Special Issue on Structural Materials. Assessment of Frost Damage of Concrete and its Repair Technique.

The deterioration caused by freeze-thaw action seems to develop gradually from the surface to the inner part. When the frost damage is limited in the cover, the weakened portion is chipped off and the recovering is made by using some repairing material. In this case, it is very important to make a perfect removal of the weakened portion, but its thickness is usually determined empirically by the chipping force and so on.In this study, experimental investigations were made on the assessing technique to the thickness of damage portion and on the performance of repairing materials to bond tightly on the concrete surface and to protect it from the frost damage.The degree of damage at different levels of depth was assessed fairly well from the mechanical degradation by applying the improved pull-off test method. The rebound number and depth of pin penetration could be also used as its measure. The rapid air permeability and water absorption tests were useful for getting the information on the changes of air and water tightness caused by the deterioration due to freeze-thaw action.By using two kinds of repairing material in nine different repairing procedures, the performance after repair was examined to evaluate the refraining effect from suffering the subsequent damage. Furthermore, four types of surface coating material were examined and their ability to prevent the freeze-thaw damage was experimentally confirmed.