# Surface Bubbles Emergence as an Indicator for Optimal Concrete Compaction

## TL;DR

This study challenges the idea that concrete is optimally compacted when bubbles stop emerging, showing that bubbles keep rising and segregation still occurs.

## Contribution

The study provides empirical evidence against using bubble emergence as a reliable indicator for optimal concrete compaction.

## Key findings

- Bubbles continued to rise on all specimens during compaction, suggesting the need for extended compaction.
- All specimens showed segregation despite bubble emergence slowing down.
- Current bubble-based compaction indicators are unreliable, highlighting the need for better online measurement tools.

## Abstract

Compaction quality significantly influences the strength and durability of concrete in structures. Under-compacting can retain entrapped air, reducing strength, while over-compacting can lead to segregation, creating local variances in strength distribution and modulus of elasticity in the concrete structure. This study examines the widely adopted concept that compaction is optimal when bubbles cease to emerge on the concrete surface. We recorded the surface activity of six comparable concrete specimens during the compaction process using a 4K video camera. Four specimens were compacted using a table vibrator and two with a poker vibrator. From the video frames, we isolated the bubbles for analysis, employing digital image processing techniques to distinguish newly risen bubbles per frame. It was found that the bubbles continuously rose to the surface in all specimens throughout the compaction process, suggesting a need for extended compaction, with some specimens showing a slow in the rate of the bubbles’ emergence. However, upon examining the segregation levels, it was discovered that all the specimens were segregated, some severely, despite the continued bubble emergence. These findings undermine the reliability of using bubble emergence as a principle to stop compaction and support the need for developing online measurement tools for evaluating compaction quality.