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Examination of the Variability in Grout Cube Specimen Testing

High strength, non-shrink grout has been used to fill the longitudinal keyway joints between girders during the construction of precast, prestressed decked bulb-tee (DBT) girder type bridges. Per Alaska Department of Transportation & Public Facilities (ADOT&PF)’s Standard Specifications for Highway Construction (ADOT&PF 2015), the grout should be “non-shrink, non-corrosive, non-metallic, cement-based grout meeting ASTM C1107, except develop a 28-day compressive strength of at least 9,000 psi when tested according to American Association for State Highway and Transportation Officials (AASHTO) T106 or ASTM C109 .” However, past experiences indicated the test results (e.g., 28-day compressive strength), especially when tested using cube specimens, had large variations. In most cases, either none of the compressive strength tests satisfied ASTM C109 (ASTM 2011) in terms of the variability requirement when the strength exceeded 9000 psi; or the compressive strength was less than 9000 psi if the test results satisfied the variability requirement in ASTM C109. Since the longitudinal joints of DBT girders are crucial to the integrity of a bridge (e.g., providing for the distribution of live load between adjacent girders), it is necessary to investigate why the test results of high strength grout show such variability. In addition, methods to reduce this variability are needed, providing a more constructible and contractually administrable procedure to satisfy the quality and durability needs of bridge keyways that are ‘grouted’.