 |
| Concrete with enhanced Fire Resistance |
Concrete
with enhanced or high fire resistance means concrete which is improved so that
it can withstand the defined high heat conditions. Concrete itself cannot burn,
but above certain temperatures it loses first its mechanical properties and
then its form. Without special measures concrete is normally heat resistant in
service up to a temperature of about80°C.
Concrete
with high fire resistance is used for
·
Emergency areas in enclosed structures
(tunnel emergency exits)
·
General improved fire resistance for
infrastructure
·
Fire resistant cladding for structural
members
Properties
of concrete with high fire resistance
·
As a rule the fresh concrete behaves like
standard concrete during placing
·
The hardened concrete has a somewhat slower
strength development than normal, but again the properties are similar
Production
of concrete with high fire resistance
·
The concrete production does not differ from
standard concrete
·
The mixing process must be monitored due to
the fibers normally included
·
It is beneficial to the future fire
resistance of this concrete if it can dry out as much as possible
Constituents
for the production of concrete with high fire resistance
·
Achievement of maximum fire resistance is
based on the composition of the aggregates used
·
The resistance can be greatly increased by
using special aggregates
·
The use of special plastic fibers (PP)
increases the resistance considerably
·
The use of selected sands improves the
resistance of the cement matrix
Mechanisms
of behavior in fire
The
capillary and interstitial water begins to evaporate at temperatures around the
boiling point of water (100ºC). Steam needs more space and therefore exerts
expansion pressure on the concrete structure. The cement matrix begins to
change at temperatures of about 700°C. The effect of the aggregates is mainly
dependent on their origin and begins at about 600°C. Concrete starts to “melt”
at about 1200°C.
No comments:
Post a Comment