PCI Journal Paper Title: Development lengths of high-strength selfconsolidating concrete beams

Overloading, corrosion, and material aging deteriorate the structural performance of prestressed concrete (PC) bridges. Strengthening techniques are needed to improve the serviceability and extend the life of these deteriorating bridges. This study examined a strengthening technique with double-layer prestressed steel wire ropes (PSWRs) to enhance the serviceability of an existing post-tensioned concrete box beam for the first time. The tested box beam was removed from a demolished 20-year-old bridge. The service-level behavior of the beam, before and after strengthening, was evaluated using four-point flexural loading. The enhancement effects of the double-layer PSWR on the service-level behavior of the beam are discussed, including details on deflection, crack width, and reinforcing steel stress. Results show that PSWR strengthening is a feasible method for improving the serviceability of post-tensioned concrete box beams. The restraining effect of PSWR on crack development is more significant than the effect on deflection and reinforcing steel stress. Crack width, deflection, and reinforcing steel stress under the code-specified service load decreased by 50, 23, and 21%, respectively, after strengthening.

Recycled concrete aggregates (RCAs) have the potential to be used as a sustainable, cost-effective, and environmentally friendly material in pavement base construction. However, there is a lack of information on the durability, strength, and hydraulic properties of RCA. The primary purpose of this study was to evaluate the properties and performances of commonly available RCAs in Oklahoma as pavement bases through laboratory testing and AASHTOWare Pavement ME simulations. For this purpose, three RCAs (RCA-1, RCA-2, and RCA-3) and a virgin limestone aggregate (VLA-1) were collected from local sources. RCA-1 and RCA-3 were produced in the field by crushing the existing concrete pavement of Interstate 40 and US 69 sections, respectively. RCA-2 was produced by crushing concrete and rubble collected in a local recycling plant. Laboratory testing for this study included particle size distribution, wash loss, optimum moisture content and maximum dry density (OMC-MDD), Los Angeles (LA) abrasion, durability indices (D_c and D_f), permeability (k), and resilient modulus (M_r). The properties of aggregates were compared and the service life (performance) of aggregate bases was studied through mechanistic analysis using the AASHTOWare Pavement ME design software (version 2.6, AASHTO, USA). The results indicated that the properties of RCAs can differ greatly based on the origin of the source materials and the methods used in their processing. Recycled aggregates from concrete pavements of interstate and state highways exhibited similar or improved performance as virgin aggregates. RCA produced in a recycling plant was found to show durability and strength issues due to the presence of inferior quality materials and contaminants. Also, the results indicated that the fine aggregate durability test is a useful tool for screening recycled aggregates to ensure quality during production and construction. Bottom-up fatigue cracking was identified as the most affected performance criterion for flexible pavements when using RCA as the base layer. The findings will help increase the use of RCA as pavement base to promote environmental sustainability.

Transfer length is a significant parameter in the design of pretensioned concrete members. The estimation of transfer length is typically achieved by measuring concrete strain or strand slip at the member ends. The end slip method is simple and requires little effort, but relies on an empirical formula with an undetermined coefficient (α), which relates to the bond stress distribution. Many studies have proposed appropriate α coefficients; however, the variability in estimating the α coefficient exists between studies depending on the chosen empirical fit. This study gives an estimation of the α coefficient using a probabilistic approach called the maximum likelihood (ML) method. Approximately 600 data points of transfer lengths and strand end slips were measured for 25 pretensioned concrete beams. Strand end slips were measured at release and at 3, 5, 7, 14, and 28 days. Concrete strains were measured at the same period of time using a detachable mechanical strain (DEMEC) gauge to determine the t...