An Analysis of Refractory Concrete Drying and a Mechanism for Explosive Spalling

The drying of refractory and civil concretes has been studied by engineers and scientists since the early 1970's and the damage to public infrastructure from fires is driving research of rapidly heated high performance concrete (HPC) and self-compacted concretes (SCC). The development of dense low cement refractory concrete (LCC), ultra-low cement refractory concrete (ULCC) and no cement refractory concrete (NCC) means drying is very unpredictable.The heating of these materials has seen numerous problems particularly when explosive spalling occurs. When explosive spalling occurs projectiles of reasonable mass (1-2 kg) can be thrust over tens of metres. While surface spalling is less violent the extent of damage can still be severe requiring repairs to be carried out.There are two drivers for spalling of concrete - thermal strain caused by rapid heating and internal pore pressure during the heating of "green" concrete. Since the Bazant and Thouguthai [1] publication in 1978 on the theory of concrete drying considerable research has been undertaken by many researchers. However, the problem of predicting safe heating rates for refractory concrete and the mechanism that causes spalling during drying is still debatable and a number of possible reasons exist.This paper will focus mainly on pore pressure spalling. Pore pressure is calculated using a one dimension (ID) finite difference model for a one or two layer plates following the theory proposed by Bazant and Thouguthai [ 2]. The numerical technique used numerical relaxation which means the model is stable for a wide range of conditions.Due to space limitations, details of permeability and concrete failure mechanisms have not been given but are available at www.palmertechgroup.com