Sessions & Events

 

Please note: All sessions and events take place in Central Daylight Time: CDT (UTC-5).

H=Hyatt Regency Dallas; U=Union Station

Research in Progress, Part 2 of 2

Monday, October 24, 2022  11:00 AM - 1:00 PM, H-Reunion B

This session will feature presentations of original, unpublished results from ongoing research projects and leading-edge concrete technology and research throughout the world.
Learning Objectives:
(1) Recognize ongoing concrete research projects from a wide range of research topics;
(2) Discuss recent techniques, research methods, and procedures related to structural and material aspects of concrete research;
(3) Describe engaging ideas in concrete research;
(4) Summarize recent technical information related to concrete materials and structure research.

This session has been AIA/ICC approved for 2 CEU/PDH credits.


Preliminary Evaluation of Performance of Hooked Reinforcing Bars in Noncontact Lap Splices

Presented By: Zachary Coleman
Affiliation: Virginia Polytechnic Institute and State Universit
Description: To accelerate bridge construction and improve economy, transportation authorities may employ noncontact hooked bar lap splices to rapidly connect adjacent precast concrete elements. Compared to straight bars, hooked bars may offer the advantage of shorter lap lengths to transfer tensile forces; however, significant test data are not yet available to justify this hypothesis. Accordingly, the objectives of this research are to examine the behavior of noncontact hooked bar lap splices and create new approaches for the design of such lap splices. In support of these objectives, six large-scale beam specimens containing noncontact hooked bar lap splices and one containing continuous reinforcing bars were tested to failure in four-part-bending. An additional 36 specimens will be tested in the coming years. The influence of the following parameters on splice strength have been studied thus far: concrete compressive strength, lap splice length, spacing of spliced bars, splice confinement, and detailing of confining reinforcement. All splice specimens failed due to the combined effects of prying action and hook side-bulging. Crack patterns at failure indicated that load was transferred between adjacent spliced bars through diagonal compression struts. All else being equal, the use of perpendicular confining reinforcement was found to most effective to increase splice strength.


Structural Rehabilitation of Post-Tensioned Concrete Bridge Cantilever Wings with Post-Tensioned CFRP Rods

Presented By: Faraj Shahrstan
Affiliation: Dalhousie University
Description: Bridge replacement is expensive; the US Federal Highway Administration (FHWA) has estimated that, in 2016, the total cost for the replacement of all structurally deficient highway bridges in more than 47 billion dollars (FHWA 2016). Thus, it is economically viable to develop efficient strengthening systems to rehabilitate existing deteriorated bridges to achieve bridge service life. Several Departments of Transportation have found compromised transverse post-tensioning (PT) steel in bridge cantilever wings, and a cost-effective rehabilitation strategy is required to fulfill the service life of the bridge structure. The current research investigates experimentally the utilization of PT carbon fiber reinforced polymer (CFRP) rods near-surface mounted (NSM) using a developed mechanical strengthening system to rehabilitate deteriorated PT bridge cantilever wings. The mechanical strengthening system is a metal anchor compromised of a stainless-steel barrel and split aluminum wedges in direct contact with a CFRP rod. The research aims to evaluate the viability of the CFRP rods in their ability to improve the service life of deteriorated PT concrete bridges and highlight the importance of corrective and protective maintenance strategies. The experimental program consists of fabricating, casting, post-tensioning, and testing under simulated service loads as per CSA S6-19 Bridge Code prior to ultimate failure of half-scale bridge deck cantilever specimens based on an existing in-situ bridge structure with compromised transverse steel post-tensioning within its cantilever wings. Two half-scale bridge cantilevers were built: one cantilever specimen as the control and the second cantilever specimen as a damaged specimen incorporating the proposed rehabilitation with PT CFRP rods.


Life Cycle Model for Microbial Induced Corrosion of Concrete

Presented By: Feyza Nur Sahan
Affiliation: Oregon State University
Description: Microbial induced corrosion of concrete (MICC) is a multi-stage deterioration process influenced by the presence and activities of bacteria in wastewater collection, storage, and treatment infrastructure. MICC reduces concrete service life significantly and is a serious issue due to enormous cost and environmental effects. Conventional accelerated laboratory methods may not accurately represent the rate of concrete deterioration that occur in field conditions. However, recently, a biogenic benchtop method for assessing MICC has been developed and standardized (ASTM 1904-20). This new approach does not rely on H2S as the nutrient source for the bacteria, but rather uses elemental sulfur species, therefore, it is practical, safer, and rapid. In this work, we developed a life cycle model approach to study MICC to correlate the results of the ASTM 1904-20 approach to real field conditions such as whose found in sewer pipes. This correlation is based the Pomeroy model that relates the field H2S concentrations, wastewater flow conditions, geometry and the properties of the concrete. The presentation will demonstrate how the ASTM 1904 data could be used to predict the performance of different types of concrete and antimicrobial products in realistic exposure scenarios.


Use of High-Alkali Natural Pozzolans (NPs) and Reclaimed Fly Ashes (RFAs) as Alternative Supplementary Cementitious Materials (SCMs) in Concrete

Presented By: Weiqi Wang
Affiliation: Clemson University
Description: Using supplementary cementitious materials (SCMs) with alkali content is generally avoided in concrete because alkalis in SCMs may exacerbate the alkali-silica reaction (ASR). This study investigates the potential of materials with this characteristic used in this concrete industry, the availability of these alkalis to be readily released into the pore solution, and the role of these alkalis in affecting concrete properties. First, this research explored the impact of high alkali SCMs on the concrete ASR by using standard test methods such as ASTM C1567, C1293, and AASHTO T380. Further, the available alkali that can release from SCMs into concrete pore solution was investigated and analyzed by ASTM C311. In addition, the pozzolanic reactivity of high-alkali SCMs was evaluated by using the R3 test (ASTM C1897) in combination with thermal gravimetric analysis (TGA). ASTM C596 drying shrinkage test, ASTM C 1012 sulfate resistance test, and ASTM C1202 rapid chloride ions penetration test were also conducted to evaluate how the high-alkaline SCMs affect concrete and other durable properties. In the next stage, we plan to determine how the SCM's available alkalis and total alkalis influence the concrete pore solution through evaluating the concrete pore solution's pH and compositions like alkalis ions concentration. Results to date indicate that all the SCMs are effective in improving concrete performance on ASR mitigation, sulfate resistance, and chloride ions penetration. The results are not proportionate to the SCM's total alkali content, which indicates the total alkali of SCMs is not the determining factor to rule on SCMs' performance.


Application of Screening Tool as Performance Based Approach to Evaluate Efficacy of Natural Pozzolans for Alkali Silica Reaction Mitigation

Presented By: Pravin Saraswatula
Affiliation: Texas A&M University College Station
Description: Our previous study developed a screening tool (ST) to determine the optimum fly ash dosage for ASR mitigation in concrete mixes. The ST uses concrete pore solution alkalinity (PSA) vs. aggregate threshold alkalinity (THA) relationship to establish a criterion, i.e., PSA = THA, to mitigate ASR. A pore solution model called TTI Model-1 was developed as a part of ST development to estimate concrete PSA based on the combined effort of soluble alkali contribution from cement and water-soluble alkali (WSA) from fly ashes. The current research extends our previous study to examine the concrete PSA vs. aggregate THA relationship for 12 Class N pozzolans (ASTM C 618), thereby investigating ST's validity in estimating the optimum dosage of pozzolans for ASR mitigation. Accordingly, quantitative X-ray diffraction measurements in conjunction with water-soluble and available alkali tests were performed to evaluate pozzolans' potential soluble alkali contribution to pore solution and investigate their efficacy in overall PSA reduction. TTI Model-1 estimations show that high alkali contribution to pore solution and investigate their efficacy in overall PSA reduction. TTI Model-1 estimations show that high alkali natural pozzolans can reduce concrete PSA to a greater extent when compared to low-moderate alkali Class F & C ashes at similar cement replacement levels. Furthermore, the ASR evaluation of the pozzolans conducted at ST-predicted replacement levels following the AASHTO TP 142 & ASTM C 1567 tests showed the expansion measurements to be lower than the respective threshold limits. Overall, the results favorably validate the application of ST's scientific and performance-based approach to determine the optimum dosage of natural pozzolans for ASR mitigation with high reliability.


Predicting Nano Mechanical Properties of Geopolymer Gel Using Machine Learning Technique

Presented By: Roshan Arachchige
Affiliation: Clarkson University
Description: Machine learning is a widely used statistical tool that is now common in most fields. Trained machine learning models can easily replace sophisticated and expensive methods used for material characterization. Here, we utilize the latest development in machine learning to predict micromechanical properties such as hardness and modulus of elasticity of Geopolymer paste (GP) from statistical nanoindentation results along with energy dispersive X-ray spectroscopy (EDS) mapping. We analyzed nanoindentation data using K-means clustering and the Gaussian mixture model to cluster and indentify the phases present in the alkali-activated pastes. Furthermore, EDS mapping was done on the samples where nanoindentation was performed. The EDS maps are later converted to RGB photographs where the color intensities represent the major elemental intensities (Si, Al, Na). Nanomechanical data and the color intensities from EDS maps are trained using Multiple Linear regression (MLR), Support Vector Regression (SVR) and Gaussian Process Regression (GPR) to build up models to predict the nanomechanical properties for given elemental compositions. The GPs are produced using calcined clays, ground bottom ashes, volcanic ashes, and fluidized bed combustion ashes as pre-cursors and sodium silicate solution as the activator. The statistical nanoindentation and the EDS maps were collected from 28-days old ambient cured paste samples. The predictive capabilities and advantages of the method will be assessed by direct comparison with experimental results for different geopolymer gels.


Investigation of Relaxation Behaviour of Irradiated Cement Paste Using Statistical Nanoindentation

Presented By: Poornima Patil
Affiliation: Kansas State University
Description: Concrete offers resistance to neutron and gamma radiation and is popularly used in the containment buildings and bio shield walls of nuclear power plants (NPPs). It is crucial to asses the time-dependent relaxation behavior of the concrete exposed to neutron and gamma radiations to forecast the long-term performance of irradiated concrete. In prestressed concrete structures, the change in length of tendons due to varying load can lead to complicated stress redistributions. Time-dependent deformation in prestressed concrete structures may experience a loss of prestress and should be considered in the design and analyses of containment structures. Such deformation can be characterized by novel relaxation indentation. Thus, in the present work, the effect of ionizing and nonionizing radiation on cement paste is studied to understand the long-term viscoelastic behavior of aging concrete in nuclear containment structures. Three cement paste samples with 0.35, 0.40 and 0.50 water to cement ratio were irradiated in K-State TRIGA Mark II research reactor. The samples were exposed to combined gamma-neutron radiations for one hour of 500 kW thermal power. The study employs statistical nanoindentation to investigate the relaxation behavior of cement paste and the obtained data is analyzed by a closed-form analytical method developed using elastic-viscoelastic correspondence principle. Nanoindentation-based results demonstrate that changes in the viscoelastic properties of cement paste can be observed and correlated to neutron-gamma-induced damage. The preliminary findings highlight the need for developing predictive models accounting for effect of irradiation on relaxation behaviour to successfully assess the damage to irradiated concrete.


Strengthening of Reinforced Concrete Diaphragms with FRP

Presented By: Hunter Hutton
Affiliation: Virginia Polytechnic Institute & State University
Description: This presentation provides an update on an ACI CRC and industry co-funded project to develop retrofit guidelines for strengthening deficient reinforced concrete diaphragms using fiber reinforced polymer (FRP). For reinforced concrete buildings, the horizontal lateral force resisting system (hLFRS) consists of the reinforced concrete diaphragm and associated chords and collectors. These hLFRS can require strengthening for several reasons: a) need to enhance seismic performance, b) inadequate strength or stiffness, c) missing load paths, d) inadequate shear transfer/connections, and e) new penetrations in the slab. Utilizing FRP to remedy these issues is a common practice; however, there are currently no guidelines for the design or detailing of FRP strengthening of deficient hLFRS. The experimental study being conducted at the Virginia Tech Structural Engineering Laboratory consists of cyclic testing of six one-half scale reinforced concrete diaphragms designed to simulate the diaphragm shear zone adjacent to shear walls. The shear behavior of the first two specimens, consisting of a baseline control diaphragm and a diaphragm strengthened with externally bonded CFRP with FRP anchorages, will be discussed and compared. The results of a finite element study, validated by the experimental data, will also be presented to better understand the specimen's experimental behavior. The findings of the experimental and the finite element studies will be used to identify knowledge gaps in current practice and outline the need for improved design principles and limit states. Finally, a preliminary design approach that is consistent with the design principles stated in ACI (2019) and the FRP design philosophy in ACI 440.2R (2017) will be outlined.

Upper Level Sponsors

Ash Grove
Baker
Conseal
Controls Group
Euclid Chemical
GCP
Master Builders
PoreShield
PS=0
ACI Northeast Texas Chapter

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