Damage mitigation and prediction of alkali-silica reaction in concrete

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Author:
Szeles, Tiffany
Graduate Program:
Civil Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 05, 2018
Committee Members:
  • Farshad Rajabipour, Dissertation Advisor
  • Farshad Rajabipour, Committee Chair
  • Nathaniel Richard Warner, Committee Member
  • Aleksandra Z Radlinska, Committee Member
  • James Rosenberger, Outside Member
  • Shelley Marie Stoffels, Dissertation Advisor
Keywords:
  • Concrete
  • Alkali-silica reaction
  • Mitigation
  • Service life
  • Aluminum
  • Design of experiment
Abstract:
The United States’ failing D+ rated infrastructure is plagued by alkali-silica reaction (ASR), a leading cause of deterioration of concrete (the number one building material). ASR is a deleterious reaction between alkali and hydroxyl ions contained in the concrete pore solution that primarily originate from typical portland cements, and the metastable silica contained in many natural aggregates. The product of ASR is a hygroscopic alkali-calcium-silica gel that swells upon contact with moisture, causing expansion, cracking and overall failure of concrete and has resulted in millions of dollars in damage of vital components of society’s infrastructure. Under many typical conditions, ASR is unavoidable and must be prevented with mitigation strategies. The future economical supply and availability of current ASR mitigation strategies, namely use of lithium-based admixtures and supplementary cementitious materials (SCMs) such as fly ash, slag, or silica fume, is uncertain and there exists an urgent need to find new reliable ASR mitigation strategies. Additionally, the dosages of required admixtures is prescriptive in nature as there currently does not exist a practical model that can accurately predict ASR under different conditions of aggregate reactivity, temperature, moisture and pore solution alkalinity. To address these needs, the purpose of this research is to develop effective and feasible next-generation ASR mitigating admixtures (research objective 1) and to formulate a model that can accurately predict the onset and rate of ASR (research objective 2) under different conditions to optimize the selection of appropriate mitigation strategies and maintenance operations by service life prediction of concrete structures prone to ASR. As it relates to development of next-generation ASR mitigating admixtures, this research further supported the potential of aluminum-based compounds for use in concrete to mitigate ASR. Specifically, using pure hydrated alumina, the potential mechanisms of ASR mitigation by aluminum-based compounds were determined to be (i) reduced dissolution of reactive silica in aggregates by surface passivation with Al, (ii) acidification of the concrete pore solution, and (ii) consumption of calcium and portlandite that are needed to produce a deleterious ASR gel. Using this information and through reliable long-term concrete prism testing (ASTM C1293), aluminum hydroxide (AH) and aluminum nitrate (AN), were shown to effectively mitigate ASR in concrete for a variety of different reactive aggregates. The feasibility of AH and AN for use in concrete was investigated by evaluation of the impacts on cement hydration and concrete properties. As it relates to prediction of ASR, a statistical design of experiments via the response surface methodology was conducted in a submerged setting over varied, yet realistic, conditions of temperature (4°C – 60°C), pore solution alkalinity (pH = 13 – 14) and aggregate reactivity (0.02% – 0.26% according to ASTM C1293 1-year expansion). The result of this methodology was a statistically-defensible regression equation that can predict the initiation time and rate of ASR expansion with time (in a submerged setting) as a function of the linear and nonlinear single and joint effects of pore solution pH, aggregate reactivity, and temperature. Using the regression equation developed herein to predict service life, the significance of pore solution acidification on extension of service life, and temperature increases on the reduction of service life, was demonstrated. Additional experimentation was designed and executed to extend the prediction model to moisture conditions of different relative humidity. Concisely, the key contributions of this research as they relate to mitigation and prediction of ASR can be summarized as follows: • Determined the mechanisms by which aluminum, namely hydrated alumina, can mitigate ASR • Provided two distinct aluminum-bearing compounds (AH and AN) as effective next-generation ASR mitigating concrete admixtures • Assessed the feasibility of AH and AN for use in concrete by quantification of their effects on concrete properties and cement hydration • Developed the first quantitative empirical model that utilizes standard laboratory test results (ASTM C1293), concrete pore solution alkalinity and climate data (temperature) to predict the initiation time and rate of ASR expansion under submerged conditions • Designed and executed the long-term experimental program needed to extend the ASR prediction model to varied RH conditions