chapter 2 literature review -...
TRANSCRIPT
15
CHAPTER 2
LITERATURE REVIEW
2.1 HISTORICAL DEVELOPMENT
The definition of Ferrocement can be drawn from a patent
application submitted by Joseph-Louis of France, in 1852. The patent for
“Ferro - cement”, which translates into, “iron-cement”. Since 1887, a
Dutchman, Mr. Boon, built a small craft of ferrocement, the seagull and
several barges of reinforced mortar to carry ashes and refuse on water canals.
During the First World War, ships and barges were built with reinforced
concrete, and this was again attempted during the Second World War due to
shortage of materials, particularly steel. In effect, Ferrocement was forgotten
and replaced by reinforced and prestressed concrete.
In early 1940’s, Pier Luigi Nervi, a noted Italian engineer, revived
the original concept of “Ferrocement” by proposing that Ferrocement be
utilized to build fishing boats. Ferrocement finally achieved wide acceptance
in the early 1960’s for boat building in the United Kingdom, New Zealand,
Canada and Australia.
The following definition of Ferrocement was given by ACI
committee 549 (1999) in a state-of-the-art report on Ferrocement first
published in 1980 and still enforced.”Ferrocement is a type of thin wall
reinforced concrete commonly constructed of hydraulic cement mortar
reinforced with closely spaced layers of continuous and relatively small size
16
wire mesh. The mesh may be made of metallic or other materials”. This is
quite close to the initial definition of Ferrocement.
Based on the past experience and advances in Ferrocement,
Antoine Naaman (2000) suggests the following definition in his Book on
‘Ferrocement and Laminated Cementitious Composites’. “Ferrocement is a
type of thin wall reinforced concrete commonly constructed of hydraulic
cement mortar reinforced with closely spaced layers of continuous and
relatively small size wire mesh. The mesh may be made of metallic or other
suitable materials. The fineness of the mortar matrix and its composition
should be compatible with the mesh and armature systems it is meant to
encapsulate. The matrix may contain discontinuous fibers”.
As a thin reinforced concrete product and as a laminated cement-
based composite ferrocement can be used in numerous applications, including
new structures and rehabilitation of existing structures. Ferrocement
applications are extended to boats, fishing vessels, ferries, barges, docks,
cargo tugs, floatation buoys and fuel or water tanks. The key criteria for such
applications are water-tightness, impact resistance, thickness and light-weight.
Since this investigation is meant for behaviour of a Ferrocement
slabs which was made of self compacting concrete, weldmesh, Polypropylene
fibers and GFRP wrapping the review has been done in the following areas:
Ferrocement
Self Compacting Concrete
Fiber Reinforced Concrete
FRP Wrapping and analytical modelling
Each of these research areas will be separately discussed.
17
2.2 STUDIES ON FERROCEMENT
Tests on Ferrocement slabs were reported since early 19th century
itself. Many aspects of Ferrocement elements had been studied and
reported in USA, Canada, Malaysia, Singapore and elsewhere as early as
1884. These studies were related to the behaviour of Ferrocement over
conventional concrete. Such tests were not considered here for review.
The tests reported below include information on the ferrocement slabs which
use as a flexural member.
The application of Ferrocement in the construction work and in the
rehabilitation work had gained more importance since 1990’s. In recent
times, the sustained efforts of researchers all over the world to innovate and
incorporate unmatched excellence in construction have led to development of
several unmatched construction materials. Of these, Ferrocement with fibers
and weldmesh has come to stay and deserves a special mention. Researches
related to such types of Ferrocement slabs are discussed below.
Mansur et al (2000) conducted tests on punching shear behavior of
restrained ferrocement slabs, which explains that an experimental study was
carried out on a total of 14 restrained ferrocement slabs under a central patch
load. The slab panels were supported and partially restrained on all four sides
by edge ribs. The influences of the degree of end restraint, size of the loaded
area, mortar strength, volume fraction of reinforcement, and overall thickness
on the behavior and punching shear capacity of the slabs were investigated.
Test results revealed that the provision of end restraint leads to a substantial
enhancement in strength and stiffness of the slabs, but the shape and location
of the critical punching shear perimeter remained unchanged. Both cracking
and punching shear loads increased with an independent increase in any of the
test parameters considered in this study, except for the thickness of the edge
18
rib. Based on test results, an equation was proposed to predict the punching
shear strength of partially restrained ferrocement slabs.
Al-Kubaisy et al (2000) presented a study of the flexural behaviour
of reinforced concrete slabs with ferrocement tension zone cover. The results
of tests on 12 simply supported slabs are presented. The parameters
considered in this study were percentage of wire mesh reinforcement in the
ferrocement cover layer, thickness of the ferrocement layer and the type of
connection between the ferrocement layer and the reinforced concrete slab on
the ultimate flexural load, first crack load, crack width and spacing, and the
load–deflection relationship were examined. The results indicate that the use
of ferrocement cover slightly increases the ultimate flexural load and
increases in the first crack load. The first crack load increased with the
increase in the percentage of mesh reinforcement and the ferrocement layer
thickness. Considerable reduction in cracks width and spacing (64–84%) was
observed for specimens with a ferrocement layer. The presence of a cold joint
between the reinforced concrete slab and the ferrocement layer lowered the
ultimate flexural load by 34%, however, cracks width and spacing were
reduced. The author concluded that the ferrocement layer thickness and the
connection type influenced the reduction in deflection.
Masood et al (2003) dealt with Performance of ferrocement panels
in different environments, which describes that addition of fly ash in different
environments affects the load-carrying capacity under flexure for panel with
both woven and hexagonal wire fabric. It also shows that the strength of panel
increases with fly ash dosage in saline casting and curing condition.
The strength of panels under saline casting and saline curing condition is
more as compared to panels under normal casting and saline curing condition
because of better pore structure minimizing the ingress of water, due to the
presence of fly ash and the saline water during casting.
19
Hag et al (2005) carried out tests to study the ultimate and service
behavior of ferrocement roof slab panels. The test results of six simply
supported roof slab panels are presented. The parameters of study include: the
effect of the percentage of wire mesh reinforcement by volume and the
structural shape of the panels on the ultimate flexural strength, first crack
load, crack spacing and load-deformation behavior. The results indicate that
the use of monolithic shallow edge ferrocement beams with the panels
considerably improves the service and ultimate behavior of the panels,
irrespective of the number of steel layers used.
Chandrasekar Rao et al (2006) dealt with the shear strength of
simply supported ferrocement rectangular plates of 6 series with different
shear span to depth ratios and with varying number of weldmesh layers 0 to 6.
All the specimens were tested under two point’s symmetrical loading. It was
concluded that the load carrying capacity and ductility of plain FRC elements
improved by several folds with the inclusion of aligned weld mesh. Increase
in the number of weld mesh layers increase both the shear load carrying
capacity as well as the ductility of the composite.
Alnuaimi et al (2009) investigated nine roof panels made of
Ferrocement the specimens are, two types of channel sections and one type of
box section. All panels were 2m long, 470mm wide and 20mm thick. Channel
type A had side edge beams 95mm deep and channel type B had side edge
beams 50mm deep. The depth of the box section was 95mm.Thin hexagonal
wire mesh was used as reinforcement. The number of wire mesh layers was
varied between two to six. The wires were impregnated midway through the
thickness of the panels. The panels were tested for bending moment with
simple supports. The main variables considered in this study were the number
of wire mesh layers, the cross sectional shape of the panel and the depth of
edge beam. Tests revealed that all panels showed acceptable strength for
20
roofing systems. The increase in the number of wire mesh layers leads to an
increase in the flexural strength. The box section showed strength similar to
that of the channel section with 95mm edge beam. The channels with 50mm
deep edge beams showed strength much less than the ones with 95mm edge
beam and box section.
2.3 STUDIES ON SELF COMPACTING CONCRETE
The introduction of the “modern” SCC is associated with the drive
towards better quality of concrete pursued in Japan in late 1980’s, where the
lack of uniform and complete compaction had been identified as the primary
factor for the poor performance of concrete structures. In the early 1990’s
there was only a limited knowledge about SCC, but in modern, present day
SCC can be classified as an advanced construction material. This offers many
advantages and benefits over conventional concrete.
Brouwers and Radix (2005) had carried out theoretical and
experiment study on SCC, which addresses experiments and theories on
SCC. First, the features of ‘‘Japanese and Chinese Methods’’ are discussed, in
which the packing of sand and gravel plays a major role. Here, the grading
and packing of all solids in the concrete mix serves as a basis for the
development of new concrete mixes. Mixes, consisting of slag blended
cement, gravel (4–16 mm), three types of sand (0–1, 0–2 and
0–4 mm) and a polycarboxylic ether type superplasticizer, were developed.
These mixes are extensively tested, both in fresh and hardened states, and
meet all practical and technical requirements such as medium strength and
low cost. It follows that the particle size distribution of all solids in the mix
should follow the grading line as presented by Andreasen and Andersen.
Furthermore, the packing behaviour of the powders (cement, fly ash, stone
powder) and aggregates (three sands and gravel) used are analysed in detail.
It follows that their loosely piled void fraction are reduced to the same extent
21
(23%) upon vibration (aggregates) or mixing with water (powders). Finally,
the paste lines of the powders are used to derive a linear relation between the
deformation coefficient and the product of Blaine value and particle density.
Domone (2006) carried out an analysis of 11 years of case studies
of self compacting concrete structure, which deals with different range and
type of case studies explaining the initial observations such as properties,
component materials and mix proportions of the concrete, fresh properties of
SCC, tests for SCC, compressive strength of SCC ranging from 20MPa to
100MPa, mixture constituents such as coarse aggregates, powder content,
admixtures, mixture proportion of coarse aggregate content, paste content,
powder content, water/powder ratio, mortar composition. This paper reveals
that 90% of the case studies were used SCC with slump flows in the range of
600-750mm and 80% had compressive strength in excess of 40 MPa. 70% of
cases used aggregate with a miximum size between 16 and 20 mm.
Approximately, half the cases used a viscosity modifying agent in addition to
superplasticizer and could therefore be considered as combined type of SCC,
which are generally more robust than mixes without a VMA.
Burak Felekoğlu et al (2006) carried out test to study the effect of
fly ash and limestone fillers on the viscosity and compressive strength of
self-compacting repair mortars, which deals with the selection of amount and
type of powders from the viewpoint of fresh state rheology and mechanical
performance. The influence of powder materials on self-compatibility,
viscosity and strength were compared with a properly designed set of test
methods (the mini slump, V-funnel tests, viscosity measurements and
compressive strength tests). It may be advised that, for each cement–powder–
plasticizer mixture, a series of test methods can be used to determine the
optimum content and type of materials for a specified workability.
22
Binu Sukumar et al (2008) had carried out tests to evaluate the
strength at early stages of self-compacting concrete with high volume fly ash.
SCC demands large amount of powder content and fines for its cohesiveness
and ability to flow without bleeding and segregation. This paper reveals that,
part of this powder is replaced with high volume fly ash based on a rational
mix design method developed by the authors. Because of high fly ash content,
it is essential to study the development of strength at early ages of curing
which may prove to be a significant factor for the removal of formwork. Rate
of gain in strength at different periods of curing such as 12 h, 18 h, 1 day, 3
days, 7 days, 21 days and 28 days are studied for various grades of different
SCC mixes and suitable relations have been established for the gain in
strength at the early ages in comparison to the conventional concrete of same
grades. Relations have also been formulated for compressive strength and
split tensile strength for different grades of SCC mixes.
Khatib (2008) had presented the performance of SCC containing
flyash. The influence of including Fly Ash (FA) on the properties of SCC is
investigated. Portland Cement (PC) was partially replaced with 0–80% FA.
The water to binder ratio was maintained at 0.36 for all mixes. Properties
included workability, Compressive strength, ultrasonic pulse Velocity (V),
absorption and shrinkage. The results indicate that high volume FA can be
used in SCC to produce high strength and low shrinkage. Replacing 40% of
PC with FA resulted in strength of more than 65 N/mm2 at 56 days. High
absorption values are obtained with increasing amount of FA, however, all
FA concrete exhibits absorption of less than 2%. There is a systematic
reduction in shrinkage as the FA content increases and at 80% FA content, the
shrinkage at 56 days reduced by two third compared with the control. A linear
relationship exists between the 56 day shrinkage and FA content. Increasing
the admixture content beyond a certain level leads to a reduction in strength
and increase in absorption. The correlation between strength and absorption
23
indicates that there is sharp decrease in strength as absorption increases from
1 to 2%. After 2% absorption, the strength reduces at a much slower rate.
Zhimin Wua et al (2009) conceded out an experiment study on the
workability of self-compacting lightweight concrete, which deals with the mix
proportion design for Self-Compacting Lightweight Concrete (SCLC) and its
workability. By considering the water absorption of Lightweight Aggregate
(LWA), two mix proportions for SCLC are designed by the overall calculation
method with fixed fine and coarse aggregate contents. The workability of the
two types of fresh SCLCs is quantitatively evaluated by the slump flow,
V-funnel, L-box, U-box, wet sieve segregation, and surface settlement tests.
The uniformity of distribution of LWAs along the specimen is also evaluated
by the column segregation test and the cross-section images. Based on the
experimental results, a detailed analysis is conducted. It is found that the two
types of fresh SCLCs have good fluidity, deformability, filling ability,
uniform aggregate distribution and minimum resistance to segregation. It can
be concluded that the two mix proportions for SCLC presented in this paper
satisfy various requirements for workability and can be used for the design of
practical concrete structures fresh SCLCs have good fluidity, deformability,
filling ability, uniform aggregate distribution and minimum resistance to
segregation. It can be concluded that the two mix proportions for SCLC
presented in this paper satisfy various requirements for workability and can be
used for the design of practical concrete structures.
Sandra Nunes et al (2008) had evaluated the interaction diagrams
to assess SCC mortars for different types, which provides a comprehensive
procedure for the design of mortar mixtures which are adequate for SCC.
A central composite design was carried out to mathematically model the
influence of four mixture parameters and their coupled effects on
deformability, viscosity and compressive strength of mortar mixtures.
24
The derived models and a numerical optimization technique were used to
determine the range of mortar mixture parameters where deformability and
viscosity coexist in a balanced manner. Interaction diagrams are suggested to
represent the optimized solutions. Six different types of cement were assessed
in combination with limestone filler and a polycarboxylate type
superplacticizers. Each type of cement has unique properties that interact with
other constituents, resulting in different interaction diagrams and mix
proportions in the concrete mixture. The utility of numerical models and
optimized solutions for quality control, tailor-made concrete mixtures and
selection of constituent materials is highlighted.
Kumar et al (2011) carried out a study on the “Flexural capacity
predictions of Self-Compacting concrete beams using stress-strain
relationship in axial compression”. An experimental investigation was carried
out to generate complete stress–strain curves for SCC in axial compression by
testing 162 standard cylindrical specimens of strength 35–70 MPa. The accuracy
of analytical models for CVC selected from the literature in predicting the
stress– strain behavior of the SCC mixtures is discussed and their
inadequacies are highlighted. The equivalent rectangular stress block
specified in current design codes for flexural capacity predictions was
developed on the basis of tests on CVC; given the observed differences in the
stress–strain behavior of CVC and SCC, its applicability to structural design
of SCC members becomes questionable. On the basis of the proposed
constitutive model for SCC, a new equivalent rectangular stress block valid
for concrete strengths of up to 70 MPa is presented for analysis of flexural
capacity. The flexural capacity predictions of the proposed stress block are
compared with experimental data from the present work and other
investigations reported in the literature, and good agreement was obtained.
A simple analytical approach is presented for predictive assessment of the load–
deflection behaviour of SCC beams with a reasonable degree of accuracy.
25
2.4 STUDIES ON FIBER REINFORCED CONCRETE
Cementitious matrices generally have mechanical characteristics
that distinguish them from metallic and polymeric matrices, which are
relatively high compressive strength, poor tensile strength and brittleness in
failure. To overcome these limitations, Fibers have been used to strengthen a
weaker matrix for many centuries, such as straw in mud bricks and horse hair
in gypsum plastering. In this present modern world many fibers have been
introduced in both research and industry fields; steel, glass, polypropylene
and polyethylene short fibers in concrete are used to strengthen the cement
concrete and cement mortar. Arresting micro cracks in concrete has got many
potential applications. Few literatures were collected about the fiber
reinforced concrete, especially with the polypropylene fiber, and the
researches are discussed below.
Matthias Zeiml et al (2005) studied the influence of the amount of
Polypropylene (PP) fibers on the spalling behavior of concrete under fire
loading. Starting from the identification of the permeability as the parameter
with the greatest influence on spalling, results of permeability tests on
normal-strength in-situ concrete without and with PP-fibers (1.5 kg/m3) are
presented in this paper. The values for the permeability, which are obtained
for concrete pre-heated to different temperature levels, are related to the pore
structure, accessible by Mercury-Intrusion-Porosimetry (MIP) tests. The
considered concrete was prepared under on-site conditions, accounting for the
workability and densification when casting at the construction site. In order to
illustrate the effect of the permeability of concrete with and without PP-fibers
on spalling, which was experienced during the aforementioned research
project, a finite-element analysis, taking the coupling between heat and mass
transport into account, is performed. The so-obtained results provide insight
into the risk of spalling of concrete with varying amount of PP-fibers.
26
Hanfeng Xu and Sidney Mindess (2006) conducted a study on the
Behaviour of Concrete Panels Reinforced with Welded Wire Mesh and Fibres
under Impact Loading. Centrally loaded round concrete panels reinforced
with various combinations of fibers and Welded Wire Meshes (WWM) were
tested under impact loading. Two strength levels (50 MPa and 120 MPa) of
the concrete matrix were studied. Both steel and synthetic fibers, at volume
concentrations of 0.5% or 1.0%, were used. The impact strengths and fracture
energies of the concrete panels were determined, as well as the strain rate
sensitivity of the various mixtures. Quite different behaviour was observed
under impact loading, compared to that under static loading. It was concluded
that a hybrid reinforcement system was more effective than any single type of
reinforcement in mitigating the brittleness of the concrete.
Sivakumar and Manu Santhanam (2007) focus on the experimental
investigation carried out on high strength concrete reinforced with hybrid
fibres (combination of hooked steel and a non-metallic fiber) up to a volume
fraction of 0.5%. The mechanical properties, namely, compressive strength,
split tensile strength, flexural strength and flexural toughness were studied for
concrete prepared using different hybrid fiber combinations–steel–
polypropylene, steel–polyester and steel–glass. The flexural properties were
studied using four point bending tests on beam specimens. Fiber addition was
seen to enhance the pre-peak as well as post-peak region of the load–
deflection curve, causing an increase in flexural strength and toughness,
respectively. The specimens tested by the author were, C1 - Control Concrete,
HST2 – Steel Fiber, HSPP3 – Steel Fiber + Polypropylene fibre , HSPO4 -
Steel Fibre+ Polyester fibre,HSGL5 - Steel Fibre+ Glass fibre. Addition of
steel fibers generally contributed towards the energy absorbing mechanism
(bridging action) whereas, the non-metallic fibers resulted in delaying the
formation of micro-cracks. Compared to other hybrid fiber reinforced
concretes, the flexural toughness of steel–polypropylene hybrid fiber
27
concretes was comparable to steel fibre concrete. Increased fiber availability
in the hybrid fiber systems (due to the lower densities of non-metallic fibers),
in addition to the ability of non-metallic fibers to bridge smaller micro cracks,
are suggested as the reasons for the enhancement in mechanical properties.
Qunshan ye et al (2009) studied the effect of polyester fiber on the
rheological characteristics and fatigue properties of asphalt and its mixtures in
this paper. The viscosity, Rheological and fatigue tests are conducted to
characterize such related properties of asphalt binder and related properties of
asphalt binder and mixture with different fiber contents of 0.1, 0.3 and
0.5 percent by weight of asphalt. To obtain homogeneous bitumen – fiber
mastics, the polyester fibers were added slowly into the preheated pure
asphalt and mixed for 2 hours. The author proved that the viscosity increased
by two to three times because the polyester fibers began to form a localized
network structure. When the fiber content was up to 0.5%, the local networks
gradually began to interact to initiate continuous network throughout asphalt,
this leads to 10 fold increase (or) additional in viscosity. The complex shear
modulus of asphalt binder is decreased with the increase in fiber content and
frequencies, but the change of phase angles with (or) without fibers are
limited.
Kalia Anurag et al (2009) had done laboratory Investigation of
Indirect tensile strength using Polyester waste fibers in hot mix asphalt. The
author used two lengths 0.635 cm and 1.270 cm of this fibre, and two fiber
contents (0.35% and 0.50% by weight of total mixture) were used to
determine the strength. 0.35% fiber mixtures had a lower toughness than the
0.50% fiber percentages at both lengths. The mixtures with 0.635 cm length
and 0.35% fibers had higher air voids that 1.270 cm length and 0.50% fibers.
28
Ali Behnood and Masoud Ghandehari (2009) presented the results
of an extensive experimental study on the compressive and splitting tensile
strength of high-strength concrete with and without polypropylene (PP) fibers
after heating to 600C. Mixtures were prepared with water to cementitious
materials ratios of 0.40, 0.35, and 0.30 containing silica fume at 0%, 6%, and
10% cement replacement and polypropylene fibers content of 0, 1, 2, and
3kg/m3. A severe strength loss was observed for all of the concretes after
exposure to 600C, particularly the concretes containing silica fume despite
their good mechanical properties at room temperature. The range of 300-600C
was more critical for concrete having higher strength. The relative
compressive strengths of concretes containing PP fibers were higher than
those of concretes without PP fibers. The splitting tensile strength of concrete
was more sensitive to high temperatures than the compressive strength.
Furthermore, the presence of PP fibers was more effective for compressive
strength than splitting tensile strength above 200C. Based on the test results, it
can be concluded that the addition of 2kg/m3 PP fibers can significantly
promote the residual mechanical properties of HSC during heating.
Sudarsana Rao et al (2010) studied on the response of SIFCON two
– way slabs under Impact loading. An experimental program was carried out
to investigate the behaviour of Slurry-Infiltrated Fibrous Concrete (SIFCON)
slabs under impact loading. Fibre-Reinforced Concrete (FRC), Reinforced
Cement Concrete (RCC) and Plain Cement Concrete (PCC) slabs were also
cast and tested for comparison purposes. The impact force was delivered with
a steel ball drop weight. The author proposed equations for energy-absorption
capacities are as given below:
The energy absorption up to first crack stage
Ef = (0.027Fv - 0.139)fck 2 (2.1)
29
The energy absorption up to ultimate stage
Eu = (0.185 + 0.036Fv)f ck 2 (2.2)
where Ef = energy absorption in kJ up to the first crack stage, Eu = energy
absorption up to the ultimate stage, Fv = fibre volume fraction in % and
fck = 28 days cube compressive strength in N/mm2
The test results revealed that SIFCON slabs with 12% fibre volume
fraction exhibit excellent performance in strength and energy-absorption
characteristics when compared with other slab specimens. Regression models
have been developed to estimate the energy absorption for SIFCON slab
specimens.
Mahmoud Nili and Afroughsabet (2011) studied the long-term
compressive strength and durability properties of concrete specimens
produced by incorporating polypropylene fibers and silica fume were
investigated. Silica fume, a cement replacement, was used at 8% (by weight
of cement) and the volume fractions of the polypropylene fibers were 0%,
0.2%, 0.3% and 0.5%. Water-binder ratios were 0.46 and 0.36. The results
indicate that the inclusion of fiber and particularly silica fume into the
specimens led to an increased long-term compressive strength. Electrical
resistance of the silica fume specimens improved remarkably, but decreased
slightly due to the fiber inclusion. Water absorption of the fiber–silica fume
specimens decreased exclusively compared to the reference samples.
Inclusion of fiber and silica fume into the specimens had no considerable
effect on the dynamic frequency results.
Sivakumar (2011) discussed the experimental results of tests
carried out on the flexural properties of various fibres reinforced concrete at
low volume fractions of fibres up to 0.5%. The poor toughness, a serious
30
shortcoming of high strength concrete, could be overcome by reinforcing with
short discontinuous fiber. The addition of steel fibres at high dosages however
has potential disadvantages interms of poor workability and increased cost.
The addition of non-metallic fibres such as glass, polyester, polypropylene
etc, results in good fresh concrete properties and reduced early age cracking.
The beneficial effects of non-metallic fibres could be attributed to their high
aspect ratios and increased fibre availability at a given volume fraction.
Because of their stiffness, these fibres particularly effective in controlling the
propagation of micro cracks in the plastic stage of concrete. The experimental
observations for toughness and ductility reveal that the best performance of
steel glass and steel-polypropylene hybrid combinations is obtained at the
level of non-metallic fibres; the reason could be that at the high levels of
non-metallic fibres there is significant enhancement in the early part of the
post peak behavior. Increased fibre availability in the hybrid fibre system,
(due to the lower sensitizes of non-metallic fibres), in addition to the
availability of non-metallic fibres of smaller micro-cracks, could be the
reasons for the enhancement in flexural properties.
Efrat Haim and Alva Peled (2011) conducted a study on the Impact
Behaviour of Textile and Hybrid Cement-Based Composites. The bending
properties under dynamic (impact) and static loadings of four composite
systems—hybrid composites reinforced with two-dimensional (2-D) fabrics
and short fibers, sandwich composites reinforced with 2-D fabrics,
composites with three-dimensional (3-D) fabrics, and composites made from
short polypropylene (PP) fibers or polyvinyl alcohol (PVA) fibers—were
compared. The hybrid combination of polyethylene (PE) fabrics and short
fibers performed well as reinforcements for cement composites exposed to
dynamic (impact) loading. The hybrid composite with the short PP fibers
outperformed the short PP fiber composite without fabric reinforcement.
Under static loading, no difference was observed between the behaviours of
31
the hybrid composites and the non-fabric composites based on short PP fibers.
The 2-D and 3-D fabrics show promise when used as reinforcements for
composites exposed to dynamic loading, but more research is needed to fully
understand the behaviours of these materials under both impact and static
conditions.
Padmanaban and Kandasamy (2011) carried out a Study on the
Impact energy variation for flyash Concrete. Concrete Structures designed for
static loads are also subjected to accidental or deliberate impact or blast loads
because of industrial or transportation accidents, military or terrorist
activities. Such structures require realistic assessment of the ultimate impact
resistance and a mode of failure of the structure. This paper presents the study
of impact characteristics of Indian fly ash mixes with locally available
ingredients. Impact study was conducted by means of drop weight test method
to evaluate the properties like impact energy absorbed, impact energy
efficiency of cement and effect of compressive strength on impact strength
with ages. The author concluded the relationship between impact energy
(EFA) and the compressive strength (fc) at their respective ages indicates the
following empirical equations.
EFA = 13.898 fc
0.9005 at 3rd day(1)
EFA = 31.137 fc
0.7544 at 7th day (2)
EFA = 1.8058 fc
1.6099 at 28th day (3)
EFA = 0.037fc
2.5215 at 56th day (4)
EFA = 8×10-5 fc
3.9746 at 90th day (5)
32
where EFA is the impact energy of fly ash mixes, fc is the compressive
strength of the fly ash mixes. The results of the investigations shows that
Indian fly ash can be effectively utilized for improving impact characteristics
of concrete structures.
Sangeetha (2011) studied on the Compression and Impact strength
of GFRC with combination of Admixtures. High performance fiber reinforced
concrete increases the Compressive, Impact and Flexural Strength. The aim of
this experimental work is to study the effect of addition of admixtures in glass
fiber reinforced concrete. Nearly Forty Standard Specimens are tested to
failure under a constant axial load for to study the compressive strength and
forty standard impact specimens are tested by drop weight method to study
the Impact strength of the material. The Parameters that are varied in the
experimental work includes Percentage of fiber. [0, 0.1, 0.2 and 0.3% weight
of concrete]. Different combinations of admixtures Superplasticiser + Air
entraining agent + Accelerator [S+AEA+A], Superplasticiser + Air entraining
agent + Retarder [S+AEA+R] Superplasticiser + Air entraining agent + Water
proofing compound [S+AEA+W]. Glass Fiber Reinforced Concrete with
Different combination of admixtures increases the compressive strength
(10%) and Impact Strength (100%).
Bensaid Boulekbache et al (2011) studied the “Influence of yield
stress and compressive strength on direct shear behavior of steel fibre-
reinforced concrete”. This study aims in examining the influence of the paste
yield stress and compressive strength on the behavior of fibre-reinforced
concrete (FRC) versus direct shear. The parameters studied are the steel fibre
contents, the aspect ratio of fibres and the concrete strength. Prismatic
specimens of dimensions 10 × 10 × 35 cm made of concrete of various yield
stress reinforced with steel fibres hooked at the ends with three fibre volume
fractions (i.e. 0%, 0.5% and 1%) and two aspects ratio (65 and 80) were tested
33
to direct shear. Three types of concretes with various compressive strength
and yield stress were tested, an Ordinary Concrete (OC), a SCC and a High
Strength Concrete (HSC). The concrete strengths investigated include 30 MPa
for OC, 60 MPa for SCC and 80 MPa for HSC. The results show that the
shear strength and ductility are affected and have been improved very
significantly by the fibre contents, fibre aspect ratio and concrete strength.
As the compressive strength and the volume fraction of fibres increase, the
shear strength increases. However, yield stress of concrete has an important
influence on the orientation and distribution of the fibres in the matrix.
The ductility was much higher for ordinary and self-compacting concretes
(concrete with good workability). The ductility in direct shear depends on the
fibre orientation and is significantly improved when the fibres are
perpendicular to the shear plane. On the contrary, for concrete with poor
workability, an inadequate distribution and orientation of fibres occurred,
leading to a weak contribution of the fibres to the direct shear behavior.
2.5 STUDIES ON FRP WRAPPING
FRP in India has taken shape in 1960s with a single manufacturer
alone as a source of fiberglass. Over the years the industry has grown steadily,
but at a slower pace. FRP materials were developed primarily for Aerospace
and Defence industries in 1940s and were widely used in many industries
today including aeronautic, marine, automotive and electrical engineering.FR
materials are finding wider acceptance among Civil Engineers. The technique
of externally bonding FRP to reinforced concrete structures was introduced
into China in 1996. In India, field application of FRP structural strengthening
sheet as both form and reinforcement. As the sheet encloses the concrete in
all three sides, the sheet gives partial confinement which is expected to
enhance the compressive strength of concrete. Hence the works related to
confined concrete are discussed in this section.
34
Tarek Almusallam and Yousef Al-Salloum (2001) the author has
presented a simple and efficient computational analysis to predict the nominal
moment capacity of RC beams strengthened with external FRP laminates.
The study presents the design of laminate thickness to attain a specified
moment capacity in a given beam. The section is assumed to have a linear
strain distribution. From the equilibrium of internal forces, a quadratic
equation is obtained as a function of the depth of neutral axis C, which leads
to the nominal moment capacity, Mn, when taking the moment about the line
at which the concrete compression force acts:
Mn = As fy (d - a/2) + Ap fp (h – a/2)
where,
a = β, c and fp = Ep Єp,
in which
d = distance from extreme compression fiber to the centroid of the
tension reinforcement.
As = area of tension steel reinforcement
Ap = area of FRP plate
β1= ratio of the rectangular compressive block to the depth of
neutral axis.
fy= yield stress of steel reinforcement
fp = the tensile stress in the FRP laminates
fpu = the ultimate tensile stress in the FRP laminates
α = stress reduction factor for the FRP laminates = 0.67
Ep = modulus of elasticity of FRP laminates
35
Єp, = the strain in the FRP laminates, corresponding to fp
The depth of neutral axis for the beam section considered is
C = 0.003h/0.003 + Єpy
The equilibrium of the forces leads to the minimum allowable
thickness:
Tmin = (2.55fc’ β1C - 3ρsdfy)/2fpu
The above equation gives the minimum thickness required to assure
tension failure (yield of steel). Any value less than the value of tmin will yield
rupture of the composite laminate, which is an undesirable type of failure.
The author concluded that the computational analysis to determine the
nominal capacity of RC beams strengthened with external FRP laminates
proved to be good and efficient in the prediction of experimental values.
Rajamohan and Sundarraja (2007) studied the compressive
behaviour of the axially loaded short concrete columns retrofitted /
rehabilitated using GFRP. Its focus is on the aspect of the structural behaviour
of RC columns strengthened in compression with Externally Bonded (EB)
GFRP in different patterns. Improvements in the axial load carrying and
deformation capacities of FRP jacketed concrete members over un–jacketed
members are reported. The main aspects of performance of columns EB with
FRP sheets considered in this research were failure mode, efficiency, strength
gain and deformability of strengthened columns. Factors influencing the axial
stress-strain behaviour of FRP confined concrete, such as, transverse dilation
and effectively confined regions and their relationship to jacket properties are
identified and discussed. Further, this work presents a simple comparative
study between the compression members strengthened with GFRP and the
36
control compression members. Significant increase in strength and ductility
of concrete can be achieved by glass fiber composite jacketing. Enhancement
in concrete axial stress and strain capacity, relative to that of un-confined
concrete, increase with FRP jacket strength and stiffness. The type of the
confinement also decides the effectiveness in terms of load carrying capacity.
Pannirselvam et al (2009) had carried out an experimental
investigation evaluate the structural behaviour of reinforced concrete beams
with externally bonded FRP reinforcement. Beams bonded with four different
types of GFRP having 3.50 mm thickness were used. Totally five rectangular
beams of 3 m length were cast. One beam was used as reference beam and the
remaining beams were provided with GFRP laminates on their soffit.
The variable considered for the study is type of GFRP laminate. The study
parameters of this investigation included first crack load, yield load, ultimate
load, first crack deflection, yield deflection, ultimate deflection, crack width,
deflection ductility, energy ductility, deflection ductility ratios and energy
ductility ratios of the test beams. The performance of FRP plated beams was
compared with that of unplated beam. The test results showed that the beams
strengthened with GFRP laminates exhibited better performance.
Revathy et al (2009) had carried out an experimental investigation
to evaluate the effects of Glass Fiber Reinforced Polymer wrapping on the
structural behaviour of corrosion damaged concrete columns of size 150 mm
x 900 mm. The columns were subjected to different degrees of accelerated
corrosion. The damaged columns were wrapped with Glass Fiber Reinforced
Polymer sheets and are tested. The test results show a marked enhancement in
ultimate strength by 30% and ductility by 110%. It was found that the strength
and ductility of the GFRP confined corrosion-damaged columns increase with
increasing wrap thickness.
37
Urmil et al (2009) carried an comparative study on the behaviour
of Prestressed Concrete (PSC) beams subjected to two point loadings in terms
of failure load, deflection and failure modes is evaluated. Effect of GFRP
strengthening on PSC beams before and after first cracking is measured.
Experiment includes testing of twelve simply supported PSC beams having
cross-section 150 mm x 200 mm with effective span of 3.0 meter. Four
unwrapped PSC beams, four PSC beams wrapped by GFRP after initial
loading up to first crack and four uncracked PSC beams strengthened using
GFRP are tested up to failure. Four different wrapping patterns are executed
on beams. For (2L/7) and (2L/ 6) span loadings, wrapping of full length at
bottom and up to 1/3rd of depth is provided, forming a U-shape around the
beam cross-section. For (2L/4) span loading, wrapping of full length at
bottom and up to 1/3rd of vertical depth is provided and extra wrapping near
the supports is provided. For (2L/3) span loading, U shape wrapping is
provided near the supports, for full depth. It is observed that in (2L/7) and
(2L/6) span loadings, compared to unwrapped PSC beams, the FRP wrapping
along longitudinal direction, reduces deflections and increases the load
carrying capacity for wrapped PSC beams. In (2L/4) span loading, combination
of vertical and horizontal GFRP sheets, together with a proper epoxy
adhesion, lead to increase the ultimate load carrying capacity for wrapped
PSC beams. In (2L/3) span loading, presence of vertical GFRP sheets near
support reduces the shear effects considerably and increase load carrying
capacity.
Jun Deng et al (2011) conducted an investigation on the “Flexural
strength of steel–concrete composite beams reinforced with a prestressed
CFRP plate”. Experimental studies have reported that externally-bonded
CFRP plate can effectively improve the stiffness and strength of steel–
concrete composite beams. This paper presents an analytical solution
developed to calculate the flexural strength of strengthened composite beams.
38
The solution assumes certain failure modes and varies the locations of the
neutral axis. Non-linear Finite Element (FE) method was also used to
calculate the flexural strength of the strengthened composite beams.
Experimental results from literature were employed to validate both the
analytical and the FE results. The findings show that the FE analyses are in
good agreement with the test data in load–deformation curves. The flexural
capacity obtained from the closed-form solution and the FE analyses have a
reasonably overall agreement with the experimental results, which
demonstrates the present closed-form solution is simple yet accurate. The
analyses also show the flexural strength is not influenced by the permanent
load and the prestressing force when failure results from rupture of the CFRP
plate, but the flexural strength reduces with the permanent load and increases
with the prestressing force when failure results from crushing of concrete.
Luciano Ombres (2011) conducted a study on the “Flexural
analysis of reinforced concrete beams strengthened with cement based high
strength composite material”. The structural behaviour of reinforced concrete
beams strengthened with a system made by fibre nets embedded into an
inorganic stabilized cementitious matrix named Fibre Reinforced
Cementitious Mortars (FRCM), was investigated in this paper. The main
issues focused in the paper are: (i) the strengthening effect of the FRCM
system on the flexural behavior of reinforced concrete beams in terms of
ultimate capacity, deflections and ductility and (ii) the influence of the fibre
reinforcement ratio on the occurrence of premature failure modes. The
analysis refers to a FRCM system made by ultra-high strength fibre meshes
such as the Polypara-phenylene-benzo-bisthiazole (PBO) fibres; PBO fibres
have, in fact, great impact tolerance, energy absorption capacity superior than
the other kind of fibres and chemical compatibility with the cementitious
mortar. A total of 12 reinforced concrete beams strengthened in flexure with
39
the PBO-FRCM system have been tested. The influence of some mechanical
and geometrical parameters on the structural behavior of strengthened beams
is analyzed both at serviceability and the ultimate conditions. Results of a
comparison between experimental results and theoretical predictions, obtained
by models usually adopted for the analysis of FRP strengthened concrete
structures, are, also, presented and discussed.
Hossain and Awal (2011) conducted a study on an “Experimental
validation of a theoretical model for flexural modulus of elasticity of thin
cement composite”. Experimental and analytical investigations for the
modulus of elasticity of thin cement composite composed of mesh and mortar
are demonstrated. Based on the analyses and experimental data, new equations
for the modulus of elasticity of thin cement composite are proposed. It is
observed that the flexural modulus of elasticity of thin cement composite
depends on the elastic modulus of mortar and some factor of the difference of
elastic modulus of mesh and mortar. Results obtained by using the proposed
equations are compared to those of the available equations. It has been found
that the newly developed equations give relatively conservative results as
compared to the typically used ones. A comparison between the analytical and
experimental findings further indicates that there is a good agreement between
the analytical and experimental results.
2.6 CRITICAL REVIEW
Since 1984 the ferrocement plates are used mainly for water
storage tanks and boat construction. Later on many researchers identified a
field wherein the ferrocement can be used for different application such as
elevations, repair, and rehabilitation and retrofitting, waterproofing with
in-situ applications etc., Later on Horizontal extension of buildings,
40
Ferrocement plated RCC structures with inbuilt formwork with steel
reinforcement incorporated used both as permanent formwork and element.
But all the applications are with conventional ferrocement where the
conventional cement mortar is only used. This kind of construction does not
resulted in full economy. To make it more ductile and converting it as a best
material for disaster resistant, to cater the needs of the present seismic
condition this study was carried out.
Only qualitative aspects of these behaviours with reference to
conventional concrete mortar are available. Experimental studies dealing with
the above characteristics are inadequate. In this research, the mechanical
properties of ferrocement elements had been improved by adding fibers with
the bundled weld mesh. In addition to avoid the vibration cost of concrete and
to place the concrete in all the nook and corners of formwork self compacting
concrete was used in this modern Hybrid Ferrocement slab. To improve the
workability and to reduce the water-cement ratio the mineral admixture
silicafume was also used as partial replacement of cement. More research
works were carried out with one and two layers of GFRP wrappings to
enhance the impact resistance characteristics at the tension face of HF slabs.
2.7 RESEARCH PLAN
The overall research plan is given in a flow chart in Figure 2.1. The
entire research work is done as mentioned in the flow chart.
42
2.8 SCOPE OF THE PRESENT RESEARCH
In light of the above observations, an experimental study of the mechanical behaviour of hybrid ferrocement slabs was carried out. The objectives of this study are to:
1. study the flexural behavior of ferrocement slab
2. study the deformation characteristics
3. study the Impact Strength
4. develop an analytical model for flexural strength, deflection at service stage, ductility factor and Impact energy absorption capacities.