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Heading: 1.1.2.1.1.4high temperature resistant concrete
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How can we make concrete resistant to very high temperatures (hundreds of degrees) ? Can addition of nano particles help in this case?


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deepika goparaju


Certainly you could use high aluminous cement concrete with a variety of different aggregate types. With respect to increasing the working temperatures and extending the service life of portland cement concrete, there has been some work published on the positive results of vacumn dewatering the freshly placed concrete. I would suspect that the addition of nano particles would also help in this case, but have no specific knowledge of their application here.
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James Mross


sir,

can the use of thermal barrier coatings(yttria-stabilized zirconia ) on aggregates be useful to make the concrete resistant to high temperatures? Can these coatings bond with cement properly?
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deepika goparaju


Clever idea Deepika! It might well be worth the trials. While I don’t have any expereience with yttria-stabilized zirconia or any other coating on the aggregate for that matter, it might have potential and could offer very interesting results. Obviously there would not be any chemical bond between paste and the coated aggregate, but in refactory applications, that wouldn’t be an issue anyway. Your interest would be in the ceramic and mechanical bond. Acting as a thermal barrier for the aggregate could help. Have you considered using crushed and sized high-alumina ingots as the aggregate? That would preclude or reduce much of the differential thermal movement between aggregate and paste.
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James Mross


What temperatures exactly? And how much repetition of thermal shock? Our admixture has been proven to make concrete highly heat resistant/survivable. One test I've participated in took identical mix design cubes into a high temp oven. The untreated concrete destructed at just over 200 degrees celsius and the treated concrete cube survived at the oven's maximum of 460 degrees celsius. Is that sufficient?
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George Clark


The fastest way to make concrete fire resistant is to make it inherently dry, free of moisture.

This is a fascinating topic. What is the 'high' temperature you refer to? The Kings Cross underground fires reached over 600 deg C. Lower than the point at which concrete starts to melt

The cause of destruction of concrete in very high temperature fires is the cause of the other 10 mechanisms of destruction of reinforced concrete. Water. In a fire of over 100deg C, moisture that is normally trapped within all normal concrete rapidly turns to super heated steam, the expansion spalls off cover concrete with it's relatively low tensile strength, exposing deeper concete to the same explosive destruction.

The less moisture trapped in the concrete, the lower the internal explosive expansion, the less destruction, the longer the protection to internal steel reinforcing.

In a large fire in Bangkok, a podium shopping centre was destroyed and required substantial repair to the inner floors and columns. But the podium roof deck itself, which used a hydrophobic (HPI type) admixture to the structural concrete to eliminate 'waterproofing', was unscathed with only one crack caused by building movement during the fire, requiring simple filling to reinstate waterproof integrity of the podium roof.

There was insufficient water/moisture in the podium roof deck to allow for explosive destructive spalling.

The addition of plastic fibres to the concrete mix, which melt and provide exit pathways for superheated steam, also seem to have a protective effect for fire exposed concretes.






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Michael Aldred
 
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