Completed Research Projects
CRC 95: Guidelines for Performance Based Seismic Design of Tall Buildings
CRC 94: Evaluation of Chloride Limits for Reinforced Concrete Phase A
CRC 93: Guide to Formed Concrete Surfaces
2019 Funded Research
The ACI Foundation is committed to progress in the industry by funding needed research and will fund six research projects this year. Summaries of each project are below.
Embodied Carbon in Construction Calculator (EC3) Tool
PI - Kathrina Simonen, Carbon Leadership Forum – University of Washington
Co-PI - Phil Northcott, C-Change Labs
The concrete industry has been a great leader in developing environmental product declarations (EPDs), helping designers and engineers calculate and reduce the amount of carbon “embodied” in the built environment; it is important to continue to promote the accessibility of concrete environmental data. Even though concrete EPDs are increasingly available, it is not easy to compare EPDs side- by- side nor is it easy for users to find EPDs for mixes available in their specific market. The proposed Embodied Carbon Construction Calculator (EC3) tool is designed to address this issue, not just for concrete, but for other materials types as well. EC3 is a software tool that aims to provide open-source data and intuitive visualizations to help designers integrate embodied carbon into design and procurement decisions. The tool will be cloud- hosted, free, and web accessible.
The goal of the EC3 tool is to be the most available, transparent, and robustly actionable embodied carbon database for construction in North America. Further, the tool aims to include performance standards as a design criterion and this will help direct the industry to pursue performance-based design standards. With consistent application of assumptions across each project, it can drive improved practice, materials innovation, and vendor accountability for embodied carbon. The EC3 project will be hosted by the Carbon Leadership Forum at the University of Washington.
Upon completion, the EC3 tool will showcase the concrete industry’s impressive work in calculating and publishing its large body of EPDs. ACI technical input and endorsement is through ACI Committee 130, Sustainability of Concrete. Sean Monkman, of CarbonCure Technologies and Chair of ACI 130 states, “Sustainable construction decisions hinge upon having accurate and actionable information. Our committee recognizes that there exists a favorable sustainability narrative concerning concrete provided it is discussed and presented fairly.” Our co-funding, along with others not only in the concrete industry, will help to give our industry the opportunity to accurately reflect these aspects of concrete performance.
An Innovative Approach to Concrete Confinement Reinforcement
PI - Ashley Thrall, University of Notre Dame
Co-PI - Yahya Kurama, University of Notre Dame
Industry encourages this exciting innovation for concrete confinement in seismic regions. The combination of high strength and high ductility of steel coil products available in the United States offers several untapped possibilities in construction. This research will investigate one: a knowledge gap in lateral confinement behavior in columns with strip reinforcement. The aim of this research is to study the behavior of seismic precast columns with ductile, high-strength (yield strength of 100 ksi or greater) steel coiled (spooled) strips as internally-placed (embedded) continuous transverse spiral confinement reinforcement. This work is an extension of current work, funded by PCI, on the effectiveness of strip confinement reinforcement for axial loading. The ACI Foundation funded research will further develop this innovation through a large-scale experimental investigation of columns under reversed- cyclic lateral loads combined with sustained axial loading.
The measured, experimental data on the behavior, will be used to validate confinement models and lead to design recommendations. Understanding the behavior of precast columns under this combined loading is critical to the accelerated application of this new confinement system in building and bridge structures subjected to seismic loading. While the research will focus on confined concrete columns, results will also be relevant to boundary regions and plastic-hinge zones of beams, walls, and piers
This innovative approach should reduce congestion and speed up fabrication. As compared to rebar hoop confinement, spiral strips have the potential to provide increased ductility and strength of concrete structures under seismic loading because: (1) wider and thinner strips in spiral configuration result in greater volume of effectively confined concrete (strips act like an internal jacket rather than individual rebar); (2) smaller thickness of strips results in a greater effective depth for the extreme longitudinal rebar; and (3) greater width and spiral configuration of strips provide better lateral support against buckling of longitudinal rebar after cover spalling. Steel coiled strips can accelerate fabrication of precast components because: (1) strips can be rapidly uncoiled, bent/wrapped, and tied to longitudinal rebar with no need for splices; and (2) strips with smaller bend radii reduce congestion, thereby easing placement of longitudinal rebar and concrete.
The focus is on precast concrete building components and supported by Joint ACI-ASCE Committee 550 Precast Concrete Structures, it is also envisioned that the results could potentially apply to bridge structures (piers) in seismic regions or other types of reinforcement with broad use in both the building and bridge industries.
Effective Characterizations of Recycled Concrete Aggregate (RCA) for Concrete Applications
PI - Jiong Hu, University of Nebraska-Lincoln
Co-PI - Tara Cavalline, University of North Carolina at Charlotte
As sources of quality natural aggregates become challenging or economically prohibitive to obtain in some markets, and the economic and sustainability benefits of concrete recycling become increasingly enticing to stakeholders, use of Recycled Concrete Aggregate (RCA) in new concrete is receiving renewed interest in recent years. Major obstacles that hinder the use of RCA in concrete construction cited by practitioners are the lack of specifications/procedures for qualifying an RCA source and the unclear impact of RCA on concrete performance. Many of these problems can be resolved by an accurate characterization of RCA, which includes geometrical properties, physical and mechanical characteristics, and chemical characteristics/compositions. While the composite nature of RCA makes it more complicated than natural aggregate, its characterization is similar – primarily focused on gradation, specific gravity, and absorption.
A more robust characterization approach is required to promote its use. However, it is not practical nor economical to include an excessive amount of testing or expensive types of characterization methods. The purpose of this research is to identify the most effective and practical RCA characterization methods and procedures through experimental study. The study intends to establish an RCA characterization protocol, provide recommendations for RCA concrete mixture designs and identify best practices for RCA to be used in concrete construction. The project was endorsed by ACI Committee 555 Concrete with Recycled Materials, which believes the success of the study will greatly encourage the use of RCA in the daily concrete production.
Deconstruction Monitoring of a Cast-in-Place Segmental Concrete Box Girder Bridge
PI - Matthew Yarnold, Texas A&M University
Co-PI - John Mander, Texas A&M University
The goal of this study is to further the state- of- knowledge about the long- term behavior of segmental concrete box girder bridges. The existing Sam Houston Ship Channel Bridge (SHSCB) is in the process of being replaced after 36 years of service due to traffic volume and ship clearance demands. A unique opportunity is presented now that the structure is being decommissioned.
The proposed research aims to take full advantage of this situation through a detailed field study that can identify the locked- in prestressing forces in addition to the in-service behavior under thermal variations and live load demands. The approach to identify these locked- in prestressing forces is through a method called deconstruction monitoring. Deconstruction monitoring is the measurement of deformation release in structural members as the structural system is being disassembled. These measurements will be valuable for understanding how well prestresssing forces are estimated over the life of a segmental concrete bridge. Long- term effects can significantly alter these forces. These long- term effects include concrete creep and shrinkage, along with steel strand relaxation. The field- measured results will be compared to a variety of current models and the original design.
The study will benefit future design and maintenance strategies for segmental concrete bridges, serving the endorsing ACI committees 342 Concrete Bridge Evaluation and 343 Concrete Bridge Design and the greater transportation community, including AASHTO, TRB, PCI, PTI, and ASBI and their constituent stakeholders.
Structural Response and Buckling Behavior of Slender Ultra High Performance Columns
PI - Mohamed Moustafa, University of Nevada - Reno
The use of Ultra-High Performance Concrete (UHPC) is currently expanding worldwide from bridge deck joints and connections to full components and larger applications. To improve structural design of UHPC members for different applications in bridge or buildings, a better understanding of the damage mechanism and sections capacity is needed. One potential application is the use of UHPC columns in buildings and bridges to reduce the members’ cross- sections and footprint. Due to the enhanced mechanical characteristics of UHPC and high compressive strength, more slender sections are expected for same applications relative to conventional reinforced concrete. Thus, it is important to investigate the elastic and inelastic buckling behavior of UHPC columns and determine whether current ACI 318 procedure for slender columns and second- order moment analysis, which involves an estimation of the composite column effective stiffness and critical buckling loads, is valid for UHPC columns.
One important aspect that requires further investigation is the effect of the confinement due to the transverse reinforcement. Confinement due to transverse reinforcement can increase the crushing ultimate load capacity of columns and might lead to buckling taking place first for the cases of higher slenderness ratio. The objective of this proposed study is to test several large- scale UHPC columns with different slenderness ratio, different confinement, and different cross- sections under concentric axial loading to determine the axial load capacity and ductility as it relates to crushing versus buckling. This experimental data can be immediately used to validate ACI 318 design procedures for columns and future validation/calibration of computational and constitutive models for capturing the UHPC columns structural response through failure.
Endorsed by ACI Committee 239, Ultra-High Performance Concrete, the work proposed will also help the committee develop guidance for the design of UHPC columns. Currently, Committee 239 is developing a report on design processes for structures constructed with UHPC, with the long-term intent to develop structural design guidance. Developing design guides that optimize the expensive material, which minimizes material volumes required, make the product a more economically viable solution in structural design
Optimization of Fiber-Reinforced Concrete Using Data Mining
PI - Emilio Garcia-Taengua, University of Leeds
Over the last decade, the use of fiber- reinforced concrete (FRC) has gained increasing presence in routine production and field applications. Fibers improve the mechanical properties of concrete. However, the residual flexural strength parameters, which are the basis of FRC characterization and specification, present high levels of variability. Therefore, the proportioning of FRC mixes and their optimization needs to consider fresh and hardened state properties as well as their variability, which is key to an effective quality control of FRC production. To date, no meta- analysis of the properties of FRC has been done and therefore a comprehensive study that considers all these dimensions (workability, mechanical properties, and variability) as a multi- objective optimization problem is urgently needed.
This project is a novel approach that will be useful for designers, practitioners, and the concrete industry in general. It aims to compile an exhaustive database with information on different FRC mixtures and their properties, and to analyze it from a data analytics perspective to develop mathematical models for their optimization. Using papers published since 1999 as the main source of information, probabilistic analysis will be used to define quality control charts for use in the monitoring of continuous production of FRC mixes. All this information and models will be implemented in a software package called “OptiFRC” that can be used to access the database compiled, to visualize and utilize the models for the optimization of FRC mix proportioning, and to calibrate and use quality control charts. Emphasis will be placed on the need for this software to be as user- friendly as possible, making all the information accessible to concrete practitioners without requiring specialist statistical knowledge. This application-oriented project is endorsed by ACI Committee 544 Fiber-Reinforced Concrete and industry is eager to be collaborative as it will advance industrial practice namely by simplifying proportioning trial mixes, reducing production costs and yielding better FRC.