The influence of restraint on salt frost damage of concrete: Deterioration of pores

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.