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Research Results of Fine-Grained Soil Stabilization Using Fly Ash from Serbian
Electric Power Plants
Les résultats de recherche de la stabilisation des sols de grains fins en utilisant les cendres
volantes des centrales électriques serbes
Vukićević M., Maraš-Dragojević S., Jocković S., Marjanović M., Pujević V.
Faculty of Civil Engineering, University of Belgrade
ABSTRACT: This paper presents the results of laboratory research of fly-ash soil stabilization. Tests were conducted on mixtures
with two types of fine-grained soils and fly ash sampled in Serbian electric power plant Kolubara. Used types of soils are low
plasticity silty clay and very expansive, medium to high plasticity clay.
Effects of fly ash on physical and mechanical properties of
soil (grain size distribution, Atterberg limits, unconfined compression strength, moisture-density relationship, swell potential, CBR)
were evaluated. Test mixtures were prepared at optimum water content from standard Proctor compaction test. Results of the research
indicate that fly ash can effectively improve some engineering properties of soil.
RÉSUMÉ : Ce document présente les résultats de recherche en laboratoire de la stabilisation des cendres volantes. Les analyses
effectuées concernent les mélanges avec deux types de sols de grains fins et de la cendre volante récupérée de la centrale électrique
serbe « Kolubara ». Les types de sols utilisés sont de l’argile silteuse d’une plasticité faible et de l’argile très gonflante d’une plasticité
moyenne à forte. Les effets des cendres volantes sur les propriétés physiques et mécaniques du sol (la distribution de la grosseur des
grains, les limites d’Atterberg, la résistance à la compression uniaxiale, la relation entre la densité et l’humidité, les possibilités de
gonflement, l’indice portant californien – CBR) ont été évalués. Les mélanges d’essai ont été préparés à teneur en eau optimale selon
l’essai Proctor normal. Les résultats de la recherche signalent que les cendres volantes peuvent améliorer de manière efficace certaines
propriétés techniques du sol.
KEYWORDS: soil stabilization, fly ash, fine-grained soil
1
INTRODUCTION
Fly ash makes the most of the combustion-by-products during
the production of electricity in thermal power plants. A very
small amount can be recycled, while significant amounts are
disposed in landfills. The use of fly ash for soil stabilization can
bring multiple benefits – protection of the environment,
financial savings and it can also make the poorly-graded types
of soils usable.
In Serbia, approximately 7 million tons of fly ash and slag
are produced every year, of which only 3% is used in cement
industry. The remaining products (about 300 million tons so
far), are disposed on landfills, taking up the area of
approximately 1600 hectares (Cmiljanić 2008, Cmiljanić 2010).
In Serbia, fly ash soil stabilization research was conducted
for the first time during the preliminary design of the Serbian
regional waste management center “Kalenic” (Report FCE
Belgrade 2011). This research was performed by the authors
during 2011. Waste management center “Kalenic” is located at
open pit near thermal power plant “Kolubara”. Disposal area of
the “Kalenic” landfill is being formed by construction of the
outer embankment, instead of soil excavation, which is the
usual way.
The construction of the embankment needs more
than 1.5 million m
3
of material and costs are about 33% of total
investment.
Therefore, the possibility of using existing material
from the site was analyzed in Laboratory for Soil Mechanics at
Faculty of Civil Engineering in Belgrade. Results have shown
that tested material is not appropriate for construction of the
embankment. Because of this, the possibility of using fly ash
from thermal power plant “Kolubara” for soil stabilization were
considered.
This paper presents the results of fly ash soil stabilization
laboratory research performed during 2011-2012, as the part of
the research project funded by Electric Power Industry of
Serbia.
2
MATERIALS
Materials used for the experimental research program include:
fly ash from thermal power plant “Kolubara” (KFA) and silty
clays from project “Kalenic” (Soil A) and from wind park
project “Kosava” (Soil B).
2.1
Fly ash
Chemical composition of KFA was determined at the Faculty
for Physical Chemistry in Belgrade and the results are shown in
Table 1.
Table 1. Chemical composition of fly ash [%]
SiO
2
Al
2
O
3
Fe
2
O
3
CaO
MgO
50.21
23.83
9.89
4.79
3.12
K
2
O
Na
2
O
TiO
2
SO
3
P
2
O
5
0.44
0.35
0.54
5.24
0.06
Because of the high percentage of SiO
2
and Al
2
O
3
, according
to ASTM C 618, KFA belongs to Class F silica mineral ashes,
with pozzolanic properties. Class C fly ash is not available in
Serbia (Cmiljanic et al. 2010).
2.2
Soils
The soils used for this study are predominantly silty clays.
Soil A
: Mineral composition consists of quartz, muscovite
and soft minerals of montmorionite (testing performed at
Faculty for Physical Chemistry, Belgrade). According to USCS,
this soil, known as alevrite, is medium to high plasticity clay
(CI/CH), with swell potential.
Soil B
: Material was collected at the site of wind park near
Vrsac, Vojvodina. Terrain at the site consists of Quaternary
loess sediments. According to USCS, this soil is low plasticity
