Abstract: Apparatus is disclosed for measuring creep stiffness of a specimen, for example, asphalt cement, or other viscoelastic material, having a flexural modulus greater than approximately 1,000 psi. The specimen and the lower part of a loading mechanism are submerged in a constant temperature coolant thereby providing buoyant support to the specimen, preventing it from deflecting under its own weight, as well as providing means for controlling the test temperature. The coolant temperature is maintained to within approximately +/-0.1.degree. C. of a desired temperature. The specimen, having known dimensions, is supported within the coolant on two spaced apart support members. A loading head actuated by an air bearing/pneumatic piston mechanism engages the specimen midway between the two support members. The deflection of the specimen is measured with an LVDT and the load imparted to the specimen by a load cell provided under at least one of the specimen support members.