Control joints are grooves intentionally tooled into the concrete to limit the visual impacts of cracking. Control joints do not prevent cracks, but they will manage where anticipated cracking occurs.
You should keep concrete control joints clean as part of routine home care and maintenance. In some regions, it may be advisable to apply a sealant. When joints are left unsealed, moisture may migrate into the joint, which could damage the underlying concrete. Consult a professional to make sure your concrete has had adequate cure time and that the treatment is done correctly.