The Feasibility of Modified Magnesia-Phosphate Cement as a Heat Resistant Adhesive for Strengthening Concrete with Carbon Sheets

Ailian Zhang,Xiaojian Gao

doi:10.3390/app6060178

Abstract

External bonding of carbon fiber sheets has become a popular technique for strengthening concrete structures all over the world. Epoxy adhesive, which is used to bond the carbon fiber sheets and concrete, deteriorates rapidly when being exposed to high temperatures. This paper presents a high-temperature-resistant modified magnesia-phosphate cement (MPC) with the compressive strength that does not decrease at the temperature of 600 °C. The bond properties of both the modified MPC and the epoxy adhesive between externally bonded carbon fiber sheets and concrete were evaluated by using a double-shear test method after exposure to elevating temperatures from 105 °C to 500 °C. The results showed that the bond strength of the modified MPC at room temperature (RT) is much higher than that of the epoxy resin. Full carbonation with almost 0 MPa was detected for the epoxy sample after the exposure to 300 °C, while only 40% reduction of bond strength was tested for the modified MPC sample. Although the modified MPC specimens failed through interlaminar slip of fiber strips instead of complete debonding, the MPC specimens performed higher bond strength than epoxy resin at ambient temperature, and retained much higher bond strength at elevated temperatures. It could be concluded that it is feasible to strengthen concrete structural members with externally bonded carbon fiber sheets using the modified MPC instead of epoxy adhesive. Furthermore, the use of the modified MPC as the binder between carbon fiber sheets and concrete can be less expensive and an ecologically friendly alternative.

Highlights

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]
The results showed that the bond strength of the modified magnesia-phosphate cement (MPC) at room temperature (RT) is much higher than that of the epoxy resin
For the specimens failed through failure mode (a), the real bond strength specimens failed through failure mode (a), the real bond strength cannot be obtained; the cannot be obtained; the following reported bond strength for such failure specimens is following bond strength for such failure specimens is lower than the real bond strength

Summary

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]. Deterioration in mechanical and/or bond properties can be expected at temperatures approaching the glass transition temperature (Tg ) of the organic epoxy adhesive [2], which is typically lower than 100 ̋ 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]. Kurtz et al [7] reported

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Conclusion