can use those ready made compaund/plaster n fill in the gaps?

but keep re occur?

please use this

http://www.pyeproducts.com/

to know whether it'd re-occur, u need to determine the causes.
is it cement?
is it improper mixture?
or is the soil underneath sinking?

small crack, normally use those putty filla to patch back can d.

i need to amend/add some comment(s) before u patch it up u need to hack about one inch width groove before patch it up if not it will not lasting..... and keep coming back ..... if it does come back after u done that groove patching then the above rules (bolded) may have answer.