Combined effects of vertical spacers and segregation on mass transport properties of reinforced concrete

F. Muslim, H. S. Wong, G. Cheng, C. Alexandrou, B. Liu, N. R. Buenfeld

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


All concrete structures contain reinforcement spacers, and deep sections can be affected by bleeding and segregation without displaying visible indications during casting. However, their effects on mass transport and long-term durability are not well studied. In this paper, reinforced concrete columns were prepared with plastic and cementitious spacers to achieve 50 mm cover, and compacted at different vibration frequencies and durations. 28d cured samples were extracted along the height, conditioned to equilibrium (21 °C, 75% RH or 50 °C, 7% RH), and then subjected to water absorption, electrical conduction, epoxy impregnation and fluorescence imaging. Samples from the top of the column consistently gave higher accessible porosity and mass transport compared to samples from the bottom. Presence of spacers caused additional increases in mass transport because of preferential flow through the spacer-concrete interface which is more porous and microcracked compared to bulk concrete farther away. Image analysis on cross-sections showed that the columns experienced some aggregate segregation despite care taken to avoid over-compaction. The resistance of concrete to ingress of aggressive agents decreases with increasing height due to the combined negative effects of reinforcement spacers and segregation.

Original languageEnglish
Article number151
JournalMaterials and Structures/Materiaux et Constructions
Issue number6
Publication statusPublished - Dec 2020


  • Bleeding
  • Durability
  • Reinforcement spacer
  • Segregation
  • Spacer-concrete interface
  • Transport properties


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