Experiential contribution to the explanation of the risk of concrete bursting

Abstract

The spalling of concrete is a particular phenomenon which couldseriously jeopardize the stability of a structure during and aftera fire. Moreover, the reparation costs of the damages induced byspalling can be very important. Recently, some studies (mainlytheoretical), have tried to find the most probable causes ofconcrete spalling. In particular, these studies tried to establishthe relative importance of mechanisms such as thermo-mechanical or thermo-hydral processes for the appearance ofspalling. However, we still do not exactly know the conditions ofspalling and this phenomenon is still not predictable bycalculations. Moreover, the existing technological solutionsagainst spalling risk (polypropylene fibres or thermalprotection) are still not well controlled.The experimental results that we present take place in a globalstudy of the spalling risk of concrete. An ordinary concrete(compressive strength 40 MPa) and a high performanceconcrete (compressive strength 60 MPa) have been tested underdifferent levels of observation. At the material scale, theevolution with temperature of several properties has beenassessed: gas permeability, water porosity, thermal propertiesand mechanical properties. These tests have been completed bythe measurement of gas pressure into small concrete samplesduring low heating. At last, fire tests (ISO curve and ModifiedHydrocarbon Curve) have been carried out on concrete slabs inorder to observe the spalling of concrete.The confrontation of the different experimental results allows usto discuss about the contribution of different parameters onspalling risk. At last, we suggest some new ways of investigation.