Ultra-High Performance Concrete: Your Questions Answered
February 3, 2023
As infrastructure continues to deteriorate, owners are looking for more durable building materials that increase service life. UHPC is becoming a material of choice, especially in repair and retrofit applications.
As demand for UHPC increases, engineers, contractors, and legal professionals should be aware of the nuances of the material and how it will play a role in restoring and repurposing critical infrastructure. CTLGroup’s building materials experts are on the leading edge of UHPC and receive questions from clients across the country. Read on to learn more about this emerging material.
What is Ultra-High Performance Concrete?
UHPC is a cementitious composite material with mechanical, durability, and bonding properties that far exceed those of conventional concrete. The mixture has an extremely low water content, contains a high percentage of steel fibers, and can be made without air entrainment.
UHPC is highly resistant to macrocracking, with any damage tending to remain as distributed microcracks, yielding a paste matrix that is exceptionally durable. Because the mix is so dense and impermeable, moisture and chlorides cannot penetrate, allowing UHPC to avoid typical concrete vulnerabilities such as surface scaling and internal cracking from freezing and thawing damage.
What are the challenges associated with using Ultra-High Performance Concrete (UHPC) on projects?
Any new product comes with challenges and learning curves. Engineers, contractors, and testing professionals are familiarizing themselves with UHPC’s proprietary mixtures, high strengths and thixotropic behavior. UHPC manufacturers are producing proprietary mixtures with technology that evolves over time. While ASTM C1856 provides guidance for how to properly fabricate and test specimens of UHPC, many project specifiers are unaware of this document or apply the tests to the wrong setting (field vs laboratory).
In the field, most contractors have little to no exposure to UHPC, and project-based specifications typically do not offer guidance around placement. While some industry associations are introducing training around UHPC, formal contractor education is not widely available. Just as many contractors are unfamiliar with self-consolidating concrete the highly flowable behavior of UHPC can lead to problems with formwork leakage or maintaining finished grade of the placed material. These conditions can lead to extra labor costs if not planned for properly.
Testing professionals are also familiarizing themselves with UHPC, and most laboratories do not have in-house capabilities or equipment to test materials with strengths of 12,000 psi or more (much less the 17,000 psi or more ultimate strength seen with UHPC). While the industry adopts UHPC as a material of choice, it’s critical that owners select testing partners who have the equipment and knowledge to run proper testing methods.
What kind of quality control measures should owners, engineers, and contractors consider when planning and placing Ultra-High Performance Concrete (UHPC)?
From design to placement, taking proper steps to manage quality control is critical for achieving UHPC performance standards and successful placement in the field. Engineers should be familiar with specifications and have an understanding of the nuances of proprietary mixes on the market. If they’re not familiar, a materials consultant with expertise in UHPC can guide specification development.
In order to ensure successful placement, contractors should be engaged prior to construction so they understand UHPC’s unique characteristics and placement risks. UHPC consultants can also provide field expertise and observe to guide contractors during placement.
When should owners, engineers, and contractors engage a consultant when planning a project?
Whether planning a project or navigating a performance issue after placement, it’s never too early to engage a consultant. Qualified UHPC consultants can add significant value in reducing risk of this emerging material.
For more information on UHPC and how CTLGroup’s experts can help on your next project, contact us.