Reuse of fly ash and dredging marine sediments on self-compacting

backfills
a a a
M. BENZERZOUR , N.-E. ABRIAK , W. MAHERZI

a
École des Mines de Douai, Département Génie Civil & Environnemental
764 Bd Lahure BP 10838. 59508 Douai Cedex
mahfoud.benzerzour@mines-douai.fr; nor-edine.abriak@mines-douai.fr; Walid.maherzi@mines-
douai.fr

Abstract
The valorization of dredged sediments has been in full rise for several years. It mainly concerns the
marine and river sediments. These sediments present particular physicochemical, mineralogical and
geotechnical characteristics with a special heterogeneity and sometimes an important contamination
that often limits their management. Consequently, many researches were carried out in order to find
perennial ways of valorization satisfying the technical and regulatory requirements.

This paper was devoted under investigation of formulations of self-compacting backfills containing
marine sediments, fly-ashes and hydraulic binders. The goal of this study is to show the impact of the
addition of sediments in the composition of the self-compacting backfills on the one side, and on the
other side to see the influence of the type and the percentage of binders and fly ashes on the behavior
of the backfills in a fresh state and on the mechanical resistances.

Key words: sediment, valorization, cement, backfill, waste management, sustainable

materials

1. Introduction
The self-compacting backfills are generally cementing liquids or suspensions which are injected under
pressure. They must be able to fill of the cracks, the cavities or the interstices of the grounds in order
to improve the mechanical performance or the hydraulic characteristics of the treated medium. In
general, the stability of backfills decreases with the increase in fluidity, resulting from an increase in
water content.

2. Materials and methods

2.1.Materials

The physicochemical, geotechnical and mineralogical characteristics of the materials used for
formulations of backfills are presented below:

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• Sediments: The marine sediment used in this study was collected from the port of Dunkirk and
taken after decantation in specific tanks. The physicochemical and mechanical characterizations
are shown in the Table 1:

Table 1. Physical characteristics of the used sediment.

Average water content w (%) 22,35
Average organic content (%) 9,10
Plasticity index Ip 13
VBS 2,99
3
Density of solid grains (t/m ) 2,44
Grains < 2μm 3
2μm < Grains < 63μm 72
63μm < Grains 25

• Fly ash: fly ashes used are alumina-silicate type, coming from the site of Eurovia Harnes. It is
composed mainly of silica (SiO2) and alumina (Al2O3). Other elements also present to a lesser
extent are the iron oxide (Fe2O3 / FeO4) and lime.

• Fibres: The polypropylene fibre is the ideal additive in the mixtures with cementing matrix to
decrease the plastic withdrawal, cracking and to increase the properties of surface. The fibres used
are of mean size of 12mm. Their characteristics are summarized in Table 2.

Table 2. Characteristics of polypropylene fibres

Characteristics Values
Elastic module 3500 – 3900 N/mm2
Extensibility 320 – 400 N/mm2
Melting point 160 – 170 °C
Electrical conductivity 0

• Hydraulic binders: In this study, two types of hydraulic binders were used: Cement CEM I 52.5
N and a road-type hydraulic binder Rolac PI:

 ROLAC® PI: It is a hydraulic binder containing clinker allowing the improvement of the
grounds by obtaining a fast traficability at the time of the realization of fill, platforms and
tracks. Cement ROLAC PI LH is composed of more than 60% lime (CAD) and 20% of
silica’s dioxide (SiO2). The chemical and mineralogical main features of Rolac PI are deferred
in the table below.

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 Table 3. Chemical composition of ROLAC PI LH

Element (%)
SiO2 20,79
Al2O3 5,40
Fe2O3 2,22
CaO 65,90
MgO 1,10
K2O 0,30
SO3 3,40
Na2O 0,18
-2
S 0,00
Cl- 0,03
Composition in element entering the
process of hydration
C3S 62
C2S 12
C3A 12
C4AF 6

 Cement CEM I 52.5 N: composed of:

- 95% to clinker 100%;
- 0% to 5% of secondary components;
- The presence of a small quantity of calcium sulphate ensures the regularity of the
catch;
- Times of initial setting with 20 °C measured on pure paste ≥ 40 min
- Stability measured on pure paste
- Density (in g/cm3) is about 3.12
- Compressive strength was determined on standardized mortar, in accordance with
standard NF EN 196-1.

Table 4. Compressive strength on mortar in MPa with a cement CEM I 52.5 (limiting values)

Short-term strength Current strength

2 days 28 days
39 62

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  Cement CEM I 52.5 PM: The characteristic PM-ES of the CEM I 52.5 N CE PM-ES CP2 NF
authorizes its use for the manufacturing of products out of concrete and backfills exposed to
aggressive environments like maritime environments, the zones of marling and water with
high contents sulphates, the gypseous grounds, freezing with salts of deicing, the acid
aggressions. It allows the manufacturing of products requiring high mechanical resistances to
28 days. It presents a limited sulphides content, necessary for the prestressed concrete.
2.2. Methods
The adopted formulations were optimized in order to answer the criteria of resistance and handiness
necessary for an application of the backfills like trench backfill materials. The essential criteria to
satisfy are as follows:

- The spreading out of a cylinder of the backfill subjected to its own weight must be between
350 and 500 mm.
- A Bearing capacity Index (IPI) equal at least to 10% at with 48 hours, in order to respect the
time of back in circulation;
- A compressive strength (Rc) with 28j lain between 0.5 and 1MPa, this strength is sufficient to
make sure of the easy handling of material;
- A depression with the slump test equal at least to 15cm, to check the accounting of the
designed material and the best coating of the drains once set up;
- A good compressive strength after immersion in order to make sure of the good behavior with
the water of material.

For this purpose, ten formulations were defined in order to evaluate mainly the influence of the type of
hydraulic binder and its percentage in the formulations on the criteria already presented. The
formulations tested contain a fixed sediment rate which corresponds to 30 % of the mass of the
mixture. The remaining 70% is the amount of fly ash and cement. The F1 formulation, which does not
contain sediment, constitutes the reference formulation.

Furthermore, we have tested 3 formulations respecting report E/C= 0.5 containing cement and
sediment. The percentage of sediment is obtained from the study of the interaction between sediment
and cement. The purpose of this step is to define a compressive constitutive law

3. Results and discussion

3.1. Mechanical study

3.1.1. Behaviour laws of mixture containing sediment and cement
Figures below show the evolution of mechanical strength depending on the sediment / cement ratio
(Fig.1). It appears that the behaviour of sediment - cement is similar regardless of the type of cement

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used. Moreover, increasing the ratio S / C adversely affects the mechanical properties of mixtures.
Indeed, the increase in the ratio S / C of 0.2 to 0.8 causes a reduction in mechanical strength of about
67 %. This can be explained by the effect of these chemical disruptive elements in sediments
(sulphates, chlorides, …) on the setting of cements

45
cement CEM I 52.5 N
40

36,465
35

30
25,66
UCS (MPa)

25

19,35 y = -35,21x + 38,63

20 R² = 0,94

15
12,19
10

0
0,00 0,20 0,40 0,60 0,80 1,00
Sediment/Cement

45,00

cement ROLAC PI LH
40,00

35,00 35,09

30,00
26,36
UCS (MPa)

25,00
y = -31,33x + 37,36
R² = 0,96
20,00 20,08

15,00
13,78

10,00

5,00

0,00
0,00 0,20 0,40 0,60 0,80 1,00
Sediment/Cement

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 45,00
cement CEM I 52.5 PM ES
40,00 38,33

35,00

29,14
30,00
y = -33,92x + 40,67
UCS (MPa)

25,00 R² = 0,94
21,04

20,00
15,58
15,00

10,00

5,00

0,00
0,00 0,20 0,40 0,60 0,80 1,00
Sediment/Cement

Figure 1. Evolution of the mechanical strength according S/C ratio

3.1.2. Marsh Cone Fluidity

The cone of Marsh is a simple and standardized tool [NF P 18-358] which is very largely used on the
characterization of building materials to measure the fluidity of the grout and to check the constancy
of the formulations (fig.2). It is composed of a truncated cone provided at its lower part of a removable
cylindrical nozzle. The characterization of the fluidity of self-compacting backfill materials to the cone
of Marsh consists in measuring the time of flow of a volume given of grouts. Before any
measurement, it is necessary to let freely run out a few milliliters of grout to drive out free water. The
container of reception is then set up, while maintaining closed the tube of flow of the cone. The time
of flow is taken between the moment of opening of the tube and the filling of the container of
reception (one liter).

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Figure 2. Realization of the test of cone of Marsh

3.1.3. Abrams cone slumping

The slump test aims to measure, before the casting of the backfills, the height of depression of
a sample poured in a metal mould of truncated form, after various times of release from the
mould. The slump test is defined by the standard NF P 18-451 which determines 4 levels of
consistency according to the height of depression, at the end 10 minutes of age.

Table 5. Results of slump test the three hydraulic binders

Rate of cement (%) ROLAC PI LH CEMENT CEM I PM CEMENT CEM I N

6 20,5 18 20
8 22 20 24
10 24 19,5 19

3.1.4. Bearing capacity Index

The California Bearing Ratio or the bearing capacity index was given by expressing the force
exerted on a piston for a fixed depression. It is expressed compared to a standardized force.
The results got on the various formulations with 24 and 72 hours are presented in the table 6.
All tested formulation satisfied the criterion of fluidity required for self-compacting grout

Table 6. Evolution of the bearing index according to the selected binder

ROLAC PI LH CEMENT CEM I PM CEMENT CEM 1 N

Rate of cement (%) CBR (24h) CBR (72h) CBR (24h) CBR (72h) CBR (24h) CBR (72h)
6 26,98 35,58 15,15 32,45 22,76 29,96
8 54,14 64,64 18,30 39,85 22,90 32,30
10 56,50 65,70 23 41,81 34,96 44,94

3.1.5. Unconfined compression strength

The values of compressive strength RC are the average of measures taken on three samples
resulting from same formulation (Fig.3). The standard deviation of measurements varies
between 0.01 and 0.1 MPa. The results got for the various formulations are included in Fig.4.
The results obtained show that the increase of the cement substitution rate generates an
increase of compressive strengths of formulated materials. Otherwise the Rolac PI cement has
the best mechanical performance compared with the other cement (CEM I PM and CEM I N)

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Figure 3. Unconfined compressive strength test on cylindrical samples (11x22)

4 4
6% CEM I 52.5 N 6% Rolac PI
3,5 3,5 8% Rolac PI
8% CEM I 52.5 N
3 10% CEM I 52.5 N 3 10% Rolac PI

2,5 2,5
UCS (MPa)
UCS (MPa)

2 2

1,5 1,5

1 1

0,5 0,5
0 0
0 20 40 60 80 100 0 20 40 60 80 100
Curing time (days) Curing time (days)

4
6% CEM I 52.5 PM ES
3,5 8% CEM I 52.5 PM ES
10% CEM I 52.5 PM ES
3

2,5
UCS (MPa)

1,5

0,5

0
0 20 40 60 80 100
Curing time (days)

Figure 4. Evolution of the compressive strengths of the various tested formulations

3.2. Environmental study

The environmental analysis presents a determining stage for the validation of one of the tested
formulations. In this context, the environmental study was carried out on blocks of backfills
made at the laboratory using ROLAC PI. They were placed in a specific device which allows
the permanent watering of the blocks and the recovery of runoff waters (Fig.5). This water
was analysed in the various term, they got results with 7, 28 and 60 days are deferred in

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Table. The environmental analyses of the runoff water of the grout’s blocks reveal that the
concentrations of the analysed elements remain very weak and evolve little or almost not with
time. It proves also as there are no major differences in the concentrations of the detected
elements. Indeed, the use of the hydraulic binders allows to trap the contaminants in the
formed products of hydration (mainly HSC), which helps to have a stability in the short and
medium term.

Figure 5. Placing devices of leaching test for grout blocks

Table 7. Results of environmental analysis

With sediment Without sediment

Thresholds
Analysis Unit 7 28 60 7 28 60

PAH µg/l <1 <1 <1 <1 <1 <1 - µg/l

PCB µg/l <0,07 <0,07 <0,07 <0,07 <0,07 <0,07 - µg/l

COT mg/l 3,2 2,8 3,4 3,0 3,0 3,5 - µg/l

Heavy metals
Arsenic µg/l <5 <5 <5 <5 <5 <5 10 µg/l

Cadmium µg/l <0,20 <0,20 <0,20 <0,20 <0,20 <0,20 5 µg/l

Chrome µg/l 5,9 3,7 2,9 <1 <1 <1 50 µg/l

Copper µg/l 8,6 <2,0 7,1 5,9 4,6 4,9 50 µg/l

Mercury µg/l <0,05 <0,05 <0,05 <0,05 <0,05 <0,05 2000 µg/l

Plomb µg/l <2,0 <2,0 <2,0 <2,0 <2,0 <2,0 50 µg/l

Nickel µg/l <3 <3 <3 <3 <3 <3 20 µg/l

Zinc µg/l 29 21 10 17 13 11 5000 µg/l

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 4. Conclusion

After application of a load well defined on the made grout in the CBR mold, we noted that all
the results of the bearing capacity index are higher than 10, they are included between 15 and
56 at 24 hours, and between 29.96 and 65.70 at 7 days. In addition, the ROLAC develops a
higher bearing capacity index compared to other cements. An index higher than 10 at 24
hours makes possible to release the building site for the circulation of the machines within a
very short time.

After crushing of three samples for each formulation in accordance with the standard, we
noted that compressive strength to 7 days lie between 0.63 and 0.67 Mpa for formulation 1,
and between 0.98 and 1.41 for formulation 3. The self-compacting backfills coulis made with
ROLAC developed strength to 28 days which vary between 0.97 (F1) and 2.5 (F3).

References

[1] Ferraris CF, Brower L, Ozyıldırım C, Daczko J, Workability of self-compacting

concrete, National Institute of Standards and Technology, The Economical
Solution for Durable Bridges and Transportation Structures, in: Proc of int symp
on high performance concrete, Orlando, Florida, 2000, 398–407.

[2] Felekoglu B, Optimization of self-compacting filling grout mixtures for repair

purposes, Construction and Building Materials 22 (2008) 660–667

[3] Maherzi W, Valorisation des sédiments de dragage marins bruts et/ou traités aux
liants hydrauliques pour une application en technique routière | ESITC Caen &
l’ABTE_Université de Caen (2013)

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