Education

Research Description

Dr. Pour-Ghaz studies the durability of reinforced concrete materials and structures, the long-term durability Fiber Reinforced Polymer (FRP) composites for civil infrastructure, and electromagnetic sensors and sensing techniques. The overall goal of his research program is to contribute to the development of mechanistic service life prediction models that integrate measurement techniques (structural health monitoring and nondestructive testing) for model updating.

Publications

Detection and reconstruction of complex structural cracking patterns with electrical imaging

Smyl, D., Pour-Ghaz, M., & Seppanen, A. (2018), NDT & E INTERNATIONAL, 99, 123–133. https://doi.org/10.1016/j.ndteint.2018.06.004

Imaging of two-dimensional unsaturated moisture flows in uncracked and cracked cement-based materials using electrical capacitance tomography

Voss, A., Hanninen, N., Pour-Ghaz, M., Vauhkonen, M., & Seppanen, A. (2018), Materials and Structures, 51(3).

Performance and damage evolution of plain and fibre-reinforced segmental concrete pipelines subjected to transverse permanent ground displacement

Pour-Ghaz, M., Wilson, J., Spragg, R., Nadukuru, S. S., Kim, J., O’Connor, S. M., … Weiss, J. (2018), Structure and Infrastructure Engineering, 14(2), 232–246.

Quantifying prestressing force loss due to corrosion from dynamic structural response

Rashetnia, R., Ghasemzadeh, F., Hallaji, M., & Pour-Ghaz, M. (2018), JOURNAL OF SOUND AND VIBRATION, 433, 129–137. https://doi.org/10.1016/j.jsv.2018.07.012

What is the role of water in the geopolymerization of metakaolin?

Park, S., & Pour-Ghaz, M. (2018), CONSTRUCTION AND BUILDING MATERIALS, 182, 360–370. https://doi.org/10.1016/j.conbuildmat.2018.06.073

Can Electrical Resistance Tomography be used for imaging unsaturated moisture flow in cement-based materials with discrete cracks?

Smyl, D., Rashetnia, R., Seppanen, A., & Pour-Ghaz, M. (2017), Cement and Concrete Research, 91, 61–72.

Can the dual-permeability model be used to simulate unsaturated moisture flow in damaged mortar and concrete?

Smyl, D., Ghasemzadeh, F., & Pour-Ghaz, M. (2017), International Journal of Advances in Engineering Sciences and Applied Mathematics, 9(2), 54–66.

Detection and localization of changes in two-dimensional temperature distributions by electrical resistance tomography

Rashetnia, R., Hallaji, M., Smyl, D., Seppanen, A., & Pour-Ghaz, M. (2017), Smart Materials & Structures, 26(11).

A functionally layered sensing skin for the detection of corrosive elements and cracking

Seppanen, A., Hallaji, M., & Pour-Ghaz, M. (2017), Structural Health Monitoring, 16(2), 215–224.

Do mechanical and environmental loading have a synergistic effect on the degradation of pultruded glass fiber reinforced polymers?

Pour-Ghaz, M., Miller, B. L. H., Alla, O. K., & Rizkalla, S. (2016), Composites. Part B, Engineering, 106, 344–355.

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Grants

Use of Moisture-Induced Stress Test (MIST) to Determine Moisture Sensitivity of Asphalt Mixtures

NC Department of Transportation(8/01/16 - 7/31/19)

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Use of Moisture-Induced Stress Test (MIST) to Determine Moisture Sensitivity of Asphalt Mixtures

Sponsor: NC Department of Transportation

Start Date: 8/01/16

End Date: 7/31/19

Abstract

Asphalt mixtures used in pavement construction are required to meet the NCDOT moisture sensitivity specifications. The current lab procedure to test moisture sensitivity uses conditioning procedures as per modified AASHTO T283. This is a fairly lengthy procedure involving specimen preparation, sample saturation, conditioning the samples for 24 hours, and then indirect tension testing. The variability involved in TSR test results is also observed to be high. The current test method uses the ratio of indirect tensile strength of the conditioned and unconditioned specimens (TSR). The indirect tensile strength is a qualitative measure of the moisture sensitivity. There is a need for a quicker test method(s) that is quantitative and has less variability. The new test should also lend itself to measure intrinsic properties such as the dynamic modulus of asphalt concrete that will allow inferior mixtures to be eliminated even though they may pass the TSR test.

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The effects of contaminated soil and groundwater on subsurface utilities, surface water and drainage

NC Department of Transportation(8/01/16 - 7/31/19)

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The effects of contaminated soil and groundwater on subsurface utilities, surface water and drainage

Sponsor: NC Department of Transportation

Start Date: 8/01/16

End Date: 7/31/19

Abstract

The North Carolina Department of Transportation (NCDOT) routinely performs road improvement projects where a portion of the right-of-way might be contaminated. Potential sources of contamination include underground storage tanks in the vicinity of the road improvement site, old unlined landfills, or abandoned industrial and agricultural operations with practices leading to soil and/or groundwater contamination. It has been reported by NCDOT in RNS#7406 that in several situations, subsurface utilities including drainage pipes are present in environments where soil and groundwater contamination exists. The effect of the contamination on the integrity and durability of the subsurface drainage pipes and gaskets is largely unknown but such integrity is a function of the type of contamination and the physicochemical properties of pipe, gasket, and other materials forming a given subsurface utility. In addition to the variety of contaminants and concentrations that prevail at these sites, a wide variation in soil geological formation and hydrogeological conditions exist across the state. While in general the groundwater table is expected to be high in the North Carolina (NC) Coastal Plain Physicographic region, it is expected to be deep in the Mountains. On the other hand, it is more likely that groundwater will feed surface water springs and streams in the NC Mountains. Therefore, a "typical" contaminated site is difficult to define. Accordingly, the adverse effect of subsurface contamination on drainage pipes and the efficacy of hardening measures are usually developed on a site-specific basis. Objectives of this project are to (i) catalog the prevalent types of contaminants and their concentrations at sites where subsurface utilities are installed, (ii) document the typical materials used in subsurface utilities and drainage systems in NC, (iii) quantify the effect of contaminants on the long-term durability of commonly used hardened and unhardened materials that are used in construction of subsurface utilities, (iv) quantify the rate and extent of migration of common contaminants through concrete utilities, (v) recommend effective hardening methods for different materials, and (vi) provide documentation and better understanding of the effect of subsurface utility installation on the contamination of groundwater and surface water through simulation of several typical scenarios. These objectives will be achieved through a multidisciplinary effort of the research team as outlined in the project plan. Objective (i) will be achieved through examination of available data from the NC Department of Environmental Quality (DEQ). If necessary, limited sampling of groundwater and surface water will be conducted in consultation with NCDOT in areas where subsurface utilities have been installed and contamination is known to exist or expected to occur. Objectives (ii), (iii), and (iv) will be accomplished through literature review and accelerated coupon testing in our laboratory. Objective (v) will be achieved by analyzing test results and literature data. Objective (vi) will be accomplished through numerical simulations.

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Durability of the Grouted Shear Stud Connection at Low Temperatures

US Dept. of Transportation (DOT)(3/01/16 - 5/15/19)

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Durability of the Grouted Shear Stud Connection at Low Temperatures

Sponsor: US Dept. of Transportation (DOT)

Start Date: 3/01/16

End Date: 5/15/19

Abstract

This research proposal addresses the design and behavior of a new, recently developed connection for steel bridge substructures. This new connection, termed the grouted shear stud connection (GSS), was shown to be an effective and improved design over current practice of directly welding hollow circular steel pipe piles to steel cap beams. In previous studies, the new connection performed well, in both quasi-static and dynamic tests at ambient (indoor) laboratory temperatures. Because this new connection relies upon the integrity of grout, a cementitious material prone to degradation from severe environmental conditions typical in Alaska, the durability of this material and the connection as a whole must be assessed. This proposed project focuses on the durability of the GSS by optimizing the grout properties through material testing, and subsequent tests of weathered and unweathered full-scale connection specimens when subjected to temperatures as low as -40° C. The outcome of this research will be a set of design recommendations to maximize the durability and hence the long term performance of the grouted shear stud connection. While developed for new bridge construction, the GSS connection is readily adapted to retrofit applications in existing steel bridge substructures with deficient pipe column to cap beam connections. The results of this study may therefore be of value in the eventual structural upgrade of Bridge No. 455, the Anchorage Port Access.

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Design of Waste Transfer Station Concrete Overlays against Premature Deterioration

Environmental Research & Education Foundation(9/15/15 - 8/14/18)

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Design of Waste Transfer Station Concrete Overlays against Premature Deterioration

Sponsor: Environmental Research & Education Foundation

Start Date: 9/15/15

End Date: 8/14/18

Abstract

The premature deterioration of concrete overlays in waste transfer stations is a major concern for the owners and operators of these facilities. Overlay replacement in these facilities has significant economic impacts including direct costs, operational delays, and planning hurdles. While the overlay deterioration is mainly attributed to the abrasion caused by scraping solid waste, anecdotal evidence suggests that other factors might equally contribute to the deterioration of the overlays. Unfortunately, published data on the contributing factors to the deterioration of concrete overlays in transfer stations and the mechanisms involved are virtually nonexistent. Some of these factors may include contact with acidic leachate from fresh waste, the type and operation of equipment used for handling waste, the amount of waste handled, and the lack of systematic structural design that accounts for concrete material deterioration. If the main contributing factors to deterioration are identified, these overlays can be designed against deterioration, resulting in better long-term performance and predictability, and consequently, reduced life cycle cost for owners and operators. The main objectives of this research are therefore (i) to identify the contributing factors to the premature deterioration of concrete overlays in transfer stations, and (ii) to establish a structural design methodology for the concrete overlay based on the observed degradation mechanism and operational conditions.

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Evaluation of Alternative Binder Material to Reduce Sewer Collection system Infrastructure Maintenance and Enhance Sustainability

NCSU Water Resources Research Institute(3/01/16 - 6/30/19)

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Evaluation of Alternative Binder Material to Reduce Sewer Collection system Infrastructure Maintenance and Enhance Sustainability

Sponsor: NCSU Water Resources Research Institute

Start Date: 3/01/16

End Date: 6/30/19

Abstract

In North Carolina, it is estimated that over 10,000 SSOs occur annually, costing hundreds of thousands of dollars in clean-up. Of those blockages, 50% are related to FOG release into the collection system. The amount of FOG that are routinely discharged into the nation’s sanitary sewer systems is increasing as commercial food preparation and serving facilities and high density dwellings increase particularly in metropolitan communities. The migration to urban centers has increased the maintenance required by pretreatment coordinators in efforts to keep the sewer pipes free of FOG deposit related blockages. The statistics of SSOs from FOG deposits and their potential environmental impact indicate the need to examine methods to reduce the accumulation of FOG deposits in the sanitary sewer collection system and enhanced strategies that remove FOG deposit chemical precursors. In addition to sewer collection system problems, North Carolina is dealing with the unfortunate discharge of nearly 40,000 tons of coal ash from a major power provider into a major waterway. Over 5.5 million tons of coal ash is produced in NC, ranking NC 9th in the US in coal ash generation. There are 37 ash ponds in NC and the majority of them are not equipped with leachate collection system to protect groundwater. The increased use of fly ash in infrastructure materials, such as production of pipelines, could introduce a way to offset the fly ash created by coal-fired power plants and contribute to reducing the risk of future pond dam failures and contaminations of water resources. The objectives of the proposed research are to: (1) Evaluate alternative binder materials used in precast concrete that significantly reduces or eliminates calcium leaching, (2) Evaluate the adhesion properties of FOG deposits on these alternative concrete surfaces, and (3) Assess the structural durability of these alternative concrete materials. The proposed research project will be the first to explore the FOG deposit formation potential and adhesive properties of alternative concrete materials using geopolymers. The research results of this project will offer North Carolinian wastewater municipalities with strategies to maintain a sustainable sewer collection system in high density metropolitan cities that are experiencing significant growth and alleviate the potential environmental and public health harm from FOG related SSOs as well as an avenue for offsetting the disposal of fly ash.

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The Use of Fiber Reinforcement in Latex Modified Concrete Overlay

NC Department of Transportation(8/01/15 - 12/31/16)

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The Use of Fiber Reinforcement in Latex Modified Concrete Overlay

Sponsor: NC Department of Transportation

Start Date: 8/01/15

End Date: 12/31/16

Abstract

A large number of bridge deck rehabilitations are performed each year in North Carolina. Latex Modified Concrete (LMC) and LMC–Very Early Strength (LMC-VES) are used in these rehabilitations because they allow for a rapid return to service. Despite the comprehensive guidelines and specifications developed by NCDOT (such as PSP003 and PSP004) for quality control, and control of cracking, substantial cracking is observed in these overlays. The observed cracking is mainly attributed to thermal cracking, shrinkage cracking, plastic shrinkage cracking or a combination of them. Cracking of all types substantially reduces the effectiveness and service life of these overlays. To address the cracking issue, the proposed research will investigate whether non-metallic fiber reinforcement can be used to control and reduce cracking in LMC materials. A multi-phased research program is proposed. First, during this project, a number of active overlay projects will be visited. The main goal of these visits is for the researchers to become completely familiar with typical field practices for process of mixing, placing, and curing the overlay. This will help in identifying the best method to add fibers to the mixture and in identifying potential difficulties that addition of fibers might introduce. The researchers will also document observations that will be used to provide guidelines on the best placing and curing practices after addition of fibers. Second, the susceptibility of the LMC to plastic shrinkage cracking will be evaluated using ASTM C1579. The evaluation of plastic shrinkage cracking is important since the type of the fibers needed to control plastic shrinkage cracking is different from the type of the fibers needed for other types of shrinkage cracking and thermal cracking. If LMC is highly susceptible to plastic shrinkage cracking, the effectiveness of an appropriate type of fibers in reducing plastic shrinkage cracking will also be evaluated. Third, the susceptibility of LMC to drying and autogenous shrinkage cracking will be evaluated using restrained ring test. The purpose of this laboratory test is to identify the minimum dosage and an effective type of the fiber in controlling the cracking. Restrained rings with three different degrees of restraint (thickness of the steel ring) will be used. Ring tests will include the test specified by the ASTM specifications. Forth, after identifying the minimum required fiber and the type of fibers, fiber reinforced LMC will be tested on large-scale slabs. For this task the actual volumetric mixer that is used in the field will be employed. Two slabs, one unreinforced and one fiber reinforced LMC, will be cast beside each other using the same equipment and the same crew. The slabs will be cured simultaneously in an environmental chamber that will enable the creation of specific curing conditions. The fiber distribution generated by the volumetric mixer will be quantified using digital image analyses. Finally, if the use of fibers proves unsuccessful or impractical, the researcher will perform a literature review on alternative materials and methods of reducing and controlling cracking that might be feasible and propose those methods to NCDOT for further study.

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Large-Area Electrical Resistance Tomography Based Sensing Skin for Reinforced Concrete Structures

American Society for Nondestructive Testing, Inc.(8/16/15 - 8/15/17)

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Large-Area Electrical Resistance Tomography Based Sensing Skin for Reinforced Concrete Structures

Sponsor: American Society for Nondestructive Testing, Inc.

Start Date: 8/16/15

End Date: 8/15/17

Abstract

Cracking of reinforced concrete (RC) structures is a major concern for owners and operators of infrastructure. Cracking is an early indicator of larger structural deformation or collapse and is a major contributing factor to the premature deterioration of RC structures. Therefore, information about the location of the cracks and the extent of cracking are critical for assessing the structural safety as well as to more accurately predict the service life of RC structures. Due to the localized nature of cracking, crack detection can be a challenging task especially in RC structures. Electrical resistance tomography (ERT) based sensing skins offer a method for monitoring localized cracking in reinforced concrete structures. These sensors are made of conductive materials (such as copper-based paints) that are applied to the surface of concrete and their spatial electrical resistivity (inverse of conductivity) is monitored. When the concrete substrate cracks, the conductive material at the surface ruptures, and therefore, the electrical resistivity of the conductive materials locally increases by orders of magnitude. ERT is then used to reconstruct the spatial resistivity (or conductivity) distribution on the sensing skin. The location and the extent of cracking are then quantified in terms of the local change in electrical conductivity. The research group has recently developed and used a sensing skin for detecting complex cracking pattern in a 50 x 20 cm (≈ 20 x 8 inch) deep RC beam. This research builds on the prior work by the research group and we aim to investigate (i) whether this sensing skin technology can be successfully extended to detect cracking in larger RC structural components (ii) and how does the resolution of the sensing skin in detecting cracking depends on the size of the sensing skin. To this end, we will perform computational and experimental investigations. Using computational simulations we will investigate (1) the dependence of the resolution of the sensing skin on its size in the presence of experimental noise, and (2) investigate the minimum number of electrodes to enhance the resolution of sensing skin. We will experimentally investigate feasibility of the sensing skin in detecting physically simulated cracking on 5x5 ft polymeric substrates and a 10x10 ft RC shear wall. These experiments will be designed to result in a complex cracking pattern. To the best of our assessment, this is the first time that such a large-area crack detection sensor is being attempted. If successful this sensing skin technology can potentially be used for rapid monitoring of critical infrastructure such as nuclear waste storage and containment facilities as well as rapid damage detection in defense applications. This technology can also be used for monitoring underground and buried structures where visual inspections are not easily feasible.

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Data Fution Approach for the Effective Inspection of Prestressed Concrete

US Dept. of Transportation (DOT)(8/26/14 - 2/25/15)

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Data Fution Approach for the Effective Inspection of Prestressed Concrete

Sponsor: US Dept. of Transportation (DOT)

Start Date: 8/26/14

End Date: 2/25/15

Abstract

While many inspection technologies are available to find corrosion in steel tendons of prestressed concrete, very few, if any, have shown consistent results over the wide range of prestressed structures and inspection settings. This project combines the results from the best proven techniques, using a data fusion approach, to obtain more consistent and useful results than any of the individual tests for inspecting and evaluating prestressed concrete. The techniques used include traditional electrochemical inspections and ground penetrating radar, as well as several emerging ultrasonic technologies. The resulting corrosion predictions will be used to create risk-based criteria for specifying inspection intervals.

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EAGER: Submicron Fracture Toughness Measurements for Cement Paste Using FIB and Nanoindentation

National Science Foundation (NSF)(5/15/14 - 12/31/16)

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EAGER: Submicron Fracture Toughness Measurements for Cement Paste Using FIB and Nanoindentation

Sponsor: National Science Foundation (NSF)

Start Date: 5/15/14

End Date: 12/31/16

Abstract

The research objective of this EAGER proposal is to measure the fracture toughness of cement paste at submicron length scales using nanoindentation experiments with Focused Ion Beam (FIB) milled sample structures. Fracture and strength measurements made at the typical scales of concrete laboratory testing are often explained and modeled by introducing the idea of microcracks, small material flaws within the cement paste matrix. Current experiments, however, are unable to reveal how fractures are generated within the microstructure. As a result, modeling the initiation, propagation, interdependence, and coalescence of microcracks for macroscopic material failure is a formidable challenge because basic input data is missing. New, small scale experimental techniques are required to quantitatively assess the complex material behaviors that lead to microcracking in cement paste. In support of the primary research objective, FIB milling techniques will be applied to cement paste and used to fabricate micropillars, microbeams, and micro-wedge-splitting samples of cement paste. These FIB milled structures will be tested using nanoindentation to assess strength and fracture properties. The research outcomes will lead to significant broader impacts in the study of failure of cementitious materials. The production, transportation, and use of concrete accounts for between 5-9% of total CO2 emissions worldwide. If the fundamental mechanics mechanisms behind failure of cement can be better understood, rationally designed engineering solutions can be deployed to provide tougher materials for civil infrastructure, reducing consumption of natural resources and production of CO2. The research outcomes will transform the concrete industry by continuing our move away from “make-and-break” testing and towards the study and design of concrete materials for specific applications. They will also have a significant impact on study of any concrete deterioration mechanism that involves formation of internal stresses in the material.

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Assessment of Deteriorated Cored Slabs Bridge No: 1050035 and 150039

NC Department of Transportation(8/16/13 - 5/08/15)

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Assessment of Deteriorated Cored Slabs Bridge No: 1050035 and 150039

Sponsor: NC Department of Transportation

Start Date: 8/16/13

End Date: 5/08/15

Abstract

Prestressed concrete cored slabs are common bridge elements used by the NCDOT for spans up to approximately 60 ft. While cored slabs are structurally efficient, serving as both superstructure and deck, their internal steel reinforcement can be vulnerable to corrosion. Corrosion is of particular concern when structures are located in aggressive environments such as coastal regions or in areas where deicing chemicals are used. The internal steel in cored slabs can corrode when salts and moisture penetrate the concrete from the road surface or are splashed onto the bridge from the bottom or sides. Recent inspections of prestressed concrete cored slab bridges in Carteret County, NC, have brought to light a significant degree of corrosion in the stirrups and prestressing strands of these members. In certain cases, corrosion has compromised layers of longitudinal reinforcement, leading to extensive delamination and spalling of the concrete cover from the soffit of the bridge superstructure. Specifically, the deterioration of the superstructure of Bridge No. 150035 and Bridge No. 150039 are such that they are scheduled for replacement within the next few months. As with most corroded reinforced and prestressed concrete structures, the extent of the deterioration that cannot be visually observed beyond the concrete cover depth is of greatest concern. For example, it is not known to what extent the layers of prestressing strands within the section have deteriorated. The bottom layer of prestressing is clearly deteriorated in several members, however, the condition of the strands above this lowermost layer is unknown. Similarly, the condition of the stirrups and strands behind large areas of delaminated concrete is not known from visual inspection alone. To address this issue a research program has been developed that will (i) critically evaluate existing non-destructive techniques used to quantify the extent of corrosion in existing in-service members, and that can be readily adopted by NCDOT maintenance engineers and contracted bridge inspectors, (ii) undertake detailed field investigations of the two bridges scheduled for superstructure replacement creating a comprehensive photographic record of the degrees and extent of deterioration, (iii) implement the non-destructive techniques on eight deteriorated prestressed concrete cored slab units identified and taken directly from the in-service bridges in order to evaluate their effectiveness and develop protocols for future use, and (iv) test the eight units to destruction in three-point bending to experimentally quantify and observe their failure mode and residual capacity. A unique feature of this research program is the direct correlation that will be established between field measurements (including both visual inspection and non-destructive testing), laboratory testing, and destructive inspection of in-service prestressed concrete cored slab units commonly used by NCDOT that were fabricated with materials common to NC and aged in an environment typical of coastal NC. The outcomes of which will enable NCDOT personnel to assess the residual strength and performance of other similar in-service bridges so that informed decisions may be made regarding maintenance, repair and replacement priorities.

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