Yes, concrete can melt, although at very high temperatures.
Scientists cannot conclusively give the exact melting point of concrete. The figure varies based on the concrete’s components.
The melting point of concrete lies between 1500ºC and 1650 ºC. Sand melts at 1550ºC, while cement melts at 1650 ºC, factoring in other elements in the process.
In such temperatures, there is cracking and high steaming. Water molecules in the concrete transition into steam at a high rate.
Properties of Concrete and How they React When Exposed to Heat
Scientifically, melting point is the temperature figure where the solid material disintegrates into liquid.
The particles in the material absorb heat from the neighbouring particles, breaking down the compactness that holds it together.
The heat disrupts the structure of the solid material pushing the particles away from each other.
As the distance between the particles becomes wider, it enables them to move freely, which is when concrete becomes liquid.
Since the particles making up concrete are naturally compact, it requires lots of heat to disintegrate, which explains why the melting temperatures are higher.
However, the process is microscopic. You cannot see it with naked eyes.
Chemical Changes of Concrete when Melting
The high temperatures needed to melt concrete makes the whole process complex.
Complexity emanates from the different melting points of individual elements in the concrete.
Secondly, concrete melting is reversible when the temperature subsides.
However, it might not revert to the original format as the high temperatures distort the original chemical and physical form.
Typically, water boils at 100ºC, but in concrete, the figure reaches up to 140ºC due to impurities.
Also, the compact pressure when making concrete contributes to this high boiling point.
As water changes to gas, pressure builds up, which might exceed the needed concrete limit. It results in concrete cracking, which weakens the concrete compactness, speeding up the disintegration process.
More pressure starts piling as the concrete’s calcium hydroxide turns into liquid.
At 400ºC, the pressure exerted after calcium hydroxide disintegration weakens the concrete’s structural bonds.
At 575ºC, the compactness further weakens, especially in quartz-based aggregates.
The temperature disintegrates the concrete elements, expanding the volume occupied by the concrete material.
As the temperature approaches 800ºC, any limestone product dehydrates and decomposes. Compared to other elements in concrete, the process is irreversible.
When the temperature exceeds 1000ºC, every structural bond in the remaining concrete elements is at its weakest.
Cement paste breaks down, which is the last straw to concrete compactness.
Important Pointers in Concrete Melting
- 65ºC, the first bonds in the concrete begin disintegrating, depending on the concrete reinforcement. In highly reinforced concrete, the process starts at 93ºC.
- Concrete melting officially begins at 600ºC. This is the temperature where cracking begins, leading to an explosion due to high pressure.
- As concrete absorbs and produces heat as the chemical reactions
- take place. The first reaction is between cement and water, a chemical process known as hydration.
Important Terminologies in Concrete Melting
Spalling
It is the disintegrating of the concrete mixture due to extreme temperatures. Spalling is in 4 parts:-
- Aggregate spalling – produces pop-sound since the intensity is still low
- Corner spalling – intensive pop sounds as the heat intensity increases.
- Surface spalling – disintegration is more vigorous, and the pop sound intensifies further.
- Explosive spalling – the peak of breakdown, characterised by damaging structural concrete properties.
Thermal Cracking
It is the sound produced as the spalling occurs, caused by the vaporisation of moisture available in the concrete.
The openings created allow the heat to penetrate the reinforcement, producing cracks in the concrete.
Fire Resistance in Concrete
Although concrete can melt, the temperatures are too high and costly. In typical scenarios, achieving the desired temperature to melt concrete is complex, making it a good construction material.
The compactness of its properties can withstand any heat, which makes concrete fire resistant. Fire resistance is the ability of materials to withstand extreme temperatures.
Combining all the elements and structural strength in concrete, a normal fire cannot melt concrete.
So, Does Concrete Melt?
Yes, concrete can melt only when exposed to temperatures above 1500ºC.
Individual components melt at different temperatures.
Impurities caused by mixing chemical elements in concrete raise the boiling and melting point. For example, water normally boils at 100ºC, but the water in concrete boils at 140ºC.
Pressure begins mounting at 400ºC when all the moisture in the concrete evaporates. It is heightened when calcium peroxide disintegrates.
Past 800ºC, all limestone products disintegrates, while temperatures above 1000ºC increasingly make concrete properties lose.
Depending on the concrete properties, any temperature above 1500ºC causes it to melt. However, it can go up to 1650ºC.
However, achieving these temperatures in ordinary discourse is hard, making concrete fire resistant.
