Applying an oscillation to a DC voltage?
It's not clear what you really want.  Your circuit looks fine if you want a square wave symmetric about ground.  It's not clear if the problem is you always want the voltage zero or positive, or that you want it able to drive more power.  To make a 0 to positive square wave:



R1 and R4 form a voltage divider to make 1/2 the supply voltage at a impedance of 10 k&Omega;.  This 2.5V and 10 k&Omega; source forms another voltage divider with R2.  Since the opamp output is always either at ground or supply, the + input will be either at 1/4 or 3/4 of the supply.  The cap will charge and discharge between these two levels.

If you want more current drive from this square wave signal than the opamp can provide, one solution is to add a double emitter follower:



In this case the opamp only supplies the base current to the transistors.  Most of the emitter (output) current will come from the collectors, which is either from the 5V supply or ground.  One drawback of this particular circuit is that a little voltage will be lost at each end.  It can only drive to within the B-E drop of the transistor to each supply rail.  There are other buffer configurations that have different characteristics, but this illustrates a simple way to get more current capability.