Glassfibre reinforced concrete pipes

Glassfibre reinforced concrete pipes – a way forward?

Farahar, Bob

Bob Farahar, Slimline Technology Ltd, considers the benefits of an established application still largely unknown in the UK

The introduction in 1970 of glassfibre for reinforcing concrete was seen as a major technical development but, although successful in niche markets, it has yet to achieve its early promise. The future of this material could lie in the heavy side of the construction industry where it could be used in conjunction with, or to replace, steel. Several early projects were abandoned through the difficulty of incorporating 12-micron glass filaments into wet concrete and compacting the result into a commercial product. However, one major concrete pipe manufacturer persisted, seeing that the new fibre could possibly provide solutions to the problems of rising steel prices and competition from plastics by enabling the development of an improved pipe offering concrete’s durability, high quality and lower cost pipelines.

These benefits would be achieved in the following ways:

Concrete reinforcement cover would be unnecessary, permitting a reduction in wall thicknesses and weights

High fibre contents to meet design stresses would be needed only in the surface layers, reducing total contents below 1 % and material costs below those of steel-reinforced concrete (SRC) Spigot and socket joint profiles could be made thinner and formed within the pipe’s wall thickness, avoiding the usual projecting bell socket.

These small dimensional changes have a large effect on pipeline costs, saving 10-20% on transport to site, 10-15% on excavation and 20-30% on bedding material. The lower dimensions reduce ground loadings on the pipe, often allowing the use of lower strength pipes to meet the pipeline design. The absence of projecting bell sockets allow faster, more accurate handling and laying.

Conventional GRC manufacturing techniques were unsuitable for large-scale commercial production and schemes were developed for all pipe-making systems. For the first development, the spinning process was chosen for its higher concrete strengths and qualities, yielding impressive results and achieving the stable strength of GRC with less fibre content, producing a less heavy, improved pipe design at a lower material cost than was possible with SRC. Computer-controlled machinery improved productivity and manufacturing flexibility, allowing any size or class of pipe to be made in any order. Later versions of the machinery produced at the rate of thirty 750 x 2500mm pipes per hour, with immediate demoulding and warm-air curing. Manufacturing flexibility improved factory programming and operating costs, mix design changes reduced wastage, and capital costs and space requirements were substantially reduced without the steel-cage-making area or steam-curing chambers. The new pipe, appropriately named Slimline, led the National Water Council to comment that it `offers advantages over its traditional counterparts in weight, bedding requirements, ease of handling and jointing, all of which lead to reduced pipeline costs’. In the next few years, the pipe gained a high reputation with over 100km installed in the UK, often with 20% cost savings.

The technology was licensed extensively overseas, gaining inclusion in British, American and Japanese national standards. Despite an open licensing policy, its popularity generated opposition from conventional producers, heightened by fears of disruption and replanting costs at the onset of the 1990s recession. Matters came to a head when the developer’s parent came under predatory attacks, forcing severe financial restrictions. These led to the shelving of UK Slimline operations, and the closure of all factories overseas, apart from Japan, where the long-term importance of the technology was recognised.

In Japan, the high costs associated with pipe-laying mitigated against the lower life expectancy of plastics and lower-quality concrete pipes, with dense spun concrete generally being demanded. Slimline comfortably passed the industry’s stringent tests and, with its cost-saving features, became recognised as a potential market leader. Over 100km of pipes up to 2400mm in diameter have been laid, with output trebling in the past two years despite the country’s construction industry recession. Japanese trenchless pipejacking systems have been particularly highly developed and the features of Slimline make it well suited for this severe duty. The Long Jacking Pipe (LJP) range has been most successful, gaining national records for lengths installed in a single thrust, frequently in difficult ground conditions. In one instance, 140m of 900mm pipe was installed, curving beneath a river as part of a 40 bar pressure irrigation pipeline.

Fundamental research on the Slimline style of GRC at Cambridge University discovered unique highstrength and strain characteristics, enabling significant improvements in the original technology. This also forms the basis for a highly economical range of 4.0 bar thin-wall smalldiameter pressure and drainage pipes. A second project, with greater potential, involves the development of steel reinforced GRC as an economical high-strength structural material where the fibre permanently increases the strain capacity of the concrete matrix, widening design opportunities by the use of different steels.

During the past 30 years, GRC has become well-established whereas Slimline pipes, although fully tried and tested and with some obvious advantages, are hardly known in most of the world. However, as many years of practical experience have shown this style of GRC to be durable, economical and competitive, perhaps it is time for its reappraisal.

Register now for ‘GRC 2001’

Early registrations for the Twelfth International GRCA Congress on 14-16 May 2001 indicate that this conference will have a international appeal, with delegates from south-east Asia, China, America, South Africa, in addition to mainland Europe. Delegates will enjoy Dublin’s cosmopolitan and vibrant atmosphere where international commerce and modern buildings sit alongside traditional architecture, complemented by the youthful buzz of a university city.

However, the main reason for the event is to talk about glassfibre reinforced concrete! Traditionally, papers delivered at GRCA Congresses represent project case studies, technical, and research aspects of the GRC industry, together with developments in production equipment and topics of general interest, such as marketing. The varying development of GRC from country to country is also highlighted.

The Congress themes include the following:

Developments in GRC production technology

GRC applications and projects

Case studies of GRC performance

Standards and codes

* GRC and the architect

Exhibitions and visits to local GRC architectural projects

Presentation of merit awards.

These international meetings are a unique opportunity for producers, suppliers, architects, engineers and researchers to become aware of current technology and applications of GRC products. If you wish to present a paper, or would like further information on the Congress, please contact on the above number at the earliest opportunity.

New members

Welcome to new members of GRCA International:

GRC Brasil, Facciostonelite, Rua Cristovao Gouveia 99, Parque Anhanguera 05120-020 Sdo Paulo, Brazil. Suppliers of architectural precast concrete and GRC. Tel: +55 11 3621 5188; Fax: +55 11 3621 4675; e-mail: marketing @grcbrasil.com.br

Trent Concrete Ltd, Colwick, Nottingham, NG4 2BG, UK. Suppliers of architectural precast concrete and GRC. Contact: Mike Downing. Tel: +44 (0) 115 987 9747; Fax: +44 (0)115 987 9948; e-mail: mdowning@trentconcrete.co.uk Blue Circle Industries plc, Bridge House, Overbridge Square, Hambridge Lane, Newbury, Berks, RG14 5UX, UK. Suppliers of speciality dry-bagged render products. Contact: Charles Hawkins. Tel: +44 (0) 1635 527 323; Fax: +44 (0)1635 527 418; e-mail: cthawkins@bluecircle.co.uk

Richard Ferry, GRCA Advisory Service, 26 Gorsey Brow, Bilinge, Wigan, Lanes, WN5 7NX, UK

Abbey Glass Fibre Products Ltd, Worth Valley Works, Pitt Street, Keighley, BD21 4PG, UK. Suppliers of architectural GRP, reconstituted stone and GRC. Contact: Mike Moore. Tel: +44 (0)1535 610 964; Fax: +44 (0)1535 690 989; Mobile: +44 (0)374 239 501, e-mail: mmoore1031@aol.com.

Golden Trend Construction Ltd, Unit 2503, 25/F Prosperity Centre, 25, Chong Yip Street, Kwun Tong, Hong Kong. Suppliers of architectural precast concrete and GRC. Contact: Harry Cheung. Tel: +852 2380 9605; Fax: +852 2414 5766; e-mail: goldentrend @chinabuildtech.com.

Emirates Contracting Co. LLC, PO Box 4583, Dubai, United Arab Emirates. Manufacturers of ornamental GRC, GRP and gypsum products. Contact: Shiva Pagarani. Tel: +971 (0) 43470 471; Fax: +971 (0) 4347 0782; Mobile: +971 (0) 5056 26464, e-mail: bolenath@emirates.net.ae.

Please could all GRCA International members remember to keep us informed of address and contact number changes. Also, if you have started to use e-mail or have your own website, links can be created from the GRCA website (www.grca.co.uk). To do so, simply go to the member sites section and follow the instructions.

Copyright The Concrete Society Oct 2000

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