Albert Einstein famously mused “If you can’t explain it to a 6-year-old, you don’t understand it yourself.” This can be applied to how many in the construction industry view ultra-high-performance concrete, or UHPC. While this type of concrete has been around for a long time, it is often dismissed as a complicated and expensive option.
“It’s complicated” may not be the best explanation for why the industry does not regularly use a material that can make buildings and infrastructure stronger and longer-lasting. While it’s an economic fact that UHPC is many times more expensive than your average 5,000 psi mix, the concrete becomes a clear financial winner when durability and space and weight optimization are key objectives.
The simple fact is UHPC can lead to a lower total cost of ownership for many applications.
But before we delve into that, let’s first discuss UHPC and the perceived barriers to using it.
What is UHPC?
UHPC uses finely tailored constituents to create mixes that will reach 35,000+ psi with careful precast curing and 20,000+ psi when poured onsite. It contains 80% of the same materials as traditional concrete, yet the particles are much smaller—they integrate with the basic matrix much better than standard materials. Several academic studies cite the area between the matrix and aggregate as the weakest part of the concrete. Hence, fewer and smaller spaces in the mix mean fewer and slower-developing problems in the concrete.
UHPC is “impenetrable.” A huge challenge for normal concrete is porosity. When moisture and contaminants enter voids in the concrete, microcracks form easily, which can then morph into larger cracks. Subsequently, the concrete begins disintegrating from the inside out in freeze-thaw and salt environments or when exposed to alkali silica reaction (ASR). That’s not the case for UHPC, which is highly resistant to penetration.
UHPC is strong. Even in its most basic, field-cured application, the compressive strength of UHPC exceeds normal concrete by a factor of four (20,000 psi vs 5,000 psi). Further, it has significantly better tensile strength.
UHPC is a great fit for high-strength or low-weight applications, and especially when both are required. Consider high-rise construction. When UHPC is used, floors can be much thinner, thanks to the material’s lack of porosity and high tensile and compressive strengths. Lower overall weight-bearing columns can be poured, and the building can be constructed on geology with less load-bearing capacity.
Another application that benefits greatly from UHPC is seawater bridge construction. Fixing “rotted” bridge abutment ends or pylons with UHPC is more cost-efficient than rip-andreplace applications, with the repairs producing a structure with higher strength than when it was newly built and providing a much longer life. For proof, look at the Ancient Roman sea structures in Italy constructed with Roman pozzolanic—arguably the original UHPC—that have remained viable for 2,000 years.
Removing the Barriers
The one thing that has prevented widespread use of UHPC has been its cost, which can fall in the range of thousands of dollars per cubic yard. Part of UHPC’s high cost has been the requirement to use specialized, highly accurate batching and delivery equipment versus using the same plants and trucks we normally deploy for “normal” concrete.
Our industry needs to cut that price substantially. Fortunately, several companies are working on that. Real-world solutions include a formula with proprietary admixtures that allow the concrete to be made in current ready mixed concrete plants and shipped in current mixers. The nearterm goal is to eliminate the need for materials producers to purchase specialized equipment and pass those costs along to their customers.
Let’s make a projection that current efforts will drive down the cost of a cubic yard of UHPC to $1,000 in the near future. How can we sell this price to project owners?
When building with UHPC, structural components can be smaller, which matters in environments where every square inch is valuable—like in New York City. A 30-floor building with a 4-inch UHPC floor thickness costs less than one with standard 15-inch-thick floors made with normal concrete, and the weight-bearing columns can be thinner. Because there is a finite limit to the weight of a building that the local geology can hold, UHPC buildings can be taller. Plus, there is simply less concrete to ship, pump and place. The benefits extend throughout the concrete supply chain. For mining, less material is required. For cement manufacturing, less cement is needed. For transport, less raw material is shipped, and more structural elements can be loaded on one truck. All this adds up both in EBITDA (earnings before taxes, depreciation, amortization) and sustainability (a lighter carbon footprint).
Consider a bridge subject to salt and ASR. Research indicates that UHPC has a projected useful life span of well over 100 years. Too many bridges across the U.S. are in desperate need of repair after 20 years, especially in coastal states like Florida. Even if the use of UHPC is good for only 50 to 75 years without repair, it would be a home run both for EBIDTA and sustainability.
Alternatively, let’s revisit that 30-story building with 4-inch-thick floors in lieu of 15 inches. From a green aspect, that means approximately a three-quarter reduction in emissions throughout the entire material chain. From a cost perspective, assume $167 per cubic yard of 5,000 psi concrete versus our projected goal of $1,000 per cubic yard of UHPC—or ~$668 versus ~$1,000 for equivalent flat coverage.
This one’s a tougher sell, but there will eventually be a significant green credit, and vertical columns also can be much thinner.
Our industry is determined to keep trying new applications and pushing the boundaries to reduce cost and carbon. UHPC is just one example. Perhaps the most salient Einstein quote about our industry is “You never fail until you stop trying.” We never stop trying.
Craig Yeack has held leadership positions with both construction materials producers and software providers. He is co-founder of BCMI Corp. (the Bulk Construction Materials Initiative), which is dedicated to reinventing the construction materials business with modern mobile and cloud-based tools. His Tech Talk column—named best column by the Construction Media Alliance in 2018—focuses on concise, actionable ideas to improve financial performance for ready-mix producers. He can be reachedat [email protected].