OKiryu: On your observation abut using clean gravel under pavement slabs. Whether compacted or not, I would be interested in the long term performance of the slabs under traffic, specifically is there a reduction in joint faulting (like driving down a set of stairs). City of Milwaukee, at least back some years, used such a clean base course, whereas, the WDOT did not, but useing rather a well graded base course. This difference was clearly shown on one street where the City paved one side and the WDOT the other. The City's side had practically no faulting whereas DOT side was a rough ride (down the stairs). With no fines to be pumped out of the joint when saturated, the city's road section performed better. In my experience as to performance of rigid pavements, faulting at the joints is one of the main problems that tends to raise the cost of maintenance of these pavements before they break up or have other major problems. Grinding the slabs extends life, but doesn't stop the faulting. This faulting isn't a problem with the continuous reinforced pavements, in my view. That's a whole different story.