| 1.IntroductionConcrete structure is one of the most extensive structures in use nowadays. In recent years, the repair, reinforcement and remake of concrete structures have become a new and expanding subject branch. The crux of the reinforcement of the concrete structure is the bond behavior of the cohering face of the new-old concrete. The bond behavior of the cohering face under normal atmospheric temperature has been studied deeply and has more conclusions. What will happen about the bond behavior of the cohering face of the new-old concrete after high temperature (e.g. fire) for reinforcing building, moreover, what will happen about the bond behavior of the cohering face for the building under high temperature frequently such as metallurgy and chemical shop which are radiated under high temperature (200-300), chimney wall(100-150)?These are not clear and definite. So it is necessary to study this question through experiments. 2.Study of this PaperIn recent years, a vast amount of experimental researches and theoretical analysis of the concrete property under high temperature have been made, but this aims at concrete itself. The study aimed at the cohering face of concrete after high temperature is little. Only did the Da lianuniversity of science and engineering carried out the study of the bond property of the new-old concrete after 200 in 1999.In this paper, we use the basic mechanical index-splitting tensile strength to judge the mechanical property of the cohering face of the new-old concrete.Through experiments and theoretical analysis, we check the splittingtensile strength of the cohering face of the new-old concrete after hightemperature(200-900), and clarify the relation between temperatureand splitting tensile strength of the cohering face. This has guiding meaning for the reinforcing project to prevent high temperature. The main content is: splitting tensile experiments were carried out about the standardized cube bonding specimens (150X 150X 150mm3)of the new-old concrete after high temperature .The temperature is divided into 9 groups from normal atmospheric temperature to 900, the cooling styles are natural cooling and spraying water cooling; Different interfacial treating methods: brushed with steel-wire brush, man-made chiseling (not evenly),man-made chiseling(quite evenly);different interfacial agents: no interfacial agent, neat cement paste, cement paste mixed with 10% expanding agent. At the same time, the new whole cubic concrete compared specimens are poured for 5 groups 15 piecesWe emphatically investigate the influence laws of splitting tensile strength of the cohering face of new-old concrete after different high temperatures, cooling style, roughness and interfacial agent, and further expound the descending mechanism of the bonding strength after high temperature.S.Experiment (1)SampIeWe adopt a butch of concrete beams which were poured in 1999,3as the old concrete of this test. This butch of beams use 525# common Portland cement, the water-cement ratio is 0.53,the design strength is C35.lt is cut apart to 150X 150X 150mm3 cube with cutter. Its compressive strength is 41.2Mpa.The design strength of the new concrete is C40,which adopts 525# common Portland cement, the sand is middle wide river-sand, the radius of coarse aggregate is 10-30mm.The surfaces of the old concrete which are harnessed are divided into I , II, III three type faces. (2) Interfacial AgentsThis experiment adopts three types of interfacial agents: no interfacial agent, neat cement paste which has the same water-cement ratio with the new concrete, cement paste mixed with 10%expanding agent which has the same ratio with the new concrete(which is called cement paste mixed with expanding agent for short).The thickness of the interfacial agent is 2~3mm. (3)Experimental PhenomenaFrom the experiment we observed that all wrecks of the bonding samples break at the interface, the broken faces are flat, but the concrete conditions have sth. to do with the suffered temperatures. |
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