We are testing the durability characteristics of novel design mix concrete. For durability characteristics of concrete at elevated temperature is our next target.
We have gone through the past literature review but did not get a clear answer to two fundamental questions.
1. What would be the upper range of maximum exposure temperature?
2. How to decide the internal between two range of temperature, i.e., 100, 200, 300……..1000
0r 200, 400, 600, 1000
Some studies show that the concrete behavior starts to change after 400°C, some disclosed after 300°C…
I need your valuable discussion on this topic before start the work.
Thanks
The compressive strength of concrete decreases at higher temperatures. At high temperatures, more than 250 to 300 0 C moisture present in the concrete creates tensile stresses and spalling of the concrete takes place. Though research works are done on concrete at different temperatures, as per my opinion, the maximum temperature of concrete to be considered for testing depends upon
1. exposure to a fire condition, duration, and temperature
2. Purpose of the testing of concrete at high temperature
3 factors like whether RCC or plain concrete
4 Objectives of the research and facilities available for testing.
Range of the temperature depends up on type of concrete wether it is plane or RCC. It also depends upon whether it is high strength concrete or some spacial type of concrete such as Self compacting, Geo-polymer, fiber reinforcement etc and other parameters like exposure condition and time of curing.
The reductions in compressive strength of concrete, when exposed to elevated temperatures, can be attributed to the dehydration of concrete by driving out of free water, interlayer water and chemically combined water. The loss of physically bound water significantly affects the mechanical properties of the concrete exposed to elevated temperatures.
If we use silica fume or other pozolanic material like alcofine then temperature range will be high.
As you asked that behaviour of concrete changes in some literature at 300 and in other 400. The reason behind this is type of concrete and which type of pozolanic material used.
I think the temperature range up to 800 C is sufficient and gives the almost all desired results.
Lastly interval of the temperature depends up on your requirements , if you take small intervals then you get more accuracy in results. So, I will suggest you to take the interval of 100 C for better results.
It depends on the requirement of your work, Materials use for concrete production, grade of concrete, PCC or RCC etc.
Normally testing the concrete at elevated temperature needs to be simulate with actual fire exposure and effect required for that condition and at the same time how you use the methodology to applied that temperature.
Thank you, Dr. Bhavin G. Buddhdev for your clear explanation; we are testing the newly design mix PCC to know the actual behavior of concrete under durability characterizes; AS you know, once we replace any waste materials with the natural, we have to go for full-scale durability analysis. Only strength characteristic is not enough to understand the long-term behavior of concrete. My question on which basis we will decide the temperature internal and maximum limit.
Thank you Dr. Shashikant Kumar for your clear explanation; we are testing the newly design mix PCC to know the actual behavior of concrete under durability characterizes; AS you know, once we replace any waste materials with the natural, we have to go for full-scale durability analysis. Only strength characteristic is not enough to understand the long-term behavior of concrete. My question on which basis we will decide the temperature internal and maximum limit. You have already explained in detail a valuable discussion. Sure it would be helpful for us. If you know, please recommend the actual code or any ASTM standard for the same,,
Thank you very much for your time
These are the some standard codes for concrete exposed at elevated temperature
ACI 216R-89: Guide for Determining the Fire Endurance of Concrete Elements (Reapproved 2001)
EN 1992, Eurocode 2: Design of concrete structures - Part 1-2: General rules - Structural fire design
ACI SP 25: Temperature and Concrete
Thank you Dr. Ishwar Sonar for nice discussion on the topic
I think this range between 300 to 400 is to be chosen depending upon local factors like the ambient temperature at the location, environmental factors like aggressive environment if any, the temperature of the water during concrete mixing, factors affecting the heat of hydration in short term and long term hydration process.
Portland cement concrete cannot withstand exposure to 1500°F without undergoing severe strength loss and cracking because the hardened paste dehydrates at such high temperatures. Concrete made with high alumina cement and refractory aggregates might be able to withstand such exposure conditions. https://www.concreteconstruction.net/how-to/spalling-of-concrete-at-high-temperatures_o
The threshold of significant degradation of concrete is around 65-93°C (150-200°F). For this reason, current codes and industry standards dealing with reinforced concrete structures specify a maximum temperature limit of about 65-93°C (15O-2OO°F) to ensure predictable concrete behavior. https://inis.iaea.org/collection/NCLCollectionStore/_Public/28/057/28057515.pdf
Past 100 degrees centigrade the cement in concrete dehydrates and loses strength.
You can see this study by HIDAWI, they say at 400oc concrete cracks.
https://www.hindawi.com/journals/amse/2019/5753232/
The maximum temperature depends on the type and the qualities of materials used to design the concrete. Nonetheless, see attached a model that can be used to predict the temperature in concrete.
Thank you Dr. Sir Armand Augustin Fondjo for sharing the document
Dear Mohammad Nadeem Akhtar ,
The threshold of significant degradation of concrete is around 65-93°C (150-200°F). For this reason, current codes and industry standards dealing with reinforced concrete structures specify a maximum temperature limit of about 65-93°C (15O-2OO°F) to ensure predictable concrete behavior
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