Currently Crucible will automatically send reviewers a reminder email one working day before the deadline. Preset reminders can also be configured to send a reminder to all of the pending reviewers some number of working days before the deadline, but this must be configured for each review individually. (Retrieved from here.)
It would be great if it were possible to configure a batch process to run on a hourly/daily/weekly/monthly basis (Cron expression?) at Project level, instead of at Review level, to send reminder notifications to all or to specific participants at once, for all outstanding reviews.