You might want to post this in the "Concrete Engineering-General Discussion" forum. You'll probably get more hits on the subject.
You might also want to preface your question with an explanation of what SAA MP20 is, for the benefit of those who are not in or do not practice in Oz. While those of us in other areas of the world might not be familiar with those standards, the information can be helpful and enlightening nonetheless.
Good luck.