Concatenate only where there is data

Hi All,
I created a macro (mostly by copying/pasting macros from other posts and tweeking) that:
1. Inserts a column C
2. Concatenates A+B into the new column C,
3. Pastes the values
4. Shades every other block of new data within column C, and
5. Deletes the column C that was created.

The issue that I am having is the fact I don't know how to limit all of the above to only rows that have data in column B. In other words, the macro is doing this for 65,000 lines! How could I limit the above to only rows with data in column B?

Sub group_and_shade()
'
' group_and_shade Macro
'

'
Dim Cll As Range
    Dim Group1Color As Long
    Dim Group2Color As Long
    Dim Group As Integer
    
    Group1Color = -4142 'No Fill
    Group2Color = 15    'Gray
    Group = 1

    Range("C1:C65000").Select
    Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
    Range("C1").Select
    ActiveCell.FormulaR1C1 = "=CONCATENATE(RC[-2],RC[-1])"
    Selection.Copy
    Range("C1:C65000").Select
    ActiveSheet.Paste
    Application.CutCopyMode = False
    Selection.Copy
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Application.CutCopyMode = False
    For Each Cll In Range("C2:C" & Range("C:C").SpecialCells(xlCellTypeLastCell).Row)
        If Cll.Offset(-1, 0).Value <> Cll.Value Then
            Group = Group * -1
        End If
        If Group > 0 Then
            Cll.EntireRow.Interior.ColorIndex = Group1Color
        Else
            Cll.EntireRow.Interior.ColorIndex = Group2Color
        End If
    Next Cll
    Selection.Delete Shift:=xlToLeft
End Sub

As always, thank you kindly for any assistance you are able to offer.
Bryan