The Influence Of Cooling System On Deterioration Of Concrete And Fiber Concrete After High Temperature

Fire is one of the major disasters which threaten the safety of human life and property seriously.After the fire,the building needs to be stable and safe enough to ensure the evacuation of personnel,the transfer of property and the safety of fire rescue personnel.When fire extinguishing and rescue is carried out,the concrete buildings after high temperature are subjected to the impact damage,temperature stress damage and cold water damage due to the action of water.These may lead to structural instability or loss of safety,and produce fatal secondary disasters.Moreover,the water spraying pressure,the water spraying time,the duration of the fire and the static time after the fire will have a certain impact on the concrete buildings.Therefore,it is very important to study the effect of cooling system on the deterioration of concrete and fiber concrete.In this paper,PVA fiber reinforced concrete,steel fiber reinforced concrete,PVA-steel fiber concrete and concrete with the different water-binder ratio were prepared.Then,all concrete specimens were subjected to the high temperature treatment at 200?,400?,600? and 800?.The effects of different cooling systems,such as natural cooling,water spray cooling,water jet pressure and water jet time on performance deterioration of concrete and fiber concrete after high temperature are studied.And the effects of fire duration and post fire static time on the performance of concrete and fiber concrete after high temperature were simulated.Meanwhile,the mechanical properties,mass loss and dynamic elastic moduli of concrete and fiber reinforced concrete after high temperature are explored.With the increase of temperature,the mass loss rate of concrete and fiber reinforced concrete increases gradually,while the compressive strength increases first and then decreases.In contrast,the splitting tensile strength and the dynamic elastic modulus show a declining trend.When the heating temperature is less than 400?,and heating time is short,the microcrack is produced inside the concrete.The internal compactness leads to the decrease of the dynamic modulus of elasticity.In the mechanical test,the splitting tensile test is more sensitive to the microcrack and the splitting tensile strength has been reduced because of the different stress forms.In the test,microcrack will be compacted and the strength will increase when cracks are few.The addition of PVA and steel fiber can improve the internal physical environment of concrete and improve the dynamic modulus of elasticity.The mechanical properties of steel fiber reinforced concrete and PVA-steel fiber reinforced concrete are better than those of PVA fiber concrete and reference concrete under different temperatures.The deterioration of concrete and fiber concrete under the water spray cooling is more serious than the natural cooling due to the impact force,temperature stress and cold water.After high temperature,the deterioration of various types of concrete is worse with the increase of water spray pressure,water spray time and constant temperature time(fire duration),and the higher the temperature,the worse the deterioration.Spraying the concrete after high temperature,it is found that the mechanical performance of concrete decreases and then increases with the increase of static time.Meanwhile,the lowest point appears in 28d,with the heating temperature of concrete is more than 400 ?.