The Potential of UHPC
Why use UHPC? Currently, there is a critical need for advanced building materials for the U.S. domestic infrastructure, not only for new high-performance construction, but also to repair and enhance the performance of existing structures. These materials are required to be increasingly more energy-efficient, environmentally friendly, sustainable, affordable, and resilient. They need to meet multi-hazard/-performance design criteria and be easily produced and incorporated into construction methods and practice. Furthermore, these materials must be cost effective through a structure’s life cycle
Concrete is the most widely used material in building construction. Within the last few decades, research has been conducted on what is known as Ultra High Performance Concrete (UHPC). The term includes a broad range of materials such as defect-free, dense particle, engineered composite, multi-scale particle, and fiber-reinforced cementitious materials with enhanced properties and characteristics. Commercial brands are available and many research mixtures have been developed to include local and “green” constituents.
For purposes of this workshop, a definition of UHPC is a class of “concrete” materials with an unconfined compressive strength over 20,000 psi (140 MPa) that usually has high binder content and special fine aggregates. For comparison, the unconfined compressive strength of conventional concrete is from 3,000 to 6,000 psi (20 – 40 MPa). Steam curing may be employed to attain strengths approaching 30,000 psi (210 MPa) and higher UHPC may contain fibers to achieve non-brittle behavior and, if possible, to dispense with passive (non-prestressed) steel reinforcement. The UHPC materials of interest have very small pores, low porosity, and disconnected pore spaces.
If viewed solely on the cost per cubic yard of material, the cost of UHPC materials can be over ten times greater than the cost of conventional strength concrete. However, UHPC materials may offer unique advantages and higher performance levels that justify the increased “first cost”. Such factors include: strength, ductility, flexibility and toughness, impact resistance, dimensional stability, durability / increased useful life, impermeability / freeze/thaw resistance, corrosion resistance, abrasion resistance, aggressive environment resistance, and chemical resistance.
Other advantages may include: ability to construct thin sections and use complex structural forms, elimination of passive reinforcement (reinforcement bars), precise replication, use of conventional
concrete equipment, ability to cast by pouring, injection or extrusion techniques, self-consolidation, off-site manufacturing, fast construction, and reduced maintenance.
From an aesthetic viewpoint and also for security purposes (such as disguising the appearance of the material), some UHPC mixtures may have color and texture options, surfaces can be sanded or polished and can even be made to look similar to materials such as stone or marble.
In summary, advanced materials known as UHPC have a strong potential to help the revitalization of our nation’s infrastructure, and in the building of new infrastructure that is sustainable, resilient and longlasting. However, adoption of UHPC in the U.S. has been slow in comparison to Europe and Asia, notably Australia, China, France, Germany, Iran, and Japan. A concerted effort will be required to accelerate its usage in the U.S. construction industry.