Air-Void Stability in Self-Compacting Concrete: Linking Fresh-Air Retention with Hardened Pore Structure Through a...

Area of Science:

• Materials Science
• Civil Engineering
• Concrete Technology

Background:

• Air entrainment in self-compacting concrete (SCC) is complex, influenced by admixtures, workability, and aggregate structure.
• Hardened air-void systems in SCC are difficult to predict from total air content alone due to fresh-state bubble dynamics.
• Understanding early air retention is key to predicting the final pore structure and performance of SCC.

Purpose of the Study:

• To evaluate the relationship between early fresh-air retention and hardened air-void characteristics in SCC.
• To investigate the influence of air-entraining admixture (AEA) dosage, binder type, water-to-binder ratio (w/b), and volumetric paste-to-aggregate filling parameter (φ) on air-void properties.
• To establish a framework for understanding air entrainment in SCC based on fresh concrete properties.

Main Methods:

• Twenty-five SCC mixtures were designed using a five-level Graeco-Latin square.
• Fresh concrete properties (slump-flow, T50 flow time, density, air content at 5 and 15 min) and hardened properties (total air content, spacing factor, micropore content, specific surface) were measured.
• Statistical analyses, including correlation and ANOVA, were performed to assess relationships between variables.

Main Results:

• Strong correlations were found between fresh and hardened air contents (e.g., A5 vs. A: r=0.920, R²=0.846).
• Hardened air content (A) was strongly and inversely related to the spacing factor (L) (r=-0.907, R²=0.822).
• Water-to-binder ratio significantly affected early air loss and micropore content; binder type showed near-threshold significance for air content.

Conclusions:

• Early fresh-air retention is a reliable indicator of hardened air-void characteristics in SCC.
• The study provides a bounded explanatory framework for air entrainment in SCC, emphasizing the link between fresh and hardened states.
• Direct durability claims, such as freeze-thaw resistance, require separate experimental verification.