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The effect of drying and rewetting on the dynamic elastic modulus of 0.4 and 0.6 W/C ratio pastes and mortar were investigated. Drying results in a significant reduction in the dynamic elastic modulus due to the moisture stress gradients. The original undried value of the dynamic elastic modulus is totally recovered upon subsequent rewetting of the dried specimen. It is concluded that effects such as microcracking caused by drying can be avoided. Therefore, miniature specimens may be used to measure the unrestrained response of cement paste and concrete. The study shows that the reduction in the dynamic elastic modulus increases with increasing aggregate content and decreases with increasing W/C ratio.