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.

41

Figure 2.1 The overall plan of research work

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.