Setting Time Study of Roller Compacted Concrete by Spectral Analysis of Transmitted Ultrasonic Signals

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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]

5



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



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°]

1 7



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

1 8



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.

9



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).

2



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

2



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

1 Bouraazel , J . P. , Moranville -Regnurd, M. and Horam in, H. 'Ear ly

a ge c onc re te s t r e ngth : a phe nom e nologic a l a pproa c h to phys ic o-

chemical processes'

I s t In t Wo rk sh o p o n H y d ra t i o n a n d S e t t i nO

Dijon France (July 3-5 1991)

2

Jacquemmoz

C., Bouraazei , J . P. and Conty, Y. 'Etude du temps

de pr i s e du BC R' Mis s ion ~ Ca c ha n,

R a p p o rt E D F - T E G G

no 214

A (1990)

3 Ca m m rd, G . a nd Pros t , J . La propa g a t ion de s onde s u l t r a sonore s

a ppl iqure ~ i '& ude de l a pr is e de s c im e nts '

Bul le t in de l ia ison de s

L P C . no 108 (1980) pp 91-92

4 Pessiki , S. and Carino, N. 'Se t t in g t ime and s trength o f concre te

us ing the im pa c t - e c ho m e thod '

Am e r i c a n C o n c re t e In s t i t u t e

Ma t e r i a l s J o u rn a l ( s e p t e m b e r - O c t o b e r 1 9 88 ) p p 3 8 9 - 3 9 9

5 Bourna ze l, J . P . Cont r ibut ion d l ' r tude du c a ra c t r r e the rm o-

m rc a niqu e du be ton ' Th r se de doc tora t , Unive r s i t6 de Pa r i s VI

(1992)

6 Ca nna rd , G . , Orc e l , G . and Pros t , J . 'Le su iv i de s br tons pa r

u i t r a sons '

Bul le t in de l ia i son des LPC.

no 168 (July 1990)

7 Ga yde c kl , P . A . , k r de ki a , F . M. , Da nm j , W. , John, D . G . a nd

Pa yne , P . A . The propa ga t ion a nd a t t e nua t ion of m e dium -

frequency ul trasonic waves in concre te : a s ignal analyt ica l

a p p r o a c h ' Me a s S c i Te c h n o l 3 (1992) pp 126-134

8 Gam ier , V. , Perfum o, J . C., Coraelon p, G. , Sprauel , J . M . ,

Le ygonie , M. a nd Va lon , R . 'Me sure du t e m ps de pr i s e du BCR

pa r m r thode u l t r a sonore . Synthr se de s r r su l t a t s ' Ra p p o r t

E D F - T E G G no 226 A (1992)

9 Lodaer , F. W. , Riehartz , W. and Sprung, S. 'Studies on the

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 ,

E indhove n , The Ne the r la nds (Apri l 13-14 1977)

10 A e ke r , P . 'Com por te m e nt m rc a nique du br ton: a ppor t s de

l ' a pproc he phys ic o-c him ique '

Ra p p o r t d e re c h e rc h e d e s LPC n o

152 (1988)

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)

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