The strength and durability of ultra-high performance concrete (UHPC) are valuable for a variety of applications, from repairing aging structures to creating efficient new designs. UHPC is championed by transportation departments and trade groups (including the U.S. Federal Highway Administration) for its ability to work in situations where traditional concrete is less suitable. It works as a connection between precast members, as protective repair material, or as a structural member itself. Each use case enjoys an extended service life thanks to UHPC’s resistance to deterioration.
Let’s look at some of these common uses of UHPC.
Bridge Deck Overlays
Deck deterioration is caused by a combination of vehicle loading, freeze–thaw degradation, cracking, delamination of cover concrete, and/or corrosion of internal reinforcement. As an overlay material, UHPC provides structural strengthening and protection from ingress of contaminants.
The amount of UHPC material required to finish a protective overlay is significantly less than traditional solutions. A typical layer of UHPC might be about one-third of the thickness and one-half of the added load versus concrete. A lower dead load equates to improved structural integrity and lower stress on members of the bridge. Less material can also mean easier and faster construction to get bridges back into service more quickly.
Using UHPC in overlays has other long-term protective benefits. Low permeability causes resistance to environmental deterioration, chemical ingress, and freeze–thaw damage that weakens traditional concrete. Its bonding strength causes resistance to abrasion, which reduces the impacts of heavy use and potential rutting. Cracking is minimized because of low shrinkage and internal reinforcement, which shields the underlying bridge components from further damage.
New UHPC overlays can be incorporated into new bridge designs or added to existing, older bridges. It adheres to roughened concrete surfaces and bonds well, requiring minimal preparation.
Connecting Prefabricated Bridge Elements (PBE)
Prefabricated elements have added significant benefits to bridge construction, thanks to design and logistical efficiencies, but they still need to be properly assembled. The long-term performance of these spans will be greatly affected by the quality of the connections. Construction speed is also important to consider. UHPC has become a popular method for field-casted connections of PBE, because it enhances the integrity of connections while reducing complexity and shortening project schedules.
Typically, PBE’s are connected with lap-spliced rebar in a concrete closure pour. Design challenges include long rebar development required to meet tensile load factors. These sections sometimes require alternative rebar designs and/or very large connections with high material needs. The reinforcement strategy must ultimately align with the constraints of the prefabricated bridge elements, resulting in complex installation and fabrication requirements. The fabrication and construction process impacts cost, schedule, and long-term durability.
Thankfully, UHPC has significantly higher tensile and flexural strength than regular concrete. This enables the connections to utilize smaller, simpler rebar development, and a more economical design. Steel costs and fabrication challenges are reduced proportionately. Closure and grouting applications can be applied with increasingly convenient ready-mix and onsite mixing capabilities.
Cor-Tuf UHPC is now used for this application and is proving the significant benefits for both design and construction efficiency. Overall, UHPC promotes more successful PBE projects.
Bridge Structural Repair
UHPC is also established as a reliable repair material. Structures with compromised steel or concrete members benefit from comprehensive rehabilitation, as opposed to patchwork mortar jobs. The use of UHPC can not only bring bridges back into service, it can correct prior deficiencies that relied on traditional concrete. Retrofitting existing structures can extend service lives and improve structural performance altogether.
Reinforced concrete corrodes because of cracking, exposed rebar, and weakening of the internal matrix and reinforcement. Repair and replacement of the compromised elements should be accompanied by a durable, long-lasting shield from continued abuse. Using UHPC to encase the repaired section distributes load where it was previously not strong enough. This prevents future absorption of moisture and contaminants, ensuring the same problems don’t reoccur.
A bridge superstructure has critical elements requiring substantial care and protection, which is why more maintenance plans are turning to UHPC. The difference between a case study in engineering failure and a generations-long bridge success story might come down to the correct repair approach. Deteriorated beam and girder ends, expansion joints, deck connections and spans, column or pile jacketing, and other repair jobs benefit from the properties of UHPC. It is also fast curing, which means bridges can be up and running again within a short time period.
Precast Structural Members
UHPC is being successfully used in precast applications. Precast concrete construction involves easier logistical planning, controlled production settings, and standardized design and installation. These factors result in efficient projects that can be performed at scale. UHPC improves the strength and durability of precast members and offers more design opportunities.
Post-tensioned box girders, prestressed I-beams, concrete piles, deck panels, and other elements can be precast with smaller dimensions and higher strength. Building and bridge sections that once required a special form, rebar, and pour in the field can now benefit from sleek, thin cross-sectional UHPC dimensions that meet the safety factors and more. Lighter and smaller elements means easier delivery to the jobsite. Safety and rigging is less risky, but the structural quality improves.
More precast operations are moving to UHPC because it makes sense. The need for less rebar, the performance in inclement weather, and the reduction in material volumes all contribute to economic supply chain advantages, without compromising on structural integrity.
More to Come!
Above are some common uses of UHPC being applied throughout the industry. There are successful UHPC projects throughout the country and the world. Because of proven efficiency, engineers are turning to UHPC in more applications. We fully anticipate that UHPC usage will continue to increase and expand. Its use for blast mitigation and seismic enhancement are emerging. Building construction is starting to implement UHPC more often for more foundations and slabs. It continues to be a primary option for bridges.
Ready-Mix and UHPC represent the nexus of traditional concrete construction and the superior qualities of this material. Cor-Tuf uses ready-mix UHPC in a typical truck with a classic mix operation to serve any jobsite. This improves projects while maintaining existing techniques and equipment. Our material is combined with your mix supply. This combination improves on traditional concrete without compromising standard construction methods.
We look forward to the next generation of UHPC projects and continuing to support this new standard of construction quality. Whether it’s a generic job or a custom request, Cor-Tuf is here for your UHPC experience. Your sand, your cement, our Cor-Tuf UHPC.