Fire spalling of concrete, as studied by NMR

The moisture transport in concrete subjected to fire is one of the most important processes with respect to fire spalling. The research on fire spalling of concrete is currently lacking experimental information of the moisture transport processes. We present combined moisture content and temperature profiles of one-sided heated concrete samples measured with our dedicated NMR setup. The concrete samples were equilibrated at different moisture contents ranging from 97 to 50% RH. The moisture content can be measured quantitatively and non-destructively while heating up the sample one-sided to 500 °C. We present the first experimental proof for the build up of a moisture peak in concrete, and the formation of a saturated layer. The temperatures measured at the boiling front indicate a vapour pressure in the order of 1.8 MPa. A simple vapour transport model was successfully used to describe the speed of the boiling front.