Spalls on the bottom corners at ends of prestressed beams or boxes are usually caused by camber and sliding at detensioning. This is more likely to be a problem when beam ends are skewed. These small spalls can be easily repaired.
For additional information, please download MNL-137 Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products. Note there is a charge for this publication.
You may also download for free PCI Northeast “Guidelines for Resolution of Non-Conformances in Precast Concrete Bridge Elements.”