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Mechanical vibrators are instrumental in compacting newly poured concrete within formwork and around reinforcements. This process is essential to eliminate trapped air pockets and establish a dense concrete mass. One widely used method is vibrating by internal vibrators, often referred to as a poker vibrator or immersion vibrator. It is rapidly inserted through the full depth of the freshly laid concrete and slightly extends into the layer below it (which remains in a plastic state). Consistent...
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Air entrainment in concrete significantly enhances the material's durability, especially in environments subjected to freeze-thaw cycles. Introducing small air bubbles into the concrete mix acts as internal voids that accommodate the expansion of water when it freezes, thereby alleviating internal stress and preventing structural cracks. This function is crucial in climates with significant freezing and thawing, as it protects the concrete from repeated stresses that could lead to premature...
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Total voids in concrete encompass gel water volume, capillary pores, and entrapped air. Gel water (retained within the cement hydration products) and physically entrapped or adsorbed water are significant for the hydration process. For complete hydration, it's estimated that the space needed for the products of a cubic centimeter of cement doubles. Capillary pores constitute the unoccupied space within the hydrated cement paste, with their size largely influenced by the water-to-cement...
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Air content measurement in concrete is critical for ensuring structural integrity and durability of concrete structures, especially in environments prone to severe weather conditions. Accurate air content analysis optimizes concrete's resistance to freeze-thaw cycles and enhances its workability and strength. Several methods are standardized under ASTM guidelines to measure the air content in fresh concrete, each suitable for different concrete types and conditions.
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The compacting factor test is a method used to assess the workability of concrete. It is  especially suitable for concrete mixes containing aggregates up to one and a half inches in size. This test involves specialized equipment consisting of two truncated cone-shaped hoppers and a cylinder, all with polished interior surfaces to minimize friction.
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  11. Surface Bubbles Emergence As An Indicator For Optimal Concrete Compaction

Surface Bubbles Emergence as an Indicator for Optimal Concrete Compaction

Hassan Ahmed1, Jouni Punkki1

  • 1Department of Civil Engineering, Aalto University, 02150 Espoo, Finland.

Materials (Basel, Switzerland)
|May 25, 2024

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View abstract on PubMed

Summary
This summary is machine-generated.

Bubble emergence is an unreliable indicator for optimal concrete compaction. This study found concrete specimens segregated even with continuous bubble activity, highlighting the need for better quality control methods.

Area of Science:

  • Civil Engineering
  • Materials Science
  • Construction Management

Background:

  • Concrete compaction quality is crucial for structural strength and durability.
  • Under-compaction leads to entrapped air and reduced strength.
  • Over-compaction causes segregation, affecting strength distribution and elasticity.

Purpose of the Study:

  • To evaluate the common practice of stopping concrete compaction when bubbles cease to emerge.
  • To investigate the relationship between bubble emergence and segregation during concrete compaction.

Main Methods:

  • Six concrete specimens were compacted using table and poker vibrators.
  • Surface activity was recorded using 4K video during compaction.
  • Digital image processing analyzed bubble emergence per frame.
Keywords:
compaction qualityconcretesegregationsurface bubbles

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Main Results:

  • Bubbles continuously emerged from all specimens throughout compaction.
  • All specimens exhibited some level of segregation, some severe.
  • A slowdown in bubble emergence rate was observed in some cases.

Conclusions:

  • Bubble emergence is not a reliable indicator for optimal concrete compaction.
  • Continued bubble activity does not prevent segregation.
  • Development of online tools for assessing concrete compaction quality is necessary.