Preliminary Characterization of Aggregate Coefficient of Thermal Expansion and Gradation for Paving Concrete (0-1700-5)

This report is primarily focused on measurement and modeling of aggregate coefficient of thermal expansion (COTE) and its effect on early age crack patterns. This report also covers the aggregate gradation effects on early-age concrete properties. A new mineralogical approach is introduced to predict the COTE of aggregate and concrete. Basically, a modeling approach is developed based on the assumption that the COTE of aggregate and concrete can be predicted from the COTE of their constituent components. Volume percentage, COTE, and elastic modulus of each constituent mineral phase are considered as inputs for the aggregate COTE model, whereas the same properties for coarse aggregate and mortar are considered for the concrete COTE model. Methods were formulated to calculate the mineral volume percentage from bulk chemical analysis for different types of rocks commonly used as aggregates in Texas. A dilatometer testing method was established to measure the COTE of aggregate and pure minerals. Calculated aggregate COTE based on the determined COTE of pure minerals and their respective calculated volume percentages show a good resemblance to the measured aggregate COTE by use of dilatometry. Similarly, predicted concrete COTE based on the calculated COTE of aggregate and mortar and their respective volume percentages compared well with the dilatometer measured concrete COTE. Such a favorable comparison between predicted and measured COTE provided a basis to establish the composite model to predict aggregate and concrete COTE. Aggregate gradation effects on cracking-related displacements of concrete were investigated in the laboratory using the German cracking frame. Concrete workability was assessed by use of the slump and drop tests (German DIN 1048) for two different concrete mixtures consisting of gap-graded and dense-graded aggregates. Shrinkage strain, cracking frame strain, and concrete strain were measured and compared with strength gain and creep development. The measured and calculated strains of the different aggregate gradations were compared with each other. Gradation effects on strength and stress development relative to tensile cracking at the saw-cut tip were also investigated.