Ultra High Performance Concrete (UHPC) is a high-strength, ductile material formulated by combining cement, microsilica,
fine sand, water,
and steel or ceramic fibers and mesh.
The
UHPC concrete provides compressive strengths up to 250
MPa / 36200 psi and flexural strengths up to 30 MPa / 4300 psi.
The
ductile behavior of UHPC is, with the capacity to deform and support
flexural and tensile loads, even after initial cracking.
Façade
elements made by UHPC, protect people and vehicles in an earthquake against fragments
litter in building structures made of concrete and brickwork.
Concrete
ceilings are rigid and brittle structures that at the an earthquake
stress the concrete structure can break partially. The fracture is
not
a slow phenomenon under load - the fracture occurs when overloading on suddenly.
a slow phenomenon under load - the fracture occurs when overloading on suddenly.
The
result is that to loosen individual fragments of the ceiling could
(fragments litter) fall on machines or people. Are the
fragments large enough, it can lead to complete component failure.
UHPC prefabricated ceiling structures prevent like a prestressed
network the fragments become loose during the quake from the ceiling.
People
and machines are protected by such a suspended ceiling construction.
Emergency
exits can win with such additional structure several times of safety.
Just as
concrete ceilings and concrete columns are complex constructions an essential safety feature of a quake. The concrete columns must take
tremendous
flexural and compressive forces. A chipping of the
concrete structure of the inner steel reinforcement would have a very
rapid component failure result.
flexural and compressive forces. A chipping of the
concrete structure of the inner steel reinforcement would have a very
rapid component failure result.
Concrete
columns can by a jacket (by shedding) of UHPC gain much
stability and carrying capacity. A chipping of the concrete structure
at a load by an earthquake of small and medium thickness is almost
impossible with the appropriate cover.
In
any case, should structural modifications such as those described
here, be agreed in consultation with
an architect, stress analysts and the competent local planning authority.
Advantages
of UHPC
- Extreme high compressive strength
- High flexural strength
- Extreme low porosity
- Extreme good flowability
- Fast increase of compressive strength (min. 70% after 48 hours)
- High wear and impact resistance
- Absolute frost and thaw resistance
- Impermeable to fluids but still vapour permeable
- Anticorrosive features
- Good bonding to sub-bases, aggregates and reinforcement
- High temperature resistant
- Jointless lining
- Usable as mortar, grout and spray
- High ductility in combination with fibres or nano fibres
- Usable with standard concrete tools
UHPC
- His entry before and after a quake
UHPC
materials can be used as additional safety in new concrete structures
such as buildings, bridges, etc. For existing buildings and very old
buildings, targeted activities involving the use of UHPC materials
can significantly increase the safety of people and buildings. With
UHPC materials, damaged buildings can be repaired to restore their
old stability or improve their stability against earthquake loads by
improving their building structure.
Possible
applications for high quality UHPC materials
Repairing
To
make existing structures safer for future earthquake
Retrofitting
To
upgrade the earthquake resistance up to a level of the present day
codes by appropriate techniques
Strengthening
To
upgrade the seismic resistance of the a damage building
Rehabilitation
Reconstruction
or renewal of a damaged building to provide the same level of
function, which the building had prior to the damage
Restauration
Rehabilitation
of buildings in a certain area
Remoulding
Reconstruction
or renewal of any part of an existing building owning to change of
usage or occupancy
Example
of retrofitting techniques
- Minor cracksRepair by injecting UHPC
- Buckled longitudinal reinforcement, broken ties and crushed concreteReplacement of new reinforcement welded with existing bars and new additionally closed ties were placed, UHPC concrete with low shrinkage properties installed.
- Severely damaged columns adjacent to added wallsRetrofitting with encasing in UHPC concrete with appropriate longitudinal and transfers reinforcement.
- Other columnsRetrofitted with wire mesh and cover with 50 mm UHPC concrete by spraying or casting
- Existing masonry wallsAre retrofitting by using wire mesh and 30 mm of UHPC® mortar or spray
Like
concrete cover constructions, concrete columns are also essential
safety aspect in a quake. The supports have enormous
bending and compression forces to take.
A spalling of the concrete structure from the internal steel reinforcement would have a very fast component failure result.
A spalling of the concrete structure from the internal steel reinforcement would have a very fast component failure result.
As
with the concrete floors, columns can be replaced by a grouting
UHPC gain significantly in stability and carrying capacity. A flaking of the concrete construction is under load from a quake of small and medium strength with
appropriate sheath almost impossible.
appropriate sheath almost impossible.
In
a quake will be in the brickwork of a building very
quickly showing cracks in the in the worst case, individual stones break loose (Rubble throw) or a whole bandage, which too can lead to
a component failure. The
cracks in the masonry after a quake are permanent and can become one
uninhabitability and demolition of
the building to lead.
the building to lead.
Damaged
masonry will be repaired differently depending on the degree of
damage.
Fine
cracks can be filled with UHPC injection methods. Loose
masonry, bad mortar can be increased by new masonry and UHPC mortar
substantially in the
strength and bending tensile strength. Masonry
can also be improved in its entire surface with a fibre reinforced
UHPC layer in combination with steel or fibreglass reinforcement
substantially in its static structure. Especially glass fibre or
carbon fibre reinforced
UHPC show a high ductility.
UHPC show a high ductility.
an architect, stress analysts and the competent local planning authority.
