Past Projects
Monitoring moisture in the cross laminated timber panels of the UA Stadium Drive Residence Halls
Project Completed: 2021
Funded by: US Endowment for Forestry and Communities
Abstract:
At the 2nd North American Mass Timber Research Workshop, the moisture behavior in cross laminated timber (CLT) was recognized as a major topic for the research community to clarify and understand. Very little data exist on the long-term movement of the moisture in CLT during a building’s construction and operation. In addition, the wetting of mass timber during construction raises serious concerns about high moisture content in CLT that could lead to decay and mold (compromising the air quality) or decrease the strength and stiffness of the material.
For a better comprehension of the moisture conditions present in mass timber constructions, a long-term moisture monitoring program will be implemented on a mass timber framed building located on the University of Arkansas campus. The University of Arkansas Stadium Drive Residence Halls building that is currently under construction is built with CLT and will be monitored in this project. The building will be monitored with an array of Omnisense wireless moisture meters to track moisture content throughout the building’s construction and post-occupancy operation. Moisture has been monitored in this fashion in other research projects, but these buildings will be the first studies on moisture in CLT in the southern United States.
Improved Mix Designs to Resist Microbially Induced Concrete Corrosion
Project Completed: 2021
Funded by: City of Fayetteville, AR
Abstract:
Some concrete manholes in Fayetteville, AR are experiencing a reduced service life due to microbially induced corrosion (MIC). The sewage or wastewater in the manholes creates conditions that are conducive to certain types of anaerobic bacteria. This bacteria attaches to the concrete and sets off a chain of reactions that ultimately lead to formation of sulfuric acid. This sulfuric acid then attacks the concrete, causing expansion and cracking. City engineers want to investigate design alternatives that will lead to longer lasting manholes resistant to MIC. The goal of this work is to compare alternative concrete mix design solutions to provide better resistance to MIC.
Using CSA Cement for Novel Waterway Repair Materials
Project Completed: 2021
Funded by: MarTREC
Abstract:
The health and performance of maritime transportation infrastructure is critical to the nation’s economic and social prosperity. Much of this infrastructure has well exceeded its 50-year design life and is often in need of repair. Because waterway transportation structures are difficult to detour, the time taken by repairs is of critical importance. The fastest repair techniques should be developed in order to minimize the time out of service. The objective of this research is to investigate the properties and behavior of Calcium Sulfoaluminate-Belite (CSA) cement mixtures for waterway repair applications. CSA cement is a rapid setting, low-shrinkage cement which can be used to form advanced new materials capable of quickly repairing the nation’s maritime infrastructure. CSA cement maintains many of the beneficial qualities of portland cement but it can reach structural strengths in only a few hours and its low shrinkage makes it an ideal repair material.
Investigating Concrete Deck Cracking in Continuous Steel Bridges
Project Completed: 2022
Funded by: Arkansas DOT
Abstract:
Concrete bridge deck cracking can cause serious serviceability issues during a bridge’s design life and compromise a bridge’s structural strength. Cracks allow water and chemical ingress, which accelerate road surface and structure damage. ARDOT has identified bridge deck cracking shortly after decks are placed and prior to applying live loads. The causes of bridge deck cracking are uncertain. Many contractors are currently using continuous deck pours at Arkansas bridges. However, this construction approach restricts concrete slab movement during shrinkage. After concrete cracking is initiated, cracks may enlarge due to excessive service load stresses.
The interaction between the concrete deck and girder flange restricts concrete slab shrinkage and therefore induces tensile stresses. Stresses developing in the concrete deck and bridge girder are a function of the bridge girder stiffness. The transition from Allowable Stress Design (ASD) to Load Factor Design (LFD) to Load and Resistance Factor Design (LRFD) has resulted in bridge girders designed with a lower stiffness. The impact of bridge pouring procedure, shrinkage, and girder stiffness need to be investigated to determine causes for bridge deck cracking at Arkansas continuous steel bridges. After determining the cause for bridge deck cracking, long term corrective measures will be recommended to ARDOT for implementation to prevent future cases of bridge deck cracking. Regardless of what causes bridge deck cracking, it is important to limit cracking in bridge decks to ensure a long lasting structure with minimal maintenance needs.
Capillary Pressure Sensor Testing to Identify Curing Regimen in Freshly Placed Bridge Decks
Project Completed: 2020
Funded by: Arkansas DOT
Abstract:
The overall performance of concrete in bridge decks can be affected by the curing regimen. The Department now recognizes and allows concrete curing compounds that are lithium based. But, do they outperform the standard curing regimens? With the advent of new testing equipment for freshly placed concrete, Capillary Pressure Sensor System (CPSS), the evaporation effects can be measured. By measuring the capillary pressure during the initial set period after finishing, shrinkage cracks can be avoided by adding moisture and/or curing compound to the concrete surface when the alarm is triggered by threshold pressure limit. Additional curing compound and/or moisture can be added to reduce or mitigate the effects of the evaporation. ARDOT currently allows the use of lithium cure under a special provision when the contractor requests it. This project would use the CPSS to evaluate the different curing regimens the contractor uses and determine which product and/or method works best.
This project aims to investigate the use of a CPSS to monitor the development of capillary pressures in the surface of fresh concrete bridge decks or pavements. This capillary pressure can be used to determine if plastic shrinkage cracking is likely to occur and alert the user when moisture should be added to the surface to prevent cracking. The sensor will be tested in the lab to verify its ability to measure plastic shrinkage pressures, then lab testing will be performed to compare curing techniques. A field study will help determine if the sensor is useful in practice to ARDOT and to contractors.
Development of Rating Tool for Prestressed Concrete Bridges Vulnerable to Shear
Project Completed: 2019
Funded by: Oklahoma DOT
Abstract:
A study was conducted examining the factors affecting shear capacity and load rating, two potential methods for assessing condition of in-service prestressed concrete bridge girders, and a simple procedure for assessing whether and how a bridge should be rated for shear was developed. First, a detailed literature review was conducted to collect results of experimental shear testing on older prestressed concrete girders and the comparison of those results to capacity calculation methods. This was followed by a parametric study to examine the effect of different design items on load distribution and the difference between AASHTO load distribution equations and grillage models for more than two hundred different bridge configurations. Two methods for assessing condition of in-service girders were examined and further refined. The results of previous shear testing and the grillage model parametric study indicate that there may be conservativism built in when AASHTO load distribution factors are used that leaves open the possibility of increased load ratings for some older bridges. Using a grillage model can increase load ratings, reducing the potential need to load post or take some bridges out of service without sacrificing accuracy and safety. The proposed procedure uses a set of simple criteria to identify bridges potentially vulnerable to shear and modifications to the typical rating procedure to produce an accurate shear rating.
Early Life Flexural Performance and Behavior of Reinforced BCSA Concrete Beams
Project completed: December 2018
Funded by: Material donated by CTS Cement
Abstract:
Belitic calcium sulfoaluminate cement (BCSA) is a hydraulic, rapid setting alternative to ordinary portland cement (OPC) with reduced energy demands and CO2 emissions. BCSA cement has numerous current and potential applications including transportation repair and precast manufacturing. Currently, limited research exists regarding the structural performance of CSA cements, restricting its potential implementation. Thus, the purpose of this research is to provide insight into the flexural performance and behavior of reinforced BCSA concrete beams. Overall, BCSA concrete had similar cracking and loading behavior to the OPC beams, with increased moment capacity for compression controlled specimens. Furthermore, BCSA concrete showed increased tensile strength and ductility when compared to OPC. Overall, the flexural strength of the BCSA concrete exceeded the predicted flexural strengths, indicating the current flexural strength equations are applicable for BCSA reinforced concrete design
BCSA beam tested approximately 2 hours after casting
Load versus deflection for tension controlled beams
Fresh BCSA concrete in formwork
Understanding ultimate shear behavior of prestressed concrete girder bridges as a system through experimental testing and analytical methods
Project completed: Summer 2017
Funded by: Oklahoma Department of Transportation
Abstract:
A prestressed concrete bridge is a complex system. The interconnectivity of several girders, a deck, and secondary elements such as diaphragms makes their behavior difficult to represent. Additionally, the shear behavior of in service prestressed concrete girders can be difficult to predict, particularly when older codes were used in design and where damage is present in the girders. This work contains laboratory testing to investigate the residual shear performance of two older American Association of State Highway and Transportation Officials (AASHTO) Type-II prestressed concrete girders, as well as the behavior of a scale prestressed concrete bridge loaded in shear to failure. The full-scale girders were found to be capable of carrying their full capacity even when corrosion affected the failure mechanism. Based on these tests, the modified compression field theory (MCFT) methods were recommended for estimating the capacities of older girders. The scale bridge provided information about load distribution at ultimate capacity, and the influence of secondary elements (diaphragms) on load transfer after girder failures. The bridge test also documented the ultimate behavior of a prestressed concrete bridge, findings that are not common in the literature. The bridge failure was controlled by punching shear, and the diaphragms were seen to provide a significant means of load transfer after a girder failed. Finally, simple computer models were built that are capable of reducing the conservativism of the codified distribution factor (DF) methodology, increasing the usable capacity of bridges. These models simplify the girders and slab into a “grillage” of beam elements with appropriate stiffnesses. A parametric study suggests that for AASHTO Type-II girder bridges, load ratings tend to be conservative for smaller girder spacing and shorter span lengths. Code DFs were generally found to be conservative for all configurations of typical Type-II girder bridges.
This was the topic of my Ph.D. dissertation, I was advised by Dr. Royce Floyd.
Click here for the dissertation
Papers resulting from this project (click for access):
Destructive testing and computer modeling of a scale prestressed concrete I-girder bridge
Experimental testing of older AASHTO Type II bridge girders with corrosion damage at the end
Scale bridge during construction
Finished scale bridge with load frame
Cracking in bridge deck during testing
46 ft. long AASHTO Type-II girder prior to testing
Durability of Silane Sealer in a Highly Alkaline Environment
Project Completed: Summer 2014
Funded by: Simmons Foods
Abstract:
Alkali-silica reaction (ASR) is a chemical reaction between siliceous minerals present in certain aggregates and alkalis in the concrete pore solution. The reaction can lead to expansion and severe damage in concrete members. One method to mitigate ASR expansion is to use a penetrating sealer such as silane. A set of columns located in a food preparation facility was treated with silane and a complimentary laboratory study was performed. A cleaning regimen involving application of an alkaline cleaner is employed at the facility, followed by rinsing with hot, pressurized water. The purpose of this research is to evaluate the effectiveness of silane when used in this alkaline environment. The research shows that silane was effective at reducing expansion in new concrete, less so when the pH of the environment is high; other measures were recommended for previously cracked concrete.
This was the topic of my M.S. thesis, advised by Dr. Micah Hale