Q.: Your August 1990 article on whitetopping a driveway says that compacted fill was placed in low areas because shrinkage cracks might start at points where the thickness changed. I attended a demonstration by the Michigan Concrete Association where the same practice was shown. A controlled density fill was placed in low areas.

Then Robert Huber reported on 9 miles of whitetopped pavement in Iowa where all the ruts and chuckholes were filled with concrete as the whitetopping proceeded. He says the extra thickness of concrete at these points is beneficial--and his pavement has been in service almost 13 years. Who's right?

A.: We asked Dale Diulus of Phoenix Cement to comment because he has been involved in many whitetopping projects. He gives two reasons for not filling chuckholes at the same time the overlay is placed. The variable cross section restrains overlay movement and causes cracking. Also, reentrant corners in the pavement cross section may induce cracking.

That said, however, we can't argue with success. The pavement in Iowa has performed well. So perhaps both methods can work.