N. E. BOUHAMOU et al.: INFLUENCE OF DREDGED SEDIMENT ON THE SHRINKAGE BEHAVIOR ...
127–135
INFLUENCE OF DREDGED SEDIMENT ON THE SHRINKAGE
BEHAVIOR OF SELF-COMPACTING CONCRETE
VPLIV IZKOPANIH SEDIMENTOV NA KR^ENJE
SAMOZGO[^EVALNEGA BETONA
Nasr-Eddine Bouhamou, Fouzia Mostefa, Abdelkader Mebrouki, Karim Bendani,
Nadia Belas
LCTPE Laboratory, Civil Engineering Department, Mostaganem University, Route de Belahcel BP 227, 27000 Mostaganem, Algeria
bendanik@yahoo.fr
Prejem rokopisa – received: 2013-10-16; sprejem za objavo – accepted for publication: 2015-02-10
doi:10.17222/mit.2013.252
Every year, millions of cubic meters of dams and restraints are dredged as part of the management and prevention procedures all
over the world. These dredged sediments are considered as natural waste leading to environmental, ecological and even
economic problems associated with their processing and depositing. Nevertheless, in the context of a sustainable development
policy, a way of their management is open aiming at assessing the sediments as a building material and, particularly, as a new
binder that can be industrially exploited and that can improve the physical, chemical and mechanical characteristics of the
concrete. This study is a part of the research made at the Civil Engineering Department at the University of Mostaganem
(Algeria) on the impact of the mud dredged from the Fergoug Dam on the behavior of self-consolidating concrete (SCC) in the
fresh and hardened states, such as the mechanical performance and its impact on different deformations (shrinkage). The work
aims to assess this mud in the SCC and to show possible interactions between the constituents. The obtained results provide the
details needed for producing the SCC based on calcined mud.
Keywords: sediment, calcined mud, self-consolidating concrete, fresh state, hard state, shrinkage
Vsako leto po vsem svetu kot varovalni ukrep izkopljejo milijone kubi~nih metrov sedimentov iz jezov in zadr`evalnikov. Ti
izkopani sedimenti so obravnavani kot naravni odpadek, ki povzro~a okoljske, ekolo{ke in celo ekonomske te`ave pri njihovi
predelavi ali odlaganju. Vseeno, v kontekstu politike trajnostnega razvoja je postavljena pot za njihovo obdelavo, za oceno teh
sedimentov kot gradbenega materiala in {e posebej kot novega veziva, ki ga je mogo~e industrijsko izkoristiti in ki lahko
izbolj{a fizikalne, kemijske in mehanske lastnosti betona. Ta {tudija je del raziskovalnega dela, opravljenega na oddelku za
gradbeni{tvo Univerze v Mostaganemu (Al`irija), o vplivu izkopanega mulja iz jezu Fergoug na vedenje samozgo{~evalnega
betona (SCC) v sve`em in v strjenem stanju, na mehanske lastnosti in na razli~ne deformacije (kr~enje). Namen je oceniti to
blato v SCC in pokazati morebitne interakcije med sestavinami. Prikazani rezultati so dobra mo`nost za izdelavo SCC na osnovi
kalciniranega blata.
Klju~ne besede: sediment, kalcinirano blato, samozgo{~evalni beton, sve`e stanje, trdo stanje, kr~enje
1 INTRODUCTION
This work addresses general problems associated
with durable development. The search for new building
materials indicates that the research is focused on the
possibilities of reusing industrial and natural waste as an
alternative to the currently used materials that will
become scarce in the near future.
River sediments in dams can be seen as an environ-
mental and economic threat. The big quantities generated
by the silting phenomena make the authorities perplexed
about their depositions.
An assessment of these sediments made in the area of
civil engineering proved that they could be used as build-
ing materials (bricks, aggregates and cementitious mate-
rials).
As these studies are in their first step, the reuse of
sediments in concrete is poorly documented, particularly
for self-compacting concrete.
It is known that SCC contains a very high amount of
a paste that requires a large quantity of cement; so, its
partial substitution with sediments can be a solution, re-
ducing the use of cement.
2 IDENTIFICATION OF FERGOUG DAM
Regarded as one of the most silted dams in Algeria,
the Dam of Fergoug (Figure 1) gave rise to the interest
of several Algerian researchers who contributed various
studies towards highlighting the causes, making it a
disastrous dam.
These studies were primarily focused on explaining
the phenomenon of silting, trying to find solutions for it
and assessing the possibility of using the dredged sedi-
ments.1,2
During its existence, the dam underwent several ope-
rations of dredging; the first one was carried out in 1984
and 1986 when more than 10 million m3 of mud were
removed. The second operation of dredging was carried
out in 1992 when 6.5 million m3 of mud was evacuated.
The last operation was launched in 2005, at a cost of 800
million DA, which is 130 DA/m3, and carried out by the
National Agency for Dams.
Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135 127
UDK 691.004.8:658.567.1 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 50(1)127(2016)
In spite of these various attempts, the rate of the
current silting is estimated to be 97.77 % according to
the bulletin published by the Agency for the Chergui
Hydro Channel [ABHC]3.
3 MATERIALS AND METHODS
3.1 Used materials
3.1.1 Cement
The cement used was CEM I 42.5, made at the
Zahana Factory (west of Algeria). The average physical
and chemical characteristics of this cement are given in
Table 1.
Table 1: Physical properties and chemical analysis of the cement
Tabela 1: Fizikalne lastnosti in kemijska analiza cementa
Physical properties of cement
Bulk density (g/cm3) 1.18
Specific gravity (g/cm3) 3.13
Fineness (Blaine) (cm2/g) 3180
Chemical analysis of cement, w/%
SiO2 20.90
CaO 63.93
MgO 1.45
Fe2O3 5.93
Al2O3 5.10
SO3 0.86
Na2O 0.17
K2O 1.34
Loss on ignition 0.86
Carbonates –
CO2 –
H2O 0.6
3.1.2 Mud
The mud was taken downstream of the dam (Figure
2a) and activated thermally by burning it in a slow oven
at a temperature of (750 ± 5) °C at a rate of 5 °C/min for
5 h, followed by steaming, crushing and sieving to 80 μm
(Figure 2b). The calcined mud (Figure 2c) was obtained
and stored away from the air and any moisture. The
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128 Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135
Figure 3: Fergoug-mud grain-size distribution (SIBELCO Laboratory,
France, 2011)
Slika 3: Razporeditev velikosti zrn iz blata Fergoug (SIBELCO Labo-
ratory, France, 2011)
Figure 1: Fergoug Dam and its effluents
Slika 1: Jez Fergoug s pritoki
Figure 2: Mud-preparation stages
Slika 2: Stopnje priprave blata
Table 2: Physical characteristics of the calcined mud
Tabela 2: Fizikalne zna~ilnosti kalciniranega blata
Test Values
Bulk density (g/cm3) 0.53
Specific gravity (g/cm3) 2.62
Fineness (Blaine) (cm2/g) 7964.00
Table 3: Chemical composition of the calcined mud
Tabela 3: Kemijska sestava kalciniranega blata
Component Content, w/%
SiO2 54.69
CaO 14.25
MgO 3.08
AL2O3 15.49
Fe2O3 7.50
SO4 –
Loss on ignition 1.87
physical and chemical characteristics of the calcined
mud are presented in Tables 2 and 3.
The grain-size analysis of the mud was carried out at
the SIBELCO Laboratory (France). The results of the
analysis of this mud are shown with a grading curve in
Figure 3.
3.1.3 Aggregates
The aggregates used in this work consist of broken
particles of limestone with a well graded distribution,
obtained from the quarry of Kristel (the Oran area) and
the sand from the siliceous sea, from the quarry of Sidi
Lakhdar (the area of Mostaganem). Table 4 gives the
characteristics of the aggregates for the whole of the con-
crete compositions.
Table 4: Physical characteristics of different aggregates
Tabela 4: Fizikalne zna~ilnosti razli~nih agregatov
Sea sand
(Ss)
Quarry
sand (Sc) Gravel (G)
Class 0/2 0/3 3/8 8/15
Nature Silicious Limestone Limestone Limestone
Specific gravity
(g/cm3) 2.56 2.68 2.66 2.66
Absorption (%) – – 0.86 0.40
Fineness
modulus 1.64 2.63 – –
Sand equivalent
(ES) 83.18 88.96
3.1.4 Admixture
The admixture employed is a superplasticizer pro-
vided by the GRANITEX Society, a high water reducer,
containing synthesized polymers combined according to
the NF EN 934-2 standard. The MEDAFLOW113 allows
obtaining concretes and mortars of a very high quality,
maintaining the workability and avoiding the segrega-
tion. Its density is 1.12 g/cm3 and its proportioning can
vary from 0.8 % to 2.5 % of the binder mass.
3.2 Concrete mixtures
Four self-consolidating concretes were made to study
the substitution effect of the cement with the calcined
mud on the behavior in the fresh and hard states of the
SCC. The concretes were made by adopting the method
of the volume of the paste. The admixture proportioning
is calculated in order to limit the segregation and
bleeding and to obtain a distribution ranging between 60
cm and 75 cm.
The aggregate proportioning (G/S), the water/binder
ratio (W/B) and the volume of the paste were kept con-
stant for all the compositions of the SCCs. Tests were
carried out on the concretes containing various percen-
tages of the substitution mud with respect to the volume
of cement, i.e., (10, 15 and 20) %. The compositions of
various mixtures are presented in Table 5.
Table 5: Mix proportions of concretes
Tabela 5: Razmerje me{anic v betonih
Mix proportion
(kg/m3)
Concrete mixes
SCCR SCCM10 SCCM15 SCCM20
Cement 450 420 408 395
Calcined mud – 35 52 66
Water 225 218 216 213
Admixture 5.7 7.5 8.3 9.8
W/B 0.5 0.5 0.5 0.5
Ss 560 560 560 560
Sc 251 251 251 251
Gravel (3/8) 333 333 333 333
Gravel (8/15) 499 499 499 499
SCCR: Reference Concrete (0 % calcined mud)
SCCM10: Concrete with 10 % of calcined mud
SCCM15: Concrete with 15 % of calcined mud
SCCM20: Concrete with 20 % of calcined mud
3.2.1 Tests of the fresh concrete
The characterization made in the fresh state of the
concretes was limited to the tests recommended by
AFGC4 including the slump flow, L-box, sieve stability
and bleeding.
3.2.2 Tests of the hardened concrete
3.2.2.1 Mechanical strength
The mechanical compressive strength is an essential
characteristic of a concrete material and a fundamental
parameter of our study. Consequently, its evolution was
measured for all the formulations of concrete studied
within this work.
The samples used to determine the mechanical com-
pressive strength of various studied concretes are cylin-
drical test tubes with a diameter of 11 cm and a height of
22 cm. Once removed from the mold, they are preserved
in water for a certain period (1, 7, 28 and 90) d. To mea-
sure the average tensile strength, three samples (7 cm ×
7 cm × 28 cm) were broken at various ages by means of
three-point-bending tensile tests.
3.2.2.2 Shrinkage deformation
It is interesting here to observe the deformations of
the hardened material (after 24 h). For this purpose, two
series of samples were produced and preserved in two
different environments with and without a hydrous ex-
change with the external medium. The tests were per-
formed to measure the total and endogenous shrinkage
deformations. The shrinkage deformations were mea-
sured with a refractometer used on the prismatic test
tubes with the size of 7 cm × 7 cm × 28 cm, placed in an
air-conditioned room with a relative humidity of (20 ± 1)
°C or (50 ± 5) %, according to the following two con-
ditions:
• A hydrous exchange of the material with the environ-
ment: the total shrinkage is obtained and it represents
the sum of the endogenous and drying shrinkages.
• No hydrous exchange with the environment because
the test tubes are covered with one or two sheets of
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Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135 129
self-adhesive aluminum paper: the endogenous
shrinkage is identified.
The drying-shrinkage deformation is obtained from
the difference between the total and endogenous shrink-
age deformations.
Once removed from the mold, six test tubes relative
to each concrete (three for the total shrinkage and three
for the endogenous shrinkage) were tested over a very
short period: first at its beginning, later the periodicity of
the measurement increased with the time.
4 RESULTS AND DISCUSSIONS
4.1 Index and the activity coefficient of the calcined
mud
The index of the activity noted, Ip, is defined as the
ratio between compressive strengths fp(t) and f0(t) (Equa-
tion (1)) with respect to the strength of the standardized
mortar containing 25 % of the calcined mud as the ce-
ment substitution p and the reference-mortar strength
(with cement only) (Table 6):
I p
f t
f t
( )
( )
( )
=
p
0
(1)
Table 6: Results of the compressive-crushing tests
Tabela 6: Rezultati tla~nih poru{nih preizkusov
Age f0(t)/MPa fp(t)/MPa I(p)
28 d 47.4 39.20 0.83
90 d 52.30 45.08 0.86
4.2 Fresh states
The characterization results carried out on the con-
cretes are presented in Table 7.
Table 7: Workability test results
Tabela 7: Rezultati preizkusov obdelavnosti
Concrete SCCR SCCM10 SCCM15 SCCM20
Slump flow R/cm 66.5 65.4 63.6 63.3
T50 cm/s, slump flow 3.5 3.3 3.1 3.2
(H2/H1)/% (L-Box) 0.85 0.83 0.82 0.80
T40/s (L-Box) 3.4 3.5 3.7 3.6
(H2/H1)/% (L-Box) 8.47 7.55 6.90 4.55
Bleeding, ‰ 1.25 1.18 1.12 1.15
4.3 Workability (slump-flow test)
It can be noted that all of the SCCs comply with the
criterion of the flow spread where specified values lie
between 63.3 cm and 66.5 cm (Figure 4), causing a
lower viscosity. Although no limit is given for the times
of the flow spread, the time needed to reach a 50 cm dia-
meter (T50) is close to the values usually noted, i.e., 3 s.
4.4 Flowability (L-box test)
The L-box test is used to assess the filling and pass-
ing ability of SCC. This is a widely used test suitable for
a laboratory as well as site use. A concrete can be
accepted if the fill ratio (H2/H1) of the L-box is higher
than 0.8 4; the flowing times can be measured in order to
assess the viscosity. The obtained results clearly show
that the concrete present satisfies the ratio of 0.80–0.85.
4.5 Sieve-stability test
For this test, the results in Table 7 show that all the
SCCs have a segregation rate lower than 15 %, indicating
a good stability.4 When determined as 0    5 %, the
resistance to the segregation is maintained to be "too
significant" which is true in the case of SCCM20 where
the paste is too viscous to run out through the sieve.5
4.6 Bleeding test
The results in Table 7 indicate that all the concretes
meet the recommended value. The values obtained vary
between 1.12 ‰ and 1.25 ‰.
4.7 Hardened state
4.7.1 Evolution of the mechanical compressive strength
According to the obtained results and curves repre-
sented in Figure 5, it is clear that the SCCR displays a
good compressive performance at various testing stages
compared to the concretes with the substitute material
(SCCM). It is observed that over short periods the con-
cretes have similar amplitudes; on the other hand, over
long periods, their amplitudes start to move away from
that of the SCC, except for the SCCM10, which displays
a trend close enough to the SCCR observed between the
28th and 90th day.
The evolution of the compressive strength with res-
pect to time shows that during a short-term period the
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130 Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135
Figure 4: Diagram of the diameter of the slump flow
Slika 4: Diagram premera pri preizkusu razleza
evolution rate of the strength of the SCCMs is deve-
loping more slowly than that of the SSCR; nevertheless,
it can be noted that the variation between the measured
values is slightly different, especially for the SCCM10.
The measured values indicate that the SCCR reached
(48, 60 and 82) % of its compressive strength after 28 d
for the testing ages of (3, 7 and 14) d, respectively. How-
ever, the SCCM10, SCCM15 and SCCM20 reached bet-
ween 48–51 % after 3 d, 64–65 % after 7 d and 89–92 %
after 14 d, which can only be explained with the densifi-
cation effect. The calcined mud acted as the filler, filling
in the pores and increasing the compactness of the
cementitious matrix.
On the other hand, between the 28th and 90th day, it
is the SCCM10 that evolves distinctly among the
SCCMs. For these testing ages, the effect of the pozzo-
lanic activity on the concretes can be distinguished. The
evolution of this compressive strength can also be clearly
noticed on the histogram presented in Figure 6, which
also shows the effect of the variation of the M/C ratio
(the proportioning of the mud to cement) on the strength
evolution.
However, it is interesting to note that even with the
20 % substitution, the compressive strength remains
within the reasonable limit of 30 MPa recommended by
various construction specifications for building concre-
tes.
4.7.2 Evolution of the mechanical tensile strength
It is known that the factors influencing the evolution
of the compressive strength also influence the evolution
of the tensile strength of concrete. The obtained results
show that SCCMs developed a low tensile strength com-
pared to the reference SCCR.
On Figure 7, we can see that the development of the
tensile strengths follows the trend of the compressive
strength and the evolutions of the strengths in the early
period are identical, confirming the hypothesis that the
mud acts as the filler.
It can also be noticed on Figure 7 that the tensile
strength of the SCCM10 displays a convergence towards
that of the SCCR as of the 28th day with respect to the
two other concretes, indicating a sufficiently attenuated
amplitude.
Figure 8 clearly shows that the reference concrete
exhibits the best performances followed by the SCCM10.
In general, the loss of the resistance to compression or
traction does not exceed the mean value of 25 % com-
pared to the reference concretes irrespective of the age
and the rate of substitution.
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Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135 131
Figure 8: Histogram of the evolution of the tensile strengths with
respect to the mud proportion
Slika 8: Histogram razvoja natezne trdnosti glede na dele` blata
Figure 6: Histogram of evolution of the compressive strength with
respect to the mud proportion
Slika 6: Histogram razvoja tla~ne trdnosti glede na dele` blata
Figure 5: Compressive strength of concretes versus time
Slika 5: Tla~na trdnost betona v odvisnosti od ~asa
Figure 7: Evolution of the tensile strength at different ages
Slika 7: Razvoj natezne trdnosti pri razli~ni starosti
4.8 Different deformations
It is known that the factor with the highest influence
on the shrinkage is the quantity of the water used. For
this reason and in order to better determine the problem,
the W/B ratio is kept equal to 0.5. The compositions of
the tested SCCs only differ in the proportion of the cal-
cined mud substituting the cement, so all the differences
in the behavior of the concretes are related only to this
parameter.
4.8.1 Endogenous shrinkage
The endogenous deformations measured from the
first day onwards are displayed on Figure 9. The types
of the kinetics of the endogenous-shrinkage
deformations of the concretes are rather similar; at the
beginning they take similar and almost identical forms
and start to differ with time.
Since this shrinkage is a consequence of the hydra-
tion phase6,7, it gives evidence of its kinetics and the
quantity of formed hydrates. It can be observed that
during the period from the 28th to 90th day, the orders of
the magnitudes of the SCCMs approach that of the
SCCR in comparison with the values displayed at the
early age. At the 28th day, the SCCMs display reduced
values, varying between 5.5 % and 15.5 % compared to
the SCCR; on the other hand, between the 60 and 90th
day, they are reduced by 4.6 % to 12.45 % compared to
the SCCR, which shows that the deformations evolve in
the same spindle, whereas the coming together of the
values is a proof of the pozzolanic activity of the mud,
which begins, a priori, after the 28th day.
The reduction in the endogenous shrinkage in the
presence of the calcined mud can be explained with the
fact that some hydrates (calcium aluminate) obtained via
the pozzolanic reaction between the silica and the port-
landite, are slightly expansive8, compensating for the
dimensional variations due to the shrinkage.9 The shrink-
ages show the same development according to the me-
chanical compressive strength10, the auto-desiccation
known as the principal phenomenon, which governs the
endogenous shrinkage growing under the influence of a
high strength.
4.8.2 Drying shrinkage
This shrinkage develops from the surfaces exposed to
the external environment; it is determined by calculating
the difference between the total shrinkage and the endo-
genous shrinkage and it is presented with respect to time
and mass loss. Figure 10 shows that the curves obtained
for the SCC appear in a spindle, indicating that, due to
drying, the component is not modified by the M/C ratio.
During the first phase, the values of the shrinkage of the
SCCMs decrease compared to the SCCR, by the percen-
tages varying between 21 % and 52 % on the 7th and
28th day. On the other hand, during the second phase, the
evolution starts to slow down until becoming almost
constant up to the 90 day. Thus, it can be noted that the
difference between the measured values decreases com-
pared to the first phase, as it varies between 16 % and
30 %, which proves that the amplitude of the shrinkage
starts to stabilize.
Nevertheless, whatever the age, the SCCR always
shows the highest values, contrary to the SCCMs as their
values decrease with the increase in the rate of the
calcined-mud substitution.
4.8.3 Mass loss
In order to try to improve the drying shrinkage, we
also carried out follow-up tests of the test-tube mass
shrinkage in order to quantify the hydrous exchanges.
The curves from Figure 11 show that the mass losses
are in agreement with the evolution of the drying
shrinkage; the values of the mass loss are very high and
almost identical as of the first day for all the concretes;
all the curves start with a linear part whose slope seems
to decrease slightly with the time. In the intermediate
zone, the curves are strongly nonlinear, which explains
the reduction to low values due to the evaporation. After
60 d, the mass losses start to decrease very slightly; they
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132 Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135
Figure 10: Evolution of the drying shrinkage versus time
Slika 10: Razvoj kr~enja zaradi su{enja v odvisnosti od ~asa
Figure 9: Evolution of the endogenous shrinkage versus time
Slika 9: Razvoj notranjega kr~enja v odvisnosti od ~asa
are weaker for the concrete with the mud-cement com-
bination than for the reference concrete. Finally, the
effect of the M/C ratio undoubtedly changes the hyd-
rous-pressure development of the curves with respect to
the degree of saturation.11
Figure 12 also shows that various drying-shrinkage
evolution curves for the mass loss are presented in two
phases; the first schematizes the first water departure
without any consequence for the shrinkage, while the se-
cond one schematizes the evolution of the shrinkage with
the water loss. The explanation is based the type of water
and two families of pores: the water contained in the
large pores leaves the material without causing a shrink-
age, whereas the water contained in the small pores
generates contractions of the material.12
4.8.4 Total shrinkage
It evolves very quickly for all the types of the test
tubes kept in the air because of their sizes that make the
desiccation more favorable. At the early stage, the
shrinkage is almost independent of the composition of
the concrete. The values of the shrinkage are concen-
trated in the same spindle and the effect of the addition
takes place only after the first week, with a slight
superiority for the SCCR. After a long period, the pre-
sence of the mud decreases the final shrinkage with
respect to the proportion of the substitute material.
Figure 13 shows a similar evolution of deformation
for all the SCCs. This is the reason why at the very early
stage we find it difficult to distinguish between the repre-
sentative graphs for each concrete. The order of the
magnitude on the 7th day presents reductions, which
vary from 14 % to 36 % for the SCCMs compared to the
SCCR. After the 7th day, the shrinkage of the reference
SCC evolves much more quickly and it is distinguished
from the others up to the 90th day, having a similar
amplitude.
It is also observed that for this shrinkage the refe-
rence SCC shows the highest values at all stages.
On Figure 14, the total shrinkage is plotted with res-
pect to the lg (t) scale, rather than the drying shrinkage,
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Materiali in tehnologije / Materials and technology 50 (2016) 1, 127–135 133
Figure 13: Evolution of the total shrinkage versus time
Slika 13: Razvoj skupnega skr~ka v odvisnosti od ~asa
Figure 11: Evolution of the loss of mass versus time
Slika 11: Razvoj izgube mase v odvisnosti od ~asa
Figure 14: Total shrinkage according to the logarithmic scale
Slika 14: Skupen skr~ek prikazan v logaritemski skali
Figure 12: Drying shrinkage versus the loss of mass
Slika 12: Kr~enje pri su{enju v odvisnosti od izgube mase
which is only a low estimate. Three phases appear; dur-
ing the first one, the shrinkage gradually increases, dur-
ing the second one, it evolves linearly with the logarithm
of time and during the third one, the curve of the shrink-
age inflects towards an asymptotic value.
5 CONCLUSIONS
Our study made it possible to confirm the possibility
of using the mud from the Fergoug Dam as a partial sub-
stitute material for cement.
The principal conclusions obtained are as follows:
1. The study of the behavior of the SCC in the fresh
state, with respect to the proportioning of the cal-
cined mud, allows us to make the following obser-
vations:
– The results indicate that the SCCs containing cal-
cined mud are more viscous and less workable
compared to the reference concrete because, beyond
the critical proportioning, the viscosity of the
concrete increases with the increased amount of the
substitute material.
– Only the SCCM20 presented too large a segregation
according to the sieve test.
– In addition to the bleeding test, the values obtained
with the tests of the simple flow, the L-box and the
sieve stability decrease when the proportion of the
calcined mud increases.
– A densification of the microstructure had a favorable
effect by decreasing the bleeding, thus providing us
with an idea on the improvement of the paste/aggre-
gate interface.
2. In the hardened state, the mechanical tests of the
compressive and tensile strengths carried out on the
test tubes made of self-consolidating concrete with
various amounts of the mud, in comparison with the
reference concrete made of cement alone, gave the
following results:
– The evolution of the strength is influenced by the
M/C ratio (the rate of the substitution of cement with
the calcined mud); the results indicate that the
compressive and tensile strengths decrease with the
increase in the calcined-mud content; these values
are very tolerable for the concretes employed for
buildings constructions.
– The best values of the SCCM compressive and
tensile strengths are obtained with the SCCM10, but
the SCCR always exhibits the highest values.
However, the use of a mineral addition involves the
formation of a new CSH, which fills in the pores of
the hardened cement paste and densifies the
structure of the paste, leading to a reduction in the
porosity. These effects lead to an improvement of the
mechanical strength.
3. With the tests of different deformations, carried out
on the same concretes, we followed the evolution of
free deformations in endogenous and drying condi-
tions. The obtained results show that the calcined
mud tends to slightly decrease the variety of defor-
mations and it can be concluded that their kinetics is
associated with the physicochemical mechanism, so:
– The endogenous shrinkage decreases with the in-
crease in the proportioning of the substitute calcined
mud.
– The compactness of the microstructure and the
refinement of the pores lead to a fall in the perme-
ability and prevent the diffusivity of water, conse-
quently, decreasing the drying shrinkage and the
mass loss.
– The total shrinkage follows the same principle, being
influenced by the endogenous shrinkage more than
by the drying shrinkage; it also decreases in accord-
ance with the M/C ratio, exhibiting a trend whereby
the total shrinkage is an intrinsic phenomenon of the
concrete.
– The analysis of the phenomenon of shrinkage in the
presence of calcined mud indicates that this addition
contributes to a decrease in the shrinkage amplitudes
compared to the reference concrete. The 20 % sub-
stitution seems to be the best option with respect to
its contribution to the improvement of the micro-
structure and, finally, to the decrease in the
shrinkage effects.
4. Finally, it is deduced that the calcined mud, due to its
reactivity and fineness, influences the mechanical and
other properties of the concretes:
– The pozzolanic reaction starts to be perceptible over
a long period by improving the compressive and
tensile strengths.
– The 10 % substitution of cement is the optimum
content to give the best mechanical performances,
followed by the 15 % and 20 % substitutions.
– The 20 % substitution is the optimum solution for a
reduction in the shrinkage and mass loss due to an
improvement in the microstructure, making the
matrix more compact and minimizing the diffusivity,
followed by the 15 % and 10 % substitutions.
– In conclusion, it can be deduced that the substitution
of 15 % of cement by the mud is the most interesting
option that proves to be optimal since it is the
average proportion that satisfies the two criteria: the
strength improvement and the shrinkage reduction.
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