Assessment of Concrete Structures Affected by Alkali–Silica Reaction and Freeze–Thaw by Use of Ultrasonic Surface Wave Method

Two of the most common causes of concrete degradation are alkali–silica reaction (ASR) and freeze–thaw (FT) cycling. ASR and FT may significantly reduce service life of concrete structures and can cause degradation in the mechanical properties of concrete, including its modulus of elasticity and its flexural strength. Cracking due to ASR and FT provides numerous open pathways for water and could cause premature failure of various concrete structures. The progression of damage due to ASR and FT was investigated by testing beams or cylindrical specimens cured under laboratory conditions or through conventional destructive methods, such as mechanical testing and petrography on the drilled cores. Coring is time-consuming and expensive, and the retrieved cores are representative of only a small portion of the structure. In some cases, extraction of cores is not feasible. The rapid in situ detection and quantification of the adverse impacts of ASR and FT are desirable. Nondestructive evaluation methods can supplant conventional destructive methods for that purpose. The relative and absolute applicability and usefulness of the ultrasonic surface wave (USW) method in characterizing the severity of cracking and surface defects in structures affected by ASR and FT were investigated. The results indicate that the USW method is an effective nondestructive evaluation method for characterizing ASR- and FT-induced damage and detecting cracked areas. The in situ modulus of elasticity measured by the USW method is correlated well with ASR and FT damage levels.