This paper reports on using the Stiffness Damage Test (SDT) to establish the degree of damage and loss of integrity in concrete structures. The SDT test method provides a quantitative non-dimensional Damage Index (DI) based on the strain energy lost in the hysteresis during load-unload cycles of low stress level. The SDT was used to establish the degree of disruption to the microstructure and reduction in stiffness of concrete, which was cast and cured during various simulated cold weather conditions. This investigation was prompted by various examples of damage to structures through curing at low temperatures. Such curing regime evidently resulted in loss of stiffness though the compressive strength was within the design expectations. The Damage Index for concrete cured at temperatures hovering about 0 °C was found to be 4 ~ 5 which is associated with about 20 ~ 25% stiffness reduction. In addition, The SDT was adopted as a tool capable of measuring and assessing the integrity of concrete after exposure to fire. There was a strong correlation between the DI and the reduction in the material stiffness and strength properties. A Damage Index of 5 was associated with 24% loss of stiffness while a Damage Index of 20 was associated with a 66% loss of stiffness, as measured by the chord modulus. Furthermore, the SDT was effectively utilized to assess the integrity of concrete dams and bridges, which were suspected to be affected by Alkali Aggregate Reaction. A large number of cores were obtained from one affected dam and tested by the first author to determine the stiffness characteristics and the Damage Index. The reliable quantitative test parameters established the degree of integrity of the dam and the results were used to develop a management strategy for the important dam. The SDT method proved to be an effective quantitative technique to assess the integrity of damaged or deteriorating concrete regardless of the damage or the deterioration mechanism.