Transfer and Development Length of High Strength Lightweight Concrete Precast Prestressed Bridge Girders

摘要

This report presents the findings of a study that developed and tested high- strength lightweight concrete (HSLC) 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 HSLC 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 girder casting. After initial curing for approximately 24 hours, transfer length measurements were taken from time of release until the beams reached an age of 14 days. The current AASHTO and ACI code provisions conservatively predicted transfer length for slate HSLC; modification of the current code specifications for transfer length was not necessary for slate HSLC. A direct pullout test was performed on both concrete design strengths to determine the bond between the slate lightweight concrete and the prestressing strand. A somewhat lower bond stress developed between the prestressing strand and the lightweight concrete when compared to similar strengths of normal-weight concrete. However, the average pullout strength for both series exceeded the minimum required value for 0.6-inch diameter strand of 43.2 kips. Tests were conducted on each girder end to determine development length characteristics.