Hydration and curing conditions significantly affect micro-structure development and consequently the resistance of concrete to chloride penetration.
Hydration is the chemical reaction between cement and water that forms binding products such as calcium silicate hydrate (C-S-H), which fills pore spaces and strengthens the material. Proper curing ensures sustained hydration and sufficient moisture for the development of a dense micro-structure.
When curing is inadequate, hydration slows or stops prematurely, leaving behind a porous structure with interconnected capillary pathways that facilitate chloride ingress.
Temperature during curing also influences micro-structure formation. Higher early-age curing temperatures accelerate hydration, causing rapid strength gain.
However, accelerated hydration can produce a less refined micro-structure over time, with larger capillary pores and weaker transition zones. Although the concrete may reach early strength targets, its long-term resistance to chloride ingress may be compromised.
Conversely, controlled curing at moderate temperatures promotes more uniform hydration, leading to denser and more durable micro-structures.
Moisture availability is equally important. Concrete that is allowed to dry prematurely develops surface pores and micro cracks, weakening the protective cover layer and making the RCPT results worse.
Continuous moist curing enhances the formation of hydration products, reduces permeability, and improves RCPT performance. Mixtures containing SCMs are especially sensitive to curing because pozzolanic reactions occur more gradually and require sufficient moisture to fully contribute to micro-structure refinement.
Curing duration is another determining factor. Longer curing periods generally produce lower RCPT charge values because extended hydration reduces pore connectivity and increases resistivity. Short curing duration may result in misleadingly high RCPT values, underestimating the long-term durability potential of mixtures that would otherwise perform well with proper curing.
Ultimately, hydration and curing govern the pore structure, ionic resistivity, and transport pathways in concrete. Proper curing practices adequate moisture, controlled temperature, and sufficient duration are essential for achieving a durable micro-structure with low chloride permeability as measured by RCPT.
