Study on the potential of repair fire-damaged reinforced concrete beams using ultra high performance concrete with curing at ambient temperature

Abstract

Fire-damaged reinforced concrete structure requires repair work to improve its serviceability and prevent structural failure. The intense fire exposure on the structure deteriorates its strength and durability. Fire-damaged concrete structure was normally repaired using the shotcrete and normal strength concrete as practised previously. In experimental work, usage of fibre reinforced polymer (FRP) as repair material to retrofit or wrap around the fire-damaged concrete indicates improve strength but has lower effect on stiffness. This study used Ultra High Performance Concrete (UHPC) as repair material. UHPC composed of fine size aggregate, cement, silica fume and superplasticizer. Another composition of UHPC that also includes steel fibre is considered as ultra high performance fibre reinforced concrete (UHPFRC). This material has an excellent mechanical properties compared to high strength concrete and steel fibre in the UHPFRC enhances its ductility behaviour. Contrary to normal practise of curing regime for UHPC, this research adopted ambient temperature curing instead of high temperature curing. This is to ease the application of UHPC on site. The aim of this research is to repair fire-damaged reinforced beam concrete with 2 types of material which is UHPC and UHPFRC. UHPC which does not incorporate steel fibre in the mix was laid on compressive face of fire-damaged beam sample. UHPC is considered as economical compared to UHPFRC and aimed to repair fire-damaged beam as additional layer of compression. UHPFRC has steel fibre in the mix and is placed on tensile face of fire-damaged beam. UHPFRC is aimed to repair the fire-damaged sample as additional tensile layer of composite structure. Assessment is made based on flexural strength, peak load capacity, toughness and elastic stiffness to evaluate the suitability of UHPC as repair material. Repair of 400°C fire-damaged samples using UHPC fully regained its original peak load capacity and toughness. Repair of 400°C fire-damaged samples using UHPFRC fully regained its original flexural strength, peak load capacity and toughness. Repair of 600°C fire-damaged samples using UHPC and UHPFRC failed to fully rehabilitate its peak load capacity, flexural strength, elastic stiffness and toughness. In conclusion, UHPC of 20mm thickness is not viable as repair material for fire-damaged concrete.