Which method can increase the hardness of concrete surfaces?

The method that can significantly increase the hardness of concrete surfaces involves using hardeners or densifiers that react chemically with the concrete. These products contain compounds that penetrate the concrete and chemically react with unhydrated lime and free calcium present in the concrete mix. This reaction leads to the formation of additional calcium silicate hydrate (C-S-H) gel, which enhances the density and overall hardness of the surface.

When these hardeners are applied, the porous structure of the concrete becomes more compact, effectively reducing the number of voids within the matrix. This enhancement not only increases hardness but also improves resistance to wear, abrasion, and even some degree of chemical attack, thereby extending the lifespan of the concrete surface. The increase in density also contributes to reduced permeability, assisting in minimizing the risks of moisture infiltration and subsequent damage.

In contrast, if a higher water-to-cement ratio is used, it can lead to a weaker concrete structure because more water creates a more porous mix, leading to reduced strength and hardness. Applying curing compounds primarily aids in moisture retention during the curing process but does not inherently alter the concrete's hardness. While adding more aggregate can improve certain mechanical properties, excessive aggregate can create an imbalance in the mix and may not necessarily contribute to increased surface hardness