At present, you cannot add a second X-Axis. Nevertheless, you can use the chart legend, positioned on top, to supply additional information to the end user. Or perhaps another indicator/legend outside the chart control.
I hope this information helps.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items