Bond, Transfer Length, and Development Length of Prestressing Strand in Self-Consolidating Concrete

Abstract

Due to its economic advantages, the use of self-consolidating concrete (SCC) has increased rapidly in recent years. However, because SCC mixes typically have decreased amounts of coarse aggregate and high amounts of admixtures, industry members have expressed concerns that the bond of prestressing strand in SCC may be compromised. While the bond performance of prestressing strand in a new material such as SCC is an important topic requiring investigation, the results are only applicable if the research is completed on strands with similar bond quality as the strands used in the field. Therefore, the objectives of this research program were to investigate the transfer and development lengths of prestressing strand in SCC and also evaluate the effectiveness of two proposed bond tests in determining acceptable bond quality of strand. Transfer and development lengths of 0.5-in. diameter (12.5 mm), Grade 270 prestressing strand were evaluated using rectangular beams constructed from normal and high strength conventional concrete and SCC mixes. End slips at release and strain readings over 28 days were used to calculate transfer lengths, and development lengths were evaluated through four-point loading at varying embedment lengths. Additionally, the North American Strand Producers (NASP) bond test and Large Block Pullout Tests (LBPT) were evaluated with strand from three different sources to determine if one test could be considered more reliable at predicting acceptable bond. Results indicated that bond performance of SCC and conventional concrete were comparable, and that AASHTO and ACI equations for transfer and development length were generally conservative. The NASP bond test and LBPT were found to be equally valid, but the acceptance limits for both tests appear to require revisions.