An Experimental Study Of High-performance Concrete On Building Fires Burning

Prompt fire suppression is needed once a building fire disaster occurs in order to extinguish the flames, stop flame spread and minimize the damage. Fire-fighting water jetting (FFWJ) is a common method for fire extinguishment, which could stop combustion through water jetting to fire, cooling and covering the comburent, diluting the oxygen by water vapor and suppressing the combustion chain reaction. Moreover, FFWJ could also prevent fire spread though decreasing the temperature and increasing the moisture of comburent. However, the FFWJ would affect the performance of the concrete, which deteriorates in the high temperature environment. The effects of water-fire-coupling may accelerate the deterioration of concrete performance, damage the structure and decrease the bearing capacity of the buildings and finally lead to partial or whole collapse. As the bearing structural system, the high-performance concrete (HPC) must have sufficient bearing capacity in a certain period of time after the fire disaster occurs in order to assure evacuation, fire-fighting and rescue.The present research studied the deterioration of the HPC, explored the mechanism of the collapse of the HPC concrete building, and proposed the collapse prediction and evaluation method in order to provide scientific basis for determining the building bearing capacity and the endurance time after fire disasters, and to provide data for the damage analysis and evaluation of the HPC and building restoration.The research contents and results of this study were as follows:1,Damage analysis of the HPC after fire disasters(1) In order to analyze the reasons for the HPC burst, the pressive strengths of HPC C35, C40 and C50 were compared with C35-A (C35 mixed with anticorrosive). The variation of external characteristics of concretes associated with fire temperature was summarized, and the relationship between the HPC bearing capacity and fire temperature was analyzed. The results indicated that the bearing capacity of HPC C35 was strongly affected by FFWJ. In the common cooling condition, the HPC bearing capacity decreased with temperature in general except for a slightly increase at 300℃; In the FFWJ condition, however, the HPC bearing capacity decreased all along with temperature. Moreover, the HPC bearing capacity in the common cooling condition was higher than that in the FFWJ condition at the same temperature. The maximum HPC bearing capacity in the common cooling condition was 1.3-fold of that in the FFWJ condition.(2) The variation of the HPC bearing capacity under high temperature was analyzed and the HPC bearing capacity under high temperature and after common cooling was compared. The results showed that the HPC bearing capacity fluctuated significantly with the temperature ranging from 300℃to 400℃, whereas the fluctuation was less marked at lower temperature. The HPC bearing capacity in high temperature process was slightly higher than that after common cooling at the same temperature.2,Damage experiment of the highway tunnel lining HPCThis experiment was conducted with HPC C50, which was widely used in highway tunnels, to explore the relationship between the bearing capacity and the fire temperature in different conditions. The results revealed that high-grade HPC showed low fire-resistant capacity despite of the high strength; in the common cooling condition, the bearing capacity of HPC C50 decreased generally with temperature except for a slightly increase at 300℃; In the FFWJ condition, however, the HPC bearing capacity decreased all along with temperature. Furthermore, the HPC bearing capacity in high temperature process was slightly higher than that after common cooling at the same temperature, while the HPC bearing capacity in the condition of common cooling was higher than that in the condition of FFWJ at the same temperature.3,The effects of the anticorrosive on the HPC fire-resistant capacityIn this experiment, the bearing capacity of HPC mixed with the anticorrosive was determined after the high temperature process, the phenomenon during the process was described, the reasons for the burst of the HPC mixed with the anticorrosive was analyzed, and the effects of the anticorrosive on the HPC bearing capacity was explored as well; Regression analysis revealed that the relationship between the bearing capacity of HPC mixed with the anticorrosive and temperature could be described by linear equation in two unknowns. Moreover, the result showed that the HPC mixed with the anticorrosive burst at 400℃, whereas the HPC without the anticorrosive did not burst during the experiment, indicating that the anticorrosive may help to increase the HPC bearing capacity, but may be adverse to the increase of HPC anti-burst capacity.4,The effects of FFWJ on the collapse of blazing buildingsBased on the fire dynamics theory and probability statistics, the building fire loads were analyzed, and the collapse probability function of given buildings due to sustained combustion and the collapse probability function of given buildings due to water-fire-coupling in the condition of FFWJ were proposed. The results indicated that the fire endurance time of the HPC decreased with the water-fire-coupling damage, and cooling by FFWJ increased the HPC collapse probability. when the HPC fire endurance time was short, FFWJ showed little effects on the building collapse; when long, the collapse probability was mainly determined by the themal load of the building during sustained combustion. It was proposed that the effects of FFWJ on the collapse of buildings should be considered when the fire endurance time was long.