STUDIES ON THE MECHANICAL PROPERTIES, FIELD TESTING AND ANALYTICAL MODELING OF A NONPROPRIETARY ULTRA-HIGH PERFORMANCE CONCRETE BRIDGE

Abstract

Nonproprietary ultra-high performance concrete (UHPC) has been developed and investigated in different places in the United States of America (USA) and around the world. Recent research at New Mexico State University (NMSU) has developed mixture proportions for nonproprietary UHPC. Using local materials reduced cost while maintaining similar mechanical properties compared to commercially available products. The research program of nonproprietary UHPC focuses on the mixture proportion design, material behavior, and implementation for the structural applications. To better understand the behavior of the UHPC and its use in structural members, the mechanical properties including compressive strength, flexural tensile strength, and modulus of elasticity were investigated. Two types of curing regimens were implemented to observe the differences in the behavior and assess the effect of curing. Compressive strength was tested using cube specimens. The modulus of elasticity was measured using cylinder specimens. The flexural tensile strength of UHPC was measured according to ASTM C1609. The small-scale specimens [prisms] were used to study the flexural behavior of UHPC reinforced with steel fibers identifying key points including the first-peak flexural strength - modulus of rupture - (first cracking), peak strength, and post cracking behavior. The specimens [cubes, cylinders, and prisms] were tested at different time intervals to monitor the change in the behavior over time. The results from the compressive strength, modulus of elasticity, flexural testing, the strength gain over time, and comparison between the two different curing regimens are provided in this research. Additionally, equations to estimate the modulus of elasticity and first-peak flexural strength were developed to assist the development of design codes and provide tools for engineers to estimate the behavior of these type of mechanical properties. The research also investigated the behavior of Bridge No. 9706 through load testing. Bridge No. 9706 was constructed in 2017 and is the first bridge in New Mexico (NM) incorporating the locally developed UHPC. The bridge consists of two simply supported spans. One span was designed with locally developed UHPC, and the other span was designed with high performance concrete (HPC). Since being open to traffic, four load tests were completed to better understand the use of the new material, UHPC, and have a direct comparison to the HPC. The bridge provides a unique study having the two different materials experience the same environment and loading conditions. This research reports the third and fourth load tests conducted on the bridge and compares the behavior all load tests. The behavior of the UHPC span is provided and compared to the HPC span. The results from the load tests were used to build a finite element model (FEM) using the CSIBridge software (CSI, 2017). The model was created using solid elements for the bridge superstructure components. The model was calibrated based on the results from the third load test. The results from the model were compared to the different load path scenarios from the third load test and verified the model captured the behavior of Bridge No. 9706. The model was then used to estimate the behavior of the bridge under the fourth load test truck weights. Finally, the model was used to predict the behavior of the New Mexico legal loads for different types of axle and weights. The results are provided in this research as well as a comparison between the two spans’ behavior. The model provides a baseline behavior for Bridge No. 9706.