Ultra High Performance Concrete is concrete which has a higher compressive strength than the ÖNORM EN206-1 standardized compressive strength class (> 115 N/mm2). Currently strengths of up to 250 N/mm2 under standard conditions are achieved through a very dense and homogenous microstructure. Therefore, this concrete displays a very good longevity and resistance against external impact. Buildings with slender and thin-walled components, which withstand great stress, can be realized through the use of UHPC. Dealing with concrete after fire exposure, damages to the structure or even spalling of concrete can occur. In comparison to standard concrete, this spalling in UHPC is more intensive due to its denser structure. The reason for this is the developed water vapor, which is caused by fire exposure and which cannot exhaust through the dense concrete structure. The addition of adequate polypropene-fiber minimizes the spalling of concrete or, respectively, prevents it completely. Apart from the examination of spalling, it was another objective of this thesis to construct a compact furnace, which facilitates the fast transport of spalled material quickly out of the oven to enable further analysis. In the scope of this thesis, various UHPC formulas were produced in extensive, experimental series, which were treated with different subsequent-treatment procedures and stored under different conditions. This was done to analysis the effects on the microstructure and on the spalling of UHPC after fire exposure. Furthermore, the strength properties of various UHPC formulas were evaluated.