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This paper presents an experimental approach to determine the coefficient of thermal expansion (CTE) of paste, mortar and concrete at early age. The deformation of specimens was measured by using high-precision linear variable displacement transducers (LVDT) and the temperature was measured by thermocouples embedded in the specimens. It was found that the CTE decreased after setting and reached minimum values at a few hours after setting, then increased with time until becoming nearly constant. At the age before the mixtures gain enough stiffness, the use of fly ash increases CTE of the pastes and concretes. However, at later age, the CTE of pastes and concretes with fly ash is smaller than that of the mixtures without fly ash. Aggregate seems to be the main factor that affects the CTE of concrete because it occupies most of the concrete volume.