Moe Pourghaz

Alkali Silica Reaction (ASR) is one of the most ubiquitous deterioration problems and is a major concern for Department of Transportation (DoTs) across the US. Since the first documentation of ASR in 1940 by T.E. Stanton [1], published based on his investigations of cracking of concrete structures in California, a plethora of papers and data have been published in the literature. While a good understanding of ASR has been established today, evaluating aggregates for the potential of ASR remains elusive. The first line of defense against ASR remains avoiding the use of aggregates with a known history of ASR and/or restricting the alkali content of concrete mixes. The use of accelerated test methods are deemed less reliable than the use of historical data and evidence, due to current test methods assessing aggregate reactivity, not concrete mixture reactivity as used in the field. The main challenge with accelerated test methods is that the mechanism of ASR seems to be very sensitive to perturbation and can change depending on the conditions of the test such as increased temperature, concentration of alkalis, and ion leaching from concrete during the test. As a consequence, rapid tests suffer from low fidelity (e.g., ASTM C 1260), and reliable tests (e.g., ASTM C 1293) are often very time consuming and may take up to two years to complete, which in many instances defeats the purpose of running the test to being with (i.e. the project is already constructed by the time the test is completed). The search for accelerated reliable tests for ASR has occupied researcher for decades. Unfortunately, many of the currently available accelerated tests rely on the same length change measurement strategy as traditional tests and expose samples to a highly alkali solution at elevated temperatures. Therefore, common accelerated tests all suffer from the same limitations as traditional tests. Additionally, due to the requirement of measuring very fine changes in length, samples must be prepared in a highly controlled manner in the laboratory. The most common test methods are summarized with relevant information in Table 1.

This proposal addresses the impact of bridge condition on behavior within the context of performance-based seismic design. Bridge engineers design structures assuming that their properties on day one remain constant throughout the life of the bridge. However, due to material degradation and lifetime transient loadings (including those from small earthquakes), the response of a structure to an extreme event such as an earthquake at some point in the future may be different from what the engineer calculates during the design phase. The research described in this proposal will assess the sensitivity of condition-dependent bridge response to inputs described below. There are five components to this research question. The interactions between these components are shown in Fig. 1 and described further to set the stage for the research that will be conducted in this multi-phase program.

The goal of this project is to engineer a biomimetic healing vasculature that remediates multiple mechanisms of degradation (i.e., cracking, chloride-induced corrosion of rebar) and maintains such biomimietic function to extend the service life of reinforced concrete structures. DoD maintains aged concrete infrastructure in shoreside and terrestrial environments. Large volumes of aged, reinforced concrete used in silos and piers are cracking and showing signs of corrosion caused by years of service in extreme environments. Additionally, unreinforced concrete airfield pavements require logistically challenging rapid repairs. This project will develop a biomimetic vascular network within aged, reinforced concrete that can also be integrated into new airfield pavements, providing a viable bio-inspired approach to DoD���s concrete repair needs. The project will address the Strategic track for surface treatment of aged, reinforced concrete and the Tactical track for runway patch repairs. While the vascular methods will be developed for the terrestrial application of missile silos, metrics will also be assessed for shoreside pier environments in early project phases to highlight compatibility for both use cases.

The NCDOT has previously funded FRP related research projects through NC State University. RP2014-09 consisted of material characterization of Glass FRP reinforcing bars and Carbon FRP prestressing strand (of the same type to be used in the Harkers Island Bridge replacement), and the design, construction and destructive testing of full-scale 45 ft. long hollow core slabs commonly used throughout North Carolina. The design was consistent with the then current ACI440 and AASHTO design guide documents. The test results demonstrated that the flexural and shear performance of the all FRP-reinforced cored slabs was ����������������equivalent��������������� to that of traditional steel-reinforced cored slabs designed to current NCDOT standards. More recently, RP2018-16 developed an innovative rapid repair solution suitable for common prestressed concrete bridge elements, including cored-slabs and C-channel beams. The system is comprised of a prestressed mechanically-fastened FRP plate that restores lost prestress force in deteriorated bridge beams such that inventory and operating load rating restrictions may be removed enabling the bridge to remain in service until replacement is scheduled. In April 2019 this repair system was implemented on Bridge No. 380080 in Franklin County, and a second application was installed on Bridge No. 810003 in Sampson County in November 2020. While there are applications of FRP materials and systems in the repair or strengthening of existing concrete bridges in North Carolina, the Harkers Island Bridge replacement will be the first to fully replace all internal reinforcing and prestressing steel with FRP alternatives in a new construction. The Harkers Island Bridge will be among the largest applications of FRP in a fully FRP-reinforced new concrete bridge in the United States. The experience and long-term performance data collected from this bridge will contribute to the validation and future editions of ASTM standards, material and construction specifications, and design codes including those from AASHTO and ACI. Ultimately, the outcomes of this research project will lead to improved NCDOT design and construction of durable bridge infrastructure resulting in reduced maintenance and repair, longer service life, and cost-savings.

Cracks are ubiquitous in concrete and reinforced concrete structures and are generally caused by the material volume instability (e.g., shrinkage), mechanical or environmental loading. To mitigate the effects of cracks, they are commonly sealed using a sealant. A variety of sealants with different chemistry are commercially available; however, their relative performance against each other is largely unknown since field experience with some of them is limited. In addition, with the recent supply chain interruptions, there is a need for alternative sealants that can deliver satisfactory performance to avoid increased cost and delay of projects. The goal of the present proposal is to address these challenges. The objectives of the present study include: (i) Literature review and survey, (ii) Evaluation of NCDOT specification and (iii) Data synthesis and recommendations. A product of this research will be an updated NCDOT specification for materials and methods of concrete crack sealant. We also envision that the product of this research will include a table (or Excel file) that provides a list of commercially available sealants with identifiers for appropriate type of application (horizontal, vertical, or overhead), their effectiveness for different crack width sealing, minimum cure time, best recommended use, their expected performance with respect to other products, and other relevant information that can help selecting the sealant.

In a recent research project a pipe material selection software was developed. This software enables estimation of the service life of pipes made from different materials based on their anticipated exposure conditions. The linked GIS database is used to automatically compute the anticipated exposure condition corresponding with GPS coordinates input by the user for a given project. The culvert pipe materials commonly used by NCDOT have been included in the software: reinforced concrete, galvanized steel, aluminized steel, cast iron, mild steel, aluminum alloy, and polymeric pipes. Based on conversations with NCDOT, additional scope for the software is desired and identified as follows: i. The developed software selection guide only considers material type and exposure condition in the selection process. It is desirable to integrate NCDOT������������������s structural requirements into the selection process such that NCDOT engineers can use a single software to select pipe materials based on both durability and structural requirements. ii. The current software does not provide an estimate of how service life can be extended by repair and rehabilitation. It is desirable to upgrade the software to account for the additional service life expected from various rehabilitation measures, and to develop a comparative analysis of possible repair methods in terms of expected impact on service life. iii. The current software does not account for the effects of approaches to mitigate adverse subsurface exposure on the service life of installed pipes. Addressing the effects of mitigation is desirable since in many projects, backfill soil is different from native soil. The work proposed herein aims to update the current software to include: (i) An upgraded pipe selection guide software that integrates structural requirements, repair and rehabilitation methods, and mitigation strategies into a unified pipe selection guide, and (ii) provisions accounting for the effects of various repair and rehabilitation methods on the service life of the pipe materials.

Recently, it has been shown that the premature deterioration of concrete overlays in waste transfer stations is a result of simultaneous exposure to leachate (organic acids) and mechanical abrasion by waste handling equipment. In our previous research, we developed a material design guide and specification that owners can use for design or bidding. There are however, important limitations to the developed guide in that it: (1) does not address repair strategies and repair material selection, (2) is limited to portland cement concrete, (3) does not cover the use of unconventional concretes such as iron aggregate and epoxy matrix, (4) applies to slabs with a minimum of 6-inch thickness and does not cover thin precast and prestressed overlays, and (5) does not include provisions for the use chemical or mineral admixtures that can increase the acid resistance of concrete. The industry is in need of low cost and effective repair strategies for existing concrete overlays. The goal of the proposed research is to develop a guideline for repair strategies and repair material selection that can be (1) used by owners and operators of waste transfer stations and (2) adopted and implemented by contractors without the need for specialized equipment and labor.

Recently, there have been reports of municipal solid waste (MSW) landfills that have been experiencing temperatures in excess of 80 ���������C. Elevated temperatures have a number of deleterious effects that are well known to landfill owners. Consequently, elevated temperature landfills often require increased monitoring and management. In recent work supported by the EREF, we developed a model of heat accumulation in a landfill. The objective of the model was to help identify and mathematically describe all sources of heat input, generation and loss in a typical Subtitle D landfill. The model simulations identified several reactions that contribute significant heat to landfills including the hydration and carbonation of calcium-containing wastes (e.g., ash) and aluminum corrosion. Model predictions however, were based on information adopted from the literature for systems other than landfills. In addition to MSW, many landfills receive non-hazardous industrial wastes including ash from both coal and MSW combustion, ash used to solidify liquid wastes, auto shredder residue (ASR) that contains Al and Fe, and perhaps other Al-containing wastes. Methods are needed to measure the heat production potential of such wastes under landfill-relevant conditions and to use the resulting heat production data to evaluate the quantity of a given waste that can be disposed without the accumulation of unacceptable heat. The objectives of the proposed research are to (1) develop laboratory methods to measure heat evolution from special wastes under landfill-relevant conditions and (2) measure rates of heat production to parameterize our heat accumulation model. The model will then be used to estimate acceptable quantities of specific heat-producing wastes for disposal. The proposal emphasizes heat release from ash and metal corrosion. However, methods will be generalized to assess the heat generation of other wastes.

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 frequently used in these rehabilitations because these materials provide reasonable installed performance and allow for a rapid return to service. Over the last 5 years, the NCDOT has completed an average of about 25 overlays per year using LMC or LMC-VES materials. The vast majority of these projects are highly successful. However, despite comprehensive NCDOT guidelines and specifications (such as PSP003 and PSP004), substantial cracking is sometimes observed in these overlays shortly after installation. Prior research funded by NCDOT has indicated that if placement and curing follows proper construction procedures, then the primary causes of cracking (such as shrinkage and plastic shrinkage) in LMC and LMC-VES materials are unlikely to develop. However, other secondary mechanisms can potentially cause cracking, including vibration of the structure during casting and curing, temperature changes during casting, and slight differential settlement/deflection of supporting decks as overlay placement progresses across a bridge. These suspected secondary causes of cracking are difficult (or impossible) to mitigate in practice. In practice, it can also be difficult to completely enforce proper construction procedure, which can lead to some shrinkage cracking. For example, fogging above fresh LMC-VES is allowable, but allowing water to accumulate on the material during placement and finishing is not ������������������ the distinction is sometimes difficult to monitor and enforce in the field.

According to the US Environmental Protection Agency (USEPA), around 23,000 to 75,000 Sanitary Sewer Overflows (SSOs) occur annually and approximately 25% of these SSOs are due to sewer line blockages related to the deposition of insoluble calcium salts of fat, oil and grease (FOG). Prior research studies have quantified the chemical and rheological properties of the FOG deposits along with its formation mechanism (Keener et al. 2008; He et al. 2011, 2013; Williams et al. 2012; Gross et al. 2017). Research performed by the PI and Co-PI on the project entitled ����������������Evaluation of Alternative Binder Material to Reduce Sewer Collection System Infrastructure Maintenance and Enhance Sustainability��������������� funded by WRRI, investigated the substitution of Fly Ash (FA) in concrete to reduce the formation and adhesion of FOG deposit on sewer line surfaces. Although exciting results from this project revealed a significant reduction in FOG formation and adhesion on FA replaced concrete surfaces, its mechanism for reduced FOG deposition at the interface is unknown. An interesting observation from these prior adhesion studies is that FOG deposits do not form or adhere on the concrete coarse aggregate (granite) surface. Understanding this unique and previously unknown phenomenon could lead to new strategies on treating pipe surfaces that would not allow any FOG deposit adhesion. The objectives of this proposed research are to: 1) understand the FOG adhesion mechanism on different sewer pipe surfaces and 2) evaluate the factors affecting FOG adhesion on different sewer surfaces. Successful completion of this project will help to determine the adhesion mechanism of FOG deposits on sewer collection system and develop new strategies during construction or the maintenance of sewer pipes that will change the surface characteristics to reduce the adhesion of FOG deposits. We anticipate that results will eliminate or significantly retard the accumulation of FOG deposits in sewer lines leading to a reduction in the maintenance cost and the occurrence of FOG related SSOs especially in ����������������Hot Spot��������������� regions known for the persistent accumulation of these solids.