## 1 Introduction  
Carbon fiber reinforced polymer (CFRP) has become in recent years one of the state-of-the-art materials in repairing and/or strengthening structural concrete elements since it has numerous advantages such as extremely high strength to weight ratio, versatility, and resistance to electrochemical corrosion [1]. However, CFRP materials are too sensitive to elevated temperatures [2]. Deterioration in mechanical and/or bond properties can be expected at temperatures approaching the glass transition temperature (\(T_{\text{g}}\)) of the organic epoxy adhesive [2], which is typically lower than 100 \({}^{\circ}\)C [3; 4; 5]. The replacement of organic epoxy adhesive with some inorganic adhesives is a promising solution. The inorganic adhesives such as magnesium oxychloride cement (MOC) and alkali activated cementitious materials [6] were used for organic epoxy adhesives replacement due to the favorable binding properties, non-toxic, low cost and excellent heat-resistance.  
Several studies have been performed on the use of alkali activated cementitious materials as a sole binding material to expand the applied range of CFRP [7; 8; 9]. [PERSON] et al. [7] reportedthat the alkali activated cementitious material increases the strength and stiffness of reinforced concrete beams as effectively as organic epoxy, with a minor reduction in ductility. [PERSON] et al. [8] presented that the increase of fatigue strength of concrete beam due to the use of alkali activated cementitious materials pasting carbon fiber sheets reaches as high as 55% when being compared with unstrengthened beams. [PERSON] et al. [9] reported that reinforced concrete beams strengthened by alkali activated cementitious materials have good fatigue performance. On the other hand, alkali activated cementitious material shows a significant shrinkage, as many studies reported [10], which could easily generate cracking between carbon fiber sheets and concrete specimen. MOC cement has many properties superior to the conventional Portland cements, including higher compressive and tensile strength, better fire resistance, lower shrinkage and creep and better durability, but the application has been limited by its poor water resistance, warping deformation, efflorescence, cracking and reinforced corrode by chloride ion [11; 12].  
Magnesia-phosphate cement (MPC) is based on the chemical reaction of acidic liquid or phosphate with a solid basic dead-burned magnesia oxide powder [13]. This cement has several advantages such as high early strength, rapid setting and hardening, excellent bonding with old Portland cement concrete [14; 15; 16; 17]. The use of this cement as a rapid patch repair material in construction field has been well studied in the past decades [14; 18; 19]. However, this material has seldom been used as an adhesive for concrete strengthening, especially in high temperature environments.  
This paper seeks to investigate the bond properties of the modified MPC between externally bonded carbon fiber sheets and concrete at elevated temperatures when being compared with epoxy resin. The compressive strength of the modified MPC does not decrease at the temperature of 600 \({}^{\circ}\)C [20]. The specimens bonded by different adhesives (epoxy resin and the modified MPC) were heated to different temperature levels of 105 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, 400 \({}^{\circ}\)C and 500 \({}^{\circ}\)C and maintained for 3 h. The bond strength and failure types of specimens after different high temperature exposures were measured.