This study assesses the effects of elevated temperatures (100, 200, 300, 400, and 500°C) on the bonding behavior of normal concrete (NC) substrate as old concrete and the new Green Universiti Sains Malaysia Reinforced Concrete (GUSMRC) as a repair material through slant shear, pull‐off, splitting tensile, and flexural tests. Sandblasting (SB) and grinding (GR) surface treatments were employed to enhance the bond strength of the NC/GUSMRC composite. The research also evaluates the mechanical characteristics of the GUSMRC mix which 50% of its content is ultrafine palm oil fuel ash prior to and after the exposure to elevated temperatures. The results showed degradation in the mechanical properties of the monolithic GUSMRC and the bonding strength of the NC/GUSMRC composite after exposure to elevated temperatures; however, the bonding quality is excellent. Moreover, the SB surface treatment enhanced the interfacial bonding more than the GR surface treatment before and after elevated temperature exposure.

The possibility of utilizing treated coal bottom ash as a partial replacement of Portland cement was examined through compressive strength test on mortar samples. A total of 16 batches of mortar mixtures with cement:sand ratio of 1:2.5 and 1:2.75 were prepared using two types of treated coal bottom ash. The chemical compositions including the unburned carbon of coal bottom ash were also analyzed. In order to remove the excess unburned carbon which will affect the potential pozzolanic properties, the coal bottom ash was heated at 550 ± 50oC and 700 ± 50°C for 60 min in an electrical furnace.The results showed that compressive strength of mortar mixtures with cement:sand ratio of 1:2.5 and 1:2.75 containing treated coal bottom ash which was heated at 550oC results in an increase in compressive strength. At 10% and 20% of treated coal bottom ash replacement levels to Portland cement, the compressive strength of the mortar mixture was significantly improved at the age of 28 days. The compressive strength of the mortar mixtures at early ages gives lower strength as compared to the plain Portland cement mortar. However, the effect of treated coal bottom ash that was heated at 700°C is to reduce the compressive strength of the mortar mixtures except for mixture with cement:sand ratio of 1:2.5 containing 10% coal bottom ash at 56 days.

The design of the concrete mixtures of Ultra High Performances Fibre Reinforced Concrete (UHPFRC) is related to a densely compacted cementitious matrix and has outstanding material characteristics involving workability and high mechanical properties. Generally it is a combination between high strength concrete and fibres. UHPFRC offers high compressive strength which is higher than a normal concrete. The application of POFA as a cement replacement enhances the transport properties of concrete and contributes to a sustainable environment. The utilization of 50% UPOFA in mix design leads to develop a new class of concrete designated as GUSMRC. GUSMRC mixtures enhance the mechanical behaviour of concrete. GUSMRC with 50% replacement of the total binder content by ultrafine palm oil fuel ash (UPOFA) could contribute sustainability of environmental. The development of UHPFRC and its application in the field may contribute a good bonding strength at interface as a repair material between a new and old material. However, complex properties of materials can change dramatically when exposed to the elevated temperatures and adversely affected. The physical and chemical will change when occurred to heat. This paper investigates the change in mechanical properties of UHPFRC at elevated temperature and to determine the bonding strength between two layers which is overlay and concrete substrate