Construction and Building Materials 13 Ž1999. 433]438

Plant fibre reinforced cement components for roofing Holmer Savastano Jr.a , Vahan Agopyanb,U , Adriana M. Nolasco c , Lia Pimentel d a Uni¨ ersidade de Sao ˜ Paulo (USP), caixa postal 23, 13630-000 Pirassununga, Sao ˜ Paulo, Brazil USP, A¨ . Prof. Luciano Gualberto, tra¨ . 3, 380, Predio da Administracao, Cidade Uni¨ ersitaria, 05508-900 Sao ˜ Paulo, Brazil c USP, A¨ . Padua Dias, 11, 13418-900 Piracicaba, Sao ˜ Paulo, Brazil d Uni¨ ersidade Metodista de Piracicaba (UNIMEP), Rodo¨ . Sta. Barbara-Iracemapolis, km 1, 13450-000 Santa Barbara D’Oeste, Sao ˜ Paulo, Brazil b

Received 13 December 1998; received in revised form 17 July 1999; accepted 25 August 1999

Abstract Composites of blast furnace slag ŽBFS. based cement mortar reinforced with vegetable fibres are presented. Roofing components are produced with these composites through a simple and low-energy consuming method, including ordinary vibration and curing in a wet chamber. Composites reinforced with eucalyptus pulp, coir fibres and with a mixture of sisal fibre and eucalyptus pulp gave a suitable performance, with compressive strength higher than 20 MPa and modulus of rupture ŽMOR. higher than 3 MPa. The performance of tiles made with these composites is in accordance with international requirements, with maximum load higher than 450 N, in wet conditions. Q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Plant fibres; Vegetable fibres; Composites; Blast furnace slag; Roofing; Alternative cements; Recycled materials

1. Introduction The consumption of building components made with fibre reinforced cement is increasing rapidly and nowadays in developed countries it is in the region of several million metric tonnes yearly. This occurs because it is possible to produce lightweight building components with this type of material, with good mechanical performance Žmainly impact energy absorption., suitable thermal-acoustic insulation and is economically feasible. Within the developing world, where the lack of housing and also of commercial, industrial and public service buildings is considerable, the introduction of these materials can help increase production of buildings

U

Tel.: q55-11-818-5550; fax: q55-11-818-5714. E-mail address: [email protected] ŽV. Agopyan.

with suitable performance. In these countries, vegetable fibres can be a good alternative due to low cost, as long as the low durability risks in an alkaline environment are eliminated. Besides, in some countries, asbestos]cement is still the sole composite in use, although health hazards are increasingly causing concern w1x. The main objective of this paper is to present the performance of roofing tiles made with blast furnace slag cement ŽBFS. mortar reinforced with vegetable fibres, following the research work already done for building partitions w2x.

2. Fibre-cements overview The use of high elasticity modulus fibres Že.g. steel and carbon. as reinforcement for cement-based matrices is well known for applications aimed at improving

0950-0618r99r$ - see front matter Q 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 9 9 . 0 0 0 4 6 - X

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strength. Low elasticity modulus reinforcements Žsuch as plastic and cellulose fibres. improve the energy absorption of composites in the post-cracking stage as their main purpose. As a general view randomly distributed short fibres in brittle matrices perform good response to impact solicitation due to enormous ability for dynamic energy dissipation w3,4x. Wood fibre reinforced cement ŽWFRC. is considered suitable for thin wall and roofing components with good mechanical performance w5x Žmodulus of rupture in the range of 20 MPa and fracture toughness of 1.5 kJrm2 . and acceptable ageing behaviour w6x. The Hatschek based processes are the most frequently used for WFRC production provided some specific procedures such as preliminary fibre mechanical refinement, composite compaction under high pressure and autoclave curing are carried out. In the asbestos-free world the WFRC products provided a successful commercial alternative since the early 1980s w7x. In developing tropical countries the challenge for cost-quality compromise still demands research efforts supporting future industrial products. The utilisation of recycled non-wood and alternative cements combined with low-energy processes seems to have an endless potential for emerging building markets w8x. 2.1. BFS-based cement BFS is the residue of pig iron production and based on world steel annual manufacturing, approximately 150 million metric tonnes of slag are prepared every year. Only in Brazil, 6 million metric tonnes of basic BFS are available every year and half of this amount is stocked without use, resulting in a serious problem for the steel industry as well as for the environment. Because it is a residue, the cost of BFS is as low as US$10.00 per metric tonne. For cement production, the

slag must be ground to a similar fineness of ordinary cement, which adds a further cost of US$15.00 per metric tonne, and it must also be activated with chemical andror thermal procedures. In this research work, the BFS was activated with lime and gypsum. As BFS cement has low alkalinity, its mortars are suitable for vegetable fibre reinforcement w2x and also for other fibres which do not resist the alkalis within the Portland cements.

3. Plant fibres As reported by Coutts w9x, plant fibres contain cellulose, a natural polymer, as the main reinforcement material. The chains of cellulose form microfibrils, which are held together by amorphous hemicellulose and form fibrils. The fibrils are assembled in various layers to build up the structure of the fibre. Fibres or cells are cemented together in the plant by lignin, which can be dissolved by the alkalinity of the cement matrix. Then the usual denomination for fibres is in fact a reference to strands of fibres with some important consequences on durability studies, as discussed later in this item. In Table 1, the most suitable Brazilian vegetable fibres are presented, based on their physical and mechanical properties, cost, durability in natural wet environments and production. As they are natural products, the fibres are heterogeneous so the coefficient of variation in some properties can be as high as 50%. Only as a comparison, the characteristics of polypropylene fibres are included in the table. As presented in the following item, there is a considerable range of short length fibre residues, without use for textile or cordage industries, but still adequate as brittle matrices reinforcement.

Table 1 Physical and mechanical properties of vegetable and polypropylene fibres Properties

Density Žkgrm3 .

Water absorption Ž%.

Elongation at break Ž%.

Tensile strength ŽMPa.

Young’s modulus ŽGPa.

Sisal Ž Aga¨ e sisalana. Coir Ž Cocos nucifera. Malva ŽUrena lobata.

1370 1177 1409

110.0 93.8 182.2

4.3 w14x 23.9]51.4 w14x 5.2 w18x

458 w14x 95]118 w14x 160 w18x

15.2 w14x 2.8 w17x 17.4 w17x

Disintegrated newsprint Ž Pinus elliottii and Eucalyptus citriodora. Bamboo Ž Bambusa ¨ ulgaris . Piassava Ž Attalea funifera. Polypropylene

1200]1500 w14x 1158 w14x 1054 w14x 913

400 w14x 145 w14x 34.4]108 w14x y

naa 3.2 w14x 6.0 w14x 22.3]26.0

300]500 w14x 575 w14x 143 w14x 250

10]40 w14x 28.8 w14x 5.6 w14x 2.0

a

na, information not available.

H. Sa¨ astano et al. r Construction and Building Materials 13 (1999) 433]438

3.1. Fibre]matrix transition zone A transition zone can be defined as a region of the paste close to the fibre, with thickness from 10 to 100 mm, and different characteristics from the bulk matrix. In cement composites, low porosity and portlandite Žcalcium hydroxide crystals . concentration on transition zone must improve the fibre]matrix bonding. With the fibre]matrix bonding increase, the elastic tensile strength also increases and sometimes the ductility reduces w10x. 3.2. Durability Vegetable strand fibres are affected by environment temperature and humidity, and also by the medium in which they are immersed, due to the hemicellulose and lignin decomposition. These components are present in the intercellular layers and their decomposition reduces the reinforcement capacity of the individual fibres Žcells.. Tensile strength of sisal and coir fibres decreases up to 50% if immersed in saturated solution of calcium hydroxide Žapprox. pH 12. for 28 days. To avoid ageing effects in the composites, some approaches are available: Ža. protection of the strand fibres by coating or sealing the dry composite to avoid the effects of alkaline water; Žb. high casting compaction and high-pressure steam curing for providing matrix carbonation, if necessary adding silica fume; Žc. low alkaline binders based on industrial and agricultural by-products such as blast furnace slag ŽBFS. and fly ash w11]13x. After 10 years of use, external wall panels based on BFS reinforced with coir fibres used in a prototype located in Sao ˜ Paulo, Brazil, still present good performance. These results give additional support to the use of BFS in the present study.

v

v

v v

Based on previous results w2,14x, BFS mortars reinforced or not reinforced with vegetable fibres were prepared with the following characteristics: v v v

v

v

v

v

v

Technical visits were carried out to inspect the field production, extraction and processing of vegetable fibres commercialised in Brazil, with the correspondent generation of residues. Based on the information collected on these technical visits, the residues were classified, following the selection criteria below: v

v

General identification of agricultural production which generates residues. Residues identification: correlation with main products and production processes.

Available amount of residues: other possible uses with actual demands. Local availability: selection between transportation or local processing. Market value of the residue. Physical and mechanical properties of composites and components produced.

4.2. E¨ aluation of BFS composites

4. Experimental procedures 4.1. A¨ ailable fibrous residues

435

Cement:sand ratio}1:1.5. Waterrcement ratio}0.40 and 0.48. Volume fraction of fibres}2%. For one of the series produced, two different types of fibres were used together Žvolume fraction of 1% each., looking for a synergetic effect between fibres of different lengths. Selection of fibres: in accordance with selection criteria previously presented in this item. All the strand fibres were cut in lengths varying from 20 to 40 mm. Cement: alkaline granulated BFS from Companhia Siderurgica Tubarao ŽCST. }Brazil, milled up to Blaine fineness of 500 m2rkg. Oxide composition of the BFS Žwt.%.: 32.27% SiO 2 , 12.74% Al 2 O 3 , 0.424% Fe 2 O 3 , 0.204% MnO, 7.731% MgO, 42.17% CaO, 0.204% Na 2 O, 0.403% K 2 O, 0.516% TiO 2 , 0.006% P2 O5 . Activators: gypsum Žcalcium sulfate di-hydrated. and lime Žcalcium hydroxide., in the proportions 0:88:0.10:0.02 and 0.86:0.10:0.04 ŽBFS:gypsum:lime.. Mixture, compaction and manual moulding of the composite. Cure by water immersion, for the 7 initial days, followed by air curing until the date of the test. Fresh state tests: bulk density and flow table Žconsistency index., for workability evaluation. Hard state tests: axial compression Žcylindrical specimen: 50 mm in diameter and 100 mm in height., 4 points bending Žprismatic specimen: 300 = 150 = 15 mm. w15x and water absorption by immersion.

4.3. Roofing components e¨ aluation Roofing tiles were fabricated in conformation to the same procedures presented for composite production and using the Parry Associates ŽUK. equipment, for moulding and compaction by vibration. The dimensions

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436

Table 2 Residues obtained from fibre processing Fibrous residues

Sisal field by-product

Waste of eucalyptus pulp

Residual short coir fibres

Original humidity Ž%. Market price ŽUS$rton. Amount Žtonryear. }source Main product Relation residuer main product Ž%.

10 Zero 30 000}1 cooperative Commercial fibre before drying

61 15 17 000}1 large industry Pulp for paper production

32 90 Žmaximum. 7500}2 large industries Fibres longer than 100 mm

300

0.5

200]2880

of the tiles are 487 = 263 = 6 mm Žframe measures. with format very similar to ceramic Roman tiles.

5. Results 5.1. Selected fibrous residues Based on the criteria presented, three different types of residues were selected, as in Table 2, all of them already available for immediate use in civil construction: v

v

v

Sisal field by-product. Large availability at the processing sites and low commercial interest. A good option as a complementary income for rural producers. This residue needs simple cleaning by passing into a manual cylindrical rotative sieve. Waste of eucalyptus pulp. Almost no commercial value and great availability. Disadvantage: very short fibres Žaverage length s 0.66 mm. and high moisture content. Residual short coir fibres. Low commercial value, great potential for production but almost no use at present time. Powder separation Žapprox. 50% in weight. and drying are required.

Fig. 2. Waste of eucalyptus pulp. Fibrillated fibres after mechanical and chemical treatments.

Samples of the selected residues were analysed by scanning electron microscopy ŽSEM. and some images are reproduced in Figs. 1]3. The sisal field by-product micrography ŽFig. 1. shows a strand of fibres covered by mucilage Žthat can work like a set delayer of cements. and also with fibrillation and striation through the length direction. The waste of eucalyptus pulp ŽFig. 2. presents particular morphology with fibrillated fibres quite altered by mechanical and chemical procedures during the pulp production. The coir fibres ŽFig. 3. have a cylindrical shape with an external cellulosic cover, for strand protection against alkaline attack; superficial protuberances can also be seen, which help fibre anchorage in the reinforced matrix. 5.2. Composites properties

Fig. 1. Sisal field by-product. Strand fibres covered by mucilage.

Physical Žfresh state and 28 days. and mechanical Ž28 days. composites properties are presented in Table 3. The modulus of rupture ŽMOR. of coir fibre reinforced composite was 18% superior to the reference with the same waterrcement ratio. The specific energy corresponds to the total absorbed energy divided by the transversal area of fracture; this property shows a sig-

H. Sa¨ astano et al. r Construction and Building Materials 13 (1999) 433]438

437

ability test, after 24 h under 250 mm of water column pressure. The water absorption was always less than 20% in weight after immersion for 24 h. These results are acceptable in compliance with Brazilian standards for fibrocement sheets for roofing purposes. During flexural tests the tiles reinforced with vegetable fibres presented absorbed energy and specific energy higher than that of plain tiles. All tested series Žwith six tiles. satisfied the minimum flexural load of 425 N Ž85% of 500 N, for saturated tiles. w16x, in spite of better results with plain material. Natural and accelerated ageing tests and also thermal insulation evaluation are in progress now, as a continuation of the present research program. Fig. 3. Residual short coir fibres. Cylindrical shape and superficial protuberances.

nificant difference between the fibrous composites and the plain matrix in the post-cracked stage. 5.3. Components’ properties

Tiles evaluation was made in compliance with the Brazilian standards for concrete tiles and the results are shown in Table 4. The warping was always less than 3 mm, which constitutes a favourable point for the adopted fabrication process. This property is concerned with the capacity of one tile to adjust with others in the roofing. All series presented no wet marks during the perme-

6. Discussion The great availability of plant fibres ensures their use in industrial scale, especially in tropical countries. The alternative cements Že.g. BFS. constitute another cheap solution for non-structural purposes, mainly for mortar production. In each case, the regional available residues need to be previously observed, avoiding additional transport and handle costs. The plant fibre composites based on brittle matrices are confirmed to be suitable as low-cost materials, with enough performance for the millions of homeless people in developing countries. Nevertheless, as durability is a major concern, each type of component must be well evaluated before widespread commercial use.

Table 3 Properties of BSF cement mortar reinforced with vegetable fibres Fibre

Slag:lime: gypsum: sand; wrc

Bulk density Žkgrm3 .

Flow table index Žmm.

Water absorption Žmass%.

MOR ŽMPa.

Reference 1 Žno fibres.

0.88:0.02: 0.10:1.5; 0.48 0.86:0.04: 0.10:1.5; 0.40 0.86:0.04; 0.10:1.5; 0.48 0.86:0.04: 0.10:1.5; 0.48 0.86:0.04: 0.10:1.5; 0.48

2107

303

nab

3.32

56

na

2113

212

8.8

3.37

75

33.8

2041

173

12.2

3.87

141

31.1

2077

201

11.2

3.02

148

25.3

2142

273

11.2

3.92

105

21.0

Reference 2 Žno fibres. Eucalyptus pulp

Sisal Ž1%. q eucalyptus pulp Ž1%. Coir

a b

Test was stopped when load decreased 70% in relation to maximum load; na, information not available. na, information not available.

Specific energy ŽNmrm2 .a

Compression strength ŽMPa.

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438

Table 4 Physical and mechanical properties of the tiles Fibre

Slag: lime: gypsum: sand; wrc

Warping Žmm.

Water absorption Ž% in mass.

Dry mass at 1008C Žg.

Reference Žno fibres. Eucalyptus pulp

0.86: 0.04: 0.10: 1.5; 0.40 0.86: 0.04: 0.10: 1.5; 0.48 0.86: 0.04: 0.10: 1.5; 0.48

0.91

14.1

2101

2.01

17.6

2.52

1.47

Sisal Ž1%. q eucalyptus pulp Ž1%. Coir a

0.86: 0.04: 0.10: 1.5; 0.48

Thickness Žmm.

Maximum load ŽN.

Absorbed energy ŽN.mm.a

Specific energy ŽN.mmrmm2 .a

9.37

672

1088

0.442

1833

9.15

629

1269

0.527

16.7

1867

8.59

556

1126

0.498

17.1

1993

454

2299

0.802

10.9

Test stopped when load decreased 70% in relation to maximum load.

7. Conclusion Plant fibre reinforced brittle matrices presented technical and economical feasibility in comparison to similar commercial materials. The composites with reinforcement of eucalyptus pulp, coir or eucalyptus pulp combined with sisal fibres reached acceptable physical and mechanical performance, mainly concerning ductility increase.

Acknowledgements The authors would like to thank FINEP-Financiadora de Estudos e Projetos, Programa HABITARE ŽBrazil. for the financial support. References w1x Giannasi F, Thebaud-Mony A. Occupation exposures to as´ bestos in Brazil. Int J Occup Environ Health 1997;3Ž2.:150]57. w2x Agopyan V, John VM. Durability evaluation of vegetable fibre reinforced materials. Build Res Info 1992;20Ž4.:233]35. w3x Brandt AM. Cement based composites: materials, mechanical properties and performance. London: E & FN Spon, 1995:470. w4x Hannant DJ. Fibre cements and fibre concretes. Chichester: John Wiley & Sons, 1978:219. w5x Coutts RS, Ridikas V. Refined wood fibre-cement products. Appita 1982;35Ž5.:395]400. w6x Akers SA, Studinka JB. Ageing behaviour of cellulose fibre cement composites in natural weathering and accelerated tests. Int J Cem Comp Lightweight Concr 1989;11Ž2.:93]97. w7x Coutts RS. Natural fibre reinforced cement and concrete. In: Swamy RN, editor. Wood fibre reinforced cement composites. Glasgow: Blackie, 1988:1]62. w8x Mattoso LHC; Frollini E, Leao A, editors. Proc 2nd Int Symp Nat Polym Compos. Embrapa Agricultural Instrumentation: Sao Carlos, 1998.

w9x Coutts RS. From forest to factory to fabrication. In: Swamy RN, editor. Proc 4th Int Symp Fibre Reinforced Cement and Concrete. ŽRILEM Proc., 17., London, E & FN Spon, 1992: 31]47. w10x Savastano Jr. H, Agopyan V. Transition zone studies of vegetable fibre-cement paste composites. Cem Concr Comp 1999;21Ž1.:49]57. w11x Guimaraes ˜ SS. Vegetable fibre-cement composites. In: Sourball HS, editor. Porch 2nd Nit Sump Vegetable Plants and Their Fibres as Building Materials ŽRILEM Proc., 7.. Chapman and Hall, London, 1990:98]107. w12x John VM, Agopyan V, Derolle A. Durability of blast furnaceslag-based cement mortar reinforced with coir fibres. In: Sobral HS, editor. Proc 2nd Int Symp Vegetable Plants and Their Fibres as Building Materials ŽRILEM Proc., 7.. Chapman and Hall, London, 1990:87]97. w13x Soroushian P, Shah Z, Won J-P. Ageing effects on the structure and properties of recycled wastepaper fiber cement composites. Mater StructrMater Constr 1996;29:312]17. w14x Agopyan V. Vegetable fibre reinforced building materials}developments in Brazil and other Latin American countries. In: Swamy RN, editor. Natural fibre reinforced cement and concrete. Glasgow: Blackie, 1988:208]42. w15x Reunion Internationale des Laboratories D’Essais et des Recherches sur les Materiaux et les Constructions ŽRILEM.. Testing methods for fibre reinforced cement-based composites. Mater Constr, 1984; 17Ž102.: 441]456 ŽRILEM Draft Recommendations, Technical Committee 49 TFR.. w16x Gram HE, Gut P. Directives pour le Controle de Qualite. St. Gallen: SkatrBIT, 1994; 69p ŽSerie Pedagogique TFMrTVM: Outil 23.. w17x Guimaraes SS. Experimental mixing and moulding with vegetable fibre reinforced cement composites. Proc Int Conf Development of Low-Cost and Energy Saving Construction Materials and Applications, vol. 1. Envo, Rio de Janeiro, 1984:37]51. w18x Oliveira MJE, Agopyan V. The influence of simple treatment in malva fibres employed in the reinforcement of Portland cements mortars. In: Sobral HS, editor. Proc 2nd Int Symp Vegetable Plants and Their Fibres as Building Materials. Latecoming papers. Chapman and Hall, London, 1990.