The Fire Damadge Of High Strength Concrete And Its Comprehensive Evaluation

The properties of construction materials are deteriorated after the fire, and the structures are weakened which leads to structural damage and descendent bearing capacity to some extent. It's a urgent problem to scientifically evaluate the bearing capacity of the concrete construction after fire in order to adopt the most proper repair and reinforcement as soon as possible. High strength concrete is having a further development and a broad application in the world while it has been at a high position and playing an important part in both fields of construction materials and materials engineering. However, it's avoidless that high strength concrete (HSC in short) does not perform as well as conventional concrete especially after fire. Therefore, it's necessary to adopt the proper repair and reinforcement based on a study of the attenuating laws of the properties of HSC after fire and an inspection of the damage and the residue bearing capacity in a scientific way to postpone the collapse and diminish the loss.It's suggested a comprehensive evaluation of concrete damage after fire according to the study of the performance of HSC after fire, which provides a scientific foundation to inspect the structural damage after fire and adopt the most proper repair and reinforcement.The general research content and achievements are outlined as follows.1. Strength variation of HSC after fireIt studies the effect of temperature system, strength grade, water content, mineral addition, aggregation, polypropylene fiber and sample size on the compressive strength of HSC after fire with an introduction of simulative fire experiments. It also works out the variation laws of flexural strength and splitting strength of HSC after fire. Besides them, it investigates the differences of ultrasonic propagation rates in HSC before and after fire and drew out the relationships between relative compressive strength and temperature, between relative ultrasonic propagation rate and temperature and between relative ultrasonic propagation rate and relative compressive strength, respectively referring to equation2.1, equation2.4 and equation2.14. These relations have important application value to the local detection of concrete after fire.2. Permeability of HSC with cracks after fire water permeability coefficient, chloridion permeability coefficient and air permeability coefficientIt takes the lead in studying the permeability variation laws of HSC after fire comprehensively and thoroughly in domestic and abroad. It discusses chloridion permeability coefficient, water permeability coefficient and air permeability coefficient, water absorbing percent, weight loss and carbonization respectively. It also studied the effect of temperature system, strength grades, aggregation, mineral addition and polypropylene fibers on permeability of HSC after fire. It presents a specific laboratory research process and a mechanism analysis of the improvement of permeability of HSC by the way of recurring after fire. And it figures out the relationships between the chloridion permeability coefficient, water permeability coefficient and air permeability coefficient. The results show that the deterioration of resist-permeability of HSC is more serious than that of NSC, and PP fiber may restrain spalling, while the resist-permeability loss is very grave.3. A mathematical model under the interaction of humidity and heat of HSC with spalling after fireIt investigates the phenomena of humidity and heat transformation inside the concrete whilethe vapor migration was under the interaction between pore pressure field and temperature field since the variation of temperature inside concrete led to vapor migration and vapor migration led to pore pressure. It indicates the pore pressure was significantly affected by the permeability coefficient and the diffusion coefficient. It discusses the process of formation and movement of the analogous saturated surface. It presents a mathematical model in the paper in accordance with the physical model of spalling mechanism brought forward by the author after the study of other correlated spalling mechanism. The mathematical model is testified a correct one by the resolution value from the mathematical model according well with the experimental data basically. It calculates the temperature field and air pressure field inside concrete under the given temperature system and validated the computing result.4. A comprehensive evaluation of the damage of HSC after fireA comprehensive evaluation of concrete damage after fire suggested in the paper using the theory of fuzzy mathematics is supposed to give HSC after fire a appropriate evaluation, which is considering the appearance loss, compressive strength loss and permeability loss as well.To reference to evaluation methods of environmental analysis, the procedure of the comprehensive evaluation of concrete damage after fire suggested in the paper is described as follows: firstly, evaluate a monomial factor, then, confirm the weighting of evaluating factor, finally, do a comprehensive calculation. It's proved the comprehensive evaluation mathematic model is accurate, scientific and easy for application. A program of the comprehensive evaluation of concrete damage after fire is developed in the computing language of C++. An example was loaded in the program, run on well and was identical with the calculated value. It is innovatory that putting forward resist-permeability as an important target for evaluating damage of HSC after fire.