Date of Graduation

7-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

W. Micah Hale

Committee Member

Mark Arnold

Second Committee Member

Prannoy Suraneni

Third Committee Member

Cameron Murray

Keywords

Calcium Oxychloride, Cementitious Paste, Concrete, Low Temperature Differential Scanning Calorimetry, Supplementary Cementitious Materials, Thermogravimetric Analysis

Abstract

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.

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