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F ~ t r l T T E R W O R T H
[~ E I N E M A N N
ND T E International ,
Vol. 28, No. 1, pp. 15-22, 1995
Cop yright © 1995 Elsevicr Scicncc Ltd
Printed in G reat Bri tain. All r ights reserved
0963-8695/95 10.00 + 0.00
e t t i n g t i m e s t u d y o f r o l l e r
c o m p a c t e d c o n c r e te b y s p e c tr al
a n a ly s is o f t r a n s m i tt e d
u l t rason ic s igna ls
V . G a m i e r , G . C o r n e l o u p , J . M . S p r a u e l a n d J . C . P e rf u m o t
* Laboratoire de Contrble Non Destructi f - MEC ASUR F A 14 29 ), Inst i tut Universi taire
de Technologie, Avenu e Ga ston Berger, 13625, Aix-en-Provence Cedex, France
+CEME TE - SQ R, Electr ic i t6 de France, 90 5 Avenue du Camp de Menthe, BP 605,
130 93 Aix-en-Provence Ce dex 2, France
Received 8 August 994; revised 5 Au gust 994
The s e t ti ng ti m e o f r o ll e r c om p ac ted c on c r e te RCC ) is de te r m i ned b y s tudy i ng t he
i nc r eas e i n t he p r opaga t i on v e l oc i t y o f u l t r as on i c wav es t r ans m i t t ed t h r ough a
sample . In the case o f a qu ick set t i ng b inder , th i s method proves unsat i s fac tory .
Concre te set t i ng i s model l ed by d i ssoc ia t i ng the chemica l k inet i cs re la ted to the
v o l um e t r ans fo r m a t i ons f r om thos e r e l a ted t o t he s u r fac e t r ans fo r m a t i ons .
Ca l c u l a t i ons s how tha t t he l a tt e r, and henc e t he pe r c o l a t ion phe nom enon , a r e
p r ev a l en t i n wav e p r opaga t i on and c onc r e te s e t t i ng . A s a r es u l t we as s um e tha t
con cre te ac ts as a t ime-va ry ing spec t ra l f il te r . We are dev e lop ing tes ts and so f tware
to s how tha t t he ene r gy and t he f r equenc y s pec t r um o f t he t r ans m i t t ed u l t r as on i c
s igna l makes i t poss ib le to an a lyse the se t t i ng process and determ ine the se t t i ng t ime.
K ey words : u l tr as on i c wav e p r opaga t i on , r o l led c om pac ted c onc r e te , s e t t ing t i m e
F o r d a m s m a d e o f r ol le r c o m p a c t e d c o n c r e te ( R C C ) , th e
i n t er f a c e b e t we e n l a y e r s h a s i t s m a x i m u m s h e a r s t r e n g t h
wh e n t h e n e w l a y e r i s p la c e d o n t h e p r e v i o u s l a y e r b e fo re
the p rev ious l ayer undergoes se t t ing . Once th i s l imi t i s
p a s s e d , s t ro n g b o n d s b e t we e n t h e g ra i n s o f b o t h l a y e r s
c a n n o t b e e s t a b l is h e d .
At p resen t th i s l imi t i s def ined as the t ime when there i s
the fo rm at ion o f a l a rge quan t i ty o f t r i ca lc ium s i l i ca te
t r ihydra tes
[ ' ( C a O ) 3 ( S i O )2 ( H 2 0 ) 3 = C S H ' I ,
which i s the
ma in b ind ing cons t i tuen t o f R CC 11]. Dete rmin ing th i s
se t t ing t ime and i t s sens i t iv i ty to t empera tu re and
h imid i ty i s necessary to ensu re the n s tu q u a l i t y o f t h e
wo rk .
S t u d y
T h e f ir s t m e t h o d fo r d e t e rm i n i n g t h e s e t ti n g t i m e , wh i c h
i s c u r r e n t l y p ro p o s e d [~ 2 ] a n d b u i l d s o n C a n n a rd s
wo rk [3], i s based on the a na lys i s o f s ingu lar it i es o n the
c u rv e s o f t h e u l t r a s o n i c w a v e s p e e d i n c o n c re t e a s a
fu n c t io n o f t i m e fo r a n R C C b o n d e d w i t h a L a fa rg e
cem en t o f the Bar la c type (F igu re 1 , Bar la c cu rve). B o th
s ingu lar i t i es (A and B) , wh ich a re charac te r ized by two
d i s t i n c t s l o p e c h a n g e s o n t h e c u rv e , c o r r e s p o n d t o a
c h a n g e i n th e t y p e o f m i c ro s t ru c t u ra l t r a n s fo rm a t i o n
dur ing the co ncre te s harden ing . S ingu lar i ty A i s re la ted
t o t h e b e g i n n i n g o f th e l i n k a g e fo rm a t i o n b y e t t ri n g it e
be tween the g ra ins . I t i s the in i t i a l se t t ing t ime def ined
5000-
4000-
3000-
2000-
1000-
0
0
Wavevelo ity
( r r~ ' s }
A ~ ~ - - - ~ ] '
~
10 20 30 40 50 60 70
13me hou~s)
igure 1 B e h a v i o u r o f t h e u l t r a s o n i c w a v e v e l o c i t y i n R C C a s a
f u n c t i o n o f t i m e f o r t w o b i n d e r s B a r l a c a n d C P A ) [ 2]
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V.
amier e t a
4
6
2O . 4O , ~ . . ~ . . . . . . . . . . a 0 F r ~
T i m e
(hm~)
k N z )
~ ~ _ . I
| |
- ' ; L P ~ - ' . ~ - : e _ _ ~ . : (k H z |
20 40 60 80
igure 2 Spec t ra l image (PSD) o f the s igna l t ransmi t ted as a
f unc t i on o f t i m e . Tes t E rP 060B , C P A bonde d R C C : (A )
t w o -d i m ens i on a l i m age ( t i m e-P S D ) ; (B ) P S D o f the tr ans m i t t ed
s ignal a t t ime 70 h
by Pessiki [4] with the penetration resistance test and the
impact-echo method. Singularity B is identified as being
the formation of a large quantity of CSH. We adopt this
definition of the setting time. This has been confirmed
by n s tu shearing tests on multi-layered blocks of this
Barlac bonded concrete with different setting times/23 and
by observations on a scanning electron microscope
(SEM) of the concrete s microst ructure at different
times 51, which indicate the chronology of the con-
stituents formation during setting. The areas in which
we can observe ettringite and CSH formations are
specified in Figure 1.
For the Barlac bonded RCC (Figure 1), the chemical
transformations are slow and distinct. The gradients of
the ultrasonic wave velocity that are related to the
transformations are well defined and the setting time is
easy to determine from ~he intersec tion of the two slopes
(Figure 1).
For other binders, such as the quick setting cement
Portland artificial 55 plus fly ashes (CPA), the wave
velocity curve as a function of time (Figure 1) displays a
continuous variation with no marked discontinuities. The
determination of the setting time is thus made uncertain.
In this case, it is necessary to develop a new parameter
to define the setting time, and in the process a new method
must be developed to analyse ultrasonic wave propaga-
tion. By measuring the time of flight and calculating the
signal energy rj, the beginning of the concrete setting can
be determined from the discontinuity in the energy
signature, but the settipg time remains determined by
temporal analysis.
As for the spectral analysis of a transmitted signal
through a specimen of set concrete T], this does not allow
the determination of the setting time, but shows any
changes in the energy distribution in the frequency
spectrum.
The fast Fourier transform (FFT) of the transmitt ed wave
shows new frequencies, after deconvolution of the transfer
function of the experimental device wi thout any samples.
These new frequencies are characteristic of the geometry
of the sample for low frequencies and of the size
distr ibution of the aggregate for high frequencies.
In our study, we first develop a model of the concrete s
setting tha t shows the importance of the linkages between
the grains on the behaviour over time of the transmitted
ultrasonic wave speed in the concrete.
We also develop an energy and frequency approach using
signal treatment. We consider that the concrete acts as
a time-varying filter which is related to the chronological
development of the microstructure in the concrete. A
software program was developed that performs, in real
time, signal acquisition, measurement of the t ime o f flight,
determination o f the wave velocity and calculation of the
energy and the power spectral density (PSD) of the signals
having passed through the concrete. The PSD is
calculated over a bandwidth limited to 15-100kHz.
Figure 2B shows an example of the PSD of a signal
recorded through a 70 h old specimen.
The construction of a two-dimensional image
(time-PSD) in which the PSD s amplitude is represented
according to a colour or a grey level scale (Figure 2A)
allows one to observe the behaviour of the frequency
spectrum of the received signal as a function of time.
Calculating the energy of the signal as well as tracing the
specific amplitude o f the frequencies characteristic o f the
PSD and the maximum of the signal s amplitude on a
bandwidth limited to 15-100 kHz make it possible to
determine the setting time. Mechanical destructive tests
together with microstructure observations on a scanning
electron microscope corroborate our results, whereas
modelling of the concrete setting underlines the
importance of the various chemical kinetics.
E x p e r i m e n t a l p r o c e d u r e
The experimental device a] makes it possible to generate
and receive an ultrasonic signal passing through an RCC
sample of length and diameter bo th of 160 ram. The
sample is mixed according to a rigorous procedure and
as soon as the concrete s consistency allows, the sample
in its cardboard mould is placed horizontally on the test
stand. A constant 40 N load is applied to the transducers
(Figure 3), coupling being achieved by molybdenum
disulphide grease.
The transmitting and receiving transducers have a
diameter of 50 mm and the frequencies transmitted are
low in order to limit at tenuation in the concrete. Spectral
analysis of a transmit ted signal through a 70 h old
specimen is given in Figure 2B.
1 6
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ett ing t ime s tudy of roller compacted concrete
Transmitt ing
transducer
Receiving
transducer
F i g u r e
3
ii ilililiiiiiii:~ il;i iiii~i
i l i i i i i : i i i i i i i i i l
S c hem a t i c o f t es t ing dev i c es t o d e t e r m i ne s e t ti ng t i m e
T h e u l t r a s o n i c wa v e p ro p a g a t i o n s p e e d i s g i v e n b y :
= L o / T , ( 1 )
whe re Lo i s the l eng th o f the sample an d T , i s the t rans i t
t i m e o f th e u l t r a s o n i c w a v e t h ro u g h t h e s a m p l e.
W e d e f i n e t h e t r a n s i t t i m e a s t h e t i m e b e t w e e n t h e i m p u l s e
o f the u l t rason ic s igna l genera to r an d the f i rs t ri s ing o r
fa l ling edge o f the t ransm i t ted s ignal . T he th resho ld i s
de te rmined as the f i r s t po in t s i tua ted more than f ive
s t a n d a rd d e v i a t i o n s f ro m t h e a v e ra g e c a l c u l a t e d o n t h e
gro und no ise o f 16 signa ls . The leve l o f th i s th resho ld i s
a b o u t 2 % o f t h e m a x i m u m a m p l i t u d e o f t h e fi rs t p e a k
of the reco rded s igna ls . The s igna l cons i s t s o f 2048 po in t s
acqu i red b y d ig ita l o sc i l lo scope . The t ime reso lu t ion i s
1/as per point .
W e c a l c u la t e t h e e n e rg y E f ro m t h e t r a n s m i t t e d t e m p o ra l
s ign us ing the re la t ion :
E t 1, t2) = a2(t) •dt (2)
w h e r e a t ) i s the a mp l i tude o f the s igna l a t t ime t .
T h e P S D a s we ll as t h e fo rm a t i o n o f t h e s p e c t ra l i m a g e
are perfo rmed in rea l t ime (F igure 2 ) . The PSD i s
n o rm a l i z e d o n t h e Y a xi s a c c o rd i n g t o t h e m a x i m u m
spect ra l po we r o f the s igna l. I t i s rep resen ted on the
1 5 -1 0 0 k Hz b a n d wi d t h i n o rd e r n o t t o t a k e i n t o a c c o u n t
t h e l o w f r e q u e n c y 7 k Hz . T h i s f r e q u e n c y , a p p ro x i m a t e l y
c o n s t a n t i n t h e t e s t, i s n o t r e p re s e n t a ti v e o f th e b e h a v i o u r
over t ime o f the u l t rason ic w ave t ransmiss ion poss ib i li -
t i es . As these poss ib i l i t i es depend on the mlcros t ruc tu re
o f the concre te , th i s low f req uency mu s t be f i l t e red ou t
i n o rd e r t o k e e p f ro m t h e P S D o n l y t h e f r e q u e n c i e s
p ro v i d i n g i n fo rm a t i o n a b o u t t h e m i c ro s t ru c t u re c h a n g e s
o f th e R C C . T h e s a m p l i n g f r e q u e n c y is 1 0 0 k H z a n d t h e
frequency in te rva l i s 0 .5 kHz.
T h e P S D o b t a i n e d f r o m a m a t u r e R C C s a m p l e w i t h a
C P A b i n d e r is s h o wn i n F i g u re 2 B . On t h is fu n c t io n we
c a n o b s e rv e t h e p r e s e n c e o f c h a ra c te r i s ti c f r e q u e n c ie s
(21 k Hz , 3 9 k Hz , 4 7 k H z a n d 5 5 k Hz ) .
T h e a m p l i t u d e o f a p a r ti c u l a r f r e q u e n c y a n d t h e
m a x i m u m a m p l i tu d e s o f t h e 1 5 - 1 0 0 k H z b a n d w i d t h a r e
d e t e rm i n e d f ro m t h e P S D. W e e x p re s s t h e m a s we l l a s
the energy in dec ibe l s (dB) . The va lue 0 dB co rresponds
t o a n a m p l i t u d e o f 0 .2 2 4 V rm s a n d t h u s t o a p o w e r o f
1 m W wi t h t h e i n p u t i m p e d a n c e o f o u r o s c i l l o s c o p e
(50 ~ ). T h i s m a x i m u m a m p l i t u d e i s a i m e d a t k e e p i n g t h e
h i g h e st d y n a m i c s o f th e c u rv e a n d a t t a k i n g i n t o a c c o u n t
a p ro b a b l e e n e rg y d i s t r ib u t i o n i n t h e f r e q u e n c y s p e c t ru m
(genera l ly the h ighes t f requency i s 21 kHz, bu t occas ion -
al ly i t is 39 kHz).
S E M o b s e rv a t i o n s a r e m a d e t o d e t e rm i n e t h e n a t u re ,
shape an d spa t ia l d i s t r ibu t ion o f the concre te ' s
c o n s t i t u e n t s a t t h e t i m e . T h e s a m p l e s a r e t a k e n a t
d i f fe ren t ages , f rozen a t 253 K to s top the hydra t ion and
t h e t r a n s fo rm a t i o n , c ry o - s u b l i m e d a n d t h e n m e t a l li z e d .
W e a n a l y s e t h e o b s e rv e d c o n s t i t u e n t s w i t h a Ke rv e x
p ro b e .
o n c r e t e s e t t i n g
A t h e o re t i c a l a p p ro a c h t o c o n c re t e s e t t i n g i s p ro p o s e d
b y L o c h e r e t a l . ta l . Bour naze l t sl syn thes izes and mo dels
m a n y o f t h e p a ra m e t e r s t h a t a f fe c t t h e s e t t in g o f R C C .
As s o o n a s wa t e r a n d c e m e n t a r e m i x e d , t h e c e m e n t ' s
cons t i tue n ts s ta r t to d i s so lve . A few min u tes l a te r , the
s o l u t i o n b e c o m e s s a t u ra t e d w i t h c a l c i u m h y d ro x i d e
Ca(OH)2 and the a lka l ine s i l i ca tes soon pass in to
s o l u t io n . M i c ro s t ru c t u re d e v e l o p m e n t e n t a i l s t h e n u c l e a -
t ion a nd g row ing o f e t t r ing i te (c rys ta ll i zed need les ), and
then th e fo rm at ion o f t r i ca lc ium s i l i ca te t r ihydra tes ,
so-cal led CSH (gel-l ike fibres). Et tringi te is a const i tuent
t h a t r e d i ss o l v e s p a r t l y o r t o t a l l y in t o m o n o s u l p h o -
a l u m i n a t e (AF m ) a c c o rd i n g t o t h e n a t u re a n d t h e
q u a n t i t y o f th e s u l p h a t e s t h a t a r e p r e s e n t. T h e d i m e n s i o n s
o f th e c e m e n t g r a i ns r e m a i n u n c h a n g e d ; t h e e t t ri n g i te
and the CSH may g row in the in te rs t i t i a l l iqu id .
The def in i t ion o f se t ting as p ro pose d by A cker l°~ i s
fo u n d e d o n t h e p e rc o l a t i o n t h e o ry , wh i c h e x p l a i n s t h e
b i r th , g row th and l inkages o f the g ra ins as in the
s impl i f i ed pa t te rns in F igure 4 .
Z S
L "
~ _
I
Isolate¢l Ck ~e r Percolalton
Events Formation
F i g u r e 4 Perco la t i on pr i nc ip l e as propo sed by Acker C1°]
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V . G a m i e r e t a l
The isolated events originate at random in the volume;
then they dus ter and eventually bridges build up between
them, which is the percolation threshold. From tha t stage,
the waves are not propagated solely through mechanisms
of transmission and reflection between the grain dusters
and the air porosity or the water, but transmission is also
ensured by these connections.
According to their density and their nature, we assume
that the vibrations of the particles change and that the
energy of the ultrasonic wave transmitted and its
frequency spectrum vary with time. We consider that the
concrete is a time-varying filter.
odell ing
Based on the preceding description of the concrete s
setting and on the completion of the hydration of the
binders (calcium silicate), a simplified model is developed
by differentiating he chemical transformations occurring
during setting into two classes.
(a) The volume transformations of the constituents that
correspond to first degree kinetics.
Calcium silicate=~ Ettringite
Calcium silicate =~ CSH
Ettringite ~ AFm
d m i / d t = kv i m i (3)
where m is the mass of the constituent i produced
from the transformation, t is the time and k~,i is the
speed and transformation coefficient.
(b) The surface transformations that cor res pon d to
second degree kinetics. They govern the density and
the quantity of the bridges created, and we express
them in terms of the percolation ratio which is equal
to 1 when the concrete is set.
d p / d t = kp. p2 (4)
where p is the percolation ratio, t is the time and k v
is the coefficient that characterizes the percolation
speed.
The transformations described are delayed in time, and
it is necessary to introduce an incubation time for each
of them.
If we know the initial masses of the elements that take
part in the hydration process (binders and water), we
can at any time calculate the masses rn of the n
constituents resulting from the transformations (first
degree kinetics). From the density pl, u assumed to be
constant, for each of these n constituents, we can
determine the volume of the pores v~ of the RCC from
the relation:
v~ = v t - - ~ m l / ( P i - - m J p g - - m h / P h
(5)
i ~
where vt is the total volume of the sample, mg, pg are the
masses and the densities of the aggregates and mh, Ph are
the remaining masses at time t and the densities of the
calcium hydroxides.
We can then calculate the equivalent density Po of the
solid portion of RCC.
Knowing the elastic modulus, Ei, and the Poisson s ratio,
Pi, of each of the RCC constituents and calculating the
proper volumes of these constituents enable us to
determine at any time, thanks to the self-coherent
patternt l a], the equivalent modulus E0 and Poisson ratio
Po of the solid s volume. The pores are considered as the
solid s consti tuents with a volume v of density p,
equivalent to those of air.
The velocity V, in the solid is then calculated by means
of the following relation:
N/p~ (1 -/~o)
V , = 1 + ~ o ~ - 1 : 2 /~ o ) 6 )
where Po is the RCC s equivalent density constantly
recalculated.
The behaviour of Vs in terms of time is shown in Figure
5 (solely solid curve) t aking in to account the parameters
specified in Table 1. The values of the incubation times
of ettringite and the CSH were determined experimentally
W a v e v e l o c i ty
5000 ~ m/s)
elld
,0 o 0 . J / - t " = * = '
r
0 . . . . . . . . . . . . . . . . . . . .
0 1 0 2 0 3 0 4 0 5 0 6 0
Time Ihours)
Figu re 5 Model o f t ransmit ted u lt rason ic wave propagat ion
velocity as a fun ctio n of time. The solid curve shows the calculated
velocity behaviour solely in the column of solid matter. The
percolation curve shows the calculated veloc ity behaviour solely in
the column of perco la t ion de lay . The global curve shows
the calculated velocity behaviour in the two columns that are in
series
T a b l e 1 . T r a n s f o r m a t i o n p a r a m e t e r s f o r a C P A
b o n d e d R C C
C P A
I n c u b a t i o n t i m e o f e t t r i n g i te 4 h
I n c u b a t i o n t i m e o f t h e C S H 7 h
T r a n s f o r m a t i o n r a t e p e r h o u r o f s i l i c a t e s
i n e t t r i n g i t e 1 6
T r a n s f o r m a t i o n r a t e p e r h o u r o f s i l i c a t e s
i n C S H 3 2
T r a n s f o r m a t i o n r a t e p e r h o u r o f e t t r in g i t e
i n A F m 8 0
P e r c o l a t i o n r a te p e r h o u r 8 0
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ett ing t ime stud y of roller comp acted concrete
< ~ S o l i d ~ <
c o lum n
T
Figure Seriesarrangement of the material
Percolat ion
c o lum n
1 2
in the course of tests for measuring setting times coupled
with SEM analyses on CPA bonded RCC samples.
Figure 5 (solely solid curve), which is calculated by
considering only the volumetric transformations, gives
an initial velocity of 3500 m s- 1 which remains constant
during the incubation period of ettringite, increases and
reaches a maximum of 4000 m s-1 during ettringite
formation. The velocity tends to an asymptotic value of
3700 m s-1 during the formation of the CSH and the
redissolution of ettringite.
If we compare this value of the calculated initial velocity
with the value measured experimentally (about 350
m s-~), we can conclude that the chemical volumetric
transformations are not the main phenomena in the
process of concrete setting. The bridges created during
setting must be taken into account in the model. These
surface transformations are integrated into the calcula-
tions with the percolation ratio. Thus, we consider a series
model for the concrete (Figure 6), i.e.:
• a column of solid traversed by the wave at a speed V
in a time TI:
T , = L / V , ) . p (7)
where L is the length of the sample and p is the
percolation ratio that changes according to second
degree kinetics.
• a column of percola tion delay with the same length
L traversed at a speed Vp in a time
T :
T z = L / V p ) . 1 - p ) (8)
where Vp is the wave propagation speed prior to setting
(350 m s- 1). The total time is:
T = T~ + T2 (9)
This column of percolation delay makes it possible to
introduce the concept of bridges into the calculation of
the ultrasonic wave propagation speed in the RCC. It
represents a time of wave flow that is in addition to the
time through the solely solid part, and characterizes the
difficulty of wave transmission from one grain to another.
At the beginning of the setting the speed in this column
only reaches 350m s -1. As the percolation ratio p
increases with time, the bridges grow in number.
The travel time through this column decreases and the
wave propagation speed increases.
The percolation curve as proposed in Figure 5 shows the
behaviour of the wave velocity in the sample taking into
account the column of percolation delay only. To
incorporate the flight time T = T 1 + T2 into the wave
velocity calculations, we consider simultaneously the
volume transformations of the constituents and the
surface linkage of the grains. The behaviour of the
velocity, as a function of time in the CPA bonded RCC,
is displayed in Figure 5 (global model). The coefficients
of Table 1 are obtained from iterative calculations
enabling us to estimate, as accurately as possible, the
experimental curves from the theoretical curve shown in
Figure 7.
The percolation phenomenon seems to be the major
element in the course of the first hours of the changes in
the wave speed in the sample. The solid part contributes
to the change of the wave speed as a function of time,
by establishing the asymptot ic value of this global curve.
This theoretical limit is lower than the experimental
values in Figure 7. This mainly results from the values
of p and E given to ettringite and the CSH. These values
are based on estimates derived from the crystalline or
non-crystalline nature of the microstructure.
In this first approach, we have modelled the behaviour
of the ultrasonic wave speed in a CPA bonded RCC by
taking into account kinetics that vary according to the
volume or surface transformations. We have shown the
importance of the percolation phenomenon in the setting
of concrete. This concept of bridge makes it easier to
understand the behaviour with time of the ultrasonic
signal in the RCC and to refine the concept of a
time-varying filter which is related to the nature and
density of the bridges between the grains.
E x p e r i m e n t a l r e s u l t s
Tests on CPA bonded RCC have been carried out for
the mixture shown in Table 2. The ETP 037 test was
used to carry out the SEM observations to determine
the nature and the temporal appearance of the RCC
constituents. The areas in which we can observe ettringite
and CSH formation are specified in Figure 7, which
gathers all the results showing the behaviour of the
ultrasonic wave speed. The ETP 058 and ETP 060B tests
were performed simultaneously on two samples; one with
a grease-coated side (the side in contact with the air), the
other free of any grease. The molybdenum disulphide
grease is to prevent water exchange with the outside
medium, and thus to standardize the hydration of the
sample.
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V. Garnier
e t a l
igure 7
5 0 0 0
4 0 0 0
3 0 0 0
2 0 0 0
1 0 0 0
0
W a v e v e l o c i t y
m / s) e t p 0 5 6
e l p 0 3 7
2 4 6
Time (hours)
Com par ison o f t heoret i ca l and exp er imenta l curves
T a b l e 2 . E x p e r i m e n t a l c o m p o s i t i o n a n d c o n d i t io n s o f t h e te s t s o n C P A b o n d e d R C C
ETP037 ETP056 ETP058 ETP060 and 060B
Qu a n t i t y Qu a n t i t y Qu a n t i t y Qu a n t i t y
Type (kg) Type (kg) Type (kg) Type (kg)
4 0 / 6 3 m m 0 3 3 8 3 3 8 3 3 8
3 1 .5 /4 0 mm : 1 5 8 1 5 8 1 5 8
20 /31 .5 mm Bu~ch : Durance 268 Durance 268 Durance 268
1 0 / 2 0 m m : 4 5 7 4 5 7 4 5 7
3 / 8 m m : 3 5 0 3 5 0 3 5 0
1 / 3 m m 6 3 2 4 3 2 4 3 2 4 3
0 / 3 m m 3 5 0 3 5 0 3 5 0
Fi ller XX XX XX 122 XX 122 XX 1 22
Ag g re g a te t o ta l 2 1 8 0 2 2 8 6 2 2 8 6 2 2 8 6
B in d e r 1 C PA 9 0 C PA 5 5 8 6 C PA 5 5 8 6 C PA 5 5 8 6
F ly ash FA 30 FA Hv 29 FA Hv 29 FA Hv 29
So l id s t o ta l 2 3 0 0 2 4 0 0 2 4 0 0 2 4 0 0
Wa ter 111 101 101 101
W ( ) 4 .2 4.2 4.2 4.2
Fresh concrete
Tota l for 1 m 3 2411 2501 2501 2501
Test tempe rature (°C) 23 24.1 24.7 18
All the results in Figure 7 show satisfying repeatability
for the experimental conditions specified in Table 2. This
repeatability is to be found for all of the experimental
results energy, specific amplitude of a part icular
frequency of the signal, maximum of amplitudes on the
15-100kHz bandwidth). Therefore we will restrict
ourselves to an analysis of the ETP 060B test performed
on a sample with grease-coated sides.
The ETP 037 test shows a divergence from the other
results, but we must bear in mind that the aggregates
that constitute this RCC have a different origin Buech)
from those that make up the other RCC Durance).
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Sett ing t ime study o f rol ler compacted concrete
Amplitude dB)
h-,,,,--*ant CSH 1 Energy 2
M a x i m u m o f
m n p i l u d ~
_ o _ \ ....... ............................................ .................................¢ _ ............... ..................................................................
6 0 . . .. . . . . . .
8 0
~ B e g i n n i n g f t h e f o r m ~ o n o f C S H
i 1
/ ~ . ~ \ , -
- ~ L B eg inn ingof ettxingit formation
- 1 2 0 t I L I I I I l
0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0
Time hours)
F i g u re 8 B ehav i ou r ov e r t i m e o f : 1 ) t he ene rgy c a l c u l a ted on t he tem pora l si gna l; 2 ) t he m a x i m um o f am p l i t udes de t e rm i ned
ov e r t he 15 -100 k H z bandw i d t h ; 3 ) t he am p l i t ude o f the f requenc y 21 k H z; 4 ) t he am p l i t ude o f the f r equenc y 39 k H z
n a l y s i s
Th e s p e c t r a l i m a g e s h o w n i n F i g u re 2 A s u m m a r i z e s t h e
c h ro n o l o g i c a l a p p e a ra n c e o f th e v a r i o u s f r e q u en c i e s i n
t h e P S D . Th i s g l o b a l t i m e - f r e q u e n c y v i e w sp ec if ie s t h e
a m p l i t u d e o f e a c h f re q u e n c y a s a f u n c t i o n o f ti m e b y
m e a n s o f a c o l o u r o r g r e y l e v e l s ca le . Th i s b e h a v i o u r o v e r
t ime i s l inked to changes in the concr e te s micros t ruc tu re .
W e c a n d e fi n e t h e ir a p p e a r a n c e w h e n t h e a m p l i t u d e c a n
b e d i s t i n g u i s h e d f ro m t h e b a c k g ro u n d n o i s e . W e t h u s
observe tha t the h igher the f requency cons idered i s , the
l a t e r is it s a p p e a ra n c e . C o n c re t e c a n b e c o n s i d e re d a s a
t ime-vary ing spec t ra l f i l t e r tha t widens the t ransmiss ion
b a n d o f t h e t r a n s m i t t e d u l t r a s o n i c w a v e a s it u n d e rg o e s
se t t ing and harden ing .
A s w e h a v e s h o w n p re v i o u s l y , p e r c o l a t i o n i s t h e m a j o r
e l e m e n t t h a t g o v e rn s t h e p ro p a g a t i o n s p e e d a n d
a c c o rd i n g l y t h e p o s s i b i li t y o f w a v e t r a n s m i s si o n t h ro u g h
t h e s a m p l e . M o d i fy i n g t h e d e n s i t y a n d t h e n a t u r e o f t h e
b r i d g e s b e t w e e n t h e g r a i n c l u s te r s m a k e s t h e r i g id i ty o f
the l inkages change wi th t ime and there i s an increase
in the energy as wel l as the f requencies o f the t ransm i t ted
v ib ra t ions .
Th e f r e q u e n c y r a n g e a n d t h e t r a n s m i t t e d e n e rg y w i l l
d e p e n d o n t h e a t t e n u a t i o n a n d s c a t t er i n g o f th e u l t r a s o n ic
w a v e s t h ro u g h t h e s a m p l e . B o t h d e p e n d o n t h e
v i scoe las t i c charac te r i s t i cs o f the l inkages an d ex i s t ing
c o n s t i t u e n t s . S t o p p i n g t h e g ro w t h i n a m p l i t u d e o r
d e c re a s i n g t h e t r a n s m i t t e d e n e rg y c o r r e s p o n d s t o
m o d i fy i n g o r s t o p p i n g t h e g ro w t h k i n e t i c s o f o n e o r m o re
of the cons t i tuen t s , o r d i s so lv ing one o f the ex i s t ing
cons t i tuen t s , as i s the case wi th e t t r ing i te in the course
of set t ing.
F i g u re 8 s h o w s t h e b e h a v i o u r o f t h e a m p l i t u d e o f t h e
f i r st two f requenc ies o f 21 and 39 kH z (cu rves 3 and 4 ),
o f t h e m a x i m u m o f a m p l i t u d e s o n t h e l i m i te d b a n d w i d t h
(cu rve 2 ) and o f the energ y (cu rve 1 ) o f the s igna l a s a
func t ion o f t ime.
Th e e n e rg y c u rv e in c r e a s es u p t o a m a x i m u m v a l u e (p o i n t
E) fo r a per iod o f abo u t 9 h . Th is sa tu ra t ion re f lec ts the
e n d o f th e m a s s i v e fo rm a t i o n o f t h e C S H , m a k i n g i t
poss ib le to fo rm the in te rg ranu lar b r idges . The increase
i n t h e w a v e s p e e d s u b s e q u e n t t o t h i s p o i n t s h o w s t h a t
c o n c re t e b e h a v e s i n a g re e m e n t w i t h t h e m o d e l . Th e
c h a n g e i n e n e rg y c o r r e s p o n d s t o t h e fo rm a t i o n o f C S H ,
b u t s e t t i n g i s o v e r b e c a u s e t h e m o s t i m p o r t a n t p a r t o f
t h e f r a m e w o rk o f R C C h a s b e e n e s t a b li s h e d.
Th e p a r t p r i o r t o t h i s s a t u r a t i o n l e v e l c a n b e a n a l y s e d
e s s e n ti a ll y b y e x a m i n i n g t h e m a x i m u m o f a m p l i t u d e s o n
t h e l i m i t e d b a n d w i d t h ( c u rv e 2 ) . W e o b s e rv e t h r e e
s ingu lar it i es (po in t s , L , M and N) . I f we com par e these
t imes wi th the resu l t s o f mec han ica l t es t s o f res i s tance to
n e e d l e p e n e t r a t i o n a n d S EM a n a l y se s , w e c a n s h o w t h a t :
• p o i n t L c o r r e s p o n d s t o t h e b e g i n n i n g o f e t t r in g i t e
fo rmat ion tha t p roduces the f i r s t in te r -g ra in b r idges ,
• p o i n t M c o r r e s p o n d s t o t h e r e d i s s o l u ti o n o f e t t r in g i t e
a n d t o t h e b e g in n i n g o f t h e fo rm a t i o n o f C S H a ro u n d
t h e g r a in s o f h y d ra t e d c e m e n t w h i c h l in k s t h e m
together , and
• p o i n t N c o r r e s p o n d s t o th e b e g in n i n g o f t h e fo rm a t i o n
o f la rg e q u a n t i t ie s o f C S H .
Th e fo rm a t i o n o f a l a rge q u a n t i t y o f C S H h a d b e e n
prev ious ly used to def ine the se t t ing t ime. Consequen t ly
po in t N charac te r izes th i s . We can use th i s s ingu lar i ty in
the cu rve to de te rmine the se t t ing t ime. Af te r th i s
s i n g ul a r it y , i t i s t o o l a t e t o o b t a i n g o o d c o h e s i o n b e t w e e n
two success ive l ayers.
C o n c l u s i o n s
Th i s w o rk a i m s a t d e v e l o p i n g a n e w t o o l t o m e a s u re
t h e s e tt i n g t im e o f c o n c ret e . Th e w a v e s p e e d c u rv e s a s
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V Garnier
e t a l
fu n c t io n s o f t i m e c a n b e u s e d fo r t h is p u rp o s e o n l y i n
t h e c a s e o f s l o w s e t t i n g (B a r l a c b i n d e r ) . F o r t h e C P A
b i n d e r, th i s m e t h o d d o e s n o t a l l o w th e d e t e rm i n a t i o n o f
t h e s e t t i n g t i m e . To o v e rc o m e t h i s p ro b l e m , w e h a v e
d e v e l o p e d a n a p p ro a c h w h i c h i n v o l v e s t h e b e h a v i o u r
o v e r t im e o f t h e e n e rg y a n d o f th e f r e q u e n c y s p e c t ru m
(P S D ) o f u lt r a s o n i c s i g na l s tr a n s m i t t e d t h ro u g h a s a m p l e .
Th e u s e o f a s p e c t r a l i m a g e i n r e l a t io n t o t i m e s h o w s t h e
ef fec t o f a t ime-var y ing f i l t er ac t ion o f the co ncre te as a
r e s ul t o f t h e c o n s t i t u e n t s c r e a t e d a n d t h e d e v e l o p m e n t
o f the b r idges tha t b ind them.
Th e i m p o r t a n c e o f t h is p e r c o l a t io n p h e n o m e n o n i s m a d e
c l e ar b y a m o d e l o f t h e R C C s s e t t in g w i t h C P A b i n d e r
which re l ies o n tw o type s o f chemica l k ine t ics :
• f ir st o rd er fo r the vo lume t rans fo rm at ions ,
• s e c o n d o rd e r f o r t h e s u r f ac e tr a n s fo rm a t i o n s (b r i dg e
fo rmat ion ) .
Th e c a l c u l a t i o n s s h o w t h a t t h e m a j o r e l e m e n t i n t h e
b e h a v i o u r o f t h e u l t r a s o n i c w a v e s p e e d i n t h e f i r s t fe w
hours o f the R CC s se t t ing i s the in te rg ra in b r idge
p h e n o m e n o n (p e rc o l a t i o n ) . Th e c h a n g e s i n t h e c o n s t i -
t u e n t s in t h e s o l i d p o r t i o n o n l y t a k e p l a c e a f t e r t h e R C C s
f i r st few hou rs o f se t t ing .
Analys i s o f the spec t ra l image , and co r re la t ions wi th the
r e s ul ts o f m e c h a n i c a l t e s ti n g a n d S E M o b s e rv a t i o n s ,
e n a b l e u s to u n d e r s t a n d b e t t e r a n d fo l l o w i n r e a l t im e
t h e b e h a v i o u r o f t h e c o n s t i t u e n t s t h a t a r e p r e s e n t i n t h e
c o n c re t e . Th i s l a s t p o i n t s h o u l d b e m a d e e a s i e r b y
a n a l y si n g t h e c h a n g e s i n t h e a m p l i t u d e s o f th e
charac te r i s t i c f requencies o f the P SD in re la t ion to t ime.
At p resen t , de te rm ina t ion o f the se t ting t ime has been
c a r r ie d o u t b y fo l lo w i n g t h e d e v e l o p m e n t o f t h e
m a x i m u m o f a m p l i t u d e s o n a b a n d w i d t h l i m i t e d t o
1 5 -1 0 0 k H z i n t h e P S D a s a f u n c t i o n o f ti m e . Th i s i s
i d e n t i f i e d a s b e i n g t h e m o m e n t c o r r e s p o n d i n g t o a
charac te r i s t i c s ingu lar i ty o f th is cu rve . Th is par t i cu la r
p o i n t o n t h e c u rv e i s re p e a t e d s y s t e m a t i c a ll y d u r i n g t h e
tes ts , wh ich a l low s the ana lys i s o f the se t t ing in rea l t ime.
A cu rren t s tudy i s a imed a t check ing under f ixed
exper im en ta l cond i t ions the re l i ab i l i ty o f th i s c r i te r ion o f
s e t t i n g t i m e d e t e rm i n a t i o n o n R C C s w i t h t h e s a m e C P A
b i n d e r a n d o n R s w i t h a n o t h e r b i n d e r . Th i s l a b o ra t o ry
s t u d y h a s a l s o t o b e c a rr i e d o u t f u r t h e r t o d e t e rm i n e t h e
i n f lu e n c e o f t e m p e ra t u r e , h u m i d i t y a n d w i n d c o n d i t i o n s
o n t h e m e a s u re m e n t o f t h e s e t ti n g t i m e .
Th is def in i t ion o f se t t ing t ime can be app l ied to o ther
t y p e s o f c o n c re t e , p ro v i d e d t h a t t h e a p p ro p r i a t e
t r a n s d u c e r s a n d b a n d w i d t h s h a v e b e e n a c c u ra t e l y
de termined .
cknowledgements
T h e a u t h o r s a r e g ra t ef u l fo r th e s u p p o r t o f C E M E T E -
E D F o f A i x - e n- P r o v en c e a n d E N S o f C ac h a n .
e f e r e n c e s
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Dijon France (July 3-5 1991)
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be ha viour o f C3A in the e a r ly s t a ge s of c e m e nt hy dra t ion ' Se m ina r
on the r e a c t ion of a lum ina te s dur ing th e s e t t ing of c e m e nt ,
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11 Francois , D. , Pineau, A. and Zaoui , A.
C o m p o r t e m e n t Me c a n i q u e
• d e s Ma t b r i a u x Edit ion Hermes, Par is (1991)