Evaluating the Time-Dependent and Bond Characteristics of Lightweight Concrete Mixes for Kansas Prestressed Concrete Bridges

摘要

This report details results from testing that was conducted to determine the bond and time-dependent characteristics of two lightweight concrete mixes. The lightweight mixes were evaluated to possibly provide a more cost-effective solution to replacing some of Kansas older bridges. Testing included use of a conventional lightweight mix and a self-consolidating lightweight mix. Sixteen Inverted T-beams were cast at a prestress plant to determine prestress losses that had occurred in the two lightweight mixes. These losses were compared to ACI, PCI, and AASHTO code equations. Creep and shrinkage prisms were also cast and measured to accurately determine creep and shrinkage variables for the two lightweight mixes. Twelve flexural beams were cast at the prestress plant and tested at Kansas State Universitys Civil Engineering Structural Mechanics Laboratory to experimentally evaluate the development lengths of the lightweight mixes and to compare results with the ACI code equations. This study found the compressive strengths of the plant-cast lightweight concrete mixes varied greatly from similar mixes in laboratory testing. Low concrete strengths caused the prestress losses to be greater than the predicted code values. Flexural beam testing revealed that several of the pretensioned beams failed suddenly due to strand slip, even though this was not the predicted failure mode.