Effect of slag on the performance of concretes in hydrocarbon fire

A hydrocarbon fire test was conducted on nine concrete slabs incorporating three different types of binders: 100% ordinary portland cement (OPC), 50% OPC, and 50% ground-granulated blast-furnace slag (GGBFS), and alkali-activated slag (AAS). The specimens (780 mm [30.71 in.] x 360 mm [14.17 in.]) were made with three different thicknesses (100 mm [3.94 in.], 200 mm [7.87 in.] and 400 mm [15.75 in.]). Specimens were tested at an age of six months when the strengths were about 75 MPa (10,877 psi). The specimens were exposed to the hydrocarbon fire on one side. Explosive spalling only occurred in the 400 mm (15.75 in.) AAS concrete specimen that had a lower moisture content and higher permeability than the OPC and OPC/slag concretes. This suggests that the well-renowned moisture clog theory is unlikely to be a predominant mechanism of spalling in AAS concrete. It is speculated that high thermal gradients caused explosive spalling in the AAS concrete specime