CHAPTER2

REVIEW OF LITERATURE

2.1 GENERAL

Ferrocement is a highly versatile reinforced composite material made of cement mortar

and layers of wire mesh, closely bound together to create a stiff structural form which

posses high strength to weight ratio. According to the definition given by ACI committee

549 in its state-of-the-art report on Ferrocement (ACI 549 R-97, 1997) is a type of "thin

walled reinforced concrete commonly constructed of hydraulic cement mortar reinforced

with closely spaced layers of continuous and relatively small diameter wire mesh".

Because of its excellent strength, cracking resistance and impact resistance, the

ferrocement has been used for housing units, as roofing or flooring elements, construction

of boats, water tanks, marine structures and grain silos etc. The strength is mostly derived

from curvilinear and undulating shape hence it can span long distance with reduced

number of costly supports.

A ferrocement construction unlike other sophisticated construction requires minimum

number of skilled labours and utilizes readily available local materials. Proper attention

should be required to control the quality of construction; otherwise the purposes of thin

shell ferrocement construction will be upset. To exploit the potential of ferrocement as a

construction material, a proper understanding of material behaviour under different

conditions is essential (Paramasivam et al., 2004).

The most important advantages of ferrocement are that it can be fabricated into almost

any desired shape to meet the need of the user. It is being extensively used in developing

countries like India, Indonesia and Srilanka for (a) Housing applications (b) Marine

application (c) Agricultural application (d) Rural energy application (e) Water and

5

Sanitation application and (f) Repair and maintenance applications (Mansur et al. 1987,

Paramasivam et al. 1990, Ganesan , 1994 ).

For highly stressed structures like boats, barrages etc, steel rods along with the wire mesh

is considered as a component of the reinforcement, imparting structural strength and

stiffness whereas in most of the terrestrial structures wire mesh is treated as the main

reinforcement. The reinforcement network should be securely welded or fastened

together, so that it remains in its original position during the application of mortar ( ACI

549R-97 1997, Swamy 1984 ). In highly reinforced structures, the arrangements of the

steel rod and mesh should be in such a manner that to allow adequate penetration of

mortar so as to resulting a void free dense material.

To obtain a good quality hardened mortar, the placing and compacting of the mortar must

be followed by proper curing in a suitable environment during the early stages of

hardening (Andal et al., 2003). The objective of curing is to keep the mortar saturated

until the originally water filled space in the fresh cement paste has been filled to the

desired extent by the products of hydration of cement.

Ferrocement is ideally suited for thin-walled structures. In addition to this many other

uses of ferrocement as a structural material are being explored throughout the world.

These includes sunscreens and sandwich wall panels for high rise buildings (Mansur

1987, Paramasivam 1990) permanent forms for conventional concrete construction,

biogas digesters, floor decks, swimming pools, water towers, small deck bridges, culverts

and ferrocement encloser for geotechnical centrifuge. Recently ferrocement has been

found to be extensively used in repair and maintenance of building (Romualdi 1987,

lorns 1987).

2.2 COMPARISON WITH REINFORCED CONCRETE

The major differences between the ferrocement and the conventional reinforced concrete

structural elements can be enumerated as follows (Swamy, 1984 ) .

6

a. Ferrocement elements are normally thin; thickness is rarely exceeding 25mm. But

conventional reinforced concrete structures are relatively thick sections exceeding

100mm.

b. Ferrocement normally contains a greater percentage of reinforcement. The

reinforcements consist of large amount of small diameter wires or wire meshes

discretely placed instead of reinforcing bars in reinforced concrete structures.

c. Ferrocement matrix mainly consists of Portland cement and sand as mortar

instead of concrete, which contains coarse aggregate.

d. In terms of structural behaviour, ferrocement exhibits very high tensile strength to

weight ratio and superior cracking performance than reinforced concrete

structures.

e. For the construction of ferrocement structures, formwork is often not needed.

This permits economical construction of certain structures such as domes, wind

tunnels etc.

2.3 ADVANTAGES OF FERROCEMENT

Ferrocement is a suitable technology for developing countries due to the following

reasons:

I. Ferrocement structures are thin and light.

2 It requires little or no formwork.

3 Its raw materials are readily available in most countries.

4 It can be fabricated to any desired shape.

5 The skills for ferrocement construction can be acquired easily.

6 Heavy plants and machinery are not involved in construction.

7 It is relatively inexpensive.

2.4 TERMINOLOGY USED IN REINFORCEMENT

Two important reinforcing parameters commonly used in charecterising ferrocement are

(i) Volume fraction of reinforcement and (ii) Specific surface of the reinforcement (ACI

549R-97 1997 , Ferrocement model code 200 I).

7

(a) Volume fraction of reinforcement: VR

It is the total volume of reinforcement per unit volume of ferrocement. For a ferrocement

reinforced with square meshes, V R is equally divided into V RL and V RT for the

longitudinal and transverse directions respectively.

Vn = V reinforcement-------------- (2.1)

V composite

The volume fraction of reinforcement can be divided into longitudinal and transverse

parts, that is

Vn = V RL + V RT -------------- (2.2)

(b) Specific surface of reinforcement: SR

It is the total bonded area of reinforcement (interface area) per unit volume of composite.

For a ferrocement unit square mesh, SR is divided into SRL and SRT in the longitudinal and

transverse directions respectively.

Sn = Total surface area of reinforcement -------------- (2.3)

Volume of composite

Sn can be divided into longitudinal and transverse components, that is

Sn =SRL + Snr -------------- (2.4)

The relation between SR and V R , when wire mesh are used in (ACI 549R-97, 1997).

SR 4VR , Where <p is the diameter of the wire

(f)

The total volume fraction of reinforcement VR in each direction should not be Jess than

1.8 percent (Ferrocement model code, 2001 ). The total specific surface of reinforcement

SR in both directions should not be less than 0.08 mm2/mm3. About 2 times these values

are recommended for water retaining structures. In computing the specific surface of the

reinforcement, any skeletal steel may be disregarded, but it should be considered in

computing V R (Ferrocement model code, 2001 ).

8

2.5 FERROCEMENT FLEXURAL ELEMENTS

The flexural behaviour and properties of ferrocement have been extensively investigated

by number of researchers. Ferrocement roofs, floor slabs, beams etc. are gaining

importance now a day. In these cases ferrocement element is subjected to flexural action.

When compared to RCC element the tensile strength to weight ratio of ferrocement is

large. The ultimate moment in the case of R.C.C is a property of the section since the

matrix in the tensile zone of the bending element is fully cracked and do not contribute to

the resistance at the ultimate stage, where as in the case of ferrocement, it is not so.

2.6 REVIEW OF STUDIES ON FERROCEMENT FLEXURAL ELEMENTS

A large number of experimental and analytical studies have been reported in this area.

The strength of flexural members can be predicted by analysing ferrocement as a

reinforced concrete member using the ACI Building Code (ACI 318-08, 2008 ). Different

analytical methods proposed by the researchers to predict the ultimate moment carrying

capacity of ferrocement gives satisfactory correlation with experimental values. The

design requirements of ferrocement includes volume fraction, specific surface,

percentage of reinforcement, orientation of reinforcement and the severability

requirements such as deflection and crack width (Balaguru et al., 1977 ). Expanded

metal and square welded mesh in their normal orientations are most effective in flexure

than any other types of reinforcement. But hexagonal mesh is particularly suited to

complex doubly-curved section, square mesh to single-curved sections and expanded

metal to planar sections. The maximum crack width in tension and flexural members for

square mesh reinforcement can be predicted by using the approaches described in

reference (Mansur, 1988). The research work carried out in the field of flexural

behaviour of ferrocement elements in Asia, Europe and USA are discussed here in the

following heads.

9

2.6.1 STUDIES FROM ASIA

In the early 1940' s Pier Luigi Nervi (ACI 549R-97, 1997) resurrected the original

ferrocement concept. After the Il0d World War, Nervi demonstrated the utility of

ferrocement as a boat-building material. The International Ferrocement Information

Center (IFIC) at the Asian Institute of Technology was established in Bangkok, Thailand

in 1976. Now ferrocement is very extensively used in the production of structural

elements in repair and maintenance work (Romualdi , 1987 ).

Mansur and Paramasivam (1986) conducted an experimental and analytical

investigation on flexural behaviour of ferrocement element to study the cracking

behaviour and ultimate strength. Based on the concept of plastic analysis a method is

proposed to predict the ultimate moment capacity of ferrocement and which is in good

agreement with the experimental values. From the study it was established that the first

crack moment and ultimate moment were increased with increase in matrix grade and

volume fraction of steel. They also concluded that higher volume fraction of steel

provides more effective control of crack width.

Walkus (1986) made an attempt to determine the parameter to perform the testing of

material of ferrocement, new laws for defining the properties of the structure and

equipments for testing and measuring devices to determine the deformation and cracking.

Atsushi Shirai and Yoshihiko Obama (1988) conducted an experimental study to check

the improvement in flexural behaviour and impact resistance of ferrocement by the use of

polymer. From their study, they found that first crack load, ultimate load and cracking

resistance were increased and the occurrences of cracks and increase in number of cracks

were considerably restrained by the addition of polymers. Impact resistance is also

increased by the use of polymer modified mortar.

10

Karunakar Rao and Jagannadha Rao (1988) proposed a theory for the computations of

ultimate moment of ferrocement structural elements based on the experimental evidence

for the crack patterns, extent and propagation of cracks.

Desayi et al. (1988) proposed a bi-linear method to predict the deflections and another

two methods for crack formation and ultimate moments of ferrocement elements. These

methods are found to give satisfactory agreement with test data.

Ganesan and Suresh Kumar (1988) carried out an experimental investigation to study

the effect of discrete short steel fibres on the strength and behaviour of ferrocement

structural elements of channel cross-section. The results indicated that the addition of

steel fibres increases the strength and energy absorption capacity of ferrocement

elements.

Desai and Desai (1988) developed and tested ferrocement roofing elements of different

shapes, in order to check the suitability and load carrying capacity for low cost housing.

The study concluded that out of all the shapes considered, folded shaped ferrocement

elements exhibited higher stiffness and ultimate moment carrying capacity. Also it was

proved that the cost of ferrocement folded plate element is about 15 to 25% less than that

of the asbestos cements sheets.

Lohtia et al. (1988) conducted an experimental study on flexural behaviour of

ferrocement slabs. They observed that cracking pattern for ferrocement slab is quite

different from that of RCC slabs. In ferrocement slabs the cracks are numerous and much

more fine and distributed over larger area than in the case of RCC slabs. Also it was

found that ferrocement slabs have greater extensibility and higher reserve strength than

RCC slabs.

Rao and Rao (1988) carried out an investigation to evolve an acceptable and rational

method for computing the ultimate moment of resistance of ferrocement channel units.

Their study indicated that the analysis of crack pattern and deflections gave an insight

11

into the mechanics of the mobilization of moment of resistance of the ferrocement

channel unit.

Ganesan et al. (1988) conducted an experimental study on development and proof

testing of a ferrocement roofing system. The development and proof testing of a

composite roof I floor system consists of partially prefabricated ferrocement trough units

and in situ concrete topping. The tests were intended mainly to study the flexural

behaviour of partially prefabricated ferrocement trough unit as an individual element and

also as a composite element with in-site concrete. The results showed that the structural

behaviour of the ferrocement trough units as well as the composite units was found to be

quite satisfactory.

Naaman (1989) conducted a study on the different levels of technology used in

ferrocement housing products. The study suggested that common housing requirements

could be satisfied from a pool of about fifteen standard panel configurations. Box shaped

panels were considered for the walls and lintels, while U shaped panels were considered

for flooring and roofing.

Vijay Raj (1990) conducted an experimental and theoretical study to predict the

structural behaviour of large span bamboo ferrocement elements for flooring and roofing

purposes. The study concluded that the large span bamboo ferrocement slab should have

a thickness of 40mm to meet the requirements of roofing and flooring elements of

reinforced buildings. Also they concluded that the cost of bamboo ferrocement slab was

only 70% of the ferrocement slab.

Mathews et al. (1991) carried out an analytical and experimental investigation of

cracking load, ultimate load, deflection, crack spacing and crack width of a hollow

ferrocement roofing system. The test results confirmed that the system has adequate

strength, stiffness and other serviceability requirements for residential applications. The

predicted theoretical values are in good agreement with experimental values.

12

Desayi et al. (1992) carried out an experimental investigation to study the first crack

strength and modulus of rupture of light weight fibre reinforced ferrocement in flexure.

From the study they found that volume fraction of steel fibre control the modulus of

rupture and first crack strength of ferrocement elements. They also developed an equation

to predict the first crack strength and modulus of rupture.

Wail AI-Rifaie and Arsalan Hassan (1994) carried out an experimental and theoretical

study on the behaviour of ferrocement one-way bending elements. Elements of different

spans and widths were chosen to study their relative feasibility for adoption to roofing of

small size residential houses. As the result of investigation it was concluded that one-way

bending element undergo large deflection before failure and this is mainly attributed to

the reinforcements. Also they found that, due to the increase in flange width, the ultimate

load capacity is decreased but the ratio of ultimate load capacity to the first cracking load

is increased due to the increase in span length.

Mathews et al. (1994) conducted a study in planning aspects of ribbed ferrocement

elements for low cost housing considering the principles of modular co-ordination. The

study concluded that construction procedure can be made simple by the adoption of

modular co-ordination and by the use of simple manufacturing plant; mass production for

the elements can be easily achieved.

Ganesan and Suresh Kumar (1994) had done an experimental investigation on

prediction of moment capacity of fibrous ferrocement flexural members. The main

objective of this study is to determine the effect of randomly oriented short discrete steel

fibers on the strength and behaviour of ferrocement flexural elements. The results

indicated that the addition of steel fibres increases the moment capacity of ferrocement

flexural elements significantly. A method for the prediction of the moment capacity of

the element was proposed in this study.

13

Hossain et al. (1997) conducted a study to develop an analytical model for flexural and

tensile behaviour of ferrocement plates in the pre and post cracking stages. From the

study they established that two-way ferrocement slabs can take 10%-30% more loads

than that of the one way slabs.

Mansur et al. (2000) carried out at flexural test on thin walled ferrocement structural T,

inverted T and symmetrical I-section to facilitate rapid assessment of flexural strength

and expedite the design charts for structural section. They developed typical design charts

and indicated the existence of considerable ductility for thin wall pandas suggesting that a

rigid plastic analysis should be applicable to predict their ultimate moment capacities.

AI-Kubaisy and Mohd Zamin Jumaat (2000) has carried out at a study on flexural

behaviour of reinforced concrete slabs with ferrocement tension zone cover. The

variances are 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 RCC slab. The results showed that the use of ferrocement cover slightly

increases the ultimate flexural loads and first crack loads and reduces the crack width and

spacing's.

Seshu (2000) conducted an experimental study on ferrocement confined reinforced

concrete beams. Their study concluded that confinement by ferrocement shell improve

the moment carrying capacity by about 9 to 15% and also increases the first cracking

moment.

Rathish kumar and Rao (2000) carried out an experimental investigation to study the

stress-strain behaviour of ferrocement confined reinforced concrete (FCRC) under axial

compression by varying the specific surface factor and confinement index. Study

concluded that improvement in ductility is proportional to the specific surface factor of

ferrocement for a given confinement index.

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Mansur et al. (2001) conducted an investigation to find the shear strength of ferrocement

structural sections. The study concluded that the flexural cracks occurred initially

irrespective of the span/depth ratio but first cracking and ultimate load were decreased

when the span/depth ratio was increased.

Imam et al. (2002) undertaken a study to simulate deflection and stress behaviour of

different type of roofing elements by finite element techniques. From the investigation

they established that the numerical results are matching quite well with the experimental

results. The principal stresses are less in the segmental shell element and this is most

economical shape as a roofing element.

Vijaya and Hedge (2003) conducted an experimental study on ferrocement confinement

of concrete beams made of brickbat and recycled concrete aggregate. Their study proved

that there was a significant increase in stiffness, strength and ductility of the beam due to

ferrocement confinement.

Andal et al. (2003) carried out a study on the flexural strength and impact resistance of

ferrocement specimens cured under seawater and ordinary water. They found that due to

the penetration of seawater in ferrocement elements, the sea water cured specimens

showed a reduced strength in flexure and impact.

Jaganathan et al. (2003) studied the suitability of polymer mesh as an alternative for

reinforcement in ferrocement flexural elements. The results indicated that the four

layered polymeric mesh reinforcement ferrocement element satisfy the IS requirements

such as lower deflection, higher young's modulus, comparable flexural strength and

reduction in crack width with increase in number of layers of mesh.

Veerappa Reddy (2003) conducted a study on industrialised production of innovative

ferrocement element. Study describes the industrial production of ferrocement elements

such as sumps and septic tanks, precast modular community toilets and pretensioned

undulated length sections for long spans.

15

Ramesh et al. (2003) conducted an experimental investigation on the behaviour of

Hybrid Ferro-Fibre concrete under axial compression. Parameters varied are specific

surface factor, reinforcing index of the fibre reinforced concrete. The results indicated

that the combined use of ferrocement and fibres has improved the ultimate strength, strain

at ultimate strength and the ductility of reinforced concrete. The improvement is

proportional to the specific surface ofreinforcement.

Jaganathan and Sundararajan (2004) carried out an experimental and theoretical

investigation to study the flexural behaviour of ferrocement slabs reinforced with 3-5

layers of polymer mesh as an alternative form of reinforcement. From the study it was

observed that polymer mesh reinforced ferrocement slabs exhibit the same linear elastic

behaviour up to the first crack load.

Paramasivam et al. (2004) conducted a detailed investigation on the origin, suitability

and application of ferrocement composite. The authors' discussed about the R&D works

done on ferrocement element and its applications such as sunscreens, secondary roofing

slabs, water tanks and repair material in building industries. The salient features of the

design, construction and performance of some of these applications of ferrocement

structural elements are highlighted.

Bhaskar Desai et al (2004) conducted an experimental investigation on the flexural

bahaviour of superplasticised partially cement replaced silica fume ferrocement elements

with shear span to depth ratio and with number of mesh layers as variables. The study

concluded that 10% of silica fume can be taken as the optimum dosage to replace cement

for giving maximum possible compressive strength, split tensile strength and modulus of

elasticity. Also found that the ultimate flexural strength increases with the increase in %

of silica fume up to 10% for a given shear span/ depth (a/0) ratio and a given number of

wire mesh layers.

16

Hago et al. (2005) conducted an experimental study on ultimate and service behaviour of

ferrocement roof slab panels. The study aimed at to determine the ultimate and service

behaviour of ferrocement roof slab panels. The results showed that the use of monolithic

shallow edge ferrocement beams with the panels considerably improves the service and

ultimate behaviour of the panels irrespective of the number of steel fibres.

Andal et al. (2005) carried out an experimental study on behaviour of ferrocement

flexural members with polymer modified mortar. The main objective of this study was to

determine the flexural strength of ferrocement element of size I 000mm x 200mm x

25mm with cement sand mortar 1: 1 and water cement ratio as 0.3. The variances used in

the study are different volume fraction of reinforcement, different percentage of SBR

polymer and different percentages of the Recrone 3S fibres. This study showed that

12.5% of SBR latex by weight of cement and a volume fraction of 3% gave the higher

collapse load.

Prem Pal Bansal et al. (2006) conducted an experimental study on effect of different

bonding agents on strength of retrofitted beams using ferrocement laminates. Study done

to determining the effect of retrofitting of beams using ferrocement laminates bonded

with cement slurry, epoxy and shear connectors. The study concluded that, the third point

loading on all the specimens showed reduced crack width, increased crack spacing, large

deflection at ultimate load and a significant increase in ductility ratio.

Prakash and Patil (2007) conducted an experimental study on effect of addition of silica

fume on strength characteristics of fibrous ferrocement using round steel fibres. Study

indicates that fibrous ferrocement is a combination of ferrocement and fibre reinforced

concrete, shows better improvement in the mechanical properties such as toughness and

impact resistance. This composite also shows higher compressive, tensile and impact

strength.

17

Anila kumar et al. ( 2007) carried out an experimental investigation to study the effect

of addition of SBR polymer in different proportion to polypropylene fibre reinforced

concrete. The results indicated that the addition of SBR polymer to the fibre required

concrete increases the workability and increases the compressive strength, tensile

strength and flexural strength.

Prakash and Patil (2007) carried out an investigation on the effect of sustained

temperatures on the strength properties of fibrous ferrocement containing steel fibres. The

study concluded that the compressive strength, flexural strength and impact strength of

fibrous ferrocement can be enhanced either by increasing percentage of steel fibres or by

increasing specific surface area of welded mesh and chicken mesh in sustained

tern perature.

Sudhikumar and Prakash (2007) conducted a test to find the compressive strength,

flexural strength and impact strength with slurry infiltrated fibrous ferrocement with

superplasticiser. The result of the study indicated that there is increase in compressive,

flexural and impact strength with increase in the partial replacement of metakaolin with

increasing temperature.

Patil and Prakash (2007) made an attempt to study the effect of replacement of cement

by fly ash on the strength characteristics such as compressive strength, flexural strength

and impact strength of fibrous ferrocement using flat steel fibers. The percentage of flat

steel fibres were varied from 0% to 2% with the increment of 0.5%. The cement was

replaced by fly ash in different percentages like 5%, 10%, 15%, 20% and 30% etc.

Prem Pal Bansal et al (2007 ) conducted a study on shear deficient RC beam initially

stressed to a prefixed percentage of the safe load, are retrofitted using ferrocement. To

increase the strength of beam in both shear and flexure, the wire mesh is placed at an

angle 45° to the longitudinal axis of the beam. From the study it was concluded that the

safe load carrying capacity of rectangular RC elements retrofitted with ferrocement

laminate is significantly increased with mesh oriented at 45° .

18

Patil and Prakash (2007) carried out an experimental investigation in effect of addition

of silica fume on strength characteristics' of fibrous ferrocement using round steel fibres.

Study concluded that the addition of round steel fibres in ferrocement composite shows

better improvement in some of mechanical properties, such as toughness and impact

resistance.

Laigude Atual et al. (2007) conducted a study of micro structural analysis with different

combination of wire mesh reinforcements. Panels' of different combinations were tested

for flexure under uniformly distributed load and its deflection and cracking patterns were

observed and studied.

2.6.2 STUDIES FROM EUROPE

The use of ferrocement as roofing for large span has been successfully used in many

European and South American countries. Large ferrocement roofs have been constructed

in Italy.

Onet and Magureanu (1993) made an attempt to study the flexural behaviour of

ferrocement beams under long term loading. Their results indicated that the long-term

deflection influences the behaviour of beams much more than the instantaneous one.

Mattone (1995) conducted a study on design and testing of a ferrocement roofing

element. This study proposed operational stages for the development of a simple roofing

element and equipment necessary for the small-scale production.

Gurdev singh and Guang Jing Xiong (1995) performed a study on rational assessment

of flexural fatigue characteristics of ferrocement for reliable design. Study based on a

stress-life (S-N) plot and a new method proposed based on a probability -stress-life (P-S­

N) for the design of the flexural fatigue characteristics of ferrocement. Study concluded

that a rectangular stress distribution is relatively more reliable and economical for

19

predicting stress when designing ferrocement against fatigue by usmg the P-S-N

relationship of wire tested in the air.

Ramesht and Vickridge (1996) made an attempt to develop a computer program

F AOFERRS to predict the ultimate moment of ferrocement under flexure. The study

proved that the F AOFERRS program has in good agreement with the experimental values

and it is easy to use.

Nedwell and Nakassa (1999) carried out an experimental investigation into high

performance ferrocement. The results showed that stainless steel and silica fume improve

the first crack load, increase the number of cracks and decrease the crack width m

addition to the cost effectiveness.

Pankaj et al. ( 2007) carried out a study on mechanical behaviour of ferrocement

composite- numerical simulation. Authors proposed an anisotropic elastoplastic models

to simulate the mechanical behaviour of ferrocement plates. The study indicates that the

mortar ferrocement layered model with orthotropic ferrocement layers performs the best.

Also determined that, a single set of material properties can be used to simulate the

behaviour of ferrocement plates under in-plane as well as out of plane loading.

2.6.3 STUDIES FROM USA

Naaman and Homrich (1986) proposed a general methodology for the analysis and

design of ferrocement flexural elements. The proposed method and the developed design

charts are very simple and could be used to predict the flexural resistance of ferrocement

element.

Balaguru et al (1990) proposed an analytical model to study the ductility of ferrocement

flexural element. The study concluded that the type of reinforcement distribution and

reinforcement ratio affects the ductility only to a small extent but ductility increases for

20

thin section. The literature shows that ferrocement flexural elements of different shapes

can be very effectively used as roofing I flooring element in developing countries.

Hani et al. (2004) have done an experimental and analytical investigation on ferrocement

concrete composite beams made of reinforced concrete overlaid on a thin section of

ferrocement. Various types of beam specimens with different types of meshes are tested

under a two point loading system up to failure. Study concluded that the proposed

composite beam has good ductility, cracking strength and ultimate capacity.

In this thesis an attempt was made to obtain an optimum ferrocement sections. So a brief

review on optimisation techniques was done. A literature review of studies done on

optimisation of ferrocement elements and reinforced cement concrete elements are given

below:

Many researches have been carried out in various optimisation techniques to optimise the

cost of construction of different shaped ferrocement elements and for the design of

reinforced concrete structures (Rajeev et al., 1998).

Goldberg (1989) has given an introduction to Genetic Algorithm (GA) approach for

engineering optimisation. This has significant applications in structural optimisation

problems. Many investigators made use of this approach for optimising the shape and

cross-section of structural elements.

Rajeev and Krishnamoorthy (1992) extended the application of GA into discrete design

variables for optimising the minimum weight of steel trusses, considering the deflection

and buckling strength as constraints.

Syam Prakash, Rajeev and Mathews (1995) carried out an analytical study to obtain an

optimal design methodology for ribbed ferrocement roofing/flooring elements using GA.

The variables considered were the cross sectional shape and the details of reinforcement.

21

The study concluded that the GA based design optimisation methodology provides

techniques for modelling in a realistic manner which leads to rational solution.

Kalyanmoy Deb (2004) has published a book on an introduction to Genetic Algorithms.

The author identified that a simple genetic algorithm is an optimisation technique that

relies on parallels with nature, and a simple analogy can be made with a mathematical

problem, made up of many parameters. These parameters can take the place of a

chromosome in the mathematical analogy of a real chemical sequence. Author suggested

the steps and the operations of the simple genetic algorithms.

Govindraj and Ramasamy (2006) have published a paper on optimum design of

reinforced concrete rectangular columns using Genetic Algorithms. Their study

concluded that the optimum design model using GA provides an ideal technique to model

practical design considerations such as predefined discrete variations in breadth and

depth of column sections, detailing and placing of reinforcement bars. They have

proposed a new optimisation technique which is less mathematically complex.

Pranab Agarwal and Anne M. Raich (2006) carried out a study on design and

optimisation of steel trusses using GA parallel computing and human computer

interaction. Authors conducted study on a hybrid structural design and optimisation

methodology that combines the strength of GA to evolve optimal truss systems. The

application of GA to the design and optimisation of truss system supports conceptual

design by facilitating the exploration of new design alternatives.

Castilho and Lima (2007) conducted an analytical study on cost optimisation of lattice

reinforced joist slabs using Genetic Algorithm with continuous variables. The results

indicate that the GA method is a viable optimisation tool for solving cost optimisation

problem for lattice reinforced joist slab.

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2.7 BEHAVIOUR OF FERROCEMENT UNDER FLEXURE

The following are the assumption made in the flexural theory of ferrocement ( Paul and

Pama 1978, Swamy 1984 ).

I. Plane sections remain plane and perpendicular to the neutral axis, i.e. the strain in

mortar and reinforcement is directly proportional to their distance from the

neutral axis.

2. The behaviour of reinforcement is elastic perfectly plastic i.e. for stress less than

yield strength, steel stress is proportional to strain and after yielding stress in steel

remains constant at the yield strength,J;,.

3. Tensile strength of mortar is neglected in flexural strength calculation of cracked

beams.

4. Maximum usable compression fibre mortar strain is 0.003.

5. For strength calculations at ultimate load, the parabolic stress-strain distribution

of mortar can be approximated to a rectangular distribution.

The behaviour of ferrocement in flexure can be analysed using a typical load deflection

plot.

The load deflection curve can be divided into three regions or stages namely: (Paul and

Pama 1978, Md. Zakaria et al. 1997 )

(a) Pre-cracking stage,( b). Post cracking stage and ( c) Post-yielding stage

a. Pre Cracking stage

Ferrocement has the highest stiffness in the pre-cracking stage. In this stage mortar

contributes to both compressive and tensile resistance of the composite. The strength

and stiffness of the beam can be calculated using the classical bending theory.

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b. Post Cracking Stage

The post cracking stage starts with the occurrence of the first crack. This stage extends

up to the point when the extreme fibre of reinforcement starts yielding. The load

deflection behaviour in this stage of loading represents the behaviour of ferrocement in

field conditions where almost all beams are cracked in the tension zone but the stress in

the extreme tension fibre is well within the yield strength.

The moment of resistance of the beam can be calculated by using the classical bending

theory as in the case of pre-cracking stage. However, since the section is cracked, some

modifications have to be made. This is because, after cracking, the tensile force

contribution of mortar is negligible compared to the contribution of reinforcement.

c. Post yielding stage

The post yielding stage corresponds to the stage when steel starts yielding and the cracks

are in the process of widening. The section attains ultimate moment capacity at the end of

this region. The ultimate tensile strain can be taken as the strain of the mesh

reinforcement at ultimate condition. The compressive strain at ultimate condition may be

taken as 0.006.

The details of evaluation of cracking moment and equations relevant to flexure are given

in Appendix.A.

2.8 COMMENTS ON REVIEW OF LITERATURE

From the review of literature the following points are noted,

(i) Large number of studies on strength and behaviour of ferrocement

elements subjected to tension, compression and flexure have been

carried out in the past.

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(ii) In most of these studies smaller scale specimen models have been

used in the investigation. Only some attempts on large scale or

prototype elements have been considered. However it may be

noted that in order to exhibit the realistic behaviour of the

structural elements it is advisable to consider prototype structural

elements.

(iii) Attempts have been made to obtain a relation between strength

parameters such as first crack load and ultimate load with variables

like volume fraction and specific surface of ferrocement.

(iv) In all the previous investigations the fine aggregate used for

making ferocement mortar was ordinary river sand. However it

may be noted that as river sand is becoming more and more scarce,

alternative to· river sand to be explored for optimum cost of

ferrocement elements.

(v) In the past, attempts were made to obtain the overall dimensions of

ferrocement flexural elements which are purely based on available

laboratory facilities, strength and stiffness concepts.

(vi) No attempts have been come across to obtain optimum cross

sectional shape of ferrocement elements with regard to (a) Flexural

strength (b) Deflection (c) Cracking and (d) Cost.

(vii) The earlier attempts were restricted to studies on strength and

behaviour of individual elements. However, investigations on the

combined action of elements are not reported. It would be more

meaningful if studies were done. on the strength and behaviour of

roofing or flooring structure which consists of number of elements.

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(viii) The matrix of ferrocement consists of cement, fine aggregate and

water. No attempts were made to improve the properties of

ordinary cement mortar by the special process like polymerisation,

which will improve many of the engineering properties like tensile

strength, fracture toughness and ducti Iity etc. of the ferrocement

composite.

(ix) In the earlier studies, the combined effects of optimum cross

section and polymer modification on prototype ferrocemnet

elements were not carried out.

From the above comments it may be noted that attempts on (a) Optimisation of

ferrocement structural element (b) the effect of polymer modification on strength,

stiffness, cracking behaviour and ductility of ferrocement elements (c) the

combined effect of the above have not been carried out. Hence there is a gap in

the existing knowledge which shows that there is a scope for research to fill the

above gap.

2.9 SCOPE FOR THE PRESENT INVESTIGATION

The main objectives of the study are,

(i) To carryout the investigation, to obtain the optimum cross sectional shape

of ferrocement flexural elements having the following cross sections,

(a) Channel (b) Trapezoidal and (c) Corrugated. As these cross sections

are often used in the building industries, this shape can be considered.

(ii) To study the strength and behaviour of polymer modified optimum

ferrocement structural elements.

(iii) To evaluate models for predicting (a) First crack load (b) ultimate load

(c) energy absorption capacity and (d) ductility.

(iv) To study the combined effect of ferrocement channel elements and to

obtain the number of connection bolts.

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2.10 METHODOLOGY

The scope of this present investigation will be carried out as per the following

methodology:

(i) To carryout the preliminary investigation to fix the optimum percentage of

polymer content and fine aggregate to be used in the study.

(ii) To carryout the optimisation techniques in Genetic Algorithm to fix the

optimum cross section of ferrocement flexural elements.

(iii) To carryout an experimental study on optimised prototype ferrocement

elements under third point loading with the different volume fraction of

mesh reinforcement and% of polymer content and

(iv) To develop models mentioned in the scope based on the test results

obtained in the experimental programme.

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