Recent architectural and structural innovations have produced construction materials with incredible strength and durability properties for civil engineering.
Many versions of steel and concrete elements are used in the construction process. One of the major innovations is Ultra High Performance Concrete (UHPC).
In this article, you will learn all about UHPC, what it is, and why it is better than traditional concrete and other building alternatives. You will also discover how to source UHPC concrete material for your construction projects.
What is Ultra-High Performance Concrete?
Ultra High Performance Concrete is a new type of concrete material that has become quite popular in the last two decades. Different types of ultra high performance concretes are used for concrete structures and building applications that require high-strength material properties and high durability properties. Two things traditional concrete cannot provide.
The thing that makes UHPC amazing is not just its tensile strength (which has exceptional performance) or its high resistance to stress but the longevity of that tensile strength. Ultra high performance concrete can retain its high tensile strength properties for more than 100 years.
UHPC also goes by another name – Reactive Powder Concrete. For cement to be classified as Ultra high performance concrete, it requires a minimum compressive strength of 120 MPa or 17,000 pounds per square inch.
Who invented ultra high performance concrete?
UHPC was developed by the US Army Corps of Engineers at the end of the 1980s. The concrete was marketed later to the masses by Bouygues, a French company, in the 1990s. However, the term ‘Ultra High Performance Concrete’ was coined in 1994.
What is ultra-high performance concrete made of?
Ultra High Performance Concrete is a combination of the following ingredients with varying quantities of each:
- Fine silica sand: Fine sand comprises about 40% of the total UHPC by weight.
- Portland Cement: Generally, high-quality UHPC contains about 29% Portland cement. For precast concrete deck panels where early mold removal is required, Type III cement is used.
- Fly Ash: One of the most widely used supplementary cementitious materials, Fly Ash increases the mechanical and durability properties of UHPC without increasing the cost. With fly ash, the early strength of concrete mix is low but ultimately very high when the concrete fully cures.
- Silica fume: UHPC usually has 8.5% silica fume. The purpose of silica fume is to increase the binder content in the UHPC, which makes the compressive strength greater.
- Quartz Flour: Quartz flour in UHPC provides a vital function; it lowers permeability. It does so by filling up the voids in the concrete. Quartz flour is also commonly known as silica flour.
- High Strength steel fibers
- Water: UHPC has a low water content, generally about 9% by weight.
- High-Range Water Reducers: High-range water reducers, also known as HRWR or superplasticizers, are vital in concrete mixes with low water content. They provide the flowing capabilities of concrete while eliminating the need for water to make the concrete.
There can be additional components in the UHPC, such as high-range water reducers, quartz flour, and organic fibers.
What are the Typical Material Specifications of UHPC?
You cannot use any random type of cement for applications that call for Ultra High Performance Concrete. There are various specifications set in place that a concrete should pass to be used as UHPC.
The strength of UHPC should fall between the following limits:
- The compressive strength should be greater than 17,000 pounds per square inch or 120 MPa. French organizations have this minimum limit increased to 150 MPa.
- The flexural strengths of UHPC should be between 2200 to 3600 psi (about 15 to 25 MPa).
- The modulus of elasticity of UHPC should be between 45 to 50 GPa (about 6500 to 7300 ksi).
Durability is a critical factor that makes UHPC incredibly useful. In order to qualify as UHPC, the concrete should show the following durability characteristics:
- It should retain 100% of its properties after 300 freeze and thaw cycles. This characteristic is tested by immersing a UHPC prism in a water bath. The water is then continuously taken through multiple cycles of freezing and thawing.
- It should have a Relative Volume Loss Index (for abrasion resistance) of 1.7. This factor is measured by calculating the amount of concrete brushed off a surface by a rotary cutter.
- The loss of residue (salt scaling) of the UHPC matrix should be less than 0.013 pounds per cubic foot (about 60 g/m2).
- The Oxygen Permeability of UHPC should be less than 10^-19 square feet (10^-20 square meters).
What are the Advantages of Ultra-High Performance Concrete?
There are several beneficial characteristics of UHPC that make this technology preferable to conventional concrete alternatives. Some of these benefits include:
As mentioned in the material specifications above, UHPC scores off the charts for durability. It is perfect for structures subjected to much stress and can’t be renovated regularly, such as highway bridges.
Ultra high performance concrete has high compressive strength, up to ten times that of traditional concrete. This means that a lot less UHPC can bear the same weight that would otherwise require a greater volume of conventional concrete materials.
A higher compressive strength helps reduce the area of structural elements such as beams, pillars, and columns made out of UHPC. This is because smaller-sized UHPC products can bear a higher weight due to their high ductility.
UHPC materials are very resistant to abrasion, as is evident from their abrasion resistance factor. Even its chloride permeability and oxygen permeability are very low, making the cement very long-lasting.
UHPC mixtures consist of small-sized particles. There are no coarse aggregate materials used in UHPC technology. Therefore, the resulting cementitious composite material is homogenous and uniform.
Due to its low water content, a UHPC mix has a short setting time, unlike conventional concrete. This leads to accelerated bridge construction and building construction. It also reduces construction costs due to lesser time spent.
UHPC structural elements have mechanical properties that are very seismic resistant. This means that the buildings, bridges, and other structures created by UHPC are not prone to earthquake damage.
Besides the reduced cost factors mentioned, UHPC applications also have reduced maintenance costs. Additionally, since this concrete is abrasion resistant, there is low depreciation in the structures. This makes UHPC a very cost-effective option.
What are the Applications of Ultra-High Performance Concrete?
There are many potential UHPC applications because UHPC is considered the premier material in today’s construction industry for various structures.
One of the earliest applications of UHPC was fabricating bridge decks for accelerated bridge construction. Even today, you will find UHPC as the preferred concrete for most bridge construction sites. Even old bridges created from other materials are now repaired by using UHPC prefabricated bridge elements such as bridge deck overlays and bridge girders.
UHPC is used for a lot of marine construction projects. For instance, the tetrapods spread across the coast to curb the erosion rate due to ocean water are made using UHPC. Since UHPC has low chloride permeability and a low abrasion rate, it does a perfect job in this application.
Building an airport requires a construction material that can handle the heavy weight on the runaway and the high-level vibrations in the building’s structural behavior. UHPC is the perfect material that can provide exceptional strength for this job.
Parking structures have important structural members, such as inverted tee beams and garage decks. Ultra-high performance concrete provides a long-lasting and high endurance option in this regard.
Treatment plants deal with the accumulation of a high volume of liquid waste that undergoes a lot of chemical reactions. As UHPC is highly abrasion resistant with low permeability, it is the perfect material for building treatment plant basins.
Imagine all the stress that railway structures constantly undergo throughout every day. Ordinary concrete materials can give up on the job quickly, requiring maintenance very often. However, with the higher tensile strengths of UHPC mixtures, the lifespan of these structures can be increased significantly.
Industrial flooring must deal with heavyweight machines, tooling, and the frequent impact of collisions on the floor. UHPC handles it very well, as its high cracking strength means little to no erosion upon collisions with heavyweight items.
Does UHPC Have Any Disadvantages?
There are no specific disadvantages of UHPC. However, there are some considerations to bear in mind when considering using UHPC for your construction project:
1. Mix Proportions
Mixing proportions are critical when it comes to UHPC. Small changes in ingredients can alter the overall structural characteristics of the concrete. Therefore, make sure you are using the correct proportions to make UHPC. Even better, procure a genuine and certified proprietary UHPC such as the one available at Premier Precast.
2. Upfront Costs
The upfront cost of UHPC is higher than traditional concrete. This might make UHPC seem like a costly alternative. However, if you calculate the overall cost savings, UHPC is the cheaper option for large projects in the long term.
How Much Does Ultra-High Performance Concrete Cost?
Ultra high performance concrete is used commercially, and generally comes as a concrete mix to which additional reinforcement fibers are added. Here we will tell you the cost of both of the above factors that make up the cost of ultra-high performance concrete.
The concrete mixture without the steel fiber add-ons starts at about $360 per cubic yard and goes up to $700. You will find higher compressive strengths the higher you go in the price range.
Now talking about the addition of fiber reinforcements, it increases the cost of the UHPC by about $500 per cubic yard.
The resulting costs of UHPC start at $850 and keep going up, depending on how much compressive strength you want your mixture to have.
Pre-bagged steel fiber reinforced concrete mixtures commonly sell at $2000 per cubic yard with all the necessary components mixed correctly.
Where Can You Source UHPC From?
The lack of competition in the Ultra-high performance concrete market has led to a high cost for this raw material. This is a concern for people who wonder ‘where they can buy good quality UHPC?’
This is why Premier Precast has become one of the most popular UHPC brands in the US. It provides very high-quality UHPC at a reasonable cost, aiming to make large-scale projects affordable for builders.
To benefit from the ‘high compressive strength’ of UHPC, it must be mixed in the correct proportions. The concrete mixtures provided by Premier Precast are certified, so you always know you are getting what you need.
In fact, you can source every line of architectural concrete from Premier Precast. It is the only certified manufacturing unit in Florida to provide all these architectural concrete mixtures.
Why is UHPC Still Limited in Practice?
After reading all this information about UHPC, you can understand how it is the best choice for many construction projects. So why isn’t UHPC more popular?
Many reasons have led to the limited application of UHPC in construction. Here are some of these factors:
- UHPC has a very low water content, so it requires mixers running at high speed to properly mix the constituents together. On a construction site with conventional mixers, significant modifications and upgrades are needed to use UHPC properly.
- Unlike conventional concrete, UHPC does not have simple and standard design procedures for engineers since UHPC technology is still relatively new. These design procedures are the instructions that give the engineers confidence to go ahead with the technology.
- The high strength of UHPC is dependent on (a) mixture constituents and (b) thermal treatment. While the first issue can be fixed by using a proprietary UHPC from reputable suppliers like Premier Precast, the thermal treatment requires special arrangements on the construction site.
When it comes to the range of building materials, UHPC has been one of the pioneering achievements of the last few decades.
The performance difference between conventional concrete and ultra-high performance concrete isn’t just theory. There are tested numbers and figures for key factors like compressive strength.
These results are, in no doubt, astonishing and significantly higher than conventional concrete’s performance characteristics.
While there are some concerns about UHPC, any risks are eliminated when you get UHPC from a reliable supplier such as Premier Precast.
With Premier Precast, you will get complete information on using UHPC to get excellent value for money. If you are considering a building material for your next project, consider ultra-high-performance concrete (UHPC).