Application of Sustainable BCSA Cement for Rapid Setting Prestressed Concrete Girders
Presented By: Stephen Roswurm
Affiliation: University of Oklahoma
Description: In recent years, urgency for adopting sustainable materials has come to the forefront of the cement and concrete industries. Belitic calcium sulfoaluminate (BCSA) cement is an alternative cement which has a production energy demand of up to 60% less than portland cement and emits 30-50% less CO2. Although BCSA cement has been used in the U.S. for pavements, bridge decks, floors, and tanks, information on characteristics relevant to prestressed concrete is lacking. The purpose of this research was to establish strand bond, prestress loss, and time-dependent performance characteristics for BCSA cement concrete to increase production efficiency and member performance for precast, prestressed concrete. BCSA cement-based concrete can reach minimum strength for prestress transfer much sooner than portland cement concrete due to inherent rapid hardening properties. These time savings could allow precasters to clear stressing beds more quickly and streamline productivity, but the impact of early loading on long-term behavior is unknown. Mix designs for self-consolidating BCSA cement concrete were developed with sufficient workable time at various temperatures while reaching compressive strength required for prestress release in 2-3 hours. Material properties including flexural strength, elastic modulus, creep, and shrinkage were established. Fifteen 20' long prestress girders were fabricated and tested for strand transfer length, development length, and long-term prestress lossess. The measured material properties were used to model prestress losses which were compared with the values measured from the girder tests. Measured prestress losses were significantly lower than existing equations indicated, while models developed from material property data were more accurate.
Flexural Behavior of Bamboo-Reinforced Sulfur Concrete Beams for Planetary Applications
Presented By: Mitchell Thiel
Affiliation: Bradley University
Description: Settlement on Mars has become the next huge leap for the human species during the 21st century. To accomplish that, there are challenges to overcome, such as the expense of transporting all construction materials from Earth to the red planet, Mars. Thus, the application of local resources available on Mars is a viable option. The research study proposes to use indigenous soil concrete on Mars (sulfur concrete) and use bamboo pieces (shipped from the home planet or grown on Martian soil in the future) for reinforcing the sulfur concrete. Bamboo has a tremendous economic advantage, as it reaches its full growth in a few months and reaches its maximum mechanical resistance in just a few years. The most important property of bamboo for the planetary application is its density (~75 lb/ft^3) which is approximately 1/7 of the density of mild steel. This lower unit weight of bamboo compared to mild steel significantly serves towards the goal of reducing the transportation cost to the red planet. It should also be mentioned that the tensile strength of bamboo is approximately 20 ksi, which is almost 60% of that of conventional steel reinforcement (36 ksi). In this research, ten sulfur concrete beams, reinforced with different amounts of bamboo as longitudinal reinforcement, have been tested using three-point-bending test to measure their flexural strength. The results showed that the bamboo-reinforced concrete has a significant higher ductility, and almost two times higher flexural strength compared to those of the plain sulfure concrete.
SHM for Damage Prediction Leveraging Kinematic Contact Enforcement-based Moving Load and Deep Learning Techniques
Presented By: Suyun Ham
Affiliation: University of Texas at Arlington
Description: This paper presents a study on the development of hybrid models featuring structural health monitoring (SHM) inspection using bridge weigh-in-motion (BWIM) physics-based models. Artificial intelligence (AI) techniques helped improve the structural damage prediction during SHM inspection of bridges. This study introduces a comprehensive assessment of 1) a unique finite element (FE) simulation approach, which leverages the kinematic contact enforcement (KCE) method, verified with the vehicle-bridge interaction theory, and 2) machine learning (ML) techniques to identify and automatically predict structural damages from the structural response. The KCE method is a new approach to simulating vehicle motion in a BWIM model, which is used to carry out actual structural responses to motion providing contact conditions between elements (i.e., contact type, material properties, and element moving speed), which enables the realistic vehicle motion and structural response to be simulated. The FE model is designed with four different classes of damages with three different damage locations applied under different load conditions. These responses obtained from the FE simulation are further examined by using the feature selection method, which provides the importance rank for ML models. A prediction model includes: 1) a decision tree, 2) a support vector machine, 3) backpropagation, and 4) XGBoost. Among these prediction models, the deep learning XGBoost with its assembly decision tree provided the most reliable results. The results in this paper verify that structural damage prediction can be achieved by using ML as well as the BWIM structural response, which provides high accuracy in bridge damage prediction.
Behavior of a Unbonded Post-Tensioned, Precast Concrete T-Wall under Lateral Loading
Presented By: Sumedh Sharma
Affiliation: University of Alabama
Description: Precast rocking shear walls with unbonded post-tensioning provide a low damage alternative to traditional monolithic reinforced concrete shear walls. However, laboratory testing of precast rocking shear walls has been limited to rectangular cross-section, despite the widespread use of nonrectangular shear in elevator cores or around hallways. This experimental study supported by National Science Foundation (NSF) aims to address this knowledge gap by conducting laboratory testing of a Tshaped precast rocking shear wall. The T-wall specimen was constructed at 1/3rd scale of a prototype wall and tested under multi-directional loading up to 1.50% drift. The T-wall specimen was 5 in. thick, 5 ft. and 6 ft. wide in flange and web direction respectively, with a loading height of 136.75 in. Observations during testing indicate that damage in the wall panel is limited to rocking corners, similar to rectangular rocking walls. The measured residual drift was less than 0.25% and the measured energy dissipation ratio exceeded the required value of 12.5%. The analysis of the measured force-displacement response indicated that the behavior of the wall specimen in the flange direction was different than that of an equivalent rectangular rocking wall. This test's unique experimental data is expected to aid in the design of non-rectangular precast rocking shear walls. Additional experimental and analytical research is required to develop uniform design guidelines for non-rectangular precast rocking shear walls. This presentation will provide a summary of experimental test results and observations.
Algorithm for Predicting Development and Transfer Length of Prestressing Strand across Multiple Variations
Presented By: John Cabage
Affiliation: Southern Illinois Univ Edwardsville
Description: In this study high-capacity strand (0.62-inch, 0.7-inch, and/or Grade 330) and the effects the strand has upon transfer and development length within prestressed concrete beams were examined. Published works indicate that current ACI and PCI formulas signifcantly overestimate the transfer and development length for high-capacity strand. As a result, the prestress concrete beam design process may not accurately predict the stresses within the end region of the beam. This may result in improper shear reinforcement design. In this study investigators observed a correlation with transfer and development length, strength of concrete, geometry of the strand, material properties of the strand, and strand spacing. An algorithm was developed using statical models which will enable the designer to predict transfer length more accurately at release and development lengths at ultimate and during the life of a prestressed component. Once the algorithm is finalized, the results will be compared to transfer and development lengths established from laboratory experimentation and published works performed upon multiple strand types and concrete strengths. The investigators will then create a software application that will aid the designer in specifying strand type and spacing.
Mechanical Properties and Electrical Resistivity of Portland Limestone Cement Concrete Systems Containing Greater than 15% Limestone and Supplementary Cementitious Materials
Presented By: Jose Garcia
Affiliation: California State University, Sacramento
Description: This investigation explored the feasability of producing strong, good quality, durable concrete in lowclinker systems (less than 50% clinker in some cases). The low-clinker content was achieved by combining interground portland limestone cement (PLC) with high limestone contents and different supplementary cementitious materials (SCMs). Seven cements, with approximate limestone contents between 3% and 31%, from two cement plants were used, in combination with SCMs, in forty two different mixtures with water-cementitious materials ratios (w/cm) of 0.40 and 0.45. The SCMs included Class F and C fly ashes, Grade 100 slag, and silica fume. Mechanical properties (compressive strength, tensile strength, elastic modulus) and electrical resistivity were measured at 1, 7, 28, and 91 days. Similar compressive strengths were observed for mixtures with equivalent effective w/cm ratios. Although the combination of PLCs with SCMs for very low-clinker systems resulted in decreased compressive strength, an increase in electrical resistivity was observed. More importantly, strong, good quality concrete can be produced without sacrificing environmental benefits.