Question: Which is correct when describing the sand quantity in a concrete mix design: sand-aggregate percentage or sand-aggregate ratio? Can you explain why?

Answer:There's a simple answer to your question, as suggested by a Virginia-based concrete company's quality control manager. He suggests that specifiers often use the terms sand-aggregate percentage and sand-aggregate ratio to describe the same material relationship. The only difference is that the former presents the relationship between sand and aggregate as a percentage, and the latter expresses the ratio. Another Web site participant suggests a mix with a sand-aggregate ratio of 0.45 also has a sand-aggregate percentage of 45%.

If you find the subject of adding sand to mix designs confusing, you might look at a copy of the recently reissued edition of Concrete Manual: Concrete Quality and Field Practices, published by the International Conference of Building Officials. The book and other similar titles can be found at www.hwbookstore.com.