Promoting macro synthetic fibre reinforcement 07 Mar 2019

Development of macro synthetic fibre began 30 years ago and has been commercially marketed for more than 20 years. The following is a brief overview on the historical development of MSF.

Macro synthetic fibre for concrete reinforcement

• Macro synthetic fibres were first developed by 3M in the USA in 1989 and the technology has spread widely since and in various applications including slabs-on-ground, shotcrete, and tunnel linings.
• Hagihara Industries in Japan developed the embossed MSF in the late 1990s. The high tenacity and the new bonding system set new milestones in performance levels.
• Australia led the way in use of MSF reinforced shotcrete (MSFRS) for ground stabilisation in mines, today with almost 100% uptake.
• Norway, as a leader in the development of wet shotcrete in the 1990s, led the way of MSF into civil tunnel applications.
• More recently, numerous MSF reinforced concrete and shotcrete tunnel lining projects have been completed internationally, including permanent shotcrete linings, cast final linings and segmental tunnel linings. A selection of these projects are presented on the MSFA website.

Key factors driving the adoption of MSF reinforcement for example in sprayed concrete linings have included:

• Economics: Macro synthetic fibre reinforced shotcrete (MSFRS) costs less compared to steel reinforcement for the same level of performance.
• Effectiveness: MSFRS works better for stabilizing deforming ground and is more durable.
• Ductility: MSFRS exhibits higher toughness than alternative forms of concrete reinforcement.
• Handling: Synthetic fibres are lighter and more readily transported and handled than alternatives.
• Durability: Water percolation in conjunction with chloride- and sulphate-containing ground has proven destructive to steel reinforcement in underground environments. Experience in mining environments has shown that small cracks enable percolating water to bring oxygen and salt ions directly to the surface of the reinforcement leading to corrosion and loss of structural competence. Numerous mines have switched to macro-synthetics based on the durability of polymer reinforcement¹.
• Long-term performance: MSFRS using high quality synthetic fibres does not show post-crack performance loss with age. In contrast, steel alternatives can exhibit loss of residual performance due to post-hardening effects of the matrix, also known as embrittlement. Neither corrosion nor embrittlement occur in MSFRC, so the long-term performance remains close to or better than the 28-day measured performance for cracks up to 0.30mm in aggressive environments².

Adoption of MSF in civil projects

The civil tunnelling industry is steadily moving in the same direction towards synthetic reinforcement. MSFRS has been used for temporary linings of numerous tunnels, but not until recently for permanent lining, with the exception of projects in Norway, Japan, the UK and Australia. MSF has been used also in linings that are sensitive to deflections and ground subsidence without adverse outcomes. An example of such an application is for the North Strathfield underpass project near Sydney, Australia³.

As designers and contractors, as well as asset owners, begin to recognize the advantages of macro-synthetics, more tunnels are being designed and constructed using this type of fibre reinforcement. There is no reported project in which excessive convergence or ground subsidence could be attributed to creep of macro-synthetic FRS. These factors are controlled by tunnel design and excavation sequences, not by the composition of the fibre.

Development of the MSFA

In order to create a united voice for the industry, leading manufacturers of macro synthetic fibre have established an association dedicated to the product and to the development of its application fields. A first meeting of the association was held at the WTC World Tunnel Congress in 2016 in San Francisco, and the Association, with a constitution, was formed, as a non-profit organisation, at a base in Switzerland in October 2017.

Three founding members were quickly followed by two additional manufacturers. After the first General Meeting of the Association, at the WTC World Tunnel Congress in 2018 in Dubai, five more applications were approved. The MSFA today comprises ten member companies.

The MSFA is aimed at bringing together a group of like-minded people dedicated to the progress of macro synthetic fibre concrete reinforcement in all facets of construction. The role of the MSFA is to provide a united voice to promote industry applications and provide confidence and support to users by education and training, as well as resolving the various technical issues that are still seen as barriers to entry into the market for this product. The MSFA represents the interest of members on national and international professional bodies, within standard and code committees, and in educational establishments around the world.

Information and education is not only necessary with regards to design and application of fibre reinforced concrete structures. Today, numerous copies of the initially engineered quality fibre types have emerged from producers in numerous countries where care must be taken with the quality and performance claims.

In this regard, important steps have been taken to treat macro synthetic fibre equally with steel fibre when it comes to standardisation, not only with regards to the general regulation of the fibre product, but also in the structural design and application in practice. Table 1 presents a brief overview on national and international guides and standards. The MSFA is devoted to support the continuous development of codification of MSF and MSFRC.

Full membership of the Association is open to companies or individuals engaged in development, manufacturing, sales or use of macro synthetic fibres, with the common interest of growing the responsible use of high quality MSF. Associate membership is open to companies, individuals or other associations who are engaged in concrete or concrete related products. This form of membership is equally open to interested individuals from the industry and academia. Members are expected to fully embrace the spirit of the MSFA by being actively involved in discussions about the Association’s role, direction and activities.

The next General Assembly of the MSFA will take place after the WTC World Tunnel Congress in Naples, Italy on Thursday, 9 May 2019. Contact MSFA via its website.