Date of Award

12-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Advisor

Rangaraju, Dr. Prasad

Committee Member

Putman , Dr. Brad

Committee Member

Amirkhanian , Dr. Serji

Abstract

This two part research study was created to first develop a new process using existing test methods to determine the Alkali-Silica Reaction (ASR) potential of hardened concrete that is exposed to external alkalis and secondly to determine the ASR mitigation potential of using rice husk ash (RHA) as a supplementary cementitious material (SCM). The first part of the research study was completed by using a new aggregate extraction procedure that uses a combination of hydrochloric acid treatments and abrasion to remove the cement paste from the aggregate. This extracted aggregate was then crushed down to the specified sizes and used in an ASTM C 1260 test. The calibration of the test was done by extracting three different types of aggregate from ASTM C 1293 samples from a previous study at Clemson University that had ASR problems and then using the extraction process to remove enough aggregate to conduct a post removal ASTM C 1260 test. The results of the post removal ASTM C 1260 test were then compared to the initial ASTM C 1260 tests that were run on the three control aggregates. The new process was successful in the sense that the aggregates were classified with the same reactivity for the pre and post removal ASTM C 1260 tests. This process was then used on cores from two airports, both of these airports are known to have ASR problems. The test was again successful in determining the reactivity of the aggregates as potentially having a deleterious behavior. As for the determination of the mitigation potential of RHA used as an SCM, this was done by first physically characterizing the material, determining the pozzolanic activity index, and then using the RHA in an ASTM C 1567 test to determine the mitigation potential. The results showed that the material has a low specific gravity with a high xi surface area and high silica content. The pozzolanic activity index was the highest at a replacement level between 10 and 15% by mass replacement. The results of the ASTM C 1567 tests showed that as the replacement level increases so does the expansions, which is a clear sign that the use of RHA failed as an ASR mitigator. The reason for this is unknown, but may be due to either the vesicular structure of the RHA grains creating direct routes or pathways for the external alkalis to be transported or the chemical makeup of the ash causing an interaction with the reactive silica and external alkali

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