Abstract
High strength concrete (HSC) has some disadvantages such as brittleness and poor resistance to fire. Fire exposure affects the concrete in way that the disintegration of concrete starts and a severe surface spalling occurs at very high temperatures. Therefore, the structural behaviour or response to the load will change after fire exposure and the structural members may not behave as they were designed. Further, the basics of flexural design depend on the stress- strain response of the concrete which is also affected upon fire exposure. Hence, this study is carried out to provide useful input to aid the provision of a fire resistance for structural behaviour of concrete by investigating the effects on mechanical properties of concrete after exposure to high temperatures up to 600°C and establishing a stress-strain relationship. The concrete cylinders of size 100 mm x 200 mm were exposed to the temperature of 2000C, 4000C and 6000C after which the residual compressive strength, split tensile strength and flexural strength were recorded. For stress strain characteristics, 100 × 200 mm cylinders with polypropylene fiber content of 0.5% by volume of concrete were subjected to temperature exposure of 6000C for durations of 1 hour. Curves for reduction factors of strength and stress strain characteristics after fire/elevated temperature exposure has been established. Just consideration of reduced strength for assessment after fire exposure will not serve the purpose as the change in load response and increased deformation capacity also needs to be addressed properly.
Highlights
With the development of concrete technology, High strength concrete (HSC) has been commonly employed in many concrete structures around the world
Polypropylene fibers were used as HSC undergoes severe surface spalling after fire exposure and surface strain using compressometer cannot be recorded on the cracked surface
These curves can be used to have an approximate values of reduction ratios for concrete with indigenous materials
Summary
With the development of concrete technology, HSC has been commonly employed in many concrete structures around the world. Studies conducted in past (Tolentino et al, 2002) on the effect of high temperature on the residual performance of Portland cement concretes using NSC and HSC and the test specimens were cast using the coarse aggregate, river sand as the fine aggregate and sulfonated melamine super plasticizer as water reducing admixture. Polypropylene fibers were added to the concrete as HSC undergoes severe spalling sometimes even explosive blast upon exposure to high temperature. Addition of appropriate amount of polypropylene fibers will significantly improve the spalling resistance of the concrete which in turn improves the integrity of the concrete specimen so that the stress strain response can be recorded. Addition of polypropylene fibers has no effect on mechanical properties of concrete at room temperature and even after exposure to elevated temperatures (Patel et al, 2019). Dosage of the polypropylene fibers as 0.5% by volume of concrete is taken as per the previous work done and other literatures (Mydin and Soleimanzadeh, 2012; Bagherzadeh et al, 2012)
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