The addition of a small portion of granite polishing waste in the design mix results in:
Correct Answer: D. Improved packing density
📚 Detailed Explanation: Granite Polishing Waste Improves Packing Density
Why D (Improved packing density) is correct: Granite polishing waste (GPW) is an ultra-fine residue generated during the polishing of granite surfaces. Its particle size is very small — finer than cement — allowing it to fill the interstitial voids between sand particles that would otherwise remain empty or be filled by excess paste. This void-filling action improves the packing density of the mix.
Effects of Granite Polishing Waste on Concrete
| Effect | Mechanism | Result |
|---|---|---|
| Improved packing density | Ultra-fine GPW particles fill voids between sand grains | Denser matrix; less void space |
| Reduced void ratio | Less empty space in the aggregated skeleton | Lower porosity; better impermeability |
| Reduced porosity | Tighter particle packing reduces capillary channels | Lower permeability; better durability |
| Reduced sand consumption | GPW partially replaces natural sand | Environmental benefit; waste utilisation |
| Improved mortar performance | Better particle gradation fills size gaps | Stronger interface bond; lower paste demand |
Why the Other Options Are Wrong
| Option | Why Incorrect |
|---|---|
| A. Lighter concrete | Granite is a dense rock (≈2700 kg/m³); GPW increases density, not lightens it |
| B. Higher void ratio | GPW fills voids; void ratio decreases, not increases |
| C. Decreased strength | Better packing density → less void space → higher strength or at worst maintained strength |
| D. Improved packing density | Correct: GPW fills inter-particle voids; better gradation; denser concrete |
- Granite polishing waste as sand replacement → improved packing density.
- Also reduces void ratio, reduces porosity, and improves mortar workability as a filler.
- Industrial waste utilisation (GPW, fly ash, GGBS, silica fume) improves both concrete properties and sustainability.