Mitigating Calcium Oxychloride Damage in Cementitious Paste and Concrete Utilizing Supplementary Cementitious Materials

It is understood among engineers in the United States (U.S.) that improvement is needed throughout the transportation infrastructure. In the 2021 Infrastructure Report Card produced by the American Society of Civil Engineers, the roadways of this nation merit a D. This leaves room for improvement in order to provide durable pavements throughout this nation. Areas with significant winter weather may have exacerbated effects in decreased roadway longevity due to freezing/thawing cycles and the use of chemical deicers to mitigate gelid roadway conditions. Much research focuses on surface scaling and reinforcement corrosion using these materials; however, joint deterioration, due to chemical interactions between the deicers/anti-icers and hydration products from the cementitious paste, may also lead to significant pavement distress. One significant interaction can lead to the formation of calcium oxychloride (CAOXY). CAOXY is a product of the interaction between calcium hydroxide, found in cementitious paste, and calcium and magnesium chloride deicing salts. While conducting a significant review of the literature surrounding CAOXY, it is observed that the use of supplementary cementitious materials (SCMs) is shown effective to mitigate CAOXY formation in cementitious systems. However, the availability of quality SCMs, such as fly ash, is in question due to a reduction of active coal fired power plants. Therefore, a portion of this research investigates alternative SCMs for use to mitigate CAOXY in cementitious paste. The other portion of this research focuses on CAOXY mitigation in concrete using SCMs and establishing a link between cementitious paste testing and concrete testing. Cementitious paste and concrete mixtures are developed for this investigation using the Arkansas Department of Transportation’s Standard Specifications for Highway Construction. Alternative SCMs include rice husk ash (RHA), bottom ash (BA), limestone filler (LS), granite filler (GR), sandstone filler (SS) and silica flour (SFL). Also, a traditional SCM (fly ash (FA)) is used for comparison. From this research it is shown that the RHA is the best alternative SCM of those tested to mitigate CAOXY, while mineral fillers are shown to be less effective. In concrete, specimens are cast using fly ash as a partial cement replacement given the prolific use of fly ash in the U.S. Concrete specimens are exposed to a 30% calcium chloride solution for 202 days at 5 °C. It is shown that the compressive and flexural strength of non-air entrained (NAE) and air entrained (AE) concrete specimens is significantly reduced in cement only specimens; however, those cast with 30% or more fly ash and 5% entrained air did not experience deterioration. For the paste and concrete specimens, low-temperature differential scanning calorimetry and thermogravimetic analysis are used to quantify calcium hydroxide and CAOXY levels. Using this data, a correlation is established to predict stoichiometric CAOXY levels in concrete based on cementitious paste samples. A maximum theoretical upper CAOXY level for AE concrete of 3.5 g/100 g powder is proposed. This new CAOXY limit for concrete could be used to supplement the AASHTO PP 84 specification which currently only provides a CAOXY limit for cementitious paste

Effect of Lightweight Aggregate Moisture Content on Internally Cured Concrete

Putting an end to the rapid deterioration of concrete structures in the United States will only occur through the introduction of better materials and construction methods. The American Society of Civil Engineers (ASCE) reports the overall condition of concrete bridges in the United States to be a C+ . Though better than other areas of the infrastructure, there is still room for improvement in concrete bridges. One major area that may be improved is that of the concrete bridge deck. The bridge deck is comprised of the actual driving surface. It is subject to many deterioration mechanisms including freeze/thaw cycles, de-icing salts, and cyclic loading. The bridge deck must be highly durable to combat the negative effects it is subjected to. A recent advancement to increase durability is the placement of a pre-saturated lightweight aggregate (LWA) inside concrete. This LWA will offset cracking associated with drying shrinkage and self-desiccation. The pre-saturated LWA is an expanded clay or expanded shale material is able to absorb water into the pores of its structure and release that water to hydrating cement. The current research is focused on determining the effects of this LWA soaking durations of 1, 3, and 7 days. A constant replacement rate of 300 lbs/yd3 was used for the current study. A control mixture was cast for comparison purposes which contained no LWA. The research program concrete mix designs were developed in accordance with the Arkansas State Highway and Transportation Department bridge deck specification. Reported results included shrinkage/strain, compressive strength, modulus of rupture, and modulus of elasticity. Findings indicated that a 1 day soaked LWA preformed equivalent or better than extended soaking durations at mitigating concrete shrinkage

Non-Destructive Evaluation of Stay Cable Bridge Systems

Stay cable bridge systems have been used for centuries and as engineering knowledge and new materials has developed, these bridges have become larger, more elegant, and overall greater engineering feats. As these bridges become more popular, it is not only important to carefully design these bridges, but also to routinely inspect the health of the in-service bridges. Detrimental conditions such as corrosion, section loss, strand breakage, segregated grout, voided grout, water infiltration, and general tendon deterioration in the anchorage system are documented issues that can occur within stay cable bridges and can have extremely harmful effects. In order to monitor the health of these bridges, non-destructive evaluation (NDE) can be a very useful tool in order to inspect these bridges without having to repair the system after inspection. In this research, ground penetrating radar, magnetic flux leakage, infrared thermography, ultrasonic tomography, sounding, and borescope inspections are all performed on a series of mock-up stay cable specimens fabricated with certain detrimental conditions located within. The applicability, capabilities, and limitations of each NDE method are evaluated based on empirical data from physical testing. Furthermore, each method is ranked in categories of precision, accuracy, ease of use, inspection requirements, and cost. This research concludes that only magnetic flux leakage has the ability to determine any sort of steel strand defects, including corrosion, section loss, and strand breakage; and it was very effective in doing so, as testing data closely matched fabricated defects. Ground penetrating radar, infrared thermography, ultrasonic tomography, and sounding were all able to accurately identify grout voids within the tendon but could not differentiate between a voided region and a region infiltrated with water or poor grout conditions. In future research, additional testing to differentiate testing results between these three conditions should be explored, as each one can require completely different solutions to remedy the problem. In addition, none of the methods explored in this research were able to detect any defects within the concrete masses representative of the anchorage regions, although infrared thermography and sounding were effective at determining voided areas within the grout caps. Lastly, borescope inspection was a very useful tool to qualitatively evaluate conditions that have already been identified by one of the other methods

Phenological Patterns of Endemic Hawaiian Angiosperms.

M.S. Thesis. University of Hawaiʻi at Mānoa 2017

IMPLICATIONS OF FUEL SHORTAGES ON COTTON AND GRAIN SORGHUM PRODUCTION AND PRODUCER RETURNS -- SOUTHERN HIGH PLAINS OF TEXAS

Crop Production/Industries,

Perceptions of Facebook and Twitter as sources of health information among African-American women

Objective: The purpose of this study was to explore how African-American women perceive Facebook and Twitter as sources for information about heart disease. Methods: A qualitative study was conducted among 23 women between the ages of 18 and 70, who selfidentified as Black and female. Participants were recruited from both urban and rural cities. Data collected during each 60-minute or less focus group session was analyzed and grouped into key themes. Results: Among the Black women who participated in the research, findings indicated that Facebook and Twitter are perceived as credible sources of health information if the material shared comes from a health care professional or organization, or a friend speaking from a personal health experience. Credibility increased if information was presented by a person of color-particularly of the same race. Knowledge gained via social media was largely deemed to be the spring board for further research via a tool or website that is established within the health care industry. Participants also expounded upon the importance of one advocating for themselves in the doctor's office and fact checking health information and professionals. Conclusion: Health professionals may be able to more effectively communicate health information to Black women via Facebook and Twitter. Recommendations such as establishing credibility and using women of color in visuals are made that may assist in prompting health behavior changes. Key words: Women, African American, health information seeking, social media, heart diseas

ESTIMATING REGIONAL OUTPUT RESPONSE TO AN EXHAUSTIBLE NATURAL RESOURCE

Resource /Energy Economics and Policy,

Addressing Information Gaps: Disparities in Financial Awareness and Preparedness on the Road to College

The rising cost of higher education and questions of affordability are concerns for many families in the United States, but particularly for those from traditionally underrepresented backgrounds. The knowledge of, information about, and perceptions related to how to pay for college can impact preparatory actions taken by families to prepare to pay for college. This commentary reviews literature published on pre-college financial awareness and preparation between 2000 and 2013 to examine what we know about the topic and to highlight existing disparities by race, ethnicity, and socioeconomic status. Implications are offered for programs and policies seeking to address these inequities, as well as suggestions for future research on this important but under-researched topic