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Ferrocement structural applications P Paramasivam*, National University of Singapore, Singapore 26th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 27 - 28 August 2001, Singapore Article Online Id: 100026009 The online version of this article can be found at: http://cipremier.com/100026009 This article is brought to you with the support of Singapore Concrete Institute www.scinst.org.sg All Rights reserved for CIPremier PTE LTD You are not Allowed to redistribute or resale the article in any format without written approval of CIPremier PTE LTD Visit Our Website for more information www.cipremier.com

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Page 1: Ferrocement structural applications - CI  · PDF fileFerrocement structural applications ... Visit Our Website for more information ... The salient features of the design,

 

Ferrocement structural applications

P Paramasivam*, National University of Singapore, Singapore

26th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 27 - 28 August 2001, Singapore

Article Online Id: 100026009

The online version of this article can be found at:

http://cipremier.com/100026009

 

This article is brought to you with the support of 

Singapore Concrete Institute 

www.scinst.org.sg 

 

All Rights reserved for CI‐Premier PTE LTD 

You are not Allowed to re‐distribute or re‐sale the article in any format without written approval of 

CI‐Premier PTE LTD 

Visit Our Website for more information 

www.cipremier.com  

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26th Conference on Our World in Concrete & Structures: 27 - 28 August 2001, Singapore

Ferrocement structural applications

P Paramasivam*, National University of Singapore, Singapore

Abstract

Ferrocement is ideally suited for thin wall structures as the uniform distribution and dispersion of reinforcement provide better cracking resistance, higher tensile strength­to-weight ratio, ductility and impact resistance. By adapting available mechanised production methods and proper choice of reinforcements it can be cost competitive in industrialised countries. Research and development works of ferrocement, at the National University of Singapore, since early 1970's, has resulted in several applications such as sunscreens, secondary roofing slabs, water tanks, and repair material in the building industries. The salient features of the design, construction, and performance of some of these applications of ferrocement structural elements are highlighted in this paper.

Keywords: ferrocement, sunscreens, secondary roofing slabs, water tanks, repair and strengthening

1. Introduction In the early 1970's, labour intensive ferrocement construction was viewed as particularly suitable for

rural applications in developing countries. In urban environment like Singapore and other developed countries, the applications of ferrocement must be viewed from a different perspective due to the competitiveness in the construction industry and the increase in labour cost coupled with shortage of skilled construction workers. In order to alleviate these problems, mechanised production and proper choice of reinforcements must be pursued to ensure the cost competitiveness and speed of construction.

The National University of Singapore has since early 1970's made effort to popularise ferrocement as a construction material through research and development. Extensive investigations were carried out on its mechanical properties and several prototypes structural elements were built to demonstrate construction technique and to evaluate their performance in service [1-10]. From the experiences gained in these studies, considerable progress has been made in the use of ferrocement in public housing in Singapore as well as neighbouring countries. Ferrocement structural elements have gained gradual acceptance by the building authorities through research and development even though ferrocement design has not been regulated by a formal code of practice. ACI publications [11,12] also provide useful guidelines and information of technical know-how.

Ferrocement has a very high tensile strength-to-weight ratio and superior cracking behaviour in comparison to reinforced concrete. This means that ferrocement structures can be relatively thin, light and water-tight. Hence it is an ideally suited material for thin wall structures. A team of researchers at the Department of Civil Engineering, National University of Singapore, has collaborated with the local housing authorities and precast industries to introduce precast ferrocement structural elements in public housing. Several case studies involving the adaptation and successful implementation of the research results into

26th Conference on Our World in Concrete & Structures: 27 - 28 August 2001, Singapore

Ferrocement structural applications

P Paramasivam*, National University of Singapore, Singapore

Abstract

Ferrocement is ideally suited for thin wall structures as the uniform distribution and dispersion of reinforcement provide better cracking resistance, higher tensile strength­to-weight ratio, ductility and impact resistance. By adapting available mechanised production methods and proper choice of reinforcements it can be cost competitive in industrialised countries. Research and development works of ferrocement, at the National University of Singapore, since early 1970's, has resulted in several applications such as sunscreens, secondary roofing slabs, water tanks, and repair material in the building industries. The salient features of the design, construction, and performance of some of these applications of ferrocement structural elements are highlighted in this paper.

Keywords: ferrocement, sunscreens, secondary roofing slabs, water tanks, repair and strengthening

1. Introduction In the early 1970's, labour intensive ferrocement construction was viewed as particularly suitable for

rural applications in developing countries. In urban environment like Singapore and other developed countries, the applications of ferrocement must be viewed from a different perspective due to the competitiveness in the construction industry and the increase in labour cost coupled with shortage of skilled construction workers. In order to alleviate these problems, mechanised production and proper choice of reinforcements must be pursued to ensure the cost competitiveness and speed of construction.

The National University of Singapore has since early 1970's made effort to popularise ferrocement as a construction material through research and development. Extensive investigations were carried out on its mechanical properties and several prototypes structural elements were built to demonstrate construction technique and to evaluate their performance in service [1-10]. From the experiences gained in these studies, considerable progress has been made in the use of ferrocement in public housing in Singapore as well as neighbouring countries. Ferrocement structural elements have gained gradual acceptance by the building authorities through research and development even though ferrocement design has not been regulated by a formal code of practice. ACI publications [11,12] also provide useful guidelines and information of technical know-how.

Ferrocement has a very high tensile strength-to-weight ratio and superior cracking behaviour in comparison to reinforced concrete. This means that ferrocement structures can be relatively thin, light and water-tight. Hence it is an ideally suited material for thin wall structures. A team of researchers at the Department of Civil Engineering, National University of Singapore, has collaborated with the local housing authorities and precast industries to introduce precast ferrocement structural elements in public housing. Several case studies involving the adaptation and successful implementation of the research results into

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economical and beneficial applications of ferrocement. The salient features of the design, construction and performance of these ferrocement structural elements are discussed briefly in this paper.

2. Sunscreens In Singapore, the housing developments consist of multistorey apartment blocks. All the west-facing

blocks were, in general, provided with cast-in-situ reinforced concrete sunscreens to prevent direct exposure to sunlight in the living rooms. In one occasion, three building estates were completed without sunscreens in some of the blocks. The existing design of reinforced concrete sunscreens was too bulky and heavy for long spans more than 3 m and also cumbersome connection details for the precast construction. A number of alternative designs using light weight materials such as glass fibre reinforcement concrete, aluminum and ferrocement were carefully assessed and compared with conventional reinforced concrete. Considerations in terms of the ease of handling and erection, architectural requirements, durability and overall cost led to the choice of ferrocement as the most suitable alternative material in this application.

An inverted L-shape sunscreen module of length 2.7 m were proposed with bolted connections. In the design of these sunscreens, due considerations were given to the aesthetic and functional requirements. The top face of the flange was provided with a backward slope to flush out, by rain, the accumulation dust without staining the front face to reduce the cost of maintenance. The design service load consisted of a concentrated live load of 5 kN applied either vertically or horizontally at mid-span and a wind load of 0.6 Pa in addition to self-weight. A thickness of 25 mm was found to be sufficient for the design loadings. The reinforcement consisted of two layers of fine welded galvanised wire mesh, 1.2 mm in diameter with a 12.5 mm square grid, separated by a layer of coarser welded wire mesh of diameter of 3.3 mm and a square grid of 150 mm (Fig. 1). For the mortar matrix, the mix proportions of cementsand:water by weight was 1 :2:0.5. The sunscreens were cast in steel moulds in a precast factory. After the necessary curing, they were painted and transported to the site. A special lifting device was used during erection.

Three stainless steel bolts were used to connect the sunscreens to the existing structures at each support; one 16 mm in diameter at the rear and two 12 mm in diameter at the front. A total of 500 sunscreens were installed on the 11-storey apartment blocks in three different estates. A typical block after installation is shown in Fig. 2. It can be seen that the slender design achieved by using a ferrocement imparts a graceful appearance to the buildings.

Another type of ferrocement sunscreens were installed in several partially completed apartment blocks. The design should be flexible enough for the long spans ranging from 3 m to 5 m, with the ends supported on two 200 mm thick short cantilever beams of depth 600 mm attached through the facade to reinforced concrete walls. The sunscreens comprised a flat panel 0.6 m x 4.0 m with a thickness of 40 mm except for a 90 mm x 90 mm edge beam at the top. The design loads were the same as in previous case. Two layers of galvanised fine wire mesh of 12.5 mm square grid and 1.2 mm wire diameter separated by a layer of skeletal steel of 100 mm square grid and 6 mm diameter were used as reinforcements. The mortar strength was 35 MPa and the mix proportions of the cement, sand and water in the ratio of 1:1.5:0.4 by weight was used. The cracking strengths of the ferrocement composite in flexure and direct tension were 7.9 MPa and 3.1 MPa, respectively. These strengths were checked

Fig. 1 Reinforcement layout in steel mould. Fig. 2 Sunscreens after installation.

economical and beneficial applications of ferrocement. The salient features of the design, construction and performance of these ferrocement structural elements are discussed briefly in this paper.

2. Sunscreens In Singapore, the housing developments consist of multistorey apartment blocks. All the west-facing

blocks were, in general, provided with cast-in-situ reinforced concrete sunscreens to prevent direct exposure to sunlight in the living rooms. In one occasion, three building estates were completed without sunscreens in some of the blocks. The existing design of reinforced concrete sunscreens was too bulky and heavy for long spans more than 3 m and also cumbersome connection details for the precast construction. A number of alternative designs using light weight materials such as glass fibre reinforcement concrete, aluminum and ferrocement were carefully assessed and compared with conventional reinforced concrete. Considerations in terms of the ease of handling and erection, architectural requirements, durability and overall cost led to the choice of ferrocement as the most suitable alternative material in this application.

An inverted L-shape sunscreen module of length 2.7 m were proposed with bolted connections. In the design of these sunscreens, due considerations were given to the aesthetic and functional requirements. The top face of the flange was provided with a backward slope to flush out, by rain, the accumulation dust without staining the front face to reduce the cost of maintenance. The design service load consisted of a concentrated live load of 5 kN applied either vertically or horizontally at mid-span and a wind load of 0.6 Pa in addition to self-weight. A thickness of 25 mm was found to be sufficient for the design loadings. The reinforcement consisted of two layers of fine welded galvanised wire mesh, 1.2 mm in diameter with a 12.5 mm square grid, separated by a layer of coarser welded wire mesh of diameter of 3.3 mm and a square grid of 150 mm (Fig. 1). For the mortar matrix, the mix proportions of cementsand:water by weight was 1 :2:0.5. The sunscreens were cast in steel moulds in a precast factory. After the necessary curing, they were painted and transported to the site. A special lifting device was used during erection.

Three stainless steel bolts were used to connect the sunscreens to the existing structures at each support; one 16 mm in diameter at the rear and two 12 mm in diameter at the front. A total of 500 sunscreens were installed on the 11-storey apartment blocks in three different estates. A typical block after installation is shown in Fig. 2. It can be seen that the slender design achieved by using a ferrocement imparts a graceful appearance to the buildings.

Another type of ferrocement sunscreens were installed in several partially completed apartment blocks. The design should be flexible enough for the long spans ranging from 3 m to 5 m, with the ends supported on two 200 mm thick short cantilever beams of depth 600 mm attached through the facade to reinforced concrete walls. The sunscreens comprised a flat panel 0.6 m x 4.0 m with a thickness of 40 mm except for a 90 mm x 90 mm edge beam at the top. The design loads were the same as in previous case. Two layers of galvanised fine wire mesh of 12.5 mm square grid and 1.2 mm wire diameter separated by a layer of skeletal steel of 100 mm square grid and 6 mm diameter were used as reinforcements. The mortar strength was 35 MPa and the mix proportions of the cement, sand and water in the ratio of 1: 1.5:0.4 by weight was used. The cracking strengths of the ferrocement composite in flexure and direct tension were 7.9 MPa and 3.1 MPa, respectively. These strengths were checked

Fig. 1 Reinforcement layout in steel mould. Fig. 2 Sunscreens after installation.

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Fig. 3 Casting of sunscreen. Fig. 4 View of installed sunscreens.

against the stresses due to dead load, wind load and accidental live loads with the appropriate factors of safety. The panels were also checked for deflection and natural frequency because of its slenderness.

The front panel of the sunscreens was cast in steel moulds in a precast factory as shown in Fig. 3 with the projecting steel bars for continuity of reinforcements with the supporting cantilever. After the necessary curing, the sunscreens were transported to the site. Prefabricated steel trusses were attached onto the reinforced concrete walls and bolted to the facade by a proprietary bolting system. The sunscreens were lifted into position and the continuity steel bars spot-welded onto the steel trusses. Additional galvanised fine wire meshes were assembled around the steel trusses and the supporting beams cast-in-situ against precast permanent formwork.

The ferrocement sunscreens were much thinner and significantly lighter than the existing reinforced concrete ones of similar design. The slender design of the ferrocement sunscreens give them a more elegant and aesthetically appealing appearance. A typical block of apartment with the sunscreens installed is shown in Fig.4. The building authorities have now accepted without any reservation the use of ferrocement in sunscreens and facades.

3. Secondary roofing slabs In tropical countries, secondary roofing slabs are installed on the roof top of the buildings to insulate

against intense heat. In Singapore these slabs consist typically of 1500 mm x 600 mm x 50 mm precast cellular concrete slabs containing a centrally placed layer of galvanised welded wire mesh of 50 mm square grid and 3.25 mm diameter. The slabs were assembled side by side, each being supported on 150 mm x 150 mm x 225 mm precast hollow blocks placed on the top of the structural roof to provide as air gap of 225 mm. The cellular concrete mix has a sand:cement ratio of 2.2 with a density of about 1500 kg/m3. These slabs pose a problem of severe cracking even before they are transported and erected in place. Although the presence of cracks may not be critical with respect to strength requirements, they are undesirable from a durabil of view. there is a need to such slabs at least

Fig. 5 Reinforcement details of ferrocement secondary roofing slab.

Fig. 6 View of installed ferrocement secondary roofing slabs.

Fig. 3 Casting of sunscreen. Fig. 4 View of installed sunscreens.

against the stresses due to dead load, wind load and accidental live loads with the appropriate factors of safety. The panels were also checked for deflection and natural frequency because of its slenderness.

The front panel of the sunscreens was cast in steel moulds in a precast factory as shown in Fig. 3 with the projecting steel bars for continuity of reinforcements with the supporting cantilever. After the necessary curing, the sunscreens were transported to the site. Prefabricated steel trusses were attached onto the reinforced concrete walls and bolted to the facade by a proprietary bolting system. The sunscreens were lifted into position and the continuity steel bars spot-welded onto the steel trusses. Additional galvanised fine wire meshes were assembled around the steel trusses and the supporting beams cast-in-situ against precast permanent formwork.

The ferrocement sunscreens were much thinner and significantly lighter than the existing reinforced concrete ones of similar design. The slender design of the ferrocement sunscreens give them a more elegant and aesthetically appealing appearance. A typical block of apartment with the sunscreens installed is shown in FigA. The building authorities have now accepted without any reservation the use of ferrocement in sunscreens and facades.

3. Secondary roofing slabs In tropical countries, secondary roofing slabs are installed on the roof top of the buildings to insulate

against intense heat. In Singapore these slabs consist typically of 1500 mm x 600 mm x 50 mm precast cellular concrete slabs containing a centrally placed layer of galvanised welded wire mesh of 50 mm square grid and 3.25 mm diameter. The slabs were assembled side by side, each being supported on 150 mm x 150 mm x 225 mm precast hollow blocks placed on the top of the structural roof to provide as air gap of 225 mm. The cellular concrete mix has a sand:cement ratio of 2.2 with a density of about 1500 kg/m3 . These slabs pose a problem of severe cracking even before they are transported and erected in place. Although the presence of cracks may not be critical with respect to strength requirements, they are undesirable from a durability of view. there is a need to re such slabs at least

Fig. 5 Reinforcement details of ferrocement secondary roofing slab.

Fig. 6 View of installed ferrocement secondary roofing slabs.

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once every 10 years. A study was carried out at National University of Singapore to examine the current design with the

intention of improving durability of the slabs. A ferrocement design of 30 mm thickness with two layers of galvanised fine wire mesh of 25 mm square grid and 1.6 mm wire diameter separated by a layer of skeletal steel of galvanised welded wire mesh of 150 mm square grid and 3.3 mm diameter, as shown in Fig. 5, was found to be adequate. Because of the reduced thickness, the dead weight of the ferrocement slabs remains approximately the same as that of the cellular concrete slabs.

The functionality of such slabs was investigated by carrying out flexural tests, patch load tests and shrinkage measurements on specimens. It was found that the slabs could be subjected to deSign service load of 1.8 kN patch load, two days after casting without cracking. The slabs also registered low long term shrinkage of about 400 microns.

The effects of weathering and thermal fluctuations were also studied. Slabs subjected to alternate wetting and drying test do not show any deterioration in first crack or ultimate strengths. Cyclic compression test to simulate the effect of thermal stresses due to heating in the day and cooling at night did not affect the strength significantly. Comparison in terms of production costs shows the ferrocement slabs to be slightly more expensive than the cellular slabs. However, it is expected that with ferrocement slabs the frequency of replacements will be reduced. The cost can be reduced through increasing productivity by demoulding them in the shortest possible time, minimising the controlled curing period and installation on site at the earliest time with less number of spoils during transportation and erection. The recent experimental study using reliability analysis [13] shows that the ferrocement slabs can develop up to 87 and 90 percent of their mean 28-day first crack and ultimate strengths, respectively, three days after casting. The reliability study indicates that the ferrocement slabs used were safe against ultimate failure one day after casting when subjected to both dead and live loads and in the case of first cracks with respect to dead load alone. In another study [14] the durability of the ferrocement secondary roofing slabs was investigated with respect to service life-cycle in relation to the actual load range that a typical slab would experience. The results show that the slabs have good fatigue properties within the stress range considered. Fig. 6 shows the ferrocement secondary roofing slabs already installed on the structural roof of some housing estates.

4. Water tanks 4.1. Rural applications

In rural areas of many developing countries, there is a scarcity of water for drinking and washing. Traditionally rain water was collected for such usage. Therefore there is a need to provide simple and economical storage facilities that can be constructed with unskilled labour. Although steel tanks have been used commonly for this purpose, they have disadvantages such as high cost, rusting and consequent maintenance and limited life-span due to corrosion. The use of reinforced concrete water tanks poses problems of a different nature being heavier and more massive with construction requiring complicated formworks. Ferrocement construction, on the other hand, being of low level technology but

Fig. 7 Reinforcement details and completed tank (5m3) capacity.

once every 10 years. A study was carried out at National University of Singapore to examine the current design with the

intention of improving durability of the slabs. A ferrocement design of 30 mm thickness with two layers of galvanised fine wire mesh of 25 mm square grid and 1.6 mm wire diameter separated by a layer of skeletal steel of galvanised welded wire mesh of 150 mm square grid and 3.3 mm diameter, as shown in Fig. 5, was found to be adequate. Because of the reduced thickness, the dead weight of the ferrocement slabs remains approximately the same as that of the cellular concrete slabs.

The functionality of such slabs was investigated by carrying out flexural tests, patch load tests and shrinkage measurements on specimens. It was found that the slabs could be subjected to deSign service load of 1.8 kN patch load, two days after casting without cracking. The slabs also registered low long term shrinkage of about 400 microns.

The effects of weathering and thermal fluctuations were also studied. Slabs subjected to alternate wetting and drying test do not show any deterioration in first crack or ultimate strengths. Cyclic compression test to simulate the effect of thermal stresses due to heating in the day and cooling at night did not affect the strength significantly. Comparison in terms of production costs shows the ferrocement slabs to be slightly more expensive than the cellular slabs. However, it is expected that with ferrocement slabs the frequency of replacements will be reduced. The cost can be reduced through increasing productivity by demoulding them in the shortest possible time, minimising the controlled curing period and installation on site at the earliest time with less number of spoils during transportation and erection. The recent experimental study using reliability analysis [13] shows that the ferrocement slabs can develop up to 87 and 90 percent of their mean 28-day first crack and ultimate strengths, respectively, three days after casting. The reliability study indicates that the ferrocement slabs used were safe against ultimate failure one day after casting when subjected to both dead and live loads and in the case of first cracks with respect to dead load alone. In another study [14] the durability of the ferrocement secondary roofing slabs was investigated with respect to service life-cycle in relation to the actual load range that a typical slab would experience. The results show that the slabs have good fatigue properties within the stress range considered. Fig. 6 shows the ferrocement secondary roofing slabs already installed on the structural roof of some housing estates.

4. Water tanks 4.1. Rural applications

In rural areas of many developing countries, there is a scarcity of water for drinking and washing. Traditionally rain water was collected for such usage. Therefore there is a need to provide simple and economical storage facilities that can be constructed with unskilled labour. Although steel tanks have been used commonly for this purpose, they have disadvantages such as high cost, rusting and consequent maintenance and limited life-span due to corrosion. The use of reinforced concrete water tanks poses problems of a different nature being heavier and more massive with construction requiring complicated formworks. Ferrocement construction, on the other hand, being of low level technology but

Fig. 7 Reinforcement details and completed tank (5m3) capacity.

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labour intensive, is ideally suitable for water tanks in rural areas of developing countries. A study [15] was conducted to propose simple, economical and durable ferrocement water tanks for potable water in the rural areas of Capiz island, Philippines, which can be constructed by means of locally available construction skills and building materials. Funded by the International Development Research Centre, Canada, two prototypes of 5 m3 and 16 m3 capacities were analysed, constructed and tested in Singapore.

The adapted water tank design consists of cylindrical wall rigidly connected to a circular base plate as the bottom and covered by a truncated conical roof on the top. The tanks were analysed using linear elastic theory of shells and designed to be uncracked under service conditions. Each of these tanks has a wall height of 1.8 m, the internal diameters were 2 m and 3.6 m with a wall thickness of 35 mm and 50 mm for the small and big prototype tanks respectively. In both cases, the roofs had a thickness of 25 mm and a slope of 1:3 with an opening of 0.8 m diameter at the centre as a service requirement. The reinforcement details and completed water tanks,S m3 and 16 m3 capacities, are shown in Figs. 7 and 8, respectively. Their successful performance confirms the viability of using ferrocement water tanks, of the proposed design and attendant construction technique, for rural applications. Such water tanks can be easily fabricated as a community project in the rural areas of developing countries. At present more than 5000 such tanks have been constructed in the province of Capiz in the Philippines.

Fig. 8. Reinforcement details and completed tank (16m3) capacity.

4.2. Urban applications For an urban environment like Singapore, mechanised methods must be used to alleviate the acute

shortage and high cost of skilled labour to expedite the construction. A pilot study [16] was carried out to propose a suitable and durable precast ferrocement cylindrical water tank for use in high rise buildings by adapting available mechanised production methods, example, spinning technique and the proper choice of reinforcement to ensure cost competitiveness.

The adopted water tank design consists of a cylindrical wall rigidly connected to a ring beam with a domed base as shown in Fig. 9. The tank had a height of 2.25 m with a diameter of 3.6 m at the base. From the strength as well as practical view point, a thickness of 35 mm is recommended for the roof and 40 mm-100 mm for the cylindrical wall. The thickness of the base should be slightly larger and a value of 60 mm-120 mm was recommended. The designs of the base, wall and roof were determined by checking the strength of each component against the maximum stress resultants acting on it. The reinforcement for wall consists of two layers of fine galvanised wire mesh of 1.2 mm wire diameter with a square grid of 12.5 mm. The meshes were separated by two layers of coarser galvanised wire mesh of 5.4 mm diameter with square grid of 150 mm. The cement mortar is designed for a strength of 35-40 N/mm2 to provide a low permeability with sufficient workability to minimise voids. A water cement ratio of 0.35-0.45 combined with a sand:cement ratio of 1.5:1 is generally used. The spinning technique was used for the walls (Fig. 10) while the bases were cast-in-situ in the factory as shown in Fig. 11. The erection and installation of the tanks are shown in Figs. 12 and 13, respectively.

labour intensive, is ideally suitable for water tanks in rural areas of developing countries. A study [15] was conducted to propose simple, economical and durable ferrocement water tanks for potable water in the rural areas of Capiz island, Philippines, which can be constructed by means of locally available construction skills and building materials. Funded by the International Development Research Centre, Canada, two prototypes of 5 m3 and 16 m3 capacities were analysed, constructed and tested in Singapore.

The adapted water tank design consists of cylindrical wall rigidly connected to a circular base plate as the bottom and covered by a truncated conical roof on the top. The tanks were analysed using linear elastic theory of shells and designed to be uncracked under service conditions. Each of these tanks has a wall height of 1.8 m, the internal diameters were 2 m and 3.6 m with a wall thickness of 35 mm and 50 mm for the small and big prototype tanks respectively. In both cases, the roofs had a thickness of 25 mm and a slope of 1:3 with an opening of 0.8 m diameter at the centre as a service requirement. The reinforcement details and completed water tanks, 5 m3 and 16 m3 capacities, are shown in Figs. 7 and 8, respectively. Their successful performance confirms the viability of using ferrocement water tanks, of the proposed design and attendant construction technique, for rural applications. Such water tanks can be easily fabricated as a community project in the rural areas of developing countries. At present more than 5000 such tanks have been constructed in the province of Capiz in the Philippines.

Fig. 8. Reinforcement details and completed tank (16m3) capacity.

4.2. Urban applications For an urban environment like Singapore, mechanised methods must be used to alleviate the acute

shortage and high cost of skilled labour to expedite the construction. A pilot study [16] was carried out to propose a suitable and durable precast ferrocement cylindrical water tank for use in high rise buildings by adapting available mechanised production methods, example, spinning technique and the proper choice of reinforcement to ensure cost competitiveness.

The adopted water tank design consists of a cylindrical wall rigidly connected to a ring beam with a domed base as shown in Fig. 9. The tank had a height of 2.25 m with a diameter of 3.6 m at the base. From the strength as well as practical view point, a thickness of 35 mm is recommended for the roof and 40 mm-100 mm for the cylindrical wall. The thickness of the base should be slightly larger and a value of 60 mm-120 mm was recommended. The designs of the base, wall and roof were determined by checking the strength of each component against the maximum stress resultants acting on it. The reinforcement for wall consists of two layers of fine galvanised wire mesh of 1.2 mm wire diameter with a square grid of 12.5 mm. The meshes were separated by two layers of coarser galvanised wire mesh of 5.4 mm diameter with square grid of 150 mm. The cement mortar is designed for a strength of 35-40 N/mm2 to provide a low permeability with sufficient workability to minimise voids. A water cement ratio of 0.35-0.45 combined with a sand:cement ratio of 1.5: 1 is generally used. The spinning technique was used for the walls (Fig. 10) while the bases were cast-in-situ in the factory as shown in Fig. 11. The erection and installation of the tanks are shown in Figs. 12 and 13, respectively.

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Fig. 9 Sectional elevation of precast water tank.

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Fig. 11 Casting the base of the tank

Fig. 12 Erection of the completed tank Fig. 13 View of the tanks after installation

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Fig. 9 Sectional elevation of precast water tank.

Fig. 10 Spinning of the ferrocement water tank during casting

Fig. 11 Casting the base of the tank

Fig. 12 Erection of the completed tank Fig. 13 View of the tanks after installation

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The ferrocement tanks weigh only six tonnes compared to the conventional reinforced concrete tank weighing 14 tonnes. Although the present production cost is 20 percent more than that for reinforced concrete tanks of similar design, the ferrocement tanks can be easily installed onto the roof tops using lower tonnage cranes and with further reduction in the cost of supporting structures on the roof. It will be more economical in the long run to use ferrocement water tanks in view of their performance and durability with possible lower production costs with more tank being manufactured.

5. Ferrocement enclosure for a centrifuge The characteristics of ferrocement such as resistance to disintegration, localisation of damage and

ease of repair when subjected to impact loads are ideally suitable in the construction of a protective enclosure for a geotechnical centrifuge at National University of Singapore. A composite construction, consisting of 350 mm thick, densely packed layer of granular material sandwiched between two ferrocement cylindrical shells each 60 mm thick was adopted for the enclosure wall. Analysis showed that the wall has to withstand an impulse 28.2 kNs and dissipate 0.88 MJ of kinetic energy [17] upon impact. Considering these requirements, the ferrocement elements had a volume fraction of reinforcements of 3.79%. For the wall, the skeletal steel consisted of 10 mm diameter plain bar at 50 mm spacing in a single layer in the vertical direction and horizontal bars of 10 mm diameter in a staggered layer at 100 mm spacing. On the conical roof, the bars were placed in meridian direction in two layers at 100 mm spacing and in the circumferential direction in one layer at a spacing of 50 mm. Two layers of galvanised fine wire mesh with a grid size of 12.5 mm and 1.2 mm diameter were placed on each side of skeletal steel cage. The designed compressive strength of the mortar was 45 MPa. The reinforcement details and completed enclosure are shown in Figs. 14 and 15, respectively. The centrifuge has been in operation for the past three years without much vibration problems .

. i II" )'! Fig. 14 Reinforcement details and casting of the

ferrocement enclosure. Fig. 15 Completed view of the ferrocement

enclosure.

6. Strengthening of RC beams using ferrocement laminates The need to repair and strengthen concrete structural elements are commonly reported due to

overloading, structural alterations, poor workmanship and non-compliances of standards. Several practical applications such as epoxy resin injections, externally bonded steel plates and encased additional reinforcing bars have been accepted as possible remedial techniques. The use of ferrocement in repair is relatively new. The material is ideally suitable due to its ability to arrest crack and high tensile strength-to-weight ratio.

Rectangular and T beams were tested failure under concentrated loads. A 20 mm thick ferrocement laminate was attached onto the tension face of the beams with different types of shear connectors (Fig. 16). The reinforcement in the laminate consisted of two plain steel bars of 6 or 8 mm diameter sandwiched between two layers of galvanised wire mesh of diameter 1.2 mm and square grid 12.5 mm. The study [18] focused on the different types of shear connectors using Ramset nails, Hilti bolts, dowel bars and epoxy resin adhesive. The effects of the volume fraction of reinforcements of the ferrocement laminate and the level of damage of the beams were also studied. The performance of the strengthened beams were compared to the control beams with respect to cracking, deflection and ultimate strength. The results show that all the strengthened beams exhibited higher ultimate strength, greater stiffness and

The ferrocement tanks weigh only six tonnes compared to the conventional reinforced concrete tank weighing 14 tonnes. Although the present production cost is 20 percent more than that for reinforced concrete tanks of similar design, the ferrocement tanks can be easily installed onto the roof tops using lower tonnage cranes and with further reduction in the cost of supporting structures on the roof. It will be more economical in the long run to use ferrocement water tanks in view of their performance and durability with possible lower production costs with more tank being manufactured.

5. Ferrocement enclosure for a centrifuge The characteristics of ferrocement such as resistance to disintegration, localisation of damage and

ease of repair when subjected to impact loads are ideally suitable in the construction of a protective enclosure for a geotechnical centrifuge at National University of Singapore. A composite construction, consisting of 350 mm thick, densely packed layer of granular material sandwiched between two ferrocement cylindrical shells each 60 mm thick was adopted for the enclosure wall. Analysis showed that the wall has to withstand an impulse 28.2 kNs and dissipate 0.88 MJ of kinetic energy [171 upon impact. Considering these requirements, the ferrocement elements had a volume fraction of reinforcements of 3.79%. For the wall, the skeletal steel consisted of 10 mm diameter plain bar at 50 mm spacing in a single layer in the vertical direction and horizontal bars of 10 mm diameter in a staggered layer at 100 mm spacing. On the conical roof, the bars were placed in meridian direction in two layers at 100 mm spacing and in the circumferential direction in one layer at a spacing of 50 mm. Two layers of galvanised fine wire mesh with a grid size of 12.5 mm and 1.2 mm diameter were placed on each side of skeletal steel cage. The designed compressive strength of the mortar was 45 MPa. The reinforcement details and completed enclosure are shown in Figs. 14 and 15, respectively. The centrifuge has been in operation for the past three years without much vibration problems.

Fig. 14 Reinforcement details and casting of the ferrocement enclosure.

Fig. 15 Completed view of the ferrocement enclosure.

6. Strengthening of RC beams using ferrocement laminates The need to repair and strengthen concrete structural elements are commonly reported due to

overloading, structural alterations, poor workmanship and non-compliances of standards. Several practical applications such as epoxy resin injections, externally bonded steel plates and encased additional reinforcing bars have been accepted as possible remedial techniques. The use of ferrocement in repair is relatively new. The material is ideally suitable due to its ability to arrest crack and high tensile strength-to-weight ratio.

Rectangular and T beams were tested failure under concentrated loads. A 20 mm thick ferrocement laminate was attached onto the tension face of the beams with different types of shear connectors (Fig. 16). The reinforcement in the laminate consisted of two plain steel bars of 6 or 8 mm diameter sandwiched between two layers of galvanised wire mesh of diameter 1.2 mm and square grid 12.5 mm. The study [181 focused on the different types of shear connectors using Ramset nails, Hilti bolts, dowel bars and epoxy resin adhesive. The effects of the volume fraction of reinforcements of the ferrocement laminate and the level of damage of the beams were also studied. The performance of the strengthened beams were compared to the control beams with respect to cracking, deflection and ultimate strength. The results show that all the strengthened beams exhibited higher ultimate strength, greater stiffness and

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106

Fig. 16 Reinforcement details for flexural strengthening

Fig. 17. Reinforcement details for shear strengthening

reduced crack width and spacing. Studies are currently under progress on shear strengthening using prefabricated reinforcement (Fig. 17). Tests are also being conducted to generate information on the performance and durability of such beams under cyclic loading. Deterioration was quantified in terms of the reduction in flexural rigidity after 100,000 cycles of cyclic loading at different stress levels. The performance can be estimated using the probabilistic evaluation of the experimental resus.

7. Conclusions This paper presents some of case studies of ferrocement applications based on the research and

development work carried out at National University of Singapore. These have demonstrated that quality and economy can be achieved using modern construction techniques. Basic considerations of the materials used, fine galvanised wire mesh and cement rich mortar coupled with good crack controlling characteristics; indicate that ferrocement can provide better durability, easy maintenance and lower life­cycle cost compared to conventional reinforced concrete. Experience at National University of Singapore with ferrocement structures built and in use for more than a decade shows that durability has not been a problem with proper construction techniques and regular maintenance.

8. Acknowledgments The author acknowledges the contributions of his colleagues involved in the research team and

engineers in the Housing and Development Board for their collaboration. The author also extend his thanks to International Development Research Centre, Canada, Daewoo Corporation, Construction Technology Pte. Ltd., and Hong Leong Manufacturing Industries Pte. Ltd. for their support in some of these works. The basic research was partly supported by RDAS research grants, C/81/01 and ST/88/04, provided by the Ministry of Trade and Industries and NUS research grants, RP880623 and RP900616.

References 1. Nathan, G.K. and Paramasivam, P., "Mechanical Properties of Ferrocement", Proc. First Australian

Conference on Engineering Materials, Sydney, pp. 309-331, 1974. 2. Paramasivam, P. and Lee, S.L., "Ferrocement Structural Elements", Proc. RILEM International

Symposium on Ferrocement, Bergamo, pp. 3/37-3/46, 1981. . 3. Paramasivam, P. and Nathan, G.K., Ferrocement Sunshade, Journal of Ferrocement, Vol. 11, No.1,

pp. 47-54,1981. 4. Paramasivam, P. and Nathan, G.K., A Prefabricated Ferrocement Water Tank, ACI Journal, Vol. 81,

No. 45, pp. 582-586,1984. 5. Lee, S.L., Tam, CT, Paramasivam, P., Das Gupta, N.C., Sri Ravindrarajah, R. and Mansur, MA,

Ferrocement: Ideas Tested at the University of Singapore, Concrete International: Design and Construction, Vol. 5, No. 11, pp. 12-14, 1988.

6. Paramasivam, P., Ong, K.C.G., and Lee, S.L., "Ferrocement Structures and Structural Elements", Steel-Concrete Composites Structures, ed. R. Narayaran, Elsevier Applied Science, London, pp. 289-330,1988.

Fig. 16 Reinforcement details for flexural strengthening

Fig. 17. Reinforcement details for shear strengthening

reduced crack width and spacing. Studies are currently under progress on shear strengthening using prefabricated reinforcement (Fig. 17). Tests are also being conducted to generate information on the performance and durability of such beams under cyclic loading. Deterioration was quantified in terms of the reduction in flexural rigidity after 100,000 cycles of cyclic loading at different stress levels. The performance can be estimated using the probabilistic evaluation of the experimental resus.

7. Conclusions This paper presents some of case studies of ferrocement applications based on the research and

development work carried out at National University of Singapore. These have demonstrated that quality and economy can be achieved using modern construction techniques. Basic considerations of the materials used, fine galvanised wire mesh and cement rich mortar coupled with good crack controlling characteristics; indicate that ferrocement can provide better durability, easy maintenance and lower life­cycle cost compared to conventional reinforced concrete. Experience at National University of Singapore with ferrocement structures built and in use for more than a decade shows that durability has not been a problem with proper construction techniques and regular maintenance.

8. Acknowledgments The author acknowledges the contributions of his colleagues involved in the research team and

engineers in the Housing and Development Board for their collaboration. The author also extend his thanks to International Development Research Centre, Canada, Daewoo Corporation, Construction Technology Pte. Ltd., and Hong Leong Manufacturing Industries Pte. Ltd. for their support in some of these works. The basic research was partly supported by RDAS research grants, C/81/01 and ST/88/04, provided by the Ministry of Trade and Industries and NUS research grants, RP880623 and RP900616.

References 1. Nathan, G.K. and Paramasivam, P., "Mechanical Properties of Ferrocement", Proc. First Australian

Conference on Engineering Materials, Sydney, pp. 309-331,1974. 2. Paramasivam, P. and Lee, S.L., "Ferrocement Structural Elements", Proc. RILEM International

Symposium on Ferrocement, Bergamo, pp. 3/37-3/46,1981. 3. Paramasivam, P. and Nathan, GK, Ferrocement Sunshade, Journal of Ferrocement, Vol. 11, No.1,

pp. 47-54,1981. 4. Paramasivam, P. and Nathan, G.K., A Prefabricated Ferrocement Water Tank, ACI Journal, Vol. 81,

No. 45, pp. 582-586, 1984. 5. Lee, S.L., Tam, C.T., Paramasivam, P., Das Gupta, N.C., Sri Ravindrarajah, R. and Mansur, M.A.,

Ferrocement: Ideas Tested at the University of Singapore, Concrete International: Design and Construction, Vol. 5, No. 11, pp. 12-14, 1988.

6. Paramasivam, P., Ong, K.C.G., and Lee, S.L., "Ferrocement Structures and Structural Elements", Steel-Concrete Composites Structures, ed. R. Narayaran, Elsevier Applied Science, London, pp. 289-330,1988.

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107

7. Paramasivam, P. and Sri Ravindrarajah, R., Effects of Arrangements of Reinforcements on Mechanical Properties of Ferrocement, ACI Structural Journal, Vol. 85, No.1, pp. 3-11, 1988.

8. Mansur, M.A., Paramasivam, P. and Lee, S.L., Ferrocement Sunscreens on High rise Buildings, Concrete International: Design and Construction, Vol. 9, No. 11, pp. 19-23, 1987.

9. Lee, S.L., Paramasivam, P., Tam, C.T., Ong, K.C.G. and Tan, K.H., Ferrocement: Alternative Materials for Secondary Roofing Elements, ACI Materials Journal, Vol. 87, No.4, pp. 378-386, 1990.

10. Paramasivam, P., Ong, K.C.G., Tan, K.H., Swaddiwudhipong, S., and Lee, S.L., Long-span Precast Ferrocement Sunscreens in Public Housing, Concrete International: Design and Construction, Vol. 12, No.9, pp. 33-36, 1990.

11. ACI committee 549, State-of-the-Art Report on Ferrocement, ACI, Detroit, ACI549-R82, 1982. 12. ACI Committee 549, Guide for the Design, Construction and Repair of Ferrocement, ACI, Detroit,

ACI549-IR88, 1988. 13. Quek, S.T., On, S.H., Paramasivam, P. and Lee, S.L., Early-age Reliability of Ferrocement Slabs, ACI

Material Journal, Vol. 88, No.6, pp. 644-649, 1991. 14. Quek, S.T., On, S.H., Paramasivam, P. and Lee, S.L., Fatigue Reliability of Ferrocement Slabs, ACI

Structural Journal, Vol. 88, No.1, pp. 78-83, 1991. 15. Paramasivam, P., Ong, K.C.G., Tan, K.H. and Lee, S.L., Rainwater Storage using Ferrocement Tanks

in Developing Countries, Journal of Ferrocement, Vol. 20, No.4, pp. 377-384, 1990. 16. Lee, S.L., Paramasivam, P. and Ong, K.C.G., "Precast and In-situ Ferrocement Structural Elements",

Proc. International Conference on The Concrete Future, C.1. Premier, Kuala Lumpur, Malaysia, pp. 79-84, 1992.

17. Tan, K.H., Lee, S.L. and Paramasivam, P., Ferrocement Enclosure for a Centrifuge, Concrete International: Design and Construction, ACI, Vol. 13, No. 12, pp. 61-66, 1991.

18. Ong, K.C.G., Paramasivam, P. and Lim, C.T.E., Flexural Strengthening of Reinforced Concrete Beams Using Ferrocement Laminates, Journal of Ferrocement, Vol. 22, No.4, pp. 331-342, 1992.

7. Paramasivam, P. and Sri Ravindrarajah, R., Effects of Arrangements of Reinforcements on Mechanical Properties of Ferrocement, ACI Structural Journal, Vol. 85, No.1, pp. 3-11, 1988.

8. Mansur, M.A., Paramasivam, P. and Lee, S.L., Ferrocement Sunscreens on High rise Buildings, Concrete International: Design and Construction, Vol. 9, No. 11, pp. 19-23, 1987.

9. Lee, S.L., Paramasivam, P., Tam, CT, Ong, K.C.G. and Tan, K.H., Ferrocement: Alternative Materials for Secondary Roofing Elements, ACI Materials Journal, Vol. 87, No.4, pp. 378-386, 1990.

10. Paramasivam, P., Ong, K.C.G., Tan, K.H., Swaddiwudhipong, S., and Lee, S.L., Long-span Precast Ferrocement Sunscreens in Public Housing, Concrete International: Design and Construction, Vol. 12, No.9, pp. 33-36, 1990.

11. ACI committee 549, State-of-the-Art Report on Ferrocement, ACI, Detroit, ACI549-R82, 1982. 12. ACI Committee 549, Guide for the Design, Construction and Repair of Ferrocement, ACI, Detroit,

ACI549-IR88, 1988. 13. Quek, ST, On, S.H., Paramasivam, P. and Lee, S.L., Early-age Reliability of Ferrocement Slabs, ACI

Material Journal, Vol. 88, No.6, pp. 644-649, 1991. 14. Quek, ST, On, S.H., Paramasivam, P. and Lee, S.L., Fatigue Reliability of Ferrocement Slabs, ACI

Structural Journal, Vol. 88, No.1, pp. 78-83, 1991. 15. Paramasivam, P., Ong, K.C.G., Tan, K.H. and Lee, S.L., Rainwater Storage using Ferrocement Tanks

in Developing Countries, Journal of Ferrocement, Vol. 20, No.4, pp. 377-384, 1990. 16. Lee, S.L., Paramasivam, P. and Ong, K.C.G., "Precast and In-situ Ferrocement Structural Elements",

Proc. International Conference on The Concrete Future, C.I. Premier, Kuala Lumpur, Malaysia, pp. 79-84, 1992.

17. Tan, K.H., Lee, S.L. and Paramasivam, P., Ferrocement Enclosure for a Centrifuge, Concrete International: Design and Construction, ACI, Vol. 13, No. 12, pp. 61-66,1991.

18. Ong, K.C.G., Paramasivam, P. and Lim, CTE., Flexural Strengthening of Reinforced Concrete Beams Using Ferrocement Laminates, Journal of Ferrocement, Vol. 22, No.4, pp. 331-342, 1992.