Assessment of the Coefficient of Thermal Expansion of Alabama Concrete
Type of DegreeThesis
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The coefficient of thermal expansion (CTE) is a fundamental property of portland cement concrete. It represents the change in unit length of concrete per degree of temperature change. The CTE is a very important property in concrete pavement design and in the design of integral structures, especially bridge decks, as it can affect early-age cracking, the serviceability, and performance of these concrete structures. The increasing recognition of the potential magnitudes of thermal movements and stresses induced in integral structures, especially bridge decks, and in pavements exposed to the daily ambient temperature, suggest the need for a realistic CTE rather than an assumed value for use in their design. The prime purpose of this research work was to quantify the CTE for concretes made with commonly used coarse aggregate types in the Alabama concrete industry. A total of fifty-four concrete samples were tested for their CTEs using the Association of the American State Highways and Transportation Officials (AASHTO) TP 60 (2004) test method at a concrete age of 28 days. The concrete was made of three different coarse aggregate types. The coarse aggregate types used were siliceous river gravel, granite, and dolomitic limestone. Three different sand-aggregate ratios of 0.40, 0.45, and 0.50 as well as water-cement ratios of 0.32, 0.38, and 0.44 were used. Thus for each coarse aggregate type, a total of nine concrete mixtures were made and a total of eighteen concrete samples were tested for their CTEs using concrete cylinders of size 4 in.(diameter) x 7 in.(height) (100 mm x 175 mm). The CTEs were calculated for each concrete sample in accordance with the procedure outlined in AASHTO TP 60 (2004). The results showed that concretes made with siliceous river gravel have the highest CTEs with an average value of 6.95 x 10-6 /oF (12.51 x 10-6 /oC) while those made of granite have lower values, with an average of 5.60 x 10-6 /oF (10.08 x 10-6 /oC). The lowest CTEs were observed for concretes made with dolomitic limestone, which had an average value of 5.52 x 10-6 /oF (9.93 x 10-6 /oC). It was determined for the materials tested that the sand-aggregate ratio and water-cement ratio did not have as much influence on the concrete CTE as does the coarse aggregate type. An increase in the volume of the coarse aggregate or a decrease in the sand-aggregate ratio increases the CTE for concretes made with river gravel and decreases the CTE for concretes made of granite.