Concatenate columns in results with GROUP BY?

Here is my original query:

SELECT EventType, InitiatedAt, COUNT(*) as cnt
FROM HS_IHE_ATNA_Repository.Aggregation
WHERE EventType = 'LOGIN'
AND LocalDateTime > '2016-02-16 11:00:00'
GROUP BY EventType, InitiatedAt

This gives me data like this:

However, I need to get the data back as two columns with all but the last concatenated and delimited, more like this:

I tried this:

SELECT EventType + ';' + InitiatedAt as k, COUNT(*) as cnt
FROM HS_IHE_ATNA_Repository.Aggregation
WHERE EventType = 'LOGIN'
AND LocalDateTime > '2016-02-16 11:00:00'
GROUP BY EventType, InitiatedAt

But the first column always comes back as zero.

is there a way to do this?