Although concrete is widely considered a very durable material, if conditions are such, it
can be vulnerable to deterioration and early distress development. Alkali-Silica Reaction
(ASR) is a major durability problem in concrete structures. It is a chemical reaction
between the reactive silica existent in some types of rocks and alkali hydroxides in the
concrete pore water. The product of this reaction is a gel that is hygroscopic in nature.
When the gel absorbs moisture, it swells leading to tensile stresses in concrete. When
those stresses exceed the tensile strength of concrete, cracks occur. The main objective of
this study was to address a method of testing concrete materials as a combination to assist
engineers to effectively mitigate ASR in concrete. The research approach involved
capturing the combined effects of concrete materials (water cement ratio, porosity,
supplementary cementitious materials, etc.) through a method of testing to allow the
formulation of mixture combinations resistant to ASR leading to an increase in the life
span of concrete structures.
To achieve this objective, a comprehensive study on different types of aggregates
of different reactivity was conducted to formulate a robust approach that takes into
account the factors affecting ASR; such as, temperature, moisture, calcium concentration
and alkalinity. A kinetic model was proposed to determine aggregate ASR characteristics
which were calculated using the System Identification Method. Analysis of the results
validates that ASR is a thermally activated process and therefore, the reactivity of an
aggregate can be characterized in terms of its activation energy (Ea) using the Arrhenius
equation. Statistical analysis was conducted to determine that the test protocol is highly
repeatable and reliable.
To relate the effect of material combinations to field performance, concrete
samples with different w/cm?s and fly ash contents using selective aggregates were tested
at different alkalinities. To combine aggregate and concrete characteristics, two models were proposed and combined. The first model predicts the Ea of the aggregate at levels of
alkalinity similar to field conditions. The second model, generated using the Juarez-
Badillo transform, connects the ultimate expansion of the concrete and aggregate, the
water cement ratio, and the fly ash content to the Ea of the rock. The proposed models
were validated through laboratory tests. To develop concrete mixtures highly resistant to
ASR, a sequence of steps to determine threshold total alkali in concrete were presented
with examples. It is expected that the knowledge gained through this work will assist
government agencies, contractors, and material engineers, to select the optimum mixture
combinations that fits best their needs or type of applications, and predict their effects on
the concrete performance in the field.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-394 |
| Date | 2009 May 1900 |
| Creators | Ghanem, Hassan A. |
| Contributors | Zollinger, Dan G. |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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