Effects of Curing on High-Performance Concrete

Effects of Curing on High-Performance Concrete

Curing is the process in which the concrete is protected from loss of moisture and kept within a reasonable temperature range.

Hooton et al., (2002) examined effect of duration of curings on resistance of the near-surface zone to Chloride(Cl) penetration. He found that there was little added benefit to curing beyond 3 days at 20 °C. They also found that the detrimental effects of poor curing were limited to the top 40 mm of concrete.

Meeks and Carino, (1999) completed a comprehensive review of information on curing of high-performance concrete. The long-term goal of the proposed research was to provide the basis for modifying current ACI standards related to curing so that structures in service will perform as required. Curing requirements should consider economy of construction and not place undue demands on the construction team. On the other hand, curing requirements should assure the owner that the potential properties of the concrete in the structure are realized.

A common feature of HPC design is development of high strength (U.S Department of Transportation). Mixture proportions commonly involve low water-cement ratios. As has been mentioned elsewhere, water-cement ratios less than 0.40 are generally thought to create a condition where the concrete will internally desiccate due to consumption of all of the mixing water by hydration, and that if additional hydration is necessary, then water must be added during curing. But since low water-cement ratio concretes tend to be relatively impermeable, there is some question about how effective externally added water will be in penetrating the concrete.

Persson, (1997) studied relative humidity depth profiles in concrete at various water-cement ratios, with and without silica fume in the concrete. As expected, the internal relative humidity of low water-cement ratio concretes (<0.4) that were sealed against any evaporation begins to drop below 100 percent within 28 days, eventually dropping to about 75 percent after 450 days.

This pattern is accelerated when silica fume is present. Similar specimens stored in water without any surface sealant show the same pattern, suggesting that the external water is in fact not getting into the concrete to any appreciable degree. The minimum depth analyzed was 50 mm.