Fire-Damaged Normal Concrete Properties And Bond Strength Evaluation Of Ultra High Performance Fibre Reinforced Concrete As A Repair Material

It is well known that the mechanical properties of concrete structure deteriorate after exposure to fire. Repair and strengthening in order to improve the performance of the affected structure has become critical. Ultra High Performance Fibre Reinforced Concrete (UHPFRC) has been used as repair material due to its superior properties. The aim of this study is to evaluate mechanical and physical characteristic of normal concrete substrate subjected to different heating duration, to identify the most suitable substrate surface moisture condition in repairing fire-damaged concrete and to investigate the effect of substrate heating duration subjected to the bond strength and type of failure occur. Firstly, at the age of 28 days all normal concrete specimens were heated up. The temperatures are 600°C for 30, 60, 90, 120 and 150 minutes. The changes of Fire-damaged Normal Concrete (FDNC) in term of quality, mass, compressive strength and colour were examined. Several tests conducted to evaluate the properties of concrete after fires were Compressive Test, Rebound Hammer Test, Ultra-sonic Pulse Velocity Test, Initial Surface Absorption Test, Porosity and Water Absorption Test. Next, all the fire-damaged samples repaired with using UHPFRC. The substrate surface was sand blasted and moistened by three methods which are Air Dry (AD), Saturated Surface Dry (SSD) and Wet (WT). From this stage, the optimum moisture condition which gives highest bond strength was used in the next step. Then, the test to verify their bond strength namely Splitting Tensile Test, Slant Shear Test and Pull Off Test conducted. The result indicates that the substrate moisture condition influences FDNC bonding strength with UHPFRC. Based on the tests conducted, SSD condition is favourable while the substrate surface should not in dry state. With same degree of temperature, the heating durations give various degree of damaged on concrete. As the heating duration increase, normal concrete loss its compressive strength, tensile strength, stiffness and cracking occurred. The quality of concrete also reduced. Heating duration of normal concrete substrate, also affects their bonding strength with UHPFRC. These substrate damages surely give negative effects to their bonding strength with UHPFRC. Most of the failure occurs in the tests are through the FDNC substrate. The most frequent failure mode occurred was the failure at the interface with minor substrate crushing. It is indicated that the substrate strength was lower than the bond strength

Effects of heating durations on normal concrete residual properties: compressive strength and mass loss

This study investigates the effects of high temperature with five different heating durations on residual properties of 30 MPa normal concrete. Concrete cubes were being heated up to 600°C for 30, 60, 90, 120 and 150 minutes. The temperature will keep constant for 30, 60, 90, 120 and 150 minutes. The standard temperature-time curve ISO 834 is referred to. After heating the specimen were left to cool in the furnace and removed. After cooling down to ambient temperature, the residual mass and residual compressive strength were observed. The obtained result shows that, the compressive strength of concrete decrease as the heating duration increases. This heating duration influence, might affects the loss of free water present and decomposition of hydration products in concrete. As the heating duration increases, the amount of water evaporated also increases led to loss in concrete mass .Conclusively, the percentage of mass and compressive strength loss increased as the heating duration increased

Potential Use of Ultra High-Performance Fibre-Reinforced Concrete as a Repair Material for Fire-Damaged Concrete in Terms of Bond Strength

The strength of concrete structures deteriorates after exposure to fire. Strength loss varies with elevated temperature, fire duration, and the mechanical properties of concrete. Repairing and strengthening affected structures are important to improve their performances. Fire-damaged concrete has been repaired using fiber-reinforcing polymer. The superior properties of ultrahigh performance fiber-reinforced concrete (UHPFRC) make it suitable as a repair material. Furthermore, an excellent repair material should be able to bond properly with the substrate and maintain its structural integrity. The aim of this paper is to review the potential use of UHPFRRC as a repair material for fire-damaged concrete in terms of bond strength. Previous studies showed that developing efficient rehabilitation techniques that enable fire-damaged structures to be restored has some challenges.  Whether UHPFRC can be used as a repair material particularly for fire-damaged concrete structure is recommended to be proven in future studies

Evaluation of bond strength between fire-damaged normal concrete substance and ultra-high-performance fiber-reinforced concrete as a repair material

This study aims to investigate and compare the interfacial bond characteristics between fire-damaged normal concrete substrate and ultra-high-performance fiber-reinforced concrete (UHPFRC) as a repair material. Design/methodology/approach - First, fire-damaged normal concrete was prepared. Then, with a cast surface, the substrate was subjected to different surface moisture conditions. Three types of moisture conditions were set, namely, air dry, saturated surface dry (SSD) and wet. Slant shear and splitting cylinder tests were conducted to determine the interfacial bond strength of the composite. Findings - In general, results indicate that surface moisture conditions significantly influence bond strength. The substrate under SSD condition exhibited the highest bond strength. The findings suggest that UHPFRC is a promising material for the repair and reuse of fire-damaged concrete structures. Originality/value - This study compares the bond strength between fire-damaged normal concrete and UHPRC