High Pressure Steam Curing

When concrete is cured at temperature higher than 100 degree Celsius that induces relative high pressure applied and concrete container known as “Autoclave” shall also be tightly sealed. The temperature will remain at 160 – 210 degree Celsius with pressure at 6 -20 atm when curing is in progress. Under highly-pressurized condition, the compound acquired from such reaction will be at variance from typical compound, which cured less than 100 degree Celsius. The following items are advantages of high pressure steam curing.

-          Enable utilization within 24 hours due to concrete has compressive strength equivalent to one that cured for 28 days.

-          Low shrinkage and fatigue

-          Durability toward sulfate salt

-          Eliminate Efflorescence

-          Low moisture after curing

In practice, the implementation is costly and often applied to the processed concrete product only. However there are some specific products that applied this principle such as fiber-optic cement tile.

Low Pressure Steam Curing

Eventhough the process is generally subject to temperature at 40 – 100 degree Celsius but the range that produces the best output is at 65 – 80 degree Celsius. In addition, temperature range is basically attributable to requirement of strength development and ultimate strength. With high temperature, compressive strength will relatively increase whilst the ultimate strength will oppositely be low. For low temperature, ultimate strength rather be applicably enhanced but reduce the rate of strength development. In Figure 10.3 clearly shown the relationship of those mentioned.

 

In spite of curing temperature, the most important thing is time consumption, which involves gradual increase of temperature, the actual optimum temperature and reduction towards normal temperature. As Figure 10.4, shows the process of controlling temperature. After casting, concrete should be left at normal temperature approximately 2 – 6 hours prior to steaming so as to pre-stimulate the hydration reaction. Rate of increase should not exceed beyond 30 degree Celsius/hour. Further more, when concrete is subject to maximum temperature; it dominates the increase of strength as it relies upon relationship of multiplied product of time and temperature so called “Maturity” as shown in Figure 10.5. On the contrast, the rate of reduction seems immaterial to this process due to concrete itself has highly gained the strength. In general, rate of reduction is at 20 – 30 degree Celsius/hour.

In many occasions, low pressure steam curing is carried out for just concrete to reach the strength that is safe to be mobilized; subsequently it will be cured by normal steam procedure until required strength is acquired.