Concrete bleeding refers to the upward migration of water to the surface of freshly placed concrete before initial setting, due to gravity-driven separation of components. Denser particles like cement and aggregates sink, while lighter free water rises, forming a layer of water or diluted slurry on the surface.
Common causes include:
1. Material-Related Issues
Cement problems: insufficient fineness, low C₃A or alkali content, poor storage or gypsum deficiency;
Poor SCM quality: low-grade fly ash or high blend ratios increase water demand;
Aggregate issues: low sand ratio, coarse sand, oversized or flaky aggregates, low mud content in fine aggregate.
2. Mix Design & Admixture Problems
High water–cement ratio (>0.5): excess free water exceeds binder capacity;
Improper use of admixtures: overdosage of superplasticizers or retarders, poor air-entraining agent performance;
Excess mineral additives: e.g., high-carbon fly ash or excessive slag leading to weak water retention.
3. Construction & Environmental Factors
Over-vibration or free-fall >3m: accelerates segregation;
Long haul time: extended truck mixing leads to component separation;
Sudden temperature or humidity changes: delays setting or creates misleading evaporation effects.
4. Hazards of Bleeding
Surface dusting, cracking, and delamination;
Reduced impermeability and durability due to bleed channels;
Potential pump blockage and settlement cracks.
✅Solutions:
Use high-reactivity cement, well-graded aggregates, control water–cement ratio, fine-tune admixtures, and improve on-site handling. Don't let bleeding silently damage your structure — fix it before it shows!
评论
发表评论