Fire spalling of concrete as studied by NMR, model validation

During the past thirty years concrete has developed enormously in both strength and durability. A downside of these improvements is the increased risk of explosive spalling in case of fire. The moisture inside the concrete plays an important role in the spalling mechanism. In order to study the moisture transport inside concrete during heating a special Nuclear Magnetic Resonance (NMR) setup was built. This setup can be placed inside a 1.5 T MRI scanner. With this setup one dimensional moisture profiles can be measured non-destructively while the concrete sample is heated up to 300 °C with heating rates of up to 10 °C/min. Four 100 W halogen lamps are used for heating. The setup can handle sample sizes up to 8 cm in diameter and 12 cm in length. Moisture profiles can be measured with a resolution of 2 mm. With this setup it is possible to investigate the role of e.g. PP fibers and different concrete mix designs on the spalling behavior. Furthermore it is an excellent measurement technique for validation of models on fire spalling of concrete. Experimental data on how the moisture is transported inside concrete during heating or how it influences fire spalling of concrete is lacking.