## 1 Introduction
In addition to this, GP concretes were found to achieve high compressive strengths within 24 h of conditioning, provided an ease of workability and controllable setting times, possessed good abrasion resistance, superior resistance to alkali environments and exhibited low shrinkage and low thermal conductivity and high corrosion resistance for the steel reinforcement elements [17; 18; 19; 20; 21]. [PERSON] et al. [22] investigated the residual compressive strength performance of 50 mm GP concrete cube specimens, having initial strengths of approximately 35 and 32 MPa, after being exposed to temperatures up to 700 \({}^{\circ}\)C. The average value over triplicate runs indicated that between 100-300 \({}^{\circ}\)C the maximum compressive strength was reached, which can be attributed to the promotion of polycondensation between chain-structures thus forming GP gels. In addition, between 300 \({}^{\circ}\)C to 700 \({}^{\circ}\)C, the residual compressive strength had deteriorated which can be assumed to occur owing to the thermal incompatibility between the paste and aggregate and also due to the fracture cracking brought about by the buildup of in situ pore pressures [22]. [PERSON] et al. [23] found that GP concrete cylinders have generally a higher conductivity than OPC concrete, owing in part to their relatively higher content of metal ions, such as, aluminum and iron. For these specimens, no spalling was found to occur and the ones with initial compressive strengths of 39-58 MPa had residual compressive strengths in the order of 83-59% at 650 \({}^{\circ}\)C, 27-29% at 800 \({}^{\circ}\)C and 16-18% at 1000 \({}^{\circ}\)C, respectively. The loss in strength was attributed to cracking and analysis by Scanning Electron Microscopy (SEM) confirmed that the GP matrix became denser at elevated temperatures, which might have provided the enhanced resistance to spalling. [PERSON] and [PERSON] [24] investigated the structural damage occurring to GP composites when exposed to elevated temperature. After exposure to 800 \({}^{\circ}\)C, GP paste gained 53% in strength, whilst the GP/aggregate composite had a strength reduction 63%. This is assumed to be due to the thermal incompatibility between GP binder and aggregate, which was subsequently proved by diametric measurements of GP and aggregate [25]. [PERSON] et al. [26] concluded that the high permeability of the GP matrix allowed the moisture to escape, which in turn reduced the buildup of pore water pressures and the tendency of spalling to occur. While GP concretes exhibit high resistance to elevated temperature levels, the high strengths achieved by RPCs cannot be generally matched. In addition to the relatively poor fire resistance of RPCs, they are also classified as materials that have a high carbon footprint, thus could result in additional adverse effects on the environment. In a study which tested the compressive strength of RPCs, where the binding material was replaced with FA and slag [27], a definite increase in the readings were reported in comparison to cement-based RPC, where all specimens achieved compressive strengths of over 200 MPa. In a similar study [28], the effects of using FA and slag as alternative materials for RPC production were investigated. At optimum proportions of the constituents of the mix design, the compressive strength reached up to 281 MPa. In a related study, it was also revealed that a combined RPC and GP concrete will contribute considerably to sustainable development, while lowering environmental impact and concomitantly providing efficient structural performance [29]. Obviously, a thorough comparative study of these two materials, especially at elevated temperature levels is highly desirable. Despite several studies were conducted on GP and RPC, research regarding the behaviour of a combination of RPC and GP under fire-related scenarios is rather limited.