Application of Silica Sand and Silica Fume for Improving Workability and Surface Hardness Properties of M30 Grade Concrete

The incorporation of silica sand and 7% silica fume significantly influences the performance of M30 grade concrete [11].   Workability improves from 0% to 15% replacement (70 mm &120 mm slump) due to better particle packing and superplasticizer efficiency [4], [8].   At 20% replacement, workability slightly decreases (100 mm slump) because of increased fines and higher water demand [17].   Rebound hammer values indicate an increase in surface hardness from 34 (0%) to 41 (15%), showing improved density and strength characteristics [13].   At 20%, rebound value drops (~37), suggesting excess silica sand negatively affects compaction and uniformity [1], [8].   The optimum replacement level is 15% silica sand, providing the best balance of workability and strength [20].   Overall, the mix with 15% silica sand + 7% silica fume results in a denser, more durable, and efficient concrete suitable for practical applications [11].   The study confirms that combined use of silica sand and silica fume enhances both fresh and hardened properties of concrete [8].   Silica fume (7%) contributes to microstructure refinement by forming additional C–S–H gel, leading to improved density [11].

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