Experimental study of secondary vibration on improving the early-age shrinkage properties of concrete.

This paper investigates the influence of secondary vibration and the time interval of secondary vibration on the shrinkage properties of freshly placed concrete. In this study, four sets of cylindrical specimens with a diameter of 30 cm and a height of 100 cm were designed with different time intervals for secondary vibration. By continuously monitoring the shrinkage strain of concrete for 17 weeks, a calculation model for the early-age shrinkage strain of concrete considering the effects of secondary vibration was proposed. Concrete compressive strength tests and water expansion tests were also designed to investigate the effects of secondary vibration on compressive strength, compactness and other properties under different environments. The study results showed that secondary vibration mainly reduced concrete shrinkage during the first three days, with a reduction ratio of 10%-20%, and then stabilized. The longer the time interval for vibration, the smaller the shrinkage strain of concrete, and the more significant the improvement in compressive strength and compactness, with an increased ratio of 15%-30%. The proposed prediction model can consider the effects of secondary vibration and reflect the early-age shrinkage variation of concrete during the first seven days. After the cast concrete undergoes water absorption and expansion, it can shrink again under natural air-drying conditions, and the shrinkage rate is not affected by the time interval of secondary vibration. • The effect of secondary vibration and time intervals on the shrinkage properties of freshly placed concrete was investigated. • A calculation model for early-age shrinkage strain was proposed considering the effects of secondary vibration. • A new test device was designed to study the improvement of concrete shrinkage properties through secondary vibration. • A new test method was devised to test concrete compactness and water expansion properties. [ABSTRACT FROM AUTHOR]