Prediction of effective vibration condition under air void reduction using mortar rheological constant

Abstract

Air voids remaining on the concrete surface are detrimental to the durability. Surface voids also affect the esthetics of concrete structures. In this study, the method of reducing the surface voids caused by entrapped air of fresh concrete was verified using 122 cases of vibration box tests with different materials, mix proportions, vibration frequencies, and amplitudes. The surface void area ratio (SVAR) decreased when the acceleration of the vibration box was increased regardless of the type of concrete. The relationship between SVAR and acceleration can be expressed through a power function. However, a segregation was observed in medium‐fluidity concrete when the acceleration exceeded 4.0 Gal (hereinafter referred to as G). In addition, the SVAR correlated with the mortar rheological constant was measured using a steel ball pull‐up test. An equation using mortar rheological constants, which can be estimated using a concrete slump, was proposed to predict the SVAR‐acceleration relationship.

Surface Bubbles Emergence as an Indicator for Optimal Concrete Compaction

“…To expel these entrapped bubbles, the concrete is compacted via vibration, in which the bubbles escape the fresh concrete by rising to the surface [6,7,12]. However, longer periods of vibration might cause the concrete to segregate, which results in uneven density distribution and further durability issues [1,4,6,7,13].…”

“…Kisaku et al [12] established a method to assess concrete compaction quality by quantifying surface bubbles on hardened concrete, discovering a significant correlation between vibrator acceleration and the surface bubble ratio. However, since this method can only be applied to hardened concrete, it is limited to post-cast analysis and cannot monitor the compaction process in real-time.…”