I want to display the text combined from few cells.

for example:

Lets assume, the contents of cells are follows, all contain text values:

A1: concrete
A2: footings
A3: excavation

Now, if I want the cell B10 to display

concrete, footings, excavation

how do i write that formula in B10?

of course when the contents of A1, A2, A3 change, the text displayed in B10 must change accordingly

Thanks