Deteriorated track-slabs have been so far found in some areas subject to cold weather conditions. For track-slab maintenance purposes, it is very important to understand the causes of this deterioration. Visual inspections of track-slabs and investigation of samples of materials used in track-slabs were therefore carried out. Visual inspections found that deterioration occurred more frequently on south facing sides of track-slabs exposed longest to the sun. Material investigations showed that track-slab deterioration was caused by an alkali-silica reaction and frost damage.