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CHAPTER - 1
INTRODUCTION
1.1 General
Concrete technology has made tremendous strides in the past decade. Concrete
is now no longer a material consisting of cement, aggregates, water and admixtures
but it is an engineered material with several new constituents performing satisfactorily
under different conditions. Concrete today can be tailor made for specific applications
and contain different materials. The development of specifying a concrete according
to its performance requirements rather than the constituents and ingredients has
opened innumerable opportunities for producers and users to design concrete to suit to
their specific requirements. One of the spectacular advances made in the field of
Civil Engineering is the production of high performance materials.
Development of modern civil engineering causes an urgent need to develop
higher performance engineering materials possessing high strength, toughness, energy
absorption and durability. Fiber reinforced concrete (FRC) is one of the conventional
engineering materials used in several structural applications in order to enhance the
structural resistance/performance under different loading combinations. It also
increases speed of construction and may even eliminate the need for conventional
reinforcement. High or ultrahigh strength concrete with very high compressive
strength values remains basically a brittle material. The inclusion of adequate fibers
improves tensile strength and provides ductility.
Since the 1980’s, the design and construction of structural members demand
more and more high performance materials. High performance construction materials
provide far greater strength, ductility, durability, and resistance to external elements
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than traditional construction materials, and can significantly increase the longevity of
structures in the built environment and can also reduce maintenance costs for these
structures considerably. These most significant high performance construction
materials include high performance concrete, high performance steel, fiber reinforced
cement composites, FRP composites, etc.
Slurry infiltrated fibrous concrete
(SIFCON) is one of the high performance material.
As the fibre concentration is increased along with fibre aspect ratio
(length/diameter), it becomes difficult to mix and place these materials. In practice it
has been found that the amount of fibre must be kept fewer than 2% volume and
aspect ratio must be kept under 100. This situation places bounds on the
improvements in the engineering properties of concrete (flexural strength, flexural
toughness index, impact resistance and fatigue resistance) that can be gained through
the use of steel fibres. In 1978, Lankard began an investigation to incorporate larger
amounts of steel fibres in steel fibre reinforced cement based composites. The result
of this investigation led to the development of new cement composite called “Slurry
Infiltrated Fibre Concrete (SIFCON)” in which steel fibres up to 20% by volume
could be used.
1.2 About SIFCON
1.2.1 Introduction
Initially steel fibers were mostly used as a substitute for secondary
reinforcement or for crack control in less critical parts of the construction. Today steel
fibers are widely used as the main and unique reinforcing for industrial floor slabs,
shotcrete and prefabricated concrete products. They are also considered for structural
purposes in reinforcement of slabs on piles, full replacement of the standard
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reinforcing cage for tunnel segments, concrete cellars, foundation slabs and shear
reinforcement in prestressed elements.
Slurry Infiltrated Fiber Concrete (SIFCON) is one of the recently developed
construction material that can be considered as a special type of high performance
fiber reinforced concrete (HPFRC) with higher fiber content. In 1979 a new material,
slurry-infiltrated fiber concrete (SIFCON), was introduced by Dr. David Lankard of
the Lankard Materials Laboratory (LML) in Columbus, Ohio. Dr. Lankard had done
some pioneer work in the development of the material, as well as some applications
using the material in the paving and metal fabrication industries. SIFCON possessed
the characteristics of both high strength as well as ductility.
SIFCON can be rightly thought of as pre- placed fibre concrete, analogous to
pre- placed aggregate concrete. In FRC the fibres are mixed along with the other
ingredients but the placement of steel fibres in a form or mould is the initial step in
the preparation of SIFCON. Fibre placement can be accomplished by hand or through
the use of commercial fibre dispersing units. Light external vibration is applied during
the fibre placement operation. Once the fibres are in place, fine grained cement based
slurry is poured on to the packed fibre bed with subsequent infiltration of the slurry
added by external vibration. High range water reducing admixtures are used to
provide suitable slurry viscosity while maintaining a low water cement ratio. Once the
slurry infiltration is completed, the method of curing of SIFCON is the same as for
any concrete material.
The matrix fineness must be designed so as to properly infiltrate the fiber
network formed in the mould. Otherwise large pores may form leading to substantial
reduction in the mechanical properties. Additives such as high range admixtures such
as super plasticizer are used for improving the flowing characteristics of SIFCON.
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1.2.2 Advantages
In general, SIFCON is very ductile and particularly well suited for structures
which require higher ductility.

SIFCON possess excellent durability, energy absorption capacity,
impact and abrasion resistance and toughness.

Modulus of elasticity (E) values for SIFCON specimens is higher when
compared with plain concrete.

SIFCON exhibits high ductility.

The balling problem of steel fibers with increase in fiber volume in
SFRC can be resolved by SIFCON, because of its fiber alignment.

Deflection for SIFCON will be very less compared to conventional
concrete structural components.
Since properties like ductility, crack resistance and penetration and impact
resistance are found to be very high for SIFCON when compared to other materials,
SIFCON should be considered as an efficient alternative construction material only
for those applications where concrete or conventional SFRC cannot perform as may
be expected/required by the user or in situations where such unique properties as high
strength and ductility are required. SIFCON is best suited for application in the
following areas:

Pavement rehabilitation and precast concrete products

Overlays, bridge decks and protective revetments

Seismic and explosive-resistant structures

Security concrete applications (safety vaults, strong rooms etc)

Refractory applications (soak-pit covers, furnace lintels, saddle piers)
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
Military applications such as anti-missile hangers, under-ground
shelters

Sea-protective works

Primary nuclear containment shielding

Aerospace launching platforms

Repair, rehabilitation and strengthening of structures

Rapid air-field repair work

Concrete mega-structures like offshore and long-span structures, solar
towers etc
1.3 Need of the present study
SIFCON is similar to FRC in that it has discrete interlocking fibre that lends
significant tensile properties to the composite. In SIFCON, the fibres are preplaced
inside the forms and rich cement slurry is poured into the moulds. Its ability to resist
cracking and spalling in many loading situations is far superior to conventional fiber
reinforced concrete and to conventionally reinforced cement concrete. All the
research in U.S.A and Europe is focused on SIFCON produced with high tensile
strength steel fibres. However, for greater applications in India and other developing
countries, it is essential to investigate the feasibility of producing different SIFCON
structural elements with locally available low tensile strength steel wire fibres and
understanding their behaviour.
Even though, SIFCON is a recent construction material, it has found
applications in the areas of pavements repairs, repair of bridge structures, safe vaults
and defense structures due to its excellent energy absorption capacities.
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It is observed from the review that very little research is carried out to study
the behavior of SIFCON slab elements using analytical methods. With this view, an
analytical investigation has been carried out using FEM software in the present work
to understand the flexural behaviour of SIFCON slab panels.
Experimental based testing has been widely used as a means to analyze
individual elements and the effects of concrete strength under loading. The use of
finite element analysis to study these SIFCON slab components will be quite
interesting. Despite its long history, the finite element method continues to be the
predominant strategy employed by engineers to conduct structural analysis. A reliable
method is needed for analyzing structures made of SIFCON, a complex but rare
ingredient in most of the structural components. As an effective alternative to
expensive experimentation, this study has been conducted to evaluate the plausibility
of finite element analysis of SIFCON slabs.
1.4 Objectives of the present Investigation
The objective of present investigation is to investigate and evaluate the use of
the finite element method for the analysis of solid SIFCON slab with and without
opening at different positions with available material properties in flexure as such
models are not available for SIFCON slabs. Accordingly, the specific objectives of
the present work are listed below.

To conduct a feasibility study of producing SIFCON slab elements with
locally available low tensile strength steel wire fibres.

To model Slabs with different edge conditions for 8%, 10% and 12% volume
fraction of fibre using FEA in flexure under uniform distributed load.
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
To evaluate and compare the strength and stiffness properties of FE modelled
slab with that of experimental values.

To verify the accuracy of the model with experimental values.

Also to evaluate the total energy absorption capacity of SIFCON slabs
modeled using FEA in flexure.

To compare the load deflection response obtained from FE analysis with
experimental values.

To study the variation in the spread of normal stresses at the bottom surface of
the SIFCON slabs by FEA.

To model SIFCON slab with different type and size openings for different
edge conditions in flexure under uniformly distributed load

To validate the proposed FE solution by comparing the solid SIFCON slab
results with experimental values available in literature.

To analyse SIFCON slabs with openings of different sizes and locations using
validated FE SIFCON models.
Thus, it is proposed to study the response of slurry infiltrated fibre concrete
slabs using finite element analysis to understand their load-deflection response under
pressure loading. A slurry infiltrated fibre concrete slab model will be developed
using FEM and the results will be compared to experimental data in this project. Slabs
with different edge conditions for 8%, 10% and 12% volume fraction of fibre will be
analysed using FEM. NISA, a general purpose Finite Element Software, will be used
for this purpose. Solid elements will be used to develop the slab model and the
accuracy of the model will be verified with experimental values. Concrete structural
components exist in buildings and bridges in different forms. Understanding the
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response of these components during loading is crucial to the construction of an
efficient and safe structure.
Different methods have been utilized to study the
response of structural components. Experimental based testing has been widely used
as a means to analyze individual elements and the effects of concrete strength under
loading. While this is a method that produces real life response, it is extremely time
consuming and quite costly. The use of finite element analysis to study the structural
components can be quite effective. In recent years, the use of finite element analysis
has increased due to progressing knowledge and capabilities of computer software
and hardware. It has now become the choice method to analyze concrete structural
components. The use of computer software to model these elements is much faster,
and extremely cost effective. Thus use of FEA has been the preferred method to study
the behavior of concrete. The results will be analyzed and useful conclusions will be
drawn. It is felt that this will lead to a chain of development in the field of SIFCON
and thus leads to greater applications of this material in this country.
1.5 ORGANIZATION OF THE THESIS
The presentation of the investigation carried out to achieve the specific
objectives mentioned in the previous section is planned in the following manner:
Chapter 1
This chapter covers the general background to the problem, motivation for the
present work, objectives of the present study and organization of the thesis.
Chapter 2
This chapter deals with the comprehensive literature review in the area of the
present work and critical review of the literature. It covers in detail the analytical
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solution for slabs using FEA. Based on this, the scope and objective of the present
study has been derived.
Chapter 3
This chapter deals in detail with the finite element techniques and constitutive
models that have been used in the analysis. The details of modeling and validation of
finite element programme used are presented in this chapter.
Chapter 4
This chapter presents the details of tests conducted on basic raw materials like
cement, fine aggregate, water and steel fibres used in the present investigation. The
experiments have been conducted as per the specifications of relevant I.S codes for
deriving properties of SIFCON.
Chapter 5
This chapter presents the FE analysis of solid two way SIFCON slabs without
openings for different edge conditions and with 8%, 10% and 12% volume fraction of
fibre.
This chapter presents a complete analysis viz., load-deflection response,
stiffness, energy absorption and normal stresses at the bottom face of SIFCON slabs
for evaluating the response of SIFCON slabs under pressure loading.
Chapter 6
Chapter 6 deals with the details of the SIFCON slab flexure model using FEA
with different openings at center and deriving the load deflection response. The
details of models of slabs with different edge conditions for 8%, 10% and 12%
volume fraction of fibre have been reported in this chapter.
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Chapter 7
This module deals with the details of the SIFCON slab flexure model using
FEA with different openings at corner subjected to pressure loading and derivation of
the load deflection response. The details of models developed for slabs with different
edge conditions for evaluating load deflection response and their behaviour with
different volume percentages of fibre (i.e. 8%, 10% and 12%) have been reported.
Chapter 8
This chapter deals with the details of the SIFCON slab flexure model using
FEA with different openings at different position in slab subjected to pressure loading
to evaluate the load deflection response. The details of models developed for slabs
with different edge conditions for evaluating load deflection response and their
behaviour with different volume percentages of fibre (i.e. 8%, 10% and 12%) have
been reported.
Chapter 9
This chapter outlines the overall conclusions and inferences drawn from this
investigation along with the suggestions for further investigation.
A comprehensive bibliographical list is provided at the end of the thesis with a
view to help present and future investigators working in the related areas.