Indus, a "pavement preservation" contractor, plans to relocate its headquarters and operations from 825 Granite St. in South Braintree to an industrial park under development in Middleborough. The move comes after the company purchased land there for $11.6 million. Indus, which was founded in Hingham nearly 70 years ago, has 65 year-round staff and usually another 160 seasonal employees. The relocation would allow the company to add 20 more employees to its workforce. However, it is unclear how many workers will accept the relocation.