Potential of alternative fibre cements as building materials for developing areas

doi:10.1016/S0958-9465(02)00071-9

Cement and Concrete Composites

Volume 25, Issue 6, August 2003, Pages 585-592

https://doi.org/10.1016/S0958-9465(02)00071-9 Get rights and content

Abstract

This project evaluated the performance of thin fibre-cement elements produced from alternative raw materials using the Hatschek process, with a view to their use in low-cost housing. Sisal and banana fibres were prepared using mechanical and kraft pulping procedures while residual Eucalyptus grandis pulp was obtained from a commercial pulp mill. Granulated blast furnace slag (BFS) was used as the major component of an alternative hydraulic binder and ordinary Portland cement as a control. Composites were prepared using a slurry vacuum de-watering process, pressing and air-curing. At fibre contents of 8–12% by mass, moduli of rupture (MOR) up to 23 MPa and fracture toughness (FT) values in the range of 0.6–1.7 kJ/m² were obtained at 28 days. After 12 months of exposure under temperate and tropical conditions, the MOR of the BFS-based composites had decreased to values in the range of 6.6–10.1 MPa. FT values remained stable or even increased with the weathering exposure. The results indicate that the mechanical performance of the composites being studied is currently satisfactory, but further optimisation of formulation and processing parameters should be investigated.

Introduction

In several developed countries, cellulose fibres derived from hardwoods or softwoods are used for the production of cement composites by adaptation of the former asbestos-cement production processes [1]. Asbestos cement still represents around 74% of the 190 million m² of fibre-cement composites produced yearly in Central and South America, mostly as corrugated roofing elements as noted by Heinricks et al. [2]. As increasing health concerns [3], [4] are leading to chrysotile asbestos bans in Latin American countries (e.g. Brazil and Chile), new products utilising available raw materials and production systems are necessary to fit consumer requirements in each application area. Research toward this end has been in progress for some time.

Tropical and equatorial countries are known for their plant fibre production [5] and the consequent generation of by-products from commercial, agricultural and industrial activities. With the low cost of raw material and simplified pulping methods, the resulting cellulose has considerable potential for fibre-cement production at significantly lower costs than those associated with the use of conventional kraft wood pulps produced for the paper market.

Granulated blast furnace slag (BFS) can provide advantages when used as a substitute for ordinary Portland cement (OPC). These may include energy savings, lower CO₂ emissions, cost reductions and an abundant availability in steel producing areas [6]. However, the hydration rate of BFS-based cement is known to be lower than that of OPC and to be strongly dependent on the degree of fineness and cure procedures employed [7].

The main objective of this collaborative work undertaken by the Commonwealth Science and Industry Research Organisation (CSIRO), Division of Forestry and Forest Products, Australia, and the University of São Paulo, Brazil, is to evaluate the production of thin alternative fibre-cement elements by the Hatschek process for use in low-cost housing. This paper presents an overview of the performances of clinker free cements reinforced with several waste-based pulps. The short term properties of these materials and the effects of ageing under three different environmental conditions are discussed.

Section snippets

Raw materials and preparation

Basic granulated iron BFS provided by Companhia Siderúrgica Tubarão (CST), Brazil, and fully characterised by Oliveira et al. [8], was ground to an average Blaine fineness of 500 m²/kg and employed as the main component of an alternative binder. Ground agricultural gypsum and construction grade hydrated lime were used as activators in proportions varying from 0.88:0.10:0.02 to 0.92:0.06:0.02 (BFS:gypsum:lime) by mass. These formulations are identified as BFS 10G2L and BFS 6G2L respectively

Composite preparation

Cement composite pads measuring $125 mm ×125 mm$ and reinforced with 4%, 8% and 12% by mass of the various pulps were prepared in the laboratory using a slurry vacuum de-watering technique previously described by Eusebio et al. [13]. The selection of fibre contents was based on the optimum levels found in a similar study [9]. Pads of each formulation were prepared in groups of three, pressed simultaneously at 3.2 MPa for 5 min, then sealed wet in a plastic bag to cure at room temperature for 7 days.

Test methods

A three point bend configuration was employed in the determination of modulus of rupture (MOR), fracture toughness (FT) and modulus of elasticity (MOE). A span of 100 mm and a deflection rate of 0.5 mm/min were used for all tests in an Instron model 1185 universal testing machine. Fracture energy was calculated by integration of the load–deflection curve to the point corresponding to a reduction in load carrying capacity to 50% of the maximum observed. For the purpose of this study, the FT was

Weathering conditions

To determine the effect of weathering on the properties of the composites, some of the prepared samples were exposed to temperate and tropical weather conditions in Melbourne, Australia, and Pirassununga, Brazil, respectively. The samples were exposed 28 days after manufacture in racks inclined 45° and facing north in Melbourne (latitude 37°49^′S) and Pirassununga (latitude 21°59^′S). The exposure in Melbourne of composites reinforced with E. grandis pulp commenced in April 1999, while the

Results and discussion

Table 3 summarises the main mechanical and physical properties of BFS and OPC matrices with different fibre types and contents when tested at age 28 days. Fig. 1, Fig. 2, Fig. 3, Fig. 4 compare the range of properties measured at each fibre content with those of corresponding composites after aging. Table 4 details the properties of composites after storage in a controlled environment or exposure to weathering in temperate and tropical conditions for 1 year.

Conclusions

Five alternative pulps based on by products from agriculture or the papermaking industry were suitable as reinforcement for fibre cements based on clinker-free binders and produced by a slurry vacuum de-watering method. When first prepared the flexural strengths and toughness of these BFS-based composites reached values up to 23 MPa and 1.7 kJ/m² respectively, very close to those achieved with corresponding OPC-based materials. However, the large amount of vegetable fibres employed (up to 12%

Acknowledgements

The authors would like to thank the Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp) and Conselho Nacional de Desenvolvimento Cientı́fico e Tenológico (CNPq), Brazil, for their financial support, and Allyson Pereira and Göran Längfors of CSIRO Forestry and Forest Products for their skilful assistance.

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Potential of alternative fibre cements as building materials for developing areas

Abstract

Introduction

Section snippets

Raw materials and preparation

Composite preparation

Test methods

Weathering conditions

Results and discussion

Conclusions

Acknowledgements

Waste Mgmt.

Cem. Concr. Compos.

Cem. Concr. Compos.

Cem. Concr. Compos.

Cem. Concr. Compos.

Int. J. Cem. Compos. Lightweight Concr.

Fiber-reinforced cementitious materials

Global review of technologies and markets for building materials

Comparative hazards of chrysotile asbestos and its substitutes: a European perspective

Environ. Health Perspect.

Occupational exposures to asbestos in Brazil

Int. J. Occupat. Environ. Health

Fibre crops: new opportunities for Australian agriculture

Design for durability and strength through the use of fly ash and slag in concrete