An experimental investigation was conducted to determine the fracture properties of a solidified composite produced from residual sludge of the steel industry. The purpose of this study was to investigate the causes of random cracking and spalling which were observed in the previous field tests. Fracture toughness (or stress intensity factor), K-1c values were determined using compactension specimens which were prepared from concrete-like solidified material. These values were used as a gauge to determine the relative effects of various factors on the cracking behavior of this composite material, such as the mix component ratios. The specimens were prepared with different specifications and were cured at different environmental conditions. The best mix and the best suitable curing temperature were investigated.