I watched a video just yesterday about wood ties vs. concrete ties. One of the arguments in favor of wooden ties in the US is that they are less brittle and thus more able to handle the frequent derailments we get. The nightmare scenario with concrete ties is that a loose wheel goes unnoticed for miles and cracks every single tie.
They mentioned a previous test experience with older concrete ties held together with naked angle-irons. A derailment severed all of the irons.