Believe it or not, concrete overlays have been in use in the U.S. for more than a century, with the first use dating back to the early 1900’s. Concrete overlays were first used to build new highways and roads in our country, but later on the focus changed to using overlays as a cost-effective way to extend the life of roads and bridges that were past their prime.
The use of concrete overlays has continued to rise in recent years, growing from roughly 3 to 4 percent of the concrete pavement placed across the country in 2005 to now hitting an average of more than 12 percent.
The use cases for concrete overlays has also expanded beyond just roads and bridges to include airport runways and industrial areas. The Federal Highway Administration (FHA) has even listed Targeted Overlay Pavement Solutions (TOPS) in the latest round of Every Day Counts (EDC), EDC-6 Innovations for 2021 – 2022.
Let’s take a closer look at the main benefits of concrete overlays and then how Ultra High Performance Concrete (UHPC)—and particularly our proprietary Cor-Tuf UHPC mix—raises the bar when it comes to ROI on concrete overlay projects.
The benefits of concrete overlays for roads and bridges
- Sustainability—Extending the life of roads and bridges with a concrete overlay is a much faster project than a complete rebuild. The work can be done more quickly, reducing traffic congestion from detours and the impact on the environment.
- Resiliency—Concrete is more durable than asphalt, making it a better choice for an overlay for road and bridge repairs.
- Cost savings—Concrete overlays that are well-designed and performed at the right time during a road’s or bridge’s life are cost effective. Less subsurface work is required, and the project moves along quickly. Overlay projects extend the life of bridges and roads, saving tax dollars from going towards more extensive repair and reconstruction jobs.
- Safety—Concrete overlays are an ideal way to improve the safety of road and bridge conditions. Overlay projects can be done relatively quickly, making it possible to repair more roads and bridges in a given period of time.
- Improved ROI—Concrete overlays can be targeted to areas that deliver the biggest return on investment. Intersections, bus lanes, and ramps are examples of areas that require more maintenance and have a shorter lifespan. Concrete overlays reduce maintenance requirements, improve driver and pedestrian safety, and minimize the amount of construction/work zones needed.
Upgrade concrete overlays with UHPC
In addition to TOPS, EDC-6 also lists UHPC for bridge preservation and repair among the 2021 – 2022 innovations. The use of UHPC for concrete bridge deck overlays is specifically mentioned as a way to extend the service life of bridges well beyond what traditional repair methods can deliver.
UHPC bridge deck overlays were recently completed by several state Departments of Transportation, including the Delaware DOT, Iowa DOT, and New York State DOT. Other projects include:
- Chillon Viaduct UHPC overlay—A 1.3-mile-long twin structure along Lake Geneva in Switzerland.
- Blackbird Road Bridge in Townsend, Delaware—A UHPC concrete overlay on a new bridge construction.
- Floyd River Bridge in Sheldon, Iowa—A bridge rehabilitation project involving a 1.75-inch-thick UHPC concrete overlay.
It’s no surprise to us that UHPC is being used for more concrete overlay projects. The material delivers all that a traditional concrete overlay provides, plus:
UHPC has ten times the compressive strength of traditional concrete. After just 14 days of curing, UHPC has a compressive strength of 20,000 pounds per square inch (psi). This number increases to 30,000 psi when fully cured for 28 days. Some mixes of UHPC have even demonstrated a compressive strength of 50,000 psi. Traditional concrete usually has a psi ranging from 2,500 to 5,000 psi.
UHPC can deliver more than 2,000 psi in flexural strength. Traditional concrete normally has a flexural strength of 400 to 700 psi. This greater flexural strength allows UHPC to actually move and flex with traffic-induced vibrations and temperature changes. As a result, the bond with the substrate retains its adhesive qualities, resulting in the virtual integration of the two layers with the supporting structures.
UHPC can be used anywhere traditional concrete can be applied, but with added strength and durability.
Reduced material requirements
UHPC delivers incredible strength and stiffness, so a thin concrete overlay can be used without sacrificing durability and longevity. You get a superior product with less material. Two inches of Cor-Tuf UHPC is stronger than ten inches of traditional concrete overlay.
Long-term cost savings (yet an even better ROI)
UHPC is more expensive than traditional concrete, but (as we just mentioned) you need less material for UHPC overlay projects. In addition, since UHPC overlays last longer, the reduced maintenance costs result in a lower lifetime cost of UHPC overlays projects versus those completed with traditional concrete.
It is also less expensive to perform a UHPC overlay on a bridge deck when compared to a complete bridge deck replacement. Since UHPC concrete overlays vastly improve the longevity of roads and bridges, a UHPC overlay is a more cost-effective solution.
Impermeability / resistance to environmental degradation
Bridges in particular are susceptible to damage from water and salt, which seep in through the bridge deck. From there, they make their way into the beams and weaken the entire understructure of the bridge. UHPC (especially Cor-Tuf UHPC) stops this process in its tracks.
UHPC is impervious to water and extremely resistant to environmental degradation from salt and other damaging substances. Using a UHPC concrete overlay on a new bridge prevents this deterioration from happening. You can also increase the longevity of existing bridges in need of repair by repairing the beams and installing a concrete overlay made of UHPC. You avoid the cost and downtime of a full reconstruction and extend the life of the bridge well beyond what a traditional concrete overlay can accomplish.
Easier substrate preparation
With any concrete overlay work, the substrate needs to be properly prepared. If it lacks integrity, the overlay won’t last as long. A benefit of UHPC, however, is that it is so much stronger than traditional concrete that it takes more pressure and slack off of the underlay. While you still want to properly prep the underlay, UHPC does provide a little more “wiggle room” in the integrity of the underlay itself, making substrate preparation easier.
A stronger bond
A main concern with concrete overlay projects is how well the overlay adheres to the substrate. UHPC is an extremely adhesive material. Cor-Tuf UHPC bonds very well, especially if you moisten the surface ahead of time. It behaves in a fashion similar to an epoxy in terms of its bonding qualities, drastically reducing any worries over bond strength with UHPC concrete overlay work. Additionally, shrinkage is virtually non-existent during and after the curing process, further enhancing the effectiveness of the bond.
Simple slope solution
Concrete overlays done on bridges often involve work on a sloped surface, making it important to use a thicker mix. It is possible to make a thixotropic UHPC mix ideal for overlay work. The thixotropic UHPC mix retains its shape once poured. It remains in a pile until energy (usually through vibrations) is applied to it. You can actually build the slope into the guides used with the overlay machinery.
Why Cor-Tuf UHPC is the best choice for UHPC concrete overlays
There are a number of UHPC concrete mixes on the market. While they all deliver some of the benefits we just described, they are certainly not all created equal.
In fact, we have spoken to contractors who have used other brands of UHPC for concrete overlay work. They have found some UHPC mixes difficult to work with. We’re pleased to say they are making the switch to Cor-Tuf UHPC simply because it delivers the same benefits but is so much easier to mix, transport, and pour.
Cor-Tuf UHPC is compatible with all industry standard production techniques, from large-scale precast facilities to small, cast-in-place applications. It has a 100-year product lifespan, making it capable of greatly extending the life of roads and bridges when used as an overlay material.
We like to describe our proprietary UHPC mix as contractor-friendly. Cor-Tuf UHPC can be mixed and poured just like traditional concrete using conventional construction equipment. It has been successfully poured into and out of ready mix trucks, Tuckerbilt dispensers, volumetric truck-mounted mixing and delivery systems, skid-steer auger buckets, and all types of conventional wheelbarrows, buckets, and buggies.
Your crew doesn’t need to learn how to use any new machinery or new techniques in order to use Cor-Tuf UHPC. They can start using this innovative concrete material right away.
- It can be mass produced using conventional methods.
- It is pumpable.
- It has a shorter mixing time than conventional UHPC.
- It has a working time of roughly one hour.
- Mixes can be customized to meet the needs of any job.
What’s even more exciting is that we will now also be able to offer an automated batch plant with automated batch plant tickets to this list.
As the use of concrete overlays on roads and bridges continues to increase and government agencies express their support for this approach, contractors have much to gain from exploring the best options when it comes to overlays. Cor-Tuf UHPC maximizes ROI with its superior strength and durability. Save money, reduce your environmental impact, and improve the longevity of roads and bridges with the only UHPC mix that delivers the highest quality and ease of use.