Base is a property of how a number is displayed, not of of the number itself or of how you do arithmetic. You can display the digits of a number in any base you want using the digits function;
julia> digits(3234, base=3)
8-element Array{Int64,1}:
0
1
2
2
0
1
1
1
and you can parse a number from an arbitrary base using parse:
julia> parse(Int, "11102210", base=3)
3234