Sub Concat()
Dim i%, Dl%
Dim Ws As Worksheet
Set Ws = ActiveSheet
Dl = Ws.Range("D" & Rows.Count).End(xlUp).Row
For i = 1 To Dl
Ws.Cells(i, "G").Value = Ws.Cells(i, "D").Value & " " & Ws.Cells(i, "E").Value & " " & Ws.Cells(i, "F").Value
Next i
End Sub