Transfer and development length of 0.6-inch diameter prestressing strand in high-strength lightweight concrete

This thesis presents the findings of a research project that developed and tested high-strength lightweight concrete mixes having strengths from 8,000 psi to 12,000 psi made using slate lightweight aggregate. Based on optimized mix designs, 6 pretensioned AASHTO Type II girders were constructed using 8,000 psi and 10,000 psi slate lightweight concrete and were prestressed using 0.6-inch diameter LOLAX strands tensioned to 75% of strand ultimate stress. The strands received no special preparation prior to beam casting. After initial curing, transfer length measurements were taken from time of release until the beams reached an age of 14 days. A direct pullout test was performed on both concrete design strengths to determine the bond between the slate lightweight concrete and the prestressing strand. Tests were conducted on each beam end to determine development length characteristics. The distance from the beam end to the load point was varied from between 70 and 100 percent of the AASHTO specified development length. Strand slip was measured on each test. Results indicated the following: a somewhat lower bond stress develops between the prestressing strand and the lightweight concrete when compared to similar strengths of normal-weight concrete; current 16th Edition AASHTO transfer and development length equations are conservative for use with slate lightweight concrete with design compressive strengths below 10,000 psi; there appears to be a tension strength ceiling on HSLC that affects flexural cracking strength and diagonal tension strength.