3175
Mechanics of Manufactured Soil Using Powder Wastes
Mécanique des sols fabriqués à partir de déchets de poudre
Baykal G.
Bogazici University
ABSTRACT: Powder wastes like fly ash are produced in large volumes. They have handling, disposal problems and poor engineering
performance due to their silt size. Manufacturing artificial sand and gravel from these silt sized powder wastes in large quantities will
solve the associated problems of having silt size. Disc pelletizers with manufacturing capacities reaching one million ton a year makes
this process economically feasible and practical for geotechnical applications. Fly ash is one of these powder wastes having silt size
and easily available in many countries where they create huge disposal problems. Cold bonding pelletization technique is used to
produce fly ash pellets of sand and gravel size and their mechanical properties are determined. The manufactured pellets are
lightweight materials with adequate strength and can be used in many geotechnical projects. The fly ash pellets show similar behavior
to that of calcareous sands. In addition to utilization of pellets as manufactured, it is also possible to manufacture soil to the desired
specification by adding additives or apply surface treatment.
RÉSUMÉ : Déchets de poudre comme les cendres volantes sont produits en grandes quantités. Ils ont la manipulation, et l'élimination
des problèmes de performance d'ingénierie pauvres en raison de leur taille limon. Fabrication de sable et de gravier artificielle à partir
de déchets de limon ces poudres de taille en grandes quantités permettra de résoudre les problèmes associés ayant une taille de limon.
Granulateurs à disques avec des capacités de production pour atteindre un million de tonnes par an rend ce processus
économiquement faisable et pratique pour des applications géotechniques. Les cendres volantes sont un de ces déchets en poudre
ayant une taille de limon et facilement disponible dans de nombreux pays où ils creat énormes problèmes d'élimination. Technique de
granulation à froid de liaison est utilisé pour produire des boulettes de cendres volantes de sable et de gravier taille et leurs propriétés
mécaniques sont déterminées. Les pellets sont fabriqués avec des matériaux légers résistance suffisante et peut être utilisé dans de
nombreux projets en géotechnique. Les granulés de cendres volantes présentent un comportement similaire à celui des sables
calcaires.
KEYWORDS: Powder wastes, cold bonding pelletisation, silt size, fly ash, calcerous sands, grain crushing.
1 INTRODUCTION
With increasing disposal costs, and growing ecological
concerns, waste materials are utilized in geotechnical
applications more and more each year. Due to its silt size,
powder materials are hard to handle, transport, compact and
dispose. Increasing the size of the powder wastes from silt size
to sand and gravel size has a lot of benefits. Powder wastes like
coal burning thermal power plant fly ash are used in many
geotechnical applications. The pelletization cost for fly ash is
around one to two Euros per ton and the capacity of one
pelletizer can be as high as one million tons per year, making
this approach a feasible and practical application in geotechnical
engineering. Annual fly ash production for many countries is in
the range of 1 to 100 million tons. This paper summarizes a
series of research work about manufacturing sand and gravel
from powder fly ash by cold bonding pelletization technique.
The pelletization mechanism is explained and physical and
engineering properties of the produced pellets are given.
The manufactured pellets behave like calcareous sands
found in the nature. The source and shape difference of the
natural calcareous sands do not exist in the manufactured pellets
having nearly perfect sphericity and roundness. The crushing
behavior of the manufactured soil is studied in detail. For
potential applications like backfill for retaining walls, fill under
the footings, pile installation in existing manufactured soil
embankment, anchor installation in manufactured fills, the
interface behavior and the influence of crushability on the
interface behavior is also studied. Finally odometer tests, direct
shear tests are conducted and the results are summarized.
1.1
Mechanism of pellet formation
Pelletization process is the agglomeration of moisturized fines
in a rotating drum or disc. The product at the end of the process
is called the “fresh pellet”. The crushing strength of the fresh
pellet must be enough for hauling and stockpiling purposes. The
pelletization technology is widely used in powder metallurgy
engineering, and medicine industry.
The pelletization theory was developed in 1940’s. The
performance of the pelletization process is a function of; i) the
engineering properties of the material pelletized; ii) the amount
of moisture in the medium; iii) the mechanical process
parameters such as the angle of balling drum or disc to the
normal and the revolution speed. Observations and analysis
performed on these parameters with respect to mechanic and
kinetic laws formed the theory of pelletization process (Baykal
and Doven 2000).
When a fine grained material is moisturized, a thin liquid
film forms on the surface of the grains, which forms meniscus
between the grains. With the rotation in a balling drum or disc,
they form ball shape structures with enhanced bonding forces
between grains due to centrifugal and gravitational forces. The
mechanism of pellet formation is presented in Figure 1. In the
pendular state water is present only at point of contact of the
grains. With more water addition some of the pores are filled
with water in the funicular state. All intergranular space is filled
