Materials

Scientists create quality concrete with 100% tire-rubber aggregate

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Particles of ground-up tires are mixed into the wet concrete
Mohammad Islam, RMIT
Three samples of the cured concrete, which meets building codes and is lighter than concrete containing a traditional aggregate
Mohammad Islam, RMIT
Particles of ground-up tires are mixed into the wet concrete
Mohammad Islam, RMIT

In recent years, we've heard about efforts to replace some of the aggregate used in concrete with crumbled used tires. Now, however, scientists have succeeded in producing good quality concrete in which all of the aggregate has been replaced with tire particles.

Concrete consists of three parts: water, a cement which binds everything together, and an aggregate such as sand or gravel. That aggregate has to be mined from the ground, and is actually now in short supply in many parts of the world.

Discarded tires can be recycled to a certain extent, but often just end up sitting in landfills or getting burned.

Several groups have tried to address the one problem with the other, by substituting ground-up tires for a portion of the sand or gravel. The resulting concrete has tended to be tougher than regular concrete, as the rubber particles within it have allowed it to bend under pressure instead of breaking.

Unfortunately, though, if too much of the aggregate is replaced with tire particles, the concrete lacks compressive strength and splitting tensile strength. This is at least partially because that the cement doesn't bond well with the pieces of rubber, so they're not held together firmly enough.

Building on research conducted by their colleagues, scientists at Australia's RMIT University determined that the bonding problem is due to the porosity of the tire rubber. More precisely, pores in the rubber fill with water when the concrete is initially mixed, but those pores simply become empty voids at the rubber/cement interface once the water evaporates and the concrete sets.

In order to address that problem, the researchers started with wet concrete in which all the aggregate consisted of tire particles, then placed that concrete in special steel molds as it was setting. These molds placed pressure on the concrete, compressing the particles and the pores within them.

As a result, once the concrete had dried and set, the cement was much better bonded to the "preloaded" tire particles. When compared to 100% tire-aggregate concrete produced by conventional means, the preloaded concrete exhibited 97%, 59% and 20% increases in compressive, flexural and tensile strength, respectively.

Three samples of the cured concrete, which meets building codes and is lighter than concrete containing a traditional aggregate
Mohammad Islam, RMIT

The scientists are now looking into ways of reinforcing the new concrete, thus making it even better suited to use in construction projects.

"As a major portion of typical concrete is coarse aggregate, replacing all of this with used tire rubber can significantly reduce the consumption of natural resources and also address the major environmental challenge of what to do with used tires," said study co-author and team leader, Prof. Jie Li.

A paper on the research was recently published in the journal Resources, Conservation & Recycling.

Source: RMIT University

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16 comments
TechGazer
Might cycling of the pressure work enough cement/microaggregate particles into the pores to lock them in, avoiding the need to keep continuous pressure on the mix?
paul314
This would be difficult for a lot of the concrete that's poured in place, but there are also lots of precast (and prestressed) pieces used in construction.
christopher
"Shortage of rock" sounds unlikely. More like someone is manufacturing not-entirely-honest excuses for why they should be allowed to play with tyre recycling ideas.

Case in point - detailed reports "97%, 59% and 20% increases in compressive, flexural and tensile strength when compared to 100% tire-aggregate concrete produced by conventional means" ... but zero mention of any of that when compared to conventional concrete.

When important numbers are missing, it's usually never a mistake - but is always an excellent clue that you should disregard using the product in question and company making it entirely - it's both not practically useful, and is being marketed by dishonest people. You also usually don't know what *other* inconvenient specifications they also chose to omit.
CAVUMark
What about drawing the air out with a vacuum? Works great with epoxies. Will need to scale up but that is feasible.
Miro
If these people are real researchers, they will know that this idea was invented 1000 times and decades before them from others.
And to call the artificial mixture in types rubber is not serious.
PoppyAnn
How about mixing the tyre fragments with cement dust whilst under vacuum to get the holes filled with cement to prevent them filling with water.
One other thing who ever wrote this article does not know how to make concrete, it is made using 4 items,
1. aggregate
2. sand
3. cement
4. Water
Using just cement
and aggregate or cement and sand would not be very good, just cement and sand would be very weak, and using aggregate and cement would be very expensive what you need is a balance between the two somthing that has enough strength plus is not to expensive so a combination of the three would be best.
martinwinlow
CAVUMark - That won't work because the 'air' would not be accessible at the time it needs to be - ie the concrete would have gone off already making 'air' extraction impossible (quotes because I doubt it is actually air that is filling the voids at this point - indeed this rather good description of the chemical process of curing concrete (http://matse1.matse.illinois.edu/concrete/prin.html) suggests no air but silicate hydrate and calcium hydroxide.

What *might* help would be to coat the rubber particles in something that makes them non-porous perhaps some of your resin or latex - the latter is used often in concrete to make it water resistant if not waterproof.
SteveMc
@christopher Wow! I assume your day job isn't as a morale guru? That's an extremely cynical outlook on life buddy, you need to chill. Calling scientists at a university "dishonest" on the basis of this article is strong to say the least. There is no shortage of rock, as such, you are correct. However filling holes in the ground with billions of used tyres (yes, the correct spelling :p), poisoning the water tables around the globe with leachate from tyre landfill, or burning them and creating highly toxic gases and particulates is a thousand times worse. Yet you don't balance your argument with those facts... you don't own or sharehold in quarries do you? ;)
RJB
Now we just have to replace the highly polluting and energy hungry production of cement.
Aross
Not to totally Poo poo the idea, but I am curious about how we will recycle the cement made with the rubber from tyres when it has reached the end of its life expectancy? Also, how will it stand up to high heat (global warming) and cold arctic temperatures?