concatenate date and time

Hello,

I am trying to concatenate 2 cells, one (A1) with a date in format dd/MM/yyyy and the other (A2) with an hour from 0 to 23 representing an hour of the day.

Therefore I use this formula:
=concatenate(text(A1;"dd/MM/yyyy");" ";A2;":00")

and I get for example
01/01/2013 6:00

sadly, Excel does not recognise it as a date and i really need to have that hour written 06:00 to do what i want to do afterwards. if i double clic on the cell and then elsewhere Excel modifies it and put it in the good format. so i get 01/01/2013 06:00, which is what I want.
However, i don't want to double clic and 16000 cells.
Can someone tell me if it is possible to do it automatically ? or maybe give me a method to write the date directly in the good format.

Thanks,
Jérôme

Works perfectly,
Thanks so much
Jérôme