Experimental and analytical analysis of the bond alteration of impregnated carbon fibre reinforcements embedded in alkali-activated concrete at elevated temperatures

The restricted operating temperature range of fibre-reinforced polymer (FRP) systems for upgrading and retrofitting reinforced concrete structures is among the key limiting factors of this technology. Indeed, an alternative reinforcing system, known as Mineral-impregnated Carbon-Fibre (MCF), has recently emerged to address this issue. This paper presents an experimental investigation of the performance of MCF systems embedded in fine-grained, Alkali-Activated Concrete (AAC), which have been pre-heated at 100 °C (or 200 °C) and then tested in pull-out at the target temperature. For the purpose of assessing the bond quality against thermal exposure, results are compared with the control group (ambient temperature 20 °C), as well as with an epoxy-impregnated commercial roving. In addition, specimens are characterised at the fibre-to-matrix interface by microscopy and by physical–chemical analytical techniques. Experimental data are fitted onto a one-dimensional stress-and-friction analytical model to determine the characteristic properties of the temperature-dependent bond–slip behaviour of MCFs. Findings suggest enhanced chemical compatibility and reinforcing capabilities at elevated temperature for MCFs, primarily ascribed to the impregnation quality and to the AAC capacity to withstand thermal strain.