If I recall correctly, in some of the early "experimental" installations of concrete ties, it was widely believed that one would need way less ties per mile (as was, in fact, the case with concrete ties on some third world RR's, which however, tended to have significantly lighter axle loadings than in North America). And, as a result of these early "experimental" installations of concrete ties, this problem described above as rail "corrugation", due to too little support for the rail between ties, was found. Nowadays on most installations I've seen, it appears that while concrete tires are wider, and do require less total ties per mile, that the spacing between ties is only a little longer than for wooden ties, which gives better support, and causes less rail damage.