A New Era? UHPC Concrete Piles Versus Steel Piles – LBM Research Associates

Amazing! A New Era? UHPC Concrete Piles Versus Steel Piles – LBM Research Associates

Information about A New Era? UHPC Concrete Piles Versus Steel Piles – LBM Research Associates

Phil Puccio

Most of us in the construction industry are very familiar with piles. Two of the most common types of piles are concrete piles and steel piles. Although these two types of stakes are very different, each offers certain advantages over the other.

With the introduction of a new and innovative concrete technology – Ultra High Performance Concrete (UHPC) – many of the benefits that steel has enjoyed need to be re-examined.

We can even predict that UHPC piles will usher in the demise of steel pile foundations.

The head-to-head race: steel versus concrete piles

Steel piles

Here, too, most of us know the advantages of steel piles:

  • Because of their impressive tensile and compressive strengths (typically in the 50,000 pound per square inch range), they are often considered to be the strongest stakes in the industry [psi]).
  • Lighter than traditional concrete piles, making them easier to transport and install.
  • Easier to splice than conventional concrete piles by welding.
  • Used to support heavier structures such as skyscrapers and large bridges.
  • Can penetrate hard layers of soil.

The disadvantages of steel piles:

  • More expensive than concrete.
  • Corrode and deteriorate more easily than concrete; This is typically the result of moisture in the area and reactive soils.

Concrete piles

There are two types of concrete piles to consider – prefabricated concrete piles and cast-in-place piles. The main difference between the two is that pre-fabricated piles can be built in various shapes and sizes to meet the needs of your project.

Advantages of concrete piles:

  • Cheaper than steel.
  • The quality of the concrete can be checked before the piles are driven into the ground.
  • More stable in softer soils; local buckling is less of a factor.

Disadvantages of concrete piles:

  • Can lead to severe soil displacement.
  • Can be damaged while driving.
  • May deteriorate over time due to adverse environmental conditions such as moisture, seawater, and freeze-thaw cycles.
  • May require extensive reinforcement such as carbon fiber or stainless steel to improve durability, adding to costs and challenges during construction.
Preview of our latest bending test session with FDOT in Tallahassee, Florida. This picture shows part one of our first major axis bending test.

UHPC concrete piles: combining the best of both worlds

Ultra high performance concrete (UHPC) is an innovative concrete material that is stronger and more durable than conventional concrete. UHPC overcomes the typical challenges of steel piles – but also offers the same strength advantages as steel, making it the best choice for any construction that requires pile foundations.

Concrete piles made from UHPC are stronger and more durable, which increases the quality and safety of the structures they support. Research has shown the benefits of using UHPC for piles over other materials.

The tests were conducted in Iowa for UHPC piles for bridges. The results indicated that the UHPC piles had strong durability and excellent performance in very difficult piling conditions; even without the presence of a pillow. UHPC piles could also be made shorter (or less used due to the added strength of the material), making the construction process more efficient.

A recent release from PCI also reported on the many advantages of UHPC piles, including the advantages over steel. UHPC piles showed little to no shrinkage and had a high modulus of elasticity. Due to the self-leveling quality of UHPC and the steel fiber reinforcements, piles made of UHPC have reduced cross-sectional requirements and have weights and stiffnesses that correspond to those of steel piles. UHPC piles have been proven to withstand harsh impacts and have superior durability.

Compared to steel piles, UHPC piles offer many of the same advantages (for practically the same price) while overcoming the disadvantages:

  • strength—UHPC has a compressive strength of 30,000 psi when fully cured and offers the option of pre-compression by prestressing. This improves the driveability and does not significantly affect the operation or the maximum axial capacity. Some UHPC blend designs can even reach 50,000 psi, which is the same as steel.
  • Resistance to environmental degradation—Tests by UHPC showed that the samples were impermeable to water, had negligible surface damage, and were resistant 1000+ freeze / thaw cycles and storms.
  • permeability—UHPC has a higher density than normal concrete. This makes it practically impossible for normal water and chloride to penetrate the surface of UHPC.

Further advantages of ultra-high-performance concrete for pile construction are:

  • Reduced material requirements– Less material is required to build UHPC concrete piles, which saves money on material costs.
  • Reduced maintenance—The many benefits of UHPC translate directly into less maintenance. Structures last longer and require less maintenance.
  • Cost savings—This new concrete technology offers much lower life cycle costs. Since less material is required for construction projects, the need for foundations and supports is reduced. Using UHPC concrete piles can reduce the total number of piles required for a bridge foundation. The extended life of UHPC practically eliminates maintenance costs and dramatically extends the life of the product. When the cost of UHPC is spread over the life of the product, it offers significant cost advantages over steel.
Part two of our test results from our last session with FDOT in Tallahassee, Florida. The results represent testing along the secondary axis of the pile.

Why use Cor-Tuf for UHPC concrete piles?

Building contractors and contractors should be aware that there are a number of UHPC products on the market, but not all are created equal. Many conventional UHPC blends are incredibly strong and long-lasting, but present different usage and consistency challenges.

For example, most conventional UHPC products cannot be mixed, poured, or transported using conventional concrete machines. Nor can they be mass produced, which can lead to undesirable downtime on the website and inconsistencies in the final product.

Cor-Tuf UHPC, however, overcomes all of these obstacles and makes it the right choice for any project, especially for concrete piles.

Cor-Tuf UHPC can be mass-produced using standard machinery. You can get a consistent product with a uniform mix throughout the batch. In fact, tests have proven Cor-Tuf UHPC to be resistant and show no delineation between batches. With conventional UHPC (and even with conventional concrete) there is often a cold joint between the concretes.

This occurs when one batch begins to solidify before the next is poured, creating weak points in the structure. Testing of Cor-Tuf UHPC has shown that no cold joints form between batches, creating a unitary piece that is stronger and more durable.

Castability is one of the main advantages of using Cor-Tuf UHPC over traditional mixes for concrete piles. Cor-Tuf UHPC can be poured like conventional concrete and is even pumpable. This makes it easier to use for large structures such as piles (while other UHPC mixes are more difficult to work with).

Another benefit of Cor-Tuf UHPC is that it can be customized to meet the needs of your concrete pile project. The proprietary mix can be modified to increase or decrease working hours. Even the strength can be adjusted to ensure you get the support you need for a particular project.

Specific testing was even awarded an award on concrete piles made from Cor-Tuf UHPC Results. In these tests, a 30-foot post-tensioning pile and two 30-foot post-tensioning piles were produced using Cor-Tuf UHPC in a large volume production facility.

Tests confirmed that the precast piles were free of voids and showed no signs of internal shrinkage during the curing process. The 30 foot pile was able to withstand a downward bending pressure of 84,000 psi and a deflection of 4.5 inches before failing. When the pile cracked, its fracture point was compacted into an area with no additional beam cracks along the sides of the pile.

The 100 foot Cor-Tuf UHPC pile was subjected to pressure from a D36 and D62 hammer. Regardless of which hammer was used or how hard or quickly we tried to hit the stake, our data from the event showed that the structural integrity of the stake never fell below 100 percent.

While steel piles offer contractors and engineers a number of benefits, the introduction of concrete piles made from UHPC heralds a new era. UHPC concrete piles offer several advantages over steel piles for virtually the same price, making them the smartest choice and investment for your future pile driving projects.

We are currently working on a number of UHPC H pile projects in the Mid-Atlantic region. Stay tuned this room for full test results and an upcoming video from our recent flex test sessions with FDOT in Tallahassee, Florida.

Breaking Story – A New Era? UHPC Concrete Piles Versus Steel Piles – LBM Research Associates

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Original Source: http://www.lbmresearchassoc.com/2019/12/19/a-new-era-uhpc-concrete-piles-versus-steel-piles/
Category – Concrete

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