Darren Loidl’s scientific contributions

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. Failures of steel strand ground anchor systems are rare, but when they occur, corrosion and human error are the primary reason. Several methods of minimising anchor system corrosion have been adopted over time to minimise ingress of corrosive substances. However, anchors are still failing due to corrosion. Advancement in the development of corrosion resistant materials has been at the forefront of materials research. In this respect, research and development of FRP materials is enabling 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 provides an overview of current best practices for the application of permanent ground anchors and investigates the current developments in FRP materials for ground anchor applications as an alternative to conventional steel tendon ground anchors. The paper also provides insight into known areas where further research is required to assist the introduction of FRP ground anchors into standards.

High capacity ground anchors currently employ the well established steel strand system using stress relieved post tensioned strands. Although such systems provide rugged tendons with readily available hardware, they are vulnerable to corrosive attack from aggressive ground environments. Current permanent ground anchor standards require the use of double protection systems encapsulating the steel strands, to ensure a serviceable design life. Fibre Reinforced Polymer (FRP) is characterised by its superior resistance to aggressive environments, compared to steel. In recent years, where steel reinforcement use was restricted due to aggressive ground conditions, FRP reinforcement was successfully used as a durable construction alternative. Whilst carbon fibre (CFRP) strands have been researched and developed for use in prestressed concrete members such as bridge construction, minimal research has been devoted to developing FRP strands for use in high capacity ground anchors. The paper summarises current research knowledge and best practices for use of CFRP strands in ground anchor systems. Research work reported in this paper involves investigation into CFRP strand performance in comparison to steel strands, when exposed to extreme aggressive environments. A series of six month long experiments are currently in progress studying these durability effects over a range of accelerated conditions including temperature and concentration levels, whilst specimens are in an unstressed and stressed state. This paper presents the interim results of unstressed CFRP specimens subjected to an alkaline and acidic based groundwater solution and a neutral solution tested under accelerated conditions (60 O C and increased salt concentration) over three months of a six month period. Based on the results of tests, the levels of corrosion protection systems required for CFRP anchor systems are critically assessed. Early progressive research results, presented by the authors, in the field of CFRP durability indicated that there are minimal overall material property changes over time when specimens are exposed to various aggressive groundwater environments.