Date of Award

Spring 1-1-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Yunping Xi

Second Advisor

Franck Vernerey

Third Advisor

Keith Porter

Abstract

This thesis consists of two topics: Thermal strain of concrete under low temperatures, and durability and processing techniques of concrete with CNTs. The low temperature test studies the anti-freezing action of concrete under cooling environment. Concrete mixes using different amounts of air-entraining agent and water/cement ratios were made and cured under different humidity environments. During the cooling process from 10 ºC to -25 ºC, the strain of concrete was measured every 3~5 ºC. The strain-temperature curve of concrete under different mixing proportion was produced from these results. A numerical model was developed based on the theory of the self-consistent model. No knowledge of real pore shapes is needed to apply in the model. The only inputs for the model came from the (Brunauer-Emmett-Teller) BET test, which gave the pore size distribution of concrete sample. The validity of the numerical model was compared to the experimental results, and showed similarity in trend and peak strain.

CNT is one of the most popular topics in engineering. CNT has an extremely high strength and Young's modulus. CNT is a nano-scale material, however, and tends to clump together, which makes it difficult to apply. Other research has successfully incorporated CNT into cement paste and polymer materials. This has not yet been done into concrete. This research mainly focuses on the important factors that must be solved to adopt CNT in concrete area. An ultrasonicator was used to aid the dispersion and distribution of CNT in water, while several chemicals were also adopted for this purpose. Both strength and durability were tested for CNT concrete of different mix designs. It is suggested that ultrasonicator can improve the strength of pure CNT concrete (without chemicals) by around 100%. In addition, the sodium polyacrylate treated CNT concrete has showed best durability result and good strength result.

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