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Concrinox TM
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Using stainless steel in concrete reiforcement structures
Available products |
BEHAVIOUR AT HIGH AND LOW TEMPERATURES
Austenitic stainless steel maintains high resistance to high temperatures. Even over 500°C the decrease of yield strength is still negligible. That is not so for austenitic-ferritic where temperatures over 300°C greatly reduce their inner toughness.
Some tests carried out in recent years within the framework of European research produce very interesting outcomes, as reported in picture 6.
When comparing the coefficients of thermic expansion reported in table 6 it transpires that stainless steels hold values slightly superior to carbon steel whereas they show a thermic conductivity of less than half.
Picture 6 - Reduction of yield strength for austenitic stainless steels (304-316) compared with carbon steel according to eurocode 3 part 1.2 (source:VTT)
| 1.4301 1.4401 | 1.4462 | ||
| Structure | Carbon steel | Austenitic steels | Austenitic-Ferritic |
| Thermic linear expansion coefficient between 20 and 100 °C | 10-12 | 16 | 13 |
| Thermic conductivity at 20°C [W/m x°K] | 40-50 | 15 | 18 |
| Tab. 6 - Characteristic stainless steel values of conductivity and thermic linear expansion for different steel grades in rebars. | |||
Overall, stainless steels behaviour is improving, compared with carbon steels, which collapse at higher temperatures.
The major thermic expansion coefficient that stainless steels show compared with carbon steels does not cause a negative effect on the reinforcement since such an effect is counterbalanced by the reduced thermic conductivity of stainless steel.
Moreover we should point out that also at high temperatures no oxide appear on steel surface with the consequent crack on the thin concrete coating (spalling), splitting the bar from the concrete.
Equally interesting is stainless steel behaviour at low temperatures, when a better steel toughness is generated without any effect of ductile-fragile transient, as it happens in carbon steels, at nearly 0°C (see picture 7).
Picture 7 - Comparisons on resilience at various temperatures between stainless steels and carbon steels.
Duplex stainless steels (austenitic-ferritic) , due to the presence of ferritic phases show a collapse of properties at around - 50°C.