Concrete Window - Sill

| Component | Proportion (by mass) | Function | |-----------|----------------------|----------| | Portland cement (Type I/II or V for sulfate resistance) | 1 part | Binder | | Well-graded fine aggregate (sand) | 2–2.5 parts | Packing, finishability | | Coarse aggregate (max size 10 mm) | 1.5–2 parts | Reduce shrinkage, increase modulus | | Water | 0.35–0.45 w/c ratio | Hydration, workability | | Air-entraining admixture | 4–7% air content | Freeze-thaw resistance | | Water-reducing admixture | As required | Lower w/c, higher strength | | Polypropylene or steel micro-fibers | 0.5–1.0 kg/m³ | Crack control |