Conventionally, during single-side freezing and thawing (SSFT) tests, concrete is permitted to deform freely. However, in practical scenarios, concrete is frequently surrounded by other materials or structures, which typically restricts its deformation when subjected to SSFT cycles. To simulate such service conditions during SSFT tests, a restraint ring and anchors are designed to confine the deformation of concrete. This study investigates the impact of restraint on the pore deterioration within concrete with a water - cement ratio of 0.60 under SSFT cycles. The internal relative humidity (IRH) and strain of both restrained and unrestrained concrete were monitored throughout the SSFT cycles. A comparison was made between the increment of IRH and residual strain of the restrained and unrestrained concrete. The results indicated that the increment of IRH and residual strain of the restrained concrete were 30 % lower than those of the unrestrained concrete. A simplified pore structure model was developed to calculate the strain resulting from pore deterioration. The rate of ice-crystal formation in restrained concrete was slower than that in unrestrained concrete. Additionally, the deformation strain and peak strain of pore deterioration caused by water freezing in concrete were respectively 55 % and 18 % lower than those in unrestrained concrete. Therefore, applying restraint effectively mitigates the internal damage of concrete subjected to SSFT cycles.

Frost action is the major threat against durability of concrete under cold region. Surface scaling and internal damage are the two main deterioration phenomenon caused by frost action. Nowadays, there is still a debate about whether surface scaling and internal damage caused by the same mechanism because of lacking direct experimental evidence. To prove that salt scaling is not analogous to internal damage, a rigid restraining ring is applied on concrete to simulate the real stress condition of concrete. Both relative dynamic modulus (RDM) and weight of surface scaling (SS) are recorded after every 4 cycles for both restraint specimens and free concrete. For the same mix proportion, the decrease of RDM of restraint specimens is less than that of free specimens, while the increase of SS of restraint specimens is higher than that of free specimens. The less decrease of RDM of restraint specimen is as expected due to the improvement of internal bond by rigid restraining ring. However the increment of SS of restraint specimens is more than that of free specimens prove that surface scaling and internal damage of concrete under frost action are dominant by different mechanisms directly. It is recommended that the testing of frost resistance shall be conducted on concrete with steel restraining ring.

At present several methods are available to predict the durability of reinforced concrete structures. In most cases, one dominant deterioration process such as carbonation or chloride penetration is taken into consideration. Experimental results as well as observations in practice show that this is not a realistic and certainly not a conservative approach. In order to test more realistically, RILEM TC 246-TDC, founded in 2011, has developed a method to determine the durability of concrete exposed to the combined action of chloride penetration and mechanical load. In this report, a test method is presented which allows determination of realistic diffusion coefficients for chloride ions in concrete under compressive or tensile stress. Comparative test results from five different laboratories showed that the combination of mechanical and environmental loads may be much more severe than a single environmental load without mechanical loading. Modelling and probabilistic analysis also showed that the obvious synergetic effects cannot be neglected in realistic service life prediction.