Influence of Oil-Based Corrosion Protection on Friction Losses During Strands Installation and Prestressing

Oil-based coatings are widely used as a short-term corrosion protection measure in bridge engineering, mainly to protect prestressing material during site storage and in the time before grout application which then provides long-term protection for tendons. The oil-based coatings should be removed prior to grouting but in practice may remain present during stressing, whereupon they may reduce friction with either beneficial or adverse effects on the design. Occasionally, oils are used solely as a lubricant during strand installation into the duct to minimize friction. Large scale experiment of two-span post-tensioned beams was conducted at Slovak University of Technology in Bratislava. The primary purpose of the experiment was to observe the impact of oil based corrosion protection on bond properties of prestressing strands. As one of the measurement techniques, Elasto-Magnetic (EM) gauges were used, which can directly record the force inside the strands during prestressing and loading cycles. Based on these records it is possible to evaluate the immediate prestressing force losses which occurred during the prestressing procedure. This paper discusses the influence of oil based coatings on immediate prestressing losses and evaluates the subsequent behaviour of grouted post-tensioned structures once in service.