The critical temperature for concrete is 500°C (932°F). There is also a reinforcement that must be taken into calculation, % of concrete construction etc.. Temperature exposure time is significant, short term or fire with high temperatures involved. For correct answers, all key points must be described and taken into calculation.

So many factors can affect its resistance, such as your concrete composite, reinforcement type and amount, and rate of your temperature rising. Also, initially, could you define what you mean by fire resistance? Is crack creation accepted, or do you need concrete to resist even without cracks?

you can find numerous papers related to this topic.