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Advancements in ground anchors: carbon fibre reinforced polymer (CFRP) strands
| Content Provider | Semantic Scholar |
|---|---|
| Author | Sentry, Matthew Robert Bouazza, Abdelmalek Al-Mahaidi, Riadh Saleh Hassan Loidl, Darren Bluff, Chris Carrigan, Len |
| Copyright Year | 2007 |
| Abstract | Steel tendon ground anchors are an integral construction technique for numerous civil engineering applications ranging from deep excavation support to resistance of structural uplift and overturning of superstructures. Corrosion and human error generally causes failure of steel tendon ground anchors. Several methods of minimising anchor system corrosion have been adopted over time to minimise ingress of corrosive substances. Anchors are still failing due to corrosion. Advancement in the development of corrosion resistant materials has been at the forefront of materials research. Research and development of FRP materials has enabled the progress of providing the industry with a more potentially robust anchor system aimed at eliminating current limitations encountered with steel strand ground anchors. This paper investigates current developments in FRP materials for ground anchor applications as an alternative to conventional steel tendon ground anchors. Introduction Technological advancements of fibre reinforced polymer (FRP) products for applications in civil construction has allowed new products such as glass fibre (GFRP), aramid fibre (AFRP) and carbon fibre (CFRP) to pave the way for research into further improvements to the currently favoured steel tendon ground anchor system. This paper investigates current developments in FRP materials for ground anchor applications as an alternative to conventional steel tendons. Corrosion limitations to steel tendon ground anchors Corrosion in steel tendon ground anchors occurs as a consequence of in-homogeneities or impurities in the steel tendon or grout, or by the existence of salts, sulphates and other dissolved solids present in grout mixtures, soils or groundwater (Littlejohn and Bruce, 1977). International standards including EN1537:2000, AS5100.1-2004, BS8081:1989 require some type of corrosion protection for permanent ground anchor applications. Permanent steel tendon ground anchors require several areas to be corrosion protected, including tendon bond length, tendon free length, transition between anchor head and free length and the anchorage head. This paper will focus primarily on permanent ground anchor systems. Littlejohn (1987) reported on 35 known cases of corrosion related failures to steel tendon ground anchors, concluding that free length corrosion comprised 60% of failures, 34% of failures occurred in at the anchorage head and only 6% of failures occurred in the fixed Sentry, Bouazza, Al-Mahaidi, Loidl, Bluff, Carrigan, Page 2 anchor length. Catastrophic structural failures can occur as a direct result of ground anchor failure due to corrosion (Figure 1). Littlejohn emphasised that the small percentage of failures within the fixed anchor length was a result of inadequate grout placement. Steel tendon corrosion occurs locally where the tendon intersects a crack in the surrounding grout, or as a result of damage to the corrosion protective sheaths (Weerasinghe and Adams, 1997). Grout cracks occur as a result of either shrinkage strains during curing or tensile loading of the anchor. Due to grout micro cracking, majority of standards do not permit grout to be considered as one of the two means for corrosion protection. Weerasinghe and Anson (1997) and Mothersille (2006) provided project examples where corrosion occurred above and below the anchor head, resulting in anchor strength reduction (Figure 1). (a) (b) (c) Figure 1: Failure of anchored quay wall (b) corroded barrels and wedges in anchor head (c) lack of corrosion protection behind anchor block (Mothersille, 2006) Tendon material choice is limiting ground anchor development. Anchor corrosion and its need for protection, performs an integral element of a permanent ground anchor. Measures to prevent corrosion failure of permanent ground anchors has developed the double corrosion protection system (EN1537:2000) (Figure 2). Double corrosion protection is currently applied over the tendon bond length, tendon free length, the anchor head and the transition between the anchor head and the tendon free length. Outer corrugated sheath (HDPE or steel) Borehole wall Outer grout tube Inner corrugated sheath (HDPE) |
| Starting Page | 321 |
| Ending Page | 321 |
| Page Count | 1 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.omranista.com/eng/pdf/tech1-5.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
