Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Civil Engineering

Advisor

Rangaraju, Prasada Rao

Committee Member

Amirkhanian , Serji

Committee Member

Putman , Bradley

Committee Member

Fortney , Patrick

Abstract

Alkali-silica reaction (ASR) is one of the most recognized durability problems in concrete leading to premature deterioration of different types of concrete structures. Recent investigation into premature deterioration of airfield concrete pavements indicated the aggressive effects of alkali-acetate and alkali-formate based deicers on concrete containing marginal aggregates, in particular on their potential to induce ASR.. This dissertation presents the results and analysis from a research study conducted to evaluate the effectiveness of selected supplementary cementitious materials-SCMs (fly ash and slag) as ASR mitigation measures in presence of potassium acetate based deicer.
Five aggregates that encompass a range of mineralogies and reactivity were studied in combination with three fly ashes with substantially different chemical compositions, and a Grade 120 slag. These supplementary cementing materials (SCMs) were evaluated at different cement replacement levels: fly ash at 15%, 25% and 35%; and slag at 40% and 50%, using standard and modified ASTM C 1567 mortar bar tests, along with standard and modified ASTM C 1260 (mortar bar) tests and modified ASTM C 1293 (concrete prism) tests. Subsequent to the initial investigation with the three fly ashes, extensive investigation was conducted to evaluate the influence of chemical composition of fly ash on mitigating deicer-induced ASR, using twelve fly ashes and one reactive aggregate (Spratt limestone). The twelve fly ashes represented the low lime-, intermediate lime- and high lime-fly ash categories. In these investigations, all the fly ashes were used at a cement replacement level of 25%.
In addition to expansion measurement on test specimens, changes in dynamic modulus of elasticity and microstructure of the mortar and concrete samples exposed to deicer solutions was investigated. Also, changes in pH of the deicer solutions were monitored. In addition to determining the bulk chemical composition of fly ashes, X-ray diffraction studies (XRD) were conducted to characterize the crystalline compounds present in the fly ashes. The role of the various chemical constituents of the fly ash and their correlation with the expansions of the mortar bars was explored by conducting regression analyses.
In general, the chemical composition of fly ash, particularly the lime (CaO) and sulfate (SO4) levels, played a significant role in determining the effectiveness of fly ashes in mitigating ASR induced by potassium acetate exposure. Low lime and intermediate lime fly ashes performed significantly better than the high lime fly ash at 25% and 35% cement replacement levels. High lime fly ashes showed a negative interaction in the presence of potassium acetate deicer and were ineffective in controlling ASR at all levels of dosages considered in the study. Slag at 50% cement replacement level was more effective in mitigating expansions compared to 40% dosage level. Besides the dosage and type of fly ash and slag, their effectiveness was also dependant on the type of aggregate.

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