Comparative study of different cement-based inorganic pastes towards the development of FRIP strengthening technology

The development of fiber-reinforced inorganic polymer (FRIP) composites for strengthening reinforced concrete (RC) structures has become an active field of research in recent years. Compared with fiber-reinforced polymer (FRP) strengthening systems, a FRIP strengthening system possesses improved fire resistance but its performance depends largely on appropriate inorganic paste selection. This paper presents a comparative study of four typical inorganic pastes, made from the following: (1) magnesium phosphate cement (MPC), (2) magnesium oxychloride cement (MOC), (3) geopolymer (GP) cement (i.e., alkali-activated slag cement), and (4) polymer-modified mortar (PMM). The aim was to investigate their performance both as a matrix and bonding adhesive for FRIP strengthening systems. The evaluated performance included the workability and mechanical properties of inorganic pastes, the bonding strength of these pastes with both a concrete substrate and dry fiber sheets, the tensile properties of the formed FRIP composites, and the flexural strength of FRIP-strengthened concrete beams. The microstructures of the four types of inorganic matrix and the fiber-to-matrix interface were also examined. The MPC-based and MOC-based inorganic pastes exhibit similar structural performance as commercially available PMM and are well-suited for the development of FRIP strengthening technology. Geopolymer seems to be the most brittle among the four studied inorganic pastes.