Influence of Heating–Cooling Regime on the Engineering Properties of Structural Concrete Subjected to Elevated Temperature

Structural concrete has become a highly preferable building material in the construction industry due to its versatile characteristics, such as workability, strength, and durability. When concrete structures are exposed to fire, the mechanical properties of concrete degrade significantly. The research on the residual mechanical properties of concrete after exposure is necessary, particularly for the repair and rehabilitation of concrete elements and for the stability of the infrastructure. Factors, such as the grade of concrete, the effect of temperature exposure, and rapid water cooling, affect the residual strength characteristics of concrete. Considering these factors, the present investigation evaluates the mechanical properties of concrete using different grades, such as those ranging from 20 to 50 MPa, with an increment of 10 MPa. The specimens were exposed to different durations of fire from 15 to 240 min, following the standard rate of heating. A loss of strength was observed after fire exposure for all the grades of concrete. The rate of reduction in tensile and flexural strengths of the concrete was greater than that of compressive strength. The experimental results also showed that the strength reduction is greater for M50 than m²0 concrete concerning the duration of heating. A microstructure evaluation confirmed the extent of damage to concrete under varied temperature conditions.

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