1. National Conference on Recent Advances in Ground Improvement Techniques
February 24-25, 2011, CBRI Roorkee, India
Waste Materials in Geoenvironmental Applications
Naveen, B.P.a, Anil Kumar Sharmaa, Sivapullaiah, P. Vb. and Sitharam, T. G.b
a
Research Scholar, Department of Civil Engg., IISc, Bangalore-560012, India.
b
Professor, Department of Civil Engg., IISc, Bangalore-560012, India.
ABSTRACT
Large quantities of waste materials are generated in the industrial world. Land and ground water contamination
is a serious issue associated with the disposal of various waste materials. Further the disposal of most of the
huge quantities of waste materials requires considerable land space. Use of these materials not only overcomes
their disposal problems but also achieves economy. Some of the prominent industrial waste materials are fly
ash, blast furnace slag, red mud, organically modified clays etc. The present paper describes the various
approaches to use these materials for ground improvement. The mechanical improvement in the soil properties
is described in this paper. To overcome the environmental concerns various methods to tests the stabilized
materials by appropriate leaching tests have to be performed.
Keywords: Solidification/Stabilization, Waste materials, Fly ash, Physical tests, leaching tests
1. INTRODUCTION
1.1 General
Although there has been concern about land pollution since the onset of industrialization, this
has been restricted to a relatively limited number of people. Consequently, until recently, land
has not been seen as deserving protection to the same extent as air or water, but now it is
recognized that land pollution cannot continue unabated. The recognition has risen because of
incidents of contamination, the scarcity of usable land and increased general concern about
the effect of industrial activity on the environment. Many technologies being considered for
treating hazardous waste may produce residues still requiring management. In many cases,
land disposal will be the only option available for these residues, which may be concentrated
with toxic contaminants. In addition, waste banned from land disposal must be manageable
by an alternative technology. If not, land disposal may still be the only option available.
Pretreatment of banned waste may also help make it more acceptable for land disposal. Use
of the waste materials is big option in finding solution to this problem.
1.2 Ground Improvement Methods
Solidification/stabilization (S/S) is being considered as a technology available for treating
selected waste prior to landfill. It is also being considered for treating residues from other
treatment technologies. S/S technology has been used for approximately 20 years to manage
industrial waste. S/S employs selected materials (e.g., Portland cement, fly ash, lime, etc.) to
alter the physical and chemical characteristics of the waste stream prior to disposal in the
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2. land. The goal of the S/S process is to limit the spread, via leaching, of contaminated
material. The end product resulting from the solidification process is a monolithic block of
waste with high structural integrity. Types of solidifying/stabilizing agents include the
following: Portland; gypsum; modified sulfur cement, consisting of elemental sulfur and
hydrocarbon polymers; and grout, consisting of cement and other dry materials, such as
acceptable fly ash or blast furnace slag. Processes utilizing modified sulfur cement are
typically performed ex situ.
2. STABILIZATION TECHNOLOGIES USING WASTE MATERIALS
2.1 Fly ash
The disposal of fly ash is becoming more expensive each year due to large land needs for its
disposal .The best way to solve the disposal problem fly ash is to decrease the quantity for
disposal with the utilization of fly ash in the industry. Fly ash has been increasingly utilized
in construction application, such as fills, concrete, pavements, wastewater treatment, landfill
barrier material, grouts and others.
Protecting the environment from hazardous pollutants associated with waste generation and
disposal is a major concern in today’s heavily industrialized world. Thus far, various
technologies have been developed which transform hazardous wastes to nontoxic, or reduce
the potential release of toxic species into the environment. One such promising technology is
stabilization/solidification (S/S) of solid wastes by means of adding cementitious binders, like
lime and cement (Conner, 1990). During S/S applications, the toxic constituents present in
the waste form are physically as well as chemically ‘‘fixed’’, that is, their mobility is
significantly reduced so as to minimize the threat to the environment and also ensure
compliance with existing regulatory standards. Moreover, the stabilized wastes may attain
adequate stress-strain properties to enable their utilization in construction applications, such
as engineering fill, road or pavement sub grade, backfill, and base material.
Fly ash can be added to wastes (coarse-grained) in order to increase the available pozzolanic
surface area, and hence improve one or all of the following properties of the waste mixture
(1) Strength
(2) Workability
(3) Buffering capacity (capacity to resist pH changes)
(4) Heavy metal leachability.
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3. The addition of fly ash during the quicklime– sulfate S/S treatment results in a high strength,
swell-resistant monolithic solid, attaining levels of strength similar to those of concrete
products. With respect to heavy metal release, the addition of fly ash was directly responsible
for the effective immobilization of both lead and hexavalent chromium, whereas it further
enhances trivalent chromium immobilization.
2.2 Ground granulated blast-furnace slag (GGBS)
Blast-furnace slag is produced as a by-product of the iron and steel production industries. Its
earthy constituents come from iron ore processing, and it consists of the same oxides as
Portland cement, but in different proportions. Immediately after its production, slag is usually
quenched for rapid cooling in a process known as granulation. The granulation results in a
reactive amorphous glass and avoids any crystallization. Like Portland cement, blast-furnace
slag also reacts with water (i.e. is hydrated) to form specific hydrated calcium silicates known
as tobermorite gels. However, unlike basic Portland cement, it forms this critical cementing
agent (tobermorite gel) by consuming the slaked lime, Ca(OH)2 provided by the hydration of
the Portland cement. Removal of some of the slaked lime is advantageous, since less of it in
the waste form will lead to less dissolution of the lime over time, and thus consequently less
long-term waste from degradation. In addition, there will be less slaked lime available to
potentially react with salts, and thus produce undesired expansive and destructive minerals in
the future.
2.3 Red mud
Red mud is a solid waste product of the Bayer process, the principal industrial means of
refining bauxite in order to provide alumina as raw material for the electrolysis of aluminium
by the Hall–Héroult process. A typical plant produces one to two times as much red mud as
alumina. This ratio is dependent on the type of bauxite used in the refining process. Red mud
is composed of a mixture of solid and metallic oxide-bearing impurities, and presents one of
the aluminium industry's most important disposal problems. The red colour is caused by the
oxidized iron present, which can make up to 60% of the mass of the red mud. In addition to
iron, the other dominant particles include silica, unleached residual aluminium, and oxide.
This waste material has a reddish-brown color and a superfine particle size distribution.
Alkalis, iron oxides and hydroxides, aluminum hydroxides, calcium carbonate, titanium, and
silica form its chemical composition. The addition of Red Mud (RM) and Cement-Red Mud
(CRM) increases the unconfined compressive strengths of composite samples. Both RM and
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4. CRM additives plays (Kalkan, 2006) an important role at the Atterberg limits. The addition
of these additives changed the soil groups from high-plasticity soil group (CH) to lowplasticity soil group (MH).In the same compaction effort, the γd max and wopt values of
composite samples increases by adding RM and CRM. Also, the addition of RM and CRM
decreased the void ratio values of composite samples due to increasing the γd,max of composite
samples.
2.4 Organically modified clays
Organically modified clays have been recently employed in conjunction with other
stabilization reagents in order to entrap the organic portion of the waste to be stabilized.
Organically modified clays are produced when natural clays are organically modified to
become organophilic. This characteristic is in contrast to their organophobic nature. The
modification process is accomplished through the replacement of inorganic cations within the
clay crystalline mineralogical structure with organic cations, typically Quaternary ammonium
ions. After this replacement process, organic molecules are adsorbed within the crystalline
structure of the clay, which then swells in the presence of organic contaminants. In the
production of organically modified clay, the exchangeable inorganic cations in the intercrystalline region are replaced with organic cations. The result is a nearly identical clay
structure where organic cations occupy the inter-crystalline region. Organophilic clays
typically are added to the waste first and allowed to interact with the organic components.
Additional agents are added to provide shear strength and solidify the material into a
monolithic mass. Several materials have been investigated for use as organic sorbents for s/s
systems. These include metal oxides, clays, natural materials (peat moss, natural zeolites,
vermiculite, etc.), synthetic materials (zeolites, fly ash, organic polymers, etc.), and activated
carbon. Most current research has focused on organophilic clays. These are typically
bentonite or montmorillonite clays in which tetra-alkyl ammonium compounds are
substituted between the clay layers to increase the inter-lamellar spacing and enhance the
adsorption of organic molecules. Initial results indicate that these modified clays may be
useful for immobilization of certain organic compounds, but not for others. The organophilic
bentonites are prepared by replacing the exchangeable inorganic cations present in bentonite
particles with a quaternary ammonium salt. Various clay-to-soil ratios were applied to
determine the efficiency of the modified bentonite in enhancing the cement-based s/s of
BTEX contaminated soils. The findings of this study by Gitipour et al. (1997) reveal that
organophilic bentonite can act as a successful adsorbent for removing the aromatic organics
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5. from contaminated soils. Thus, this material is viable for enhancing the performance of
cement-based s/s processes, as an adsorbent for petroleum spills, and for landfill liners and
slurry walls. Organophilic clays have been shown to play a significant role in removing
contaminants from liquid wastes (Boyd et al. 1988b; Smith et al. 1990) concluded from their
study that modified clays are recommended for use as stabilizing agents at sites contaminated
with aromatic wastes.
2.5 Asphalt emulsions
Asphalt emulsions are very fine droplets of asphalt dispersed in water that are stabilized by
chemical emulsifying agents like detergents. The emulsions are available as either cationic or
anionic emulsions. The emulsified asphalt process involves adding emulsified asphalts
having the appropriate charge to hydrophilic liquid or semi-liquid wastes at ambient
temperature. After mixing, the emulsion breaks, the water in the waste is released, and the
organic phase forms a continuous matrix of hydrophobic asphalt around the waste solids. In
some cases, additional neutralizing agents, such as lime or gypsum, may be required. After
sufficient time to set and cure, the waste is uniformly distributed throughout the resulting
solid asphalt, which is impermeable to water.
3. PROMINENT USES AFTER SOLIDIFICATION/STABILIZING
S/S-treated soil, sediment, and sludge are often reused. Most frequently this occurs on a
property that is being cleaned up. Reusing treated material on-site, rather than hauling it away
and bringing in new material, protects the surrounding community from the hazards posed by
increased truck traffic, truck noise, air pollution, and damage to roadways. Some of the most
prominent uses are:
1.Provides an excellent base for pavement placed over the entire site.
2.Used as structural fill.
3.Port redevelopment.
4.Reuse of treated material saved developers significant cost while providing for site
Re-development that is protective of human health and the environment.
Some the examples of the S/S technology are as follows:
1.Former Wood Treating Facility, Port Newark, New Jersey
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6. 2.Re-Use of New York Harbor Sediments.
3.Hercules 009 Landfill Superfund Site, Brunswick, Ga.
3.1 Alternate to stabilize soil
Stabilization converts hazardous elements into less soluble, mobile or toxic forms. Mixing
the right combination of binding reagents into contaminated soils allows them to be either
excavated and disposed of in a landfill, or re-used on site to support redevelopment. The
solidification treatment has the further benefit of improving the structural properties of the
site as well. The improved compressive strength of this type of soil treatment versus other
treatment methods, can serve to improve the site conditions for development in addition to
treating the contamination.
3.2 Efficiency of solidification and arrest of contaminant
Solidification/stabilization (S/S) treatment does not generally result in a reduction of the total
concentration of hazardous constituents (contaminants) in a treated material. S/S protects
human health and the environment by immobilizing hazardous constituents within the treated
material. Protection is achieved by preventing migration of hazardous constituent to human
and environmental receptors. Contrast that with "dig and dump" remedies that merely move
the hazardous constituents to another place. S/S fits into a risk-based remedy decision.
Further, an in-situ remedy lowers risks to surrounding communities since less excavation is
involved. S/S can treat a very broad group of hazardous constituents, both inorganic and
organic. Most other remediation treatment technologies cannot. This lowers cost of the
remediation of properties. Protective remedies at a lower cost conserve resources that can be
applied to other sites. More sites remediated means greater overall protection of human health
and the environment.
4.PHYSICAL AND CHEMICAL TESTS
Most S/S projects require treatability studies and final performance testing of the treated
contaminated material. These tests can be placed into two groups: physical and chemical.
Physical tests are conducted to characterize and contrast waste before and after
solidification/stabilization. It provides basic information on the treatability of the waste
material and allows some estimate to be made of the cost of waste treatment and handling.
Physical property characterization of unstabilised/unsolidified wastes focuses on treatability,
excavation,
transport,
storage
and
mixing
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considerations.
Physical
testing
of

7. stabilized/solidified wastes helps to demonstrate the relative success or failure of a
stabilization/solidification process.
4.1 Physical Tests
The commonly specified physical tests in project performance standards include:
1. The Paint Filter Test (pass/fail), (USEPA Method 9095-SW846)
-5
2. Hydraulic conductivity (<1X10 cm/sec),(EPA Method 9100-SW846)
3. Unconfined compressive strength (0.34 MPa (>50 psi)).ASTM D2166-85)
4. Atterberg Limit test(ASTM D4318-84)
5. Suspended Solids(USEPA Method 208C)
4.1.1 Paint Filter Test), (USEPA Method 9095-SW846)
This method is used to determine the presence of free liquids in a representative sample of
waste. A predetermined amount of material is placed in a paint filter. If any portion of the
material passes through and drops from the filter within the 5-min test period, the material is
deemed to contain free liquids.
4.1.2
Hydraulic conductivity,(EPA Method 9100-SW846)
Hydraulic conductivity is one of the hydraulic properties of the soil; the other involves the
soil's fluid retention characteristics. These properties determine the behavior of the soil fluid
within the soil system under specified conditions. More specifically, the hydraulic
conductivity determines the ability of the soil fluid to flow through the soil matrix system
under a specified hydraulic gradient; the soil fluid retention characteristics determine the
ability of the soil system to retain the soil fluid under a specified pressure condition. The
-5
Hydraulic conductivity should be (<1X10 cm/sec)
4.1.3 Unconfined compressive strength , (ASTM D2166-85)
This test method covers the determination of the unconfined compressive strength of
cohesive soil in the intact, remolded, or reconstituted condition, using strain-controlled
application of the axial load. This test method provides an approximate value of the strength
of cohesive soils in terms of total stresses. This test method is applicable only to cohesive
materials which will not expel or bleed water (water expelled from the soil due to
deformation or compaction) during the loading portion of the test and which will retain
intrinsic strength after removal of confining pressures, such as clays or cemented soils. Dry
and crumbly soils, fissured or varved materials, silts, peats, and sands cannot be tested with
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8. this method to obtain valid unconfined compression strength values. The UC strength value
should be 0.34 MPa (>50 psi).
4.1.4
Atterberg Limit test, (ASTM D4318-84)
These test methods are used as an integral part of several engineering classification systems
to characterize the fine-grained fractions of soils and to specify the fine-grained fraction of
construction materials .The liquid limit, plastic limit, and plasticity index of soils are also
used extensively, either individually or together, with other soil properties to correlate with
engineering behavior such as compressibility, hydraulic conductivity (permeability),
compactibility, shrink-swell, and shear strength.
4.1.5
Suspended Solids(USEPA Method 208C)
A well-mixed sample is filtered through a weighed standard glass-fiber filter
and the residue retained on the filter is dried to a constant weight at 103 to 105°C. The
increase in weight of the filter represents the total suspended solids. If the suspended material
clogs the filter and prolongs filtration, it may be necessary to increase the diameter of the
filter or decrease the sample volume. To obtain an estimate of total suspended solids,
calculate the difference between total dissolved solids and total solids. One must know the
suspended solid of the supernatants.
4.2
Chemical Tests (Leaching tests)
Chemical tests are more devoted to leaching tests which are used to compare the
effectiveness of various stabilization/solidification processes. A simple definition of leaching
is the transfer of a substance or compound from a solid to a liquid phase when the two are in
contact. It is a complex phenomenon and occurs in nature as a result of physical and chemical
weathering processes involving the interaction between a soil or rock and water. Chemical
tests are more often used to evaluate the performance of Solidification/Stabilization as a
treatment process for hazardous waste.
1. The TCLP: Toxicity Characteristic Leaching Procedure
2. Extraction procedure(EP) Toxicity test Method
3. Equilibrium leach test
4. Acid Neutralization capacity
4.2.1
Toxicity Characteristic Leaching Procedure(The TCLP)(Federal Register 1986)
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9. The TCLP, or Toxicity Characteristic Leaching (not Leachate) Procedure is designed to
determine the mobility of both organic and inorganic analytes present in liquid, solid, and
multiphasic wastes. This is usually used to determine if a waste may meet the definition of
EP Toxicity, that is, carrying a hazardous waste code under RCRA (40 CFR Part 261) of
D004 through D052. As it is the generator's responsibility to make this determination, but
generators often contract outside labs to perform the TCLP test, these questions and answers
may be helpful to generators. For this reason and sometimes in cleanup actions, businesses
are often asked to perform an analysis on their waste using the TCLP.
4.2.2 Extraction procedure Toxicity (EP Tox) test Method(USEPA 1986)
This method is used to determine whether a waste exhibits the characteristic of Extraction
Procedure Toxicity. The procedure may also be used to simulate the leaching which a waste
may undergo if disposed of in a sanitary landfill. Method 1310 is applicable to liquid, solid,
and multiphase samples.
4.2.3 Equilibrium leach test (Environment Canada and Alberta Environmental Centre
(1986)
This leach test involves static leaching of hazardous constituents in distilled water.The
particle size of the crushed sample is much smaller than that of TCLP and EP Tox to allow
greater contact surface area and to reduce the time needed to achieve equilibrium conditions.
4.2.4 Acid Neutralization capacity (Environment Canada and Alberta Environmental
Centre (1986)
Acid-neutralizing capacity or ANC in short is a measure for the overall buffering capacity
against acidification for a solution, e.g. surface water or soil water.ANC is defined as the
difference between cations of strong bases and anions of strong acids (see below), or
dynamically as the amount of acid needed to change the pH value from the sample's value to
a chosen different value. [1] The concepts alkalinity are nowadays often used as a synonym to
positive ANC and similarly acidity is often used to mean negative ANC. Alkalinity and
acidity however also have definitions based on an experimental setup (titration).
5. CONCLUSIONS
The paper describes various types of materials to improve the geotechnical behavior of soils.
Apart from greatly enhancing the properties of soils, the use of waste materials can greatly
reduce the disposal problems and consequent land and ground water contamination problems.
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10. The mechanical and leaching concerns can be checked with appropriate physical and
chemical test.
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