Study On Neutralization Depth Of The Concrete After Fire

In the detection and identification of concrete structures after fire,the damage assessment of concrete is an important part of the field testing,and the concrete neutralization depth test method is one of the commonly used technical methods for the evaluation of concrete damage after fire.However,it is found that the concrete strength value of the rebound method in the current neutralization depth method is relatively large in comparison with the strength result of the core method.Therefore,the effect of cooling method and concrete type on the results of neutralization depth test method is studied,which provides more theoretical basis for the proper application of neutralization method in concrete engineering.In the paper,the composite silicate cement concrete and slag Portland cement concrete were subjected to high temperature simulation test,compressive strength test,neutralization depth test and XRD microscopic analysis.The color change and shape effects of different types of concrete under different heating temperature and time and strength change under different cooling methods were studied.The differences of the results of the neutralization test of the concrete under different cooling modes after the fire were analyzed,and the damage mechanism of the high temperature to the concrete is clarified from the microscopic point of view.In this paper,the unreasonable results of the neutralization test of concrete after cold water cooling were analyzed through the analysis of the detection and identification of the scientific and technological building in a geological survey center.Through the above analysis and research,the main conclusions are as follows:(1)After changing the temperature of the two kinds of concrete,the change of the color of the concrete surface after the high temperature is basically the same as that of the heating condition.The color of the concrete changes from red to pink to gray as the temperature rises.The change in the color of the concrete is closely related to the heating temperature,but not to the heating time.(2)Strength tests have shown that cold water cooling and natural cooling have different effects on the strength of concrete under different temperatures.In the 500 ?? 700 ? high temperature environment,directly with cold water cooling,concrete strength made of composite portland cement will be lower than the natural cooling,and slag cement concrete is just the opposite.(3)Tests show that different concrete types made of cement and different cooling methods after fire for the use of neutralization test results to determine the concrete component surface layer experienced the highest temperature is affected.The neutralization depth test method is applied to the slag concrete components after cold water cooling,and the results are difficult to be determined.Therefore,the detection of such concrete components burn depth is not recommended neutralization depth test method.(4)XRD analysis shows that the two types of concrete undergoes decomposition of the hydration product CH after high temperature,and the increase of CaCO3 is due to the high temperature of the fire which makes the concrete become loose,and the physical changes and chemical changes of the internal materials make a lot of cracks,making CO2 more easily spread and deep into the concrete to promote the re-carbonation of concrete.(5)According to the current neutralization test method,the carbonization depth of fire concrete is detected,and the rebound strength value is compared with the result of drilling method.The results show that the strength error of the rebound method is relatively large.Concrete types and cooling methods have a certain impact on the results of neutralization of the depth,in the actual project,the use of neutral depth method to determine the depth of burn is not feasible.