The failure behaviour of glass polyalkenoate cements was investigated using a linear elastic fracture mechanics (LEFM) approach. Cements were based on Drayton gasifier slag and four poly(acrylic acid)s with number average molar masses ranging from 3.03 x 10(3) to 6.44 x 10(4). Cement properties were studied at time intervals of one, seven and twenty eight days. Compressive and flexural strengths of the cements increased with increasing molar mass of the poly(acrylic acid)s and time. The Young＇s modulii increased with time and were independent of poly(acrylic acid) molar mass. Fracture toughness increased with increasing molar mass of the poly(acrylic acid)s. Fracture toughness increases over an ageing time of one week and subsequently decreased over one month. Toughness increased with poly(acrylic acid) molar mass, these increases being most pronounced at higher molar mass. The toughness values decreased with time for the higher molar mass cements, which is consistent with increased crosslinking of the poly(acrylic acid) chains and reducing molecular flow at the crack tip. Plastic zone size increased with poly(acrylic acid) molar mass and decreased with time for lower molar mass cements, remained constant for intermediate molar mass cements and increased with high molar mass cements.