UHPC HT
Products
UHPC,
Ultra High Performance Concrete, is a combination of a cement, micro
particles and wear resistant (very hard) particles. Due to the
micro
particles it is possible to create a perfect physical packing
ensuring improved chemical reactions. These chemical reactions
secures the formation of minerals with superior properties at room
temperature. Hence around 60% of the full strength will be obtained
after 48 hours. Final strength of a UHPC is 100-250 MPa / 14500-36250 psi.
Water
added to UHPC to secure a proper
rheology is limited, and shortly
after setting there will be no more free water in the system, as all water will be bond in the structure of the chemical reactions.
When
heating UHPC HT the risk of cracking due to evaporation of water is
limited. However too fast heating of a virgin installation could lead
to this. Hence it is recommended to firstly heat up the installation
at a rate of 50°C/hr. The heating does not contribute to the
strength of the system however it will increase the rate of strength
building.
Refractories
Unshaped
refractories typically contains an alumina cement as the bonding
material and other metallic minerals depending on the
temperature and
environment it is installed. Water is mixed in to create the right
rheology for installation. As such this product at ambient
temperature can be viewed as an ordinary mortar. As such the product
is relative porous and strength at ambient temperature is not likely
to exceed 45 MPa. This system will also reach around 60% of final
strength after 48 hours of hydration.
This
system will contain free water after installation, hence there is a
risk of cracking when heated. Hence it is necessary to heat it at
specific heating rate in order to avoid such cracks. In
order for refractories to work they need to be heated so that the
metallic minerals is calcinated
and sintered into the wanted minerals
with the needed properties.
Comparison
The
strength and density of UHPC HT is a lot higher than that of
refractories. Hence these products will be better at withstanding
inner pressure from internal water evaporation, reducing the risk of cracks and ultimate process destruction of the product.
UHPC HT does not need heat to form the minerals needed in the mix in order to obtain the properties.
Heat will however increase the rate of
property formation.
