Research On Fire Resistance Of Magnesium Phosphate Cement Concrete Frame Joint

Magnesium phosphate cement concrete has virtues such as early strength, good durability, good application prospect in quick repairing. Research on fire resistance performance of full-scale magnesium phosphate cement concrete frame joint is carried out under standard fire(ISO834) and dead load in this paper. Temperature distribution, deformation regulation, fire resistance and failure character of magnesium phosphate cement concrete frame joint are analyzed, which is compared with properties of reinforced concrete frame joint. The preliminary achievements are summarized as follows:1,Temperature distribution, fire resistance of magnesium phosphate cement concrete frame joint are the same as the equal strength reinforced concrete frame joint's under standard fire(ISO834) and dead load.2,Compared with reinforced concrete frame joint, concrete cover of magnesium phosphate cement concrete frame joint explodes seriously. Most of concrete cover flake off, stirrups and partial longitudinal bars appear when joint reaches fire resistance.3,The end of joint beam reaches fire resistance when it comes up to fire resistance standard under the experiment condition. Failure of beam originates with failure of beam end plastic hinge. Deflection of beam end increase rapidly when joint reaches fire resistance. Major deformation originates from plastic hinge rotation of inside beam (beam end of outside core area). Plastic hinge rotates rapidly and deformation accelerates. Joint lost its bearing capacity at short notice, and is destroyed suddenly. The experiment results indicate that plastic hinge is not on the edge of joint core where the value of moment is max. Main vertical crack of beam bottom (tensile region) and core boundary have a certain distance. Based on measured temperature distribution, there is temperature reduction from beam end near joint core to joint core, which is reason for plastic hinge movement. Remain plastic hinge deformation of joint beam is obvious after elevated temperature test.