UMich has developed a new type of superstrong concrete

[kernals12]

In 2017, the University of Michigan developed a new type of Ultra High Performance Concrete. UHPC is a type of concrete that has a compressive strength of at least 17,000 psi, vs around 4,000 for regular concrete and a tensile strength of 1400 psi vs 400-700 for regular concrete. It is also exceptionally durable, withstanding frost, salt, and abrasive damage far better than regular concrete. But it's very expensive, regular concrete costs about $100 per cubic yard whereas UHPC is $2800. But the team at UMich figured out a less expensive way to make it, they say it costs 70% less. And the Michigan DOT has already used it on bridges in St Clair County. This could open up very exciting possibilities in highway engineering.

[GCrites]

Does this mean projects can use a lot less product?

[kernals12]

Does this mean projects can use a lot less product?

Yep, and that means you need fewer supports, and less labor and machinery to put it in place. And it will require less maintenance and last longer.

[kphoger]

The article you linked to is from 2018, so I decided to text my friend who designs concrete bridges for a living and see what he knows/thinks about UHPC.  He's seen it at conferences but never been involved in a project that uses it.  Here are a few nuggets from our conversation:

He expected that it would be attractive, even at a higher price point, for very heavy traffic applications–places where you really want to avoid closing traffic lanes to do maintenance.  Only over time, having seen it used in such applications would he expect the technology to trickle down into more "normal" applications.

Something he's heard within the industry:  "What they say is hard is getting the durability requirements (permeability, crack performance)."

When I asked about the possibility of using less material, he guessed so, at least up to a point.  But the followed that up with "I don't know about the tensile capacity of UHPC".

And then he summed up with this:  "I'm skeptical because if that was legit near term I'm sure we would have all heard about it".

[kernals12]

The article you linked to is from 2018, so I decided to text my friend who designs concrete bridges for a living and see what he knows/thinks about UHPC.  He's seen it at conferences but never been involved in a project that uses it.  Here are a few nuggets from our conversation:

He expected that it would be attractive, even at a higher price point, for very heavy traffic applications–places where you really want to avoid closing traffic lanes to do maintenance.  Only over time, having seen it used in such applications would he expect the technology to trickle down into more "normal" applications.

Something he's heard within the industry:  "What they say is hard is getting the durability requirements (permeability, crack performance)."

When I asked about the possibility of using less material, he guessed so, at least up to a point.  But the followed that up with "I don't know about the tensile capacity of UHPC".

And then he summed up with this:  "I'm skeptical because if that was legit near term I'm sure we would have all heard about it".

Interesting. Did he mention why it costs so much more than regular concrete?

[kphoger]

Did he mention why it costs so much more than regular concrete?

No.  But, just reading through the article you linked to in the OP, even the lower-cost UHPC produced by the UofM students has...

(1)  Sand instead of gravel as its aggregate, which makes for smaller voids but also therefore presumably more material.  I don't know how the per-cy prices compare between the type of gravel used for typical PCC and the type of sand selected for UHPC.  However, I might assume that the "carefully selected ... particle sizes of the sands" is no cheap thing.

(2)  Most of the Portland cement switched out in favor of ground slag.  Ground slag tends to run slightly more (but not a whole lot) more expensive than Portland cement.

(3)  The real kicker:  the steel fibers that are added for strength.  The article specifically states that this ingredient has "an outsize impact on the final price of UHPC" because it is a specialty product and therefore "quite expensive".  Didn't you read that?

[seicer]

Interesting tidbit on the scarcity of sand: https://99percentinvisible.org/episode/built-on-sand/

[kernals12]

Interesting tidbit on the scarcity of sand: https://99percentinvisible.org/episode/built-on-sand/

I can only think of Milton Friedman's quote: "If you put the Federal Government in charge of the Sahara desert, in 5 years there'd be a shortage of sand".

[Dirt Roads]

UHPC is certainly not the first round of advanced concrete mixtures using superplasticizers and silica flour.  In addition to reinforcement with steel fibers, these concrete formulas can also be adapted to use advanced polymers (think graphite as used in Graphine cement).  Over the past 20 years, the differences between cements, plastics and glues are beginning to blur.  But the superplasticizers used in concrete go well beyond the reinforcement of the concrete, signficantly reduce the volume of water going into the mix.  Almost all superplasticizers are made from petroleum oil.

One of the ways we have started to use advanced concrete mixtures in the transit industry is in the area of specialized precast switch ties and concrete beds beneath railroad switches and related appurtenances (such as switch machines and switch heaters).  All those thingies need special notches, nooks and crannies in the wooden ties beneath them.  These can be designed in a factory, pre-assembled in the factory (think testing the layout for fit), unassembled and then reassembled in the field.  But the best feature is that the factory can perform advanced imagery (we used to depend on ultrasounds) to verify the quality of the concrete pour and elasticity.

All that being said, the most interesting use of UHPC appears to be for precast panels for bridge decks.  The website specifically mentions waffle panels, which I'm sure is to highlight the use of airspace to dramatically reduce the volume of UHPC in each panel.  This also reduces the weight of each panel to allow them to be removed and replaced.

[kernals12]

The Michigan DOT concluded successful tests in 2018
https://www.michigan.gov/documents/mdot/SPR-1670-2019_644044_7.pdf

They got the cost down to just $900 per cubic yard and they say using inexpensive Chinese steel fibers would reduce it to $344. That's getting very close to regular concrete but since it lasts much longer and is stronger, there's probably many projects where the lifecycle costs are lower.

[kphoger]

The Michigan DOT concluded successful tests in 2018
https://www.michigan.gov/documents/mdot/SPR-1670-2019_644044_7.pdf

They got the cost down to just $900 per cubic yard and they say using inexpensive Chinese steel fibers would reduce it to $344. That's getting very close to regular concrete but since it lasts much longer and is stronger, there's probably many projects where the lifecycle costs are lower.

I've been chewing over the "permeability" comment my friend made, and that article just confirmed to me that UHPC is likely a product that would only be used for high-traffic areas.  It looks like UHPC is very, very impermeable (as one would expect due to its much smaller voids), which means it cannot hold any storm water.  I imagine such would be less desirable for lower-traffic residential roads that are prone to flooding.

Thoughts?

[kernals12]

The Michigan DOT concluded successful tests in 2018
https://www.michigan.gov/documents/mdot/SPR-1670-2019_644044_7.pdf

They got the cost down to just $900 per cubic yard and they say using inexpensive Chinese steel fibers would reduce it to $344. That's getting very close to regular concrete but since it lasts much longer and is stronger, there's probably many projects where the lifecycle costs are lower.

I've been chewing over the "permeability" comment my friend made, and that article just confirmed to me that UHPC is likely a product that would only be used for high-traffic areas.  It looks like UHPC is very, very impermeable (as one would expect due to its much smaller voids), which means it cannot hold any storm water.  I imagine such would be less desirable for lower-traffic residential roads that are prone to flooding.

Thoughts?

Wouldn't that work well for bridges and parking garages?

[kernals12]

UHPC is certainly not the first round of advanced concrete mixtures using superplasticizers and silica flour.  In addition to reinforcement with steel fibers, these concrete formulas can also be adapted to use advanced polymers (think graphite as used in Graphine cement).  Over the past 20 years, the differences between cements, plastics and glues are beginning to blur.  But the superplasticizers used in concrete go well beyond the reinforcement of the concrete, signficantly reduce the volume of water going into the mix.  Almost all superplasticizers are made from petroleum oil.

One of the ways we have started to use advanced concrete mixtures in the transit industry is in the area of specialized precast switch ties and concrete beds beneath railroad switches and related appurtenances (such as switch machines and switch heaters).  All those thingies need special notches, nooks and crannies in the wooden ties beneath them.  These can be designed in a factory, pre-assembled in the factory (think testing the layout for fit), unassembled and then reassembled in the field.  But the best feature is that the factory can perform advanced imagery (we used to depend on ultrasounds) to verify the quality of the concrete pour and elasticity.

All that being said, the most interesting use of UHPC appears to be for precast panels for bridge decks.  The website specifically mentions waffle panels, which I'm sure is to highlight the use of airspace to dramatically reduce the volume of UHPC in each panel.  This also reduces the weight of each panel to allow them to be removed and replaced.

sounds very exciting.

[kernals12]

Delaware is using UHPC in the repair of the Delaware Memorial Bridge
https://delawarebusinessnow.com/2020/09/6-2-million-project-to-test-new-form-of-concrete-paving-on-delaware-memorial-bridge/

[mgk920]

Didn't the Romans use volcanic ash in their concrete, used in things that are still standing and the some might even still be in use?

Mike

[kernals12]

Didn't the Romans use volcanic ash in their concrete, used in things that are still standing and the some might even still be in use?

Mike

The Romans also didn't have steel rebar, so they didn't have to worry about it rusting, expanding, and damaging the concrete. And thanks to their mild Mediterranean climate, they also didn't need to worry about freeze-thaw cycles.

And I suspect plenty of Roman Concrete structures have disintegrated over the years but we have no way to know about them.

[kernals12]

Here are some implications:

-More intersections can be cost effectively turned into grade separated interchanges
-SPUIs are currently held back by the need for a wide and expensive bridge structure, so they'd become more common
-More cloverleaf interchanges can be replaced with stacks
-More railroad crossings can be grade separated
-Crosswalks could get replaced by footbridges
-Buildings could be put on stilts with the ground floors used for parking
-Longer bridge spans would be possible