SikaFiber®-12-34 is used to prevent concrete spalling that can happen when exposed to the high and rapidly increasing temperatures experienced in fires, mainly in underground structures. In the event of a fire, as the temperature of the concrete increases, the moisture in the concrete becomes steam. If this steam is unable to escape an increase in pressure inside the concrete builds up to the point where it exceeds the tensile capacity of the concrete causing pieces of concrete to be violently and explosively dislodged. The addition of suitable polypropylene fibres in cast concrete has been accepted to counteract explosive spalling. The fibres melt inside the concrete creating the necessary voids for the steam to escape thereby preventing spalling and so maintaining the integrity of the structural element.