FABRIC FORMED CONCRETE

Cyprus International University Department of Civil Engineering

Ibrahim Inuwa Adamu

8TH December, 2015

TABLE OF CONTENT

• Title Page

• Table of Content

• Introduction

• Materials

• Mix Design and cost

• Techniques of Construction

• Applications

• Advantages

• Disadvantages

• Conclusion

• References

INTRODUCTION

Fabric formed concrete is a concrete which involves the use of geotextile fabrics as formwork for

concrete members. After the concrete hardens the fabric is either removed or left as an aesthetic.

Concrete which is a composite material composed of aggregates and a binder can be traced to a

few thousand years back. It was noticed from some Greek structures which still stand erect today

that some floors, arches, domes, vaults etc. were made of lime(binder) and pebbles(aggregate).

Modern day concrete came into existence after the discovery of Portland cement by Joseph

Aspdin in 1824. Concrete has evolved in terms of mix consistency, constituents, homogeneity and

applications over the centuries . Fabric formed concrete dates back to the roman times as history

has mentioned of a roman architect and engineer called Vitruvius explaining a method of

constructing two retaining walls by filling woven reed baskets with clay.

INTRODUCTION CONT’D

Reed is flexible and strong and was abundant at the time. This allowed the romans to build vaults,

cofferdams and underground chambers with it. Late within the second millennium some crucial

developments in fabric formed concrete took place and most of it is attributed to Gustav

Lilienthal. He was a German architect, builder, entrepreneur and inventor who had interest in

textile which led to him constructing a fabric formed suspended slab in 1899. The developments

made in the past 2 to 3 decades can be attributed to Prof. Mark West who is a builder and a

leading researcher of fabric formed concrete, Miguel Fisac, Kenzo Unno, Sandy Lawton and

Richard Fearn. These developments in fabric formed concrete has now allowed individuals to

freely express themselves through concrete with complex shapes, curves and forms.

MATERIALS

In the construction of fabric formed concrete the following materials are used

Geotextile fabrics

Self compacting concrete

Reinforcement

Concrete Canvas

GEOTEXTILE FABRICS are flexible fabrics of high strength which do not tare easily under loading.

They are sometimes referred to as polymer fabrics. They are made using polyolefin compounds

made from non-aromatic carbon and oxygen molecules. The woven geotextile fabrics are mostly

used.

There are two types that are used for fabric formed concrete

Woven Polyethylene fabrics

Woven Polypropylene fabrics

Woven Polypropylene is the most widely used in fabric formed concrete construction

POLYETHYLENE FABRICS

This was introduced in 1930

Properties :

It is flexible

They are resistant to Strong acids or strong bases and to gentle oxidants and reducing agents do

not harm it

Relatively lower melting point(Depending on its density)

Relatively weaker in strength(compared to polypropylene fabrics)

Non bio-degradable

POLYPROPYLENE FABRIC

This was introduced in 1950

Properties:

• It has a higher melting point(compared to polyethylene fabric)

• Relatively stronger and doesn’t tare easily

• It is relatively Lighter and degradable

• Relatively lower resistance to chemical deterioration

• It is Flexible

Fig. 1. Polypropylene Fabric

Fig. 3. Polypropylene Fabric

Fig. 2. Polyethylene Fabric

The figures below show examples of these fabrics

SELF COMPACTING CONCRETE is concrete which has a low yield stress, high deformability, and

moderate viscosity allowing it to flow easily and compact itself as it is placed without the use of

external compactor.

It consists of:

Aggregates

o Coarse aggregates: the shape and gradation are of concern here as they affect the mix

design. There should be a considerable amount of round shaped aggregates.

o Fine aggregate: the proportion is of concern(quantity)

Cement: Portland Cement is used in most cases but gypsum and other types of cement may also

be used depending on the outcome required.

Water

Mineral admixture such as fly ash are sometimes used to replace some quantity of cement

Viscosity Modifying Agent (in small quantity)

This is added so that fines content of a mix may be reduced without affecting the quality of the

concrete

Effects:

o Controls bleeding and segregation

o Enables flexibility in mix proportion

o Improves stability

High Range Water Reducers

Types

Steric hindrance: when this is used, a lower dosage is required.

o Acrylic copolymers

o Polycarboxylate

Electrostatic Repulsion

o Sulphunnated condensates of malamine

o Naphthalen Formaldehyde

Effects:

o It lowers the pumping pressure

o Increases workability

o Increases durability

REINFORCEMENT

Steel rebar

Steel wire mesh

Carbon Fibre mesh

Steel Fibre

Glass Fibre

CONCRETE CANVAS is a flexible, concrete impregnated fabric that hardens when hydrated to form

a thin, durable, water proof and fire resistant concrete structure(member).

The PVC backing is impermeable; water can not seep through it . It is prefabricated in a factory.

Fig. 4. Concrete CanvasFig. 5. Structure of concrete canvas

MIX DESIGN AND COST

MIX DESIGN

Normal concept of mix ratios are used except that the fines content is reduced if VMA is to be added

and increased if not. The proportions may be varied to suit the purpose for which the mix is to be

used. If mineral admixtures are to added they are considered when obtaining mix ratios.

Round aggregates are mostly used because they allow easier flow and thus minimum blockage

A low water cement ratio is used; water content of mix should be with in 160-200litres per cubic

meter of the concrete mix

Content of High Range Water Reducer is between 0.2% to 1.5%

Content of Viscosity Modifying Agent is Between 0.05% to 0.3%

Fig. 6. Difference of SCC mix and Normal concrete mix

COST

Woven Polypropylene fabrics cost with in a range of $1,ooo to $2,500 per ton(1000kg) or about $1 per

square meter.

The construction of fabric formed concrete is relatively cheaper.

• The flowability of the fresh concrete can be tested with the V-funnel test, whereby the flow time is

measured. The funnel is filled with about 12 litres of concrete and the time taken for it to flow through the

apparatus is measured. T 5min is also measured with V-funnel, which indicates the tendency for segregation,

wherein the funnel can be refilled with concrete and left for 5 minutes to settle. If the concrete shows

segregation, the flow time will increase significantly. According to Khayat and Manai, a funnel test flow

time less than 6s is recommended for a concrete to qualify for an SCC.

• The passing ability is determined using the L- box test. The vertical section of the L-Box is filled with

concrete, and then the gate lifted to let the concrete flow into the horizontal section. The height of the

concrete at the end of the horizontal section is expressed as a proportion of that remaining in the vertical

section (H2/H1). This is an indication of passing ability. The specified requisite is the ratio between the

heights of the concrete at each end or blocking ratio to be ≥ 0.8.

• From Table 7; Mixes TR1 to TR9 were considered as trial mixes, as these mixes do not fulfil all the

requirements of the SCC mix. SCC1 to SCC5 are the SCC mixes that satisfy all the properties of SCC mixes

and determination of optimum water-powder ratio was carried out for these mixes.

Fig. 7. SCC Requirement for Concrete Members

Fig. 8. Effects of Constituents on SCC

Techniques of construction

The techniques of construction can be categorized by the type of falsework used and the configuration of

the fabric and the falsework.

There are two types of false work used

Conventional falsework: the most widely used falsework in construction which is made of wood or steel.

Pneumatic falsework: is an inflatable balloon like falsework which is mostly used in the case of concrete

canvas or in the construction of domes and shells

There are different configurations of falsework and mostly each configuration is for a particular job. Some

of the configurations are:

The fabric is anchored at all edge and prestressed before the concrete is casted. The applied stress(pulling

or pushing) dictates the form of the casted member.

The fabric is anchored freely at the edges allowing the weight of the concrete to dictate the form and

shape of the casted member.

The fabric is anchored at four corners to create some buckling patterns; this is mostly done for shells.

The fabric is draped over two edges or rails; mostly used for beams. It could also be draped over two

tables.

The fabric is hung vertically from clips

The fabric is anchored at edges and draped over interior falsework

Two opposite edges of the fabric are joined clipped or stapled together to form a tube like formwork

The concrete can be applied in four different ways namely:

oBy hand- hands are used to rub and gently compact the concrete on an anchored fabric.

o Shotcrete- the use of shotcrete is mostly for fabric hung from clips to form thin shell after shotcreting.

o By pumping- the concrete is pumped using a concrete pump

o By pouring- this involves the use of pans, buckets or some kind of container to fetch and pour the

concrete into the fabric formwork.

Fig. 9. Column Formwork Fig. 10. Fabric Formed Beam

Fig. 11. Column Formwork

Fig. 12. Wall Panel Faleswork with Edge Anchorage and Interior Falswork

Fig. 13. Hanging formwork for Thin Shells

The influence of mechanical prestress is explained in terms of the two prestress directions which typically

correspond to the weave directions in woven fabrics. Figure 14 offers an indication as to what possibilities

are inherent in increasing one or both prestress values. Of course, these stresses act relative to the chosen

stiffness of the fabric and support conditions. The Gaussian curvature K is also shown for some categories,

where K is not equal 0 denotes double curvature, positive values = convex or concave shapes, and negative

values = saddle-like shapes. However, the type of fabric formwork does not necessarily dictate the expression

of curvature. If the applied prestress is low, the concrete loads will govern and force the formwork to bulge

outwards (forcing positive curvatures).

Fig. 14. Taxonomy of fabric formwork and formwork liners

APPLICATIONS

BEAMS

Rectangular and form-active structurally efficient beams can be constructed using fabric

formwork. The form-active structurally efficient beam consumes approximately 35% less

embodied energy than a comparable rectangular beam. The web of the beam is shaped to follow

the bending moment diagram for a specific type of load. The thickness of the flange of the beam

increases from the midpoint to the support and the web reduces in depth but widens to meet the

flange. Therefore the flange follows the shape of the corresponding shear force diagram. This

design configuration allows the beam to fail in flexure at mid-span by the primary steel yielding

and evades shear failure.

Fig. 11. Form-active Structurally Efficient Beam

Fig. 12. Form-active Structurally Efficient Beam

The concrete canvas is applied in

DOMES

REVETMENT BLANKET: to prevent river bank and shoreline erosion

FURNITURE: TABLES, COUCH ETC

DITCH LINING

How this is done can be seen in Fig. 17

Figures 15 and 16 show the step by step construction of a concrete canvas shelter

1. The concrete canvas is opened and unfolded

2. Then the attached inflatable balloon like falsework is inflated

3. The external surface of the concrete canvas is watered

4. Then it is left to dry and gain strength giving a rigid concrete structure

Fig. 16. Pneumatic falsework for concrete canvas

Fig. 15. construction of concrete canvas shelter

Fig. 17.

Professor mark West and his research team have applied their knowledge of fabric formed concrete in

the construction of some structures. Two of theses structures are :

Hanil Engineering & Construction Co. Ltd corporate guest house and visitors centre in Seoul Korea

where wall panels of fabric formed concrete where needed.

Women’s Hospital in Winnipeg Canada where slabs 6x3.5m supported by columns were constructed.

And also branch columns were constructed.

Figures 20, 21, 22, 23, 24 and 25 show these fabric formed concrete members and their formworks.

COLUMNS

WALL PANELS

TRUSSES

SHELL STRUCTURES

UNDERWATER PILES

Fig. 18. Hanil guest house

Fig. 20. Construction of Fabric Formed wall Panels for Hanil guest house

Fig. 19. Women’s Hospital Winnipeg Canada

Fig. 25. Wall Panel combined with Branched Column

Fig. 21 Falsework for 6x3.5m slab supported by column

Fig. 22 fabric formwork for 6x3.5m slab supported by column

Fig. 23 6x3.5m slab supported by columns for the Women’s hospitalFig. 24. Branched Column

ADVANTAGES

Less concrete is used due to the ability of the fabric to form structurally efficient members

Less reinforcement is required due the same reason

Beautiful surface finish and architectural aesthetics

Improved concrete quality is achieved

Strength and impermeability is increased by filtering of air bubbles and excess water

Cost savings ; fabric costs less than conventional formwork

carbon dioxide emissions reduction due to the less concrete used to form structurally efficient

members; for the manufacture of cement accountable for some 5% of global CO2 emissions.

DISADVANTAGES

Complexity of shapes and forms makes structural analysis of members difficult

The use of finite element method is required for structural analysis and design

In some cases it may take longer time to construct due to the fact that the formwork has to be

designed and in some cases modelled.

The structural efficiency of some members have not yet been understood

CONCLUSION

Fabric formed concrete has pushed the boundaries of shape and form in regards to concrete

structures or elements further out.

Both precast and in-situ members can be constructed with fabric formed concrete.

Much research has been done on the architectural aspect of fabric formed concrete and more

research needs to be done on the structural aspect.

REFERENCE

Prof Mark West, 2009, “Fabric Formwork for Concrete Structures and Architecture”, International

Conference on Textile Composites and Inflatable Structures, Structural Membranes.

Lee S H, 2010, Study of Construction Methodology and Structural Behaviour of Fabric Formed

Concrete Beam, PhD Thesis, University of Edinburgh.

B. Persson, “A Comparison Between Mechanical Properties of Self-Compacting Concrete and the

Corresponding Properties of Normal Concrete,” Cement and Concrete Research, Vol. 31, 2001, pp.

193 – 198.

A.M. Manelius, 2009, “Ambiguous Chairs Cast in Fabric Formed Concrete”, International

Conference on Textile Composites and Inflatable Structures, Structural Membranes, Centre for

Industrialised Architecture (CINARK ), Institute of Technology at the Royal Danish Academy of Fine

Arts, School of Architecture, Copenhagen, Denmark.