p o s i t i o n s o f t h e g r o u n d b r i c k s
Mineral
(%) B10
-
B30 D10
-
D30 L10
-
L30 P10
-
P30
49
5
10
12
7
6
60
23
6
12
4-
43
24
20
13
88
3
5
4
Quartz
Feldspar
Haem at i te
Cr istobal i te
Spinel
Gypsum
Anhydr i te
+ denotes a trace - denotes absence.
a d d e d b y r u n n i n g i t d o w n t h e s id e o f t h e r e s e rv o i r at a
s low r a te un t i l the w a te r sur face w as jus t in conta c t w i th
t h e u n d e r s i d e o f t h e s p e c i m e n w h e n a n i n cr ea s e i n t h e b a l -
ance r ead ing w as obse r ved . T his inc r ease i s due to surf ace
t e n s i o n f o rc e s a n d t h e e v e n t w a s u s e d a s a r ef e re n c e p o i n t
to ind ica te con tac t o f w a te r w i th the te s t sur face .
T h e t e s t su r f ac e w a s v i s u a ll y e x a m i n e d t o e n s u r e t h a t
n o a ir w a s t r a p p e d u n d e r t h e s p e c i m e n . I f t h is o c c u r r e d ,
or ve r y occas iona l ly , i f the f r ee w a te r sur f ace w as s ign i f i -
c a n t l y ab o v e t h e b o t t o m s u r fa c e o f t h e s p e c i m e n ( s ig -
n a l l e d b y a d e c r e a s e i n t h e b a l a n c e r e a d i n g d u e t o b u o y -
a n c y e f f e c t s ) , t h e n t h e t e s t w a s a b a n d o n e d a n d t h e
s p e c i m e n r e c o n d i t i o n e d f o r a r e p e a t t es t .
T h e w e i g h t m e a s u r e m e n t s y s t e m u s e d e n a b l e d t h e
a c q u i s it i o n o f d a ta a t p r e d e t e r m i n e d t i m e i n t e rv a l s w i t h o u t
caus ing any d i s tur bance to the te s t r ig . Th is e l imina ted any
r a n d o m o p e r a t o r e r r o rs i n h e r e n t i n t i l e g e n e ra l ly a d o p t e d
m a n u a l m e t h o d s o f w e i g h t m e a s u r e m e n t . I n t h e te st s c o n -
d u c t e d i n t h e p r e s e n t s t ud y , w e i g h t m e a s u r e m e n t s w e r e
t a k e n a t o n e m i n u t e i n t e r v a l s o v e r a t o t a l t e s t t i m e o f
a p p r o x i m a t e l y o n e h o u r w i t h t o ta l m a ss c h a n g e s i n t h e
r ange 5 - 8 g . T he w a te r r e se r voi r w as suf f ic ien t ly l a rge to
e n s u r e t h a t a n y c h a n g es in b u o y a n c y o f t h e s p e c i m e n
un der g oin g te s t w e r e negl ig ib le .
5 MATERIALS AN D MIXTURE DETAILS
I n to ta l , f our d i f f e r en t g r o un d br ick mate ria ls , o ne f r o m
e a c h c o u n t r y p a r t i c i p a t i n g i n t h e r e s e a r c h p r o g r a m m e ,
w er e the subjec t o f t e st ing . T able 1 g ives the desc r ip t ions
a n d c o u n t r y o f o r i g i n o f t h e v a r i o u s b r i ck s u s e d . C h e m i c a l
a n d X - r a y d i f f r a c t o m e t r y a n al y se s w e r e c a r r i e d o u t , s e e
[ 1 0] , o n t h e g r o u n d b r ic k . T h e c h e m i c a l c o m p o s i t i o n s a n d
m i n e r a l o g ic a l d if fe r e n c es b e t w e e n t h e f o u r g r o u n d b r i ck s
a re s h o w n i n T a b le s 2 a n d 3 , r e sp e ct iv e ly . T h e O P C i n t h e
con t r o l mor t a r w as pa rt ia l ly r ep laced w i th 10 , 20 an d 30
g r o u n d b r i c k . I n a l l , t h i r t e e n m o r t a r m i x t u r e s w i t h p r o -
p o r t i o n s 1 : 3 : 0 . 5 ( O P C : s a n d : w a t e r ) w e r e i n v e s t i g a t e d .
S t a n d a r d s a n d ( D I N E N 1 9 6 - 1 ) w a s u s e d t h r o u g h o u t t h e
invest iga t ion . T he m ix tu r e des igna t ions w e r e based on th e
c o u n t r y o f o r ig i n ( B ri ta in B , D e n m a r k D , L i t h u a n i a L a n d
P o l a n d P ) a n d t h e O P C r e p l a c e m e n t le v e l ( 10 , 2 0 a n d
30 ) a s ind ica te d in Table 1.
T h e g r o u n d b r i c k w a s o b t a i n e d b y p la t e g r i n d i n g 2 0 -
5 0 m m p i e c es o f b r i c k a n d t h e n s u b j e c ti n g t h e r e s u lt i n g
5 7
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Sabir, W ild, O'Farrell
X
5 .0
4 . 5
4 . 0
3 .5
3 .0
2 .5
2 .0
1 .5
1 .0
0 .5
0 . 0
0 1
f 7 da y s
/ / j 2 8 d a y s
~ ~ S O d a s
~ ~ _ . ~ e ~ ' Y
a I r ~ i i i
2 3 4 5 6 7 8 9
t o . s , ( r a i n 0 . s )
F i g . 2 - E f f e c t o f c u r i n g
t i m e o n c u m u l a t iv e
w a t e r
a b s o r p t i o n f o r
g r o u n d b r i c k m o r t a r
( B 3 0 ) .
m a t e r i a l t o b a l l m i l l i n g t o t h e r e q u i r e d p a r -
t i c le s ize . The f ina l ma te r ia l had a spec i f ic
s u r fa c e i n th e r a n g e 3 2 0 - 3 5 0 m 2 / k g s e e
[1 0 ] w h i c h i s a p p r o x i m a t e l y t h e s a m e as
t h a t o f O P C .
F r o m e a ch m i x t u r e f o u r 1 00 m m
c u b e s w e r e p r e p a r e d f o r e ac h c u r i n g t i m e .
T h e c u b e s w e r e c u r e d i n w a t e r a t 2 0 ~ a t
e a c h o f t h e c u r i n g t i m e s o f 7 2 8 a n d 9 0
d ay s. T h r e e c u b e s w e r e u s e d f o r c o m p r e s -
s i o n s t r e n g t h t es ts a n d t h e f o u r t h w a s u s e d
t o p r o d u c e a c y l i n d r i c a l c o r e f r o m w h i c h
f o u r d i s c s w e r e c u t f o r t h e s o r p t i v it y a n d
a b s o r p t i o n m e a s u r e m e n t s .
6 . R E S U L T S A N D D I S C U S S I O N
6 . 1 S o r p t i v i t y
T y p i c a l p l o t s o f c u m u l a t i v e w a t e r
a b s o r p t i o n a g a i n s t t h e s q u a r e r o o t o f t i m e
a re s h o w n i n F i g . 2 . T h e s e p l o t s g iv e t h e
w a t e r a b s o r p t i o n fo r t h e B 3 0 m i x t u r e s c u r e d
a t 7 28 an d 90 days . Each se t o f th r ee p lo t s
s h o w n r e f e r s t o t h e t h r e e s a m p l e s t e s t e d
f r o m e a c h o f t h e m i x t u re s . T h e t es ts c o n -
d u c t e d o n t h e t h r e e s a m p le s a t e ac h o f th e
thr ee cur ing t imes g ive pr ac t ica l ly iden t ica l
s lopes pa r t i cu la r ly du r ing the ea r ly pa r t o f
t h e t e s t. T h i s d e m o n s t r a te s t h e r e p r o d u c i b i l -
i t y o f t h e b e h a v i o u r a s o b t a i n e d f r o m d i f fe r -
en t s amples of the same mo r ta r . T he r esu l ts
a ls o c le a rl y s h o w t h e i n f l u e n c e o f c u r i n g
t i m e o n t h e s o r p t i v i ty o f t h e m o r t a r .
F o r t h e m a j o r i t y o f s a m p l e s t e s t e d t h e
r e l a t i o n s h i p b e t w e e n c u m u l a t i v e w a t e r
a b s o r p t i o n a n d t h e s q u a re r o o t o f t i m e o f
e x p o s u r e b e g i n s t o d e v i a t e f r o m l i n e a r i t y
a f t e r a b o u t 2 0 - 3 0 m i n u t e s . I n a d o p t i n g a
s y s te m a t ic m e t h o d o l o g y fo r d e t e r m i n i n g
t.8
1.6
2.0
.. 1.4
1.2
1.0
E o . ~
~ 0 .6
9 -" 0 . 4
0 . 2
0.0
,o,
w 9 ' ~ * X *
, e * a : W
t '
i I I ) P I F
2.0
a )
1 . 6 / r
t . ,
x t . 2 4 1 9 e 2 o : ' ~ . ,
1.0 a 7 ~ '- = : *
Q * ~ & . * ~ . d e *
9 , o j [ ~
,E~ 0 . 8 o . o ~ . x *
, ~ 0.6 9 _,~,/~ .=:.
; 0 ; : - : . : : : : -
0.2 : *
0 . 0 I I i I I I I I
( b )
..,.-
, , X * ~ ~ , , ~ , , 4 . *
x ~ . x
i ' i : '
c )
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
t 0 . s ( m i n o . s )
F i g . 3 - C u m u l a t i v e w a t e r a b s o r p t i o n f o r m o r t a r c o n t a i n i n g v ar i o u s g r o u n d b r i c k s
a t d i f f e r e n t r e p l a c e m e n t l e v el s : ( a ) 1 0 % , ( b ) 2 0 % a n d ( c ) 3 0 % .
5 7 1
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M a t e r i a l s a n d S t r u c t u r e s / M a t 6 r ia u x e t
C o n s t r u c t i o n s V o l . 3 1 , O ct o ber 1998
t he sorp t iv i t i e s for the va r ious mix tures t e s t ed , i t was
dec ided to base the ca lcu la t ions on the f i r s t 16 minutes
o f e lapsed tes t t ime. Fo r a ll the sam ples tes ted, this dura-
t i o n o f t i m e p r o d u c e d l i n e a r r e la t io n s h i p s w h i c h g a v e
cor re l a t ion coe f f i c i en t s grea te r than 0 .996 . Typica l p lo ts
o f c u m u l a t i v e a b s o r p t i o n o v e r t h e f ir s t 1 6 m i n u t e s f o r
m o r t a r s w i t h v a r y i n g O P C r e p l a c e m e n t l ev e ls b y g r o u n d
b r i c k c u r e d a t 9 0 d a y s a r e s h o w n i n F i g . 3 . T h e m e a n
s l o p e s o f s u c h p l o t s f o r a ll t h e m i x t u r e s i n v e s t i g a t e d
( three s amples each) a t d i f fe ren t cur ing t imes a re shown
in Table 4.
F ig. 4 shows the change in the m ean o f the measu red
sorpt ivi ty with cur ing t ime . Analys is of variance was car-
r i ed ou t o n the re su lt s for the sorp tiv ity ob ta ined f rom the
indiv idua l te s ts . Th e ana lys is was pe r form ed o n se ri es of
r es u lt s g r o u p e d a c c o r d i n g to b r i c k s o u r c e t o g e t h e r w i t h
the con t ro l mor ta r a t each of the c ur ing t imes of 7, 28 and
9 0 d a y s. I t w a s f o u n d t h a t , w i t h t h e e x c e p t i o n o f o n e
result , the differences betw een th e m eans o f the sorpt ivi t ies
f o r t h e m o r t a r s, w i t h v a r y i n g a m o u n t s o f g r o u n d b r i c k ,
were s ignif icant a t the 0.01 level a t a l l curing t imes . The
except ion was in the case of the P l0-P 30 se ri es for which
the d i f ference b e twe en the mean s o f the sorp t iv i ti e s mea-
sured at 90 days was o nly jus t s ignif icant a t the 0.09 level.
O n exam ina t ion of F ig . 4 (d), one m ay a t tr ibu te th is to the
u n e x p e c t e d s h a r p d r o p i n s o r p t i v i t y f o r t h e P 3 0 m o r t a r
observ ed at 90 days . A closer exam inat ion o f the results for
the P3 0 m or ta r a t a l l cur ing t imes , ho wever , revea led tha t
the coe ff ic i en t s of va r ia t ion be twee n the ind iv idua l me a-
surement s , i nc luding those obta ined a t 90 days , were a l l
wi th in 3 , and th is behaviour could not be a t t ribu ted to
poss ible expe rime ntal errors. As the level of s ignificance in
th is case i s h igh (> 0 .05), w e m ay con c lude tha t the sorp-
T a b le 4 - Sorpt iv i t ies in g / m m 2 / m i n l / 2 1 0 4 f o r co n t ro l
an d g ro u n d b r i ck m o r ta rs
Curing ime days)
Mixture
2 8
9 0
Control 3 .58 3 .58 3 .58
B I O 4 . 51 4 . 29 4 . 22
B 20 4 . 71 4 . 32 4 . 08
B 30 6 . 21 4 . 58 3 . 48
D I O 4 . 97 4 , 5 7 3 , 84
D20 5 .67 5 .11 4 .10
D30 5 .85 5 .32 4 .85
L I O 3 . 81 3 . 42 3 . 21
1.20 4 .56 3 ,96 3 ,80
L 30 4 . 84 4 . 54 4 . 33
P IO 4 .47 4 .22 3 .99
P 20 4 . 73 3 . 91 3 . 69
P 30 5 . 38 4 . 95 3 , 45
t iv i ty a f te r 90 days of cur ing i s no t in f luen ced by P - typ e
grou nd br i ck .
I t can genera l ly be s een f ro m F ig . 4 tha t the con t ro l
m or ta r exhib i ts g rea te r re si st ance to w a te r absorp t ion b y
capil la ry suc tion than the mor ta rs c onta in ing grou nd br i ck ,
the sorpt ivi t ies o f w hic h increase w ith increa s ing level of
O P C r e p l a c e m e n t b y g r o u n d b r i c k . H o w e v e r , w i th
increas ing cu r ing t ime the sorp t iv i ti e s of ground br i ck m or-
t a rs dec rease , and a t 90 days and for ce r t a in rep lacem ent
l eve l s some mo r ta rs exhib i t sorp t iv i ti es be low tha t o f the
c o n t r o l m o r t a r . T h e a b o ve b e h a v i o u r c o n f i r m s p r e v i o u s
r e p o r t s b y t h e a u t h o r s [ 1 2] o f th e p o z z o l a n i c e f f e c t o f
g r o u n d b r i c k w h i c h p r o d u c e s p o r e r e f i n e m e n t a t e x t e n d e d
curin g t imes , bu t is no t manifes t at the early ages w he n th e
gro un d brick imparts increased poros ity to the m ortar .
I t is general ly acce pted [13 , 14] that water absorpt ion of
c o n c r e t e i s r e d u c e d a s t h e d u r a t i o n o f m o i s t c u r i n g
7
4 -
~ 3 - 3
_
i i .. ~_L lO i i
[ - ~ L 0 i
i a ) I i ~ r c ) I
O r
g 7 7
i
i ~ P 1 o I
i
P2
i
b ) ~ , d )
, 1 ~ ) lO O , l O , o o
Curing tim Curing time days)
F i g. 4 - V a r i a t i o n o f s o r p t i v i t y w i t h c u r i n g t i m e f o r m o r t a r s w i t h g r o u n d b r i c k f r o m : a ) B r i t ai n , b ) D e n m a r k . , c ) L i t h u a n ia a n d d ) P o la n d .
5 7 2
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S a b i r , Wild, O Farrel l
T a b le 5 - T o t a l w a t e r a b s o r p t io n a f t e r 2 4 h i m m e r s i o n
i n wa t e r e xp r e sse d a s a p e r ce n t a g e o f
i n i ti a l m a s s
C u r i n g
ime (days)
Mixture
7 28 90
C o n t r o l
7.21 7.03 6.61
BIO 7.93 7.57 7.25
B20 8.36 8.09 8.09
B30 8.91 8.65 8.28
DIO 7.98 7.79 7.58
D20 8.39 8.23 8.01
D30 8.51 8.44 8.12
LIO 7.68 7.39 7.06
L20 8.23 7.96 7.69
L30 8.61 8.45 8.05
PIO 8.03 7.52 7.62
P20 8.43 7.74 7.62
P30 8 .68 8 .26 8 .34
T a b le 6 -
C o m p r e s s iv e s t r e n g t h f o r
c o n t r o l
a n d g r o u n d b r i c k m o r t a r s ( M P a )
C u r i n g ime (days)
Mixture
7 28 90
C o n t r o l
52.2 65.3 67.0
BIO 43.8 61.2 74.0
B20 39.4 55.4 66.2
B30 31.2 45.2 55.7
DIO 40.3 55.0 65.2
D20 30.1 45.0 55.0
D30 28.9 35.6 49.1
LIO 44.7 59.4 69.1
L20 33.5 48.5 61.5
L30 27.8 40.5 55.1
PIO 39.8 55.6 65.5
P20 34.5 50.1 62.7
P30 28.3 39.8 57.5
increases . Further mo re, Parrot [13] has observed that the
influence o f mois t curing t im e on the rate of water absorp-
t i o n o f O P C c o n c r e t e is v e r y s m a l l b e y o n d 3 d a y s .
How ever, i f the O PC in the concrete is part ial ly replaced
by pozzolans i . e . 30 PFA or 50 GGBS) absorp tion
rates are initially m uc h grea ter and con tinue to fall signifi-
cant ly with increased specimen curing t im e up to at least
28 days. Th e cur ren t observations follow similar trends to
those observed by Par ro t [13] . I t i s sugges ted tha t the
observed reduct ions in so rp tiv i ty wi th increased cur ing
t ime (up to 90 days) of the groun d brick mortars (which
are condi t ioned in an identical m ann er to the control) i s
indicat ive ofpo zzolanic act ivi ty which occurs muc h m ore
s lowly than does cement hydra t ion and has therefo re a
m uch greater effect at ex tended ages .
6 . 2 T o ta l w a t e r a b s o r p t i o n
The disc specimens used for the sorptivity tests were
recondi t ioned, by oven drying for 24 h at 105~ for use in
the wa ter absorpt ion tests. The specimens were imm ersed
in water at 20 + 2~ for a period o f 24 h and the total mass
of water absorbed was d etermined . Four samples were used
for each mea sure m ent and the results are given in Table 5.
Analysis of variance ca rried ou t o n th e absorption results
on the same basis as that used for the sorptivity measure-
ments , show ed that the differences betwe en the m eans of
each set of four results wer e alw ays significant at the 0.01
level . Fig . 5 shows the variat ion in the total absorpt ion
wi th cu ring time. It is seen that, irrespective of curin g time
and source o f brick, the m ortars sho wed increased absorp-
1 0 -
1
- - C o n , r o ,
9 I ~ L I O
1~ 83~ j L L~O ~
8 - : = 8
s (a ) s (c )
1
1 - -
I , - ~ -o n t r o l ~
= ~
. o to i 9 ~ i ~Plo
g - ~ - D 2 0 [ | ~ a - P 2 0
