Research On Properties Of Fiber Reinforced Lightweight Aggregate Concrete About High Temperature Performance

Building fire has a serious threat to the safety of human lives and the building structures and the research on the high temperature performance of concrete,the most widely used building materials,is significant.While light-weight aggregate concrete(LAWC)is widely used,the research on its fire resistance is just in the initial stage,and the depth and breadth of the study are not as good as ordinary concrete.In this paper,steel fiber and polypropylene fiber were used to enhance the lightweight aggregate concrete with 0%,0.3% and 0.6% content as single or compound admixture.Then heated the LAC to 200? 400?,600? and 800? with a high temperature electric furnace,respectively.The specimens were taken out after cooling in the furnace and then the mechanical properties?mass loss and other properties were studied.Fiber could effectively improve the failure form of lightweight aggregate concrete and slightly increase the compressive strength of lightweight aggregate concrete.With the temperature rise,the compressive strength continued to decline while steel fiber and steel-polypropylene hybrid fiber could still increase the compressive strength under high temperature.The concrete with hybrid fiber could still maintain a 90% growth of compressive strength under 400? which showed a better strength retention ability than that of other single fiber reinforced concrete.The polypropylene fiber was harmful to the high temperature compressive strength of the concrete.The fracture performance was studied by the three-point load notch beam method.The result suggested that the peak load of concrete at elevated temperature firstly increased and then decreased and the fiber could increase the peak load of concrete slightly.The variation law of fracture toughness was similar to the peak load while the fracture energy showed different variation rules.The reinforcing effect of 0.6% steel fiber was the most obvious while the fracture energy at normal temperature was 16 times of that at ordinary temperature,and the enhancement of fiber decreased with the increase of temperature.The change of macroscopic mechanical properties after high temperature was caused by the change of concrete structure.This paper studied the structural change of LAWC heated at elevated by combining the mass loss with other performances to reflect this structural change in multiaspect.After the treatment of 200? and 400?,the mass loss of concrete was obvious and when the temperature continued to increase,the mass loss of concrete decreased.The mass loss of PP was slightly lower than the mass loss of plain concrete,and the mass loss of SF or SP was larger.When the temperature was above 400?,the cracks appeared on the concrete surface.Between 400? and 600?,the PP had smaller crack width than other concrete and in 600? and above 600?,the SP had the smallest crack width.After the high temperature,there would be many microcracks inside the concrete,which can reflect the internal structural changes and could be detected by the ultrasonic pulse velocity.Heated in 200?,the ultrasonic pulse velocity of the specimen decreases slightly.At 400? and above,the ultrasonic pulse velocity decreased with the amplitude of 1km/s,The effect of fiber to the ultrasonic pulse velocity was not obvious.But above 400?,the ultrasonic pulse velocity of PP was lower than that of concrete without polypropylene fiber and the higher the dosage was,the lower the ultrasonic pulse velocity was.The ultrasonic pulse velocity of SF and SP was slightly higher than the PP and PC.