Benchmarking the Bond of 19-Wire-28.6-mm-Diameter Prestressing Strands to Normal-Weight Concrete

For the last 4 decades, concrete bridges have benefited from larger diameter prestressing strands, which have increased from 13 to 15 mm in diameter and are now the standard in the US. The largest commercially available strands in the US are 7-wire-18-mm-diameter strands, but they are not used as often despite researchers finding that they can provide longer spans and lighter structures. This research seeks to experimentally benchmark the bond of 28.6-mm-diameter grade 1780 prestressing strands to normal-weight concrete and mortar for the first time. The large-block pullout test (LBPT), the North American strand producer test (NASP), and concentrically reinforced prism (CRP) pullout test were conducted to quantify the pullout force of these strands when they were embedded in concrete as well as to determine an experimental reference value. The results showed that the strands exhibit adequate bonding to the concrete when implementing the LBPT, NASP, and CRP tests to evaluate them in combination with extrapolated values from the literature using a ratio of strand diameters. Furthermore, CRP tests indicated that the transfer length would likely be approximately 1,200 mm and the development length between 1,800 and 2,400 mm for 58-MPa concrete. It was also determined that due to their much larger surface area, the bond stress of these large-diameter strands was lower than that of 13-, 15-, and 18-mm-diameter strands for similar case scenarios of bond evaluation or transfer length estimation using prisms. However, there is limited information for comparison, and the testing program presented is the only one of its kind for this strand size.