Study On The Bonding Performance Of High Performance Concrete Mixed With Polypropylene Fiber After High Temperature

High performance concrete,with compact internal structure,is a great possibility to burst and spall when the structure is subjected to a fire,which leads to instant loss of bearing capacity and causing the collapse of buildings.Polypropylene fiber has a significant effects on improving high temperature compressive strength performance and anti-burst performance of concrete,and is used in roads,bridges,tunnels and other projects widely.Extensive research on mechanical properties and structural components of polypropylene fiber reinforced concrete were conducted at home and abroad in the past ten years.However,there were few studies on the bonding performance between polypropylene fiber reinforced concrete and steel after high temperature.Funded by the National Natural Science Foundation(51278325),in this paper,high-performance concrete with strength C60 was designed as the research object,and the basic mechanical performance and bonding performance of concrete mixed with polypropylene fiber after high temperature were conducted.The main contents in this dissertation were presented as follows:?.Test on compressive strength of high-performance concrete.By four kinds of polypropylene fiber(volume content were 0,0.1%,0.2%,0.3%),eight kinds of temperature(room temperature and 100?-700?,temperature interval was 100?),two kinds of cooling methods(natural cooling and water cooling),the phenomenon of concrete high temperature test,appearance of specimens and compressive strength were conducted.The influence of the temperature of fire,the cooling method and the content of polypropylene fiber on the compressive strength of concrete were discussed in detail,and the content of polypropylene fiber was optimized.The results show that the compressive strength of high performance concrete gradually decreases with the increase of temperature,and the strength loss was aggravated by water cooling.0.2%of polypropylene fiber(mass content was 1.8kg/m3)was better in improving the anti-cracking performance and the compressive strength.?.Test on splitting tensile strength of high-performance concrete.Based on the compressive strength test,The splitting tensile strength was studied on unbonded and preferably blended polypropylene fiber reinforced concrete.The relationship of high temperature,cooling method and polypropylene fiber on the splitting tensile strength of concrete were discussed mainly.The results show that the splitting tensile strength decreases gradually with the increase of temperature.Water cooling aggravates the damage of concrete splitting tensile strength,and the addition of fiber could improve the splitting tensile performance.?.Test on bonding performance of high-performance concrete.The central pullout test was carried out on unbonded and preferably blended polypropylene fiber reinforced concrete bonded specimens.The test phenomena of center pullout of each set of specimens were recorded.The failure modes and high temperature bond damage mechanisms were analyzed.The influence of high temperature,polypropylene fiber,cooling method,and steel type on the ultimate bond strength and ultimate slip value were discussed mainly.Gray system theory was used to analyze the influence of various factors on bond strength.And an empirical formula between the ultimate bond strength,ultimate slip and temperature were established.The results show that the bond performance of steel-concrete decreases gradually with the increase of temperature,and the bond strength was further degraded due to water cooling.The smaller the diameter of the steel,the better the bond performance,and the addition of fiber could improve the bond performance.The strength of concrete had the greatest influence on the bonding performance of all factors.?.Relationship in bond-slip constitutive of high-performance concrete.By fitting and analyzing the bond-slip curve obtained from the center pull test,the bond-slip constitutive relationship between polypropylene fiber reinforced concrete and steel was established,and the bond-slip interface energy was obtained.The effects of temperature,addition of polypropylene fibers,and cooling modes on the interfacial energy were investigated mainly.The results show that the continuous curve model can be applied to the bond-slip constitutive relation of polypropylene fiber reinforced concrete after high temperature.