Due to the temperature differential between the surface and the centre of the specimens, surface cracking was very prominent in many of the samples after exposure to fire. The most noticeable surface cracking was found in the OPC concrete specimens, due to the rapid moisture loss of the concrete. The surface cracking has occurred also as a result of the differential strain which is caused by a temperature gradient through the cross section of the concrete. At some stages during the fire exposure, the temper- ature differential between the centre and surface of the specimens was as high as 600 oC which created large amount of differential strain. This huge differential strain caused large amounts of surface cracking, with more cracking evident in the samples exposed to the higher temperature ranges.