Affordable Superstrong Concrete for Bridges

Ultra-high performance concrete mixes cost $360-650 per cubic yard and have compressive strength from 22,500 PSI to 29000 PSI. There are proprietary makers of stronger concrete with costs of $2000 per cubic yard. There have been test blocks of concrete with strengths of 60000 PSI. Regular concrete is usually at 3000-5000 PSI compressive strength.

The Federal Highway Administration is studying how to make stronger concrete at lower cost in high volumes for bridges and other infrastructure.

Four UHPC matrices with fine aggregates only and three UHPC matrices including coarse aggregates were recommended using locally available materials from three different regions. The three regions included the Northeast, the upper Midwest, and the Northwest. Their material costs without fiber reinforcement ranged between about $360 and $500/yd3 ($470 and $650/m3) and $355 to $380/yd3 ($460 and $500/m3) for fine and course UHPC, respectively. The workability of these mixes can facilitate the use of these UHPCs in many structural applications. The compressive strength of the recommended UHPC matrix mixes ranged from 22.5 to 29 ksi (155 to 200 MPa)and exceeded the minimum required compressive strength of 20 ksi (138 MPa).

Future research efforts are suggested to tailor the weight ratio of cement to silica fume to supplemental material of 1:0.25:0.25 in terms of performance versus cost ratio. A reduction in the amount of the most expensive material and an increase in the amount of the least expensive material might lead to a further improvement in performance versus cost. This optimization was not the scope of this research project and has been left for future research efforts.

Adding fiber reinforcement of 1.5 percent by volume to the UHPC matrix increases the costs by about $470/yd3 ($615/m3). This value, when combined with the cost of the cementitious matrix, results in a total material cost for a fiber-reinforced UHPC of about $850/yd3 ($1,110/m3). More research effort is needed to find an alternative cost effective solution to provide sustained tensile strength and enhanced ductility due to the high costs of fiber reinforcement. This can be achieved by finding an alternative fiber reinforcement of lower cost and by reducing the required amount of fiber reinforcement through improved material utilization. A more effective fiber material utilization could be obtained by tailored matrix fiber bond and by combining continuous reinforcement with discontinuous fiber reinforcement.

Background on Concrete

Pounds per square inch (psi) measures the compressive strength of concrete. A higher psi means a given concrete mixture is stronger. Stronger is usually more expensive. Stronger concretes are also more durable, meaning they last longer.

The ideal concrete psi for a given project depends on various factors, but the bare minimum for any project usually starts around 2,500 to 3,000 psi. Each concrete structure has a normally acceptable psi range.

Concrete footings and slabs on grade typically require a concrete of 3,500 to 4,000 psi. Suspended slabs, beams, and girders (as often found in bridges) require 3,500 to 5,000 psi. Traditional concrete walls and columns tend to range from 3,000 to 5,000 psi, while 4,000 to 5,000 psi is needed for pavement. Concrete structures in colder climates require a higher psi in order to withstand more freeze/thaw cycles.

Traditional concrete costs about $90-125 per cubic yard as a ballpark figure. All prices are up currently with inflation in material costs. Concrete slab cost will vary by region. Expect a fee of about $60 per load for delivery from a concrete truck for concrete cost.

How UHPC compares to traditional concrete:

Tensile strength—UHPC has a tensile strength of 1,700 psi, while traditional concrete typically measures between 300 and 700 psi.

Flexural strength—UHPC can deliver more than 2,000 psi in flexural strength; traditional concrete normally has a flexural strength of 400 to 700 psi.

Compressive Strength—The advanced compressive strength of UHPC is particularly significant when comparing to traditional concrete. While traditional concrete normally has a compressive strength ranging anywhere from 2,500 to 5,000 psi, UHPC can have a compressive strength of up to 10 times that of traditional concrete.

After just 14 days of curing, UHPC has a compressive strength of 20,000 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.

SOURCES – Federal Highway Administration
Written By Brian Wang, Nextbigfuture.com

40 thoughts on “Affordable Superstrong Concrete for Bridges”

  1. It was Grace Admixtures. As a consumer not so much I suspect. It was setup to inject into a batch of a few yards as at a time. It was 3 to 4 chemicals and a packet of small fibers.

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  2. There wouldn't be thousands of parts. I'm talking about cutting to spec. They already do this in some cases. I'm wondering why they don't do it every time.

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  3. If you type "basalt rebar" into google you'll find dozens of suppliers selling it in industrial quantities, ready for delivery to your building site.
    It's well and truly an available product these days.

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  4. I haven't worked in the construction industry, but I have worked in the manufacturing industry. And having thousands of individual parts, all of a specified length and shape, and then having the administration system required to have them all turn up, on time, in the right order, and be put in the right place…
    It would be enormously more expensive than having stock items that can be cut and shaped as they are used.

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  5. High strength concrete is advantageous in precast forms. However, the physically smaller cross sections lower acceptable moment loads.

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  6. It's upper floor concrete, if you ask me. The concrete in the provided table has no coarse aggregate, so it's not concrete in the common sense of the word. It's aggregate to cement ratio is 1.5. Regular concrete runs between 4, and 6 a to c.

    This will be great for repairs. More importantly any new construction must have no steel rebar. It's gonna rust in most climates, and destroy the structure. That's what happened at Champlain Towers South in Florida. The damage is often deep in the concrete.
    There is a manufacturer of basalt fiber in the US, ironically in Florida. They make rebar, mesh, connectors for mesh, loose fiber, and presumably spools of yarn.

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  7. Why wouldn't they just make the rebar to spec? Couldn't you just design the house and spec out each piece of rebar, its length and shape and so forth? Then it could be made with the bend.

    This reminds me that I don't understand why we ever need to tie rebar. Why don't they just cut it to spec? 20 feet, 40 feet, whatever. It might actually have some structural strength advantages to have a single piece of rebar instead of a bunch of short bars tied together, though I could also see it being weaker in some cases…

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  8. Brett, it's being used? Where? So if you were building a concrete home, say an ICF style, you could dial that solution up right now? Would contractors need any special training? Would you expect them to resist or refuse to use basalt fiber rebar? I've heard of masons in the US turning down jobs to build homes out of AAC concrete blocks (Autoclaved Aerated Concrete or Aerated Autoclaved Concrete…)

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  9. Fiberglass rebar would be the choice for rust prevention. And epoxy coated steel. There's research on basalt fiber, but I've never heard of it existing in the marketplace.

    Flash bainite isn't a popular steel for some reason, and lots of metallurgists dislike that guy as maybe over-hyping his product. There are lots of strong steels that are more widely used. And I think the US Air Force's Eglin steel and USAF-96 are much stronger than flash bainite: https://en.wikipedia.org/wiki/USAF-96

    USAF-96 is supposed to be cheaper than Eglin, forgoing tungsten in the alloy or something, but almost as strong.

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  10. How much does it cost?

    Note that flash bainite might have been over-hyped. It's not the go-to super strong steel. There are lots of strong steels, and it's not clear that flash bainite is even widely used.

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  11. There's a lot of room for improvement between 3,000 psi to UHPC that starts at 18,000 psi. The default in a lot of countries these days is 5,000+ psi, and I'm not clear on why the US is still using grades that aren't even available in other countries anymore.

    I also don't think the 2,500 to 4,000 psi mixes are actually producing the stated strengths in a lot of applications. If people use too much water or don't mind other factors like weather they'll land below those values. And given how weak those values are to begin with, the actual obtained strength for a lot of projects is super weak.

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  12. The article is talking about UHPC. This hasn't "been used for decades" in the US, because it's not even being used now. The minimum compressive strength for UHPC is 17,000 or 18,000 psi, depending on who you ask (see here: https://www.cement.org/learn/concrete-technology/concrete-design-production/ultra-high-performance-concrete).

    Some authorities will give a minimum over 20,000 psi.

    A good example of the strongest the US works with is the new One World Trade Center tower built after Sep. 11. They used high-strength concrete ranging from 8,600 psi to 14,000 psi, depending on which part of the building and structure. (Link: https://www.concreteconstruction.net/projects/commercial-industrial/one-world-trade-center-rises-with-high-strength-concrete_o)

    That's far short of UHPC, and 14,000 psi was the strongest ever poured in New York City, so evidently no one had ever used UHPC there. I'm not aware of any use since, or anywhere in the US. Texas used some Energetically Modified Cement based concrete for some road work, but I don't know if it was UHPC level. EMC was invented in Sweden.

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  13. Exactly, the latest generation of supertall skyscrapers in NY have been using 12-14ksi concrete, and even the last generation were using 8-10ksi.

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  14. Glad you enjoyed the course mate. You are the first person I've ever seen to include concrete and interesting in the same paragraph.

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  15. I worked on some of this using Grace Admixtures around 2002.

    We had zero slump concrete that was exceeding 11,000psi in a week and our machine only tested up to 26,000psi – we stopped testing after that, because 30day we couldn't crack it. The job only required 3,000psi. At one point the engineer was putting in too much rebar at the penetrations and he was trying to argue that they needed it. (6in wall with 4" of rebar) and I said we were running 26,000psi concrete and he said his calculations could only go to 6,000psi.

    It was almost the same cost as regular concrete, in fact it became our regular mix for items because it was both far faster to pour (being zero slump) and because items exceeded 1800psi within 12 hours and 3000 within a day, we we could ship it and by the time it made it onsite it was ready to install. Even when still green.

    Insanely tough.

    Doesn't need to be expensive.

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  16. It would be wonderful to have bridge beams strong enough to allow a dressing coat topping that can be resurfaced on highways. Anywhere studded tires are allowed the road becomes a rutted mess in no time.
    Is it my imagination or has the material become more fragile recently?

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  17. More than proposed, it's in use. Downside is that it's not as easy to modify on site. Not like steel rebar that you can bend and weld.

    Technically you can bend the basalt fiber rebar, by heating it until the binder softens, (It's a fiber composite, not solid basalt.) but I believe it compromises the strength. Mind, it's stronger than steel rebar anyway, so maybe that's not a big deal.

    If I were building a concrete home today, I'd certainly consider using it.

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  18. For most applications it doesn't make sense to use anything beyond 3-4Kpsi concrete. It's enough cheaper than the strong stuff that you're better off just using thicker sections of the lowest grade. It's only when you're doing highly stressed pavement, or structural sections that can't, as a practical matter, be thicker, that it makes sense.

    I mean, when I built my house I shelled out for the chopped fiber additive when they poured my basement and garage floors, because I didn't want to see any cracking, but it wouldn't have made the least sense to do more than that.

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  19. The rebar needs to have an expansion coefficient that is precisely matched to the concrete so that when it freezes or heats up, the two materials don't wear against each other and cause cracks.

    I've heard that there are some experiments with a concrete formulation that is suitable for stainless. Probably sitting in an outdoor lab somewhere scheduled for another decade of real world weather exposure so we can see how it handles over time.

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  20. You must be talking about residential and small commercial construction. Tall structures and pre/post stressed girders have been using this for decades.

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  21. I've read a lot of research on UHPC lately, and one thing I soon discovered is how the construction industry in the US knows almost nothing about it.

    Hardly anyone ever uses anything more than 3,000 to 4,000 psi concrete. They don't know the word "pozzolan" and hadn't heard of Energetically Modified Cement, which is another approach to very high strength.

    There's been almost zero progress in construction in many decades. It's a bummer. Our houses are still made of extraordinarily weak materials like cheap lumber framing and particle board / OSB sheathing. Stronger concrete would be very interesting in Insulated Concrete Forms style builds. The concrete core could be thinner. The US also tends to use the weakest steel grades in the world, for rebar and studs. It would be interesting to use strong concrete and strong steel for an ICF house. The real breakthrough will be factory built homes made of strong, modern materials, transported on huge vehicles.

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  22. That is because you are seeing concrete where the designer has done at least the minimum level of calculation.

    (May not be an explicit calculation. Just following the precalculated design rules and/or copying earlier designs does the same thing.)

    So anyway they've used enough of the right concrete so that it doesn't fail right away. Instead it lasts for years… until corrosion of the rebar occurs.

    This article is addressing the earlier issue: how much concrete do we need to use to stop it falling down in the first week. Then you also have to worry about how the material will last over time.

    And there is also an interaction there: If the concrete is a bit too weak it cracks. The cracks let water in to wet the rebar. Rebar starts to rust. Concrete now under more load and cracks more. Process accelerates.

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  23. That sounds like a great practical course that keeps student's attention! Though in the age of youtube, I guess some students would be satisfied with a recap video…

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  24. flash bainite does get weaker at the welds though, so traditional rebar usage welding rods together might negate some of the advantage. Might be better for the tension rods for factory built beams though.

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  25. Stainless for rebar can't always be rust free in reality. Basalt fiber has been proposed for corrosion sensitive concrete applications though. It would be interesting to see beams made with woven basalt fiber textiles in place of traditional rebar nets, chopped fiber in the aggregate, plus prestress tension rods made with basalt fiber somehow.

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  26. You can use stainless steel. but it cost more. But in th long run your maintenance cost may be lower. There are also other materials that offer corrosion protection. Galvenized and epxoy coated Steels for example. Glass and plastic fiber can also be used.

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  27. I always wondered why we couldn't use stainless steel for the rebar so it doesn't rust.
    Now I'm wondering why we can't use flash bainite steel for super strength.

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  28. That IS the usual cause of concrete failure, that and freeze/thaw cycles in cold climates, salt damage near the sea.

    Basalt fiber rebar doesn't have that problem, but it's a little harder to pre-stress. You need to pre-tension it in the form while the concrete is still wet. Steel rebar gives you the option of post-stressing, too.

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  29. I don't know much about the subject. Where I normally see concrete failing is rusting rebar that causes spalling. Different reinforcing fibres may be a solution to that, but how can you pre stress them?

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  30. One of the more interesting courses at UC Berkeley was Materials Science 201A, B & C. Basically we got to experiment with all nature of construction and industrial bulk materials; everything from fiber composites to steels, to wickedly high performance alloys, ceramics and of course, concretes.  

    Lot of B was on concrete. The properties of the various cements, pozolites, magnesium-to-calcium ratios, the detrimental effect of sodium ions, especially salt in curing.  Aging, from fully-wet thru kind-of-moist to basically dry with seasonal rewetting (Winter rains, fogs, etc.).  

    The laboratory included a most amazing piece of 1960s testing equipment, a compressive strength press, capable of delivering up to 25,000,000 newtons of force (about 6 million pounds); cylindrically cast samples were give caps (red wax, molten sulfur and finely powdered silica) which when fresh would act like plastic, to quickly deform and spread compressive force over the caps.  Then 'lock-harden' at about 500 PSI.  

    A huge rotary dial with a fine vernier 'hand' (like the second-hand of a clock) slowly spun up to read out the pressure; all the while, a insertion-micrometer (electronic) measured off the compression amount in micrometers.  

    Eventually all 1000 samples were tested.  Then plotted. Then discussed.  

    Great stuff, University!!!

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

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